Atributos químicos e frações da matéria orgânica em latossolo sob diferentes sistemas de uso

Abstract

The soil organic matter (SOM) determines the key attributes that define the quality of the soil, being directly influenced by management practices. Thus, the aim of this work was to evaluate the changes in chemical attributes, organic carbon and nitrogen and organic matter fractions in oxissol submitted to diferente use systems. The survey was conducted in commercial crop areas located in Dourados-MS, where soil samples were collected in two years (2010 and 2011), at the depth of 0-10, 10-20 and 20-30 cm. The management systems evaluated were: no-tillage (NT), conventional tillage (CT), integrated crop-livestock systems (SIAP), pasture (PAST) and eucalyptus (EUC), having like a reference the native vegetation (NV). It was determined carbon and total nitrogen and also the contents of pH in CaCl2, Al+3, H+Al, Ca+2, Mg+2, K+ and P, carbon and nitrogen labile, carbon management index and the carbon and nitrogen of humic substances. In soil under NV had higher TOC stocks than other systems use, especially in 0-10 cm depth. However, the adoption of conservation tillage systems, such as NT and ICL, resulted the recovery of TOC, indicating that in the medium to long term, plant biomass aborted the cultures associated with the management may increase levels of soil organic matter. In 2011, the ICL was the largest contributor to this increase with 21.3 and 18.2% over the PAST and CT, respectively, while the NT was increased by 9.5 and 5.6% over the PAST and CT, respectively. However, the ICL and the NT did not differ from EUC. With respect to the stocks of total nitrogen (TN), the SIAP, NT and CT showed the largest stocks in the 20-30 cm layer. As regards to the chemical attributes soil, the lowest pH in CaCl2, higher acidity and higher concentrations of aluminum were found in NV. The contents of calcium were higher in NT and CT. The stocks of labile carbon (CL) and labile nitrogen (NL) were not significantly influenced by the year of the sample soil collection, whereas the comparison between the systems of soil use, the largest stocks of CL in both years evaluated, at the layer of 0-10 cm were observed in the SIAP, NT, and EUC when compared to the CT and PAST. However, the SIAP, NT, and EUC did not differ from the NV stock of CL. In the study of humic fractions, it had reduction of carbon in humin fraction (C-HUM) and in humic acid fraction (C-HA) with the adoption of the CT. In assessing the carbon management index (BMI) verified significant effect of the sampling year only at the layer of 0-10 cm, with reduction in the second collection of soil at CT. With respect to systems of soil use, the SIAP and NT provided higher carbon management index of the soil than the native vegetation, showing the conservationist potential of these systems. The use of cropping systems, both conservationists, as with soil tillage, promoted reduction of the active acidity, potential acidity and aluminum content, and increased contents of calcium, magnesium, potassium and phosphorus in the soil solution.