Soil Nitrate Testing as a Guide to Nitrogen Management for Vegetable Crops Joseph R. Heckman, Ph.D., Extension Specialist in Soil Fertility Bulletin

In-season soil nitrate testing is a diagnostic tool thatcan aid in predicting the sufficiency of the soilN (nitrogen) supply for a variety of annual crops. The testing procedure is often referred to as the presidedress soil nitrate test (PSNT). The PSNT was originally devel-oped for use with field corn to predict need for sidedressing N. Its usefulness, however, has since moved beyond corn to an increasing number of vegetables. Approaches to using the PSNT or soil nitrate testing in general depend on the crop and soil system. This fact sheet will describe cropping systems where soil nitrate testing is most useful. Matching supply of N from soil with plant demand for this nutrient is one of the nutrient management challenges of crop production. Striking a balance between having too little or too much N available from soil is important to yield, crop quality, farm profitability, and the environment. Nitrogen availability from soil can change rapidly, and soil testing for nitrate should be viewed as a snapshot in time of the soil’s current N status which is reflective of the ability of the soil to supply available N to the crop. Crop demand for N uptake also changes during the course of the growing season. Thus, time of soil sampling is critical to the correct use and interpretation of soil nitrate test data. Appropriate use of soil nitrate testing should, therefore, be guided both by an understanding of the dynamic behavior of nitrate in soil and crop demand for nitrate uptake