Characteristics of Soil Organic Carbon Mineralization and Its Influencing Factors Under Long-Term Conservation Tillage

This study aimed to investigate the characteristics of soil organic carbon (SOC) mineralization and its influencing factors under different tillage practices, clarify the stability of OC under conservation tillage, and reveal the transformation patterns of C, so as to provide a scientific basis for farmland management in arid areas.

This study utilized a long-term conservation tillage field experiment established in 1999 in Luoyang, Henan Province. Three treatments were selected: conventional tillage with straw removal (CT), subsoiling with straw mulching and incorporation (SS), and no-till with straw mulching (NT). Soil samples were collected from the 0-10 cm, 10-20 cm, and 20-30 cm soil layers. Soil physicochemical properties and carbon mineralization were measured, and the characteristics of SOC mineralization and its influencing factors were analyzed.

After 26 years of continuous contrasting tillage practices: (1) Compared with CT, NT significantly increased soil nutrients, soil water content (SWC), redox potential (Eh), and microbial biomass carbon (MBC) content in the 0-10 cm layer. SS significantly increased soil nutrients, SWC, and bulk density (BD) in the 10-20 cm and 20-30 cm soil layers, while significantly decreasing soil inorganic carbon (SIC) content in the 0-10 cm and 10-20 cm soil layers. (2) Compared with CT, SS significantly increased the content of SOC, particulate organic carbon (POC) and its fractions, and mineral-associated organic carbon (MAOC) across 0-30 cm soil layers. NT significantly increased the content of SOC, POC, fine particulate organic carbon (f-POC), and MAOC in the 0-20 cm layers by 10.8%-20.6% compared with CT. (3) Compared with CT, both SS and NT significantly increased SOC stocks across 0-30 cm soil layers by 10.2%-56.2%. The SOC sequestration rates under SS were significantly higher than under CT by 245.7% (1999-2015), 20.3% (1999-2019), and 35.8% (1999-2024). (4) Compared with CT, SS significantly reduced the initial and final cumulative SOC mineralization in the 0-10 cm and 20-30 cm layers. NT significantly reduced the initial and final cumulative SOC mineralization in the 10-20 cm soil layer. (5) Partial Least Squares Path Modeling (PLS-PM) analysis revealed that soil physical properties (pH, SWC and BD) had a direct negative effect on MBC (path coefficient =-0.82), and indirect positive effects on MAOC (0.11) and POC (0.33). MBC had an indirect positive effect on the SOC mineralization rate (0.27) and cumulative mineralization (0.28).

Continuous SS practice for 25 years reduced MBC content, decreased SOC mineralization, and promoted SOC accumulation and soil fertility enhancement. MBC and MAOC were key driving factors influencing SOC mineralization.