Defining dynamic soil property and soil health reference conditions for soil survey

Correlating soil health indicator values with the soil map units defined by United States Department of Agriculture - Natural Resources Conservation Service (USDA-NRCS) Soil Survey can help identify soil health indicator benchmark values for a particular soil under a certain management condition and define what is achievable for a given soil. To support the inclusion of soil health metrics in soil survey products, USDA-NRCS organized Dynamic Soil Properties for Soil Health (DSP4SH), a nationwide effort to measure a common set of soil health metrics across a range of soil types, landscapes, management systems, and climates, and characterize context-specific reference values of these properties. Here, we present total soil organic carbon (SOC) stock data and Soil Health Assessment Protocol and Evaluation (SHAPE) peer group SOC scores and benchmark values from ten initial DSP4SH project sites. Data was collected across the continental US in diverse systems ranging from tilled cropland on deep Mollisols to forests on highly weathered Ultisols. Despite variability in total SOC stocks by soil series, we observed significantly greater SOC stocks and SHAPE SOC scores in perennial reference ecosystems compared to soil health management and business-as-usual agricultural systems. Our findings demonstrate the utility of the USDA-NRCS ecological site approach for defining dynamic soil property benchmarks and thresholds associated with management alternatives, which could help guide other global soil health benchmarking efforts. This study demonstrates that soil survey products can be used to effectively organize and present context-specific soil health data and interpretations.