Effects of Different Regulation Measures on Soil Agronomic Properties, Labile Organic Carbon Content, and Humus Composition in Camellia Oil Plantations

To evaluate the effects of different regulation measures on the soil agronomic properties, labile organic carbon content, and humus composition of oil tea plantations in Ninghua County, five regulation measures were designed as application of biochar-based organic fertilizer alone（T1）, planting Chamaecrista rotundifolia alone（T2）, planting Indigofera amblyantha Craib alone（T3）, biochar-based organic fertilizer combined with planting Chamaecrista rotundifolia（T4）, and biochar-based organic fertilizer combined with planting Indigofera amblyantha Craib（T5）, with a control treatment（CK）receiving no regulation measures. The results showed that:（1）Compared with the control（CK）, the fertilization, grass planting, and combined fertilization-grass regulation treatments（T2–T5）all significantly（P＜0.05）increased soil pH value, organic matter content, and total and available nutrient contents. Specifically, soil pH value increased by 0.11–0.39 units, organic matter content by 7.96%–69.79%, total nitrogen, phosphorus, and potassium contents by 159.09%–327.27%, 15.71%–104.29% and 67.77%–103.62%, respectively, and available nitrogen, phosphorus, and potassium contents by 126.00%–299.08%, 17.23%–120.95% and 58.63%–135.10%, respectively.（2）The application of biochar-based organic fertilizer, grass planting, and combined fertilization-grass regulation had positive effects on soil labile organic carbon in oil tea plantations.（3）The application of biochar-based organic fertilizer, grass planting, and combined fertilization-grass regulation measures increased soil humus content and its components, thereby improving soil organic matter content and quality. Comprehensively considering planting and fertilizer costs, the optimized soil regulation measures for the Camellia oleifera plantation in Ninghua County was biochar-based organic fertilizer with planting Chamaecrista rotundifolia, i.e., applying 3 kg of biochar-based organic fertilizer per Camellia oleifera tree（trench application with a wide and depth of 30 cm）, while simultaneously planting Chamaecrista rotundifolia（row sowing with a plant and row spacing of 30 cm）.