A MODEL FOR NITRITE ACCUMULATION IN SOILS

There have been recent reports of high nitrite concentrations occurrin g in both terrestrial and aquatic ecosystems. In the present study, mo delling procedures were applied to results from soil incubation studie s in order to quantify the relative contribution of nitrification and denitrification to nitrite accumulation. In order to quantify the simu ltaneous rates of nitrite formation from these processes, N-15 pool di lution calculations were employed. These rates were employed as rate-d etermining steps in an empirical model describing the kinetics of the how of N between ammonium, nitrite and nitrate compartments in order t o simulate nitrite accumulation. Employing nitrification as the sole p rocess generating nitrite results showed excellent agreement between o bserved and predicted nitrite accumulation. The rate of ammonium oxida tion was only required to be slightly in excess of nitrite oxidation i n order to generate nitrite accumulation. The available evidence sugge sts this imbalance in rates was due to nitrite oxidizers (Nitrobacter) being inhibited by free ammonia to a greater extent than ammonium oxi dizers (Nitrosomonas). (C) 1997 Elsevier Science Ltd.