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Soil testing for corn nitrogen recommendations

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Quick facts

Over-applying nitrogen (N) to corn causes concern due to the environmental consequences of unused N. There’s also a significant economic advantage to applying the correct rate of N fertilizer.

Excess, unused N can be lost from the soil system via denitrification and/or leaching, get tied up in the soil organic N pool or stay in the crop’s rooting zone as residual N.

Research indicates that measuring residual, available N through a soil test can refine earlier N recommendations for corn. This soil N test involves collecting 0- to 2-foot soil samples in the spring before planting and analyzing samples for nitrate-N. The quantity of nitrate-N found is then used to calculate a residual N credit.

Soil N test research

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Using the soil N test

This soil N testing option, which accounts for residual N, isn’t appropriate for all fields and conditions.

Use Figure 4 to help decide which fields you may need to test for residual nitrate-N. This flowchart uses factors such as previous crop, manure history and a knowledge of previous rainfall.

crops flow chart
Figure 4: Flowchart decision-aid for determining the probability of having significant residual N in the soil.

 

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Other procedures for N recommendations

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Reviewed in 2018

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