The characteristics and influencing factors of soil organic carbon sequestration of different maize straw returning years under the shallow buried irrigation

The soil organic carbon sequestration characteristics and influencing factors of maize straw returning years under shallow drip irrigation were explored. Based on seven consecutive years of field positioning experiments, treatments of 0 year (0a), 3 years (3a), 5 years (5a) and 7 years (7a) of full straw returning were applied to study the effects of straw returning year on soil structure, extracellular enzyme activity, carbon components content, storage, sequestration and pool management index. Compared with 0a, the generalized soil structure index in 0−30 cm soil layer of 3a, 5a, 7a respectively increased by 1.65%, 1.99%, 3.33%, and the soil three-phase structure distance respectively decreased by 5.55%, 6.65%, 12.7%; the activities of β-1,4-N-acetylglucosamine glycosidase and β-glucosidase in 0-30 cm soil layer of 3a, 5a, 7a respectively increased by 4.33%, 13.0%,15.9% and 12.1%, 16.2%, 20.8%, and the activities of cellulase and sucrase in 0 - 30 cm soil layer of 3a, 5a, 7a also respectively increased by 5.79%, 13.7%, 19.2% and 12.4%, 20.5%, 32.6% as well; the geometric mean enzyme activity and total enzyme activity of different treatments were significantly different, and the geometric average enzyme activity and total enzyme activity of 3a, 5a, 7a in the 0−30cm soil layer respectively increased by 8.62%, 15.89%, 22.13% and 9.11%, 17.06%, 24.84%. The content and storage of soil organic carbon, oxidized organic carbon, water-soluble organic carbon and microbial carbon in 3a, 5a and 7a treatment were all significantly higher than those of 0a, and compared to 0a, the content of soil organic carbon and easily oxidizable organic carbon in 0−30 cm soil layers of 3a, 5a, 7a respectively increased by 13.4%, 32.7%, 42.7% and 17.5%, 27.5%, 42.5%, and the content of soil water-soluble organic carbon and microbial carbon also respectively increased by 13.2%, 18.5%, 28.5% and 33.9%, 45.3%, 56.1% as well; the storage of soil organic carbon and easily oxidizable organic carbon in 0-30 cm soil layers of 3a, 5a, 7a respectively increased by 11.6%, 29.5%, 36.2% and 14.9%, 23.8%, 35.5%, and the storage of water-soluble organic carbon and microbial carbon also respectively increased by 10.7%, 15.2%, 22.3% and 31.0%, 41.0%, 48.5% at the same time. The soil carbon sequestration in 0-30cm soil layer of 5a and 7a were significantly higher than those of 3a. There were significant differences in the carbon pool index and carbon pool management index of each treatment in the 0~30 cm soil layer, and the carbon pool index of 5a and 7a respectively increased by 17.0%, 26.1% and 7.00%, 19.9% compared with 3a. Redundancy analysis and correlation analysis of influencing factors and soil organic carbon sequestration showed that the soil β-1,4-N-acetylglucosaminidase activity, liquid phase volume fraction, soil three-phase structure distance, soil cellulase activity and soil β-glucosidase activity were the main factors affecting soil organic carbon sequestration at different years of straw returning, and the explanation rates were 76.0%, 4.10%, 3.30%, 1.70% and 3.40%, respectively (P<0.05). Under shallow buried drip irrigation, maize straw continuous returning for seven years improved the stability of soil structure and the activity of soil extracellular enzymes related to soil carbon, promoted the decomposition and transformation of returned straw by soil microorganisms, and thus improved the soil organic carbon sequestration and carbon pool index.