Soil physical quality response to sugarcane straw removal in Brazil: A multi-approach assessment

摘要

Crop residues have an essential role in sustaining soil functions and the removal of sugarcane straw for bioenergy production can exacerbate the adverse impacts of mechanized harvesting on soil quality. A long-term field experiment was carried out to evaluate the effects of straw removal on soil physical quality in southern Brazil. We performed a multi-approach assessment including quantitative physical indicators (bulk density-BD; soil resistance to penetration-SRP; macroporosity-MaP; microporosity-MiP; mean weight diameter of aggregates-MWD), biological indicator (earthworm abundance), apparent electric conductivity (ECa) and visual evaluation of soil structure (VESS). In addition, VESS scores were correlated with quantitative indicators for testing its potential as a feasible integrative soil quality indicator. Straw removal rates (total removal, TR-0 Mg ha(-1); high removal, HR-5 Mg ha(-1); low removal, LR-10 Mg ha(-1); no removal, NR-15 Mg ha(-1)) were arranged in a randomized block design with four repetitions. Except for MaP, straw removal for four years affected all soil physical attributes, with higher soil degradation observed in TR and HR plots. Soil moisture, earthworm abundance and ECa values were reduced by higher rates of straw removal. The VESS method was able to detect the changes in soil structural quality, and VESS scores averaged 4.5 and 3.9 for the TR and HR plots respectively, thus revealing signals of severe structural degradation. The data also showed that VESS scores correlated with quantitative indicators broadly used for soil assessments, which suggest VESS as a reliable and integrative indicator for monitoring soil structural quality in sugarcane fields. Our findings support that LR, keeping about 10 Mg ha(-1) of straw on the soil surface, can be a management target to ensure the sustainability of bioenergy production.