Comparison of greenhouses

Ordinary greenhouse: low cost and simple structure. But few devices can be added.

Greenhouse: the cost is higher than that of ordinary greenhouses, and the structure is complex, so certain equipment can be installed.

Intelligent greenhouse: high cost, complex structure and relatively complete equipment. 1957 was extended from Beijing to Tianjin, Shenyang, Northeast China, Taiyuan and other places, and was welcomed by all localities. From 65438 to 0958, China has been able to produce agricultural polyethylene film by itself, so the production of vegetables covered in greenhouses has been very extensive. In the mid-1960s, the shed was arched, with a height of about 1m and a width of 1.5-2.0m, so it was called a small arch shed. Because the shed is short, it is not suitable for application in the cold area of Northeast China. 1966 First, the small arch shed was transformed into a 2-meter-high square shed in the suburbs of Changchun. But it collapsed because of its poor snow resistance. After repeated transformation and trial use, an arched greenhouse with a height of about 2 meters, a width of 15 meters and an area of 1 mu was finally built. 1970 extended to all parts of the north. At 1975, 1976 and 1978, three consecutive "National Cooperation Conferences on Vegetable Production in Plastic Greenhouse" were held, which promoted the development of greenhouse production. From 65438 to 0976, 29 kinds of greenhouses with different specifications were built in the suburbs of Taiyuan, which provided rich experience for the structure and construction scale of greenhouses. 1978 greenhouse production has been extended to all parts of the south, and the greenhouse area in China has reached 654.38+10,000 mu. So far, China's greenhouse area has basically stabilized at more than 65,438+10,000 mu. Among them, there are about 70,000 mu in the arid areas of northern China. It is estimated that during the Seventh Five-Year Plan period, the greenhouse planting area will grow to about 200,000 mu. The greenhouse is covered with plastic film. Suitable for large area coverage, because it has light weight, good light transmission and heat preservation performance, strong plasticity and low price. Moreover, due to the use of light skeleton materials, it is easy to build and shape, and can be selected on site, with less construction investment and higher economic benefits. It can resist natural disasters, prevent cold and keep warm, resist drought and waterlogging, cultivate early and late, prolong the growth period of crops, and achieve the goals of early maturity, late maturity, increase production and stable production, which is well received by producers. Therefore, it has developed rapidly in the arid areas of northern China.

The application scope of greenhouse is still developing. Especially in cold regions, deserts and arid regions, it plays an important role in resisting the harm of low temperature drought and sandstorm. In order to develop agricultural production, countries all over the world have built plastic greenhouses. At the end of 1970s, the area of plastic greenhouses in Japan was 10-20 hectares. The Spanish area of Al Merilli, with a total land area of 365,438+05 square kilometers, is an arid area. In order to develop vegetable production, it covers 65,438+020 square kilometers of greenhouses, which is the largest greenhouse in the world. Greenhouse covering materials are as follows:

1. Ordinary membrane: made of polyethylene or polyvinyl chloride, with a thickness of 0. 1mm, colorless and transparent. The service life is about half a year.

2. Multifunctional long-life film: it is made by adding proper amount of anti-aging materials and surfactants during polyethylene blow molding. Its service life is twice as long as that of ordinary membrane, and the greenhouse temperature at night is higher than other materials 1-2℃. Moreover, the film is not easy to form water droplets, and the covering effect is good.

3, grass quilt, grass cover: woven from straw, good thermal insulation performance, is a night thermal insulation material.

4. Polyethylene high foaming film: it is a white plastic film with many bubbles, with a width of 1 m and a thickness of 0.4-0.5 cm. It is light and can be rolled up, and its thermal insulation is similar to that of grass quilt.

5. Non-woven fabric: a kind of polyester filament, which is not woven or spun. There are two kinds: black and white. They have different densities and thicknesses. The common specification is 50g/? In addition to heat preservation, it is often used as a sunshade net.

6. sunshade net: a plastic woven net. Commonly used are black and silver gray, and there are several density specifications with different shading rates. It is mainly used for sun protection and rain protection in summer, and can also be used for thermal insulation and covering in winter. (1) temperature condition

Plastic film has the function of heat insulation. After film mulching, the turbidity in the greenhouse will increase with the increase of external temperature and decrease with the decrease of external temperature. Seasonal changes are obvious, and the temperature difference between day and night is large. The lower the temperature, the greater the temperature difference. Generally, the daily warming of greenhouse in cold season can reach 3-6℃, and the warming capacity in cloudy days or at night is only 1-2℃. In warm spring, the temperature difference between the shed and the open field gradually increases, and the temperature rise can reach 6- 15℃. When the outside temperature rises, the temperature of shed meat rises relatively, and the highest temperature can reach above 20℃, so there is danger of high temperature and freezing in the shed, which needs manual adjustment. In the high temperature season, the high temperature above 50℃ can be generated in the shed. The whole shed is ventilated, and the outside of the shed is covered with a straw curtain or a "arbor", which is lower than the outdoor temperature 1-2℃. On sunny days in winter, the lowest temperature at night is 1-3℃ higher than that in the open field, and on cloudy days, several items are the same as those in the open field. Therefore, the main production seasons of greenhouses are spring, summer and autumn. The greenhouse temperature can be kept at 15-30℃ by heat preservation and ventilation.

(2) Lighting conditions

The light transmittance of the new plastic film can reach 80-90%, but the light transmittance decreases 10-30% due to dust pollution, water droplet adsorption, film aging and other reasons during use. The lighting conditions in the greenhouse vary greatly due to the season, weather conditions and covering methods (shed structure, orientation, scale, etc.). ), film types, and the use of old and new conditions. The higher the greenhouse, the greater the difference of vertical irradiance in the greenhouse, and the difference of irradiance between the upper layer and the ground in the greenhouse is 20-30%. In winter and spring, the illumination conditions of greenhouses extending from east to west are better than those extending from north to south, and the local illumination conditions are almost the same. However, the irradiance difference between the north and south sides of the east-west greenhouse can reach 10-20%. Different shed structures have great influence on the light reception in the shed. Although the double-layer film mulching has good thermal insulation performance, the light receiving condition can be reduced by about half compared with the single-layer film mulching shed. In addition, the use of multi-span greenhouses and different shed materials also has a great influence on the light (Table 4-2-3). As can be seen from the table, the greenhouse with single-layer steel hard plastic structure has better lighting, which only reduces the light transmittance by 28% compared with the open field. The lighting condition of multi-span shed is poor. Therefore, when the materials used to build the shed can bear a certain load, we should try to choose light materials and simplify the structure, which can not affect the lighting, but also protect it firmly, economically and practically. Table 4-2-3 Light intensity of different shed types Lux (ten thousand) light transmittance (%) Single steel structure Single hard plastic structure Multi-span reinforced concrete exposure contrast 7.67 6.65 7.65 5.9910.6472.0 62.5710.956.310000. /kloc-25% after 0/0, and less than 28% after half a month. Generally speaking, dust pollution can reduce the light transmittance by 10-20%. When it is seriously polluted, only 7% of the light received in the shed is unusable. Generally, the film easily absorbs water vapor and condenses into water droplets on the film, which reduces the light transmittance of the film by 10-30%. Therefore, it is very important to prevent film pollution and condensation of water droplets. Moreover, during the use of the film, due to the influence of high temperature, low temperature, sunlight and ultraviolet rays, the film "aged". After aging, the light transmittance of the film decreased by 20-40%, and even lost its use value. Therefore, the film covered in the greenhouse should be a long-life film with temperature resistance, aging resistance and dust removal, so as to enhance the light reception, raise the temperature and prolong the service life in the greenhouse.

(3) Humidity conditions

The air tightness of the film is strong, and the air temperature in the shed is high due to soil moisture evaporation and crop transpiration after covering. If there is no ventilation, the relative humidity in the shed is very high. As the greenhouse temperature increases, the relative humidity decreases and the relative humidity increases. The relative temperature is low in sunny and windy days, and high in cloudy and rainy days (foggy days). Without ventilation, the relative humidity in the shed can reach 60-80% during the day, often around 90% at night, and the highest is 100%. The suitable air relative humidity in the shed varies with different crops, and it is generally required to be kept at 50-60% during the day and 80-90% at night. In order to reduce the harm of diseases, the humidity at night should be controlled at about 80%. When the relative humidity in the shed reaches saturation, increasing the shed temperature can reduce the humidity. For example, when the humidity is 5℃, the humidity will decrease by about 5% with every increase of 1℃, and when the temperature is 10℃, the humidity will decrease by 3-4% with every increase of 1℃. Without increasing the water vapor content in the air in the shed, the relative humidity is about 7% when the shed temperature is 65438 05℃. When the temperature rises to 20℃, the relative humidity is about 50%. Due to the high temperature in the shed and small soil evaporation, irrigation should be reduced in winter, spring and cold season. However, when the temperature in the greenhouse rises, or the temperature is too high, ventilation is needed, which will reduce the humidity, accelerate the transpiration of crops, reduce the transpiration rate of plants due to lack of water, or cause physiological disorders. Therefore, according to the requirements of crops, keep proper humidity in the shed. Fourth, the cultivation season and conditions of plastic greenhouses are mainly cultivated in spring, summer and autumn. The lowest temperature in winter is-15℃- 17℃, which can be used for cold-tolerant crops to overwinter in the shed. In cold and arid areas, greenhouse can be used for early cultivation. Nursery seedlings in greenhouses in winter in northern areas, so that seedlings can be planted in greenhouses for early cultivation in early spring. Sow in summer, postpone cultivation after autumn, 1 year. Due to the advance of spring and the delay of autumn, the greenhouse cultivation period was extended by two months. In some frozen areas in Northeast China and Inner Mongolia, the yield per mu of cucumber is 2-4 times higher than that in the open field when the seedlings are planted in spring and pulled out after autumn. Watermelon planting in greenhouse in Heilongjiang Province was successful. In the arid areas of northwest China and the border areas of Inner Mongolia, greenhouse is used to realize year-round production, and cold-resistant vegetables are planted in greenhouse in winter, which creates a precedent for greenhouse planting in winter. In order to improve the utilization rate of greenhouse, measures such as temporary heating in greenhouse in early spring and late autumn, adding double curtains to prevent cold, building a sunny bed in greenhouse, adding a small arch shed or a middle shed, covering with plastic film, and covering the periphery of greenhouse with grass curtains are often adopted to prolong the growth period, increase the number of planting stubbles and increase the yield.

(4), 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%).

(5) Air composition in the shed:

Because of the film covering, the air flow and exchange in the shed are limited. In the case of tall vegetable plants and lush foliage, the concentration of carbon dioxide in the air in the greenhouse changes dramatically. 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.

(6), 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. Cultivation techniques of greenhouse vegetables in Dalangdian township. Greenhouse vegetables are arranged once a year, and only eggplant fruits are cultivated early in spring. In greenhouse, it is only 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.