Abstract
Sugarcane planting area in Brazil has considerably increased during recent years by occupying areas used for pasture and grain crops production. Land use change (LUC) processes related to sugarcane expansion can affect the soil organic carbon (SOC) stocks, and the quality of the soil organic matter. Preliminary studies have shown that the land-use transition into sugarcane leadto a decrease in the SOC, however no studies have accessed the impact of LUC on the SOC distribution within soil particle-size classes. The study investigated the modifications on total SOC, particulate organic carbon (POM) and mineral-associated C (MOC) in response to conversion from native vegetation (NV), pastures and annual cropland (AC) to sugarcane crop (SCN). Soil samples were collected at 34 field-sites to 20 cm depth and POM fraction separated through 53-mm sieve after soil dispersion. The study results indicated that LUC affects both the labile as well as the more stable SOM fraction, with a mean C content decreasing of 40 and 30% in POM and MOC respectively, following the transition from NV to SCN. The replacement of pastures caused C depletion by 33% at POM and 30% at MOC; meanwhile C accumulation at MOC (5%) was detected for the conversion from AC to SCN. The impact of LUC on POM for AC-SCN transition could not be totally clarified, however the result could be an indication that the POM response to LUC varies as function of previous management in AC. Key words: Soil organic carbon, C fractionation, particulate organic matter, mineral-associated C, land use change.
Highlights
The study investigated the modifications on total soil organic carbon (SOC), particulate organic carbon (POM) and mineral-associated C (MOC) in response to conversion from native vegetation (NV), pastures and annual cropland (AC) to sugarcane crop (SCN)
The study results indicated that Land use change (LUC) affects both the labile as well as the more stable Soil organic matter (SOM) fraction, with a mean C content decreasing of 40 and 30% in POM and MOC respectively, following the transition from NV to SCN
The total C (TOC) content was quantified for all the land use systems-involving both layers: 0 to10 and 10 to 20 cm depth (Figure 1)
Summary
Sugarcane (Saccharum officinarum sp.) is a perennial grass originating from New Guinea that has been cropped in Brazil since the colonial period, reaching a harvested area of 9.7 Mha which accounts for 40% of worldwide production (FAOSTAT, 2011). Since sugar from sugarcane is the main feedstock used to produce ethanol in Brazil, the planted area with this energetic crop has meaningfully grown in the last decade, and the trend is to continue expanding for the years in order to achieve the national goals of production (Conab, 2013; Brasil, 2009; Cerri et al, 2010). As the soil is an important natural reservoir of carbon.
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