Soil Water Dynamic and its Response to Rainfalls in an Apple Orchard of the Loess Plateau, China: Implication for Irrigation Management

Soil water is the main water source for plants, which is replenished by rainfall in the water-limited agricultural systems. Quantifying temporal dynamics of water soil deficit and its replenishment by rainfall can evaluate whether soil water meet the water demand for plants. This would provide accurate guide for when and how the irrigation practices conducted. However, this topic has not been deeply elucidated. In this study, soil water content at varied soil depths and precipitation were continuously monitored during two growing seasons in an apple orchard in the Loess Plateau of China. Soil water storage, soil water deficit and replenishment were also quantified. The results showed that soil water content varied temporally due to the impacts of rainfalls. Soil water storage at 0 ~ 200 cm depth ranged from 272.5 mm to 355.6 mm and the degree of soil water deficit ranged from 0.34 to 0.53 correspondingly. Meanwhile, replenishment of soil water by rainfall was 13.00% in 2017 and 9.78% in 2018, respectively. The qualitative relationship between monthly rainfalls and replenishment indicated that soil water was replenished by rainwater only at soil layers shallower than 160 cm. From the temporal dynamics of soil water content and deficit conditions, soil water could meet the water demand at the fruit expanding stage of apple trees. Irrigation measures should be taken to reduce the soil drought stress at this stage. This study provided an effective hydrological basis to improve the irrigation management of orchards and the efficiency of water resource.