Sugarcane mulch C and N dynamics during decomposition under different rates of trash removal

Abstract

Abstract Sugarcane is a worldwide crop that leaves a considerable amount of crop residues (called trash) on the soil surface each year after green cane harvesting. However, the recent industrial valorization of these residues raises the question of how much trash to leave as mulch after harvest. Here, we studied the decomposition of three different trash quantities (4, 8 and 12 Mg ha −1 ) across five experimental sites from a subtropical climate over one year. We quantified the dry matter (DM), carbon (C) and nitrogen (N) contents of the remaining mulch at one-month intervals for one year after trash addition at all sites. The chemical composition of the trash was characterized by proximate analysis at one site. Our results showed that mulch degradation was proportional to the initial amount of trash left on the soil surface, i.e., the degradation rates were similar for the three trash treatments at each site, suggesting no limiting factor to decomposition associated with trash quantity and its contact with the soil. On average, 64% of the trash was degraded after 12 months in all treatments, leading to considerable differences in the mass of C degraded after one year (1.2 ± 0.1, 2.3 ± 0.2 and 3.5 ± 0.3 Mg ha −1 for the 4, 8 and 12 Mg ha −1 treatments, respectively). An interaction between trash quantity and site was observed, which translated into more differences in the C degradation rates between sites for the 4 Mg ha −1 trash treatment. The N content of the remaining mulch was rather stable throughout the year, which indicated the efficient use and recycling of N by the decomposing microflora during trash decomposition. These results will help determine the amount of sugarcane trash that should be left on fields to preserve soil C and soil fertility.