RATE OF ACCUMULATION AND EMISSION OF N-2, N2O AND CH4 FROM A FLOODED RICE SOIL

In a field experiment using microplots, a flooded Crowley silt loam (Typic Albaqualfs) rice soil was fertilized with N-15 labelled (60-74 atom %) urea and KNO3. Emission of N2, N2O and CH4 and accumulation in soil were measured for 21 d after fertilizer application. Emission of N-15(2)-N measured from the urea and KNO3 treated plots ranged from < 15 to 570 and from 330 to 3,420 g ha-1 d-1, respectively. Entrapped N-15(2)-N in the urea treated microplots was significantly lower (< 15 g to 2.1 kg ha-1) on all sampling dates compared to the N-15(2)-N gas accumulation in the KNO3 treated plots (6.4 to 31.5 kg ha-1). Emissions of N2O-N were low and did not exceed 4g ha-1 d-1. Fluxes of CH4 from the fertilizer and control plots were low and never exceeded 33 g ha-1 d-1. Maximum accumulation of CH4 in the flooded soil measured 460 and 195 g ha-1 for the urea and KNO3 treatments, respectively.