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Nutrient Deficiencies - Wheat

DIAGNOSTIC TECHNIQUES FOR CORN AND SMALL GRAIN

C. Owen Plank and Dewey Lee1

For proper growth, development, and production plants require a continuous, well-adjusted supply of eighteen essential nutrients. If any of these nutrients are in limited supply, crop performance decreases and ultimately results in nutritional disorders. When the supply of mineral nutrients is slightly low the shortage is often exhibited as slow growth, reduced crop yields and/or poor quality of the crop. If the supply of nutrients is more acute the shortage is manifested on the leaves as nutrient deficiency symptoms. For some nutrients, considerable yield and crop quality losses may have already occurred by the time deficiency symptoms are evident or it may be too late in the season to apply corrective treatments.  If the nutrient disorders are diagnosed early enough in the growing season, corrective treatments may be either soil applied, applied through the irrigation system or by foliar sprays thus minimizing the affect of the nutrient deficiency.

Nutrient deficiency symptoms on leaves are varied and may include: pale green color, yellowing of leaves, darker than normal green color, purpling of leaves, reddening of leaves, interveinal chlorosis, leaf necrosis, marginal leaf scorch, or curling and twisting of leaves. As a result growers are urged to confirm suspected nutrient deficiencies by a plant analysis before applying a corrective treatment. Numerous cases can be given where incorrect diagnosis in the field has led to crop failures, as well as costly and ineffective corrective treatments. While visual observations along with soil test information may give some clues as to the problem at hand, such observations can sometimes be misleading. This is due to the fact that the visual symptoms on the leaves are somewhat similar for several nutrients. For example, it is easy to misdiagnose nitrogen, sulfur, zinc, and manganese deficiencies of corn and wheat at different growth stages.

Plant analysis, when properly used, has proved to be a very effective tool in diagnosing nutritional disorders and in monitoring the nutrient level of corn and small grain during the growing season.  In order to effectively use a plant analysis in diagnosing growth disorders, one must employ specific sampling and evaluation techniques. Failure to do so can significantly limit the effectiveness of the evaluation and may lead the interpreter into drawing incorrect conclusions. Sampling instructions, sample submission form, and mailing instructions are available on this web site as well as at the UGA Soil, Plant, and Water Analysis Laboratory.

Collect plant samples from both abnormal as well as normal plants. 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 when 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. Once the plant sample has been collected allow it to air dry for one or two days. Then place it into a 10 x 13 or 9 x 12 manila envelope. (Caution: never place a moist sample in the manila envelope nor place a moist sample in a plastic bag for mailing. Doing so will result in damage to the mailing envelope and some sample decompostion respectively. Both can result in invalid results). Complete the information requested on the sample submission form and place it into a 41/8 x 91/2 envelope. Add the mailing address and securely attach it to the manila envelope using scotch tape or other suitable adhesive.

Collect soil samples from both the affected and normal areas for chemical and nematode analyses. Soil test results indicate the relative availability of nutrients in the soil for plant use, and plant analysis provides information on how the plant responded to the nutrient supply and growing conditions. Nematode analyses are essential in diagnostic work because nematode affected plants manifest nutrient deficiency symptoms in a similar manner to a nutrient deficiency in the soil. When nematode tests are positive plant analysis results are invalid.

Comprehensive interpretative guidelines or sufficiency ranges have not been established for all crops at each growth stage. Therefore, in diagnostic work it is sometimes necessary to compare results for normal versus abnormal samples. 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 may occur. The comparison of analyses can be quite useful in assessing the problem in the absence of known interpretative values. However, when known sufficiency range values are available use them to establish that the nutrient concentrations in the normal plants are adequate.

There are several management, soil, and environmental factors that can cause the nutrient concentration in plants to be deficient, or excessive. Therefore, examine associations between a soil test value and the plant analysis value of similar or related elements. 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. Also, information on fertilizer practices, climatic conditions, pest problems, etc. will be of considerable value to in assessing the problem and prescribing corrective treatment. With experience, one can become quite efficient in the evaluation of plant analyses for diagnostic purposes.

The following links provide information relative to sufficiency ranges for interpreting plant analysis results and suggestions for corrective treatments.

1Assoc. Prof. - Retired and Prof., Crop and Soil Science Department, The University of Georgia, Athens and Tifton, GA, respectively

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