Four main points of watermelon planting techniques in greenhouse: air, temperature, soil and air humidity

The watermelon listed by netizens as the "three treasures of summer" can be seen how much people like it. It's not too cool to sit under the air conditioner, play with your mobile phone and eat iced watermelons in summer. Watermelon taste sweet, a wide variety, pulp is very sufficient, there are two colors of red flesh and yellow flesh, the latter taste better and more delicate. In recent years, many farmers have started to plant watermelons. What are the key points of watermelon planting techniques in the greenhouse?

I. Lighting

It depends on the solar radiation intensity outside the greenhouse, the optical characteristics of the covering material and the degree of pollution. The light transmittance of the new plastic film is 80% Mur85%, and the light transmittance of the old film contaminated by dust is often less than 40%. The film surface condenses water droplets, and due to the diffuse effect of water droplets, the light in the shed can be reduced by 10% and 20%. Scaffolding and film-pressing lines as well as tall vegetable shelves will block the light, so it is necessary to avoid and eliminate the factors that weaken the light in the greenhouse as far as possible in the greenhouse management.

Second, temperature

The main results are as follows: (1) the law of temperature change: the diurnal variation trend of air temperature in greenhouse is the same as that in open field, but the temperature difference between day and night varies greatly. There is plenty of light during the day, and if the temperature in the closed shed rises quickly, the highest temperature can reach 40 ℃ and 50 ℃, which is more than 20 min higher than that outside the shed. In cloudy and rainy days, the warming effect is poor, and the minimum temperature in the shed at night is generally 1 Mel 3 ℃ higher than that outside the shed. The temperature in the interior of the shed is more stable than the temperature, usually 10 murals and 20 ℃. (2) temperature inversion phenomenon: in the polyethylene covered greenhouse, there is a clear breeze in winter, and the temperature inside the greenhouse is sometimes lower than that outside the greenhouse. The reason is that at night, the temperature outside the shed is higher than that in the lower place. Due to the disturbance of the wind, the heat can be replenished from the upper air near the ground outside the shed, while this part of the heat can not be obtained in the greenhouse due to the barrier of the cover. In winter, the daytime is cool, the soil storage heat is less, and the polyethylene film has higher long-wave emissivity, slightly poor thermal insulation, large effective thermal radiation and more heat dissipation, resulting in the phenomenon that the temperature inside the shed is lower than that outside the greenhouse. (3) temperature control: the temperature control of the greenhouse is mainly carried out through ventilation and heating. The use of uncovering film for ventilation is the most commonly used method to reduce and control the temperature in the greenhouse during the daytime. The use of sunshade materials to reduce the amount of light in the greenhouse can also prevent the temperature in the greenhouse from getting too high.

III. Soil moisture and salinity

The distribution of soil moisture in greenhouse is uneven. The soil near both sides of the scaffolding has more water infiltration outside the shed and higher humidity of water droplets on the greenhouse film. The middle part of the shed is drier. The quality of cucumber and eggplant planted in greenhouse in spring, especially those cultivated with plastic film, is often seriously affected by the lack of soil moisture. It is best to lay hose drip irrigation belt and apply fertilizer and water at any time according to actual needs, which is an effective measure to increase production. Due to the long-term covering of the greenhouse and the lack of Rain Water leaching, the salt moves up with the groundwater, which is easy to cause excessive accumulation of soil salt in the tillage layer, resulting in salinization. Therefore, attention should be paid to deep ploughing and application of organic fertilizers to avoid long-term application of fertilizers containing chloride or sulfate ions.

IV. Regulation of air humidity

The main results are as follows: (1) the change law of air humidity in greenhouse: the sealing of plastic film is strong, the exchange of air between greenhouse and outside is hindered, and the moisture of soil evaporation and leaf transpiration is difficult to diverge. Therefore, the humidity in the shed is high. During the day, under the condition of ventilation in the greenhouse, the relative humidity of the air in the greenhouse is 70ml 80%. It can reach more than 90% on cloudy and rainy days or after irrigation. The relative humidity of the air in the shed decreases with the increase of temperature, which is usually 100% at night. When the wet air in the shed is not as expected, it condenses into a water film or water droplets are attached to the inner surface of the film or to the plant.

(2) the regulation of air humidity: the excessive air humidity in the greenhouse not only directly affects the photosynthesis and mineral nutrition absorption of vegetables, but also is beneficial to the germination and infection of bacterial spores. Therefore, it is necessary to carry out ventilation to promote the exchange of high humid air and external low humid air, which can effectively reduce the relative humidity in the shed. Heating the hotline in the interior of the shed can also reduce the relative humidity. The use of drip irrigation technology, combined with plastic film mulching cultivation, reduce soil water evaporation, can greatly reduce the air humidity (about 20%).