Effects of winter cropping patterns on soil organic carbon fractions and the carbon pool management index in topsoil of paddy soil

Clarifying the effects of different winter cropping patterns on the variations in soil organic carbon (SOC) fractions and rice grain yields can provide a theoretical basis for green and sustainable agricultural production in the rice-growing areas of China. In this study, conducted in the Hanzhong Basin in southern Shaanxi Province, we quantitatively examined the effects of different winter planting patterns winter fallow as a control and winter planting of rape (Ra), Chinese milk vetch (Mv) and hairy vetch (Hv) on SOC, total labile organic carbon (TLOC), high labile organic carbon (HLOC), medium labile organic carbon (MLOC), low labile organic carbon (LLOC), recalcitrant organic carbon (ROC), carbon pool management index (CPMI), and rice grain yields. The results revealed that compared with the control, the average annual rice grain yield under Hv was significantly increased by 6.6%, although we detected no significant differences among Hv, Mv, and Ra. Furthermore, compared with the control, the cultivation of Hv and Mv contributed to significant increases in SOC contents of 12.4% and 8.4%, and increases in TLOC contents of 19.6% and 13.7%, respectively. However, compared with the control, we detected no significant differences in the contents of SOC and TLOC under the Ra treatment. In addition, compared with the control, the growth of Ra, Mv, and Hv resulted in significant enhancements of HLOC contents of 12.5%, 26.1%, and 37.0%, respectively. Similarly, under the Mv and Hv treatments, there were significant increase of 10.0% and 14.4% in the contents of MLOC, respectively, relative to those under the control conditions. Moreover, compared with the control, we recorded significant increases of 14.8% and 29.4% in the CPMI under the Mv and Hv treatments, respectively. We also found that under the Hv treatment, the CPMI value was 19.4% higher than that in plots sown with Ra. Our findings thus indicate that in paddy fields of the Hanzhong Basin in Shaanxi Province, winter planting of green manure, particularly the winter planting of hairy vetch, can simultaneously achieve increases in rice grain yield and enhanced soil carbon sequestration, which is conducive to the green and sustainable utilization of paddy fields in this region and the realization of China’s goal of carbon neutrality.