Water and sediment runoff and soil moisture response to grass cover in sloping citrus land, Southern China

Soil erosion is recognized as one of the major environmental problems in the hilly red soil region of Jiangxi province, southern China. An eight-year field experiment was conducted to evaluate the effects of grass cover in the sloping citrus land on water and sediment runoff. Soil moisture regimes were also analysed based on the in-situ soil moisture measurement. Four treatments were carried out in the runoff plot experiment: (1) no vegetation, bare land (BL); (2) conventional treatment, citrus without grass cover (CK); (3) citrus with strip planting of Bermuda grass (SP); (4) citrus with full cover of Bermuda grass (FC). Results showed that the annual runoff volumes were significantly (P &lt; 0.05) reduced using SP (27.2 mm) and FC (33.0 mm) compared with CK (311.4 mm) and BL (456.7 mm) treatments. The SP and FC treatments significantly (P &lt; 0.05) reduced the annual average sediment yield by as much as 99.38% to 99.67%, compared with CK treatment. Soil moisture variations at the four depths (0–10, 10–20, 20–30, and 30–40 cm) were consistent with the seasonal precipitation patterns. Within the soil profile, soil moisture content increased with depth. In 3 of the 4 depths, the soil moisture contents of SP (21.20–27.84 m³/m³, mean value) were the highest. Soil moisture contents of FC (14.92–26.30 m³/m³,<br /> mean value) were lower than in SP because of the water consumption by plant transpiration, but were still higher than those of CK (16.03–25.00 m³/m³, mean value). Based on Richards’ equation numerical model, optimization tool and observed soil moisture data, actual evapotranspiration was calculated, and water balance analysis was carried out during drought and rain periods. The results indicated that planting grass in sloping citrus land can effectively reduce surface water runoff and soil erosion and increase water infiltration, but the risk of drought, resulting from planting grass, should be noticed. Compared with FC, the drought risk of SP was much lower during the drought period, and SP contributed to storage of more water in the root zone during the rain period. In conclusion, SP was a recommendable treatment.