Soil quality index to access the impacts of long-term vinasse application in sugarcane areas

Soil quality index (SQI) helps quantify management practices impacts on the soil, providing information for producers in decision-making. Through evaluation in sugarcane areas, soil indicators were used to develop SQI to access and quantify the impacts of long-term vinasse application on the soil. The treatments consisted of two soil types: clayey (490 g kg⁻¹ clay) and sandy (80 g kg⁻¹ clay) and two conditions: with (70 m³ ha⁻¹ year⁻¹) and without vinasse application for 10 years. Soil samples were collected in the 0- to 10-cm, 10- to 20-cm, and 20- to 30-cm layers in each treatment. Four soil functions were developed to calculate SQI: root environment quality (REQ), air/water ratio (AWR), soil chemical quality (SCQ), and soil tolerance to erosion (STE). Twelve soil indicators related to soil fertility and aggregation/structure were used. The long-term vinasse application increased water storage (32%–58% of soil porosity), sum of bases (11–19 mmol_c dm⁻³) and aggregate stability index (41% vs. 78%) compared to without vinasse treatment in sandy soil. In the clayey soil, vinasse increased (p < 0.05) the REQ, SCQ, and STE functions by 10%, 14%, and 13%, respectively, besides not affecting AWR. The long-term application of vinasse promoted greater benefits, proportionally, in the sandy soil, with increments (p < 0.05) of 30% in AWR, 25% in SCQ, and 27% in STE. According to the SQI, long-term vinasse application increased the capacity of the clay soil to perform its functions by 8%, while it increased to the sandy soil was 22%.