Corn is one of Maryland's most important crops, with over 5,000,000 acres being planted annually. To help producers accurately assess their corn crop nutrient requirements, Maryland Cooperative Extension nutrient management advisors can provide a pre-sidedress nitrogen test (PSNT).

PSNT is a widely used test for optimizing N fertilizer use. The test is based upon the timely measurement of mineralized soil nitrate in the top foot of soil just before the corn crop starts its rapid period of N uptake. PSNT can predict the amount of N released from previous legumes, manure applications, soil organic matter and residual nitrate. It can therefore be used to confirm the amount of N credited from these sources.

PSNT is best used as an integral part of a farm nutrient management plan. It is particularly useful on fields that, in the past, have received organic sources of N such as manure or biosolids. This is even true if such applications have not been undertaken for several years. The PSNT is not recommended on fields where commercial fertilizer is the only source of N for corn production. PSNT is only a reliable tool when the total N fertilizer application prior to sidedress, including preplant and starter band N, is less than 50lb/acre.

PSNT is conducted when the corn is between 6-12 inches tall. The soil sample core is collected from the top 12 inches of the soil. To obtain an accurate measure, 30-40 soil cores should be taken from each field or area with similar management histories. MCE advisors can conduct sampling and soil nitrate testing at the appropriate time. The Agricultural Nutrient Management Program has developed a procedure which uses cheap, commercially available meters to provide accurate test results, so therefore the PSNT can be performed at your local Extension office.

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

Soil Fertility Management (SFM-2) - "Making Decisions for Nitrogen Fertilization Using the PSNT"