Nitric and nitrous oxide emissions following fertilizer application to agricultural soil: Biotic and abiotic mechanisms and kinetics

Emissions of nitric and nitrous oxide (NO and N 2 O) from agricultural soils may have several consequences, including impacts on local tropospheric and global stratospheric chemistry. Elevated NO and N 2 O emissions following application of anhydrous ammonia to an agricultural field in California were driven by the biological generation of nitrite (NO 2 − ) and subsequent abiotic decomposition of nitrous acid (HNO 2 ). Maximum fluxes of > 1000 ng NO‐N cm −2 h −1 and > 400 ng N 2 O‐N cm −2 h −1 were observed, and emissions of > 100 ng NO‐N cm −2 h −1 and > 50 ng N 2 O‐N cm −2 h −1 persisted for >4 weeks. Laboratory experiments were performed to determine rate coefficients and activation energies for HNO 2 ‐mediated NO and N 2 O production. Kinetic parameters describing the conversion of NO to N 2 O were measured and were found to vary with water‐filled pore space (WFPS). Regression models incorporating HNO 2 , WFPS, and temperature accounted for 75–77% of the variability in field fluxes. A previously developed NO emissions model was modified to incorporate a kinetic expression for HNO 2 ‐ and temperature‐dependent production. The model tended to underestimate fluxes under low‐flux conditions and overestimate fluxes under high‐flux conditions. These data indicate that (1) control of acidity may be an effective means for minimizing gaseous N losses from fertilized soils and possibly for improving air quality in rural areas, (2) the transformation of HNO 2 ‐derived NO may be an important mechanism of N 2 O production even under relatively aerobic conditions, and (3) mechanistic models which account for spatial heterogeneity and transient conditions may be required to better predict field NO fluxes.