The relative humidity of greenhouse vegetable production is significantly higher than that of open field because it is carried out under relatively closed conditions, and most of the water produced by surface evaporation and crop transpiration is in greenhouse. The excessive air humidity in the greenhouse is one of the main reasons for the serious damage caused by many diseases. Therefore, scientific control of the humidity in the greenhouse is an important link in the cultivation of complete agreement.
Moisture regulation according to crop requirements
Vegetable varieties grown in greenhouses have different requirements for relative air humidity. Solanaceous vegetables: 60% - 70%, cucumber: 85% - 90%, watermelon, melon: 50% - 60%.
In addition, vegetable crops require different air humidity at different growth stages and different planting seasons. For example, in Winter Cucumber planting, due to weak light, low temperature and slow growth, air humidity should be controlled as low as possible, generally 70% - 80% is appropriate. In spring, the temperature is high, the light is abundant, and the growth reaches its peak. The air humidity can be increased to 85% - 90%.
Change humidity by changing the temperature in the shed
According to the investigation, when the humidity in the shed is 100% and the temperature in the shed is 5%, the humidity decreases by 3% - 4% for each increase of 1 C. When the humidity rises to 20 C, the humidity is about 70%, the temperature rises to 30 and the humidity decreases by 40%. On the contrary, when the temperature drops to 18 C, the relative humidity can rise to 85%, and when the temperature drops to 16 C, the relative humidity can reach almost 100%.
Controlling Soil Moisture
Irrigation in low temperature period should be strictly controlled according to the water requirement of different vegetables. The results showed that the soil moisture of tomato should be lower in early stage, 16-18% in early stage, 20% in peak stage, 22-23% in early stage of cucumber, 18-20% in sweet pepper and eggplant, 23% in early stage of celery and a little decrease in later stage. Loosening soil in time after irrigation is also an important measure to reduce the humidity in greenhouse. In addition, drip irrigation can significantly reduce the humidity in the greenhouse.
Ventilation and ventilation
Ventilation is the main measure of dehumidification. It should be carried out at high temperature around noon, mainly in the top wind and waist wind, not in the bottom foot wind, in order to prevent low temperature in the shed and "sweeping wind" injury to seedlings.
If the humidity in greenhouse is high and the temperature is above the lower limit of suitable temperature for crop growth, the ventilation rate should be increased gradually to reduce the air humidity as soon as possible, but the cooling caused by ventilation should be based on the premise that crops do not suffer from cold damage.
Therefore, the diurnal variation of humidity in the greenhouse is very large. After 100% April at night and 30 C at noon, the relative humidity in the greenhouse can be reduced to about 40% under ventilation conditions, which will cause vegetable wilting for a short time and affect the continuation of photosynthesis. The main causes of excessive air humidity in greenhouses are irrigation and low temperature condensation.
Stacking dehumidification materials
Lime and other hygroscopic materials can be stacked at the corner of the shed to absorb moisture in the air and achieve the purpose of reducing air humidity.
Rice husk can be used to dehumidify the southern region, which has a good absorption effect. Sometimes, if you are in a farm, you will often spread some of this thing on the ground. The humidity on the ground is too heavy, in fact, it can be used in the greenhouse, it must be paved thicker, about four centimeters, so that it can absorb some humidity in the air very well.
And this air permeability is very good, will not affect the problem of the soil, then do not have to clean it up, when ploughing together into the soil, at the beginning can make the soil more loose, until after decay can also improve fertility. In addition to rice husks, other straws, such as various crops, can also be laid inside after being crushed.
Plastic film dehumidification
In the greenhouse, when the weather is colder, many people will cover a layer of plastic film, which can protect the soil temperature, but also reduce the evaporation of water, water evaporation reduced, and the humidity in the greenhouse is not so high. However, when laying mulch, we must pay attention to the fact that it can't be close to the soil, otherwise it will be very airtight, and then make a lot of water in the plant's stem. We must support the mulch, and make a small bracket every few centimeters. In this case, it can be well ventilated if it is not close to the soil surface.
Air humidity affects transpiration, which is not only the motive force of water absorption, but also the motive force of mineral nutrition transportation. When air humidity is high and transpiration is weak, the ability of plants to transport mineral nutrients decreases. Transpiration can also regulate the temperature of leaves. If the temperature is high, the air humidity is high and the transpiration is weak, the leaves may be burned. Long-term low air humidity will cause the necrosis of the blade edge and tip. The main reason is that the difference between the air pressure inside the blade chamber and the external water pressure is too large, resulting in insufficient water vapor supply inside the blade and necrosis.
Within a certain range, the temperature of plants also rises. In order to release heat, stomata become larger and transpiration is enhanced. If the stomata remain open, the plants will lose water. Therefore, stomata are closed under the action of guard cells to inhibit transpiration. Laser plant illumination is a precise light source, which will not affect the transpiration of plants because of the strong illumination.
Laser plant supplementary light can solve the problems of short sunshine time, fog and haze, rainy and snowy days in winter, resulting in slow growth, low yield and late ripening of vegetables and fruits in intelligent greenhouse and greenhouse. It's just like sunlight, it's good for plant growth, and it's good for crop production and increment.