Evapotranspiration and crop coefficient of greenhouse cucumber in the Hamedan region

An experiment was conducted in a commercial greenhouse to determine cucumber (Negin cultivar) evapotranspiration and crop coefficient in two seasons of winter and spring cultivation in Hamedan province. Irrigation was done to meet 100% of the water requirement based on reaching the suction tensiometer to the field capacity (40 to 50 cm). The soil water balance was used to estimate plant evapotranspiration in the greenhouse. Stanghellini and FAO Penman-Monteith evapotranspiration methods were 214.2 and 181.5 mm in winter and 222.3 and 227.6 mm in spring, respectively. The evapotranspiration ratio by the FAO Penman-Monteith method inside and outside the greenhouse in winter and spring cultivation was 0.8 and 0.81, respectively. The actual evapotranspiration from soil water balance in winter and spring cultivation were 148.2 and 210.4 mm, respectively. The results showed that the average crop coefficient in the initial, middle, and final stages of the growing season in winter planting was 0.69, 1.43, and 1.05, and in spring planting were 0.63, 1.15, and 0.9, respectively. The results of this study showed the necessary scientific basis for optimizing irrigation and saving water consumption, creating appropriate irrigation planning, and improving the crop water use efficiency in the greenhouse. Also, by reducing excessive water consumption, it can reduce energy consumption and provide a maximum increase in product production efficiency and economic efficiency. The investigation of evapotranspiration, crop canopy growth, and humidity changes during the growing season also showed that it is necessary to prevent the development of plant diseases, to use a higher ventilation level or forced ventilation in greenhouses.