Stimulation of microbial activity following spring applications of nitrogen

Soil microbial biomass (SMB) activity was investigated in a long-term experiment in which grazed swards received annual inputs of 200 N kg ha^–1. SMB total C and total N, specific respiration, ammonification and nitrification were examined over a 10 week period, following the first and the second seasonal applications of N. Whilst there was no effect on biomass C and N, additions of N appeared to increase biomass activity. Nitrification was weakly correlated with ammonification (r ²=0.413) and the latter was stimulated by the addition of N (P<0.05), suggesting a ‘priming’ effect. Received: 28 February 1997