Cover crops and soil health in rainfed and irrigated corn: What did we learn after 8 years?

Duration of cover crop (CC) management, CC biomass production, and other factors could impact how CC affects soil health. We studied the 8-year cumulative impacts of winter rye (Secale cereale L.) CC on soil physical, chemical, and biological properties in rainfed and irrigated no-till corn (Zea mays L.)-based systems in the western US Corn Belt. Average annual CC biomass production was 0.56 ± 0.51 Mg ha⁻¹ at the rainfed site and 0.98 ± 0.95 Mg ha⁻¹ at the irrigated site. After 8 years, CC improved particulate organic matter (POM) and mean weight diameter of water-stable aggregates (MWD) compared with no CC in the 0–5 cm soil depth at both sites. Cover crop increased total POM concentration by 2.8 mg g⁻¹ at the rainfed site and by 13.4 mg g⁻¹ at the irrigated site, while it increased MWD by 0.39 mm at the rainfed site and by 0.79 mm at the irrigated site. Also, CC increased soil C at a rate of 0.125 Mg ha⁻¹ year⁻¹ in the 0–5 cm depth but only at the rainfed site. Cover crop affected neither water infiltration nor available water but improved microbial biomass. Changes in other properties were site-dependent. Cover crop improved many soil properties after 8 years even though measurement taken after 4 years showed no significant effect of CC, which indicates CC slowly impacts properties in this environment. Low CC biomass production and high biomass input from corn-based systems may explain the slow soil response. In general, winter rye CC enhances near-surface soil properties in the long term.