Multilocation changes in soil carbon stocks from sugarcane straw removal for bioenergy production in Brazil

Sugarcane (Saccharum spp.) straw has been identified as a valuable asset for bioenergy production, but it is also a primary carbon input for sustaining soil resources. Therefore, excessive removal of this crop residue can potentially decrease soil organic carbon (SOC) and have negative environmental consequences. Most crop residue management studies focus on site-specific responses which are important, but do not provide comprehensive assessments across the multiple edaphoclimatic conditions needed by decision makers to guide sustainable sugarcane straw management. Temporal modifications in SOC stocks induced by straw removal were quantified in 10 field experiments located in south-central of Brazil. Each field experiment was arranged in a randomized block design with four replications, including four straw removal rates: total (TR), high (HR), low (LR) and no removal (NR). Soil sampling was performed to a 30 cm depth at the trial establishment (baseline) and after 2 and 4 consecutive years of straw removal. The data indicate that about 19% and 25% of the C added via straw were retained in areas of sandy and clay soils, respectively, and show that excessive removal rates depleted SOC stocks across the evaluated sites. Furthermore, regardless of removal rate, maintenance of straw on sandy soils was not sufficient to sustain SOC stocks, which were depleted by 2.3, 1.9, 1.5, and 1.4 Mg ha(-1) year(-1) for the TR, HR, LR, and NR. Our measured data provide scientific information to support policy and management decisions for straw-derived bioenergy in Brazil. They also suggest straw removal from clay soils will be less deleterious to SOC stocks than from sandy soils, where removal should be avoided. (AU)