Nitrite-driven nitrous oxide production under aerobic soil conditions: kinetics and biochemical controls

Nitrite (NO(2)(-)) can accumulate during nitrification in soil following fertilizer application. While the role of NO(2)(-) as a substrate regulating nitrous oxide (N(2)O) production is recognized, kinetic data are not available that allow for estimating N(2)O production or soil-to-atmosphere fluxes as a function of NO(2)(-) levels under aerobic conditions. The current study investigated these kinetics as influenced by soil physical and biochemical factors in soils from cultivated and uncultivated fields in Minnesota, USA. A linear response of N(2)O production rate (P(N2O)) to NO(2)(-) was observed at concentrations below 60 mu gNg(-1) soil in both nonsterile and sterilized soils. Rate coefficients (K(p)) relating PN(2)O to NO(2)(-) varied over two orders of magnitude and were correlated with pH, total nitrogen, and soluble and total carbon (C). Total C explained 84% of the variance in Kp across all samples. Abiotic processes accounted for 31-75% of total N(2)O production. Biological reduction of NO(2)(-) was enhanced as oxygen (O(2)) levels were decreased from above ambient to 5%, consistent with nitrifier denitrification. In contrast, nitrate (NO(3)(-))-reduction, and the reduction of N(2)O itself, were only stimulated at O(2) levels below 5%. Greater temperature sensitivity was observed for biological compared with chemical N2O production. Steady-state model simulations predict that NO(2)(-) levels often found after fertilizer applications have the potential to generate substantial N(2)O fluxes even at ambient O(2). This potential derives in part from the production of N(2)O under conditions not favorable for N(2)O reduction, in contrast to N(2)O generated from NO(3)(-) reduction. These results have implications with regard to improved management to minimize agricultural N(2)O emissions and improved emissions assessments.