title: Molecular characterization of soil organic matter from native vegetation-pasture-sugarcane transitions in Brazil.
abstract: Replacing pastures (PA) with sugarcane (SG) has been deemed an agronomically feasible strategy for sugarcane expansion in Brazil. However, there are some uncertainties about the environmental impacts regarding this land use change (LUC), mainly related to soil organic matter (SOM), a key factor of environmental sustainability of Brazilian ethanol. LUC-related losses of SOM can overcome the C savings from biofuels. The molecular composition of SOM was evaluated to understand the C dynamics regarding LUC from PA to SG, using native vegetation (NV) as reference. Our study area was located in the south-central region of Brazil. Soil sampling was performed at three depths (0-0.1m, 0.2-0.3m and 0.9-1m) in three representative sites with known LUC history and management practice since 1970. Pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS) was chosen to study SOM chemistry. Content and isotopic composition of soil organic C and N were also determined. The LUC caused decreases on C and N contents and on δ(13)C isotopic values. Depth was the major factor that influenced SOM composition, while the influence of LUC was mainly evident in surface soils and diminished rapidly with depth. The main difference in SOM composition undergoing the conversion PA-SG was a higher contribution from compounds associated to fresh litter inputs. The high contribution from fresh litter, having a relatively low mean residence time and increasing decomposition rates, is probably a major factor that drives C losses in areas undergoing sugarcane expansion.
authors.affiliation: University of São Paulo, Luiz de Queiroz College of Agriculture, Department of Soil Science, 11 Páduas Dias Avenue, 13418-900 Piracicaba, SP, Brazil; Colorado State University, Natural Resource Ecology Laboratory, 1231 East Drive, 80523-1499 Fort Collins, CO, USA. Electronic address: denermsoliveira@gmail.com.
authors.forename: Dener Márcio da Silva
authors.initials: DMDS
authors.lastname: Oliveira
authors.affiliation: University of São Paulo, Luiz de Queiroz College of Agriculture, Department of Soil Science, 11 Páduas Dias Avenue, 13418-900 Piracicaba, SP, Brazil.
authors.forename: Judith
authors.initials: J
authors.lastname: Schellekens
authors.affiliation: University of São Paulo, Luiz de Queiroz College of Agriculture, Department of Soil Science, 11 Páduas Dias Avenue, 13418-900 Piracicaba, SP, Brazil.
authors.forename: Carlos Eduardo Pellegrino
authors.initials: CEP
authors.lastname: Cerri
keywords: Biofuels; Land use change; Pyrolysis–GC/MS; Soil carbon