The effects of the soil environment on soil organic carbon in tea plantations in Xishuangbanna, southwestern China

Increasing soil organic carbon (SOC) reserves in agricultural land is important for mitigating global climate change. The soil environmental factors that affect SOC storage in agricultural cultivation are relatively easy to manage, but the effects of these factors on SOC have not been studied systematically, especially the relative weight of each factor is still unclear. In this study, more than 30 soil environmental factors including SOC, soil physical and chemical properties, mineral types, and microorganisms present in the 0-140 cm soil layer were determined hierarchically within tea plantations. The main and secondary factors affecting SOC storage were then analyzed quantitatively using a structural equation model. The most important factors affecting SOC storage in tea plantations included water content (18.9 %), total nitrogen (N, 18.8 %), oxalate-extractable iron (active iron, poorly crystalline iron, Fe-ox, 16.3 %), sulfur (S, 13.1 %), total phosphorus (P, 8.6 %), calcium (6.1 %), oxidation reduction potential (5.4 %), clay (4.5 %), bromine (4.3 %), and manganese (4.0 %). Variations in soil temperature and pH on this small scale were small and thus these factors had negligible effects on SOC storage in this study. Organic fertilizer application increased C, N, S, and P concentrations, which can contribute to SOC storage. Appropriate irrigation can also improve SOC storage. We identified a set of Fe-N-S-P coupling mechanisms that promoted SOC storage. Soils with high Fe, N, and S concentrations, high water content, and high oxidation reduction potential relate to an increased Fe-ox concentration, which is important for enhancing SOC stability. Therefore, the application of magnetic (iron oxide) fertilizer to increase Fe-ox in soil promotes SOC storage.