Characteristics of carbon mineralization and accumulation under long-term conservation tillage

Abstract

Conservation tillage has been widely practiced to increase soil organic carbon (SOC), and reducing SOC mineralization has the potential to improve accumulation. To assess the effects of conservation tillage on characteristics of SOC mineralization and accumulation, as well as their relationship, a site experiment was established in 2008 using data from 2012 to 2019 under wheat-maize cropping system. Four treatments were investigated: no-till with straw retention (NTS, conservation tillage), no-till with straw removal (NT), conventional tillage with straw incorporation (CTS), conventional tillage with straw removal (CT). The results showed that NTS significantly improved SOC concentration than the other treatments at 0–10 cm soil depth (P < 0.05) by 5–18% in 2012 and 31–93% in 2019 (increasing increments over time). There was a negative correlation (R2 = -0.60) between SOC concentration and mineralizability. On average, the SOC mineralizability under NTS was 39.0 mg C kg−1 SOC at 0–10 cm depth, significantly lower than CTS and CT (P < 0.05). Furthermore, relative SOC mineralizability of NT/NTS, CTS/NTS, and CT/NTS was>1 and showed a linear relationship with time, indicating that NTS can increase SOC accumulation by reducing SOC mineralizability over time. A negative correlation was observed between SOC mineralizability and mean weight diameter (MWD) (R2 = -0.34), and the highest MWD under NTS, suggesting reduced mineralizability due to enhanced physical protection of soil macro-aggregates. Furthermore, the particulate organic carbon (POC) concentration was highly correlated with MWD (R2 = 0.76). Conclusively, results elucidated that higher POC under conservation tillage contributed to the macro-aggregate formation and aggregate stability at 0–10 cm depth, and thus protected SOC from mineralization, and additional SOC sequestration could be accelerated by improving the duration of conservation tillage.