University of Maryland Extension

Pre-Sidedress Soil Nitrate Test (PSNT)

The Pre-sidedress Soil Nitrate Test (PSNT) is a widely used test for optimizing nitrogen fertilizer use for corn grain and corn silage. It is a soil test that measures the amount of nitrate nitrogen available in the soil at the time when the crop is most likely to start using it. This nitrogen is a by-product of the mineralization of manure and/or last year's forage legume crop, and its availability is influenced by soil temperature and moisture.

The PSNT should be run when corn is between 6 and 12 inches tall. This is the time period when corn is getting ready for a rapid growth spurt and will require nitrogen to fuel this growth. If the PSNT shows enough nitrogen is present in the soil, it may be beneficial to forego the application, thus saving time and money. If the test shows nitrogen is low, it may be beneficial to consider sidedressing additional nitrogen to avoid any potential compromise in yield.

PSNT is applicable on fields where:

  • Corn for silage or grain is being grown
  • Manure or biosolids have been applied this year or in the past two (2) years
  • A forage legume was grown last year
  • Less than 50 pounds of commercial fertilizer nitrogen per acre were applied prior to sidedress

PSNT is not applicable on fields where:

  • More than 50 pounds of commercial fertilizer nitrogen per acre have been applied prior to sidedress
  • Commercial fertilizer has historically been the only nutrient source
  • Irrigation is used

Want more information on the PSNT? Download the following free publication:

SFM-2 "Making Decisions for Nitrogen Fertilization Using the PSNT" (revised April 2010).


For details on how to take soil samples for the PSNT, please visit the Soil Sampling for the PSNT web page.

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