Design and experiment of closed culture system for solar greenhouse

Abstract: The traditional cultivation of a solar greenhouse is to use the soil, but soil-borne diseases lead to continuous cropping obstacles, and with the fertilizer going into the soil along with water, often the environment and groundwater has been polluted, so that it is impossible to achieve sustainable development. Therefore, these problems must be solved, not only as to saving water and fertilizer, but also for protecting the environment, while improving the level of automation in the solar greenhouse. So a closed cultivation system was presented.The traditional cultivation methods are with soil or substrate piled in a ridge on the ground, and crops have been planted on the ridge. In this system of digging a ditch on the ground from south to north, the width of the ditch was 35cm, the depth of the ditch was 25 cm, and the fall of ditch from south to north was about 5~10 cm. Substrate was bagged up or completely wrapped by plastic film, and then it was placed in the ditch, so the substrate was isolated from the outside world, the incidence of soil-borne diseases was avoided, and the same heat energy saved by the soil can also be used. The system designed was a wireless sensor network using the 433MHz frequency, and it developed the environment monitoring node, the microcontroller of node was PIC16F876A, and it connected sensors of SHT15, ISL29010, FDS100, and MF52.Traditional irrigation in the solar greenhouse was conducted in the following method: water irrigation first, then fertilizers were added for a period of time, and finally irrigation with water was again carried out. An integrated water and fertilizer irrigation mode was applied in this system, with the function of irrigation by controller implementation, the core of the irrigation controller was a ARM7 processor, the operating voltage was provided by the power supply module, the processor was connected with an EC measuring module, a pH measurement module, and a relay control module through the I2C bus module. The EC measurement module and pH module were respectively connected to the EC and pH measuring instrument, with measurement of the solution in a mixing fertilizer tank. The values of EC and pH detected by the electrode, were transmitted to the processor through the I2C bus. The switch of the solenoid valve was controlled by a processor based on the PID control method, and the nutrient solution was automatically mixed and adjusted according to the set value of the program. An already adjusted nutrient solution was supplied to the water lines by a pump, and every irrigation line for a greenhouse, with the irrigation lines starting and stopping regulated by a solenoid valve. The solenoid valves were controlled by a relay control module worked through the program. Any excess nutrient solution was recycled. When the water level of the recycle tank reached a certain height, the nutrient solution in the recycle tank would be pumped into the mixing tank, and then recycling was implemented.Experimental results showed that the yield of a closed culture system increased by 11.7% more than the traditional soil planting, along with saving 2% of the water and fertilizers. If the same kind of substrate case was used to achieve recycling of the nutrient solution, then 17.2% of the water and fertilizers of the closed culture system were saved. It was able to effectively enhance the degree of automation in greenhouse production, conserve resources, protect the environment, and promote sustainable development of the greenhouse industry.