Zero Discharge of Nutrient Solution to the Environment in a Soilless Greenhouse Cucumber Production System

With the development of the economy and society, more attention is being paid to energy costs and the potential environmental pollution caused by vegetable cultivation. The aim of this study was to investigate the impacts of zero discharge of nutrient solutions on cucumber growth, leaf photosynthesis, and the yield and quality of cucumber under greenhouse conditions. The results show that zero discharge treatment did not change plant height, stem diameter, internode length, leaf area, net photosynthetic rate (P_n), stomatal conductance (G_s), intercellular CO₂ concentration (C_i), transpiration rate (T_r), and leaf relative chlorophyll content on the most measurement days. Only P_n and relative chlorophyll content were significantly reduced after 16 days of treatment but soon recovered over time. Cucumber plants can adapt to treatment circumstances over the course of days. Leaf mineral element contents showed significant differences on some treatment days compared to the control, and trace elements of Fe, Mn, Cu, and Mo can be appropriately supplied during the treatment days. The cucumber yield and fruit quality in the zero discharge treatment did not change during the whole experimental period. This study confirmed that the irrigation method of a nutrient solution with zero discharge can be applied in cucumber cultivation practices. The strict management of irrigation strategy, plant growth, and greenhouse climate are very important for zero discharge cultivation. The cultivation method with zero discharge of nutrient solution can reduce the energy costs of disinfection, save water and fertilizers, and reduce the environmental pollution in cucumber cultivation.