The temperature in winter and spring is low, the air permeability in the greenhouse is poor, and the humidity is high. Vegetables are vulnerable to poisonous and harmful gases, causing poor plant growth and even withering. Therefore, it must be effectively controlled. When the poisonous temperature room in the fuel is heated by coal fire, a large number of toxic gases, such as carbon monoxide and sulfur dioxide, are often generated in the greenhouse due to the quality of the coal, improper heating method, or unfavorable wind direction. The hazards of these gases can be divided into three types: First, hidden poisoning. No obvious symptoms of vegetables, but the reduction of assimilation and quality deterioration; the second is chronic poisoning. Gases invade the plant from the stomata on the back of the leaf, brown spots appear in the stomata and its surroundings, and the surfaces of the leaves are yellow; third, acute poisoning. Hypochromic symptoms similar to those of nitrous acid gas were produced, and the cotyledons of vegetables seedlings turned white and litter. The internal cells of the leaves, leaf margins, and veins of the plants died and the whole plant died. At the same time, these gases are also harmful to people entering the greenhouse. Therefore, we must improve the heating facilities and provide timely ventilation. When the greenhouse is heated with coal fire, it must be fully burned, and the flue can't have smoke leakage. When temporarily warming up in order to prevent cold current, install a chimney on the stove to discharge harmful gases. Biogas digesters can also be constructed near greenhouses, replacing coal fire heating with biogas combustion during the cold season. This can avoid the production of carbon monoxide, which can increase the temperature and supplement carbon dioxide gas fertilizer for vegetable growth. The use of farmyard manure in the protection of toxic gas in fertilizers, excessive use of chemical fertilizers, or improper use methods, especially when raw manure is applied to land, will produce a large amount of ammonia that is toxic to vegetables. Ammonia and water can be absorbed by vegetables and become toxic substances. In the cultivation of facilities, the concentration of ammonia gas is in the range of 1000ppm to 2000ppm, and some sensitive vegetables such as cucumbers and tomatoes will be damaged. In the beginning, the leaves were burnt like water, and they turned brown after they had dried off. This caused wilting poisoning. When ammonia concentration reaches 4000ppm, the whole plant will die. Nitrogen fertilizers such as urea, ammonium sulfate and carbon ammonia will also release large amounts of ammonia when applied under high temperature conditions. If the concentration is too large, leaf poisoning may occur. In the case of low ammonia levels, nitrite gas is also generated and nitrous acid poisoning occurs. If the amount of nitrous acid in the air reaches 2 to 3 mg/l, sensitive vegetables such as eggplant, tomatoes and peppers will suffer. Most of the symptoms of the victim appear 10 to 15 days after fertilization. The leaves near the ground are initially hot-water-like, and due to the acidification of nitrous acid, the veins gradually turn white. In severe cases, only the veins are left. Indoor fertilization in sheds should be dominated by high-quality soil-based miscellaneous fertilizers. Phosphorus and potash fertilizers should be applied appropriately. Nitrogen fertilizer should be minimized, rapeseed cake without application, human feces and urine without compost, and chicken manure must not be used in greenhouses. Neodymium fertilizer. Adhere to the "basic fertilizer, supplemented by top dressing" principle of fertilization. The specific method: from the beginning of October, before the film covering the greenhouse, a one-time application of fertilizer. Mix the various fertilizers thoroughly, spread them evenly on the ground and plunge into the soil. After the fertilizer is applied a small number of times to prevent overdosing. When chasing urea, it should not exceed 0.6 kg per 10 square meters. When applying topdressing, it is necessary to deepen the ditch, cover the soil after application, and water in time to release the fertilizer. Scientific application of nitrogen fertilizer, timely ventilation, prevention and control of ammonia harm. Try to control the amount of nitrogen fertilizer, timely watering, deep application of fertilizer and cover soil. In addition, when the temperature is high at noon, vents are opened to allow air to circulate. Even in cloudy or rainy days, ventilation should be performed for a short period of time. Do not ventilate for a few days because the temperature is low. In plastics, toxic gases, such as plasticizers, stabilizers, and active agents added during the production of plastic films, can cause toxic gases such as ethylene, chlorine, or phthalic acid to evaporate when they are exposed to high temperatures. 2-isobutyl ester and so on. These toxic gases can invade the interior of the plant body through the pores or pores of the leaves, destroy the cell structure, and affect the yield and quality of the vegetables. According to data, 2-isobutylphthalate is dissolved in the water droplets of the greenhouse film. When the content reaches 10 to 20 mg/l, the water droplets are absorbed by the vegetables after they are atomized or absorbed by the vegetables. Poisoning effect. The concentration of chlorine in the air reaches 0.1 mg/l, and it takes only 4 hours for most vegetables to suffer. Initially, white or light brown irregular spot-like or massive lesions appeared between the veins, and the entire blade turned white and even fell off in severe cases. When the concentration of ethylene gas in the protected area exceeds 1 mg/l, yellowing may occur between the leaf edges and veins of the vegetables, and finally it turns white until it dies. The use of plastic film should be selected through the relevant departments of the test, identification of qualified products, and try to use non-toxic plastic film. Commonly used pesticides such as Bordeaux mixture, DT and other copper preparations, and organophosphorus pesticides are safe for use in open field cultivation. However, when used in a confined protected environment, it is often caused by excessively high temperature in the greenhouse, excessive separation of toxic ions, and slow air flow to accumulate harmful substances. If copper pesticides are used in greenhouses, they will release copper ions and produce phytotoxicity when they encounter high temperatures. Trichlorfon will produce free chlorine ions and cause poisoning during high-temperature transpiration. Attention should be paid to prevention.
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