Putting the soil health principles to the test in Iowa

Abstract One of the most popular soil conservation campaigns is based on the USDA Natural Resource Conservation Service's Soil Health Principles (NRCS‐SHPs). The NRCS‐SHP program identifies four principles—maximize presence of living roots, minimize disturbance, maximize soil cover, and maximize biodiversity—with the underlying assumption that the more principles one follows, the greater improvements in soil health. Despite the popularity of the NRCS‐SHPs, this underlying assumption has not been rigorously tested. To do so, we used nine long‐term experiments all located in central Iowa, but with varying degree of NRCS‐SHP adoption, to determine if greater adoption increases three slow‐changing (maximum water holding capacity, bulk density [BD], and soil organic carbon) and three dynamic (microbial biomass carbon [MBC], potentially mineralizable carbon [PMC], and permanganate oxidizable carbon [POXC]) soil health indicators. We regressed these indicators with a soil health principle score that can scale soil management based on adoption of the NRCS‐SHPs. Of the slow‐changing soil properties, increased adoption of NRCS‐SHPs only decreased soil BD ( R 2 = 0.22, p = 0.024). On the other hand, increased adoption of NRCS‐SHPs strongly predicted increases in both MBC and PMC and across two sampling dates ( R 2 > 0.23, p < 0.015); POXC, however, did not increase with greater adoption. The consistent increases in MBC and PMC with greater adoption of NRCS‐SHPs supports their usefulness as sensitive indicators of positive soil health change. Our study provides scientific evidence to support the NRCS‐SHPs concept, improving its usefulness as an extension campaign, and stands as a step toward evidence‐based soil conservation.