Field and Modeling Study on Manual and Automatic Irrigation Scheduling under Deficit Irrigation of Greenhouse Cucumber

The primary goal of all those working in the field of sustainable water management, particularly in the arid and semi-arid zones, is to increase irrigation efficiency, reduce irrigation water losses, and improve water productivity for all crops. This study assessed the automatic irrigation scheduling and irrigation management on the growth, yield, and water productivity of cucumber under greenhouse conditions. A field experiment was conducted using cucumber grown in aplastic greenhouse during the winter of 2017/18 and 2018/19 at the research farm station of the National Research Centre (NRC), El-Noubaria Region, Behaira Governorate, Egypt. In a split-plot experiment, two different methods to control irrigation scheduling (manual control (MC) and automatic control (AC)) were used in the main plots and three deficit irrigation treatments (100% of full irrigation (FI), 80% of FI, and 60% of FI). Through the obtained results, it was found that the use of the automatic control of the irrigation schedule led to an improvement in the productivity and quality characteristics of the cucumber crop. Automatic irrigation control created healthy conditions for the plant roots located under the least water stress. This led to an increase in nitrogen uptake at the ages of 3, 5, 7, and 9 weeks after planting in addition to improving the total leaf area and the chlorophyll content of leaves, which consequently had a greater effect on increasing yield and water productivity of cucumber. Although the highest values of cucumber productivity were obtained with irrigation at 100% of FI, there were no significant differences between 100% FI and 80% of FI, therefore it is preferable to irrigate at 80% of FI, and this means saving 20% of irrigation water that can be used to irrigate other areas. The SALTMED model simulating all of the following evaluation criteria performed well for soil moisture content and N-uptake as well as the leaves area, the yield, and water productivity of cucumber for all treatments for the two growing seasons 2017/18 and 2018/19, with the overall R-2 of 0.882, 0.903, 0.975, 0.907, and 0.933, respectively.