A simple tool for implementation of US Farm Bill programs: Can a practice-based index predict soil function in organic and conventional farming systems?

Background/Question/Methods Nationally, the focus on soil quality and soil ecosystem function as a foundation for natural resource conservation is rising in importance. The 2002 Farm Bill’s Conservation Security Program (CSP) considers soil quality a key component for good land stewardship. Similarly, the draft Senate and House farm bill versions include language about the soil resource quality and indices of environmental outcomes. In addition, the USDA’s national organic certification standards also consider soil quality. Yet, it is not clear that the tools and evaluations used to determine program eligibility and certification yield accurate results. To test the assumption that conservation effort is commensurate with resource outcome and that program eligibility tools work equally well in conventional and organic farming systems, we compared outcomes of a new CSP eligibility tool with measured soil properties from organic and conventional farming systems trials in IA and IL. The eligibility tool was the Soil and Water Eligibility Tool (SWET), a practice-based index of management effort scored in relation to five soil ecosystem functions, planned for use in the next CSP sign-up. Comparative approaches included t-test and ANOVA of tool outcomes and measured data. We also compared tool outcomes to results from the Soil Management Assessment Framework (SMAF), a tool for site-specific interpretation of laboratory data that helps to eliminate potential bias in research interpretation. Results/Conclusions Preliminary results from the IA study indicate both SWET and SMAF followed the same outcome pattern of organic corn-soy-2yr oat-alfalfa (C-S-oA-A) > organic corn-soy-alfalfa > conventional corn-soy. While trends were similar, no significant differences were observed in measured total organic carbon at the 0-15 cm depth. Tool outcomes were most closely correlated with the macroaggregate stability results, which were significantly higher for C-S-oA-A compared with the other rotations. For the IL study, no significant differences were found for TOC among vegetable and row crop rotations regardless of organic amendment applied. However, the SWET tool outcomes were greater for the row crop rotations compared with the vegetable crop rotations, suggesting a need to better calibrate the tool for vegetable crops. This assessment will be used to help validate and calibrate SWET for future policy implementation.