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Information Collection & Exchange
Peace Corps' Information Collection & Exchange (ICE) was established so that
the strategies and technologies developed by Peace Corps Volunteers, their
co-workers, and their counterparts could be made available to the wide range
of development organizations and individuals who might find them useful.
Training guides, curricula, lesson plans, project reports, manuals, and other
Peace Corps-generated materials developed in the field are collected and
reviewed. Some are reprinted "as is;" others provide a source of field based
information for the production of manuals or for research in particular pro-
gram areas. Materials that you submit to the Information Collection & Ex-
change thus become part of the Peace Corps' larger contribution to development.
Information about ICE publications is available through:
Information Collection & Exchange
Office of Programming & Training Coordination
806 Connecticut Avenue, NW
Washington, DC 20525
Add your experience to the ICE Resource Center. Send materials
that you've prepared so that we can share them with others working
in the development field. Your technical insights serve as the
basis for the generation of ICE manuals, reprints, and resource
packets, and also ensure that ICE is providing the most updated,
innovative problem-solving techniques and information available to
your and your fellow development workers.
TRADITIONAL FIELD CROPS
Information Collection & Exchange
Appropriate Technologies for Development
Manual Number M-13
This publication was produced for Peace Corps by the Transcentury
Corporation, Washington, DC, December 1981, under contract No. 79-043-0129.
This edition of Traditional Field Crops, printed by the AID Resources
Report, differs from the edition printed by the Peace Corps Information
Collection and Exchange (PC/ICE). This edition was edited by Marcia Roman and
Patricia Scully of Creative Associates, Inc., Wahington, DC, incorporating
corrections and changes made by the author, David Leonard, and changing the
format to reduce the size of the volume. The illustrations have been
reproduced exactly as they appeared in the December 1981 edition. Some
corrections have been made in the tables. Thanks to Diana Talbert without
whose networking this revised edition would not have been possible and to
Barbara Tymann for her assistance in composition of the book.
ABOUT THIS MANUAL
The Traditional Field Crops manual is designed as a learning tool and
on-the-job reference for Peace Corps Volunteers involved in small farmer crop
improvement programs in maize, sorghum, millet, peanuts, beans, and cowpeas.
Although written to be readily understood by non-specialists, the manual
contains much information useful to trained agriculturalists and to planners
Primarily designed to help Volunteers develop and strengthen the agricul-
tural skills they need for successful work with the target crops, this manual
focuses on the following areas:
o surveying and interpreting the local agricultural environment
and individual farm units;
o developing agricultural extension techniques and practices;
o providing basic "hands-on" and technical skills for extension
workers in operations from farm land preparation through
harvest, including some routine troubleshooting.
To do this, the manual provides a summary of current crop production re-
commendations under varying conditions of climate, soils, management ability,
and available capital; identifies useful field references and other technical
resources, including information on improvements in equipment for small farmer
row crop production; and reviews recent research advances and extension ef-
forts in target crop yield improvement with special emphasis on the role of
international crop institutes. Scientific names are used along with common
names to avoid confusion, as one common name may refer to a number of differ-
ABOUT THE AUTHOR
David Leonard has been associated with the Peace Corps off and on for the
past 18 years. Originally a B.A. generalist (history), he served as an agri-
culture extension Volunteer in Guatemala from 1963 to 1965 and then went on to
get a Master of Agriculture degree in agronomy from Oregon State University in
1967. Since then, he has been an agriculture trainer for 35 groups of Peace
Corps Volunteers bound for Latin America, Africa, and Asia. He also grew
maize, potatoes, and peanuts for three years on a 120-hectare farm in
The author would like to express special thanks to John Guy Smith of
Washington, DC, for assistance in planning this manual and for permission to
use materials from several of his publications. No one better understands the
realities of small farmer agriculture and the development and introduction of
improved farming practices.
Also, thanks are due to TransCentury's Paul Chakroff, Marilyn Chakroff,
and Nancy Dybus for their editing assistance; to Marilyn Kaufman for her fine
illustrations; and to Cade Ware for his excellent typing and layout of the
TABLE OF CONTENTS
About this Manual . . . . . . .
About the Author . . . . . . .
Acknowledgements . . . . . . .
Chapter 1. Introduction . . . . .
Chapter 2. The Agricultural Environment .
Chapter 3. The Reference Crops . . .
Chapter 4. Planning and Preparation . .
Chapter 5. Soil Fertility and Management .
Chapter 6. Pest and Disease Control . .
Chapter 7. Harvesting, Drying, and Storage
A. Common Units of Measure and Conversion . . . . .
B. How to Conduct a Result Test (Field Trial) . . . .
C. How to Conduct a Result Demonstration (Demonstration Plot)
. . 211
D. How to Conduct an Elementary Statistical Analysis .
E. How to Convert Small Plot Yields . . . .
F. How to Take Soil Samples . . . . .
G. Hunger Signs in the Reference Crops . . . . .
H. Miscellaneous Pulses . . .. . . . .
I. Troubleshooting Common Crop Problems . . . .
J. Guidelines for Using Pesticides . . . . . .
K. Guidelines for Applying Herbicides with Sprayers .
L. Important Planting Skills for Field Extension Workers
Glossary . . . . . . . . . . .
Bibliography . . . . . . . . . . . .
Research Institutions . . . . . . . .
Sources of Illustrations . . . . . . . . .
. . .. 217
. . . 221
. . . 222
S. .. 224
S. . . 228
. . . 232
S. . .. 236
. . . 256
. . . 260
. . . 265
. . . 267
. . . 270
. . . 271
Index . . . . . . . . . . . . . . . ..272
CHAPTER 1. INTRODUCTION
From 1961 to 1975, total food production in developing countries
increased about 47 percent. This seemingly impressive gain was reduced to
only 10 percent in terms of food production per person because of rapid
population growth rates. In more than half of the developing nations, per
person cereal grain production was less in 1979 than in 1970. Presently, some
two-thirds of all people in the developing countries are considered
Current world food supplies compared with dietary requirements show only
a minor deficit on paper, but the reality is far more serious for two reasons.
Food supplies are distributed inequitably among countries,
different income groups, and even within the family. Since the
quantity and quality of food intake is strongly linked to
income level, increases in per person food production will have
little effect on hunger and malnutrition without a large rise
in the incomes of the world's poor.
Postharvest food losses of cereal and legumes (dry beans,
peanuts, etc.) during processing and storage are conservatively
estimated to be 10 percent on a world basis, but losses of 20
percent are common in developing countries.
Looking to the future, there is little reason for optimism. A 1974 UN
study predicted that in the next 30 years, human population will increase by
26 percent in the developed countries, but by 119 percent in the developing
nations. The study concluded that if current food production trends continue
in developing countries, they will need to increase their grain imports
fivefold between 1970 and 1985. Aside from the problem of financing such
imports, it is very questionable whether the major grain exporters can meet
It is not likely that developing countries can increase food production
rapidly enough during this decade to achieve self-sufficiency. However, the
food deficiency can be narrowed if these countries strengthen their recent
interest in crop improvement practices and introduction of new techniques to
both small- and large-scale farmers.
THE SMALL-SCALE FARMER AND AGRICULTURAL DEVELOPMENT
The great majority of farmers in developing countries operate on a small
scale. Despite much local and regional diversity, they share a number of
Most small farmers operate as independent economic units,
either as independent proprietors or under a rental arrangement
allowing them to make production decisions. In some cases,
however, individual decision making may be subject to tribal or
village controls, or restricted by insecure tenancy.
*Population and food data are based on figures from the Food and Agricultural
Organization (FAO) of the United Nations (UN).
S Since they have a small amount of land and capital, they depend
mainly on the family labor supply.
The small-scale farmer is less likely than large-scale farmers
to use capital for commercial inputs like fertilizers,
pesticides, and equipment.
The small farmer tends to use credit for consumption needs
rather than for purchasing farming inputs.
Compared to larger farmers, small farmers have limited access
to important production factors associated with agricultural
development, such as agricultural credit and supplies, adapted
technology, technical assistance, market information, roads,
ASSISTING SMALL FARMERS
In the developing world, most small-scale farmers with whom the extension
worker is in contact are farmers in transition from traditional to improved
production practices. They are aware of outside inputs like fertilizers,
insecticides, and vaccines for livestock and may actually be using one or more
of these, though often in a haphazard manner. Although their first production
priority is usually subsistence, there is a strong motivation to produce a
marketable or exchangeable surplus once the family food needs are met.
Much of the solution to hunger and rural poverty in the developing
countries hinges on the small farmer's ability to increase his or her returns
from traditional crops by adopting appropriate improved production practices.
"Appropriate" means in harmony with the environment and the cultural and
economic situation of the farmer. "Improved" refers to the use of
non-traditional inputs like fertilizers, agricultural chemicals, new equipment
suited to small-scale farming, and technical advisory services. It does not
imply the total abandonment of traditional growing practices but rather the
incorporation of suitable new elements.
Most small-scale farmers will benefit by participating in agricultural
development programs. Since nearly all of them want to increase their yields
and incomes, they will adopt new techniques--if these offer a reasonable
assurance of a meaningful return without excessive risk and if the necessary
inputs are available.
Until fairly recently, yield-improving technology was usually developed
with little regard to the realities of the small farmer's situation. It is
not surprising that these so-called "improved" practices often encountered a
cool response. Crop production research and extension are becoming more
attuned to the small farmer's needs, and there are numerous examples of
successful yield-improving programs involving small farmers throughout the
-- 2 --
The Small Farm As a Viable Economic Unit
When yield-improving practices are used in developing countries,
competitively low production costs can be realized over a wide range of farm
sizes. Increasing the size of the farm alone is usually not the answer to
production problems for all small farms, although it can be an important
factor for some.
There are basically two types of small farm. One is the family-size
farm, which can gainfully employ the equivalent of two to four adults and a
team of oxen. This type of farm is much smaller in size and capital than its
equivalent in the developed countries, probably because land and machinery are
more expensive than labor in most developing countries.
The sub-family farm is too small to effectively employ the equivalent of
two adults and a team of oxen. Unfortunately, in countries like Guatemala, El
Salvador, and Peru, up to 80-90 percent of the total farm units are classified
as sub-family. The sub-family farm is too small to become economically
successful no matter how much improved technology is used. In this case,
increased size is vital to production.
The Availability of Improved Production Practices
Since the 1960s, there has been a growing effort on the part of national
and international crop research organizations to develop feasible
yield-improving practices for the reference crops included in this manual.
This is a long, ongoing process, but for many farming regions in developing
countries there is now a group of improved practices that will provide
significant increases in both yields and returns over traditional methods.
These developments are the small farmers' best hope for increasing yields and
returns so that they can remain (or become) competitive economically and
improve their standard of living.
The ideal conditions for promoting improved crop production practices
among small farmers would ensure that:
the new practice does not increase farmer risks, depart
radically from current practices, or require considerable
retraining of the farmer;
the potential gains exceed the added costs by at least two to
one. (This is the cost/benefit ratio.);
the commercial inputs and associated services required for the
practice are readily obtainable on reasonable terms;
the pay-off from the new practice occurs in the same crop cycle
in which it is applied;
the costs of the new practice are within the farmer's means;
this usually implies access to credit.
-- 3 --
All of these conditions are seldom fully met in small farmer agriculture
in a developing country. Nonetheless, with a good extension service and a
well-developed "package of practices," agricultural extension workers can
improve crop yields on small farms dramatically.
THE "PACKAGE" APPROACH TO IMPROVING CROP YIELDS
In most cases, low crop yields are caused by the simultaneous presence of
several limiting factors, rather than one single obstacle. When a specially
developed and adapted "package" of improved practices is applied to overcome
these multiple barriers, the results are often much more impressive than those
obtained from a single factor approach. A crop "package" consists of a
combination of several locally proven new practices. (Few packages are
readily transferable without local testing and modification.) Most include
several of the following: an improved variety, fertilizer, improved control
of weeds, pests, and diseases, improvements in land preparation, water
management, harvesting, and storage.
The likelihood of a positive response is greatly increased using a
package approach. However, there are possible disadvantages.
If the package fails, farmers may conclude that all of the
individual practices are unproductive.
More adaptive research and extensive local testing are required
to develop a proven package for an area.
The package may favor the larger farmers who have easier access
to credit for buying the added inputs.
Unavailability of a component input or its faulty application
may make the entire package fail.
It should be stressed that a package does not always have to involve
considerable use of commercial inputs. In fact, an extension program can
focus initially on improvement of basic management practices that require
little or no monetary investment such as weeding, land preparation, changes in
plant population and spacing, seed selection, and timeliness of crop
operations. This helps assure that small farmers benefit at least as much as
larger ones, especially in those regions where agricultural credit is poorly
THE ROLE OF THE EXTENSION WORKER
To work with small farmers to improve yields of the six reference crops
(maize, sorghum, millet, peanuts, cowpeas, and beans), extension workers need
both agricultural and extension skills. The general agricultural skills
required by extension workers who will be involved in crop improvement
projects as intermediaries with a limited advisory role include:
understanding the need for crop improvement programs;
interpreting the agricultural environment;
-- 4 --
e knowledge of the reference crop characteristics;
knowledge of crop improvement practices; and
understanding of reference crop management principles.
Extension workers also will need to have an appropriate level of
"hands-on" and technical skills relevant to the reference crops, and an
ability to adjust recommendations for variations in local soils, climate,
management, and capital.
This manual provides most of the information extension workers need to
work with the six reference crops. In promoting any crop improvement
practice, however, it is very important to work with the local farmers,
extension service, universities, and national and international agricultural
research institutions. These individuals and organizations are much more
familiar with the prevailing local environmental, economic, social, and
cultural conditions and should be consulted first before attempting any crop
-- 5 --
CHAPTER 2. THE AGRICULTURAL ENVIRONMENT
The purpose of this chapter is to identify how extension workers can
survey and interpret important features of the local agricultural environment
and the individual farm units which are a part of it. This is vital to
effective extension since it enables workers to fully comprehend the area's
farming systems and practices.
The local agricultural environment is made up of those factors which
influence an area's agriculture. The most important of these are natural
(physical) environment and the infrastructure.
THE NATURAL ENVIRONMENT
The natural environment consists of the climate and weather, the land and
soils, and the ecology, the interaction among crops, weeds, insects, animals,
diseases, and people.
Weather refers to the daily changes in temperature, rainfall, sunlight,
humidity, wind, and barometric pressure. Climate is the typical weather
pattern for a given locality over a period of many years. To quote one
definition, people build fireplaces because of the climate, and they light
fires in the fireplaces because of the weather.
The climate and weather factors that have the greatest influence on crop
production are solar radiation (sunlight and temperature), rainfall, humidity,
Solar radiation markedly influences crop growth in several ways.
It provides the light energy needed for photosynthesis, the fun-
damental process by which plants manufacture sugars for use in
growth and food production. Sugars are made by this process in
the green cells of plants when carbon dioxide from the air com-
bines with water from the soil using sunlight and chlorophyll
(the green pigment in plants) as catalysts.
The daily duration of sunlight (daylength) and its yearly varia-
tion greatly affect time of flowering and length of growing
period of some crops.
Solar radiation is the primary determinant of outside tempera-
ture, which strongly influences crop growth rate and range of
Unlike the temperate zone latitudes, the region between the Tropic of
Cancer (23.5ON) and the Tropic of Capricorn (23.50S) has relatively little
seasonal variation in solar radiation, since the sun remains fairly high in
the sky all year long. Measurements above cloud level show an annual
-- 6 --
variation in solar radiation of just 13 percent at the equator versus 300 per-
cent at a latitude of 400. However, this supposed advantage of the tropics
may in some cases be largely offset by cloudiness, which can be excessive in
the higher rainfall zones, particularly near the equator (cloudiness can
reduce solar radiation by 14-80 percent depending on depth and extent of the
cloud cover). For example, due to heavy cloud cover, the equatorial Amazon
Basin receives only about as much total yearly solar energy at ground level as
the Great Lakes region of the United States.
The length of time from plant emergence to flowering as well as the
actual date of flowering can be strongly affected by daylength in the case of
some crops. Among the reference crops, soybeans and the photosensitive vari-
eties of millet and sorghum are the most affected.
Maize is less influenced by daylength unless a variety is moved to a
latitude where daylength is markedly different from that of its point of
origin. (See Chapter 3.) Daylength is usually not a critical factor with
peanuts, beans, and cowpeas.
As shown by the table below, both latitude and season influence day-
length. Note that the annual variation in daylength markedly decreases as the
equator is approached.
Length of Day in Various Northern Latitudes
MONTH EQUATOR 200 400
December 12:07 10:56 9:20
March 12:07 12:00 11:53
June 12:07 13:30 15:00
September 12:07 12:17 12:31
Temperature is the major factor controlling a crop's growth rate and
range of adaptation. Each crop has its own optimum temperature for growth,
plus a maximum and minimum for normal development and survival. Even varie-
ties within a crop differ somewhat in their temperature tolerance. Exces-
sively high daytime temperatures can adversely affect growth and yields by
causing pollen sterility and blossom drop. In addition, the hot nights common
in the tropics can reduce crop yields. This is because plants manufacture
sugars for growth and food production by the daytime process of photosynthe-
sis, but "burn up" some of this at night through the process of respiration.
Since high nighttime temperatures increase the respiration rate, they can cut
down on the crop's net growth.
-- 7 --
Several factors affect an area's temperature pattern.
Latitude--Seasonal temperature variations are pronounced in the
temperate zone where solar radiation and daylength fluctuate
considerably over the year. In the tropics, this seasonal tem-
perature difference is much smaller. Nighttime lows are seldom
below 10-30oC near sea level and are usually above 180C.
Seasonal variations become more pronounced as the distance from
the equator increases.
Elevation--Temperature drops about 0.650C for each 100-meter
rise in elevation. This greatly affects a crop's length of
growing period as well as its adaptation to the area. For ex-
ample, at sea level in Guatemala, maize matures in three to four
months and the climate is too hot for potatoes; however, about
50 km away in the highlands (above 1500 m), maize takes five to
ten months to mature and potatoes thrive.
Topography, or the shape of the land surface, can cause differ-
ences in local weather and climate (micro-climates). A work
area may have two or more micro-climates.
Cloud cover has a definite buffering effect on diurnal (daily)
temperature variation. It will lower the daytime high but raise
the nighttime low.
Humidity exerts an effect similar to cloud cover on temperature.
Humid air takes longer to heat up and cool off and therefore is
subject to considerably less daily temperature variation than
dry air. Maximum shade temperature rarely exceeds 380C under
high humidity, while maximums of 54oC are possible under dry
In dryland (non-irrigated) areas of the tropics with year-round growing
temperatures, rainfall is the major environmental factor that determines which
crops can be grown, when they are planted, and what they will yield. Rainfall
varies greatly from place to place (often within surprisingly short distan-
ces), especially around mountainous or hilly terrain. The dryland farmer is
keenly aware of his area's seasonal rainfall distribution. This includes dev-
iations from the normal cycle such as early or late rains, or unseasonable
droughts. Too much rain, which can drown out the crop, delay harvest, and
accelerate soil erosion, can be just as serious as too little. It may be too
wet for plowing one day, yet too dry the following week for good seed germina-
When gathering rainfall data for an area, one should keep in mind that
annual rainfall averages have little meaning. Seasonal distribution and reli-
ability are far more important in terms of crop production.
For example, Ibadan, Nigeria, is located in the transition zone between
the humid and semi-humid tropics and receives about the same annual rainfall
(1140mm) as Samaru, Nigeria, which is located to the north in the savanna
zone. Ibadan's rainfall is spread out over nine months from March to November
-- 8 --
in a bi-modal pattern, i.e., two rainy seasons with a drier period in
between. The first season is long enough for a 120-day maize crop, although
there is some periodic moisture stress. The second season is shorter, and
soil moisture is usually adequate for only an 80-90 day crop. On the other
hand, Samaru's equal rainfall is spread out over five months in a uni-model
pattern, providing for a single maize crop not subject to moisture stress.
From the example, it is apparent that annual rainfall averages alone are
not a dependable gauge of the rainfall in an area. The same goes for seasonal
rainfall distribution. Although it gives a good general indication of the
amount of moisture available for crop production, it does not tell the whole
story. The amount of rainfall that actually ends up stored in the soil of a
farmer's field for crop use depends on other factors such as water run-off and
evaporation from the soil surface, and the soil's texture and depth.
When interpreting the rainfall pattern of a work area, it is good to
remember that averages are somewhat misleading. Variations to the average can
be expected even though the general seasonal distribution curve usually
maintains a consistent shape (Figure 1).
Monthly Rainfall Pattern, Managua, Nicaragua, 1958-67
M A M J J A S O N D J
Wettest year, 1958 -----------
Driest year, 1965 ............
Annual total: 1437 mm
Annual total: 757 mm
Annual average: 1909 mm
Highest monthly rainfall between 1958-1967 **********
Lowest monthly rainfall between 1958-1967 +++++++++++
Cropping cycles are determined by using the cropping calendar (planting
and harvest dates for crops involved) and are closely tied to the seasonal
rainfall distribution. This can be seen by comparing the cropping calendar on
the following page with the rainfall chart in Figure 1.
-- 9 --
Crop Calendar, Managua Area
maize -------4 ---------
sitive sorghum ------------------
J F M A M J J A S 0 N D J
A primary source of rainfall information in a given area is the local
farmer. Although official weather station rainfall data is handy to have if
it is reliable and representative, it is not essential. Most of the informa-
tion needed about rainfall distribution can be found by talking to experienced
Relative humidity affects crop production in several ways.
Daily temperature variation is greater under low humidity; high
humidity exerts a buffering effect on temperature.
High humidity favors the development and spread of a number of
fungal and bacterial diseases. (See the disease section in
The rate at which crops use water is highest under hot, dry
conditions, and lowest when it is very humid.
Wind and Storm Patterns
High winds associated with thunderstorms, hurricanes, and tornadoes can
severely damage crops. Among the reference crops, maize, sorghum, and millet
are most prone to damage from heavy rain. Hot, dry winds can markedly in-
crease the water needs of crops. The frequency of high winds is also a factor
that warrants investigation when surveying a work area's climate.
The shape of the land surface influences agriculture by causing local
modifications in climate and weather and often is the major factor that deter-
mines the suitability of land for various types of farming. A work area may
include several topographic features such as mountains, hills, and valleys.
Individual farms, too, often have significant topographic variations that
affect crop production. Mountains and hills can greatly alter rainfalls, and
-- 10 --
it is not uncommon to find a drier, irrigated valley on one side of a mountain
range and a wetter, rainfed valley on the other side. Cold air usually set-
tles in valleys, making them considerably cooler than the surrounding slopes.
Steep slopes drain rapidly, but are very susceptible to erosion and drought,
while flat or sunken areas often have drainage problems. Slopes angled toward
the sun are warmer and drier than those angled away from it.
After climate and weather, soil type is the most important local physical
feature affecting cropping potential and management practices. Most soils
have evolved slowly over many centuries from weathering (decomposition) of
underlying rock material and plant matter. Some soils are formed from depos-
its laid down by rivers or seas (alluvial soils) or by wind loesss soils).
Soils have four basic components: air, water, mineral particles (sand,
silt, and clay), and humus (decomposed organic matter). A typical sample of
topsoil (the darker-colored top layer) contains about 50 percent pore space
filled with varying proportions of air and water depending on how wet or dry
the soil is. The other 50 percent of the volume is made up of mineral par-
ticles and humus. Most mineral soils contain about two to six percent humus
by weight in the topsoil. Organic soils like peats are formed in marshes,
bogs, and swamps, and contain 30-100 percent humus.
Climate, type of parent rock, topography, vegetation, management, and
time all influence soil formation and interact in countless patterns to pro-
duce a surprising variety of soils, even within a small area. In fact, it is
not uncommon to find two or three different soils on one small farm that
differ widely in management problems and yield potential.
Important Soil Characteristics
There are seven major characteristics that determine a soil's management
requirements and production potential: texture, tilth (physical condition),
water-holding capacity, drainage, depth, slope, and pH.
Texture refers to the relative amounts of sand, silt, and clay
in the soil.
Tilth refers to the soil's physical condition and capability of
Water-holding capacity refers to the ability of the soil to re-
tain water in its spaces.
Drainage refers to the soil's ability to get rid of excess water
and affects the accessibility of oxygen to roots.
Depth is the depth of the soil to bedrock and the effective soil
depth is the depth to which plant roots can penetrate.
Slope is the inclination of the land surface, usually measured
in percentage (i.e., number of meters change in elevation per
100 m horizontal distance).
-- 11 --
pH is a measure of the acidity or alkalinity of the soil on a
scale of 0 to 14.
These characteristics are discussed in detail in Soils, Crops and Fertil-
izer Use, U.S. Peace Corps Appropriate Technologies for Development Manual #8,
Parts I & II, by D. Leonard, 1969, and Crop Production Handbook, U.S. Peace
Corps Appropriate Technologies for Development Manual #6, Unit I, 1969.
For our purposes, ecology refers to the presence of people and inter-
action among the reference crops, weeds, insects, diseases, animals, and the
environment in general. Agriculture is a perpetual contest with nature, and
farmers have developed many preventative and control measures, as well as
special cropping systems, to give agriculture the advantage over natural
succession. Each area will have its own combination of weeds, insects,
diseases, and wildlife (including rats and grain-eating birds) that affect
crop production. Identifying these and learning how farmers cope with them is
crucial to understanding and dealing with the agricultural environment.
Modern technology, land shortages, and increasing populations have in-
creased agriculture's ability and need to "beat back" and manipulate nature.
Often little thought is given to the possible environmental consequences of
agricultural development. Potential ecological impacts of agricultural pro-
agrochemical poisoning of soil, water, animals, and people; and
The infrastructure, which refers to the installations, facilities, goods,
and services that encourage agricultural production, consists of these
local farming practices;
the physical infrastructure, such as roads and other transportation
*For further information, refer to Environmentally Sound Small-Scale Agricul-
tural Projects, VITA, 1979.
-- 12 --
* land distribution and tenure;
agricultural labor supply;
incentives to farmers.
Local Farming Practices and Systems
Farming practices include:
land preparation--tillage methods, type of seedbed, and erosion
planting methods, plant population and spacing, choice of
soil amendments--kind, amount, timing, placement of chemical or
organic fertilizers and liming materials.
control of weeds, insects, diseases, birds, rodents, and
nematodes (tiny, parasitic roundworms that feed on plant roots).
special practices such as irrigation or "hilling up" maize.
harvest and storage methods.
The term "cropping system" not only refers to the overall cropping
calendar (planting and harvest dates for the crops involved) but more
specifically to the actual crop sequences and associations involved.
Monoculture versus crop rotation--Monoculture is the repetitive
growing of the same crop on the same land year after year. Crop
rotation is the repetitive growing of an orderly succession of
crops (or crops and fallow) on the same land. One crop rotation
cycle often takes several growing seasons to complete (for
example, maize the first two years, followed by beans the third,
and cotton the fourth).
Multiple cropping--There are two types of multiple cropping.
One is sequential cropping, which means growing two or more
crops in succession on the same field per year or per growing
season. The other is intercropping, which is the most common
definition of multiple cropping and involves the growing of two
or more crops at the same time on the same field. See Chapter 4
for details on the different types of intercropping.
Due to differences in soils, climate, management ability, available
capital, and attitudes, important differences in farming practices and systems
may be found within a particular area.
The Physical Infrastructure
The physical infrastructure refers to the physical installations and
facilities that encourage agricultural production such as transportation
-- 13 --
(farm-to-market roads, railroads), communications, storage and market facili-
ties, public farm works (regional irrigation, drainage, and flood control
systems), and improvements to the farm (fencing, wells, windbreaks, irrigation
and drainage systems, etc.). All of these are important, but adequate and
reasonably priced transport is especially critical since agriculture is a
business that involves handling bulky materials. A farmer's distance from the
road network is often the prime factor determining whether or not he or she
can profitably use fertilizer or move his or her surplus crops to market.
Land Distribution and Tenure
In a settled area, all the agricultural land may be occupied. The land
distribution and tenure situation in an area thus has enormous social and
economic consequences and greatly affects farmer incentives. The two most
important issues in this regard:
Who occupies the land and on what terms do they use it or allow
others to use it?
What is the ratio between the number of people dependent on
farming for their livelihood and the amount and kinds of land
The Agricultural Labor Supply
The ratio of farmers and farm laborers to the amount and types of land
provides a good indication of land use intensity. The existence of adequate
farm labor for peak periods is another important consideration affecting farm
practices and returns. For most of the year, many farming areas in developing
countries have a generally high rate of agricultural underemployment, except
during a few peak periods such as planting at the start of the rains or
weeding time, if mechanical cultivation is not used. At these times, the
scarcity of labor can become the most critical factor limiting production, and
labor productivity assumes an unusual importance.
Incentives for Farmers
These can be very broadly interpreted, since they include equitable land
tenure and distribution, adequate markets and prices for farm produce, and the
existence of a viable improved technology.
UNDERSTANDING THE INDIVIDUAL FARM UNIT
Each farm has its own unique characteristics, but those located in the
same area usually share enough similarities to allow grouping them into
several general types of farm unit, such as subsistence, market-oriented field
crop, plantation, etc. If an area's environment is fairly uniform, only one
type of farm unit may predominate. If it is characterized by irregular
topography and lopsided land distribution, the area may have two or more types
of farm units.
-- 14 --
There are eight basic criteria that can be used to differentiate types of
type of occupancy;
size of farm, parcelling, and land use potential;
size of the farm business;
type of farm enterprise;
farm labor supply.
The principal factors here are:
natural characteristics such as soil type, slope, soil depth,
drainage, access to water, etc.;
proximity to the transportation network and other facilities
such as public irrigation and drainage systems;
location in relation to other farm units;
local name of the farm's location.
Type of Occupancy
The principal considerations:
Who owns the land?
If not owner-operated, what is the tenancy arrangement (i.e.,
cash rent, crop share, or work share) and on what specific
terms? How secure is the arrangement?
If no one has legal title to the land, is it occupied under
squatters' rights that are protected by law?
Who manages the farm unit and makes the basic decisions?
Size of Farm
The primary considerations are:
total farm size in terms of local units of measure.
-- 15 --
location of farm parcels: If they are dispersed, distance from
the farmer's house;
actual land use: tillable versus pasture versus forest;
irrigated versus non-irrigated.
characteristics of its soils: local name, color, texture,
depth, drainage, slope, plus farmer's opinion of them.
Size of Farm Business
Primary factors are:
land value of the farm unit;
value of other fixed assets;
amount of operating capital employed per land or livestock unit;
the value of production per land or livestock unit.
The value of the farm unit compared to its number of workers indicates
whether it is capital-intensive (using machines and money to harvest) or
labor-intensive (using human labor to perform farm operations). The value of
production per land unit indicates the intensity of land use.
Type of Farm Enterprise
Some farms are engaged in only one enterprise such as growing sugarcane,
coffee, rice, etc., but this type of monoculture is unusual among small
farms. More likely, some form of mixed agriculture will exist. The main
relative importance of each enterprise;
the yields obtained from each enterprise;
the disposal of the products from each enterprise (subsistence
or cash sale) and where sold;
crop rotations and associations;
relationship between crop and livestock production, if any.
The specific factors used in agricultural development.
Rate, method, and time of application.
Structures and Buildings
Condition of the farm family home (or the farm manager's and
farm workers' homes).
-- 16 --
Presence and condition of fences, wells, irrigation works, field
access roads, storage facilities, livestock shelters, corrals,
The Farm Labor Supply
degree of reliance on the family's own labor force and the
composition of that force;
degree of dependence on hired labor;
the seasonal nature of work requirements;
use of animal or tractor-drawn equipment.
GUIDELINES FOR THE ORIENTATION OF THE EXTENSION WORKER
These guidelines are designed to help newly assigned agricultural field
workers (AFW) orient themselves to the local agro-environment and its
individual farm units within one or two months after arrival in the area.
When using the guidelines, keep in mind the following.
Do not undertake a highly detailed survey of local resources at
the start of the assignment unless the host agency specifically
requests it. Such a survey is likely to arouse local
suspicions, especially if you are over-zealous or overbearing
with your initial contacts.
The host agency may provide a basic orientation to the work
area, but it may be very limited.
If there are discrepancies between the information gathered from
local sources (farmers, etc.) and that from outside or official
sources, trust the local "grass roots" information until it is
proven wrong. Local farmers are the ultimate authorities on the
The guidelines that follow are organized mainly by subject area
but do not have to be followed in a set order. You will be
picking up bits and pieces of information from a single
informant that may deal with a number of areas, and you will
have to put them into their proper context.
The initial phase focuses on the agricultural environment in general and
is designed to help you familiarize yourself with it and adjust your work
schedule and activities to the seasonal rhythm of the area's agriculture.
Unless severely limited by your local language ability, you should be able to
complete this phase in two to four weeks if you spend several hours a day
talking with local farmers and other sources of agricultural information
throughout the area.
-- 17 --
A major part of your time will be spent talking with and listening
to farmers and other knowledgeable sources (local residents) who have a
vested interest in agriculture.
Get a general idea of how farmers are distributed geographically.
Get a specific idea of where likely client farmers are located
(i.e., those with whom your job description deals).
Locate Other Knowledgeable Individuals
Agricultural technicians stationed or working in the area, local buyers
of farm produce, agricultural supply dealers, and truckers are good sources of
Select Reliable Local Sources
At the early stage, your contacts do not have to be completely represen-
tative so long as they are knowledgeable. The best farmer-informants are
usually among the more progressive farmers. For example, a progressive small
farmer will provide more information and insight into small farming operations
than a larger-scale commercial farmer. Likely initial contacts are your
landlord's relatives, the local mayor or other local official, the more easily
accessible and talkative farmers, or farmers who have worked with extension
services for some time. Keep a careful record of all initial contacts.
Learn How to Interview
Introductions--Ideally, you should have a third party make the
initial contact and introduction. If this is not possible, be
prepared with a practiced explanation of your presence. It is
important that you emphasize that you are the learner at this
Suggested techniques--Allow the farmer to talk as spontaneously
as possible. Any leading questions almost always get "yes"
responses. Use a memorized interview schedule rather than a
written one which is likely to inhibit responses. Avoid over-
It is generally not a good idea to take written notes in front of a
farmer, although in some cases he may expect you (as a "technician") to
do so. Some farmers may view written notes as having some possible
connection with future tax collections, etc. It's best to wait until an
unobtrusive moment such as the mid-day break to summarize information in
Become Familiar with the Principal Physical Features
In order to locate farms, farmers, agricultural suppliers, etc., you
should pinpoint their locations with reference to roads and trails and
-- 18 --
dominant topographic features. The principal physical and demographic
features of the work area should also be located and understood. These
topographical features--altitude, streams, principal features
(landmarks) recognized locally as reference points, valleys,
farms, and non farm lands;
communications (roads and trails)--seasonal access, distances,
travel times, and modes of travel between points;
demographic--locations of communities (and their local names),
infrastructure--irrigation systems, drainage systems,
agricultural supply stores, schools, extension offices, etc.
You can make a base reference map yourself which shows these features,
relying on your own observations as well as road maps, geographic maps, or
soil survey/land use maps available from government agencies and international
or regional organizations working in the area.
Become Familiar with Climate and Weather Patterns
Sources of Information
Weather station records--Obtain all available meteorological
data from the official weather station nearest to your area of
assignment. Its orientation value will depend on the station's
proximity and how well it represents your area's conditions.
Relief maps--Altitude is the main temperature determinant in the
tropics; remember that for every 100 m rise in altitude, average
(mean) temperature will drop about 0.650C.
Local farmers--Official weather data can be valuable, but it is
not essential. Information about local climate and weather
conditions can be learned from experienced local farmers.
You can draw a rainfall chart which is accurate enough for the initial
orientation simply by systematically recording farmer's comments about the
seasonal distribution of rainfalls; the same can be done for seasonal
Climate and weather checklist. Make tables and/or charts showing the
monthly distribution of rainfall using these criteria:
Dry to wet scale: (See rainfall section, Chapter 2.)
Rainfall frequency: the number of times it normally rains in a
week or month.
Risk factors associated with climate and weather (i.e., droughts, hail,
high winds, flooding) can be established by having farmers recall bad crop
years over a span of years. Be sure to distinguish weather factors from other
causes such as insects and diseases.
-- 19 --
As for temperature, be sure to record:
monthly temperature averages;
periods of significantly high or low temperatures;
occurrence of first and last killing frosts if applicable.
Become Familiar with Prevailing Farming Systems and Practices
Identify the major crop and livestock enterprises in the work area.
For each of the crop enterprises which predominates in the area, indicate
the following and note any local variations.
Note the growing season--Indicate the normal growing season and
its variations (early-late), and make a cropping calendar using
line bar graphs. (See page 22.)
Describe production practices--Do not confuse the practices
recommended by extension with those generally accepted by
farmers. Your interest is in the prevailing practices used by
most of the farmers in the area. Make notes of any significant
differences among different groups of farmers.
Describe the principal land preparation practices--Specify the
earliest and lates dates of application and indicate what the
practices are called locally. For example, in many areas of
Central America, the practice of hilling up maize (throwing soil
into the row) is called "aprogue."
Describe the kind and amount of inputs associated with the
practice. This includes the amount applied, method and timing
of application, and worker-days of labor.
Estimate yields and returns
At this stage of the orientation, it is not necessary to make a detailed
account of costs and returns. Seeking such data can arouse local suspicions
or fears of future tax levies. Rough estimates of production costs and gross
and net returns are sufficient.
Record reported yields per unit of land.
Record recent prices at normal time of sale.
Multiply recent prices by approximate average yield to get
approximate gross returns.
Subtract approximate production costs from gross returns to
obtain approximate net returns. There are two ways to do this:
net return to capital, land, and family labor where the only
labor costs you account for are hired labor, or net return to
land and capital in which case an opportunity cost (exchange
value) must be assigned to family labor and subtracted from the
gross return. The first way is the easier.
-- 20 --
Indicate the relative tendencies of production.
Estimate the percentage of the crop that is marketed.
Identify the principal local market outlets (buyers).
Indicate the seasonal movement of production off the farms: is
it sold at harvest, some sold at harvest, some held for higher
Indicate the seasonal price fluctuations (average over several
List the outside production inputs which are available locally. ("Available"
means when needed.)
Crop production supplies (give brands, grades, and unit prices):
fertilizers, insecticides, fungicides, herbicides, hand tools,
hand-operated equipment, seeds, etc.
Agricultural machinery and equipment (if used): tractors
(horsepower and make), implements, irrigation pumps, etc.
Services such as custom machinery services and rates charged,
professional services (indicate whether public or private),
technical assistance and soil testing, etc.
Summarize the Information
Every area's agriculture is tuned to a time schedule or seasonal rhythm
to which work schedules and activities must be adjusted. Getting oriented in
time is vital to effective agricultural extension.
The best way to do this is to summarize the initial phase of orientation
by making graphs and calendar charts that show the area's seasonal rhythm of
climate, agriculture, and social life.
The following graphs, charts, and observations were made by a group of
Peace Corps Volunteers assigned as rural credit agents in the Pacific region
of Nicaragua during an orientation-training exercise. The principles involved
Make a generalized climate and weather calendar
Chart the normal monthly distribution of rainfall as related by farmers
using terms such as wet, dry, some rain, wettest time, rainfall drops off,
etc. There are three ways to do this. (See charts on next page.)
1. Use the frequency of rainfall to measure seasonal distribution.
2. Use a dry-to-wet scale.
3. Measure rainfall, if you have access to reliable meteorological
data. Indicate the range and frequency of possible deviations
from normal rainfall patterns from information passed on to you
from farmers, or recorded by a weather station.
-- 21 --
J F M A M J J A S O N D
Frequency of Rainfall
Example: Crop Calendar, Crops and Order of Importance in the
Esteli Area of Nicaragua
1. Maize, long season
2. Rice, dryland
4. Improved, non-
~~ --- - -
J F M A M JJ A S O N D J
Example: Distribution of Work and Timing of Principal Farming
Operations in the Esteli,Area of Nicaragua
J F M A M J J A S 0 N D J
1. Land clearing
2. Land preparation
3. Principal seeding
-- 22 --
Make a calendar of agricultural activity
For each of the major crop enterprises, display the length and
possible range of growing season, including likely variations in
planting and harvest times.
(See example in the middle of previous page.)
Indicate the time for performing critical operations and
relative labor requirements of those operations.
(See example at the bottom of previous page.)
Indicate the relative seasonal labor demand, whether there are
any periods of labor movement into or out of the area. Deter-
mine the seasonal demand for other critical inputs: keep in
mind an input is not considered critical unless farmers feel it
is. (For example, if fertilizer is not generally used, it is
not presently a critical input.)
Make a calendar of economic activity related to agriculture
Indicate relative demand for short-term production credit.
(See example below.)
Indicate seasonal marketing patterns (the rate at which the crop
Graph the seasonal range of prices.
Make a calendar of social activity that includes religious holidays and other
holidays or seasonally determined social obligations.
The summary concludes the initial orientation phase. With a good under-
standing of the local agricultural environment and farming practices, you are
ready to move on to the next step: orientation to the individual farm unit.
Example: Demand for Production Credit, Branch Office of the
National Bank of Nicaragua
Number of 200
per Month 1
100 \ \
J F M A M J J A S 0 N D J
-- 23 --
ORIENTATION TO THE FARM UNIT
Learning to communicate effectively with individual farmers about their
farm enterprises and their farm businesses will help move you out of the
questioning stage into a more active role. Expressing an interest in and
being knowledgeable about the farm business can be the means as well as the
purpose of communicating with farmers and will definitely increase your
rapport and credibility with them.
Describe Typical Farm Units
Make a general farm profile which is representative for each of the types
of farm unit with which you will be working.
Describe the Annual Agricultural Cycle as Perceived by the Farmer
For each type of farm unit with which you are likely to work, make an
annual diary which indicates:
normal operations by months or seasons;
the decisions which the farmer has to make that are related to
the farmer's concerns throughout the year, such as the timing of
the rains, dry spells, bird damage to crops, flooding, obtaining
inputs, completing operations in time, etc.
-- 24 --
CHAPTER 3. AN INTRODUCTION TO THE REFERENCE CROPS
There are several reasons why the six reference crops--maize, grain sor-
ghum, millet, peanuts, field beans, and cowpeas--are grouped together in one
manual. All of the reference crops are row crops (grown in rows) and because
of this, they share a number of similar production practices. Also, in devel-
oping nations, two or more of the crops are likely to be common to any farming
region and are frequently interrelated in terms of crop rotation and inter-
cropping. (See Chapter 4.) In addition, all of them are staple food crops.
The developing countries are major producers of the reference crops, with the
exception of maize.
CEREAL CROPS VERSUS PULSE CROPS
Maize, grain sorghum, and millet are known as cereal crops, along with
rice, wheat, barley, oats, and rye. Their mature, dry kernels (seeds) are
often called cereal grains. All cereal crops belong to the grass family
(Gramineae) which accounts for the major portion of the monocot (Monocotyle-
donae) division of flowering (seed-producing) plants. All monocot plants
first emerge from the soil with one initial leaf called a seed leaf or
Peanuts, beans, and cowpeas are known as pulse crops, grain legumes, or
pulses, along with others such as lima beans, soybean, chickpeas, pigeonpeas,
mung beans, and peas. The pulses belong to the legume family (Leguminosae)
which produce their seeds in pods. Some legumes like peanuts and soybeans are
also called oilseeds because of their high vegetable oil content.
The pulses belong to the other major division of flowering plants called
dicots (Dicotyledonae). Unlike the monocots, dicot plants first emerge from
the soil with two seed leaves.
World and Regional Production of the Reference Crops
(1977 FAO data)
Crp Total World Production Percent of World Production
(millions of metric tons) Developing Developed
MAIZE 350.0 32.4 67.6
GRAIN SORGHUM 55.4 59.9 40.1
MILLET 42.9 95.1 4.9
PEANUTS (Groundnuts) 17.5 88.2 11.8
FIELD BEANS, COWPEAS 12.9 86.1 13.9
-- 25 --
(Left) A germinating maize seedling; note that it has only one seed
leaf which makes it a monocot. Monocots emerge through the soil
with a spike-like tip. They generally have fewer problems with
clods and soil dusting than dicots.
(Right) A germinating bean plant; note the two thick cotyledons
(seed leaves) which originally formed the two halves of the seed.
In addition, the pulses have two outstanding characteristics for farmers
and for those who consume them.
They contain two to three times more protein than cereal
grains. (See Table 3.)
Legumes obtain nitrogen for their own needs through a symbiotic
(mutually beneficial) relationship with various species of
Rhizobia bacteria that form nodules on the plants' roots. (See
illustration on the following page.) Nitrogen is the plant
nutrient needed in the greatest quantity and is also the most
costly when purchased as chemical fertilizer. The Rhizobia live
on small amounts of sugars produced by the legume and, in
return, convert atmospheric nitrogen (ordinarily unavailable to
plants) into a usable form. This very beneficial process is
called nitrogen fixation. In contrast, cereal grains and other
non-legumes are totally dependent on nitrogen supplied by the
soil or from fertilizer.
Despite the urgent need to increase both cereal and pulse production in
the developing countries, most crop improvement efforts of the "Green Revolu-
tion" emphasized the cereals. (See Chapter 7.) As a result, pulse yields in
-- 26 --
the region have shown little, if any, increase. In some areas, total pulse
production has actually declined in favor of the cereal grains, even though
many developing nations suffer from a chronic protein shortage. Fortunately,
this situation is now being reversed.
Nitrogen-fixing nodules on the roots of
Sa bean plant. Note that they are
attached to the roots but are not an
actual part of them.
THE NUTRITIONAL VALUE OF THE REFERENCE CROPS
The cereal grains have relatively low protein contents (7-14 percent) as
shown in Table 3, and they are also deficient in several essential amino acids
which determine protein quality. However, their high starch content and much
lower in price compared to the pulses makes them (along with starchy root
crops) the major source of energy (calories) in developing countries. In
these countries, cereals consumption is high enough to contribute a substantial
amount of protein to the diets of older children and adults, although still
well below quantity and quality requirements. Infants and young children have
much higher protein needs per unit of body weight and a smaller stomach
capacity which prevent them from getting as much protein benefit from the
cereals. In addition, the cereal grains contain a number of vitamins and
minerals, although vitamin A is found only in the yellow varieties of maize
and sorghum. However, studies on traditional preparation methods for maize,
Nutritional Value of the Reference Crops
(dry weight basis)
CrQp Percent Protein Calories/100 grams Calories/lb.
MAIZE 8-10 355 1600
GRAIN SORGHUM 7-13 350 1600
MILLET (Pearl) 10-13 330 1500
COMMON BEANS 21-23 340 1550
COWPEAS 22-24 340 1550
PEANUTS GROUNDNUTSS) 28-32 400 1800
-- 27 --
sorghum, and millet that involve milling and alternate soaking and drying have
shown losses up to 45 percent in dry matter, 45 percent in protein, and 90
percent in vitamins and minerals.
The pulses have considerably higher protein contents than the cereal
grains (17-30 percent in the reference pulses) and generally higher amounts of
B vitamins and minerals. Unfortunately, they also may have some deficiencies
in amino acids.
All animal proteins (meat, poultry, fish, eggs, milk, and cheese) are
complete proteins (contain all essential amino acids), but their high cost
puts them out of reach of much of the population in developing nations.
Fortunately, it is possible to satisfy human protein requirements without
relying solely on animal protein sources. The cereals and pulses, though not
complete proteins in themselves, can balance out each other's amino acid
deficiencies. Cereals are generally low in the essential amino acid lysine,
but relatively high in another, methiomine. The opposite is true for most of
the pulses. If eaten together or within a short time of each other and in the
right proportion (usually about a 1:2 ratio of pulse to cereal), combinations
like maize and beans or sorghum and chickpeas are complete proteins. In most
developing countries, however, pulses are more expensive than the cereal
grains, a fact which creates difficulties in achieving a balanced diet.
AN INTRODUCTION TO THE INDIVIDUAL CROPS
Maize (Zea mays)
Distribution and Importance
In terms of total world production, maize and rice vie for the number two
position after wheat. Several factors account for the importance of maize.
Maize can adapt to a wide range of temperature, soils, and
moisture levels and resists disease and insects.
It has a high yield potential.
It is used for both human and animal consumption.
Types of Maize
There are five principal types of maize.
Dent: The most widely grown type in the United States. The
seed has a cap of soft starch that shrinks and forms a dent at
the top of the kernel.
Flint: Widely grown in Latin America, Asia, Africa, and
Europe. The kernels are hard and smooth with very little soft
starch. It is more resistant to storage insects like weevils
than dent or floury maize.
-- 28 --
An ear of maize. Each silk leads to an ovula (potential kernel) on the cob.
Varieties vary in length and tightness of husk covering, which determines
resistance to insects and moisture-induced molds which may attack the ear in
-- 29 --
-- 30 --
Floury: Mainly soft starch and widely grown in the Andean
region of South America. It is more prone to storage insects
and breakage than harder types.
Pop: Really an extreme form of flint maize.
Sweet: At least twice as high in sugar as ordinary maize and
meant to be consumed in immature form when only about one-third
the potential grain yield has accumulated. It is more prone to
field insect damage, especially on the ears.
A potentially very valuable type called hi-lysine maize with more than
double the content of lysine is nearing the mass application stage, but still
has some field and storage problems to overcome. (See the section on maize
improvement at the end of this chapter.)
Average yield of shelled grain (14 percent moisture) under varying
conditions are shown below.
Average Yield of Shelled Grain
Top farmers in the
TT S rC 'n 1t -
9 Cnn -) nn000
.-,. o. n Puuu--./, uuM-r IU, UUU-.LJ, UU
U.S. Average 5,050 5,700
developed countries 4,200 4,700
Average for LDC's 450-1,350 500-1,500
Feasible yield for small
scale LDC farmers with 3,500-5,500 4,000-6,000
Source: FAO and USDA data, 1977.
Climatic Requirements of Maize
Rainfall. Non-irrigated (rainfed) maize requires a minimum of around
500mm of rainfall for satisfactory yields. Ideally, the bulk of this should
fall during the actual growing season, although deep loamy or clayey soils can
store up to 250 mm of pre-season rainfall in the future crop's root zone. Any
of the following factors will act to increase the moisture needs of maize (and
long growing periods due to cool temperatures;
-- 31 --
* shallow and/or sandy soils with low water-holding ability;
excessive water runoff due to lack of erosion control on sloping
low humidity, especially when combined with wind.
Maize has some ability to resist dry spells but is not nearly as
drought-tolerant as sorghum and millet.
Temperature. The optimum growth rate of maize increases with tempera-
tures up to about 32-350C if soil moisture is abundant, but decreases
slightly with temperatures around 27-300C when soil moisture is adequate.
If soil moisture is low, the optimum growth rate temperature drops to 270C
or below. At temperatures of 100C or below, maize grows slowly or not at
all and is susceptible to frost. However, daytime temperatures in excess of
320C will reduce yields if they occur during pollination. Yields are also
reduced by excessively high nighttime temperatures, since they speed up the
plant's respiration rate and the "burning up" of the growth reserves.
Soil requirements. Maize grows well on a wide variety of soils if drain-
age is good (no waterlogging). It has a deep root system (up to 185 cm) and
benefits from deep soils which allow for improved moisture storage in dry
spells. The optimum pH for maize is in the 5.5-7.5 range, although some trop-
ical soils produce good yields down to a pH of 5.0 (very acid). The liming
and nutrient needs of maize are covered in Chapter 5.
Response to daylength. The length of growth period of many plants is
affected by daylength. This is known as a photosensitive (photoperiodic)
response. Most maize varieties are short day plants which means that they
will mature earlier if moved to a region with significantly shorter daylengths
than they were bred for. In the tropics, there is relatively little variation
in daylength during the year or between regions. Because most temperate zone
maize varieties are adapted to the longer daylengths of that area's summer,
they will flower and mature in too short a period for good yield accumulation
if moved to the tropics. Sweet maize seed from the temperate zone may reach
little more than knee height in the tropics, and produce disappointingly small
ears, although in record time! Likewise, the "giant" novelty maize advertised
in some gardening magazines is nothing more than a variety adapted to the very
short daylengths of the tropics. When grown in the temperate zone, the much
longer daylengths retard maturity and favor vegetative growth. Some maize
varieties, however, are day neutral with little response to variations in
As mentioned earlier, maize's relatively low protein and high starch
content makes it important as an energy (calorie) source. Many people believe
that yellow maize has more protein than white maize, but the only nutritional
difference between the two is the presence of Vitamin A (also called carotene)
in the yellow variety.
Unlike production in the developed countries, maize production in devel-
oping countries is almost entirely used for human food in the form of meal,
flour, tortillas, or a thick paste. In humid areas where increased spoilage
problems make grain storage more difficult, a significant portion of maize may
-- 32 --
be consumed much like sweet corn while it is still in the semi-soft, immature
Maize has numerous industrial and food uses in the form of some 500
products and by-products. Various milling and processing methods can produce
starch, syrup, animal feed, sugar, vegetable oil, dextrine, breakfast cereals,
flour, meal, and acetone. Maize also is used for making alcoholic beverages
throughout the world.
Maize Stages of Growth
Depending on the variety and growing temperatures, maize reaches physio-
logic maturity (the kernels have ceased accumulating protein and starch) in
about 90-130 days after plant emergence when grown in the tropics at eleva-
tions of 0-1,000 meters. At higher elevations, it may take up to 200-300
days. Even at the same elevation and temperature, some varieties will mature
much earlier than others and are known as early varieties. The main differ-
ence between an early (90-day) and a late 130-day) variety is in the length
of time from plant emergence to tasseling (the vegetative period). This stage
will vary from about 40 to 70 days. The reproductive period tasselingg to
maturity) for both types is fairly similar and varies from about 50 to 58
days. The following discussion describes the growth stages and related
management factors of a 120-day maize variety.
Phase I: Germination to Tasseling. Plants will emerge in four to five
days under warm, moist conditions but may take up to two weeks or more during
cool or very dry weather. Little if any germination or growth occurs at soil
temperatures below 130C. Harmful soil fungi and insects are still active in
cool soils and can cause heavy damage before the seedlings can become
established. Fungicide seed treatments are usually most beneficial under
cool, wet conditions and may increase yields from 10 to 20 percent. (See
Maize seeds are large and contain enough food reserves to sustain growth
for the first week or so after emergence. Then the plants must rely on
nutrients supplied by the soil or fertilizer. Up until knee-high stage, the
three major nutrients--nitrogen, phosphorus, and potassium--are required in
relatively small amounts, but young seedlings do need a high concentration of
phosphorus near their roots to stimulate root development.
The primary roots reach full development about two weeks after seedling
emergence and are then replaced by the permanent roots (called nodal roots)
which begin growing from the crown (the underground base of the plant between
the stem and the roots). Planting depth determines the depth at which the
primary roots form but has no effect on the depth at which the permanent roots
begin to develop.
Until the plants are knee high, the growing point (a small cluster of
cells from which the leaves, tassel, and ear originate) is still below the
soil surface, encased by a sheath of unfurled leaves. A light frost or hail
may kill the above-ground portion of the plant, but usually the growing point
(if below ground) will escape injury, and the plant will recover almost com-
pletely. However, flooding at this stage is more damaging than later on when
the growing point has been carried above ground by the stalk.
-- 33 --
The growing point plays a vegetative role by producing new leaves (about
one every two days) until the plants are knee high; then a major change
occurs. Within a few days, the underground growing point is carried above
ground by a lengthening of the stalk and switches from leaf production to
tassel initiation within the plant. (Slit a plant lengthwise at this stage,
and you can easily see the growing point as a peaked tip inside the stalk.)
At this time roots from adjacent rows have reached and crossed each other in
the between-row spaces (for rows up to one meter wide).
From tassel initiation until tassel emergence takes about five to six
weeks and is a period of very rapid growth in plant height, leaf size, and
root development. Maximum root depth can reach 180 cm under optimum soil,
moisture, and fertility conditions and is attained by the time of tassel
Maximum nutrient uptake occurs from about three weeks before to three
weeks after tasseling and maximum water use from tasseling through the
soft-dough stage (about three weeks after tasseling).
Phase II: Tasseling and Pollination. Tasseling occurs about 40-70 days
after plant emergence in 90-130 day varieties. The tassel (flower) is thrust
out of the leaf whorl about one to two days before it begins shedding pollen.
Pollen shed starts two to three days before the silks emerge from the ear tip
and continues for five to eight days. If conditions are favorable, all the
silks emerge within three to five days and most are pollinated the first day.
Each silk leads to an ovule (a potential kernel). When a pollen grain
lands on a silk, it puts out a pollen tube that grows down the silk's center
and fertilizes the ovule at the other end in a matter of hours. Shortage of
pollen is rarely a problem since about 20,000-50,000 pollen grains are pro-
duced per silk. Poor ear fill (the number of kernels on an ear) or skipped
kernels are nearly always caused by delayed silk emergence or by ovule abor-
tion, both of which are caused by drought, overcrowding, or a shortage of nit-
rogen and phosphorus. Extreme heat (above 350C) can diminish pollen vigor
and also affect ear fill. Some insects such as the corn rootworm beetle
(Diabrotica spp.) or Japanese beetle (Popillia japonica) can cut off the silks
Maize is cross-pollinated, and usually 95 percent or more of the kernels
of a cob receive their pollen from neighboring maize plants. This also means
that different maize types such as the hi-lysine varieties must be kept isola-
ted from other maize pollen if they are to retain the desired characteristics.
Pollination is a very critical time during which there is a high demand
for both water and nutrients. One to two days of wilting during this period
can cut yields by as much as 22 percent and six to eight days of wilting can
cut yields by 50 percent.
A few days after pollination, the silks begin to wilt and turn brown.
Unpollinated silks will remain pale and fresh looking for several weeks but as
mentioned above, they can only receive pollen for a week or so after they
emerge from the ear tip.
-- 34 --
Phase III: Kernel Development to Maturity. Most maize ears have 14-20
rows with 40 or more ovules per row and produce about 500-600 actual kernels.
Any shortage of water, nutrients, or sunlight during the first few weeks of
kernel development usually affects the kernels at the tip of the ear first,
making them shrivel or abort. Maize is very prone to moisture stress (water
deficiency) at this stage due to a heightened water requirement (up to 10 mm
per day under very hot and dry conditions).
Wind damage during early kernel development is seldom serious, even
though the plants may be knocked almost flat, since they still have the
ability to gooseneckk" themselves (curve up) into a nearly vertical position.
Stages of Kernel Development in Maize
Blister stage: About 10 days after pollination when the ker-
nels begin to swell, but contain liquid with very little solid
Roasting ear stage: About 18-21 days after pollination.
Though field maize has a much lower sugar content than sweet
maize, at this stage it is still sweet. At this stage the
kernels have accumulated only about one-third of the total dry
matter yield they will have at physiologic maturity. From this
time on, any type of stress is more likely to affect kernel
size than grain fill at the ear tip.
Dough stage: About 24-28 days after pollination.
Approaching maturity: As maturity nears, the lower leaves
begin to turn yellow and die. In a healthy, well-nourished
plant, this should not occur until the ear is nearly mature.
However, any serious stress factor--drought, low soil fertil-
ity, excessive heat, diseases--can cause serious premature leaf
death. Ideally, most of the leaves should still be green when
the husks begin to ripen and turn brown. Early death of the
maize plant can greatly reduce yields and result in small,
Physiologic maturity: About 52-58 days after 75 percent of the
field's ear silks have emerged. The kernels have reached their
maximum yield and have ceased accumulating more dry matter.
However, they still contain about 30-35 percent moisture which
is too wet for damage-free combine harvesting (picking and
shelling) or for spoilage-free storage (except in the form of
husked ears in a narrow crib; see Chapter 7). Small farmers
usually let the maize stand in the field unharvested for sev-
eral weeks or more to allow some further drying. In some
areas, particularly Latin America, it is a common practice to
bend the ears (or the plants and the ears) downward to prevent
rain from entering through the ear tips and causing spoilage.
It also helps minimize bird damage and lets in sunlight for any
intercropped plants that may be seeded at this time.
Number of ears per plant. Most tropical and sub-tropical maize varieties
commonly produce two to three useful ears per plant under good conditions. In
-- 35 --
contrast, most U.S. corn belt types are single eared. One advantage of
multiple-eared varieties (often called prolifics) is that they have some built
in buffering capacity in case of adverse conditions and may still be able to
produce at least one ear.
Grain Sorghum (Sorghum bicolor)
Distribution and Importance
Although grain sorghum accounted for only 3.6 percent of total world
cereal production in 1977 (FAO data), several factors make it an especially
important crop in the developing world.
The developing nations account for about 60 percent of the
world's grain sorghum production.
It is drought-resistant and heat-tolerant and particularly
suited to the marginal rainfall areas of the semi-arid tropics
(such as the savanna and Sahel zones of Africa where food
shortages have been critical).
Types of Sorghums
Grain sorghum vs. forage sorghum. Where sorghum is grown in the devel-
oped world, a definite distinction is made between forage sorghum and grain
sorghum types. For example, in the United States (where grain sorghum is
often called "milo"), nearly all grain types have had dwarf genes bred into
them to reduce plant height to 90-150 cm for more manageable machine
harvesting. In contrast, forage sorghum types are much taller and have
smaller seeds and a higher ratio of stalk and leaves to grain. They are used
largely for cattle feed as fresh green chopped forage or silage (green forage
preserved by a fermentation process), but are sometimes grazed. Sudangrass is
a variety of forage sorghum with especially small seedheads and thin-bladed
leaves and sorghum-sudan crosses also are available.
In the developing countries, especially where cattle are important, most
traditional grain sorghum varieties have some forage type characteristics such
as tallness and a high proportion of stalk to leaves. There are many regional
variations among local grain sorghum types.
Sweet sorghum (Sorgo) and broomcorn. Sorgo types have tall, juicy stalks
with a high sugar content and are used for making syrup and also for animal
feed in the form of silage and forage. Broomcorn is a sorghum type grown for
its brush, which is used mainly for brooms.
Grain sorghum exhibits greater yield stability over a wider range of
cropping conditions than maize. Although it will outyield maize during
below-normal rainfall periods, the crop might suffer some damage under very
high rainfall. Yields of dry (14 percent moisture) grain are shown under
varying growing conditions on the following page (based on FAO, USDA, and
international research institute data).
-- 36 --
-- 37 --
Protein content vs. yield. The protein content of sorghum kernels can
vary considerably (7-13 percent on soils low in nitrogen) due to rainfall
differences. Since nitrogen (N) is an important constituent of protein,
kernel protein content is likely to be highest under very low rainfall that
cuts back yields and concentrates the limited amount of N in a smaller amount
of grain. Protein fluctuation is much less on soils with adequate nutrition.
Yields of Dry Grain
Top yields in the U.S.
under irrigation 9000-12,000 10,000-13,4000
Top rainfed yields in
the U.S. 5000-8000 5600-9000
U.S. Average 3130 3520
Average for the
developed countries 2900 3260
Average for developing
countries 400-800 450-900
Feasible rainfed yields for 3360-5000 3000-4500
farmers using improved
Climatic Requirements of Sorghum
Grain sorghum tolerates a wide range of climatic and soil conditions.
Rainfall. The sorghum plant, aside from being more heat- and drought-
resistant than maize, also withstands periodic waterlogging without too much
The most extensive areas of grain sorghum cultivation are found where
annual rainfall is about 450-1,000 mm, although these higher rainfall areas
favor the development of fungal seed head molds that attack the exposed
sorghum kernels. The more open-headed grain sorghum varieties are less
susceptible to head mold.
Several factors account for the relatively good drought tolerance of
Under drought conditions the plants become dormant and will
curl up their leaves to reduce water losses due to
transpiration (the loss of water through the leaf pores into
The leaves have a waxy coating that further helps to reduce
-- 38 --
The plants have a low water requirement per unit of dry weight
produced and have a very extensive root system.
Temperature and soil requirements. Although sorghum withstands high
temperatures well, there are varieties grown at high elevations that have a
good tolerance to cool weather as well. Light frost may kill the above ground
portion of any sorghum variety, but the plants have the ability to sprout
(ratoon) from the crown.
Sorghum tends to tolerate very acid soils (down to pH 5.0 or slightly
below) better than maize, yet it is also more resistant to salinity (usually
confined to soils with pH's over 8.0).
Response to daylength (photosensitivity). Most traditional sorghum vari-
eties in the developing countries are very photosensitive. In these photosen-
sitive types, flowering is stimulated by a certain critical minimal daylength
and will not occur until this has been reached, usually at or near the end of
the rainy season. This delayed flowering enables the kernels to develop and
mature during drier weather while relying on stored soil moisture. (This is
actually a survival feature which allows seed heads to escape fungal growth in
humid, rainy conditions.) These local photosensitive varieties usually will
not yield as well outside their home areas (especially further north or south)
since their heading dates still remain correlated to the rainy season and day-
length patterns of their original environment. Despite this apparent adapta-
tion to their own areas, the traditional photosensitive varieties have a rela-
tively low yield potential and may occupy land for a longer period to produce
a good yield (due to their fixed flowering dates). In addition, there is
always the danger that the rains will end early and leave an inadequate
reserve of soil moisture for kernel development. Breeding programs are
attempting to improve these photosensitive types, and many of the improved
varieties show little sensitivity to daylength.
Other Sorghum Characteristics
Ratooning and tillering ability. The sorghum plant is a perennial (cap-
able of living more than two years). Most forage sorghums and many grain var-
ieties can produce several cuttings of forage or grain from one planting if
not killed by heavy frost or extended dry weather. New stalks sprout from the
crown (this is called ratooning) after a harvest.
However, ratooning ability has little value in most areas where non-
irrigated sorghum is grown. In these areas, either the rainy season or frost-
free period is likely to be too short for more than one grain crop or too wet
for a mid-rainy season first crop harvest without head mold problems. How-
ever, forage sorghums take good advantage of ratooning, since they are harves-
ted well before maturity, usually at the early heading stage. Cattle farmers
in El Salvador take three cuttings of forage sorghum for silage-making during
the six-month wet season. In irrigated tropical zones with a year-round grow-
ing season such as Hawaii, it is possible to harvest three grain crops a year
from one sorghum planting by using varieties with good ratooning ability.
Some grain sorghum varieties have the ability to produce side shoots that
grow grain heads at about the same time as the main stalk (this is called til-
lering). This enables such varieties to at least partially make up for too
thin a stand of plants by producing extra grain heads.
-- 39 --
The Toxicity Factor: Hydrocyanic Acid
Young sorghum plants or drought-stunted ones under 60 cm tall contain
toxic amounts of hydrocynaic acid (HCN or prussic acid). If cattle, sheep, or
goats are fed on such plants, fatal poisoning may result. Fresh, green
forage, silage, and fodder (dried stalks and leaves) are usually safe if over
90-120 cm tall and if growth has not been interrupted. The HCN content of
sorghum plants decreases as they grow older and is never a problem with the
mature seed. An intravenous injection of 2-3 grams of sodium nitrite in
water, followed by 4-6 grams of sodium thiosulfate, is the antidote for HCN
poisoning in cattle; these dosages are reduced by half for sheep.
Nutritional Value and Uses of Sorghum
Nearly all grain sorghum used in the developed world is fed to livestock
(mainly poultry and swine). However, in developing countries it is an impor-
tant staple food grain and is served boiled or steamed in the form of gruel,
porridge, or bread. In many areas, it is also used to make a home-brewed
beer. In addition, the stalks and leaves are often fed to livestock and used
as fuel and fencing or building material.
Like the other cereals, grain sorghum is relatively low in protein (8-13
percent) and is more important as an energy source. If eaten along with
pulses in the proper amount (usually a 1:2 grain/pulse ratio), it will provide
adequate protein quantity and quality. Only those varieties with a yellow
endosperm (the starchy main portion of the kernel surrounding the germ)
contain vitamin A.
Because sorghum is very susceptible to bird damage during kernel develop-
ment and maturity, bird-resistant varieties have been developed. Because it
has a high tannin content in the seeds, stalks, and leaves, it is partly
effective in repelling birds from the maturing seedheads. However, these high
tannin varieties are more deficient in the essential amino acid lysine than
ordinary varieties which has consequences for humans and other monogastrics
like pigs and chickens. In the United States, this is overcome by adding
synthetic lysine to poultry and swine rations that are made from
bird-resistant sorghum grains. In developing countries a slight increase in
pulse intake can overcome this problem in humans.
Grain Sorghum Growth Stages
Depending on variety and growing temperatures, non-photosensitive grain
sorghum reaches physiologic maturity in 90-130 days within the 0-100 m zone in
the tropics. However, the local, daylength-sensitive varieties may take up to
200 days or more because of delayed flowering. At very high elevations, all
varieties may take 200 days or more.
As with maize, the main difference between a 90-day and 130-day sorghum
variety is in length of vegetative period (the period from seedling emergence
to flowering). The grain filling period (pollination to maturity) is about
-- 40 --
the same for both (30-50 days). The following sections describe the growth
stages and management factors of a typical 95-day variety. These principles
remain the same no matter what variety is grown.
Phase I: Emergence to Three Weeks. Sorghum seedlings will emerge in
three to six days in warm, moist soil. Under cool conditions where emer-
gence is delayed, the seeds are especially prone to harmful soil fungi and
insects, and a fungicide/insecticide seed dressing may be particularly
beneficial. (See Chapter 6.) Compared with maize, the small sorghum seeds
are low in food reserves which are quickly exhausted before enough leaf area
is developed for photosynthesis. For this reason the seedlings get off to a
slow start during the first three weeks, after which the growth rate speeds up.
This sluggish beginning makes good weed control extra important during
For the first 30 days or so, the growing point which produces the leaves
and seedhead is below the soil surface. Hail or light frost is unlikely to
kill the plant, since new growth can be regenerated by the growing point.
However, regrowth at this stage is not as rapid as with maize.
Phase II: Three Weeks to Half-Bloom (60 days after emergence). Growth
rate and the intake of nutrients and water accelerates rapidly after the first
three weeks. The "flag" leaf (the final leaf produced) becomes visible in the
leaf whorl about 40 days after emergence. "Boot" stage is reached at about 50
days when the flower head begins to emerge from the leaf whorl but is still
encased by the flag leaf's sheath. The head's potential size in terms of seed
number has by now been determined. Severe moisture shortage at boot stage can
prevent the head from emerging completely from the flag leaf sheath. This
will prevent complete pollination at flowering time.
Half-bloom stage is reached at about 60 days when about half of the
plants in a field are in some phase of flowering at their heads. However, an
individual sorghum plant flowers from the tip of the head downward over four
to nine days, so half-bloom on a per plant basis occurs when flowering has
proceeded halfway down the head. Although time to half-bloom varies with
variety and climate, it usually encompasses two-thirds of the period from
seedling emergence to physiologic maturity. In keeping with the rapid rates
of growth and nutrient intake, about 70, 60, and 80 percent of the nitrogen,
phosphorus, and potassium requirements (respectively) have been absorbed by
the plant by the time of half-bloom. Severe moisture shortage at pollination
greatly cuts yields by causing seed ovule abortion and incomplete pollination.
Phase III: Half-Bloom to Physiologic Maturity (60-95 days). The seeds
reach the soft dough stage about 10 days after pollination (70 days after
emergence) in a 95-day variety, and about half of the final dry weight yield
is accumulated during this short period. Hard dough stage is reached in
another 15 days (85 days after emergence) when about three-fourths of the
final dry weight grain yield has been attained. Severe moisture stress during
this period will produce light, undersized grain. Physiologic maturity is
reached in another 10 days (95 days from emergence in the case of this
variety). At this stage, the grain still contains 25-30 percent moisture
which is well above the 13-14 percent safe limit for storage in threshed form
(after the seeds have been removed from the head). Small-scale farmers can
cut the heads at this stage and dry them in the sun before threshing or let
the heads dry naturally on the plants in the field.
-- 41 --
Types of Millet
The millets comprise a group of small-seeded annual grasses grown for
grain and forage. Although of little importance in the developed world, they
are the main staple food grain crop in some regions of Africa and Asia and are
associated with semi-arid conditions, high temperatures, and sandy soils. Of
the six major millet types listed below, pearl millet is the most widely grown
and will receive the most emphasis in this manual.
Other Names: Bulrush, cattail, and spiked millet, bajra, millet, mil.
Scientific Name: Pennisetum typhoides, P. glaucum, or P. americanum.
Main Areas of Production: Semi-arid plains of southern Asia (especially
India) and the Sahel (sub-Saharan) region of Africa.
Important Characteristics: The most drought- and heat-tolerant of the
millets; more prone to bird damage than finger millet.
Other Names: Birdsfoot millet, eleusine, ragi.
Scientific Name: Eleusine coracana.
Main Areas of Production: The southern Sudan,
India, the foothills of Malaysia and Sri Lanka.
higher rainfall; higher in
Unlike other millets,
protein than the others.
it needs cool weather and
-- 42 --
Other Names: Common, French, and hog millet, panicum, miliaceum.
Scientific Name: Panicum miliaceum.
Main Areas of Production: Central Asia, USSR.
Important Characteristics: Used mainly as a short-duration emergency crop or
Scientific Name: Eragrostis abyssinica.
Main Areas of Production: Mainly the Ethiopian and East African highlands up
to 2700 m where it is an important staple food.
Japanese or barnyard millet
Other Names: Sanwa or shama millet.
Scientific Name: Echinochloa crusqalli, E. frumentacea.
Main Areas of Production: India, East Asia, parts of Africa; also in the
eastern United States as a forage.
Important Characteristics: Wide adaptation in terms of soils and moisture;
takes longer to mature (three to four months total) than the others.
Scientific Name: Setaria italica.
Main Areas of Production: Near East, mainland China.
Important Characteristics: Very drought-resistant.
Average millet yields in West Africa range from about 300 to 700 kg/ha.
They tend to be low due to marginal growing conditions and the relative lack
of information concerning improved practices, compared with maize, sorghum,
and peanuts. Research efforts with millet have only yielded 1000 to 1500
kg/ha, and improved varieties have produced up to 3500 kg/ha.
Climatic Requirements of Millet
Rainfall. Pearl millet is the most important cereal grain of the north-
ern savanna and Sahel region of Africa. It is more drought resistant than
sorghum and can be grown as far north as the 200-2500 mm rainfall belt in the
Sahel, where varieties of 55-65 days maturity are grown to take advantage of
the short rainy season. Although pearl millet uses water more efficiently and
yields more than other cereals (including sorghum) under high temperatures,
-- 43 --
marginal rainfall, sub-optimum soil fertility, and a short rainy season, it
does lack sorghum's tolerance to flooding.
Soil. Pearl millet withstands soil salinity and alkaline conditions
fairly well. (For more information on salinity and alkalinity problems, refer
to Peace Corps Soils, Crops, and Fertilizer, 1980 edition.) It is also less
susceptible than sorghum to boring insects and weeds, but shares sorghum's
susceptibility to losses from bird feeding, which damages the maturing crop.
Nutritional Value and Uses of Millet
Pearl, foxtail, and proso millets all contain about 12 to 14 percent pro-
tein which is somewhat higher than most other cereals. The most common method
of preparing pearl millet in West Africa is as "kus-kus" or "to," a thick
paste made by mixing millet flour with boiling water. Millet is used also to
make beer. The stalks and leaves are an important livestock forage and also
serve as fuel and fencing and building material.
Traditional Pearl Millet Growing Practices in West Africa
The traditional West African pearl millet varieties are generally 2.5-4.0
m tall with thick stems and a poor harvest index. They are usually planted in
clumps about a meter or so apart, very often in combination with one to three
of the other reference crops, usually sorghum, cowpeas, and groundnuts. Many
seeds are sown per clump, followed by a laborious thinning of the seedlings
about two to three weeks later. The tiny millet seeds are low in food re-
serves which become exhausted before the seedlings can produce enough leaf
area for efficient photosynthesis and enough roots for good nutrient intake.
Therefore, as with sorghum, the growth rate is very slow for the first few
Two general classes of pearl millet are traditionally grown in West
The Gero class whose varieties are 1.5-3.0 m tall, early matur-
ing (75-100 days), and neutral or only slightly photosensitive
in daylength response. In some parts of the savanna, these
short-season Geros mature at the peak of the wet season, but
have good resistance to the fungal seedhead molds and insects
favored by the rains. The Geros make up about 80 percent of
the region's millet and are preferred for their higher yields
and shorter maturity over the Maiwa class. They mature during
July and August in the Guinea savanna and during August and
September in the Sudan savanna.
The Maiwa class is taller (3-5 m), later maturing (120-280
days), and much more photosensitive in daylength response than
the Gero group. As with the photosensitive sorghum varieties,
the Maiwas will not flower until at or near the end of the
rains, which allows them to escape serious head mold and insect
damage. However, they yield less than the Geros and account
for only about 20 percent of the region's millet.
-- 44 --
In the higher rainfall portions of the savanna (500-600 mm per
year) where both millet and sorghum can be grown, farmers
usually prefer to plant photosensitive sorghum varieties.
These have about the same growing period, but yield more than
the Maiwas due to a longer grain-filling period. However, the
Maiwas are favored over the sorghums on sandier soils with
lower water storage ability. Some farmers will also choose the
Maiwas over the sorghums because the former mature slightly
sooner, thus spreading out the harvest labor demands for these
late season crops. (The Maiwas are harvested a month or so
into the dry season.)
Many of the traditional millets produce abundant tillers (side shoots
produced from the plant's crown). However, this tillering is non-synchronous,
that is, tillering development lags behind that of the main stem. As a re-
sult, these secondary shoots mature later than the main stem. If soil mois-
ture remains adequate, two or more smaller harvests can be taken.
Aside from the normal rainfed millet production, the crop is also planted
on flood plains or along river borders as the waters behind to recede. This
system is referred to as recessional agriculture and also may involve sorghum.
Peanuts (Arachis hypogea)
Distribution and Importance
Peanuts are an important cash and staple food crop in much of the devel-
oping world, particularly in West Africa and the drier regions of India and
Latin America. The developing nations account for some 80 percent of total
world production, with two-thirds of this concentrated in the semi-arid
tropics. Because of repeated droughts, disease problems, and other factors,
Africa's share of the world peanut export market declined from 88 percent in
1968 to 43 percent in 1977, while its share of total production fell from 36
percent to 26 percent during the same period.
Types of Peanuts
There are two broad groups of peanuts.
S Virginia group: Plants are either of the spreading type with
runners or of the bunch (bush) type. Their branches emerge
alternately along the stem rather than in opposed pairs. The
Virginia varieties take longer to mature (120-140 days in the
tropics) than the Spanish-Valencia types and are moderately
resistant to Cercospora leafspot, a fungal disease that can
cause high losses in wet weather unless controlled with fungi-
cides. (See Chapter 7.) The seeds remain dormant (do not
sprout) for as long as 200 days after development, which helps
prevent premature sprouting if they are kept too long in the
ground before harvest.
Spanish-Valencia group: Plants are of the erect bunch type and
non-spreading (no runners). Their branches emerge sequentially
(in opposed pairs), and their leaves are lighter green. They
have a shorter growing period (90-110 days in warm weather),
-- 45 --
are highly susceptible to Cercospora leafspot, and have little
or no seed dormancy. Pre-harvest sprouting can sometimes be a
problem under very wet conditions or delayed harvest. They are
generally higher yielding than the Virginia variety if leafspot
Average peanut yields in the developing countries range from about 500 to
900 kg/ha of unshelled nuts, compared with the U.S. average of 2700 kg/ha,
based on 1977 FAO data. Farmers participating in yield contests have produced
over 600 kg/ha under irrigation, and yields of 400-500 kg/ha are common on
experiment station plots throughout the world. Feasible yields for small
farmers who use a suitable combination of improved practices are in the range
of 1700-3000 kg/ha, depending on rainfall.
Climatic and Soil Adaptation of Peanuts
Rainfall. Peanuts have good drought resistance and heat tolerance. They
mature in 90-120 days in warm weather, which makes them especially well suited
to the short wet season of the northern savanna zone of West Africa. They can
be grown in moister climates if diseases (especially leafspot) can be con-
trolled and if planted so that harvest does not coincide with wet weather.
Temperature. During the vegetative (leaf development) phase, temperature
has little effect on yields. However, the rate of flowering and pollen via-
bility are greatly influenced by temperatures during flowering (about 35-50
days after emergence). Pod production is adversely affected by temperatures
below 240C or above 330C. At 380C, for example, flowering is profuse,
but few pods are produced.
Soils. Peanuts do not tolerate waterlogging, so good soil drainage is
important. Soils that crust or cake are unsuitable, since penetration of the
pegs is unhindered.
Clayey soils can produce good results if well drained, but harvest (dig-
ging) losses may be high due to nut detachment if the plants are "lifted" when
such soils are dry and hard. On the other hand, harvesting the crop on wet,
clayey soils may stain the pods and make them unsuitable for the roasting
Peanuts grow well in acid soils down to about pH 4.8, but do have an
unusually high calcium requirement which is usually met by applying gypsum
(calcium sulfate). Peanut fertilizer requirements are covered in Chapter 5.
Nutritional Value and Uses of Peanuts
The mature, shelled nuts contain about 28-32 percent protein and vary
from 38-47 percent oil in Virginia types to 47-50 percent oil in Spanish
types. They are also a good source of B vitamins and vitamin E. Although
lower in the essential amino acid lysine (a determinant of protein quality)
than the other pulses, peanuts are a valuable source of protein.
In the developing nations peanuts are consumed raw, roasted, boiled, or
used in stews and sauces. The oil is used for cooking and the hulls for fuel,
mulching, and improving clayey garden soils.
-- 46 --
Each peg has an
ovary at its tip
the soil about
3-7 cm before
-- 47 --
Commercially, the whole nuts are used for roasting or for peanut butter.
Alternatively, the oil is extracted using an expeller (pressing) or solvent
method and the remaining peanut meal or cake (about 45 percent protein) is
used in poultry and swine rations. Peanut oil is the world's second most pop-
ular vegetable oil (after soybean oil) and can also be used to make margarine,
soap, and lubricants. The hulls have value as hardboard and building-block
Plant Characteristics of Peanuts
Peanuts are legumes and can satisfy all or nearly all of their nitrogen
needs through their symbiotic relationship with a species of Rhizobia bac-
teria. A characteristic of the peanut plant is that the peanuts themselves
develop and mature underground.
Peanut Stages of Growth
Depending on variety, peanuts take anywhere from 90 to 100 days to 120 to
140 days to mature. The peanut plant will flower about 30 to 45 days after
emergence and will continue flowering for another 30 to 40 days. The peanuts
will then mature about 60 days after flowering.
Phase I: Emergence. Within a day or so after planting in warm moist
soils, the radicle (initial root) emerges and may reach 10-15 cm in length
within four to five days. About four to seven days after planting, two coty-
ledons break the soil surface where they will remain while the stem, branches,
and leaves begin to form above them. The plants grow slowly in the early
stages and are easily overtaken by weeds.
Phase II: Flowering to Pollination. Flowering begins at a very slow
rate about 30-45 days after plant emergence and is completed within another
30-40 days,. The flowers are self-pollinated, but bees and rain improve fer-
tilization (and therefore kernel production) by "triggering" the flowers and
aiding in pollen release. The flowers wither just five to six hours after
opening. A plant may produce up to 1000 flowers, but only about one out of
five to seven actually produces a mature fruit.
Phase III: Peg Emergence to Maturity. The pegs (stalk-like structures,
each containing a future fruit at its tip) begin elongating from the withered
flowers about three weeks after pollination and start to penetrate the soil.
After the pegs penetrate to a depth of about 2-7 cm, the fruits begin to
develop rapidly (within about 10 days) and reach maturity about 60 days after
flowering. Those pegs that form 15 cm or more above the ground seldom reach
the soil and abort.
It is important to note that the fruits do not all mature at the same
time, since flowering occurs over a long period. An individual fruit is
mature when the seed coats of the kernel are no longer wrinkled and the veins
on the inside of the shell have turned dark brown. Harvesting cannot be de-
layed until all the fruits have matured or heavy losses will result from pod
detachment from the pegs and from premature sprouting (Spanish-Valencia types
only). Choice of harvesting date is an important factor in obtaining good
-- 48 --
Traditional Peanut Growing Practices
Small farmers in some developing countries, especially in West Africa,
often plant peanuts together with one or more other crops such as sorghum,
millet, cowpeas, cotton, and vegetables. Whether intercropped or sown alone,
peanuts are usually planted on ridges (raised up mounds or beds) about one
meter apart; this improves soil drainage and facilitates digging. In the
northern savanna areas of West Africa, they are generally planted in June and
harvested in September or October. In the southern, higher rainfall sections
of the savanna, it is often possible to grow two crops (April or May until
August for the first, and August or September to November or December for the
second). Most of the local varieties, especially in the more humid areas, are
of the Virginia type which has much better leafspot resistance.
Common Bean and Cowpeas
Importance and Distribution
Along with peanuts, this group makes up the bulk of the edible pulses
grown in tropical and sub-tropical developing nations. Aside from their
importance as a protein source, the crops play an important role in the
farming systems of these areas.
They are especially well suited to climates with alternating
wet and dry seasons.
Being legumes, they are partly to wholly self-sufficient in
meeting their nitrogen requirements.
They are the natural partners of the cereals in intercropping
and crop rotations. (See Chapter 4.)
According to FAO estimates for the 1975-77 period, world dry bean produc-
tion was about 12.4 million tons annually. Latin America accounts for a third
of world production and produces mainly common (kidney) beans which are also
the major type grown in East Africa. Cowpeas are the major grain legume
(peanuts excluded) of the West Africa savanna zone.
This section deals with common beans and cowpeas (dry beans). In the
appendices are similar descriptions of other pulses such as pidgeonpeas,
chickpeas, lima beans, mung beans, soybeans, and winged beans.
Common (Kidney) Beans (Phaseolus vulgaris)
Other names: Field beans, frijoles, haricot beans, string beans
(immature stage), snap beans (immature stage).
Types: Bean varieties can be classified according to three basic
characteristics--seed color, growth habit, and length of growing period.
Seed color: Most are black or red seeded, and there are usually
distinct local preferences regarding color.
-- 49 --
Part of a bean plant
with flowers. A bean pod
Growth habit: Varieties can be erect bush, semi-vining, or vining
types; the latter have a vigorous climbing ability and require
staking or a companion support crop like maize. Bush varieties
flower over a short period with no further stem and leaf production
afterwards; these are called determinate. The vining types flower
over a longer period and continue leaf and stem production; these
are called indeterminate. Semi-vining varieties can be of either
type. Given their longer flowering period, most indeterminate
have uneven pod maturity with the harvest period stretched out over
a number of weeks.
Growth period: In warm weather, early varieties can produce mature
pods in about 70 days from plant emergence, while medium and late
varieties take 90 days or more. Time to first flowering ranges
between 30 and 55 days. With some exceptions, the erect bush types
reach maturity earlier than the vining indeterminate types. Plant
breeders are developing indeterminate varieties with shorter grow-
ing periods and more compact maturity.
Climatic Requirements of Beans
Rainfall. Common beans are not well suited to very high rainfall areas
(such as the humid rainforest zones of tropical Africa) because of increased
disease and insect problems. Ideally, planting should be timed so that the
latter stages of growth and harvest occur during reasonably dry weather.
Temperature. Compared with sorghum and millet, beans do not tolerate
extreme heat or moisture stress well. Few varieties are adapted to daily mean
temperatures (average of daily high and low) over 280C or below 14oC.
Optimum temperatures for flowering and pod set is a daytime high of 29.50C
and a nighttime low of 210C. Blossom drop becomes serious over 360C and
is aggravated also by heavy downpours.
-- 50 --
Soil. The plants are very susceptible to fungal root rot diseases, and
good drainage is very important. They usually grow poorly in acid soils much
below pH 5.6, since they are especially sensitive to the high levels of sol-
uble manganese and aluminum which often occur at the lower pH levels.
Daylength. Unlike some sorghums and millets, most bean types show little
response to daylength variations.
Nutritional Value and Uses of Beans
Common beans contain about 22 percent protein on a dry seed basis. They
provide adequate protein quality and quantity for older children and adults if
eaten in the proper proportion with cereals (about a 2:1 grain:pulse ratio).
In the green bean form, they provide little protein, but are a good source of
vitamin A. The leaves can be eaten like spinach and also are used as live-
Cowpeas (Vigna sinensis, V. unguiculata, V. sesquipedalia)
Other Names: Black-eyed peas, southern peas, crowder peas.
Cowpeas have much the same variations in seed color, growth habit, and
length of growing period as common beans, except that cowpea seeds are usually
brown or white. There are three separate species:
Vigna Sinensis: the common cowpea in Africa and most of Latin
America. The large, white seeded types are preferred in most
of West Africa.
Vigna unguiculata: catjung cowpea, a primitive type found
mainly in Asia, but also in Africa.
Vigna sesquipedalia: the asparagus or yardlong bean widely
grown in Asia mainly for its immature pods.
Most traditional varieties tend to be late maturing (up to five months)
and vining. Improved bush (little or no vining) types are available and cap-
able of producing good yields in 80-90 days.
Growing Practices and Yields of Cowpeas
Traditional practices and yield constraints of cowpeas are similar to
those of common beans. Average yields in the developing countries run from
400-700 kg/ha of dry seed, compared with a California (U.S.) average of about
2200 kg/ha under irrigation. Field trial yields in Africa and Latin America
are largely in the 1500-2000 kg/ha range with some over 3000 kg/ha.
Climatic Requirements of Cowpeas
Rainfall. Cowpeas are the major grain legume (peanuts excluded) of the
West African savanna zone. However, they also are grown in many other re-
gions. They have better heat and drought tolerance than common beans, but the
-- 51 --
dry seed does not store as well and is very susceptible to attacks by
weevils. (See Chapter 7.)
Temperature. High daytime temperatures have little effect on vegetative
growth but will reduce yields if they occur after flowering. High
temperatures at this time can cause leaves to senesce (die off) more quickly,
shortening the length of the pod-filling period. High temperatures will also
increase the amount of blossom drop. As with common beans and most crops,
humid, rainy weather increases disease and insect problems. Dry weather is
needed during the final stages of growth and harvest to minimize pod rots and
Soil. Cowpeas grow well on a wide variety of soils (if they are well
drained) and are more tolerant of soil acidity than common beans.
Nutritional Value and Uses of Cowpeas
The dry seeds contain about 22-24 percent protein. The immature seeds
and green pods also are eaten. They are considerably lower in protein than
the mature seeds, but are an excellent source of vitamin A while green, as are
the young shoots and leaves. The plants are a good livestock forage and are
sometimes grown as a green manure and cover crop. (See Chapter 5.)
INCREASING REFERENCE CROP PRODUCTION
There are basically four ways of increasing the production of the
improving existing cropland;
extending cultivation to new, uncropped areas;
improving the infrastructure; and
establishing crop improvement programs.
Any meaningful production increase will require varying emphasis on all
Improving Existing Cropland
Unquestionably, improved drainage (by land leveling, runoff canals, or
underground tile drains). and erosion control are high-gain investments.
Erosion control not only reduces soil losses and yield deterioration, but in
many cases actually improves production by increasing the amount of rainfall
retained by the soil.
In the case of irrigation projects, however, the results are often mixed.
Many irrigation projects have paid little attention to the potential
environmental damage or to the technical problems and soil types involved.
Huge dams and artificial lakes have definite appeal on paper, but have often
led to drainage and salt accumulation problems, as well as to weed-choked
canals and serious health hazards like malaria and schistosomiasis (bilharzia).
-- 52 --
Pumping projects relying on wells face similar problems and can seriously
lower the water table to the point of endangering the supply. Water alone is
not enough to assure profitable yieldswhich must be high to cover the added
costs of irrigation. Unless such projects are carefully planned and combined
with a crop improvement program, the results are likely to be disappointing.
Extending Cultivation to New Areas
The FAO estimates that total world food production increased by about 50
percent from 1963 to 1976, while cultivated land area grew by only two
percent. Estimates concerning the amount of additional cultivable land differ
considerably, but suggest that the world as a whole is utilizing only about
one-third to one-half of actual and potential arable land (suitable for crops
or for livestock). The largest areas of "new" land are in the lowland tropics
of Latin America, Africa, and Southeast Asia.
There are, however, some drawbacks.
Only a small percentage of these lands are capable of sustain-
ing intensive agriculture because of soil or climate factors;
an alarming proportion has been claimed by land speculators or
is being divided up into ranches by investors, as in Brazil.
Whether in high rainfall or in arid regions, much of this land
is prone to accelerated erosion or irrigation-induced saliniza-
tion (accumulation of salts at the soil surface).
As we have seen, most of the reference crops are not well adap-
ted to high rainfall and humidity. Pasture and perennial crops
may be the best choices under these constraints.
Improving the Infrastructure
In agriculture, the infrastructure refers to those installations, facili-
ties, inputs, and services that encourage production. The most important of
roads and transport;
markets and marketing standards;
improvements to land such as drainage, erosion control, and
a viable extension service;
availability of agricultural machinery and equipment;
-- 53 --
an equitable land tenure and distribution system;
national planning for agricultural development;
crop prices that encourage increased output.
The small farmers in most areas of the developing world do not enjoy the
same access that larger farmers do to these essential factors of production.
Agricultural public works projects such as irrigation, flood control, and
farm-to-market roads are usually undertaken according to pure economic feasi-
bility or in response to special interest groups. Larger farmers in a number
of developing countries, especially in Latin America, are often organized into
producer's associations with very effective lobbying powers.
Inequities in land tenure and distribution can have tremendous social and
economic consequences and can effectively dampen farming incentives for those
affected. In El Salvador, 19 percent of the farms occupy about 48 percent of
the land and belong to wealthy latifundistas (ranch-type farmers) who grow
cotton, coffee, and sugarcane, frequently on an absentee basis. These farms
are concentrated on the country's best soil, while the campesinos (small far-
mers) are restricted to the eroded and rocky hillsides where they grow maize,
sorghum, and beans. About 47 percent of the country's farms are smaller than
2.47 acres (one hectare) and occupy only four percent of the total land. The
majority of the farm units in El Salvador, Guatemala, and Peru have been
designated as sub-family.
While the implementation of most other infrastructural essentials is hin-
dered mainly by insufficient capital, land reform faces heavy political
obstacles and in some cases is not feasible in terms of land supplies. Fur-
thermore, when small farmers purchase land in densely populated regions like
the Guatemala Highlands, the Cibao area of the Dominican Republic, and the
lake region of Bolivia, competition frequently drives land prices too high for
farming to be economical.
Crop Improvement Programs
More than any other single factor, the development of yield-improving
technology associated with the crop improvement programs of the national and
international research institutes will play the major role in increasing the
yields of the reference crops in the developing countries.
REFERENCE CROP IMPROVEMENT PROGRAMS
The term "crop improvement" is a broad one and refers to any attempt to
improve crop yields, quality, palatability, or other characteristics through
plant breeding or the development of improved growing, harvest, and storage
practices. The most successful efforts are well-organized, multidisciplinary
(involving several relevant skill areas such as entomology and soil fertil-
ity), and crop-specific and aim at developing a "package" of improved prac-
tices centered around high-yielding, adapted varieties.
A large number of yield-determining factors and crop characteristics can
be at least partially manipulated or controlled by plant breeding and improved
production practices, as shown in the table on page 55.
-- 54 --
SUCCESS OF CONTROL ATTAINED BY PLANT BREEDING AND IMPROVED
A. Crops in Harvest
Fair to Good
Poor to Fair
heat and cold
low or high
Poor to Good
B. The Ref-
to leaf spot
Beans and Growth
-- 55 --
Farming Practices Affecting Crop Yields and/or Quality
Method of land preparation (type of tillage and seed-bed).
Fertilizer use (kind, amount, timing, placement).
Plant density and spacing.
Water management (soil drainage, erosion control, moisture
Control of weeds, insects, diseases, nematodes, and birds by chemical
or non-chemical methods.
Adjustment of soil pH.
Control of soil compaction due to equipment or animals.
Cropping system (monoculture versus intercropping; crop rotation).
Harvesting, drying, and storage methods.
In contrast to the production factors listed above, there are a number of
others largely beyond the control of both the farmer and the crop improvement
worker. These include variables such as the weather and certain soil charac-
teristics, i.e., texture, depth, tilth.
CROP IMPROVEMENT PROGRAMS FOR INDIVIDUAL CROPS
Potential for Improvement
Of all the reference crops, maize has the highest yield potential in
terms of grain production per unit of land area under conditions of adequate
moisture and improved practices. Maize is generally less troubled by insects
and diseases than the pulses, especially beans and cowpeas. In addition, more
breeding work has been done with maize than any other major food crop.
Current Research Activities and Crop Programs
The International Maize and Wheat Improvement Center (CIMMYT)* in Mexico
is the institute most involved in maize improvement and acts as the caretaker
and shipping agent for the world's most complete collection of maize germplasm
(plant genetic material). It cooperates extensively with the International
Institute for Tropical Agriculture (IITA)* in Nigeria and the International
Center for Tropical Agriculture (CIAT)* in Colombia in their respective maize
*See Research Institutions, page 270, for international institute addresses.
-- 56 --
programs as well as with national improvement programs throughout the world.
In 1979, CIMMYT sponsored international maize variety trials in 84 countries
at 626 sites to compare its varieties with those from local and other foreign
The CIMMYT-developed varieties originate from a well-organized breeding
program. During the 1970s the center developed 34 germplasm pools (genetic
groups) classified according to three climate types (tropical lowland, tropi-
cal highland, and temperate), four grain types (flint, dent, white, yellow),
and three lengths of maturity (early, medium, late). Advanced lines are de-
veloped from these pools by selecting for yield, uniformity, height, maturity,
and resistance to diseases, insects, and lodging (tipping over). They are
then grown at a number of locations in Mexico. The most promising are used in
preliminary international trials, and the best of these become experimental
varieties for more extensive trial work overseas.
Spreading Improvement Practices for Maize
From 1961 to 1977, total maize production in the developing countries
rose by 66 percent, while acreage increased by 33 percent and yields by 24
percent. However, on an individual country basis, only about half the
developing countries have made significant gains (1979 CIMMYT Annual Report).
The bulk of adaptive research work with maize in the developing countries has
occurred in certain areas of Latin America. Africa and Asia, however, have
location-specific growing problems in terms of soils, climate, insects, and
diseases for which varieties and improved practices still must be developed.
CIMMYT is presently cooperating with national maize programs in Tanzania,
Zaire, Ghana, Egypt, and Pakistan as well as Guatemala and is providing staff
support to most of them. In addition, it cooperates on a regional basis with
Central America and the Caribbean, South and Southeast Asia (11 countries),
and the Andean zone (Bolivia, Colombia, Ecuador, Peru, and Venezuela--all
grain importing countries).
Disease and insect resistance is a top priority at CIMMYT. This organi-
zation has a cooperative breeding program with six national maize programs
(Thailand, Philippines, Tanzania, Zaire, Nicaragua, and El Salvador) to
develop resistance to downy mildew (important in Asia and spreading to other
regions), maize streak virus (Africa), and corn stunt virus (tropical Latin
Maize Production Achievements
The Puebla Project in Mexico was the first large-scale attempt to improve
small-farmer maize production.
Under CIMMYT administration, the project involved 47,000 farm families in
a highland region of Puebla State. Average farm size in the project area was
2.7 ha, operating mainly under dryland (non-irrigated) conditions. Several
"packages" of improved practices were developed to suit varying climatic and
soil conditions in the zone, and adequate support and delivery systems were
sought for the needed inputs, including agricultural credit. By 1972, maize
production had increased in the project area by some 30 percent, and average
family income had increased by 24 percent in real terms. Rural employment was
also favorably affected due to an increased in labor needed for every hectare
-- 57 --
The Puebla Project was innovative in moving the "Green Revolution" (the
first organized attempt to develop yield improving practices for staple food
crops in developing countries) off the experiment station and into the field
and in concentrating on dryland rather than irrigated farming.
Similar examples exist in many other developing countries. Experimental
plots frequently yield over 6000 kg/ha and it is generally agreed that 3000
kg/ha or more is a reasonable yield goal for small farmers in most regions.
Since the real test of an improved variety is its performance under actual
farm conditions, CIMMYT is encouraging the cooperating countries to run exten-
sive trials on farmers' fields rather than confining them to the experiment
station where conditions are often unrealistically ideal.
On the Horizon.
Scientists have been working on breeding a nitrogen-fixing ability similar
to that of legumes into maize. By 1985, they hope to have experimental varie-
ties capable of satisfying up to 10 percent of their nitrogen requirements.
Potential for Improvement
Yields of grain sorghum are generally not as spectacular as those of
maize, since the crop is often grown under less than ideal conditions. Sor-
ghum's advantage over maize is its much better yield stability over a wider
range of climatic conditions, especially under high temperature and low rain-
fall. Many of the traditional varieties in the semi-arid tropics are overly
tall, are photosensitive, and have an excessive ratio of stalk and leaves to
grain. Their delayed flowering enables them to escape serious grain head mold
problems and insect damage, but often there is too little soil moisture for
grain development which takes place at the start of the dry season. These
factors, along with poor management and the large plants' intolerance to
healthy plant densities (populations), account for low yields averaging around
600-900 kg/ha in the semi-arid tropics.
Current Research Activities and Crop Programs
The International Crops Research Institute for the Semi-Arid Tropics
(ICRISAT), located in Andhra Pradesh, India, is the major international insti-
tute engaged in sorghum improvement. Some of its major goals include the de-
velopment of varieties with little or no photosensitivity. These varieties
would have a shorter growing season and be better adapted for drier areas or
shallow soils with low water holding capacity. They would be planted later,
but flower about two weeks earlier than traditional types and therefore need
good head mold resistance for maturing under more humid conditions. Plant
height would be about 2.0-2.5 meters with a better ratio of grain to stalk and
leaves. Since sorghum plants are an important livestock forage in much of the
semi-arid tropics dwarf varieties like those used in the United States would
not be acceptable. The new varieties would mature in 90 to 120 days.
Also under consideration are plants with heavy tillering ability to allow
compensation for low plant populations and a variety with resistance to striga
(a serious parasitic weed), sorghum midge, sorghum shoot fly, and drought.
(See Chapter 6.) Work is also being done to develop more cold-tolerant
-- 58 --
varieties for highland or cool-season tropical conditions, and plants with
improved disease resistance, especially to downy mildew, charcoal rot, smuts,
anthracnose, and rust. (See Chapter 6.) Finally, the Institute hopes to
develop a hi-lysine and higher protein sorghum that has better cooking quality
Spreading Improvement Practices for Sorghum
In the southern savanna region of West Africa, improved photosensitive
varieties have yielded over 3500 kg/ha in 120-140 days, some two months less
than local varieties. They can be sown later in the wet season and will flow-
er about 8-14 days earlier than the local types, thus assuring better moisture
availability for grain filling.
As of yet, highly photo-insensitive (day neutral) varieties with good
head mold resistance have not been developed. There are improved types of
this class that are available with 90-120 day maturities, but their planting
must be scheduled late enough in the wet season so that the grain fill period
occurs at the start of the dry season to avoid head mold. This, however, sub-
jects them to probable moisture stress.
Improvements in sorghum protein. In 1974, two lines of sorghum with 30
percent more protein and double the lysine of conventional types were discov-
ered in Ethiopia. However, these lines suffer from some of the same drawbacks
as hi-lysine maize in that the grain has a soft starch, floury endosperm (the
major portion of the seed surrounding the germ (embryo]) that is very suscep-
tible to storage insects and to breakage under grain threshing using animal
trampling. Also, studies, have shown these extra protein benefits to vary
greatly under different environmental conditions. For example, low soil nit-
rogen content can cause both the lysine and protein percentage to drop to nor-
mal levels. It may be 1985 or later before such improved nutrition varieties
Nitrogen-fixing ability. As with maize, attempts to breed some nitrogen-
fixing ability into sorghum are only in the early experimental stages.
Production improvements and the future. Sorghum lags behind maize in
successful on-farm yield improvement campaigns. Most successes have occurred
in the less marginal rainfall areas. For example, although high-yielding sor-
ghum varieties were released in India in the mid-60s, they spread little
beyond regions with assured rainfall or irrigation. A major factor is the
highly variable climatic environment of the semi-arid tropics where standard-
ized technology packages have only limited suitability, thus requiring greater
adaptive research efforts. However, organized efforts at sorghum improvement
are much more recent than those for maize, and the future does look promising.
Potential for Improvement
Millet yields are generally lower than those of sorghum due to harsher
growing conditions and a shorter period of grain filling. Traditional West
African varieties have major limiting factors such as poor plant architecture.
They tend to be overly tall and have a poor harvest index. In addition, the
photosensitive types often flower too late in the season, causing moisture
-- 59 --
stress during grain filling. Those varieties which are not as affected by
daylength (the Geros) have moderate tillering ability, but it is not synchron-
ous with the main stem. Thus, most of the tillers flower too late, when mois-
ture is not adequate for grain filling.
Current Research Activities and Crop Problems
The ICRISAT breeding program concentrates mostly on pearl millet, and it
aims at improved drought, insect, and disease resistance, increased response
to improved practices, better harvest index, and varieties with a range of
maturities to suit varying rainfall patterns. It is selecting also for varie-
ties particularly suited to intercropping combinations. Protein content and
early seedling vigor are other concerns.
In West Africa and the Sudan, ICRISAT has a program to develop high-
yielding sorghum and millet varieties. This cooperative program includes the
countries of Mali, Upper Volta, Niger, Ghana, Chad, The Gambia, Senegal,
Nigeria, Mauritania, Cameroon, and Benin.
Achievements in Millet Improvement
As with sorghum, millet improvement efforts in the developing countries
are relatively recent and at an early stage. The ICRISAT trials in West
Africa during 1976 and 1977 showed that new varieties were not much better
than the existing West African types with a few exceptions. The major problem
was lack of disease resistance and overly early maturity. On the other hand,
breeding efforts in Senegal have produced high-yielding dwarf types capable of
better fertilizer response. These have an improved harvest index and a matur-
ity range of 75-100 days. Some of the best ICRISAT varieties have yielded up
to 4000 kg/ha in international trials. Progress also is being made in the
development of varieties with good resistance to downy mildew (Scleropsora
graminicola), a serious fungus disease encouraged by high humidity. As with
maize and sorghum, attempts are being made to develop some limited nitrogen-
fixing ability in millet, but results are at least four to five years away.
On the Horizon
Millet production should expand significantly in the future as more
marginal rainfall land is brought under cultivation. Additional research is
expected to make the millets one of the most productive cereals on a yield per
area per time basis (yield of crop in a certain area per cropping cycle per
Potential for Improvement
When grown under ideal moisture conditions, peanut and other pulse crop
yields are about one-third to one-half those of maize. However, since peanuts
are about three times higher in protein than maize, the yields are actually
very similar on a protein per area basis (a 2000 kg/ha peanut crop produces
about the same total amount of protein as a 6000 kg/ha maize crop). This is
also the case with the other pulses, all of which have two to three times more
protein than the cereals. In short, the pulses are geared more to producing
modest yields of high protein seed rather than high yields of starchy seed as
with the cereals. Although the lower yields of the pulses should be kept in
-- 60 --
mind, there is potential for yield improvement in the developing countries
where production per hectare lags considerably behind that of the developed
Research Activities and Crop Improvement
Since peanuts are self-pollinating, the development of new varieties by
crossing is difficult and time-consuming. The individual flowers must be man-
ually emasculated and then hand pollinated. Since seed production per plant
is comparatively low, multiplication of improved types is very slow, although
they can be propagated by cuttings. Most efforts concentrate on collecting
and improving local and introduced varieties by selecting for adaptability,
drought resistance, oil and protein content, disease and insect resistance,
and shelling percentage (ratio of shell weight to kernel weight).
Spreading Peanut Improvement Activities
The major international institute involved with peanut improvement in the
developing countries is ICRISAT. Advanced work is also being done in several
of the developed countries such as the United States (especially in Georgia,
North Carolina, and Texas), Australia, and South Africa, but it is designed to
serve their local conditions. Other centers of peanut improvement are
Senegal, Nigeria, Sudan, Mexico, Argentina, and Brazil.
Breeding for earliness (to suit short rainy seasons), seed dormancy (to
prevent in-ground sprouting), and resistance to rust, leafspot, and aflatoxin
are all being conducted by ICRISAT. Work in Senegal has developed several
lines resistant to rosette virus, a serious problem in the wetter peanut zones
Of the reference crops, peanuts are the most complicated in terms of
growing and harvesting practices needed for good yields. Seedbed preparation,
weed and disease control, and harvesting require particular attention to
detail and timeliness. Being a much higher value crop than the cereals,
repeated applications of foliar fungicides for leafspot control have a good
cost-benefit ratio and are another example of the relative sophistication re-
quired for good yields. Undoubtedly, plant breeding has a role to play in
peanut improvement, but improved management practices are particularly impor-
tant for boosting yields.
In those developing countries where peanuts are a major export crop, mar-
keting is usually controlled by a government board which also provides storage
facilities and may act as a supplier of seed, fertilizer, and other inputs.
Under these conditions, adaptive research work is also given greater priority,
but the weak link is also the extension system, which must bridge the gap bet-
ween the farmer and the experiment station. In general, yields are far below
the 1700-3000 kg/ha range that is feasible under improved practices where
moisture stress is not serious.
Beans and Cowpeas
Until the early 1970s, pulse improvement had been largely neglected.
Compared with the cereals, these grain legumes seemed to offer less promising
opportunities due to their relatively low yields and greater susceptibility to
-- 61 --
insects and diseases. However, in view of their high protein contents and
potential as nutritional complements to the cereals, research and extension
programs can no longer afford to ignore them. The best yields of the cereals
and the pulses are fairly similar when compared on a protein produced per area
Potential for Improvement
Early research seemed to suggest that common beans were one of the least
productive of the pulses. However, a comparative growth study by the Inter-
national Center for Tropical Agriculture (CIAT) in 1978 involving five grain
legumes showed that common beans and cowpeas were the two most efficient on a
yield per day of growth basis (the other three involved were pigeon-peas, soy-
beans, and mung beans).
Unfortunately, current average yields for Africa and Latin America are a
low 600 kg/ha, while CIAT has obtained up to 4300 kg/ha under monocropping
(beans as the sole crop) and 3000 kg/ha in mixed plantings with maize.
Current Research Activities and Crop Programs
The major international institute involved in common bean improvement is
CIAT. In 1973, it established a Bean Production Systems Program to increase
the production and consumption of the crop in Latin America. In addition, it
also cooperates with developing countries in other areas. This effort is now
being supplemented by a recently organized U.S. government-sponsored program
for cooperative dry bean research by eight U.S. universities and developing
The CIAT program aims to increase bean yields through several methods:
Development of improved varieties resistant to major diseases
and several stress factors like low soil phosphorus, soil acid-
ity, drought, and temperature extremes. Special attention is
being given to mixed cropping with maize.
Breeding for improved nitrogen fixation. Currently, common
beans are one of the more inefficient nitrogen fixers and re-
quire moderate rates of supplemental fertilizer.
Developing improved management practices for both monoculture
and mixed cropping systems. (See Chapter 4.)
Training personnel from national programs in other developing
countries and developing a strong bean research network in
Latin America and East Africa.
As part of its international trials program, CIAT maintains an Interna-
tional Bean Yield and Adaptation Nursery (IBYAN), consisting of 100 entries.
This IBYAN is replicated by CIAT and shipped to many other countries to be
used in their experimental work with beans. The Center for Tropical Agricul-
ture, Research, and Training (CATIE) in Turrialba, Costa Rica, also is in-
volved in bean improvement work.
-- 62 --
Spreading Bean Improvement Practices
After nearly some five years of breeding work, most of the improved vari-
eties CIAT sent out for international trials in 1979 carried some resistance
to major pest problems like common mosaic virus, rust, common bacterial
blight, angular leafspot, anthracnose, and a damaging species of leafhopper
(Empoasca Kraemeri) prevalent in Latin America. Strains were found also that
showed some tolerance to low levels of soil phosphorus and to aluminum and
manganese toxicity which often affects beans in highly acidic soil (much below
pH 5.5). Both CIAT and CATIE have made significant progress in improving
bean-maize multiple.cropping systems through improved management and bean var-
Due to the relatively recent interest in bean research, on-farm yield
improvement programs have made nowhere near the impressive and widespread
gains of maize, rice, and wheat. However, research achievement in breeding
and management are at the point where farmers can increase their yields with a
well-organized extension program.
Progress in Cowpea Improvement
The International Institute for Tropical Agriculture (IITA) in Nigeria is
the major international institute involved in cowpea improvement and is work-
ing toward good pest resistance, improved yields, and the development of a
package of improved practices for cowpeas under multiple cropping conditions
common in tropical Africa. By 1978, IITA had released a total of five new
strains (VITA 1-5) with better yield and pest resistance and a good protein
content. They are capable of producing 1500-2500 kg/ha under small-farmer
improved management, compared with the current West African average of around
500 kg/ha. The creamy white seed color of VITA 5 is favored in much of
Africa. As with common beans, on-farm yield improvement extension efforts are
still in their early stages.
-- 63 --
CHAPTER 4. PLANNING AND PREPARATION
This chapter deals with reference crop production fundamentals and
current recommendations concerning cropping systems, land preparation, seed
selection, and planting. The production fundamentals section describes the
how, what, and why of these farm operations. The compendium section provides
a current summary of reference crop production recommendations based largely
on information from international research institutions and some national
extension services. Although the compendium section does offer general
suggestions for the various crops, agriculture is a location-specific
endeavor. This section is mainly designed to show how recommendations vary
according to differences in each area's physical environment and specific
As explained earlier, the term "cropping system" refers both to a far-
mer's or region's overall cropping pattern, and to the specific crop sequences
and associations involved.
1. Monoculture: the repetitive growing of a single crop on the same
field year after year.
2. Crop Rotation: the repetitive growing of an orderly succession of
crops (or crops alternating with fallow) on the same field.
3. Multiple Cropping:
a. Sequential cropping: growing two or more crops in succession
on the same field per year or per growing season, sometimes
referred to as double or triple cropping. (Example: Planting
maize in May, harvesting it in August, and then planting
beans. Only one crop occupies the field at a time.)
b. Intercropping: the most common definition of multiple cropping
involves growing two or more crops at the same time on the same
field, there are four basic variations:
1) mixed intercropping: two or more crops without a distinct
2) row intercropping: same as mixed intercropping but with a
distinct row arrangement;
3) relay intercropping: growing two or more crops simultane-
ously during part of the life cycle of each, the second
crop is usually sown after the first has reached its repro-
ductive stage (i.e., around flowering time), but before it
is ready to harvest; (Example: Planting a climbing bean
variety alongside maize that has recently tasseled.)
4) strip intercropping: growing two or more crops in separate
strips wide enough for independent cultivation, but narrow
enough to react agronomically.
-- 64 --
Monoculture vs. Crop Rotation
It is difficult to compare the pros and cons of monoculture with crop
rotation since much depends on the crops, soils, management practices,
climate, and economics involved. Monoculture is frequently blamed for soil
"exhaustion" (erosion problems and declining fertility and tilth) and a build-
up of insects and diseases, yet this is not always the case. Some very pro-
ductive areas of the U.S. Corn Belt have over 50 percent of their cropland
devoted to continuous maize, which yields as well as that grown under crop
rotation. In fact, Corn Belt research has shown that maize grown continuously
under that region's conditions results in a less serious insect buildup than
when maize is grown in a crop rotation with soybeans or pasture and hay. On
the other hand, monoculture cotton in the southern United States in the 19th
and early 20th centuries led to serious soil degradation and insect problems.
Monoculture is uncommon under small farmer conditions in developing coun-
tries, since intercropping is prevalent, and a variety of crops must be pro-
duced for subsistence needs. It is mainly confined to perennial cash and
export crops such as coffee, sugarcane, citrus, and bananas. Whether or not
monoculture is harmful depends on the type of crop and soil management and
Type of Crop
Row crops which provide relatively little ground cover or
return only small amounts of residues (stems, leaves, branches,
and other debris left in the field after harvest) to the soil
are poorly suited to monoculture (e.g., cotton, peanuts, maize,
or sorghum grown for fodder or silage).
Some crops like beans, potatoes, and many vegetables are espec-
ially prone to insects and soil-borne diseases which usually
build up under monoculture.
Soil Management and Climate Factors
A soil's physical condition (tilth and permeability), natural fertility,
and nutrient-holding ability are directly related to its organic matter
Row crop monoculture will seriously lower soil humus levels
unless all crop residues are returned to the soil along with
supplemental additions of manure in sizeable amounts (around 30
metric tons/ha or more per year).
The tillage and cultivation operations associated with mechan-
ized (or animal traction) row crop production aereate the soil,
which accelerates the microbial breakdown and loss of humus.
That is part of the reason why many farmers in the United
States and Europe have switched to minimum tillage systems such
as plowing and planting in one operation. Minimum tillage
leads to problems with weeding and herbicidal use.
*Humus is organic matter that has been fairly well decomposed.
-- 65 --
The problem of humus loss is especially serious in the tropics
due to higher temperatures. Decomposition takes place three
times as fast at 32oC than at 15.50C.
Erosion problems associated with row crops are more serious in
the tropics due to higher intensity rainfall (even in semi-arid
Crop rotation may or may not be beneficial in terms of soil condition,
insects, and diseases. In terms of soil condition, the ideal would be to
rotate low-residue crops like cotton and vegetables with medium-residue crops
like corn, sorghum, and rice or, better yet, with pasture, but few small
farmers can afford this type of flexibility. Including a nitrogen-fixing
legume crop like peanuts or beans in the rotation will not necessarily boost
the soil's nitrogen content significantly, since much of the nitrogen produced
ends up in the harvested seeds themselves. Some areas have experimented with
green manure (legume) crops like cowpeas, which are plowed under around
flowering time to add humus and nitrogen to the soil (no harvest is taken),
but there are several problems with this approach.
Few farmers are willing to tie up their land growing a
The effect of green manure crops on soils is short-lived under
The green manure crop may use up soil moisture needed by the
Suggested Crop Rotation for the Reference Crops
The variables are too great to make specific recommendations of wide
applicability. Much depends on the area's soils, climate, prevalence and type
of intercropping, and common insects and diseases.
Some general recommendations can be made.
Crops which share similar diseases (especially soil-borne ones
like root rots) should not be grown on the same field within
three years of each other. For example, peanuts, tobacco,
beans, soybeans, and sweet potatoes are all susceptible to
Southern stem rot (Sclerotium rolfsii), as well as to the same
types of nematodes, and should not be grown on the same field
A crop like peanuts or beans which is especially susceptible to
soil-borne diseases should not be grown on the same field more
than one year out of three. Again, intercropping may lessen
these problems, but not always.
Monoculture is less of a problem if disease-resistant varieties
are available and are being continually developed in response
to new disease strains.
-- 66 --
Intercropping (Multiple Cropping)
Intercropping combinations involving two or more of the reference crops
(sometimes along with others) are very common on small farms in the developing
Intercropping is not ordinarily suited to mechanized farming, but strip
intercropping is sometimes used when multiple-row machinery can be operated.
The Pros and Cons of Intercropping
Less risk since yields do not depend on one crop alone.
Better distribution of labor.
Some diseases and insects annpar ton nrpro lac reani'ln nanaar,
Better erosion control due to better ground cover.
Any legumes involved may add some nitrogen to the soil.
Mechanization is difficult.
Management requirements are higher.
Overall costs per unit of production may be higher due to
reduced efficiency in planting, weeding, and harvesting.
The type of multiple cropping is closely related to rainfall and length of
rainy season as shown below:
Annual Rainfall Prevalent Type of Multiple Cropping
300-600 mm Simultaneous mixed intercronnina with
Over 1000 mm
crops of similar maturities.
Crop mixes of different maturities.
Three types of multiple cropping:
sequential, simultaneous, and relay.
Advances in Intercropping Systems
Multiple cropping is a diverse and complex subject; the guidelines are
often very location-specific. Research interest in multiple cropping has
increased markedly over the past decade with most attention being focused on
cereal-legume combinations which appear to have the greatest potential,
particularly maize or sorghum with beans or cowpeas.
-- 67 --
The following research results are presented not to imply their direct
applicabilty to a given area but to provide ideas of the many factors involved
in intercropping and the state of the art of these complex systems.
The National Maize Program in Zaire has been looking into maize rotations
and intercropping with legumes to improve soil fertility without commercial
fertilizer. Rotations using soybeans and Crotalaria (a green manure crop
poisonous to livestock) have been tried. So far, Crotalaria looks superior in
nitrogen-fixing ability with the succeeding maize crop yielding up to 900
kg/ha. Maize following a soybean green manure crop has yielded up to 6700
kg/ha. The National Maize Program has also worked with an intercrop combina-
tion of cowpeas and maize, but has not yet found suitable cowpea varieties.
Both rotation and intercropping of maize with legumes appear to offer
some promise in Zaire, but there are two main problems.
Legume seeds are harder to store from one year to the next
under humid conditions.
Even though legumes used as green manures may contribute a good
deal of soil nitrogen, farmers are still likely to need fertil-
izer, since legumes will not do well on the low-phosphorus
soils prevalent throughout much of the tropics.
Pearl millet-peanut intercropping trials by the International Crop Research
Institute for the Semi-Arid Tropics (ICRISAT) in India showed yield advantages
of up to 25-30 percent. An arrangement of one row millet to three rows
peanuts appeared to provide the optimum balance of competition.
Maize-Bean Intercropping Research
The International Center for Tropical Agriculture (CIAT) has run numerous
maize-bean intercropping trials at various locations in Colombia. The trials
involved simultaneous or near-simultaneous planting of the two crops rather
than relay planting. Results were as follows.
For the farmer the optimum ratio of maize plants to bean plants
depends not only on the relative yields but also on the maize-
bean price ratio which ranges from 1:2 up to 1:7 in some Latin
A larger number of trials involving simultaneous or near-
simultaneous plantings of maize with beans showed that bush
bean yields were about 30 percent lower and climbing bean
yields about 50 percent lower than when the plants were grown
Maize yields were usually not adversely affected by the associ-
ation with beans at a maize population of 40,000 plants/ha.
Maize plant densities over 40,000/ha decreased bush bean yields
by shading, while densities s below 40,000/ha lowered climbing
bean yields because of inadequate support.
At 40,000 maize plants/ha, relative yields of the two crops
were best at bush bean densities of 200-250,000 plants/ha and
at climbing bean densities of 100-150,000 plants/ha.
-- 68 --
Yields of climbing beans were highest when they were planted
simultaneously with maize; bush bean yields were highest when
the beans were planted one to two weeks before maize, although
this caused a significant yield decrease in the maize. Results
varied with temperature and the relative early vigor of the
bean and maize seedlings.
In a 1976 Center for Tropical Agriculture, Research, and Training (CATIE)
trial in Costa Rica, i-ntercropped populations of 50,000/ha for maize and
200,000/ha for bush beans were found to be the best combination and produced
yields of 3400 kg/ha and 1800 kg/ha respectively.
A 1976 study in the Minas Gerais area of Brazil by the Universidade
Federal de Vicosa focused on relay intercropping of maize and beans. Maize
populations of 20-, 40-, and 80,000 per hectare were intercropped with
climbing beans of 100-, 200-, 300-, and 400,000 plants/ha. The maize was
planted in the wet season, and the beans were planted between the maize rows
when the maize was nearing maturity. The following results were obtained.
Maize yield was not affected by the beans and was highest at
Bean yields were highest at the lowest maize population and
were not affected by bean plant density.
Even though the beans were planted as the maize was starting to
dry out, the maize still exerted a strong competitive effect,
mainly due to shading. When grown alone under trellising, the
bean variety normally yielded a 1200 to 2000 kg/ha at a density
of 250,000/ha, but yielded 800 kg/ha when grown with a maize
population of 20,000/ha.
Cowpeas-Millet-Sorghum. Experience in Africa has shown that cowpea
yields are reduced about 45-55 percent when intercropped with millet and
sorghum. However, when grown alone, the improved cowpea varieties become more
prone to serious insect attack and often require chemical pest control.
Furthermore, intercropped cowpeas are not usually sown until later in the wet
season and are viewed more as a bonus crop which does not reduce the millet
and sorghum yields.
Improving Traditional Multiple Cropping Sysytems
In southeast Guatemala, small farmers usually plant maize, sorghum, and
beans by hand on steep to rolling rocky land, and yields average around 530,
630, and 410 kg/ha respectively. Due to a severe labor shortage for planting
at the start of the season, the farmers plant the beans in dry soil. They
then overplant the maize and sorghum once the rains arrive without regard to
where the yet-to-germinate beans are. With the local varieties used, if the
beans emerge first, they will dominate the maize and sorghum; the reverse will
happen if the maize and sorghum germinate first. Hoping for a balanced har-
vest, the farmers are in a race against time to finish planting the maize and
sorghum before the beans germinate. The main disadvantage of this traditional
system is the risk that the dry-planted beans may receive only enough rainfall
to germinate without sufficient additional precipitation to sustain growth
(i.e., a wet season "false start").
-- 69 --
Researchers have experimented with several alternatives. The most prom-
ising one involves strip intercropping of maize, sorghum, beans, and cowpeas.
At the start of the wet season, beans are planted in strips consisting of
three rows spaced 30 cm apart. Sufficient space is left between these strips
to accommodate sets of double (twin) maize rows with two "varas" (164.0 cm)
between the centers of the twin rows. Two more of these twin row sets of
maize can be planted between bean strips depending on the desired cropping
mixture. The 30 cm bean row spacing is unusually narrow but gives better weed
control due to earlier inter-row shading. Also, the strips are narrow enough
to be hand-seeded from the sides to avoid compacting the soil or trampling the
Once the beans emerge, the maize rows are planted. If the rains stop for
a while after bean planting, maize sowing can be delayed without danger of the
beans dominating the young maize seedlings (one advantage of strip intercrop-
ping). The beans are a short season variety that matures in 60 to 65 days.
As soon as the beans are harvested, a short season sorghum variety is
planted in the space between the sets of twin maize rows. Later, the nearly
mature maize plants are doubled over to reduce any shading of the young sor-
ghum plants, which are slow starters. This points the ear tips downward, pre-
venting water entry (which favors fungal grain rots) and reducing bird damage.
About two weeks before the maize is doubled, cowpeas are sown along the
outer edges of the twin maize rows (i.e., along the edges of the harvested
bean strips). The leaves of the maize plants are stripped off as they die off
with maturity and used as a mulch (soil covering) to conserve soil moisture.
The cowpeas use the maize stalks to climb on and cause no competition due to
their late planting.
Shifting Cultivation as a Cropping System
Shifting cultivation (slash and burn agriculture) is a traditional crop-
ping system that was once widely practiced throughout the humid tropics. Due
to increasing population pressure on land, the system is now mainly confined
to the dense forest areas of the Amazon Basin, Central and West Africa, and
While there are some variations, shifting cultivation consists of three
1. The land is incompletely cleared by hand cutting and burning trees
and other vegetation. The burning has several effects.
All the vegetation's nitrogen and sulfur is lost to the atmo-
sphere as gasses. However, the other nutrients (phosphorous,
potassium, calcium, etc.) are deposited on the ground as ash.
Even though much organic matter is lost, a lot has already been
added to the soil over the years by leaf fall and root decom-
Burning only kills some insects, diseases, and weed seeds, not
all of them.
-- 70 --
2. Crops are grown on the land for two or three years, usually under
some form of intercropping that may include long-cycle crops such
as manioc (cassava) and yams in humid regions. Little, if any,
tillage (hoeing, etc.) is required for seedbed preparation, since
the soil is usually in good physical condition as a result of the
previous fallow. The crops utilize the naturally accumulated
nutrients from the fallow period. Yields are fair the first year,
but then rapidly decline, causing the land to be temporarily
abandoned after several years of cropping.
3. The land is then allowed to revert to a natural vegetation fallow
for 5 to 10 years in order to "rejuvenate" the soil in several ways.
The vegetation, especially if it consists largely of trees and
other deep-rooted species, recycles leachable nutrients like
nitrogen and sulfur that may be carried into the soil by
rainfall during the cropping and fallow periods. Some of the
fallow vegetation may be leguminous and actually add nitrogen
to the soil.
The fallow increases the amount of soil humus which is a vital
storehouse and source of nutrients, as well as being a great
improver of soil physical condition.
Small, but significant, amounts of nitrogen are produced by
lightning, and these are added to the soil by associated rain-
The fallow period also helps avoid a buildup of pests and diseases.
Shifting cultivation requires no outside inputs and is in complete harmony
with the natural environment of the humid tropics. However, the system's
success depends heavily on maintaining an adequate length of fallow cycle. As
the frequency of clearing and burning increases, trees and brush are eventual-
ly killed off and give way to a very inferior grass (savanna) fallow, which is
shallow-rooted, inefficient at recycling and accumulating nutrients, and very
difficult to clear off for cropping. (Many tropical grass species are actual-
ly stimulated into dense regrowth by burning.) Under these conditions, slash
and burn agriculture becomes a menace to the environment, causing severe
deforestation, erosion, and soil exhaustion. Many areas of Central America
have been denuded in this manner.
Improving Shifting Cultivation
As explained, the system is basically suited only to the humid tropical
forest zones under low population density. European attempts to replace
shifting cultivation in parts of Africa with "modern" agriculture usually met
with disaster (erosion, pests, diseases, and a serious decline in soil condi-
tion). Some tropical soils have an iron-rich laterite layer which may become
exposed through erosion. Unless such soils are kept under continuous shade,
the laterite can harden irreversibly, making the soil useless.
Listed below are some of the most promising possibilities for improving
-- 71 --
The "Taungya" system of Burmese origin involving agriculture
and forestry consists of clearing land for a cropping cycle
followed by planting fast-growing trees to provide lumber and
rural improvement. Both phases would be operating simultane-
ously within an area.
Using fertilizers (chemical or organic) to increase yields
during the cropping period.
Seeding the fallow area with specially selected plants that may
be more beneficial than the natural species; the improved
fallow might include dense growing vining legumes or leguminous
trees and shrubs.
LAND PREPARATION FOR CROPPING
On small farms, land preparation methods for the reference crops may or
may not involve actual tillage (working the soil with hoes, plows, or other
equipment) or seedbed shaping (leveling land or making raised beds or ridges).
Methods Involving No Tillage or Seedbed Shaping
Under conditions of shifting cultivation, low management, or steeply
sloping or rocky soils, land is often cleared by simpling slashing and/or
burning, followed by making the seed holes with a planting stick or hoe. No
attempt is made to actually till the soil or to form a specific type of
Slash, burn, and plant. This method is most suitable for sandy
soils which are naturally loose or for other soils that are
maintained in good tilth (a loose, crumbly condition) by a
lengthy vegetative fallow which produces soil humus. It may be
the only feasible method for rocky soils or those with pro-
nounced slopes where tillage would accelerate erosion.
Slash, mulch, and plant. This method is suited to the same con-
ditions. The vegetation is slashed down or killed with a herbi-
cide and then left on the surface to form a mulch (a protective
covering). The seeds may be planted in the ground or may even
be scattered over the ground before slashing. The mulch is val-
uable for erosion and weed control, conserving soil moisture,
and keeping soil temperatures more uniform. The International
Institute for Tropical Agriculture (IITA) has found this system
very beneficial for maize and cowpeas and has developed two
types of hand-operated planters capable of planting seed
through a mulch.
There is nothing basically wrong with either of these methods. However,
in some cases, tillage and seedbed shaping may have some important advantages.
Soils prone to drainage problems due to topography, soil condi-
tions, or high rainfall usually require the use of raised beds
or ridges for successful crop production (except for rice).
-- 72 --
If liming is needed to correct excessive soil acidity, it must
be mixed thoroughly into the top 15-20 cm of soil to be fully
Chemical fertilizers containing phosphorous and potassium and
organic fertilizers should be incorporated several centimeters
into the soil for maximum effectiveness. Under non-tillage
methods, they can still be correctly applied using a hoe or
machete, but it is definitely more work. Chemical fertilizers
containing phosphorus are best applied to the reference crops
in a band 7.5-10 cm deep that parallels the crop 5-6 cm to one
side. Fertilizer furrow can be made easily with a wooden
plow or other animal-drawn implement.
Most animal- or tractor-drawn planters require a tilled seedbed
for successful operation. There are exceptions, however, such
as the IITA planters.
Methods Involving Tillage
Tillage refers to the use of animal- or tractor-drawn equipment or hand
tools to work the soil in preparation for planting, and has five main purposes:
to break up and loosen the soil to favor seed germination,
seedling emergence, and root growth;
to chop up and/or bury the previous crop's residues so they
will not interfere with the new crop;
to control weeds (an ideal seedbed is completely weed-free at
to incorporate (mix into the soil) liming materials and fertil-
izers (chemical or organic); and
e to shape the kind of seedbed most suited to the particular
soil, climate, and crop (e.g., raised beds, ridges, flat seed-
Primary tillage refers to the initial breaking up of the soil by plowing
or using a heavy-duty digging hoe. Depth of plowing usually ranges from about
15 to 30 cm, depending on the type of plow used, its traction source, and the
soil. For example, an ox-drawn wooden plow will not have the penetration
ability of a tractor-drawn moldboard plow, especially in heavy soils.
Secondary tillage refers to any additional tillage operations between
plowing and planting to break up clods, cut up trash, kill weeds, and smooth
out the seedbed. It is most commonly performed with some type of harrow (an
implement used to pulverize and smooth the soil). Secondary tillage is shal-
lower than planting and requires less power. Ridging and bedding (forming
ridges or beds for raised planting) also can be included in this category.
-- 73 --
Reference Crop Tillage Systems
The reference crops share the same basic tillage methods, but these vary
with the particular soil, the available tillage equipment, and the need for
incorporating lime or fertilizer. There are three basic tillage systems, each
with advantages and disadvantages.
Plow (or hoe)/plant. If plowed at the right moisture level,
some soils (especially loams and sands) may be suitable for
sowing with a planter without any secondary tillage to break up
the clods. Most soils can be hand-planted after plowing, since
the farmer has better control over seed depth than he has when
a mechanical planter is used. He can also push any big clods
aside or break them up while walking down the row. This type
of rough seedbed is actually advantageous in terms of weed
control since the cloddy surface discourages their growth. It
also favors moisture penetration and reduces runoff. On the
other hand, if bedding or ridging is needed, a better job can
be done if any large clods are first broken up by harrowing
Plow/harrow/plant. This is the most common system where animal-
or tractor-drawn planters are used, unless the soil breaks up
well enough under plowing alone. If soil conditions are condu-
cive to weed growth, the ground should be harrowed as close to
planting as possible to give the crop a head start on the weeds.
Minimum tillage. Farmers with access to tractor- or animal-
drawn tillage equipment may overdo tillage, especially through
repeated harrowings to control sprouting weeds or break up
clods. Killing one crop of weeds by stirring the soil only
stimulates another by moving other weed seeds closer to the
soil surface. Excessive tillage stimulates the microbial
breakdown of humus and may further destroy good soil physical
condition by over-pulverizing the soil. The machinery, animal,
and foot traffic also compact the soil impairing root growth
Tillage is seldom excessive when hand tools are used to prepare
ground for the reference crops, because of the amount of labor
it would involve. Slash-and-burn and slash-and-mulch methods
fall under zero tillage, as do methods using specially adapted
mechanical planters to sow seed into unplowed ground (common in
the United States). The plow/plant system described above or
plowing and planting in one tractor pass are examples of
minimum tillage. The savings on equipment wear and fuel are
advantages where tractors are used.
Tillage and Seedbed Fineness
The degree to which clods need to be broken up depends mainly on seed
type and seed size and whether hand planting or mechanical planting will be
-- 74 --
1. Seed type. Maize, millet, and sorghum are monocots with seed-
lings that break through the soil with a spike-like tip. This
reduces the need for a clod-free seedbed. Peanuts and other
pulses are dicots and emerge in a blunt form, dragging the two
seed leaves with them; they tend to have more trouble with
2. Seed size. Large seeds have more strength than small seeds,
enabling young shoots to push more effectively through rough
seedbeds. Maize seeds are large monocots, which gives them
especially good clod handling ability. Peanuts and the other
pulses are large-seeded, but this advantage is partly offset
since they are dicots. The small seeds of sorghum and especi-
ally millet are less powerful, but this is offset by the fact
that they are monocots. Small seeds require shallower planting
than larger ones, and cloddy soils do not allow this type of
precision if mechanical planters are used.
3. Farmers can usually get by with cloddier seedbeds when hand
planting. They have more control over planting depth and can
push any large clods aside. In addition, it is very common
under hand planting to sow several seeds per hole, which gives
them a better chance of breaking through.
Clayey soils, especially those low in humus, are usually in a cloddier
condition after plowing than loamy or sandy ones. Most plowing takes place at
the end of the dry season, when soils are very dry, which accentuates the
problem. Rainfall following plowing may significantly reduce clod problems on
some soils by breaking up the clods.
A plowing depth in the 15-20 cm range is usually adequate, and there is
seldom any advantage in going deeper. In fact, shallower plowing is often
recommended for low rainfall areas like the Sahel to conserve moisture.
In some areas, tractor-drawn sub-soilers (long narrow shanks that pene-
trate down to 60 cm) are used in an attempt to break up deep hardpans (compac-
ted layers). Results are fair to poor, depending on the type of hardpan;
those consisting of a dense clay layer often re-cement themselves within a
About 65 to 80 percent of the reference crops' roots are found in the
topsoil, since this layer is more fertile (partly due to its higher organic
matter content) and less compacted than the subsoil. However, any roots that
enter the subsoil can utilize its valuable moisture reserves, making a criti-
cal difference during a drought. Proper fertilization of the topsoil will
encourage much deeper root development. On the other hand, poor drainage and
excessive acidity in the subsoil will hinder or prevent root penetration.
Handling Crop Residues
There are three basic ways of handling the previous crop's residues
(stalks, leaves, branches) when preparing land: burning, burying, and
-- 75 --
1. Burning. This destroys the organic matter contained in the
residues, but may be the only feasible solution where suitable
equipment is lacking or where time is short.
2. Burying. Chopping residues up with a disk harrow or slasher
and then plowing them under is a common practice in mechanized
3. Mulching. Chopping up residues and leaving them on top of the
ground has some definite benefits such as greatly reducing soil
erosion caused by rainfall and wind as well as water losses due
to evaporation. However, there are two disadvantages to mulch-
ing which should be considered.
Residues are left on the surface and can interfere with the
operation of equipment such as planters, plows, and culti-
vators which may plug up.
Mulching is not recommended for peanuts, especially in wet
regions, since they are very susceptible to Southern stem
rot (Sclerotium rolfsii), which can incubate in unburied
residues from any type of plant. (See Chapter 6.)
Animal vs. Tractor Power: Some Considerations for the Small Farmer
In the developing countries, tractor power and its associated equipment
are mainly confined to large farms and to areas where labor costs are high.
The large investment, fuel and repair costs, and maintenance requirements all
weigh heavily against the purchase of such machinery by small farmers. Spare
parts and the necessary repair facilities are commonly lacking, meaning that a
breakdown can be disastrous. A study by ICRISAT on the economics of full-size
tractors in India showed little evidence that they significantly increase
yields, cropping intensity, timeliness, or gross returns per hectare. Money
can usually be better spent on animal traction equipment, improved seeds, fer-
tilizers, and other high-return inputs.
However, there are two situations where tractor power can be justified.
Animal-drawn equipment may not be sufficient to meet the pro-
duction needs of the intermediate farmer who has about 5-20 ha
of land. In this case, small horsepower equipment may be very
suitable. The IITA farming systems program has developed a 5
hp gasoline-powered multipurpose equipment unit that can plant
field crops with a two-row "punch" planter, haul 500 kg in a
trailer, and convert to a walk-behind tractor for rotary til-
lage, ridging, brush slashing, and plowing rice paddies. Other
types of low-horsepower units are available from other manufac-
The small farmer can sometimes benefit by hiring tractor work
on an as-needed basis during peak periods when his normal labor
supply is insufficient to meet demands.
-- 76 --
Basic Tillage Equipment for Plowing and Harrowing
Hand implements. Heavy duty digging hoes can be very effective for small
areas. In Kenya, for example, nearly all small holdings are prepared this
way, although an average family cannot handle much more than 0.5 ha with this
method. In a wet-dry climate, most land preparation takes place when the soil
is hard and dry, which poses obstacles for hand tools. Some extension ser-
vices recommend that land be prepared at the end of the previous wet season
before the soil dries out. However, this is not always possible due to
Wooden plow. Designs of wooden plows go back many centuries. They often
are animal-drawn, and some have a metal tip. They do not invert the soil or
bury crop residues but basically make grooves through the soil. Their effec-
tiveness depends a lot on soil type and moisture content. The grooves they
make also serve as seed and fertilizer furrows.
A digging hoe and a moldboard
heavy duty hoe blade. plowshare--
SA moldboard plow. The
moldboard section is
curved so that it turns
One common type of wooden plow. over the soil slice that
Most of them have metal tips to is cut by the plowshare.
Moldboard plow. This is the ideal plow for turning under grass, green
manure crops, and heavy crop residues such as chopped-up maize stalks. It
also buries weed seeds deeper and damages perennial weeds more than other
equipment. Moldboard plows are available in animal-drawn models (usually just
one plow bottom) and tractor models (usually two to six bottoms). Depending
on the plow size (width of the moldboard as viewed from the front or back) and
soil condition, they will penetrate to 15-22 cm.
Unless equipped with a spring trip device, moldboards do not handle rocky
soils well. They are not as well suited to drier areas as disk plows. They
also encounter problems in sticky clay soils and may form a plow pan (a thin
compacted layer that can hinder root growth) if used at the same depth year
-- 77 --
Disk plow. This plow is better suited than the moldboard to hard, clayey,
rocky, or sticky ground, but does not bury residues as effectively. This is
an advantage in drier areas where surface residues reduce wind and soil erosion
and cut down moisture evaporation. Disk plows are not recommended for peanut
ground where Southern stem rot is a problem, because surface plant residues
harbor spores. They also will not do an effective job turning under grass
sod. Disk plows are mainly available in tractor-drawn models. Unlike mold-
board plows, they are less likely to form a plow pan if used at the same depth
year after year.
Ridging plows (Lister plows or "middlebreakers"). These basically consist
of a double-sided moldboard that throws soil both ways. This will produce a
series of alternative furrows (trenches) and ridges when operated over a
field. Depending on the climate and soil, the crop is either planted in the
furrows (in low rainfall areas with no drainage problems) or on top of the
ridges (in high rainfall areas or those with drainage problems). Such furrow
planting is advantageous in drier areas for cereal crops, since it conserves
moisture. Soil is thrown into the row as the season progresses for weed con-
trol, and this also sets the roots deep into the soil, where moisture is more
adequate. Such furrow planting is not recommended for peanuts and often not
for beans due to increased root rot and stem rot problems.
Rototillers (rotovators). These are available in tractor-powered models.
They thoroughly pulverize the soil and partially bury crop residues. Heavy
duty models can be used for a once-over complete tillage job. They disadvan-
tages are that power requirements are very high and the soil can be easily
overworked with this implement. In fact, rototillers do a far more thorough
job of seedbed preparation than is needed for the reference crops and are best
used for vegetable ground.
A ridging plow or A rototiller or rotavator.
middlebreaker for making Note the revolving blades
raised beds or ridges
raised beds or ridges under the hood behind the
Disk harrows. Disk harrows are commonly used after plowing to break up
clods, control weeds, and smooth the soil before planting. They are also used
to chop up coarse crop residues before plowing (especially if a moldboard or
-- 78 --
disk plow will be used), but heavier models
with scalloped disks (disks with large serra-
tions) are most effective for this purpose.
Both animal- and tractor-drawn models are
available but they are expensive and prone to
frequent bearing failure unless regularly
greased. Large, heavy duty versions pulled by
tractors are often called Rome plows and can
sometimes substitute for plowing. The gangs
of disks are offset to the direction of travel
so that they cut, throw, and loosen the top
7.5-15 cm of soil but pack down the soil
immediately below that. Repeatedly harrowing
a field prior to planting can actually leave
it harder than before plowing if done when the
soil is moist.
Animal-drawn disk harrow
Spike-tooth harrows. These consist of metal or wood frames studded with
pegs or spikes; extra weight in the form of stones or logs may be needed under
some conditions for maximum effectiveness. They are used to smooth the seed-
bed and break up clods (at the right moisture content), and are especially
suited for killing small weed seedlings that may emerge before planting.
Spike tooth harrows are made in many widths and are classified by weight and
the length of the tines. In some cases, this type of harrow can be run over
the actual crop rows from several days after planting up until the seedlings
are a few centimers tall to control early germinating weeds or to break up any
soil crusting. Spike-tooth harrows will clog up if trash is left on the soil
Two models of a spike-tooth harrow A spring tine harrow
Spring-tooth harrow. These have tines made from spring steel that dig,
lift, and loosen the top 7.5-10 cm of soil, break up clods, and smooth out the
seedbed. Both animal- and tractor-drawn models are available. They are not
suited to hard or trashy ground but handle stones well.
Field cultivators. These are similar in appearance to chisel plows, but
usually are not as heavy-built. They can be used for initial tillage on
ground with little surface residue, but are mainly used as a secondary tillage
implement for weed control. Most models are designed for tractor use.
-- 79 --
(Additional information on the use of animal-drawn equipment can be found
in Animal Traction, U.S. Peace Corps Appropriate Technology for Development
Manual Series #12, by Peter Watson, 1981.)
The best seedbed shape depends more on the climate and soil involved than
on the particular reference crop.
Flat seedbeds. This shape is used where soil moisture is adequate for
crop growth and where there are no drainage .problems. Under such conditions,
the reference crops are often planted on a flat seedbed and then "hilled up"
with soil (soil is moved into the crop row and mounded around the plants) as
the season progresses to control in-row weeds, provide support, and improve
drainage. In warm, humid areas where stem rot is a problem, this practice is
not recommended for peanuts.
Raised seedbeds (ridge or bed planting). Under heavy rainfall and/or
poor drainage, the reference crops are usually planted on ridges or raised
beds to keep them from getting "wet feet." This also helps minimize soil-
borne disease problems like root rots and helps control water erosion if the
ridges are run on the contour. Water infiltration is encouraged and runoff
minimized. In addition, ridge planting makes for easier entry of digging
equipment when peanuts are harvested. Finally, more topsoil is provided for
crop growth under this system. The main disadvantage of ridge planting is the
accelerated loss of soil moisture from the mounds--normally not a serious
problem in wet areas except during dry spells. In drier areas mulching would
be beneficial. In regions where the wet season starts out slow, the crops may
be flat-planted and then later "hilled up" as the rains increase. Furrow
irrigation always requires ridge planting.
Beans grown on raised beds
Land leveling with a board
Furrow planting. Under conditions of low rainfall or poor soil water-
holding capacity (e.g., sandy soils), crops are often planted in the furrow
bottom between ridges where soil moisture is greater. Soil can then be thrown
I.: ~ ~ b*
bottom between ridges where soil moisture is greater. Soil can then be thrown
-- 80 --
into the furrows to control in-row weeds and improve drainage (if rainfall
picks up) as crop growth progresses. This type of sunken planting is not
recommended for peanuts in moist areas, since it encourages stem and root
rots, particularly if soil is thrown into the row.
Note: Local farmers usually have good seedbed experience, so beware of
tampering with time-tested methods without first considering all the angles
and running some trials.
Equipment for Seedbed Shaping
Flat seedbeds usually require no special efforts beyond plowing and pos-
sibly harrowing. If additional land leveling is required, the small farmer
without access to special tractor-drawn leveling equipment can do a satisfac-
tory job dragging a heavy board hitched to two draft animals over the field.
Ridges or beds can be made with digging hoes, special ridging plows (see
tillage equipment section), or tractor-drawn disk-bedders (rolling disks
arranged at opposing angles to throw soil up to form beds). The crop can be
planted either on top of the ridges or in the furrows, depending on the soil
SUMMARY OF LAND PREPARATION REQUIREMENTS FOR THE REFERENCE CROPS
Land preparation is a very location-specific practice varying with soil
type, climate, crop, management level, and available equipment. The following
is a summary of the principal factors involved in choosing the most feasible
and appropriate land preparation method and.seedbed shape for the reference
1. Seedbed Fineness (thoroughness of preparation).
Maize's large seeds and spikelike emergence gives it the best
clod-handling ability of the reference crops.
Rough cloddyy) seedbeds discourage weed growth and reduce ero-
sion caused by rain or wind; they also increase water retention
by cutting down water runoff.
The reference crops can tolerate a rougher seedbed when planted
by hand than when typical mechanical planters are used.
To cut down on soil compaction and other effects of overworking
the soil as well as to reduce labor, machinery, and fuel costs,
it is best to use the minimum amount of tillage consistent with
adequate seedbed preparation.
2. Tillage Depth
There is seldom any advantage to plowing deeper than 15-20 cm.
Shallower plowing may be advisable in drier areas to reduce
wind erosion and moisture losses.
-- 81 --
3. Crop Residue Management
Leaving crop residues on the soil surface is especially advan-
tageous in drier areas since it reduces moisture losses and
wind erosion. It also reduces erosion due to rainfall and in-
creases water retention.
When growing peanuts (and sometimes beans), complete residue
burial is usually recommended where Southern stem rot (Sclero-
tium rolfsii) is a problem, since the disease can incubate on
surface plant residues.
With the other reference crops, surface residues may sometimes
aggravate certain insect and disease problems.
4. Suitability of Equipment
The moldboard plow is the most effective implement for burying
crop residues and grass sod.
A disk plow is better suited than the moldboard to hard,
clayey, rocky, or sticky ground but does not bury residues or
grass sod effectively.
Chisel plows are best suited to lower rainfall areas and leave
trash on top of the soil. They are fairly ineffective on wet
Disk harrows handle clods better than spike- (peg) tooth and
spring-tooth harrows but are more costly and prone to repair
5. Seedbed Shape
Ridge planting is recommended for all the reference crops under
high rainfall or poor drainage.
Flat planting is best suited to soils with good drainage. How-
ever, soil can be mounded into the crop row as growth progres-
ses to control weeds and improve drainage if rainfall increases.
Furrow planting is best suited to low rainfall areas since it
Peanuts and beans are especially susceptible to root rots fav-
ored by excess moisture. They should be either flat-planted or
Factors Affecting Variety Selection
The selection of a locally-adapted variety with good yield potential and
acceptable grain characteristics is fundamental to successful crop production.
There are several important variety-related characteristics that should be
considered when selecting seeds.
-- 82 --
1. Yield potential. This is related to inherent natural vigor and
other characteristics listed below.
2. Time to maturity. Varieties fall into three general maturity
classes: early-, medium-, and late-maturing (when grown under sim-
ilar temperatures). Early varieties produce a crop more quickly,
but yields may be about 10-15 percent lower compared with slower-
maturing types if both receive adequate moisture. However, early
varieties are especially well suited to short rainy seasons or
sequential cropping. Since temperature has a strong influence on a
variety's actual length of growing period, some countries like the
United States are now labeling maize varieties in terms of the
growing degree days (total heat units) required for maturity rather
than calendar days.
3. Elevation adaptation. This has to do with a variety's time to mat-
urity and growth ability at different elevations and temperatures.
In regions with pronounced variations in elevation such as Central
America, the Andean countries, and Ethiopia, maize and sorghum
varieties are classified according to their elevation adaptation
(e.g., 0-1000, 1000-1500, etc.); a similar system may also be used
for beans and other pulses.
4. Heat or cold tolerance. Varieties vary in their tolerance to ex-
cessive heat or cold.
5. Drought tolerance. Even varieties within a crop can vary consider-
ably in this respect. In a 1978 CIMMYT maize trial, a variety
selected for drought tolerance outyielded the best full-irrigation
variety by 64 percent under conditions of severe moisture shortage.
6. Resistance (partial tolerance) to insects, diseases, and nematodes,
as well as to bird damage and soil problems such as excessive acid-
ity and low phosphorous levels. Reference crop varieties can dif-
fer considerably in their tolerance to these problems, which are
some of the major concerns of plant breeding work. Resistance to
lodging also is an important consideration in selecting a maize
7. Growth habit and other plant characteristics. For example, bean
varieties can be bush, semi-vining, or vining in their growth
habit; millet varies in tillering ability and sorghum in its ra-
tooning potential. (See Chapter 3.) Plant height and the ratio of
leaf and stalk also varies with variety.
8. Daylength sensitivity (photosensitivity) varies markedly among sor-
ghum and millet varieties. (See Chapter 3.)
9. Seed color, shape, size, storability, etc.
Traditional versus Improved Varieties
In selecting a variety, it is important to understand the differences
between traditional varieties, hybrids, synthetics, and other improved
-- 83 --
1. Traditional (local varieties). They tend to be relatively low-
yielding but are usually hardy and have fair to good resistance to
local insect and disease problems. However, most are adapted to
low levels of soil fertility and management and often do not
respond as well as improved types to fertilizer and other improved
practices. Native varieties of maize, sorghum, and millet tend to
have an overly high ratio of stalk and leaves to grain, but this
may be an advantage where livestock are important.
Despite certain disadvantages, local varieties may be the best
choice in some situations. During the first years of the Puebla
maize project in Mexico, some of the local varieties consistently
outyielded anything the plant breeders could come up with.
2. A hybrid is a type of improved variety produced by crossing two or
more inbred lines of a crop. This is relatively easy to do with
maize and sorghum, and a number of hybrids of these two crops are
available. Hybrid development in peanuts, beans, and the other
pulses has proven more difficult; such hybrids are not generally
available. Millet research is still at too early a stage for
hybrids to assume much importance.
When grown under similar conditions, an adapted hybrid may outyield
the best adapted, normally produced varieties by 15-35 percent, but
not always. Despite these possible yield benefits, hybrids have
Unlike naturally produced varieties, the seed harvested from a
hybrid should not be replanted by the farmer. If reseeded, a
hybrid begins to degenerate and revert back to the original
(and usually less desirable) lines from which it was
developed. Yields may drop as much as 15-25 percent with each
successive crop. Many small farmers lack the inclination or
the money to buy new seed for each planting unless special
arrangements and educational efforts are made.
Hybrid seeds may be several times more expensive than that of
Hybrids require good management or they may not yield much more
than other types.
Hybrids show a narrower range of adaptation to different grow-
ing conditions than other varieties; this makes finding a
suitable hybrid more difficult. It is estimated that 131
different hybrids had to be developed to suit varying maize
growing conditions in the United States.
3. Synthetics are improved varieties that have been developed from
cross-pollinating lines (naturally pollinated with no purposeful
inbreeding as in hybrids). These lines are first tested for their
combining ability and then crossed in all combinations. Synthetic
varieties often yield as well as hybrids under small farmer condi-
tions and have several advantages over them.
-- 84 --
They have greater variability than hybrids, which makes them
more adaptable to different growing conditions.
The seed costs less than that of hybrids.
Unlike hybrids, seed harvested from a synthetic can be re-
planted without loss of vigor as long as farmers are willing to
select it from the plants with the best characteristics.
4. Varieties improved through mass selection. This is the most
elemental form of varietal improvement and consists of natural
crossing between lines with no attempt made to test for combining
ability (as with synthetics) and continually selecting seed from
plants showing the best combination of desirable characteristics.
While yields may not be as good as those from hybrids or synthet-
ics, the seed is cheaper and also can be replanted.
Guidelines for Selecting Quality Seed
Seed quality can be influenced by the following factors.
1. Varietal purity. Farmers who use their own harvested seed for re-
planting can be reasonably assured of varietal purity, especially
with crops that are naturally self-pollinated (millet, sorghum,
peanuts, cowpeas, beans, and most other pulses). Since maize is
cross-pollinated, there is no opportunity for "contamination" from
other nearby maize varieties. This can be minimized by selecting
seed for replanting from the inner part of the field.
Commercially available seed may or may not have good varietal puri-
ty, depending on its source and the country's commercial seed stan-
dards. In some areas, certified seed is available with guaranteed
genetic purity and tested germination.
2. Germination and vigor depend largely on the seed's age and the
conditions under which it has been stored. High temperature and
humidity as will as insect damage can drastically reduce both ger-
mination and vigor. Certified seed is usually labeled with a
tested germination percentage, but post-tested storage conditions
can make this a worthless guarantee. You should encourage farmers
to run their own germination tests before planting seed, regardless
of source. (See below.)
3. Visual traits. Mold, insect damage, cracking, and shrunken or
shriveled seed can mean trouble.
IMPORTANT NOTE: Beans, soybeans, and shelled peanuts are very sus-
ceptible to damage from rough handling of dry seeds in harvesting,
processing, and shipping. Dropping a sack of beans on a cement
floor is enough to harm them. Both the seedcoats and seeds crack
very easily; careless handling can also cause invisible damage. In
both cases, these injuries can lead to stunted, malformed seedlings
lacking in vigor.
-- 85 --
4. Impurities such as weed seeds are more of a problem in crops with
small seeds like millet and sorghum, where separation is more
5. Seed-borne diseases. Some diseases like anthracnose may show visi-
ble symptoms on contaminated seeds, while many others do not. Cer-
tified seed, if grown under the proper procedures of inspection and
roguing (elimination of diseased plants), is free from certain
seed-borne diseases and is especially recommended for beans when
available. Some common fungal diseases are carried mainly on the
seed coat surface and can be controlled by dusting the seed with a
fungicide; others (especially viruses) are internal and have no
control. (See Chapter 6.)
How to Select Home Grown Seed
Most farmers not using hybrids will set aside some of their harvested
seed for replanting future crops. This is fine as long as the variety is
suitable, storage methods are adequate, and seed-borne diseases are not a
problem. If the guidelines below are followed, farmers actually may be able
to improve the varieties they are using or at least prevent a decline in their
1. Seed selection should start while the crop is still growing in the
field. Most farmers wait until after harvest to select seed for
replanting and go largely by seed or ear size. Selecting maize
seed from the largest ears may have little, if any, value. This is
because the ear's size may be due less to the plant's inherent
genetic ability than to environmental or management factors like
fertility, plant density, and available moisture.
2. When selecting plants as potential seed sources, keep in mind the
important plant characteristics that favor good yields.
General. Resistance to disease, insects, drought, and nema-
todes; general plant vigor, ratio of stalk and leaves to grain;
and time to maturity.
Maize. Resistance to lodging, extent and tightness of husk
covering (for insect, bird, and water resistance), and number
of well-formed ears per plant. When selecting maize plants,
make selections from well within the field to avoid possible
3. Mark the selected plants with cloth or stakes.
4. Additional guidelines for maize. When choosing among good ears
after harvest, physical differences like the number of kernel rows,
kernel size, and filling of the tips and butts of the cob are rela-
tively useless as indicators of yield potential. However, the very
small, misshapen seeds at the extreme ends of the cob should be
discarded. Check also for uniformity of kernel color and for in-
-- 86 --
How to Conduct a Germination Test
Farmers should be encouraged to run a germination test on seed before
planting, regardless of the source. The same holds true for extension workers
receiving shipments of improved seed. Germination figures that appear on seed
labels can be inaccurate even if the tests were conducted fairly recently.
Warm, humid conditions in the tropics can rapidly lower the germination rate.
To run the test:
count out 100 seeds and place them on top of several thick-
nesses of moist newspaper; spread them out enough so you can
distinguish which ones have germinated;
carefully roll up the moist newspaper so that the seeds remain
separated from each other and remain pressed against the news-
paper; place them in a plastic bag or periodically remoisten
the.newspaper to keep it from drying out;
sprouting time will vary with temperature, but you should be
able to get a good idea of germination within three to five
days unless it is unusually cold; good seed should have a
germination rate of at least 80-85 percent under these condi-
tions; up to a point, you can compensate for low germination by
planting more seed, but below a 50 percent or so seedling vigor
may suffer also.
It is a good idea where possible to supplement this type of test with an
actual field test, since soil conditions are not usually as ideal. Plant
50-100 seeds, keep the soil moist enough, and then count the emerged plants.
If germination is very much lower than with the newspaper method, do some
troubleshooting to see if insects or weeds may have caused problems.
The Goals of Successful Planting
When planting, farmers must accomplish four objectives in order to
promote good crop yields.
1. Attain an adequate stand (population) of plants. This requires
seed with good germination ability, adequate land preparation, suf-
ficient soil moisture, correct planter calibration (adjustment) if
mechanical planters are used, proper planting depth, and control of
soil insects and diseases that attack seeds and young seedlings.
In some areas, birds and rodents also cause problems.
2. Attain the desired plant spacing both in the row and between the
3. Observe timeliness in land preparation and planting. The right
time to plant depends'on the crop's characteristics (e.g., peanuts
should be planted so that harvesting will occur during reasonably
dry weather), the onset of the rains and overall rainfall pattern,
the influence, if any, of planting date on insect and disease
problems such as sorghum head mold.
-- 87 --
4. Use the right type of seedbed for the particular crop, soil, and
Planting Methods and Equipment
1. Hand planting with a planting stick, hoe, or machete. This is the
most common method used by small farmers in the developing world.
Equipment costs are negligible.
Less thorough seedbed preparation is needed than for most
mechanical planters. The farmer who hand plants can push large
clods out of the way while walking down the row or can plant
directly into untilled soil.
Time and labor requirements are high: it takes three to four
person-days to plant a hectare by hand.
When hand planting, farmers usually put several seeds in each
hole and space the holes rather far apart, partly to save
labor. This practice can often reduce yields be resulting in
too low an overall seedling rate and too much competition among
the plants that emerge from the same hole.
2. Improvements in Hand Planting
Hand-operated, mechanical "punch" or "jab" planters are avail-
able that make the planting holes and drop in the seed in one
movement (the seed is automatically metered out from a
reservoir). They are operated like an ordinary planting stick
(jabbed or punched into the ground) but are much quicker and
are also very useful for filling in any "skips" (vacancies) in
larger fields. A hectare of maize can be planted in 15-20
person-hours. The farming systems program of IITA in Nigeria
has designed a very successful punch planter suitable for
planting maize, sorghum, cowpeas, beans, and soybeans into
untilled ground. It is also capable of planting through a
dried mulch. The IITA punch planter can be built in a workshop
with access to metal shears (no welding is needed). (Write
IITA for plans.) Other types of punch planters are available
commercially in some countries.
Hand-pushed planters. Most models require a fairly loose
clod-free seedbed for satisfactory operation. However, IITA's
farming systems program has designed a very effective rolling
punch planter (called a rotary injection planter) that can be
built in any workshop with welding and metal-shearing capability
and is being manufactured by Geest Overseas Mechanization Ltd.,
West March Road, Spalding, Lincolnshire, PE11-2BD, England
(price is about U.S. $225).
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The rotary injection planter uses the same principles as the
hand punch planter, but has six punch-injection devices on a
rolling wheel plus a following press wheel to firm down the
seed row. The standard design produces a seed spacing of 25
cm, but alternate rollers can be made for different spacings.
The rotary injection planter is also available as a four-row,
hand-pulled model for planting direct-seeded rice.
Hand planting into furrows made with an animal- or tractor-
drawn implement. A wooden plow, cultivator shank, or other
implement can be used to make seed furrows in plowed ground.
If certain precautions are followed, the fertilizer can be
placed in the same furrow. (See Chapter 5.)
Reasonably parallel crop rows are required if weeding is to be
done with an animal- or tractor-drawn cultivator. Farmers can
easily construct a parallel row "tracer" consisting of a wood
or bamboo frame with hardwood or steel teeth for marking out
rows. (A design for this handy implement can be found in the
Peace Corps Animal Traction manual.)
Improved seed-spacing accuracy can be achieved by running a
rope or chain down the row with knots or paint marks to
ncate te proper spacing. Otherwise, farmers commonly make
large errors in spacing when using planting sticks or dribbling
out seeds into a plowed furrow.
3. Animal- and tractor-drawn mechanical planters are available in many
different models. A farmer using a one-row, animal-drawn planter
can sow about 1-1.5 ha in a day and about 5-8 ha using a two-row,
tractor-drawn planter. Here are some important considerations
concerning these types of planters.
Most mechanical planters require more thoroughly prepared
seedbeds than is needed for hand planting. Some models have
special soil openers that permit satisfactory operation in hard
or cloddy soil.
The farmer must be able to calibrate (adjust) the planter so
that it drops the seeds at the correct intervals along the
row. (See below.)
Some models have attachments for applying fertilizer in a band
beneath the soil and slightly to the side of the seed row.
This is an especially effective method for fertilizers con-
taining phosphorous. Farmers using planters without fertilizer
applicators will often broadcast the fertilizer and plow it
under before planting or leave it on top of the ground; this
should not be done with fertilizers containing phosphorous!
Farmers buying mechanical planters should be encouraged to
purchase a fertilizer attachment if available and effective.
(NOTE: The applicator should not dribble the fertilizer on top
of the ground or place it in direct contact with the seed.)
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An animal-drawn planter
with a separate hopper
for banding fertilizer
The rolling "punch"
planter developed by
IITA and now manufac-
It also can be built
in a workshop.
The IITA designed hand-operated
"jab" or "punch" planter, which can
be made in a workshop. The attached
metal bracket firms the soil over
the seed and spaces the next seed
A hand-pushed fertilizer band appli-
cator. This model places the fer-
tilizer below the soil surface,
which is essential for phosphorus-
bearing fertilizers. The attachment
at the left is used to close the
furrow but usually is not needed.
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Plant Population and Its Effects on Crop Yields
Both plant population and spacing affect the yields of the reference
crops, and extension workers should understand the relationships.
Up to a point, crop yields will increase along with increases
in plant population until the competition for sunlight, water,
and nutrients becomes too great.
Excessively high populations will reduce yields, encourage
diseases, and seriously increase lodging in maize, sorghum, and
millet by promoting spindly, weak stalks.
Excessively low plant populations will cut yields due to unused
space and the limitations on maximum yield per plants.
Under most conditions, changes in plant population will not
affect yields as much as might be expected. This is because
most crops have a good deal of built-in buffering capacity,
especially if the population is too low. In this case, the
plants respond by making yield-favoring changes such as
increased tillering (millet, sorghum) and branching (peanuts,
other pulses), more pods or ears per plant or larger ears or
grain heads. In maize, a plant density that is 40 percent
below the optimum for the given conditions may lower yields by
only 20 percent.
Plant population changes have a more pronounced effect under
conditions of moisture stress.
What is the ideal plant population? There is no easy answer to this,
because the optimum plant density depends on several factors.
Type of crop and variety. Because of differences in plant size
and architecture, crops and their varieties vary in their
tolerance to increasing plant populations. For example, early
maturing maize varieties are usually shorter and smaller than
later maturing ones and therefore may benefit from higher plant
densities. Beans and cowpeas respond well to populations three
to four times higher than for maize due to their smaller plant
size and a growth habit that favors better light interception.
Available soil moisture. The optimum plant population density
varies directly with rainfall and the possibility of moisture
stress. Plant population has a stronger effect on yields under
low moisture conditions than when moisture is adequate. This
is because increased populations also increase water use,
although plant spacing can make a difference. This is par-
ticularly true for maize and sorghum, because yields can be
significantly reduced by relatively small increases in plant
populations when grown under moisture stress
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SAvailable nutrients. Adequate soil fertility is especially
essential with high plant populations. In fact, fertilizer
response is often disappointing when popluations are too low
for the given conditions. This is one of the main reasons that
small farmers often do not get their money's worth out of
fertilizer. An ear of maize can only grow so big, and even
high rates of fertilizer can not make up for too few ears
produced by a small number of plants.
Management ability. High populations require more soil fertil-
ity and moisture as well as better overall general management.
Plant Spacing and Its Effects on Crop Yields
The reference crops are row crops for some very good reasons. A row
arrangement permits quicker and easier weeding and facilitates most other
growing operations. Row cropping with its handy space for equipment, animal,
and human traffic allows for ease of mechanization and handling, no matter
what the level of sophistication. Distributing a given plant population over
a field involves both plant spacing within the row and the distance between
the rows (row width).
Plant spacing within the row. The number of seeds that need to be
planted per meter or foot of row length depends entirely on the plant
population and row widths that have been chosen according to recommendations.
The main concern then becomes whether hill planting or drill planting should
be used. In drill planting, mechanical planters drop seeds out one at a time
along the row. Small farmers who hand plant their crops usually use hill
planting, sowing several seeds per hole and spacing the holes rather far
apart. This reduces time and labor and also may improve seedling emergence
under crusty soil conditions, but it may lower yields somewhat because of
inefficient use of space and increased competition between the plants within a
hill for sunlight, water, and nutrients.
Row width. Space between rows is determined by the type of equipment
used as well as by plant size or "spread." The use of tractor- or animal-
drawn equipment requires more space between rows (wider row widths) than when
only hoes and backpack sprayers are used. Beans can be spaced in narrower
rows than maize or other tall crops and still be weeded with an animal-drawn
cultivator without knocking the plants down. Row width influences crop yields
in the following ways.
As row width is narrowed, the plants can be spaced farther
apart within the row and still maintain the same population.
Up to a point, this makes for better weed control due to
earlier and more effective between-row shading by the crop.
Narrower rows allow for higher plant populations without over-
As row width is widened, plants have to be crowded closer
together within the row in order to maintain the same
population. This may lower yields.
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