Nitrogen Availability For 2009

Editor’s note: This article is from the archives of the MSU Crop Advisory Team Alerts. Check the label of any pesticide referenced to ensure your use is included.

Soil nitrogen test results so far this year have indicated that less available N is present in the soil than expected, especially in fields where manure has been applied. This may be partially the result of the heavy rains and the cool soil temperatures. Available N may have been lost due to water leaching down through the soil and by denitrification (conversion of nitrate to nitrous oxide) when the soils were saturated. Denitrification has probably been the more important one. As soils dry and warm up, N bound in the organic forms of manure, crop residues and soil will be released as microorganisms decompose these materials. This has occurred more slowly this year than in other years. The question is how much additional N will be released? This is difficult to predict. Where manure has been applied or legume cover crops have been incorporated, additional N release through the growing season will likely range from 30 to 70 lbs N/a, depending on the amount of manure (amount of organic N in the manure) applied or amount of biomass incorporated. Normally about 50 percent of the organic N in manure is expected to mineralize the first year. The sidedress N rate can be adjusted according to how much additional N is anticipated to become available.

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