A SMAF Assessment of U.S. Tillage and Crop Management Strategies

Abstract The Soil Management Assessment Framework (SMAF) was developed to collectively assess biological, chemical, and physical soil health changes due to management practices. SMAF scoring curves were designed to be site-specific but were never validated at national scale. Our goal was to verify the national effectiveness of SMAF for detecting changes induced by conservation practices. Data from 456 articles representing the U.S. was compiled as input for a SMAF analysis. Soil organic-C (SOC), microbial biomass-C (MBC), β-glucosidase activity (BG), macroaggregate stability (AS), bulk density (BD), pH, soil-test P and K indices and an overall soil quality index (SQI) were computed. Measured, scored, and SQI values were used to evaluate tillage intensity [conventional (CT), reduced tillage (RT), no-till (NT), and zero disturbance (perennial systems; PER)] and soil cover [annual cropping systems without cover crops (ANCC), annual cropping systems with cover crops (ACC), and year-round soil cover (perennial systems; PER)]. Reducing tillage intensity and increasing soil cover increased topsoil SOC, MBC, BG, and AS values (measured and scored). SMAF scoring curves were sensitive to agronomic practice effects on soil function. The highest SQI values were associated with perennial systems (zero soil disturbance) and year-round living roots. Within annual cropping systems, cover cropping, and NT demonstrated better soil biological and physical functioning. However, SMAF scores underestimated the effects for SOC and BG and overestimated the effects for AS, suggesting the algorithms for those indicators should be reevaluated and improved. Overall, this national assessment confirmed the utility of SMAF and highlighted benefits of conservation practices.