Objective The aim was to explore the impacts of the annual period of the Chengdu Plain's rice-garlic rotation on the stability of the organic carbon pool of rice and soil, which could provide the theoretical basis for the fixed and conversion of soil organic carbon in Chengdu Plain.

Method Based on the farmland of typical rice-garlic rotation with different planting years in the Chengdu Plain, four treatments were set up: rice-garlic rotation 0 year (0 a, rice-wheat rotation), rice-garlic rotation 5 years (5 a), rice-garlic rotation 10 years (10 a) and rice-garlic rotation 20 years (20 a). The effects of rice-garlic crop rotation years on the stability of soil organic carbon pool were investigated.

Result Over the 4 years, 5 a treatment had the most obvious improvement in soil organic matter, reached 0.70 - 5.75 g kg⁻¹ in the 0 - 60 cm soil layer. 20 a treatment had reduced total nitrogen and available phosphorus decreased to varying degrees in the 0 ~ 60 cm soil layer, while the contents of alkaline hydrolyzable nitrogen and available potassium increased significantly. Under the rotation system, in the 0 - 60 cm soil layer, soil dissolved organic carbon (DOC), microbial biomass carbon (MBC), and potassium permanganate easily oxidized organic carbon (POXC) contents increased in the 0 - 60 cm soil layer. The treatment of 20 a had the highest DOC content, an increase of 75.26% - 281.57% compared with 0 a. The contents of 5 a MBC and POXC were the highest, compared with 0 a, increases were 21.44% - 283.06% and 5.52% - 147.22%. The active organic carbon ratio in 5 a treatment was the highest, the proportion of activated organic carbon increased by 6.33% to 62.86% compared with that in 0 a treatment. Under different years, Carbon Management Index (CPMI) in 5 a treatment was the most, followed by 20 a. 5 a's was lowest stability, and 20 a improved compared to 5 a. The years of rice-garlic rotation reduced soil pH, which in turn affects unstable organic carbon components. Unstable organic carbon components affected the organic carbon pool stability of soil organic carbon pools to a great extent.

Conclusion Short-term (5 a) rice-garlic rotation decreases the stability of soil organic carbon pool, with more unstable organic carbon components. Long-term (20 a) rice-garlic rotation reduces soil organic carbon content and improves the stability of soil organic carbon pool, which is not conducive to the improvement of soil fertility.