Proceedings 2006

Indiana Certified Crop Adviser Conference

Efficacy of N Use from Fall Applied Ammoniated Phosphates and Ammonium Sulfate

R.G. Hoeft, G.W. Randall, J. Vetsch, E.D. Nafziger, F. Fernandez, and K. Smith.

Fall application of ammoniated phosphate fertilizer along with potash is a common practice in much of the Corn Belt. Often times, these applications are made while soil temperatures are warm, greater than 60F, a temperature warm enough to result in rapid nitrification. Nitrate resulting from that process would be susceptible to loss if soils are excessively wet in the following spring. To evaluate the efficacy of N from fall applied diammonium phosphate (DAP), monoammonium phosphate (MAP), and ammonium sulfate (AMS), relative to spring application of the same products, field experiments were established at Waseca, MN and Urbana and Brownstown, IL. At each location, DAP, MAP, and AMS were applied at 3 N rates, 0, 40, and 80 lb N/acre and at 2 times of application- fall and spring. As expected, fall applied ammonium N, irrespective of source, nitrified rapidly in the early spring resulting in less N present as ammonium in early May as compared to the spring applied materials. Source of N had little impact on grain yield. The impact of fall versus spring N on grain yield ranged from none to as much as 20 bushel less for fall N depending on site year. This differential response between sites was attributed to differences in N loss between years.

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Bob Hoeft