Modeling Nitrogen Oxide Emissions from Current and Alternative Pastures in Costa Rica

Abstract

AbstractEmissions of nitrogen (N) oxide were simulated for one current, unsustainable pasture management system (Natural) and two alternative, sustainable systems (Grass‐Legume and Fertilized Improved) relevant to the Northern Atlantic Zone (NAZ) of Costa Rica. To produce frequency distributions of N oxide emissions, an expert system for generating technical coefficients of pastures was linked with a process‐based simulation model. The expert model generated parameter sets representing different options for the three management systems. The simulation model was rerun for each parameter set. Simulated nitrous oxide (N2O)‐N losses 25 yr after pasture establishment were 3 to 5 kg ha−1 yr−1 for natural pastures, 12 to 15 for grass‐legume mixtures, and 7 to 28 for fertilized grasses. Losses of nitric oxide (NO)‐N were 1 to 2 kg ha−1 yr−1 for natural pastures, 7 to 8 for grass‐legume mixtures, and 3 to 16 for fertilized grasses. Stepwise multiple regression showed that N2O‐N losses were explained by annual C input to the soil (R2 = 0.997), and NO‐N losses by attainable dry matter production (R2 = 0.972). Carbon input and dry matter production were controlled by stocking rate and fertilizer level. Soilatmosphere N oxide emissions from pastures may increase by a factor 3 to 5 when natural pastures are converted to improved pastures. Such conversion may increase the sustainability of the pasture by stopping the decline of soil N. However, the change is not necessarily sustainable from a global perspective because it increases the emission of N oxide greenhouse gases.