Effect of the nitrification inhibitor nitrapyrin on the fate of nitrogen applied to a soil incubated under laboratory conditions

The aim of this study was to examine the effect of the nitrification inhibitor nitrapyrin on the fate and recovery of fertilizer nitrogen (N) and on N mineralization from soil organic sources. Intact soil cores were collected from a grassland field. Diammonium phosphate (DAP) and urea were applied as N sources. Cores were equilibrated at -5 kPa matric potential and incubated at 20 °C for 42 to 56 days. Changes in NH4+-N, accumulation of NO3--N, apparent recovery of applied N, and emission of N2O (acetylene was used to block N2O reductase) were examined during the study. A significant increase in NH4+-N released through mineralization was recorded when nitrapyrin was added to the control soil without N fertilizer application. In the soils to which N was added either as urea or DAP, 50-90 % of the applied N disappeared from the NH4+-N pool. Some of this N (8-16 %) accumulated as NO3--N, while a small proportion of N (1 %) escaped as N2O. Addition of nitrapyrin resulted in a decrease and delay of NH4+-N disappearance, accumulation of much lower soil NO3--N contents, a substantial reduction in N2O emissions, and a 30-40 % increase in the apparent recovery of added N. The study indicates that N recovery can be increased by using the nitrification inhibitor nitrapyrin in grassland soils at moisture condition close to field capacity.