Evaluating assessment tools for soil ecosystem function used to implement US Farm Bill policy: How well do they work?

The 2002 Farm Bill’s Conservation Security Program (CSP) considers soil quality as a key component for good land stewardship. The USDA’s 2007 Farm Bill proposal includes several similar approaches.  Most policy focuses on management practices as surrogate measures of soil function. To test the assumption that conservation effort is commensurate with resource outcome, we compared two soil quality assessment tools with measured data from farm management systems and research stations in CA and IA, to help validate both tools. Iowa data included 0-15 cm soil samples collected from paired (~30ha) watersheds after 30 years of conservation or deep-disk tillage. Soil organic carbon (SOC) contents were significantly greater for conservation tillage compared with conventionally-managed systems. At another Iowa site, SOC within organic corn-soybean production systems was significantly greater than conventionally managed systems after 7 years of organic management. In CA, our first experimental site consisted of a 8-year tillage and cover crop system comparison. The second CA experiment included data from 1.2 ha plot vegetable production systems. Results showed SOC was significantly greater in the organic system compared with the low input and conventionally fertilized systems. The assessment tools were the ‘Soil Conditioning Index’, a predictive model of soil carbon trend, currently used in CSP, the ‘Soil Quality Tool’, a practice-based index of soil function, proposed for use in soil resource evaluation. Comparative approaches included ANOVA and t-test to compare scores, a survey of researchers’ expert opinions. Preliminary results show the SQ tool to be representative of expert opinion.