Humic substances and aggregation in oxisol (Rhodic eutrudox) with brachiaria grass and other systems of use

Abstract

The systems of use determine the quality of the soils, by their influence on the quantity and quality of organic matter of the soil (MOS), making it necessary to know the influence of the different systems on carbon, the MOS fractions and the aggregation of the soil. Therefore, the research evaluated the total contents of Organic Soil Carbon (COT). the carbon contents in humic acids, fulvic acids and humina and the relationship with the aggregation in an Oxisol (Rhodic Eutrudox), located in the municipality of Jaboticabal São Paulo-Brazil. The systems of use were: grazing withBrachiaria brizantha (PB); grain production (Glycine max and Zea mays L) under conventional system (SC); direct sowing system, with maize / maize succession (SDMM) and with soybean / maize succession (SDSM) and native forest (BN) as reference. The soil samples were collected from 0-0.1 m evaluating: the weighted average diameter (DMP), the aggregate stability index (IEA), total organic carbon (COT) and carbon contents in fulvic acids (C-AF), humic acids (C-AH) and humina (C-HUM). The results show similarity between PB and SDMM systems with increased TOC, where the values ​​of DMP and IEA were significantly higher in relation to the SDSM and SC, this aggregation increases when the succession is corn. A decrease in IEA was observed due to the reduction of DMP, the increase in smaller aggregates and the lower values ​​of organic carbon in SC. Positive significant correlations were obtained between TOC and aggregation indices (IEA and DMP) in the systems evaluated. In conclusion, the contents of organic carbon and the aggregation indexes are measures to detect changes in soil stability, depending on the use.