The location and persistence of ammonia (aqueous, anhydrous and anhydrous + ‘N-serve’) injected into a sandy loam soil, as shown by changes in concentrations of ammonium and nitrate ions

Abstract

SUMMARYAqueous and anhydrous ammonia were injected into a sandy loam soil, using equipment fitted with commercial injector knives. Ammonium and nitrate concentrations around the injection slits were sampled at intervals in three experiments, from March to November, December to September, and June to December.The depth of placement and pattern of distribution of ammonium nitrogen resulting from the two designs of injector knife employed were measured.The rate of disappearance of ammonium nitrogen was followed, and the process described by a computer program which took account of soil temperature. The rate of decay of both aqueous and anhydrous ammonia could be described approximately by assuming a decay rate of 1% per day at 0 °C and Q10of 2·1. When 1·5% ‘N-serve’ was added to anhydrous ammonia the rate of decay was approximately halved.The distribution pattern of nitrate ions in the soil was less well defined than that of ammonium ions. When ‘N-serve’ had been added to anhydrous ammonia nitrate concentrations were much depressed for the whole duration of the experiment. The conversion of ammonium to nitrate nitrogen in this soil appeared to be inefficient. The nitrate concentrations found in the soil were consistent with a conversion rate of one-third and with the predictions made by a leaching model using the local meteorological data.The implications of the findings are discussed.