Long-term cover crop management effects on soil properties in dryland cropping systems

Replacing summer-fallow by growing cover crops (CC) in semi-arid regions might provide several soil health benefits. This study examined the effects of long-term CC management in place of fallow on soil properties in a no-till (NT) winter wheat (Triticum aestivum L.)-grain sorghum (Sorghum bicolor Moench)-fallow (WSF) cropping system. Fallow replacement treatments were spring-planted and included peas (Pisum sativum L.) for grain as well as one-, three-, and six-species CC mixtures compared with summer-fallow. Half of each CC treatment was harvested for forage and the other half remained standing after termination. Soil organic carbon (SOC) stocks within the 0- to 15-cm soil depth increased by 0.14 Mg ha-1 yr-1 for each Mg ha-1 CC residue added from 2008 to 2012 and were unaffected by CC diversity. However, SOC stocks were not different than fallow in 2018 likely because CC residue inputs declined due to a succession of drought years. Residue contribution from grain sorghum in the WSF rotation best predicted SOC in 2018 compared to 2012. Soil aggregation was greater with CCs compared to peas or fallow and was unaffected by CC diversity. Mean weight diameter (MWD) of water stable aggregates in 2018 was greater with standing CCs (1.11 mm) compared to peas (0.77 mm) but was similar to fallow (0.84 mm). The MWD of dry aggregates with standing (3.55 mm) and hayed (3.62 mm) CCs were greater compared to fallow (2.75 mm). Our findings suggest simple CC mixtures and CCs managed for hay provide similar soil benefits as diverse CC mixtures or CCs left standing in this semi-arid environment.