Labile fractions of organic matter in cropping system with straw of brachiaria and sorghum

Abstract

The key role of organic matter (OM) in the physical, chemical and biological soil features justifies the growing interest in identifying use and management systems which contribute to increase the stock of carbon (StC) in tropical soils. The aim of this study was to evaluate the stock of carbon in the particulate (>53 μm) and mineral-associated soil organic matter fractions smaller 53 mm. Soil samples from a Rhodic Udox collected in Montividiu, Goiás State (Brazil), were taken at five depths in the following agricultural systems: a) brachiaria cultivated in the soybean fallow period (SB), b) sorghum cultivated in the soybean fallow period (SS) and Cerrado as reference area. The levels of total organic carbon (TOC), granulometric fractioning of soil organic matter and the stock of carbon in each of the fractions were quantified. There were significant differences in the TOC levels at all depths. The highest values were found in the StC of SB system, at all depths. The fraction of particulate organic matter (POM) was an effective parameter to demonstrate differences between management systems, achieving the highest levels in the SB system due to the higher biomass input in this system, however for the mineral-associated fraction, the highest levels were recorded in the reference area, followed by the SS system.