Objective To investigate the regulation effects of green manure cover on soil water and heat dynamic characteristics and rainfall response in citrus orchards, with the aim of providing a scientific basis for green manure selection and rainfed water-saving management.

Method Using a citrus orchard at the Lijian Experimental Base of the Guangxi Academy of Agricultural Sciences in Wuming, Guangxi, as the study site, four green manure cover treatments were established: Vicia villosa (T1), Raphanus sativus (T2), Arachis pintoi (T3) and mixed sowing (T4). Soil moisture and temperature in the 0−20 cm and 20−40 cm layers were continuously monitored from February to June 2025. Clean tillage (CK) was used as the control. Soil moisture and temperature changes in the 0−20 cm and 20−40 cm soil layers were continuously monitored from February to June 2025. By integrating data on typical rainfall events with citrus yield and fruit quality indicators, this study analyzed the effects of different green manure cover treatments on soil water and heat dynamics, rainfall response characteristics, and citrus growth.

Results (1) Grass manure cover significantly altered the soil moisture dynamics. Under the T3 treatment, soil moisture in the 0−20 cm layer exhibited a “sawtooth-like” fluctuation , ranging from 2.66%−43.61%, indicating the strongest water retention in the surface layer. Under the T2 treatment, soil moisture in 20−40 cm layer was maintained within 5.12%−33.53%, showing a clear advantage in deep-layer water replenishment, characterized by a “dry upper layer and moist lower layer” pattern. (2) Compared with the CK treatment, grass manure cover played a significant role in buffering temperature fluctuations. Among the treatments, T4 showed the best performance in maintaining higher temperatures in early spring and cooling in summer.Compared with the clean tillage treatment, green manure cover played a significant role in buffering soil temperature fluctuations. Among the treatments, T4 showed the best performance in maintaining higher temperatures in early spring and warming the lower soil layer during summer. (3) Green manure mulch significantly improved soil moisture conditions in citrus orchards during rainfall events. Under light and moderate rainfall conditions, it primarily helped retain moisture and slow evaporation, while under heavy rainfall conditions, it promoted rainfall infiltration and deep-layer water storage. Specifically, the T3 and T2 treatments exhibited higher soil moisture content in the 20−40 cm soil layer, demonstrating stronger deep-layer water retention capacity. (4) Green manure coverage significantly increased single-tree citrus yield and improved certain fruit quality traits, with the T3 treatment achieving the highest average yield.

Conclusion Green manure cover can significantly improve the soil hydrothermal environment in the root zone of citrus orchards, enhances rainfall regulation and storage capacity, and slow the rate of soil moisture depletion. Citrus yield and fruit quality varied among different green manure coverage treatments. Arachis pintoi was the most effective for yield improvement, Raphanus sativus and mixed coverage performed better in enhancing fruit quality. Proper selection of green manure coverage can simultaneously optimize soil moisture retention and citrus production. These findings provide practical guidance for the scientific selection of green manure and efficient water resource management in citrus orchards in the hilly regions of southern China.