Abstract:  Agricultural facilities will be improved to be more large-scale, simplified, lighter and easier to be assembled as facility agriculture production moves towards mechanization and intensification. As the most important type of horticultural facility in northern China, solar greenhouses are mainly used for the annual production of warm-season vegetables. However, the span of solar greenhouses are mostly 8-10m, and the back wall are mainly made of clay or brick. All these result in the small cultivation area, low efficiency of wall construction and low utilization of land. In addition, plastic greenhouses have poor thermal insulation property and cannot be used in winter in northern China. Therefore, neither of these two common facilities can meet the production requirements. The large-span plastic greenhouses with external thermal insulation property are designed and put into practice. The span is extended from 8-12m to 20m and external thermal insulation system is equipped. They have a north-south orientation, steel structure skeleton and bolt connection, with the advantages of strong temperature buffering capacity, high land utilization rate, low production cost and high degree of assembly. However, the internal microclimate environment is not clear, that makes it impossible to produce scientifically. In order to find out the microclimate environment in the large-span external thermal insulation plastic greenhouse and effectively guide the cultivation. The microclimate environment, such as temperature, ground temperature, relative humidity and light conditions inside and outside the greenhouse had been monitored annually. And the application prospect of the new greenhouse had been discussed. The calculation showed that new plastic greenhouse had good heat-insulating property in winter. The average temperature indoor in January was 10.9℃, and the average ground temperature indoor was 12.7℃. The lowest indoor temperature was 6.8℃, and the lowest indoor ground temperature was 12.3℃, which were 8.9℃ and 9.5℃ higher than the open ground. In summer, the air and ground temperature in the shed was higher than the open field, but the raise of air temperature was smaller, and the ground temperature was slightly larger. The relative humidity in the shed was large, which was close to saturation in the day and night during November to following February. The light transmittance of the shed was 51.8%-67.5% in sunny days. There was a moving shadow band of 2.0-3.5m wide. The study showed that microclimate environment in the new greenhouse could basically meet the requirements of warm-season vegetables. In some areas of Zhumadian city, large-span external thermal insulation plastic greenhouses could basically meet the environmental conditions required for thermophilic fruits and vegetables, and could be used for their annual production.

Key words:  Wide-span, External thermal insulation, Plastic greenhouse, Temperature, Relative humidity, Light intensity