Nitrogen Oxide Trace Gas Transport and Transformation: Ii. Model Simulations Compared With Data

The development of process-based models describing N oxide trace gas emissions from agricultural soils will assist in the assessment of present sources, prediction of future trends, and development of mitigation strategies. We compare the predictions of a transport and transformation model with data from intact soil core experiments and then use the model to evaluate the relative importance of individual processes after application of anhydrous ammonia to moderately acidic soil. Soil-gas concentrations of NO and N2O are adequately described using previously obtained kinetic expressions. Net NO surface fluxes are shown to be the result of high rates of subsurface gross NO production (>100 mg N m−2 h−1) balanced by gross consumption rates equivalent to 92–97% of gross production. The overall temperature dependency of NO emissions is described adequately as the net result of individual temperature-dependent processes. Denitrification was estimated to contribute only 8–14% of the total N2O source under primarily aerobic conditions, with the balance caused by abiotic nitrous acid decomposition. The bulk soil reactivity of NO2 was estimated to be at least 500 times greater than the reactivity of NO. The potential for nonbiological nitrate formation is examined, and the effectiveness of pH control and subsurface fertilizer injection for minimizing gas losses are evaluated.