This week we’ve been exploring how the nitrogen cycle and rainfall timing affect fall N availability. Keeping this in mind, consider these real-world scenarios on the likelihood of nitrogen loss from fall-applied fertilizer.
Anhydrous ammonia is applied with a nitrification inhibitor like N-Serve that delays the conversion of ammonium to nitrate in early November when soils are below 50℉. Soil temperatures don’t get above 50℉ until the following April. Nitrogen loss is likely to be low in this scenario. Very little ammonia is likely to have converted to the vulnerable nitrate form before soil freeze-up. This represents the lowest-risk scenario you can have with fall application of nitrogen. A 15-year study conducted in south-central Minnesota on the timing of nitrogen application found that late October application of anhydrous ammonia with N-Serve out-yielded late October application of anhydrous ammonia without an inhibitor by 9 bushels/acre. However, over this same 15-year period, spring application of anhydrous ammonia without N-Serve out-yielded the late fall application with an inhibitor by 3 bushels/acre.
Anhydrous ammonia is applied with a nitrification inhibitor in mid October. Soils remain above 50℉ for the next two weeks, and then stay below 50℉ until the following April. Nitrogen loss is likely to be moderate in this scenario. This is a situation where the use of a nitrification inhibitor is very likely to produce higher yields than if an inhibitor was not used.
For questions about this post contact:
Greg Klinger, UMN Extension Regional Office Rochester, MN
Anne Struffert, UMN Extension Regional Office St. Cloud, MN