Soil carbon stocks under burned and unburned sugarcane in Brazil

Burning sugarcane leaves and tops on standing mature crops has been practiced for centuries in Brazil, in order to facilitate the harvest, transportation and processing of sugarcane stalks. Currently, due to economic, environmental and legal reasons, the unburned harvest, with residues left on the soil, has been increasingly adopted. There is little information, though, about the effects of the addition of sugarcane trash on the soil carbon dynamics of the sugarcane crop. The objective of this study was to evaluate the effect of trash management on carbon dynamics of the sugarcane crop. The study area is located in the Sao Martinho farm, in Pradopolis, Sao Paulo, in Southeastern Brazil. Two chronosequences were studied, in plots where sugarcane had been replanted 2, 6 and 8 years before the soil samplings, with and without pre-harvest burning. An area of native vegetation adjacent to the sugarcane fields was also sampled, as a reference. The soil in the area is classified as a clayey Oxisol. The soil samples were analyzed for bulk density, sand, silt and clay content, total carbon, carbon in the particulate organic matter and microbial biomass carbon. The soil microbial biomass carbon and the particulate organic matter carbon were more sensitive to residue management changes than total carbon. The area with the longest period of adoption of the unburned management, 8 years, had higher contents of total carbon (30% higher), microbial biomass carbon (by a factor of 2.5), and particulate organic matter carbon (by a factor of 3.8) than the area where the residues were burned. The total carbon stocks were also higher in the unburned treatment, markedly in the area with 8 years of green cane management. (C) 2009 Elsevier B.V. All rights reserved.