Production capacity of the summer vegetables is often required for the solar greenhouses in northern regions. In this study, the temperature regulation was proposed and then validated to mitigate the severe high-temperature stress on the crops. A water circulation temperature-control system (WCTCS) was also utilized, the water as the primary medium of the heat exchange. Differential pressure and gravitational potential energy were then designed for the self-circulation. A better balance was achieved in the low-cost and high-efficiency temperature control under the greenhouse environment. There were several key components in the WCTCS. Among them, the water bags and heat exchangers were strategically placed inside and outside the greenhouse, in order to serve as the thermal storage and release units, respectively. The high- and low-level water tanks were integrated with the circulation pumps into a closed-loop network for heat management. A systematic investigation was conducted to evaluate the system’s performance and energy balance after exergy analysis. Furthermore, the comparison was also made on an experimental greenhouse that was equipped with the WCTCS and a control greenhouse with conventional natural ventilation. The results demonstrated that there was the remarkable efficacy of the WCTCS. Firstly, the internal air temperature of the experimental greenhouse was significantly lowered during peak summer high-temperature periods. The average air temperature was consistently 1.5–5.1 ℃ lower than that of the control under standard natural ventilation, with the maximum difference of the average temperature reaching 8.2 ℃. Since a slight gradient of the horizontal temperature was observed, there was a uniform vertical distribution of the air temperature, thus promoting a consistent microclimate over the crop canopy. Secondly, by analyzing the variation characteristics of the light and thermal environment inside the solar greenhouse, the maximum temperature difference between the experimental greenhouse with the water circulation temperature control system and the control greenhouse on sunny days reached 7.1 ℃. Compared with the control greenhouse, the water circulation temperature control system extended the duration within the most suitable temperature range of 22–25 ℃ by 170 min, prolonged the period within the normal growth temperature range of 20–30 ℃ by 120 min, effectively shortened the duration of high-temperature stress, and provided longer suitable temperature periods for tomatoes. Thirdly, the water circulation temperature control system operated stably, with a daily cooling capacity of 34141.4 to 49230.8 kJ provided by the gravitational potential water circulation, demonstrating good cooling buffer performance. Fourthly, the experimental greenhouse covered an area of 1536 m². Based on the analysis, it was deduced that the optimal heat dissipation effect was achieved when the number of finned-tube radiators was increased to 15 sets, the total water volume of the system was raised to approximately 25 m³, and the number of water bags was increased to 18. Finally,the water circulation during the cooling process was a closed loop, with only minimal water evaporation occurring locally in the pipeline near the water tank. As a result, the water resource recycling rate reached 95%, and the system saved 53.8% more energy compared to the wet curtain fan cooling system. In conclusion, the effective and low-cost control system of the supplementary temperature was successfully developed to provide the critical technical support for the safe production of vegetables in solar greenhouses during summer. This work can hold substantial practical and theoretical significance to extend the summer production cycle for the overall sustainability and productivity of the facility agriculture.

The shortage of water resources is a key factor restricting the sustainable development of agriculture, and the optimal allocation of agricultural irrigation water resources is of great significance to guarantee food and water security. Based on the main types of optimal allocation models of agricultural irrigation water resources, the research progress on single crop irrigation optimal decision-making, multi-crop water and soil resources optimal allocation, and canal system water resources optimal operation were systematically reviewed. In the traditional single crop irrigation optimal decision-making, the maximum crop yield or economic benefit was usually selected as the optimization objective. With the improvement of people’s living standard, consumers pay more attention to crop quality. And the optimal decision-making of water-saving irrigation theory based on the response of water and quality for improving quality of crop has gradually become a research focus. The multi-crop water and soil resources optimal allocation mainly includes the adjustment of crop planting structure and allocation of irrigation water resources in the irrigation district, which has undergone a transformation from single objective to multiple objectives, structural optimization to spatial layout optimization, and only focusing on the improvement of crop yield to the water-energy-food-ecology collaborative optimization. According to the different optimization objectives, the canal system water resources optimal operation is usually divided into two categories. Firstly, the objective is to optimize the benefit indicators of irrigation district, such as crop yield, economic benefits, water fee income of the irrigation management department, and the utilization efficiency of water and soil resources. Secondly, the objective is to optimize the operation and management indexes of hydraulic engineering in irrigation districts, such as the least water loss during the canal operation, water delivery time, differences in the continuous water diversion time of each rotating irrigation group, water shortage, and smooth water flow transition. In addition, the main problems and future research plans in the optimal allocation model of agricultural irrigation water resources were pointed out. The study suggested that the optimal allocation model of irrigation water resources should be improved in the following four aspects: 1) Building more physiological crop water-quality models; 2) Achieving optimal allocation of irrigation water resources under the scenarios of climate change and human activities; 3) Building systematic optimal allocation model of irrigation water resources that fully consider canal systems, irrigation districts, crops, and growth stages; 4) Establishing irrigation optimization decision-making models with the objective of minimum soil evaporation; Overall, this review provides valuable information for domestic researchers.