The Pre-Sidedress Soil Nitrate Test (PSNT) is a management tool for corn that agronomists use more and more each year. In Iowa, you may hear this test called the Late-Spring Soil Nitrate Test (LSNT). PSNT is a soil nitrate test used when corn is about V6 growth stage (~12 inch at whorl) to determine if additional sidedress N fertilizer is needed.
Since PSNT is being used more frequently in our region, we have added the crop choice called “Corn Sidedress N” in our AGVISOR program. You can submit PSNT soil samples online by choosing the “Corn Sidedress N” crop choice and submitting 0-12 inch soil samples for nitrate analysis (see link for online submission directions). The program will generate sidedress N fertilizer guidelines based on research from Iowa State University, using the PSNT critical level of 25 ppm nitrate-N (0-12 inch depth). Across several Midwest states, university research has confirmed the PSNT critical level between 22-25 ppm. You can also submit PSNT samples on paper submission forms by writing the crop choice as “Corn Sidedress N” and sample depth as 0-12″.
The Iowa State University publication link below has additional information on PSNT (2017). This publication explains how you can use PSNT results to guide sidedress N application and rates under different field situations (e.g., recent rainfall, manure application). Please call our technical support staff if you have any questions on PSNT and interpreting the test results for sidedress N application.