Soil Health: An Emergent Set of Soil Properties That Result from Synergy Among Agricultural Management Practices.

The responses of a selected soil microbial property to a single agricultural management practice are often inconsistent among field studies, possibly reflecting the site-specific nature of field studies. An equally compelling explanation is that in complex systems where outcomes are the result of numerous interacting factors, a consistent response may not appear if there are insufficient factors being applied to produce the emergent property. It is likely that soil health, and measures thereof, are the result of multiple management practices acting in synergy to produce positive changes in soil properties. In our research studies, we have found that combining no-till with factors such as crop rotational diversity, cover cropping, or residue retention results in consistently improved soil health and associated outcomes. Adding crop rotational diversity to a no-till system resulted in 24% less N₂O emissions, increased SOC, and 22% higher soybean yields. Adding corn residue retention to a no-till system resulted in decreased N₂O emissions and increased SOC. Combining residue retention and cover cropping in a no-till system resulted in consistently elevated fungal:bacteria ratios and eventually improved SOC and soil aggregation. Adding cover crops to a no-till, diversified rotation doubled the number of arbuscular mycorrhizal propagules in the soil. Studies of crop rotation and crop sequencing continue to affirm benefits, yet still implicate unspecified functional changes in soil microbial communities. Our on-going studies of crop sequence effects suggest changes in the soil fungal communities that correlate with increased crop yields. The factors that produce soils that are disease- and weed-suppressive are poorly understood, and are likely an emergent property due to synergy among multiple management factors. Field experiments that stack management factors or are conducted as a system may be required to demonstrate consistent improvements in soil health and advance understanding of the most meaningful measures.