Applying Soil Management Assessment Framework (SMAF) on short-term sugarcane straw removal in Brazil

Abstract

There is a growing interest by the Brazilian sugarcane (Saccharum sp.) industry in removing sugarcane straw from the field to use as raw material for increasing bioenergy production (e.g., second generation and co-generation). In contrast, straw has an essential role in sustaining critical soil functions, so indiscriminate straw removal can jeopardize soil quality and consequently reduce crop yield. The objectives of this study were: (i) to apply the Soil Management Assessment Framework (SMAF) tool to investigate the short-term effects of sugarcane straw removal on a sandy clay loam Oxisol and on a sandy loam Ultisol, and (ii) to correlate soil quality attributes (i.e., chemical, physical and biological) and the overall Soil Quality Index (SQI) with plant yield (straw and stalk) in areas managed with straw removal. A 2-year experiment was conducted in a randomized block design replicated four times with three rates of straw removal: 0, 50 and 100% (i.e., no removal, moderate removal, and total removal, respectively). Soil samples were collected at the 0–5, 5–10, 10–20 and 20–30 cm layers and following indicators were analyzed: physical [bulk density (BD)], chemical [soil-pH, phosphorus (P) and potassium (K) content] and biological [soil organic carbon (C) and microbial biomass carbon (MBC)]. For the Oxisol, 100% straw removal decreased soil physical attribute scores (i.e. bulk density) in 5–10 and 10–20 cm depths and decreased SQI in the 0–20 cm depth, while the 0% and 50% straw removal rates enhanced SQIs in all depth increments. Furthermore, 50% straw removal sustained soil quality and increased feedstock availability for bioenergy production. Straw and stalk yields were correlated to soil physical attribute score and SQI for 0–10 cm soil depth in the Oxisol. For the Ultisol, straw removal did not influence SQI and there was no relationship between soil quality scores and phytomass. Our results highlight soil-specific responses to sugarcane straw removal and total straw removal in the Oxisol site leads to physical quality degradation even in the short term. Despite no short-term effect of straw management on Ultisol soil quality, the long-term benefits of the straw on the soil-plant system may be reduced with total removal, thus indiscriminate straw removal is not advocated. Based on our findings, partial straw removal can be a win-win scenario in Brazil, where a considerable volume of biomass can be used for bioenergy production with minimal impacts on soil quality.