Use sun screens or other similar materials to control lighting. Or the light is too strong and the time is too long. It depends on what crops are planted in your shed. Generally, the daytime temperature of crops is 32 degrees, and the lowest temperature at night is below 12 degrees. You have to make a comprehensive reference and analyze the reasons in combination with your own problems. Environmental characteristics and regulations
Because the greenhouse is covered with plastic film, it forms a special microclimate which is relatively closed and different from the open field. In order to cultivate vegetables in greenhouse, we must master the characteristics of greenhouse environment and take corresponding control measures to meet the conditions of vegetable growth and development, so as to obtain high quality and high yield.
(1) Environmental conditions in the greenhouse:
1. illumination: it depends on the solar radiation intensity outside the shed, the optical characteristics of the covering material and the pollution degree. The light transmittance of new plastic film is 80-85%, and the light transmittance of old film polluted by dust and soil is often below 40%. The water droplets condensed on the film surface can reduce the illumination in the shed by 10%-20% due to the diffusion of water droplets. The shed frame, the film pressing line and the frame material of tall vegetables will be blocked, so the factors that weaken the light in the shed should be avoided and eliminated as far as possible in the management of the shed.
2. Temperature:
(1) Temperature variation law: The daily variation trend of temperature in greenhouse is the same as that in open field, but the temperature difference between day and night changes greatly. There is plenty of sunlight in the daytime. If the temperature in the film closed shed rises rapidly, the highest temperature can reach 40-50℃, which is more than 20℃ higher than that outside the shed. The effect of warming in rainy days is poor, and the lowest temperature in the shed at night is generally higher than that outside the shed 1-3℃. The ground temperature in the shed is more stable than the air temperature, usually 10-20℃. The temperature in the greenhouse also changes with different locations. The greenhouse is horizontally distributed with high middle and low sides, so the plants in the middle of the greenhouse are often higher than those on both sides. Greenhouse is vertically distributed. The sun shines during the day, and the temperature is high and low, but it is the opposite at night and cloudy days.
(2) Inversion phenomenon: In a polyethylene-covered greenhouse, the temperature inside the greenhouse is sometimes lower than that outside the greenhouse on the night when there is a breeze and sunshine in winter. The reasons are as follows: at night, the temperature outside the shed is higher than that in the lower part. Due to the disturbance of wind, heat can be supplemented from the high altitude outside the shed, but it can't be obtained in the shed because of the obstruction of shelter; It is cool during the day in winter, and the soil stores less heat. In addition, the polyethylene film has high long-wave emissivity, poor thermal insulation, large effective thermal radiation from the ground and much heat dissipation, which leads to the phenomenon that the temperature inside the shed is lower than that outside the shed.
(3) Temperature control: The temperature control of greenhouse is mainly carried out by ventilation and heating. Uncovering the film is the most commonly used method to reduce and control the air temperature in the shed during the day. The use of shading materials can reduce the amount of light received in the shed and prevent the air temperature in the shed from being too high.
In winter, in order to reduce heat loss and improve air temperature and soil temperature, the greenhouse film should be covered as tightly as possible. You can set up a wind wall around the greenhouse, build a small shed in the greenhouse, and then cover it with grass, non-woven fabric, foam plastic and other layers. Heating measures can also be taken to raise the temperature, such as using electric heating wires to raise the soil temperature, and areas with conditions can use the waste heat from factories, geothermal water or coal stoves to raise the temperature in the shed. Water bags (plastic bags filled with water) are built in greenhouses. Water bag takes advantage of the high specific heat of water, which absorbs a lot of solar energy during the day, converts it into heat energy and stores it, and gradually releases it at night, which can increase the temperature of greenhouse.
3. Air humidity control
(1) Variation law of air humidity in greenhouse: The plastic film is tightly sealed, which hinders the exchange between the air in greenhouse and the outside air, and the water vapor generated by soil evaporation and leaf transpiration is difficult to disperse. So the humidity in the shed is high. During the day, under the condition of ventilation, the relative humidity of air in the greenhouse is 70-80%. It can reach more than 90% in rainy days or after irrigation. The relative humidity of air in the shed decreases with the increase of temperature, and it is often 100% at night. The wet air in the shed condenses into water film or water drops when it is cold, and adheres to the inner surface of the film or plant.
(2) Control of air humidity: Excessive air humidity in the greenhouse not only directly affects the photosynthesis of vegetables and the absorption of mineral nutrients, but also facilitates the germination and infection of pathogen spores. Therefore, the relative humidity in the shed can be effectively reduced by ventilation and promoting the exchange between high humidity air in the shed and low humidity air outside. Heating the hot wire in the shed can also reduce the relative humidity. Using drip irrigation technology combined with plastic film mulching cultivation to reduce soil moisture evaporation can greatly reduce air humidity (about 20%).
4. Air composition in the shed: The film coverage limits the flow and exchange of air in the shed. In the case of tall vegetables and plants and lush leaves, the concentration of carbon dioxide in the air in the shed changes greatly. Before sunrise in the morning, due to crop respiration and soil release, the carbon dioxide concentration in the shed is 2-3 times higher than that outside the shed (about 330 ppm); After 8-9 o'clock, with the enhancement of leaf photosynthesis, it can be reduced to below 100PPM. Therefore, ventilation should be carried out as appropriate after sunrise to replenish carbon dioxide in the shed in time. In addition, artificial carbon dioxide fertilization can be carried out, and the concentration is 800- 1000 ppm, which can be used after sunrise and before ventilation. Artificial application of carbon dioxide, in the case of weak light and low temperature in winter and spring, has a very significant effect on increasing production.
In the low temperature season, greenhouses are often sealed and insulated, and it is easy to accumulate toxic gases, such as ammonia, nitrogen dioxide, sulfur dioxide, ethylene and so on. When the ammonia gas reaches 5PPM in the greenhouse, the tip of plant leaves will be soaked in water, and then turn black and die; When nitrogen dioxide reaches 2.5-3 ppm, irregular green and white spots appear on the leaves, and in severe cases, all the leaves are bleached except the veins. The production of ammonia and nitrogen dioxide is mainly caused by improper use of nitrogen fertilizer. The production of carbon monoxide and sulfur dioxide is mainly caused by coal fire heating, incomplete combustion or poor coal quality. Because the aging of plastic film (plastic pipe) will release ethylene, which will lead to premature aging of plants, so excessive use of ethylene products is also one of the reasons.
In order to prevent the accumulation of harmful gases in the shed, fresh manure can not be used as base fertilizer or topdressing; It is forbidden to use ammonium carbonate for topdressing. When topdressing with urea or ammonium sulfate, water or cover the soil in time after acupoint application. Fertilization amount should be appropriate, not excessive; Proper ventilation is also needed in low temperature season to eliminate harmful gases. In addition, the coal used is of good quality and should be fully burned. If possible, use hot air or hot water pipe to heat it, and exhaust the burnt waste gas outside the shed.
5, soil moisture and salt:
The distribution of soil moisture in greenhouse is uneven. The soil near the two sides of the shed has more water infiltration outside the shed, and the water droplets flowing on the shed film have higher humidity. The middle of the shed is relatively dry. Cucumber and eggplant planted in greenhouse in spring, especially those cultivated with plastic film, often have insufficient soil moisture, which seriously affects the quality. It is best to lay a hose drip irrigation belt and fertilize water at any time according to actual needs, which is an effective measure to increase production. Due to the long-term coverage of greenhouses, the rainwater leaching is insufficient, and the salt moves from bottom to top with groundwater, which is easy to cause excessive accumulation of salt in cultivated soil and cause salinization. Therefore, we should pay attention to proper deep ploughing and application of organic fertilizer to avoid long-term application of fertilizers containing chloride ions or sulfate ions. Topdressing should be light, and it is best to test soil and fertilize. Every year, there must be a certain period of time without plastic film, or in summer, only the sunshade net is covered for shading cultivation, so that the soil can be leached by rain. When soil salinization is serious, flooding can be used to suppress salt, and the effect is very good. In addition, using soilless culture technology is the fundamental measure to prevent soil salinization.
Third, the annual stubble arrangement of greenhouse vegetables
Greenhouse only has early cultivation of eggplant in spring, which only takes 4-5 months a year, so the utilization rate and benefit are not high. If the greenhouse is also used for autumn, winter and Xia San cultivation, seedling raising and seed storage, the production benefit can be improved.
(1) seedling type; It is characterized by seedling raising in winter → early maturity cultivation in spring → seedling raising in summer → autumn and winter cultivation. In winter, seedlings are usually raised from June 1 1 to the middle and late March of the following year, and seedlings of solanaceous fruits, melons and beans are cultivated. Sow in the middle and late March and cultivate early in spring. Raise seedlings in summer from June to August, such as cabbage, cauliflower and tomato. Plant autumn tomatoes, cucumbers, leafy vegetables, celery, onions and garlic in autumn and winter.
(2) Cultivation type: mainly cultivated vegetables, combined with seedling raising. There are two main forms: one is to plant eggplant, tomato, cucumber and pepper in early spring, fast-growing vegetables in summer, cucumber, tomato, cabbage and cauliflower in autumn, celery, spinach, lettuce and onion and garlic in winter; The second is intercropping, in which tomatoes and peppers are planted in early spring, and loofah is planted next to the arch pole in the greenhouse in April-May, so that it can climb along the arch pole, or in the later stage of tomato growth, wax gourd is planted in the border, and vines are climbed by tomato brackets; Planting lettuce and cabbage in autumn; Seedling raising is carried out in winter.
(3) Seed-keeping: There are two main ways: one is to keep seeds of eggplant and melon in spring, and the stubble-keeping way is to raise seedlings in winter → keep seeds in spring → cultivate celery and cabbage in autumn; One is to collect and reserve seeds mainly from Cruciferae self-incompatibility in winter and spring, raise seedlings in summer and cultivate eggplant and melon vegetables in autumn.
Four, several forms of greenhouse vegetable cultivation
(1) Early Spring Cultivation in Natsuna
Early-maturing cultivation of eggplant and melon vegetables is the most common project in greenhouse cultivation. Open field cultivation is generally planted from late March to mid-April, and harvested from early May to July. Greenhouse cultivation can be planted1-March in advance and harvested from late March to July. Early listing, high yield, long flowering and fruiting period and obvious economic benefits. In addition, according to market demand, warm green leafy vegetables such as amaranth, auricularia auricula and water spinach can be planted in advance and listed in advance.
1. Variety (combination) selection: early-maturing tomato varieties are Zaofeng, Japanese Red× Aihong; Zheza No.5, Su Kang No.4 and No.5 were selected as mid-mature varieties, and the excellent varieties with early maturity, disease resistance, high yield and marketability were selected as sweet pepper. Pepper: chicken feet × Jilin F 1, Zaofeng1; Sweet pepper: add No.3; Eggplant: Fujian eggplant 1, Pingtung eggplant; Cucumber: Jinchun No.2 and No.3, etc.
2. Planting: 65,438+00 days before planting, cover the shed with plastic film. 3000 kg of manure or decomposed garbage manure, 2000 kg of human excrement and urine, and 50 kg of compound fertilizer are applied per mu, which are applied in deep ditches or in the whole layer and turned into the soil. Tomato is planted in two rows, with the border length of 1.5m, the row spacing of 75cm and the plant spacing of 20-30cm, with 2500-3000 plants per mu. There are 3000 peppers per mu. Eggplant spacing is 40-50 cm, and 2,000-2,400 plants are planted per mu. Plant 2000-2400 cucumbers per mu.
3. On-site management:
(1) Temperature management: No ventilation is needed for one week after planting, mainly heat preservation, especially for eggplant and cucumber, so as to keep a high temperature to facilitate the seedlings to turn green. After returning to seedlings, keep the temperature high. The optimum temperature for tomato seedling growth is 20-25℃ during the day and 10- 15℃ at night. The optimum temperature for eggplant growth is 20-30℃. When the temperature is lower than 15℃, it will cause poor pollination and fertilization. The optimum growth temperature of sweet (spicy) pepper is 25-28℃; The temperature of cucumber is 28-30℃, and the temperature at night shall not be lower than 10℃. The temperature rises gradually in the middle and late May, and the skirt film can be gradually removed. After 9: 00 pm-10 and 16: 00 pm, the cover should be closed.