Soil organic carbon trade-offs under conservation tillage: Carbon stock versus stability mediated by particulate and mineral-associated fractions

Conservation tillage (CS) has been widely applied to maintain the sustainability of agricultural systems. Soil organic carbon (SOC) fractions, including particulate organic carbon (POC) and mineral-associated organic carbon (MAOC), facilitate the comprehension and prediction of further dynamics of SOC. However, there is a limited understanding of how CS affects the interplay of SOC fractions stocks and SOC stability (POC:MAOC ratio, briefly noted as P/M ratio) across soil layers. Herein, we conducted a meta-analysis to quantitatively examine CS-induced changes in the SOC fractions stocks and their stability in the two depth soil layers (0–10 cm for upper topsoil and 10–20 cm for lower topsoil) under varying climatic factors, initial soil conditions, and agronomic practices. Our findings indicate that relative to conventional tillage (CT), CS notably increased SOC stock (14.7 %) in the upper topsoil by increasing POC stock (27.4 %), while decreasing SOC stability (P < 0.01). Adverse changes were observed in the lower topsoil layer. Experiment duration, straw-C input rate, and cropping system were the key factors moderating POC and MAOC stocks and SOC stability under CS (P_M < 0.05). The positive effects of CS on SOC stock and its stability diminished with duration time in the upper topsoil layer. Conversely, CS significantly decreased POC stock (- 9.2 %) and enhanced SOC stability in the lower topsoil layer (P < 0.01). Compared to CT, the highest SOC stocks and the lowest SOC stability were observed under CS in the C input range of 4–6 Mg C ha⁻¹ yr⁻¹. Our results highlight the importance of soil depth- and duration-induced differences in the accurate estimation of SOC stocks and stability dynamics under CS. The balance between SOC stock and its stability is calling for more attention.