Determining Nitrogen Sufficiency in Corn

The End-of-Season Cornstalk Test

The end-of-season cornstalk test can be used to determine nitrogen deficiency, sufficiency, or excess in silage and grain corn, and in sweetcorn. The test is based on research in Iowa, Connecticut and Massachusetts. When N is in excess of the plants requirement, nitrate accumulates in the lower cornstalks and the extra N does not contribute to a greater yield. Rather, it can adversely affect crop growth, crop economics and the environment. When the plant is N deficient, nitrates are removed from the lower cornstalk during grain filling and an indicator of deficiency is the yellowing and drying of lower leaves. Similarly, an indicator of excess is lower leaves remaining dark green through to maturity. However, with dark green leaves to maturity you are uncertain as to how much excess N was supplied.

The cornstalk test can be used, to gain confidence in N management in the nutrient planning process. It can be used to check availability of N from manure and the effectiveness of pre-sidedress N test (PSNT) in predicting variations between fields. In certain years, cool wet spring years, the soil PSNT may indicate the need for N fertilizer when sufficient N may still be released from the manure and soil organic reserve. The cornstalk test can show you if fertilizer was needed and help you decide N application in future years.  Tom  Morris, a soil scientist at  UConn., believes the only way to make good use of the cornstalk test, is to keep field-by-field records of management practices to compare with test results.


Sampling Procedure

The test requires collection of corn stalks at end of season. For silage corn collect stalk samples one week before silage harvest to one day after harvest.  For grain corn collect stalk samples between one and three weeks after black layer formation on 80% of kernels.

Cut an 8 inch segment 6 inches above ground level from 15 plants for every 10 acre field. Since you may not chop corn at a stubble height of 14 inches for silage, an option is to momentarily raise the chopper in 3 to 5 typical areas of the field. Then collect 3 to 5 cornstalks from the 6 to 14 inch segment of the stubble from each area within 24 hours.

Place stalk samples in a paper bag (not plastic, as this promotes fungus growth) then dry or freeze.

Send samples to: UMass Soil Test Lab

       West Experiment Station

       University of Massachusetts

       Amherst, MA 01003

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Last updated: 11/11/02.