CAMBIOS EN LAS PROPIEDADES QUÍMICAS DE UN SUELO DE SABANA LUEGO DE LA INTRODUCCIÓN DE PASTURAS MEJORADAS

Change on the chemical properties of a savanna soil by the introduction of improved perennial pastures The Venezuelan Trachypogon savannas are mainly used for extensive cattle rising, but the biomass production is generally limited by soil fertility. In order to evaluate the change in the soil chemical properties by the introduction of pastures, evaluations were made in a Typic Plinthustults located in the savannahs of Guarico State. The cover crops were Brachiaria dictyoneura (BD), Centrosema macrocarpum (CM), and the natural savannah (SN). Two samplings were made: one initial, before the establishment of the treatments, and the other two years later. The treatments were distributed in great parcels of 26.250 m 2 (BD and CM) and 20.000 m 2 (SN). In each plot 24 samples to three depths were taken (0 to 5, 5 to 15 and 15 to 30 cm). Soil pH, exchangeable acidity, cationic exchangeable capacity, organic carbon, nitrogen, and available phosphorus and sulphur were evaluated. The results showed statistical differences between treatments by effect of the introduced pasture and the depth of sampling; these differences were associated to the effect of the amount and quality the covers on pH and extraction of nutrient. In SN the effect of burnings on the soil properties was evident. It was concluded that some properties are favored when the cover crop is a grass and others when it is a leguminous.