Evaluating Brazilian Sugarcane Expansion Effects on Soil Structure Using Vess.

Increasing global demand for biofuel has accelerated land-use change (LUC) in Brazil, primarily by replacing degraded pasture with sugarcane (Saccharum officinarum). The intensive mechanization associated with this LUC has increased concerns regarding soil structural quality (SSQ). Through decades of research focused on identifying sensitive indicators of soil degradation due to land use and management, the Visual Evaluation of Soil Structure (VESS) protocol has emerged as a simple, cheap, fast, reliable and accurate semi-quantitative approach for assessing SSQ. VESS integrates soil properties related to size, strength and porosity of aggregates, root characteristics and soil color into a single score (Sq - structural quality) that ranges from 1 (good structural quality) to 5 (poor structural quality).  Our objective was to evaluate SSQ changes associated with a LUC sequence (native vegetation – pasture – sugarcane) at three sites across south-central Brazil using the VESS. Soil physical properties, previously identified as potential indicators of SSQ, were also quantified and correlated with the VESS scores. Our results showed increasing SSQ degradation due to this LUC within the largest sugarcane producing region of the world. Average Sq ratings were 2.0, 2.7, and 3.1 for native vegetation (Cerrado), pasture, and sugarcane, respectively. Sq scores were strongly correlated (p<0.01; n= 72) with several soil physical properties including bulk density (r= 0.35), macroporosity (r= -0.63), total porosity (r= -0.33), water-filled pore space (r= 0.46), soil resistance to penetration (r= 0.68), water hydraulic conductivity (r= -0.47) and a structural stability index (r= -0.40). We conclude that VESS scores provide an efficient method to identify SSQ degradation due to LUC, and recommend that VESS evaluations be incorporated into monitoring protocols for evaluating soil quality/health in areas of sugarcane expansion in Brazil.