摘要
During the next 10 years Brazil's agricultural area will expand to meet increased domestic and worldwide demand for food,fuel,and fiber.Present choices regarding land use will determine to what degree this expansion will have adverse effects that include soil erosion,reservoir siltation,water quality problems,loss of biodiversity and social conflict,especially around indigenous reservations.This paper presents an up-to-date inventory of soil erosion in Brazil caused by crop and livestock activities and provides estimates based on three different hypothetical land-use scenarios to accommodate the expansion of Brazilian agricultural activity by 2020:Scenario 1-expansion of cropping into areas of natural vegetation,without adoption of conservation practices;Scenario 2-expansion of cropping into areas of degraded pasture,without adoption of conservation practices;Scenario 3-expansion of cropping into areas of degraded pasture,together with conservation practices in 100%of the expanded area.The worst-case scenario involves expansion of agriculture into areas of native vegetation in the Brazilian Savannah(Cerrado)and Brazilian rainforest(Amazon)biomes,and could increase total soil erosion in Brazil(currently about 800 million metric tons a year)by as much as 20%.In the best-case scenar-io,crop expansion under a conservation agriculture model would utilize currently degraded pasture,especially in the Savannah(circa 40 million hectares),reducing soil erosion in Brazil by around 20%.For this to occur,however,a national soil and water conservation policy needs to be implemented in Brazil to support a sustainable model of agriculture in which the environment can be preserved as much as possible.
