Mineralisation of nitrogen and metabolism of ammonium sulphate in some soils of Niue Island

Abstract

Asbtract Mineralisation of nitrogen and nitrification have been studied in the laboratory with a relatively deep soil, Fonuakula silty clay loam, and an alkaline calcareous shallow soil. Fonuakula silty clay loam, shallow phase, from Niue, a tropical Pacific Island. Nitrate and mineral nitrogen were generally present in greater amounts in samples of the deep than cf the shallow soil, but their rates of increase on incubation did not differ consistently between the soils. Increases in nitrate on incubation were significantly correlated with amounts of ammonium-nitrogen present initially in the soils. There were no consistent differences between the amounts of nitrogen mineralised by samples taken from the same depth of soil under Pangola grass or the legume Crotalaria anagryoides. An appreciable accumulation of nitrite occurred on incubating the shallow soil, but not the deep soil, with added ammonium sulphate. Losses of ammonia through volatilisation were negligible in the deep soil but could be very considerable in the shallow soil on incubation with added ammonium sulphate under conditions where nitrification was partially inhibited. Some of the agronomic aspects of these results are briefly discllssed.