Atributos químicos de argissolo amarelo sob floresta e savana naturais e cultivados com pastagem em Roraima

Abstract

The Roraima state can be characterized by three major biomes. The areas of Forest occupy the greater portion of the state, the areas of Savannahs that are distributed in the regions center- east and northeast of the state and finally the field of Campinaranas which occupy the south- center portion of the state. The livestock is a traditional activity, of great economic importance being widespread both in biomes of savanna and Forest. As a result of the huge need of food production, the natural resources of Roraima suffer strong pressure of occupation, being replaced by agriculture and livestock. This situation brings, many times, undesirable results to environmental sustainability, already that agriculture and slash and burn. Because of this, the present study was carried out with the aim to evaluate and compare the chemical attributes of an Ultisol under ecosystems of savanna and natural forest, converted into pasture system. The treatments were representative areas of savanna and natural savanna converted into pasture, natural forest and forest converted to pasture. The delineation were a randomized blocks in Split plot scheme (treatments and depth), being evaluated the following chemical attributes: pH, potential acidity, Aluminum saturation, exchangeable Aluminum, soil organic matter, exchangeable Potassium, exchangeable Magnesium, exchangeable Calcium, sum of bases, bases saturation, available phosphorus and remaining and Total and effective Cation Exchange Capacity. The soil pH values showed no statistical difference between themselves and with the environment NF obtaining the lowest average observed. For potential acidity converted environments showed lower values than the natural environments. For the Aluminum saturation there was a remarkable reduction in environments converted, mainly in the most superficial layers. The exchangeable Aluminum showed significantly lower levels in SCP when compared to NF and in forest environments there was a significant difference only in the first 10 cm of the soil. The levels of organic matter were more frequently observed in environments NF, followed by FCP and SCP, the latter showing a greater tendency toward accumulation of organic matter. In exchangeable Potassium was not observed statistically significant differences between the environments and depths analyzed. For exchangeable Calcium and Magnesium, sum of bases the highest levels were found at a depth of 0-10 cm, with evident reduction along the soil profile. For bases saturation, the environment SCP was fully above the environment SN and the FCP environment was statistically higher than the FN until a depth of 20 cm. The averages of phosphorus remainder obtained showed no difference in any environment and any depth analyzed, already available Phosphorus showed no significance for interaction, where the highest average observed for this variable has occurred in the environment SCP. For CTC effective and total the most expressive values were found in depth 0-10 cm, with a slight tendency to decline as increase in depth. The conversion of natural environments by pasture has caused significant changes to the majority of chemical characteristics of Ultisol. In general, the chemical attributes showed a slight improvement, especially in the most superficial layers subject to greater influence of major growth in.