Volatilization Losses of Nitrogen from Surface‐Applied Fertilizers, as Measured by Crop Response

Abstract

Abstract Yields and uptake of N by corn forage grown in pot experiments with N fertilizers mixed with and surface‐applied to moist soils a week prior to planting were determined. Losses of N were low with mixed placement. High losses of N, presumably as NH 3 , occurred from granular urea surface‐applied to Hartsells fine sandy loam limed to pH 6.2 and 7.5 and to Webster silty clay loam (pH 8.2). Losses were reduced by coating urea with S or by including phosphate in the granules as urea ammonium phosphate. Severe losses of N also occurred with surfaceapplied ammonium sulfate and diammonium phosphate, especially from the naturally calcareous Webster soil. Maximum recoveries from soils of pH 6.2 to 8.2 were obtained from monoammonium phosphate, ammonium nitrate, ammonium phosphate nitrate, and ammonium polyphosphate. Differences in losses of N as NH 3 among N fertilizers can be explained largely in terms of urea hydrolysis or the reaction of certain acid radicals of ammonium salts with calcium compounds in soil.