Impact of pre-harvest burning versus trash conservation on soil carbon and nitrogen stocks on a sugarcane plantation in the Brazilian Atlantic forest region

Owing to the increased demand for ethanol biofuel from sugar cane, the area planted to this crop in Brazil has increased from 4.8 to 9.5 Mha since 2000. At the same time there has been pressure from environmental groups and others to cease the pre-harvest burning of cane, and today over 40% of the crop is harvested without burning, thus conserving the trash on the soil surface. While most trash decomposes during the year, it is generally assumed that this transition from burning to trash conservation will have benefits for cane productivity and increase soil carbon stocks. To investigate the possible benefits of this change of practice an experiment was carried out in the state of Espírito Santo, south-eastern Brazil, to investigate the long-term effects of the practice of pre-harvested burning compared to trash conservation on soil fertility and soil C and N stocks. The results showed that over a 14-year period, trash conservation marginally decreased soil acidity and significantly increased soil C and N stocks in 0-10 cm depth interval. Although the trash conservation treatment accumulated 13 Mg C ha⁻¹ more than the burned treatment, this difference was not statistically different. However, the stocks of N to 100 cm depth were 900 kg ha⁻¹ higher under the trash conservation treatment and this difference was statistically significant. The ¹³C abundance data suggested that where trash was conserved, more soil C was derived from the sugar cane than from the original native vegetation.