Microclimate Inside Sunlight Greenhouse in Semi arid Rain Feed Region in Loess Plateau

Monitoring and analysis on microclimate inside sunlight greenhouse are carried out in semi arid rain feed region which lies in Loess Plateau. The results show that during the whole growing period of autumn planting cucumber, the daily mean air temperature maintains between 12—23.5 ℃ with falling fluctuately, which is very in accordance with the cucumber growth demand of high temperature in the prophase and low temperature in the anaphase. The ground temperature also falls wavily in general. Relative humidity, which keeps between 52.4%—93.4%, increases before the initial gathering period, but declines wavily after widespread gathering period. These three factors all change along with the variation of height and horizontal position in the greenhouse. In different growing period of autumn planting cucumber, the trend and fluctuation of daily variation of climate factors are basically similar, but variation degree is different and the time that peak value appears in a day is different too. In the upright direction inside the greenhouse, the air temperature and relative humidity (RH) are distinct at different height (0.5 m, 1.0 m and 1.5 m above the ground respectively). The air temperature increases gradually from 0.5 m to 1.5 m. In other words, air temperature inversion phenomenon occurs. However, RH is the opposite, which is smaller in the upper level than that in the lower level. In this way, there is a microenvironment of low temperature and high humidity at 0.5 m in comparison with 1.5 m, where there is a microenvironment of high temperature and low humidity. The daily variation of air temperature and RH is sharp relatively. In addition, ground temperature and its daily variation are obviously different in different depths (10 cm, 30 cm and 50 cm under the ground respectively). The variation of ground temperature at 10 cm level is most sensitive and its variation degree is the biggest among 10 cm, 30 cm and 50 cm. It has less variation degree on the ground temperature at 30 cm under the ground. In comparison with 10 cm and 30 cm, it has little variation in a day of the ground temperature at 50 cm level, where it is in a state of low temperature all the time. There is a clear lag effect in ground temperature when comparing with air temperature. The appearing time of maximum temperature of 10 cm depth soil is delayed about 5 hours than air temperature, and the delaying degree is more than that of the air temperature outside the greenhouse and the observation data in the weather station. A longer delaying time occurs at the 30 cm depth ground temperature, which reaches more than 7 hours.In horizontal direction inside the greenhouse, the air temperature and ground temperature in the south are higher than that in the north. RH is the reverse, that is to say, RH is lower in the south than that in the north. But these differences are very small, it is regarded approximately that the distribution of temperature and RH in horizontal direction is relatively evenly distributed. It is fit to the planting of vegetation.