Transformation of ammonium and nitrate fertilisers in two soils of low and high nitrification activity

摘要

Abstract Transformations of (NH4)2SO4 and Ca(NO3)2 applied to a soiI of low (Wharekohe silt loam) and a soil of high (Waimate North clay loam) nitrification activity were studied using both unlabelled and 15N-labelled fertilisers. The problems associated with both techniques are briefly discussed. Total recovery of applied N in soil and plant estimated from 15N recovery, was similar for both forms offertiliser 84 days after application (about 65%) to Waimate North clay loam, but was superior for (NH4)2SO4 (70%) relative to Ca(NO3)2 (33%) on Wharekohe silt loam. Isotopic dilution occurred in the A horizon, decreasing the 15Nenrichment in the mineral N pool and leading to an underestimation of the effect of fertiliser N on N uptake by pasture.