Effect of no-tillage on soil aggregate and organic carbon storage

No-tillage (NT) is an increasingly agronomic practice in China. Tillage practices deeply affect soil quality and organic carbon (SOC) accumulation. The effect of NT, as a form of conservation tillage, on soil organic carbon storage had remained highly contentious. To shed further view on the effect of NT on soil structure and quality in the Huang-Huai-Hai Plain (HP), a long-term no-tillage experimental site for the main crop rotation — winter wheat (Triticum aestivum L.) and summer maize (Zea Mays L.) — was investigated. The experimental site belongs to the Yucheng Comprehensive Experimental Station (YCES) of Chinese Academy of Sciences (CAS) and has been used in studying the changes in soil aggregates and organic carbon storage under different tillage systems for 7 years now. NT, no-tillage with removed residue and organic fertilization (NTRR) and conventional tillage (CT) treatments were set up in the study. The impact of the three tillage systems on total soil organic carbon content and storage, water-stable aggregate stability, water-stable aggregate SOC content and storage, and relationship between total SOC content and water-stable aggregate SOC content were analyzed. Compared with CT, SOC content and storage, and water-stable aggregate mean weight diameter (MWD) and geometric mean diameter (GMD) along with macro-aggregate organic carbon content and storage in the 0~20 cm soil layer significantly increased in NT and NTRR treatments. This was possibly due to reduced soil disturbances and residue mulch and organic fertilizer applications. No tillage plots with residue mulch stored more SOC and macro-aggregate organic carbon than those with applied organic fertilizer. For the treatments, the order of the content of SOC and macro-aggregate organic carbon in the 20~60 cm soil depth was NT < NTRR < CT. In comparison with NT and NTRR, CT limited deep-soil organic carbon accumulation. Compared with straw mulch, the application of organic fertilizer enhanced deep-soil organic carbon accumulation under no tillage. On the average, SOC storage in NT and NTRR was lower than in CT in the 0~60 cm soil depth. There was a significant positive correlation between SOC and 0.25~2 mm aggregate organic carbon, indicating that the 0.25~2 mm soil macro-aggregates could be used as a proxy for changes in SOC. In conclusion therefore, no-tillage significantly improved the distribution and stability of surface soil water-stable aggregates. While no-tillage significantly increased the storage of surface total SOC in the 0.25~2 mm soil aggregates, reduced it in deep soil layers. Compared with organic manure, straw mulch promoted the accumulation of SOC in surface soils and reduces it in deep soils under no tillage practice.