Crop Recovery and Nitrification of Fall and Spring Applied Anhydrous Ammonia¹

To evaluate the relative agronomic efficiency of and potential NO 3 , pollution by fall and spring applied anhydrous NH 3 , N uptake and yield response by corn, and detailed sampling of the NH 3 , bands were conducted. Nitrogen significantly increased grain yield and N uptake by corn ( Zea mays L.) on a Plano sil (0.216% N) and a Pella loam (0.447% N) in south central Wisconsin. There were no differences between fall and spring application of N. Crop recovery of applied N depended on soil type and rate of application, and at most amounted to 40% of the N applied. Depending on rate of application, from 68 to 86% of the fall‐applied NH 3 , was nitrified before mid‐May. Nitrite accumulated within both fall and spring applied bands, the highest concentrations being detected in early spring within fall applied bands. Persistence of NO 2 was more prolonged on a neutral than on a slightly acid soil. Accumulation of NO 2 must be considered undesirable because of possible phytotoxicity and losses through biological or chemical denitrification, and fall application appears to offer a great potential for these processes to occur.