Plant Analysis HandBook for Georgia
C. Owen Plank
Extension Agronomist - Soil Testing & Plant Analysis
Disclaimer!This information pertaining to Plant Analysis was written for use in Georgia and may not be applicable in other states.
Trade and brand names are used only for information. The Cooperative Extension Service, The University of Georgia College of Agricultural and Environmental Sciences does not guarantee nor warrant the standard of any product mentioned; neither does it imply approval of any product to the exclusion of others which may also be suitable.
- PURPOSE & USE
- NUTRIENT CONTENT OF PLANTS
- INTERPRETING A PLANT ANALYSIS RESULT
- PLANT ANALYSIS AS A DIAGNOSTIC TOOL
- DATA LOGGING USING PLANT ANALYSIS
- INTERPRETATION & RECOMMENDATION BY CROP
NUTRIENT CONTENT OF PLANTS
The nutrient content of a plant varies not only among its various plant parts but changes with age and stage of development. There are also varietal differences which will affect the nutrient element content found in various plant parts. A plant analysis interpretation is based on a comparison of the nutrient concentration found in a particular plant part taken at a specific time with known desired value or ranges in concentration. One method of interpretation is based on "critical values," a critical value being the concentration below which deficiency is likely to occur. This system of interpretation has a serious limitation since it defines only the lower limit of the sufficiency range, providing no guidance when the concentration found exceeds the critical value. A more useful method of interpretation is based on sufficiency ranges, the optimum element concentration range below which deficiency occurs and above which toxicity or imbalances occur. This system of evaluation is currently in use in the Georgia Plant Analysis Laboratory.
Critical values are still quite useful and are frequently referred to when interpreting a plant analysis result. A brief discussion of the known critical values for the elements included in a plant analysis is given below:
The critical level of N in many plants is around 3 percent. For several crops, when the N level in leaves drops below 2.75 percent, N deficiency symptoms appear and yield and quality decline. The primary exceptions are for the very young plants when the critical level may be 4 percent or more, and for leguminous plants, such as soybeans, peanuts, alfalfa, etc., where the critical N percentage is 3 to 4.25 percent. For some tree fruits and ornamentals, N levels may be as low as 2 percent before deficiency occurs. Deficiencies as well as excesses can be a problem. Nitrogen leaf levels in some varieties of pecans exceeding 3.50 percent may result in early defoliation. Nitrogen leaf levels greater than 4.50 to 5 percent retard fruit set in greenhouse tomato. High N levels (>3.50 percent) in forage crops such as fescue is thought to be related to the incidence of grass tetany.
Small changes in N content for some crops can result in large effects on yield, plant growth, and the quality of forage and fruit. Therefore, it is important that the N level be maintained within the prescribed limits of the sufficiency range by the proper use of N fertilizer.
The P requirement of plants varies considerably. Tree crops have relatively low P requirements with the critical values ranging from 0.12 to 0.15 percent. Grasses have higher P requirements with critical values ranging from 0.20 to 0.25 percent. Legumes and some vegetable crops have relatively higher P requirements with critical values being 0.25 to 0.30 percent or slightly higher. Most plants grow to the extent to maintain a near constant P level within the plant. When a P deficiency occurs, it is usually due to a severe inadequacy of P in the soil solution or in some cases it may be due to a restricted root system as a result of cool-moist growing conditions. Phosphorus deficiencies normally occur early in the growth cycle of the plant when the P requirement is high. The P content of plants is initially high and declines with age. Since P is a fairly mobile element in plants, deficiencies generally occur on older tissue.
The excess range of P is not clearly known. The P level in young plants can be very high such as 0.50 to 1.00 percent, but these high levels may reflect actual need. In some instances, high P plant levels may cause imbalances and deficiencies of other elements, such as Zn, Cu, Fe, etc. Plant P can be maintained within the sufficiency range by proper P fertilization and the maintenance of the soil P level within the medium to high soil test range.
The K requirement of plants varies widely depending on plant species. The tree crops such as pecans, peaches, apples, etc., have relatively low K requirements. The critical value for K in tree leaves ranges from 0.75 to 1.25 percent. For grasses, the K requirement is higher with the critical value in leaves ranging from 1.20 to 2.00 percent. For legumes, the critical value for K generally ranges from 1.75 to 2.00 percent. The K level in a plant can change quickly as K is quite mobile and moves readily within the plant. Potassium can be easily leached from growing plants by rain to be reabsorbed through the roots. Because of K mobility, both in the plant and soil, deficiency symptoms can develop quickly. Deficiencies frequently occur during both the early stages of growth and the latter stages of growth particularly during fruiting. Young plants may contain 3.00 to 5.00 percent K although the actual requirement may not be that high. Because it is mobile in the plant, K deficiency symptoms appear in the older plant tissue first. The K concentration in the plant decreases with age. Potassium balance in plants is important. The K/Ca+Mg balance, and, more recently, the K to N balance must be maintained at a proper level to avoid deficiencies of Mg in the first instance and K in the second. High K can induce Mg deficiency in most plant and tree crops. Plants which are Mg deficient may have high K and Ca contents as the plant tends to maintain a constant cation concentration. As a result of these balance phenomena, heavy applications of K or N fertilizer, respectively, can induce a Mg or K deficiency. Under Georgia soil conditions, K deficiency is difficult to induce unless the K soil test level is low and the soil is heavily limed or fertilized with large quantities of N. The K to N balance is becoming increasingly important in pecans. As the N level in tree leaves increase, the K level must also be increased to maintain the proper balance and prevent K deficiency from occurring. Plant K can be maintained within the sufficiency range by proper K fertilization and the maintenance of the soil K level within the medium to high soil test range.
Magnesium deficiency occurs in many plants when the leaf level is less than 0.10 to 0.15 percent. Small grains may exhibit deficiency symptoms when the Mg level is less than 0.10 percent. When corn is less than 12 inches in height, magnesium deficiency may occur when the Mg level is below 0.15 percent. However, as corn matures, deficiencies may not be evident until the Mg level is less than 0.13 percent. For legumes such as peanuts and soybeans, the critical level is 0.25 to 0.30 percent. The critical level for cotton and pecans is 0.30 percent. Several vegetable crops such as tomato, turnips, and collards have a high Mg requirement with the critical level near 0.40 percent Mg. Magnesium is a fairly mobile element in the plant, therefore, deficiency symptoms occur in the older plant tissue. The Mg concentration in the plant tends to increase with age.
Magnesium deficiencies can be induced by excessive K and NH4-N fertilization. When the soil pH is less than 5.4, Mg availability and uptake by plants is greatly reduced. The usual cause for Mg deficiency in Georgia is generally low soil pH and/or low soil Mg. Depending on the soil conditions, the effect of K and NH4-N fertilization can vary depending on the soil pH and level of soil Mg. Continued liming with only calcitic lime will result in a Mg deficiency. Adequate soil Mg can generally be maintained by liming with dolomitic limestone to keep the soil pH between 6.0 and 6.5. Supplemental applications of fertilizer Mg may be needed in some cases to supply some of the Mg crop requirement.
It has been generally thought that the S requirement of plants was comparable to that of P. This has not proven to be so. The S requirement for grasses is quite low, the critical value being around 0.10 percent. Sulfur deficiencies in corn do not generally occur until the S level is less than 0.10 percent in the leaves. Under Georgia conditions, legumes, cotton, tobacco, and tomatoes have a critical S level of about 0.20 to 0.25 percent. The S critical level for crops such as cabbage, spinach, turnips, and collards is around 0.30 percent. However, additional research in this area should aid in pinpointing the critical level for these crops. There is a critical N to S percentage ratio which should be maintained. As suggested by Reneau (1983) the N:S ratio may be a better indicator of the S status of corn than the S concentration. For crops such as corn, this ratio should not exceed 18:1 if S deficiency is to be avoided. Stewart and Porter (1969) suggested that a N:S ratio above 16:1 indicates a lack of S may be limiting protein formation and a ratio of 20:1 or greater indicates that S is severely deficient. For optimum corn grain yields, the N:/S ratio should be maintained between 10:1 to 15:1 (M. E. Sumner, personal communication). The optimum N:/S ratio for Coastal bermudagrass ranges from approximately 9:1 to 12:1 (Martin and Matocho, 1973). Maintaining the N:S ratio within the range for optimum production of Coastal also provides the N:S ratio that is about optimum (10:1 to 15:1) for ruminant nutrition (Allaway and Thompson, 1966). Sulfur deficiencies occur primarily on the very sandy soils of South Georgia and when low S containing fertilizers are used over several years. Sulfur deficiencies tend to occur early in the plant growth cycle. The proper S level can be maintained in the plant by providing a S source near the germinating seed, or by adding S with sidedress and topdress N applications particularly in sandy soils. Most Georgia subsoils contain sizeable quantities of S. Provided the pH is not too low when roots enter the subsoil, sufficient S will generally be available to satisfy the crop requirement.
Since S is not a mobile element in the plant, deficiency symptoms tend to first appear in the upper or newly emerging leaf tissue.
The Ca requirement for plants varies widely with grasses having the lowest requirement, legumes intermediate, and fruit crops and cotton the highest. Calcium levels from 0.20 to 0.25 percent are quite adequate for pasture grasses and corn. Soybean has a critical Ca concentration in the mature leaves of 0.50 percent while the level for peanuts is 1.25 percent. Apple leaves should contain about 1.00 percent Ca and peach leaves 1.25 percent. Greenhouse tomato has a critical concentration for leaves of about 1.00 percent. Of the crops grown in Georgia, cotton probably has the highest critical Ca concentration at 2 percent for leaves.
Calcium deficiencies are not unusual, although the crops where Ca is particularly important are the fruit crops, such as apples, peaches, and tomato. Calcium deficiency will significantly affect fruit quality. Brown rots, easy bruising of fruit, and blossom-end rot of tomato are frequently associated with inadequate Ca. Pod-rot in peanuts is also a Ca deficiency. These deficiencies are not easily "uncovered" by leaf analysis. When Ca deficiency is severe, newly emerging tissue is affected. The margins of the leaves tend to stick together, giving a ragged edge to new leaves. Older leaves will show a browning of the margins. Since Ca is not a mobile element, deficiencies occur in the newer tissues. The Ca level in plants tends to increase with the age of the plant.
There is increasing evidence that Ca is more like a micronutrient as the critical concentration may be in the parts per million range. Several plant physiologists have grown plants successfully at low Ca levels in artificial growth media. In these experiments, the balance of Ca with the other essential elements such as Mg, Cu, Fe, B, and Mn was critical. Calcium was found to be sufficient with plant and leaf concentrations between 600 ppm to 1000 ppm. It is known that relatively little Ca is in a soluble form in many plants. Crystals of calcium oxalate have been observed in the leaves of most fruit trees as well as some field crops which are thought to have high Ca requirements. Therefore, the sufficiency of Ca in such plants may be related to the soluble fraction in the leaves rather than the total. Unfortunately at this time, all of the current literature related to Ca and its sufficiency concentration are based on total Ca contents of sampled plant parts. No doubt there is need to change the method of analysis for Ca to determine the soluble Ca content and relate this to sufficiency range standards.
Manganese deficiency normally occurs when the leaf tissue concentration is less than about 15 ppm. Depending upon the crop, ample but not excessive concentrations of Mn may range from 15 to over 1,000 ppm. Although there is limited data to delineate when toxicity occurs, leaf levels in excess of several hundred ppm are probably toxic to many plants. Plants which are sensitive to Mn deficiency are equally sensitive to excessive Mn. Growth of soybeans, which are particularly sensitive to Mn deficiency, is reduced when leaf Mn levels approach 200 ppm (Ohki, 1976). Several plant species have higher Mn critical levels. For example, the critical Mn level for alfalfa is about 25 ppm.
Some plants can tolerate extremely high Mn levels without detrimental effects. Pecan leaves may contain up to 1000 ppm Mn with seemingly no adverse effect. Similarly, cotton and peanuts will accumulate Mn up to 500 ppm without apparent toxicity. However, a high Mn level in plants is a sign of low soil pH, and is frequently associated with Mg deficiency. When the Mn concentration in peach leaves exceeds 150 ppm, this is generally a good indication that the soil pH is low according to George Cummings.
The Mn level in plants is usually quite high at the initial period of growth. It decreases rather rapidly and then levels off to remain fairly constant during most of the season. Since Mn is not a mobile element, deficiency symptoms will occur in the newer leaves or upper portion of the plant.
Iron analyses are probably invalid unless the leaf tissue has been washed in dilute acid or detergent solutions. Therefore, for unwashed leaves, iron analyses are of no real value. When soil contamination is suspected, usually Al is also high.
The Fe content in a plant can vary considerably. In general, when the Fe concentration in leaves is 50 ppm or less, deficiency is likely to occur. The grasses and corn have a lower Fe requirement, the critical level being 20 ppm. Iron toxicity has not been reported for any field crops growing under natural conditions in Georgia. The only Fe sensitive field crops would be pecans and soybeans, with possible deficiency occurring only on soils with pH's at 7.0 or above. Iron deficiency is common in Centipede grass and azaleas, particularly when grown in soils with pH's above 6.0
Iron deficiency is very difficult to correct in some crops. The application of some forms of Fe to the soil is not practical. Foliar applications of Fe have been found to be effective in correcting Fe deficiencies in plants such as turf grasses. However, on crops such as pecans, foliar applications for correction of low Fe levels have been erratic.
Since Fe is an immobile element in plants, Fe deficiencies appear in the new tissue or upper portion of the plant. Iron deficiency symptoms may appear early in the growth of the plant only to disappear in several days or weeks. The Fe level in the plant usually remains fairly constant during the growing season.
Boron requirements vary considerably among crops. The optimum range in leaf tissue of most crops is from 20 to 100 ppm. Some crops are particularly sensitive to B and can be injured when the leaf B level is too high. For example, B levels in excess of 50 ppm have been associated with B toxicity in peaches. The B critical level for corn is about 4 ppm, while alfalfa, cotton, peanut,and soybeans have critical levels of 20 ppm. Corn, having a fairly low B requirement, is also sensitive to excess B. Toxicities may occur when the B level in young corn leaf tissue exceeds 25 ppm. Members of the Papilionaceae and Cruciferae have fairly high B requirements with critical levels being about 25 to 30 ppm B in the leaf tissue. Those plants which have fairly high B requirements are also ones with fairly good tolerance to excessive B. Boron is not a very mobile element and deficiency symptoms occur in the newly emerging tissue. The B concentration in leaves remains constant during the growth cycle. Boron deficiencies result in various physiological diseases in plants, such as "hollow heart" in peanuts, a fairly common disorder occurring in Georgia peanut fields.
The normal range of Cu in many plants is fairly narrow, ranging from 5 to 20 ppm. When the Cu concentration in plants is less than 3 ppm in the dry matter, deficiencies are likely to occur. When Cu levels exceed 20 ppm in mature leaves, toxicities may occur. There is some variation in the critical values for various plant species; however, most critical values have been determined to be somewhere between 3 to 10 ppm for most crops. The Cu level in leaves tends to remain constant during the growing season.
Copper deficiency symptoms often depend on plant species or variety and the stage of deficiency. In the early stages of deficiency, symptoms are generally reduced growth. In the moderate to acute stages of deficiency on crops such as wheat, terminal or new leaves are pale green, lack turgor, and become rolled and yellowed; older leaves become limp and bent at the ligule. The leaves die, and dry to a bleached gray (Reuther and Labanauskas, 1966).
The normal range of Zn in most plants is between 20 to 100 ppm. Zinc deficiencies occur in a wide variety of plants when the leaf level drops below 15 ppm. The critical Zn value for apple is about 14 ppm with the first symptom of the deficiency being small fruit size. Zinc deficiency in pecans occurs when the Zn leaf level is 30 ppm or less.
In order to avoid Zn deficiency, Zn levels in most crops should be maintained at 20 ppm or better except for pecans when 50 ppm Zn is the desired minimum.
Zinc toxicity is an uncommon problem and does not generally occur until the Zn level exceeds 200 ppm. However, in crops such as peanuts, Zn toxicity has been reported in Georgia when tissue levels reach 220 ppm (Keisling and others, 1977). More recently (Parker and Walker, 1986) reported that Zn levels up to 287 ppm did not adversely affect peanut yields nor show any of the symptoms associated with Zn toxicity. However, the author has observed plants exhibiting Zn toxicity symptoms, described by Keisling and others (1977), with Zn concentrations of 117 ppm. Apparently, there are other plant growth factors or nutrient relationships in addition to just the Zn concentration that affect the manifestation of Zn toxicity. One such relationship appears to be the Ca:Zn ratio in the tissue. Upon evaluating unpublished data of Parker in which the Zn concentration in tissue varied from 50 to 302 ppm, and Zn concentrations could not be related to Zn toxicity, the author noted that when the Ca:Zn ratio was less than approximately 45 to 50:1 Zn toxicity symptoms were evident. However, when the ratio was greater than 45 to 50:1 even where the Zn concentration was 302 ppm, no toxicity symptoms were detected. Continued research in this area should elucidate the nature of this relationship. Excessive Zn also interferes with the normal function of Fe in plants giving rise to symptoms similar to Fe deficiency.
Zinc is not a very mobile element in plants and deficiency symptoms occur in the newly emerging leaves. Stunting is a frequent symptom associated with Zn deficiency. Normally leaves remain fairly constant in Zn concentration with a fairly rapid increase at the end of the growth cycle.
Aluminum is not considered a plant nutrient; therefore, it is not required by plants. However, its presence in plants can affect the normal function of some other elements. As with Fe, probably no accurate measure of the Al status of the plant can be obtained unless the tissue is free from dust and soil contamination. High Al in plants is usually an indication of poor soil aeration due to compaction or flooding. Aluminum levels in excess of 400 ppm in young tissue or 200 ppm in mature plants and leaves are undesirable.
Molybdenum deficiencies occur in many plants when the plant concentration is less than 0.10 ppm. Toxicity levels in plants have not been established. Molybdenum is quite toxic to animals if the forage being consumed contains more than 15 ppm Mo. The Mo requirement of legumes is higher than that of other plants since Mo is essential for the fixation of atmospheric N by the symbiotic bacteria. For the non-legumes, Mo is probably not needed if all the N requirement is supplied by the ammonium form. Molybdenum is essential for the conversion of nitrates to ammonium in the plant. In Georgia, Mo application has been found beneficial for alfalfa, particularly when the soil pH is low. The need for Mo on soybeans has also been confirmed in Georgia, particularly on the heavier Piedmont, Mountain and Limestone Valley soils which are low (approximately 5.5 or less) in pH. Significant responses to Mo application has not been consistent on Coastal Plain soils.
INTERPRETING A PLANT ANALYSIS RESULT
Difficulties have been encountered in the use and interpretation of plant analyses, although the quantitative association between absorbed nutrients and growth has been studied by many. Reliable interpretive data are lacking for a number of crops, particularly for plants during the initial stages of growth, and concentrations near or at toxicity levels. Initially, single concentration values were sought, but it became evident with continuing study that ranges in concentration would better describe the nutrient status of the plant. Prevot and Ollagnier (1956) and Smith (1962) have drawn a figure to represent the association between plant growth and nutrient concentration of a selected plant part (Fig 1). Although this response curve shows a fairly large slope change in the deficiency range, Ulrich (1961) has obtained response curves in which the slope change in the deficiency range is extremely small (see Fig 2).
Figure 1. Relation of Mineral Composition of Tissue to Growth. (According to Prevot and Ollagnier, 1956 and Smith, 1962).
The nature of Ulrich's observed curve indicates several areas for application of plant analysis technique. With extreme deficiencies, element concentrations may be greater than those found in plants free of the deficiency. The range in concentration between deficiency (with visual symptoms) and the critical concentration (no visual symptoms) can be small. For some elements and plants, the techniques needed to detect these small changes in concentration have yet to be adequately defined. One suggested solution is to determine total plant element content (uptake) and thereby eliminate or minimize the dilution effect. However, this technique has several limitations. It is not applicable when dry-matter differences are large. It requires careful sampling and plant sample preparation, as the dry-matter content must be determined for the entire plant.
Figure 2. Relation of Mineral Composition of Tissue to Growth. (According to Ulrich, 1961).
The same trend that was followed in soil testing is being pursued in plant analysis; that is, great efforts are being made to define the entire left hand side (deficiency range) of the response curve shown in Fig. 3. From a practical standpoint and in light of the current use of the plant analysis technique, the limits of the sufficiency range are in far greater need of exact determination. Most plant analysis recommendations are not made on the basis of degree of deficiency or excess. Considerable efforts have been made to define the deficiency area of the response curve where little by comparison has been done to define and pinpoint where toxicity occurs.
Some have based plant analysis interpretations on "critical" or "standard values." A critical value is that concentration below which deficiency occurs. Critical values have been widely published and used, although they have limited value since they only designate the lower end of the sufficiency range. Kenworthy (1961) developed an interpretative system for fruit trees based on "standard values." These values were determined from the analyses of large numbers of leaf samples collected from normal producing orchards. An interpretation is made by comparing an analysis to the standard value for that tree species. Standard values are single values and, therefore, have the same limitations as those for critical values.
Ranges in concentration have been published giving the limits of nutrient classification (for example, low, adequate, high, ...etc. Several references (Chapman, 1966, 1967; Neubert and others, 1969; Walsh and Beaton, 1973; and Reuter and Robinson, 1986) give the most comprehensive listing. Other references are:
1. Jones (1967) for corn, soybeans, and alfalfa.
2. Sedberry and others (1987) for several agronomic crops.
3. Ulrich (1961) for sugar beets.
4. Worley (1969) and Sparks (1978) for pecans.
5. Shear and Faust (1980) for deciduous tree fruits and nuts.
6. Criley and Carlson (1970) and Mastalerz (1977) for flower and ornamental plants.
The effects of time of sampling, variety or hybrid, and environmental factors, such as soil moisture, temperature, light quality and intensity may significantly affect the relationship between nutrient concentration and plant response. Consequently, a defined sufficiency range may not apply to all situations or environments. Nutrient uptake and internal mobility, as well as dry-matter changes, can affect the nutrient concentrations in plant tissues. Concentration and dilution occur due to the difference between plant growth and nutrient absorption as well as movement of the nutrients within and between plant parts. Under normal growing conditions, nutrient absorption and plant growth closely parallel each other during most of the vegetative growth period. Exceptions occur during the very early growth period shortly after germination, after seed set, and at the beginning of senescence. However, if the normal rate of growth is interrupted, nutrient accumulation or dilution can occur.
Jones and Mederski (1964) observed that nutrient concentrations in soybean plants oscillated considerably. Analyses to determine the nutrient concentration in leaves, stems, and pods, as well as dry-matter yield, were made every third day during the entire growth cycle. When the total plant uptake (concentration times dry matter) was plotted versus time, the curves were fairly smooth. Therefore, much of the oscillation in nutrient concentrations was essentially due to concentration or dilution associated primarily with changes in dry-matter production. Thus, it is essential that the time of sampling, stage of growth, and character of growth prior to sampling be known and considered when interpreting a plant analysis result.
It has been observed that plants within the same species will vary in their ability to absorb nutrients (Gorsline and others, 1965; Munson, 1969). Similar observations have been made for cotton Anderson and Harrison, (1970). At first glance, one may conclude that such differences complicate the plant analysis technique of relating nutrient concentration to plant growth sufficiently to invalidate its use. A similar opinion was probably expressed some years ago when it was discovered that the same soil test interpretation did not fit all soil types. Soil type is usually considered when making soil test interpretations. Accordingly, genotype may become a factor in the interpretation of a plant analysis.
Gorsline and others, (1965) noted that the ability of a corn plant to absorb a nutrient is an inherited characteristic and can be genetically transferred. The characteristic is one of imparting a high nutrient-accumulating ability. This characteristic should not affect the interpretation of a plant analysis. It has been noted that analyses of leaf tissue of different varieties or hybrids that were responding differently to the same environment did describe correctly the plant's appearance. However, much more research is needed to properly evaluate the effect of genotype on the interpretation of plant analyses.
Interactions, or the balance of the elements within the plant have been given considerable study Bingham, (1963); deWit, Dihkshoorn & Noggle, (1963); Emmert, (1961). Clark (1970) in an interesting work found that the nutrient concentrations of corn plants varied substantially as one nutrient was varied from deficiency to near excess. However, until recently, little had been done to apply balance concepts to a practical system for interpreting plant analyses. The importance of these interactions as they relate to yield has been revealed in work by Peck, Walker, and Boone (1969) and Walker, Peck and Carmer (1969). These techniques of evaluating plant analyses should add much to our knowledge of the association and interaction or nutrient concentrations on plant growth and yield.
An interpretation of a plant analysis at the Plant Analysis Laboratory is based on comparing the elemental concentration found against a sufficiency range. The concentration of each element analyzed is reported as less than, greater than, or within the sufficiency range. If soil test data and cultural practice information are supplied, an explanation for element concentrations outside the sufficiency range is given. Corrective treatments when required are also normally given.
The cause(s) for a nutrient concentration to fall outside the sufficiency range are many and varied. Low or high soil test levels, low or high soil water pH, improper fertilization, soil compaction, nematodes, and climatic factors are common causes. For most crops and cropping situations, the nutrient concentration found in leaf or plant tissue more closely follows the soil test level and/or soil pH than amount of fertilizer applied. The one major exception is nitrogen. The utilization of a balanced lime and fertilizer program over a period of years will do more to maintain the proper nutrient balance in plants than any one specific lime or fertilizer treatment. As a general rule, a soil testing MEDIUM to HIGH in the essential plant nutrients will produce plants with elemental concentrations which will normally test within the sufficiency range.
There are some common occurring soil-plant growth conditions. Soil test P and plant P, and soil test K and plant K are usually significantly and positively correlated, irrespective of other soil factors. Phosphorus uptake can also be affected by cool soil temperatures, water-logged soil conditions, and extremely low soil pH.
Soil test Ca and plant Ca are usually positively related, but soil pH, fertilizer treatments and climatic factors can have some affect on this relationship. As the soil pH increases, the correlation between soil test Ca and plant Ca decreases. Heavy applications of N and K fertilizer will tend to decrease the uptake of Ca.
Plant Mg can be affected by several factors. A decreasing soil pH and an increasing K soil test level can markedly reduce the uptake of Mg irrespective of the Mg soil test level. The uptake of Mg decreases sharply when the soil-water pH drops below 5.4. This is why a Mg deficiency can be partially corrected by just increasing the soil-water pH by liming. When the soil test level (in lbs./A) of K to Mg exceeds 4:1 or when the soil test level (in lbs./A) of Ca:Mg exceeds 8:1, Mg uptake by some plants may be depressed. This is of primary importance with forages where greater ratios could lead to increased incidence of grass tetany. Therefore, with some crops, extra precautions should be taken to ensure that the proper balance of Mg to both K and Ca is maintained. As with Ca, the correlation between soil test Mg and plant Mg decreases as the soil-water pH increases.
The effect of soil pH on the availability of most of the micronutrients is well known. In general, as the soil pH increases, the availability and, therefore, the uptake of Cu, Fe, Mn, and Zn decreases. Also, as the organic matter content of the soil increases, the soil pH effect is intensified. The primary exception is Mo where availability tends to increase with increasing soil pH.
Boron deficiencies are due primarily to lack of adequate B in the soil. The corrective treatment is to apply B fertilizer according to current recommendations. Excesses would only result from over fertilization with B.
Copper deficiencies occur primarily on high organic matter soils and possibly on sandy soils which contain low amounts of indigenous Cu and which have pH values approaching 7.0. Excessive Cu plant levels could occur where large quantities of some animal manures, particularly poultry litter, have been applied over a prolonged period.
Iron availability and uptake is a complex subject as many soil and plant factors can influence the Fe level in the plant. Deficiency may occur when the soil-water pH is near neutral and the soil is high in organic matter. Iron deficiency has been observed in centipede grass, azaleas, blueberries, and camellias as well as pecan trees, some sorghum and a few soybean varieties, and in pin oak trees. In pecans, high Zn in the trees is thought to be a contributing factor in inducing Fe deficiency. From soil and plant conditions, the only corrective treatment is to change varieties or try another tree.
Manganese availability is markedly influenced by soil-water pH, probably more so than any other micronutrient. Manganese toxicities can occur when the soil-water pH is less than 5.4 and deficiencies when the soil-water pH is greater than 6.3. For most Georgia soils, soil-water pH exerts the greatest influence on Mn availability to plants.
Molybdenum is an interesting element. Deficiencies are not easily detected by a plant analysis. The Mo requirement of legumes is high since the N fixing bacteria require higher levels of this element than the plant itself. The normal corrective treatment is a seed treatment with Mo. Also, the Mo related deficiency of poor N fixation is affected by soil-water pH. The response to Mo seed treatments for most legumes is most pronounced at low soil pH (5.2) and decreases as the soil-water pH increases. Therefore, maintenance of the proper soil pH will do much to eliminate the potential of a Mo deficiency.
Zinc availability is related to both soil-water pH and level of soil Zn. Zinc uptake normally decreases as the soil-water pH increases. However, soil test Zn is usually a good indicator of Zn availability. A Zn deficiency can be readily corrected by applying Zn according to current recommendations.
Aluminum is not an essential plant nutrient, but can be a factor affecting plant growth. High Al (if not due to soil or dust contamination) levels in the plant are the result of either a very low soil-water pH (pH's less than 4.8) or anaerobic soil conditions such as flooded or heavy compacted soils. Aluminum does not readily enter the plant, therefore its presence in the plant in high concentrations indicates an extreme soil condition.
It is evident that the interpretation of a plant analysis and a corrective recommendation based on such an analysis can become a complex task requiring considerable skill on the part of the interpreter and sufficient knowledge of the site conditions. One of the common errors made by those submitting plant tissue for analysis is to fail to supply the essential information needed to properly interpret the analysis and prescribe corrective treatments. A properly completed questionnaire (see Fig 1) is an essential part of the submitted plant tissue. Without it, proper evaluation of a plant analysis result is impossible.
PLANT ANALYSIS AS A DIAGNOSTIC TOOL
Plant analysis has been considered and primarily used as a diagnostic tool. Farmers and growers are urged to confirm suspected nutrient element deficiencies by a plant analysis before applying a corrective treatment. In order to effectively use a plant analysis in diagnosing growth disorders, employ specific sampling and evaluation techniques.
Sampling procedures were discussed in some detail earlier in this bulletin. (See section, PURPOSE AND USE). Collect plant samples from both affected as well as normal plants whenever possible. If plants have been under nutrient stress for a long period, a comparative analysis may be misleading, particularly when the stressed and nearby normal plants are at markedly different stages of growth. Therefore, sample the plants they are at the initial stages of a developing nutrient deficiency. This is essential when using a plant analysis in a diagnostic situation. Exercise great care to ensure that the proper sampling procedures are used. Plants selected for sampling and exhibiting symptoms of the suspected nutrient deficiency should be similar in appearance and all at a similar stage of development. Avoid dead or severely affected tissues and do not include in the sample. Confine the sampling area to plants in close proximity to each other. Use the same sampling procedures for those plants selected as the normal counterparts. Collect soil samples should be collected from both the affected and normal areas.
By comparing the analysis of both soil and plant tissue from the normal and affected areas, differences in test levels and concentration of particular elements can be evaluated. The comparison of analyses may be far more useful in the interpretation than using known interpretative values for this comparison and evaluation. Associations between a soil test value and the plant analysis value of similar or related elements should be examined. For example, differing soil pH's can result in changing levels of Mg and Mn in plant tissue. Variations in the soil test P and K levels are usually reflected in the P and K levels of the plant tissue. The presence or lack of such commonly occurring associations can be significant clues. With experience, you can become quite efficient in the evaluation of plant analyses when used for diagnostic purposes.
The most common error made when a plant analysis is used as a diagnostic tool relates to the failure to use sufficient care when collecting the plant tissue and soil samples. The effectiveness of a plant analysis to diagnose a particular nutrient problem is hampered by improper sampling and the failure to include both sets of tissues and the necessary soil samples. Therefore, follow the procedures prescribed with great care when collecting these samples. Failure to do so can significantly limit the effectiveness of the evaluation and may lead the interpreter into drawing incorrect conclusions.
DATA LOGGING USING PLANT ANALYSIS
Repeated plant analyses during the growth cycle of a plant or from one season to another can profile changes which are occurring with time as a result of applied fertilizer treatments. These analyses can provide a guide for corrective treatments. For long seasoned crops, analyses made at the critical periods can be effectively used to prescribe immediate corrective treatments. Supplemental treatments can be scheduled based on a series of analyses. For example, using a series of leaf analyses for greenhouse tomatoes, the need for supplemental fertilizer treatments can be determined in order to maintain a high level of productivity over a long growing season. For the pecan grower, yearly leaf analysis results should be plotted versus time to determine what effect lime and fertilizer treatments are having on leaf composition. Up-or-downward trends can be observed and adjustments in yearly lime and fertilizer treatments made before deficiencies or excesses develop which would reduce yield or quality.
Similar examples can be given for other crops or cropping sequences. Such analyses and the maintenance of leaf analysis result logs are invaluable to any farmer. Since most of the more common nutrient deficiencies experienced by many farmers are the result of long term effects of improper lime and fertilizer practices, developing deficiencies or excesses can be seen before they appear as visual symptoms, or reduce yield and quality.
Base supplemental applications of N on a plant analysis, particularly when there is a suspected or anticipated N deficiency. Analyze crops which are particularly sensitive to excess N such as cotton, forage grasses, fruits, and vegetables prior to the application of additional N. Keying N treatments to actual need can save the farmer unneeded fertilizer and reduce potential excesses.
Therefore, in order to obtain the maximum value from a plant analysis, establish a regular schedule of plant analyses and keep careful records to provide a usable history of test results.
INTERPRETATION AND RECOMMENDATION BY CROP
The following tables provide a guide for interpreting plant analyses and where feasible relate the plant analysis results to probable causes for elemental concentrations falling outside the sufficiency range. In the case of vegetable and ornamental crops common nutrient ranges found in normal appearing plants are presented. In some cases, these ranges may approximate the actual sufficiency ranges, but more information is needed to delineate these limits. However, when properly used, these ranges should be useful in giving the interpreter a clue as to whether or not a nutrient is substantially out of line with what is commonly found in normal appearing plants. Due to the wide variation in crops and in the methods for making corrective treatment, no attempt is made in this publication to cover all the corrective treatments for each crop. The list of crops is limited to those commonly grown in Georgia, and where there is sufficient plant analysis data and experience to justify such a compilation.
The sufficiency ranges and common nutrient ranges found in normal appearing plants are based on known literature as well as that obtained from summaries of plant analyses. The interpretation and recommendations given are primarily related to Georgia's soils and climatic conditions. They are not intended to cover all circumstances but present explanations which describe those that are most likely to occur.
The sufficiency ranges given are related to a particular crop, plant part, and time of sampling. Therefore, they are not applicable to other crops or sampling situations.
The interpretations given are not valid for crops infected with nematodes, insects, and diseases. Restricted root development due to compacted subsoils, plants damaged by chemicals or mechanically injured can exhibit typical nutrient deficiency symptoms. Tissues will frequently test below the sufficiency range for some elements due to such causes. No attempt is made in the following tables to cover these contingencies. In most cases only those causes which are related to soil, lime, and fertilizer effects are explained.
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