Soil organic carbon recovery and soil health in semi-arid drylands with years of transition to perennial grasses

Semi-arid drylands face unique challenges for sustainable land management and soil carbon (C) sequestration due to significant depletion in soil organic carbon (SOC) storage, increasing water scarcity, and climate change. Restoring perennial grasses could regenerate these lands, enhancing SOC storage and soil health. This study investigated the SOC recovery potential, C saturation limit, and time required for the saturation in semi-arid drylands with perennial grass sequences. Soil samples were collected from 0 to 15 and 15–30 cm depths of an annual winter wheat system (AWWS) and three perennial grass sequences, i.e., 3-years of perennial grass (3YPG), 6-years of perennial grass (6YPG), and 20-years of perennial grass (20YPG), each replicated four times. Results reveal significant depth-dependent variations in soil parameters while maintaining the ranking of 20YPG > 6YPG > AWWS > 3YPG in SOC storage at 0–15 cm soil depth. Linear regression analysis showed a SOC sequestration rate of 0.46 Mg ha⁻¹ yr⁻¹ across grass sequences. Total nitrogen (TN), potentially mineralizable nitrogen (PMN), mineral-associated organic carbon (MAOC), and particulate organic carbon (POC) accumulated at rates of 0.04 Mg ha⁻¹ yr⁻¹, 0.34 kg ha⁻¹ yr⁻¹, 0.24 Mg ha⁻¹ yr⁻¹, and 0.22 Mg ha⁻¹ yr⁻¹, respectively, across all treatments in the surface soil layer. A regression model predicted that the 20YPG field would reach MAOC saturation in approximately 80 years at the 0–15 cm depth and 230 years at the 15–30 cm depth if the current condition persists. This research shows the enormous potential of SOC sequestration in arid and semi-arid drylands with grassland restoration. It also underscores the significance of perennial grass systems in enhancing soil health and SOC sequestration. Identifying grass species producing high, economically useful biomass in water-limited semi-arid environments may provide agricultural sustainability and climate change solutions for dry regions.