The sampling of soil is extremely important since the sample must correctly represent the area about which information is desired. The plow zone is a volume of soil that is very heterogeneous due to natural phenomena.The fact is that this is the layer of soil into which "materials" are incorporated. Plant and animal residues, or other added materials such as lime and fertilizers, cannot be uniformly distributed or thoroughly mixed with total volume of soil in the plow zone. Therefore, care must be taken to assure that samples submitted to the laboratory are representative of the areas which information is desired. This can only be done by carefully following these instructions and/or those on sampling bags.
SAMPLING FOR ROUTINE ANALYSIS:
To obtain a representative sample of a given area (volume) of soil, a large number of cores or sub samples must be taken. For most cultivated fields, each composite sample should consist of a minimum of 30 cores. Each core should have a volume of about 30 ml (diameter 2.5 cm or 1 inch, length 15 cm or 6 inches).
The size of area to be included in a composite sample depends
on the variability of the field. Past management practices, such
as liming or fertilizing and/or differences in soil type or crop,
etc., generally dictate the size of fields or areas to be sampled.
If the information is desired about specific spots or areas in a field, a composite sample must be taken from the area. The number of cores to take per composite sample, however, does not relate to the size of the area sampled, but is related to the variability. The more variable an area is, the more cores will be needed to get a representative sample. Thus, 30 cores are still recommended even if the area is small.
Mark each bag with a sample number. Then prepare a map of the areas sampled, noting sample number on the map so you will remember the area from which the sample came from when the results are returned.
Plow depth or the plow zone is the layer most commonly sampled for soil fertility evaluation. This is the zone which reflects past management practices including application of lime, fertilizers and the accumulation of plant and animal residues. It is also the zone where most of the microbiological activity (changes brought about by bacteria, fungi, protozoa, etc.) takes place and where there is greater accumulation of plant roots. Soil erosion and deposition also take place mostly in the plow zone. Thus the plow zone is the layer of greatest activity in the soil, and correctly evaluating the properties of this layer go far in predicting fertilizer and lime requirements.
Lower horizons in the soil are important too, but they do not change much from one year to another. If basic information is available relative to characteristics of the soil from the plow depths usually will suffice for soil fertility purposes.
Fields which are not plowed but receive broadcast applications of fertilizers and lime, such as permanent pastures, should be sampled only to a depth of 0--3 inches or 0-6 cm, since the phosphorus and lime move downward very slowly into the soil. Sampling lower depths may not reflect the accumulation of phosphorus or lime from previous surface. If samples are taken for trees and walnut trees sampling depth should be 0-9".
For green houses or nurseries sample, submit 1 lb potting material.
Special soil conditions may necessitate sampling other depths. If an adverse soil condition is anticipated, then the depth affected should be sampled. For example; soluble salts may accumulate at or near the soil surface and the concentration may be sufficiently high to be detrimental. A sodium soil layer may exist just below the plow zone, and obviously a plow depth sample should not reflect this condition, etc.
FREQUENCY OF SAMPLING:
The frequency of sampling a soil is related to the amount of
change that takes place. Sandy soil, low in organic matter,
have little resistance (buffer) to change. Heavy applications
of fertilizer, especially those high in Nitrogen, in order to
attain high growth, may change the lighter textured soils markedly
even within a few months. Such soils should be sampled annually
in order to monitor changes and to avoid nutrient imbalances or
acid conditions developing. If light textured soils are multi
cropped, then more frequent sampling will be desirable to adequately
monitor changes. On finer textured soils that have a high exchange
capacity, where only one crop a year is removed and where moderate
amounts of fertilizers are applied, then two or three years may
elapse before a sufficient change takes place to warrant other
Remember soil analysis is a source of information to guide you in the proper use of fertilizers, lime and other soil amendments. It is far better to take samples more frequently that might be needed than to err by waiting too long to obtain the information. One decreased crop yield can more than pay for many soil analysis.
For walnut trees take sample in spring for maintenance program
and in fall for corrective recommendations.
MIXING CORES FOR COMPOSITE SAMPLES:
Failure to thoroughly mix the 30 cores of soil is a potentially large source of error. If one of the cores (sub samples) have a few grains of fertilizer in it, then it must be thoroughly mixed with the other sub samples to give a representative, homogeneous, composite sample.
SAMPLE SIZE TO SUBMIT TO THE LABORATORY:
About 300 ml (350 grams or 3/4 lb) of soil is needed for a routine analysis. This will be obtained by filling the K Labs. Intl., Inc. sample bag up to the mark.
Since undesirable chemical changes may take place when wet
soil is kept in a closed sample bag for many hours, the soil should
be air dried before closing the bag for shipment.
Soil samples may be carriers of many pests including insects, nematodes and both plant and animal diseases. Therefore, it is important that all precautions be taken to avoid transmitting pests from one area to another. For samples that come from outside the United States, permits are required. Quarantine labels must be placed on each container containing soil samples. This may mean one quarantine label for 25-30 small samples and one for the one or two bags for greenhouse study samples. The quarantine labels for submitting soil samples for analysis or for greenhouse studies may be obtained by contacting K Laboratories International, Inc.
Samples can be packed in corrugated cardboard or wooden boxes. However,
care should be taken to assure that samples are tightly packed
in the box and cannot move around during transportation causing
either sample bags or the shipping boxes to break.
INFORMATION THAT SHOULD ACCOMPANY EACH SAMPLE:
Complete the questionnaire on the K Laboratories sample information sheet or send an information sheet for each sample (either laboratory analysis or greenhouse sample) with the following information:
FARM LOCATION: _________________________________________________
FIELD AND SAMPLE: ______________________________________________
CROP TO BE LAST
FERTILIZE : _________________________ CROP: ___________________
APPLIED __________________________________ YEAR ___________
APPLIED __________________________________ YEAR __________
LIST ANY ABNORMAL CONDITIONS OR SPECIFIC INFORMATION DESIRED:
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