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*This content was previously published by Corteva Agriscience. Farmers who apply nitrogen fertilizer in the fall understand that nitrification—the process that contributes to nitrogen loss—is chemically halted when the weather gets cold and then begins again as temperatures rise. However, gaining a deeper knowledge of what happens to fall-applied nitrogen over the winter and into spring can help them be better prepared to make the best nitrogen management recommendations year-round. Here are a few things to know about fall-applied nitrogen as it hibernates over the winter: |
50° F is the temperature benchmark |
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• The nitrification process is set in motion by a bacteria called Nitrosomonas that causes the conversion of nitrogen to a nitrate form that can be easily lost. Nitrosomonas bacteria is very active when it is warm, but decreases activity significantly at 50° F and nearly halts under 40° F. • For fall nitrogen application, temperatures can be anywhere above, at or below this Nitrosomonas activity threshold, but ideally application should be made at 50° F or colder to minimize the amount of potential nitrogen lost. |
Beware of the transitional weather danger zone |
• Fall-applied nitrogen must endure two transitional weather periods—spring and fall—when nitrogen is particularly vulnerable to loss.
• Spring can be unstable and unpredictable, often with large shifts in temperatures and rain amounts.
• Fall can be equally unpredictable. Unexpected heavy rain, extended periods of warm weather and delayed harvest can impact when (and if) fall nitrogen can be applied, and can especially affect how vulnerable it is to loss before crops are ready to use it.
Moisture + warmth = more loss potential
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