Organic cropping systems enhance soil health indicators in a Mollisol of the US Corn Belt

Abstract

Organic cropping systems may potentially improve soil and environmental health relative to simplified conventional systems due to the use of extended crop rotations, perennial crops, and animal manure. However, few studies have evaluated the impacts of organic row crop systems on a suite of soil health indicators relative to conventional systems across time. Thus, our objective was to assess how cropping system (conventional corn [Zea mays L.]–soybean [Glycine max L.] vs. organic corn–soybean–oat [Avena sativa L.]/alfalfa [Medicago sativa L.]–alfalfa vs. organic perennial pasture) and duration of management affect surface soil health indicators (soil biological, chemical, and physical properties) after 1–9 years of management in a Central Iowa Mollisol. Overall, the organic rotation improved six of 14 soil health indicators compared with the conventional system and the organic pasture improved eight indicators. The improved indicators included soil biological indicators, labile C and N pools, and wet-aggregate stability, but not organic C or total N concentrations. Organic systems had fewer effects on most soil chemical properties. The conventional system reduced soil C by 0.35 g kg⁻¹ year⁻¹ (r = −0.84, n = 9, p = 0.005), unlike the organic systems in which soil C levels were generally maintained. The changes in soil health indicators were attributed to use of perennials, reductions in tillage frequency (during perennial phases), manure, and differing plant residue amounts among the three systems. In conclusion, organic cropping systems can enhance soil biological and related indicators in the medium term, but have fewer effects on soil fertility indicators under the conditions of this study.