Carbon sequestration and mineralization in soil aggregates under long-term conservation tillage in the North China Plain

Understanding the process of soil organic carbon (SOC) sequestration and mineralization in aggregates is pertinent to mitigate climate change and minimize risks of soil degradation. Thus, soil samples were obtained after a 10-year field experiment to identify the influences of tillage on aggregate-associated SOC sequestration and mineralization in the North China Plain (NCP). Four tillage practices investigated were as follows: no-till with straw retention (NTS, conservation tillage), rotary tillage with straw incorporation (RTS), conventional tillage with straw incorporation (CTS), and conventional tillage with straw removal (CT). Significantly negative correlations were observed between SOC concentration and potentially mineralized carbon in aggregates under different treatments for the 0-10 cm soil layer. The large macro-aggregates ( > 2 mm) with the highest proportion of size distribution represented the major pool of SOC stock (47.3-51.2%) and mineralization amount (38.2-43.6%) in the 0-30 cm layer, followed by that in the small macro-aggregates (0.25-2 mm), regardless of tillage practices. However, the mineralization quotient (mineralization per unit SOC concentration) of macro-aggregates ( > 0.25 mm) was lower than that for the other size classes. The NTS enhanced the macro-aggregate formation in the 0-20 cm layer and associated SOC concentration in the 0-10 cm layer. Furthermore, NTS decreased total potential mineralization in the 0-30 cm layer compared with the other tillage practices, attributed to decrease in the large macro-aggregates (30.0-51.4%) with low particulate organic carbon (POC) concentration. The NTS with low straw inputs had higher incremental efficiency with straw incorporation than that in the RTS and CTS by 45.0% and 13.5%, respectively (P < 0.05). Overall, the higher proportion of macroaggregates recorded under NTS decreased carbon mineralization, and consequently, increased incremental efficiency with straw incorporation, and improved SOC sequestration in the surface soil layer in the NCP.