Transition from irrigated agriculture to dryland agriculture
Soil carbon (C) in arid and semi-arid regions is in danger of loss due to low annual precipitation and decreasing water availability for irrigation. As farmers are forced to transition from irrigated to dryland agriculture, climate-smart tools, like cover cropping and perennial cropping, are promoted for improving soil health and soil C sequestration in agroecosystems. Yet, their role in agriculture facing irrigation retirement is still uncertain. This study examined various C and N fractions and microbial community structure and function in irrigated and irrigation retiring systems in silage corn (Zea mays) production for two years. To address these, three cover cropping strategies, i.e., grass, brassica, and legume mixture with residue left in the field after termination (GBL) and residue removed (GBL-Rem) and grass only (GO) mixture with reside retention were tested in irrigated systems and perennial grass (PG) instead of GO in the irrigation retiring systems. Cover-cropped systems and PG improved C storage, with 17% more soil organic carbon (SOC), 11% more mineral-associated organic C (MAOC), 80% more particulate organic C (POC), 81% more potentially mineralizable C (PMC), and 35% more microbial biomass C (MBC) than fallow plots (NCC), regardless of irrigation management. Cover cropping and PG also promoted key bacterial and fungal groups while lowering those with slow growth. Finally, we explore how microbial communities regulate soil C and N components, showing the role of some taxa in explaining C fractions variations. These findings highlight the implications of climate-smart practices on C sequestration regulation in irrigation retirement in semi-arid regions.