Andrew Stammer, Lab Director UW Soil and Forage Analysis Lab
The growing season is in full swing and the UW Soil and forage lab is receiving questions about how to use plant tissue analysis for in season nutrient management. Plant tissue analysis is a way of measuring macro and micronutrients in plant tissue. It is a direct measure of plant nutritional status during the growing season. When sampling plant tissue, a clear understanding of the plant part and growth stage to be sampled is essential. Nutrient concentrations vary between plant parts. Additionally, processes such as dry matter accumulation and movement of nutrients from one part of the plant to another influence nutrient concentrations across the growing season. These fluctuations require that sample results be compared to recommended nutrient sufficiency ranges for the same plant part and growth stage or to tissue results from healthy looking plants in the same field.
Nutrient concentration in the plant are influenced by a variety of factors. Soil conditions such as pH, soil temperature, compaction and moisture influence plant nutrient concentrations occasionally leading to situations where tissue nutrient concentrations are depressed when the soil has adequate nutrient levels. Conversely, plant tissue can show abnormally high results when testing leaves recently sprayed with a foliar fertilizer, while excessively high concentrations of iron are usually the result of a small amount of soil contaminating the plant sample. Different varieties or maturities of crops may have different optimal tissue nutrient concentration ranges. Because of these possible interferences, collecting separate tissue samples from good and bad areas within a field can be a helpful comparative diagnostic.
The interpretation ranges available for plant tissue can be used as rough guidelines, but do not provide enough information to advise fertilizing on their own. Collecting soil samples from the same areas that plants are sampled allows an evaluation of both the crop and the soil. These samples may explain plant tissue levels and may be used to guide fertilizer application next season.
For additional information on plant parts and growth stages to sample and interpretation data see: https://ipcm.webhosting.cals.wisc.edu/blog/2016/06/plant-analysis-are-you-using-it-and-interpreting-the-results-correctly/
For more information on tissue testing and lab Submission Sheets visit: https://uwlab.soils.wisc.edu/plant-tissue/