Study On Key Technologies For Closed Cultivation Systems In Solar Greenhouses

Facility horticulture which has advantages such as high land utilization rate, short production cycle and high technical content is an important form of production from transition agriculture to modern agriculture. In recent years, with the growing of vegetables consumption demand, the government has gradually increased the attention and support on protected horticulture and horticultural facilitie.Facility horticulture in China has a total area of3.862millions ha, accounting for more than85%total planting area of the world by the end of2014. Solar greenhouse is an important component of horticulture, as it is suitable for vegetable production in cold regions of northern of China. Hence, the number of construction areas of solar greenhouse has been increasing year by year. The area of solar greenhouse accounting for about25.2%of the total area of protected horticulture is0.9742million ha at the end of2014. But there are some problems including soil borne disease, soil cultivation in China solar greenhouse, soil borne disease, continuous cropping obstacles, environmental pollution, low resource utilization and so on by the soil cultivation. These problems have seriously restricted the sustainable development of solar greenhouse. In order to solve this problem, the advanced technology for the greenhouse management should be learnt from the other countries and research on closed cultivation in solar greenhouse should be consider with the actual situation in China.The research project was supported by National Natural Science Foundation and the University PHD Subject on Special Scientific Research Fund.The main research works are as follows:(1)The research of construction method for the closed cultivation of solar greenhouseA method for constructing a closed cultivation system for solar greenhouse was presented and the system was designed. There are three subsystems included:close cultivation system which integrated substrate cultivation subsystem, environment monitoring subsystem and integrated management subsystem of water and fertilizers for the control and irrigation.It was realized that the effective separation of root zone and the external environment, and the nutrient solution could be recycled. It has shown that the closed cultivation model efficient than the traditional soil cultivation in the use of water, yield and efficiency of fertilizer by the results of experiment. There are certain advantages in the closed cultivation to achieve the water saving and fertilizer saving, and environmental protection.(2) The research of equipment for Environment control, water and fertilizer control and irrigation controlThe equipment for the Environment control, water and fertilizers control, and irrigation control was designed. The equipment can not only regulate the environment control, but also automatically implemented nutrient solution control and irrigation control. There were two aspects included in regulation of nutrient solution:water and fertilizer ratio and irrigation control. The regulation of nutrient solution was implemented with the greenhouse environment and crop growth condition monitoring information based on the environment perception system, and the regulation according to the EC value and pH value. The irrigation control can be carried out automatic by the various control modes. (3)The control method for solar greenhouse environment based on temperature integral algorithm The microclimate environment of solar greenhouse was controlled by using temperature integral algorithm. The expected average temperature value was determined according to the crop varieties and growth stages, and then24hours per day was divided into several periods with shorter length, finally the temperature control point for each period was calculated using temperature integral principle. So the microclimate environment of solar greenhouse was controlled combined with the actual temperature by the calculation result of calculation. The results of the experiment shown that the energy consumption for the solar greenhouse heating in winter was reduced compared with threshold control method in manufacturing solar greenhouse, and it had obvious energy saving effect.(4) The regulation of nutrient solution based on incremental PID control and improved Smith predictorThe two order delay system model for the nutrient solution fabrication was established, and the ratio of nutrient solution was controlled using incremental PID control and improved Smith predictor based on the model. The output of the incremental PID control is Au(k) which amounts of changes in value, and it is related to e(k) which is the system error at the sampling time, e(k-1) which is the system error at the last sampling time, and e(k-2) which is the system error at the first two sampling time.As a result the system overhead was reduced and the calculation time was saved. There was some time delay when nutrient solution was made, but the time delay would be compensation if a gain adaptive Smith predictor was added to the incremental PID control model. And the stability of the ratio of nutrition model would be increased too.(5)The method of adaptive control for nutrient solution irrigation based on Neural NetworkThe evapotranspiration calculation model was made using temperature, relative humidity and solar radiation based on neural network method. The evapotranspiration was calculated using the environment parameters in the last216hours, and the irrigation program was implement when the value of evapotranspiration was calculated by model reached the threshold, then the truly evapotranspiration would be drew by the difference between the actual and the discharge amount of evapotranspiration. So the evapotranspiration calculation model was circuit training and modified through the error of the actual evapotranspiration and crop evapotranspiration model, then the adaptive irrigation of nutrient solution was implemented.