Modeling nitrogen oxide emissions from current and alternative pastures incosta rica

Emissions of nitrogen (N) oxide were simulated for one current, unsustainab le pasture management system (Natural) and two alternative, sustainable sys tems (Grass-Legume and Fertilized Improved ed) relevant to the Northern Atl antic Zone (NAZ) of Costa Rica, To produce frequency distributions of N oxi de emissions, an expert system for generating technical coefficients of pas tures nas linked with a process-based simulation model. The expert model ge nerated parameter sets representing different options for the three managem ent systems. The simulation model was rerun for each parameter set. Simulat ed 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 mixture s, 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 mixtur es, and 3 to Ib for fertilized grasses. Stepwise multiple regression showed that N2O-N losses were explained by annual C input to the soil (R-2 = 0.99 7), and NO-N losses by attainable dry matter production (R-2 = 0.972), Carb on input and dry matter production were controlled by stocking rate and fer tilizer level. Soil-atmosphere N oxide emissions from pastures may increase by a factor 3 to 5 when natural pastures are converted to improved pasture s, Such conversion may increase the sustainability of the pasture by stoppi ng the decline of soil N, However, the change is not necessarily sustainabl e from a global perspective because it increases the emission of N oxide gr eenhouse gases.