Due to its good airtightness, the greenhouse cannot emit the evaporated water under the control of the facilities under non ventilated conditions, resulting in high air humidity. The relative humidity often ranges from 80% to 90%, and sometimes reaches 100% at night, often in a saturated state, providing conditions for the occurrence and development of diseases, which is extremely unfavorable for vegetable growth. Generally, the temperature is low at night and the relative humidity is high; During the day, the temperature is high and the relative humidity decreases; The relative humidity increases on cloudy and rainy days; The relative humidity decreases on sunny and windy days; When the soil humidity is high, the relative humidity of the air increases. A portion of the moisture in soil vapor condenses into small water droplets on the inner surface of the cover, and a portion is emitted into the atmosphere. The water droplets drip back into the soil from around the cover, causing uneven distribution of water within the protected area, with high humidity around or in front of the area and low humidity in the middle or behind. Therefore, in terms of management, it is necessary to separate the front and back, and pour more if necessary, and less if not.
Humidity condition adjustment: mainly open the sunroof and let out the top and waist wind, do not let out the foot wind to prevent damage to the seedlings. If the humidity is too low, it is not conducive to the normal process of assimilation. Measures such as sealing, reducing wind resistance, watering, and spraying water can be taken to improve soil and air humidity.
Reasonable irrigation is the main measure to regulate humidity. The frequency and amount of irrigation should vary depending on the production season, soil moisture level, and climatic conditions. When the external temperature is high, the amount of watering can be appropriately increased according to the drought situation; In cold seasons, to prevent the decrease of ground temperature and air temperature, small water should be used as the main method, and excessive water should be avoided. The watering time should be chosen between 10:00 am and 12:00 pm in order to cooperate with ventilation to remove excess moisture and reduce the relative humidity of the night air.
Furthermore, covering the protective facilities with plastic film not only reduces evaporation and humidity, but also has the effect of increasing ground temperature. According to experiments, covering the greenhouse with plastic film can reduce the relative humidity of the air by about 10%. Covering the ground with straw such as straw can also reduce the humidity in the protected area and have a good yield increase effect.