Subsurface drip irrigation scheduling for cucumber (Cucumis sativus L.) grown in solar greenhouse based on 20 cm standard pan evaporation in Northeast China

The experiment was conducted in a solar greenhouse to determine the optimum irrigation frequency and quantity for cucumber under subsurface drip irrigation based on evaporation from a 20 cm diameter pan (Ep) placed above the crop canopy. Two irrigation intervals (I1: 4-day and I2: 8-day) and three plant-pan coefficients (Kcp1: 0.6; Kcp2: 0.8 and Kcp3: 1.0) were compared. Crop evapotranspiration (ET) and fruits yield increased with the increasing of irrigation water. The Kcp3 treatments had the highest yield, while Kcp2 had the highest irrigation water use efficiency (IWUE) and water use efficiency (WUE) values in both irrigation intervals. The yields of Kcp2 treatments decreased only 4.87% and 5.93% in both intervals though total irrigation water decreased 14.3% compared to Kcp3 treatment. Irrigation water amount significantly (P < 0.01) and positively affected the fruit number and fruit water content, whereas significantly and negatively affected the soluble sugar (SS), Vitamin C (Vc) and free amino acid (FAA) content in fruits. In conclusion, I2Kcp2 (0.8Ep with 8-day interval) was the optimum irrigation schedule for cumber plants grown in solar greenhouse under subsurface drip irrigation in arid and semi-arid areas that are in lack of water resources.