MASS SPECTROMETRIC INVESTIGATION ON DENITRIFICATION

Abstract

A quantitative mass spectrometric technique utilizing Ar of air as an internal standard was applied to investigate the denitrification process under air atmosphere in closed containers. The disappearance of O2 and nitrate and the production of CO2, N2O and N2 were investigated as a function of added NO3− concentrations, liming and flooding using a near neutral soil. The added NO3− acted as the electron acceptor whenever oxygen supply was depleted. The first product to appear was nitrite, and gaseous N2O and N2 followed. The microbial activity of unit weight of the soil as measured by CO2 production was not affected by the addition of varying concentrations of NO3−. Consequently, the initial rate of NO3− disappearnace which is probably proportional to microbial activity was independent of NO3− concentration. The accumulation of N2O gas as intermediate was dependent upon the NO3− concentration. Higher concentration of NO3− favored the accumulation of N2O, thus reducing the formation of N2 primarily because of the competitive nature of NO3− and N2O as electron acceptor under constant microbial activity. Thus, the initial rate of N2 formation was faster with lower NO3− concentration. Also the appearance of N2 due to reduction of N2O took place earlier when NO3− concentration was lower. Liming reduced the accumulation of N2O thus producing N2 early. However, flooding induced the accumulation of N2O. Increasing the microbial activity and lowering the NO3− concentration would decrease the N2O accumulation.