Vegetables in greenhouses can keep warm and cold in winter, and adequate carbon dioxide can also be injected into greenhouses.

Seedling raising in nutrient bowl

The black plastic nutrition bowl has the functions of absorbing heat during the day and protecting roots at night. When the outside temperature is about-10℃, the temperature in the pot is about 6 ~ 7℃, and the temperature in the nutrition pot is about 10℃, the seedlings can grow slowly without freezing injury.

Preparation of hot nutrient soil

Chicken manure is hot manure, and cow manure is breathable manure rich in mucus. After they are decomposed, 20% is taken away and 60% is mixed with fine soil. This nutrient soil has good heat absorption and power generation performance, good seedling ecological environment, developed root system, strong absorption capacity and strong plant frost resistance.

Root irrigation with rooting agent during seedling division.

Rooting element is composed of several nutrient elements related to long roots, such as calcium, phosphorus and zinc. Calcium determines the thickness of roots, phosphorus determines the number of roots, and zinc determines the growth speed and length of roots. After using rooting agent, the root system can be increased by about 70% and the deep root can be increased by 25%. The root system is developed and the absorption capacity is strong, and seedlings and vines will not be frostbitten because of poor cold resistance caused by lack of water and elements.

Enough water to keep warm and prevent frostbite.

The specific heat of water is higher than that of air, and the heat dissipation is slow. In winter, the indoor soil moisture content is moderate, the pore cracks in the plough layer are fine, the roots are not suspended, the soil is warm, and the roots are not damaged by freezing. Therefore, the frost damage of seedlings is mostly caused by lack of water. Therefore, pouring enough water before winter or when the weather is fine (watering above 20℃) can prevent freezing injury.

Intertillage heat preservation and cold prevention

The floor is hard, which restricts hot air from entering the tillage layer during the day, and the soil stores less heat energy. In addition, the cracks in hard soil are large and deep, and the aggregate structure is poor, so it is easy to dissipate heat in the first half of the night, and the room temperature is low in the second half of the night, which is easy to cause freezing damage. Shallow intertillage can break the ground and close the seam, which can not only control the transpiration of groundwater to take away heat energy, but also keep moisture, keep warm, prevent cold and protect seedlings.

Spraying cold-resistant nutrients on leaves

In winter, the temperature is low, the light is weak, and the absorption capacity of roots is weak. Spraying photosynthetic micro-fertilizer on leaves can supplement the element deficiency caused by insufficient absorption of nutrients by roots. Spraying rice vinegar on leaves can inhibit bacteria and repel insects, and mixing with white sugar and calcium superphosphate can increase the sugar content and hardness of mesophyll and improve the cold resistance. After freezing injury, the leaf surface is alkaline atrophy, and spraying vinegar can reduce the degree of injury. It is advisable to use 100 ~ 300 times liquid, and use less or no growth hormone to prevent the cold resistance from decreasing.

Repeated exercise on sunny days

On sunny mornings in winter, the highest temperature in the shed can reach above 32℃. At this time, it is necessary to repeatedly reduce the outdoor temperature difference, so that plants can slowly adapt to the environment and grow healthily. Beware of sudden growth in one day and sudden cold in ten days, causing flash seedlings and freezing damage. ?

Supplementing carbon dioxide

The yield effect ratio of carbon and nitrogen on crops is 1: 1, and the demand of crops for carbon and nitrogen ratio is 30: 1. At present, most farmers have realized the role of nitrogen in increasing production, but neglected the role of carbon in increasing production. In winter, vegetables in greenhouses grow yellow easily. The carbon dioxide produced by crop respiration and soil microbial decomposition at night can be absorbed after the sun comes out 1 hour, and it will be in a state of carbon hunger about 12 hours. When the temperature is high, the greenhouse film can be opened and closed to release external carbon dioxide and improve resistance and yield. When the temperature is low, closing the greenhouse and artificially supplementing carbon dioxide can enhance the cold resistance of crops and greatly increase the yield.

Timely covering and heat preservation

Generally, greenhouses absorb heat and store energy during the day and release energy at night, accounting for 50% ~ 60% of the total indoor volume; Soil heat absorption and release accounts for 20% ~ 30%; Space thermal storage accounts for 20% ~ 30%. Depending on the temperature of the day, after covering 1 hour, the room temperature may remain around 18℃. It can be covered later when it is higher than 18℃, and earlier when it is lower than 18℃.

Select straw mulch

The thermal conductivity of straw mulch is lower than that of cattail mulch, and it has good cold resistance. In addition, the straw mulch is soft and compact, which can reduce the conduction heat loss and increase the indoor minimum temperature by 2 ~ 3℃ at night.

Covered multilayer film insulation

Seedling is raised in greenhouse, the seedbed is covered with film, then a small arch shed is supported at the height of 1 m, and a film is covered outside the small arch shed or 20 cm away from the greenhouse at night. In this way, various seedlings can be cultivated without heating. After planting, cover the ridge with plastic film, keep moisture, control humidity and raise the temperature, but don't seal the ground too tightly, leaving 15 ~ 20 cm, so that the heat energy stored in the soil can slowly radiate to the space through the bare ground at night, and the minimum temperature will increase 1 ~ 2℃ at 5 ~ 7 in the morning. Cover the grass with a film, or support a film 20 cm away from the film to form an insulation layer, which can increase the room temperature by 1 ~ 3℃.

Choose purple film

The ultraviolet in the solar spectrum in winter is only about 5% of that in summer. The white film can't penetrate ultraviolet rays, but the purple film can. Ultraviolet spectrum can inhibit diseases and sterilization, control plant overgrowth and promote nutrient accumulation. The room temperature of purple film is 2 ~ 3℃ higher than that of green film in winter.

Matters needing attention

Plastic greenhouses are closed in winter and spring, with high temperature and high humidity. Vegetables with vigorous growth are easily affected by harmful gases, which makes the plants grow poorly and wither and die in severe cases.

I. Types and hazards of harmful gases

1, ammonia gas and nitrous acid gas mainly come from nitrogen fertilizer and organic fertilizer applied to the soil, especially in the case of excessive fertilization and soil drought, when the fertilizer encounters high temperature in the shed, it will decompose to produce a large amount of ammonia gas in a short time. When the concentration of ammonia exceeds 5ppm, some sensitive vegetables, such as cucumbers and tomatoes, will be hurt. At first, the leaves turned brown after drying, as if they had been scalded by boiling water. When the concentration of ammonia reaches 4%, the vegetable seedlings will die after 24 hours. When the content of nitrite gas in the air reaches 2-3ppm, it will harm sensitive vegetables such as eggplant, tomato and pepper, and its symptoms mainly occur on leaves near the ground, and rarely harm new leaves. It was like being scalded by boiling water at first. Later, due to the acidification of nitrite, the veins gradually turned white, and in severe cases, only the veins were left, and the mesophyll bleached and died.

2. When the plastic greenhouse containing carbon monoxide and sulfur dioxide gas is heated by coal fire, a large amount of carbon monoxide and sulfur dioxide gas will often be produced due to incomplete combustion or unsmooth flue. The harm of these two gases can be divided into three types: first, hidden poisoning, vegetables themselves have no obvious harm, but the assimilation function is reduced and the quality is worse, which generally has little effect on yield; Second, chronic poisoning, gas invades from the stomata on the back of the leaves, brown spots appear in and around the stomata, and the surface is yellow; The third is acute poisoning, which produces whitening symptoms similar to the harm of nitrous acid gas.

3. Toxic gas emitted by plastic film itself Some plastic films will produce some volatile substances, such as ethylene and chlorine. It can invade plants through stomata or water holes on leaves, destroy cell tissues and chloroplasts, obviously weaken photosynthesis, and seriously affect the yield and quality of vegetables. According to some data, the concentration of chlorine in the air reaches 0. 1ppm, radish can be damaged after 2 hours of contact, and the concentration reaches 0.5-0.8ppm. Most vegetables can be damaged after only 4 hours of contact. At first, white or light brown irregular spots or blocks appeared between the veins, and in severe cases, the whole leaves turned white or even fell off. When the concentration of ethylene gas in the protected field reaches more than 1ppm, the leaves between the veins of vegetables can turn yellow, and then turn white until they die. According to experimental observation, ethylene can also make many vegetable leaves droop and inhibit tomato seedlings; In the concentration range of 0. 1-3ppm, the flowers, buds, young fruits and leaves of tomato and eggplant will fall off abnormally.