Quantifying economic and biophysical sustainability trade-offs in tropicalpastures

Sustainability of tropical pastures has various economic and biophysical di mensions and is affected by species composition, age and management. The su stainability of pastures in cattle ranching systems was analyzed in terms o f economic viability, soil nitrogen stock change, CO2 loss/sequestration, N 2O and NO emissions, pollution by herbicides, and nitrogen leaching loss, f or a case study in the Northern Atlantic Zone of Costa Rica. Development sc enarios were explored for the next 25 years based on degradation and yield decline of current pastures, and on possible introduction of grass-legumes and fertilized improved grass species. With degradation of current pastures , gross margin, soil nitrogen stock, nitrogen leaching and N2O and NO emiss ions are simulated to decrease in time, whereas CO2 emission and herbicide use increase. With the introduction of grass-legumes or fertilized grasses, the reverse takes place. The conversion of degraded pasture to grass-legum es or fertilized grasses is calculated to lead to a sequestration of CO2 of up to 50 ton C ha(-1), which might be a potential mechanism in mitigating the greenhouse effect. Quantitative, exploratory studies point out the ofte n conflicting nature of different dimensions of sustainability and show pos sible pathways of sustainable development. (C) 1999 Elsevier Science B.V. A ll rights reserved.