The latest course of vegetable planting techniques and methods in greenhouse

Vegetable cultivation in greenhouse is a common technology, which has good heat preservation performance, and it is very popular because out-of-season vegetables can be eaten at any time. In general, greenhouse vegetables use bamboo and steel-based structural skeleton, and then covered with one or more layers of thermal insulation plastic film, such a simple structure to create a complete greenhouse space.

Greenhouse construction

1. Type and structure of scaffolding

There are many types and structures of plastic greenhouses. At present, there are two kinds of prefabricated galvanized thin-walled steel pipe type (referred to as steel pipe greenhouse) and bamboo-wood arch greenhouse. It is mainly used for early ripening cultivation in spring and delayed cultivation in winter, as well as seedling and hybrid seed production of summer vegetables such as tomato, sweet (spicy) pepper, eggplant, cucumber and so on. There is also a bamboo shed, which is often used alone or in cooperation with the greenhouse (that is, the greenhouse is covered with a small shed), which is used for raising seedlings of eggplant and melon vegetables in winter and spring and precocious cultivation in spring.

The steel pipe greenhouse has two specifications: one is 2.2 meters high, 4.5 meters wide, 20 meters long and 90 square meters long, and the other is 2.5 meters high, 6 meters wide, 30 meters long and 180 square meters in area. The service life is generally 15 years.

In order to reduce the production cost, bamboo frame greenhouse can also be used. The scaffolding is made of bamboo or small logs, about 2 meters high and 4 ─ 5 meters wide, with a general service life of 3 years.

2. Covering material

There are several kinds of greenhouse covering materials:

① ordinary film: polyethylene or PVC as raw materials, film thickness 0.1mm, colorless and transparent. The service life is about half a year.

② multi-functional longevity film: it is made by adding appropriate amount of anti-aging material and surfactant in the process of polyethylene blow molding. The multi-functional film produced by Zhejiang Xinguang Plastics Factory has a width of 7.5m and a thickness of 0.06mm. Its service life is twice as long as that of ordinary film, and the greenhouse temperature at night is 1 ─ 2 ℃ higher than that of other materials. And the film is not easy to form water droplets, the covering effect is good, the cost is low and the benefit is high.

③ straw quilt, straw fan: woven with straw, good heat preservation performance, is a night heat preservation material.

④ polyethylene high foaming film: it is a white bubble plastic film with a width of 1 meter and a thickness of 0.4 ─ 0.5cm. It is light and can be rolled up, and its thermal insulation is similar to that of the grass quilt.

⑤ non-woven fabric: a kind of polyester filament that is not woven. Divided into black and white, and have different density and thickness, commonly used specifications of 50 grams, in addition to heat preservation, but also often used as a sunshade net.

⑥ sunshade net: a kind of plastic wire mesh. Commonly used are black and silver gray, and there are several density specifications, shading rates are different. It is mainly used for sunshade and rain protection in summer, and can also be used for heat preservation and covering in winter.

3. Greenhouse construction

Choose sunny, wind shelter, high dryness, good drainage, no soil infectious diseases to build a shed.

4. Maintenance of plastic film

The mechanical damage of the greenhouse film should be avoided as far as possible when the ① film is fastened, especially the bamboo shed. The protruding part of the shelf surface should be cut flat or wrapped with old cloth before the film is fastened. When fixed with a spring, a layer of old newspaper should be added to the card slot. In addition, we should pay attention to avoid long-term contact with new and old films, so as not to accelerate the aging of new films. Be careful when ventilating.

② film frozen or exposed, will promote aging, steel pipe exposed to the sun in summer, the temperature can rise to 60 ─ 70 ℃, thus accelerating the aging and breaking of the film.

In the process of using ③ film, it is hard to avoid holes, so it should be mended with adhesive or tape in time.

Environmental characteristics and regulation

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 grasp the characteristics of the environment in the greenhouse 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 greenhouse, the optical characteristics of the covering material and the degree of pollution. The light transmittance of the new plastic film is 80 ─ 85%, and the light transmittance of the old film contaminated by dust is often less than 40%. The film surface condenses water droplets, which can reduce the light in the greenhouse by 10% ─ 20% due to the diffuse effect of water droplets. 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.

(2) temperature

① temperature variation law: 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 in the daytime, and if the temperature in the closed shed rises quickly, the highest temperature can reach 40 ─ 50 ℃, which is more than 20 ℃ higher than that outside the greenhouse. In cloudy and rainy days, the warming effect is poor, and the minimum temperature in the shed at night is generally 1 ─ 3 ℃ higher than that outside the shed. The temperature in the interior of the shed is more stable than the temperature, usually 10 ─ 20 ℃. The temperature in the greenhouse also varies with different locations, and the horizontal distribution of the greenhouse is high in the middle and low on both sides, so the plants in the middle of the greenhouse are often taller than those on both sides. The greenhouse is distributed longitudinally. When the sun shines during the day, the temperature is high at the top and low at the bottom, but on the contrary in night and cloudy days.

② inversion phenomenon: polyethylene covered greenhouse, there is a clear breeze in winter night, the temperature inside the shed is sometimes lower than 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: greenhouse temperature control 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.

In winter, in order to reduce heat loss and increase air temperature and soil temperature, the greenhouse film should be covered as tightly as possible. Wind barriers can be set up around the greenhouse, and small sheds can be set up in the greenhouse and then multi-layer covering measures such as grass slices, non-woven fabrics, foam and so on. Heating measures can also be used to increase the temperature, such as the use of electric hot lines to increase soil temperature, conditional areas can use factory waste heat, geothermal water or coal stove to increase the temperature in the shed. There is a water bag (plastic bag full of water) in the greenhouse. Taking advantage of the high specific heat of water, the water bag absorbs a large amount of solar light energy during the day, which is converted into heat energy and stored, which is gradually released at night, which can increase the temperature of the greenhouse.

(3) the regulation of air humidity.

The change law of air humidity in ① 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, when the greenhouse is ventilated, the relative humidity of the air in the greenhouse is 70 ─ 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.

Regulation of ② air humidity: excessive air humidity in the greenhouse not only directly affects the photosynthesis and mineral nutrition absorption of vegetables, but also is beneficial to the spore germination and infection of the pathogen. 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%).

(4) Air composition in the shed

Due to the film mulching, the air flow and exchange in the greenhouse are restricted, and the concentration of carbon dioxide in the air in the greenhouse changes dramatically under the condition of tall vegetables and luxuriant branches and leaves. Before sunrise in the morning, due to crop respiration and soil release, the concentration of carbon dioxide in the greenhouse was 2 ─ 3 times higher than that outside the greenhouse (about 330PPM), and after 8 ─ 9 o'clock, with the enhancement of leaf photosynthesis, it could be reduced to less than 100PPM. Therefore, after sunrise, ventilation should be carried out as appropriate to replenish carbon dioxide in the shed in time. In addition, artificial carbon dioxide fertilization can be carried out at a concentration of 800 ─ 1000PPM, which can be used after sunrise and before ventilation. Under the condition of weak light and low temperature in winter and spring, the effect of artificial application of carbon dioxide is very significant.

In the low temperature season, the greenhouse is often closed and insulated, which is easy to accumulate toxic gases, such as ammonia, nitrogen dioxide, sulfur dioxide, ethylene and so on. When ammonia reached 5PPM in greenhouse, water-immersed spots appeared at the tip of leaves, and then blackened and withered; when nitrogen dioxide reached 2.5 ─ 3PPM, irregular green-white spots appeared, and in serious cases, all leaves were bleached except veins. The production of ammonia and nitrogen dioxide is mainly due to the improper use of nitrogen fertilizer. The production of carbon monoxide and sulfur dioxide is mainly caused by heating with coal fire, incomplete combustion, or poor quality of coal. Due to the film aging (plastic pipe) can release ethylene, causing premature senescence of plants, so the excessive use of ethylene products is also one of the reasons.

In order to prevent the accumulation of harmful gases in the shed, fresh barnyard manure can not be used as base manure, nor manure that has not yet been mature can be used as topdressing; it is strictly forbidden to use ammonium carbonate as topdressing, urea or ammonium sulfate as topdressing should be mixed with water or cover soil in time after hole application; the amount of fertilizer should be appropriate and not excessive; ventilation should also be appropriate in the low temperature season in order to remove harmful gases. In addition, the quality of coal should be good and should be fully burned. If possible, hot air or hot water pipe should be used to heat up and discharge the burned waste gas out of the shed.

(5) 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. Topdressing should be light, and it is best to test soil and apply fertilizer. There should be no film cover for a certain time every year, or only cover the sunshade net for sunshade cultivation in summer, so that the soil can be dissolved by Rain Water. When the soil salinization is serious, flooding and pressing salt can be used, and the effect is very good. In addition, the use of soilless cultivation technology is a fundamental measure to prevent soil salinization.