Effects of different crop covers on vertical groundwater recharge

Irrigation infiltration is the main source of recharge for groundwater in the Weining Plain. Studies of groundwater recharge from irrigation under different crop covers are important for the accurate evaluation of groundwater resources. In this study the Hydrus-1D is used to simulate the moisture migration in the vadose zone using the observation data of two in situ experiments which were carried out in Zhongwei and Zhongning. The effects of four factors, such as the single irrigation amount, growth duration, maximum root depth and leaf area index, on groundwater recharge via infiltration are analyzed. The groundwater recharge via vertical infiltration during the different crop planting periods is calculated. The results suggest that the groundwater recharge via infiltration mainly comes from irrigation. The single irrigation amount has the most significant effect on the groundwater recharge via infiltration, followed by growth duration and the maximum root depth. The leaf area index has the smallest impact on it. With the increasing groundwater depth, the impact of crop factors on groundwater recharge will also increase. The coefficients of recharge from rainfall in different periods range from 0.02 to 0.25, which is greatly affected by the rainfall amount and frequency. The coefficient of recharge from irrigation is closely related to crop species which is 0.78 in the maize planting period, 0.51 in the eggplant planting period, and 0.6-0.63 in the Lycium barbarum planting period. Considering the crop type and groundwater depth (117-267 cm) in the study area, the reference value of coefficient of recharge from irrigation under the condition of single irrigation amount ranging from 50 mm to 150 mm is given.