Impacto do manejo agrícola em Organossolos no estado do Rio de Janeiro

Abstract

Histosols are defined by the high levels of organic matter and they are very important for storing carbon and nitrogen, thus contributing in mitigating greenhouse gases (GHG). Proper management of these soils should preserve organic matter, consequently, mitigating GHG production. This study aimed to evaluate the following changes in the properties of Histosols due to the soil tillage and artificial drainage: organic matter and sulfate content, C and N stocks, availability and content of P fractions. Three areas with different coverages were selected: secondary forest in natural regeneration, conventional cultivation of cassava (Manihot sculenta) and intercropped coconut (Cocos nucifera) with cassava; in which soil pits were opened for profiles description and sampling. The following analyzes were carried out: chemical characterization, von Post scale of decomposition of organic matter, percentage of rubbed fibers, organic matter content, percentage of mineral material, bulk density, electrical conductivity, soluble sulfate, total organic carbon (TOC) and total nitrogen (NT). There were calculated the stocks of C and N, and obtained fractionation of organic matter and sequential fractionation of P. The results of chapter I showed that the values of COT and NT decreased in 33 and 20%, respectively, in the histic horizon of the area with cassava crop. In the area with coconut intercropped with manioc, the TOC and NT values decreased by 31 and 18% respectively, in the histic horizon. There were losses of labile organic carbon and the sulfurization process was evidenced in the profiles with agricultural usage. In the chapter II, the results show that in the cassava cultivation area there was a reduction in the total P content in the subsurface by 35.6 and 37.9%, when compared to the area with coconut intercropped with cassava and the secondary forest, respectively. In all areas, there was predominance of the highly recalcitrant residual P fraction (> 70%). The available P content was reduced only in the cassava cultivation area. Drainage and soil tillage reduced the C and N stocks in the soil, and affected P adsorption and mineralization processes, in all the inorganic fractions.