THE EFFECT OF CATTLE GRAZING ON SOIL PHYSICAL AND CHEMICAL-PROPERTIESIN A SILVOPASTORAL SYSTEM IN THE PERUVIAN AMAZON

In a six-year-old peach palm (Bactris gasipaes) plantation, centrosema (Centrosema macrocarpum), a leguminous forage plant, was established as a cover crop which was eventually grazed. This experiment was desig ned to monitor probable changes in soil physical and chemical properti es and measure peach palm fruit production and live-weight gain of cat tle grazing this silvopastoral system. The experiment was installed on land that was previously cleared by a D7 bulldozer having a straight blade that mixed the thin layer of topsoil with the acid subsoil (20-4 0 cm) and severely compacted the soil. The results demonstrated that t he centrosema cover crop reduced soil bulk density, increased water in filtration rates and reduced mechanical resistance. In general soil ph ysical properties were improved with the use of Centrosema as forage a nd cover crop. Soil acidity and aluminum saturation decreased consider ably, while potassium concentrations increased. Calcium and magnesium concentrations decreased over time as these minerals were stored in th e pasture biomass, translocated to fresh peach palm fruits and/or expo rted to animals. A strong competition for nutrients was observed betwe en the peach palm plants and Centrosema. The low production of peach p alm fruits was in response to mechanized land clearing during initial establishment of the plantation, and also probably due to deficits of N, P, K, Ca and Mg in the soil instead of being a consequence to the p resence of cattle. The average increase in live-weight gains of the ca ttle was at a rate of 445 g/animal/day during the four-years of the st udy. Such an increase is substantially greater than those registered i n the area under traditional grazing systems used in the region.