Developing a Subsurface Drip Irrigation Scheduling Mode Based on Water Evaporation: Impacts Studies on Cucumbers Planted in a Greenhouse in the North China Plain

China is a country short of water resources, and improving the water use efficiency (WUE) in agriculture has become the only way to ensure sustainable development. In this article, subsurface drip irrigation (SDI) experiments of cucumber were implemented with a randomized block design comprising two factors and three levels, and the two factors were depth of drip belt buried and irrigation amount, which were determined by a 20 cm diameter pan's water evaporation times its coefficient (K-p). The effects of schedule of SDI on soil evaporation (E-s), evapotranspiration (ET), K-p, root dry matters, yield, and WUE of cucumber were studied. The results indicated that the E-s and the ET decreased along with increasing depth of drip belt buried or decreasing amount of irrigation water applied. The relationships between ET and its total irrigation amount were significant linear positive correlations. Proportions of plant transpiration accounting for the ET were about 41 similar to 69% in two years, and it became bigger along with the increase of ET within a year. The Kp became smaller along with the reducing of ET. The roots of cucumber were mainly concentrated in the soil layer of 0 similar to 20 cm, and the two factors could only influence root dry weights of 0 similar to 60 cm soil layers significantly. The relationships between yield and ET were quadratic polynomial correlations. At last, an ultimate SDI scheduling mode based on water evaporation was established.