Considerations on the sustainability and environmental impact of intensive pastures.

Intensive pastures form an important component of livestock production systems in South Africa. The sustainability and environmental impact of intensive pastures via their effects on soil properties and nutrient fluxes vary considerably depending on the systems adopted. Soil organic C and N data from various pasture systems provide evidence of a rapid decline in organic matter levels under annual pastures, particularly on coarse or medium-textured soils. This evidence, coupled with the vulnerability of annual pastures to soil erosion during establishment, places their sustainability at risk. Soil acidification, accelerated by the use of nitrogenous fertilizers, must be counteracted by liming to ensure the sustainability of pasture systems. Phosphorus and K, both relatively immobile in pasture topsoils, are not susceptible to much loss. Nitrogen, on the other hand, is susceptible to both gaseous and leaching losses. Balanced fertilization may limit N losses and soil acidification by ensuring more efficient plant utilization of this element. Research priorities indicated are the development of systems that enhance the sustainability of annual pastures, and the improvement of the efficiency of soil and fertilizer N usage in both annual and perennial intensive pastures.Keywords: acidification; environmental impact; erosion; fertilization; fertilizers; leaching; livestock; nitrogen; nutrient flux; organic matter; pastures; phosphorus; production; run-off; soil; soil acidification; soil erosion; soil organic matter; south africa; sustainability; topsoi