Effect of cellulose and straw incorporation in soil on total denitrification and nitrogen immobilization at initially aerobic and permanent anaerobic conditions

Laboratory experiments were used to examine the influence of cellulose and straw on denitrification and N immobilization in a sandy loam soil. The soil was mixed with 300 μg nitrate-N/g and incubated in a special vessel under conditions that changed from aerobic to anaerobic or in the permanent absence of O2. Gases (O2, CO2, N2, N2O, NO and CH4) were analysed by gas chromatography at regular intervals and the soil was examined for nitrate, nitrite, ammonium and cellulose. Compared with controls, the application of straw and cellulose (0.5% and 1.0%, respectively) enhanced nitrate immobilization and decreased denitrification, under both anaerobic and originally aerobic (PO2 = 20 vol%) conditions. However, a comparison of results from the aerobic and the anaerobic incubations shows that an increase in denitrification and N immobilization was apparent at an original O2 concentration of 20 vol%. N2 was the major product of denitrification in all experiments. Free methane was apparent as soon as nitrate was respired. The stimulating effect of O2 on total denitrification in the presence of relatively high amounts of easily decomposable cellulose is ascribed to a higher turnover and an intensified mineralization rate (CO2 production), which increased the total demand for electron acceptors.