PRODUCTION OF NITRITE IN SOIL BY SIMULTANEOUS NITRIFICATION AND DENITRIFICATION

Recent studies have shown relatively high nitrite concentrations occur ring in soil. The contribution to nitrite accumulation of the two majo r source processes, nitrification and denitrification, was studied by differential N-15-labelling of nitrate and ammonium pools in soils inc ubated at a range of moisture contents. Nitrite concentrations and app arent sources varied greatly over 10 days. At the beginning and at the end of the incubations, when concentrations were low, denitrification appeared to be the major source process; nitrification appeared to be responsible for the bulk of the much larger concentrations accumulate d at intermediate periods, during which an observed rise in pH suggest ed that high free ammonia concentrations might have inhibited nitrite- oxidising bacteria. Throughout most of the incubation nitrification an d denitrification appeared to be producing nitrite simultaneously. The effect of moisture content was not clear, though there were some indi cations that nitrate reduction was favoured in wetter soil. A full int erpretation of the complex interactions at work requires modelling. Co pyright (C) 1996 Elsevier Science Ltd