In-season plant tissue testing can be useful in diagnosing nutrient deficiencies in field crops, but it must be used with caution, write Antonio Mallarino and John Sawyer, Professors, Department of Agronomy, Iowa State University. Extra care is needed this year given the unusual crop planting and growing conditions.
Iowa State University (ISU) Extension and Outreach has research-based interpretations for in-season tissue testing only for phosphorus (P) and potassium (K) in corn and soybean, and for sulfur (S) in alfalfa. Interpretations and guidelines for using the end-of-season cornstalk nitrate test are in ISU Extension and Outreach publication CROP 3154. There are no interpretations for other nutrients or crops due to lack of research, infrequent deficiency that precludes meaningful test calibration, or research results show tissue testing is an unreliable diagnostic tool.
As is the case for soil testing, use of tissue testing as a reliable diagnostic tool requires field research to correlate nutrient concentrations with crop yield response. Establishing reliable tissue test interpretations is even more difficult than for soil testing, however, because tissue nutrient concentrations vary greatly with the crop growth stage and the plant part sampled, and may also vary across hybrids or varieties and growing conditions. For example, effects of drought or plant diseases on plant growth and nutrient uptake often result in tissue nutrient concentration (increase) or dilution (decrease) in tested plant material.
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