The effect of increasing nitrogen fertiliser on emission of nitrous oxide when growing sorghum on Vertosols

Abstract

Key findings • Sorghum grain yield increased with nitrogen (N) fertiliser rate up to 120 kg N/ha at two trials on N-deficient Vertosols (cracking clay soils). Higher N rates only increased grain protein not yield. • Intense rainfall on the heavy clay soil type at the Quirindi site led to prolonged waterlogging and denitrification (N loss from the soil as N gases, including nitrous oxide (N2O)). The loss of N led to reduced grain yield and protein. • At both sites more N2O was emitted from the soil as N fertiliser rate increased. At the Tamworth site, 0.79% of the N applied as fertiliser was emitted as N2O. At the Quirindi site, the proportion of N emitted as N2O also increased with N rate, from 1.43% up to 3.3% at the highest N rate. • N supply for sorghum (soil N + fertiliser N) should be matched to potential grain yield to minimise N2O production.