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

Abstract

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 () to NO 2− was observed at concentrations below 60 μg N g−1 soil in both nonsterile and sterilized soils. Rate coefficients (Kp) relating 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 N 2 O 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.