In winter and spring cold seasons, crops grown in greenhouses, such as vegetables, fruit trees, flowers, etc., are often exposed to harmful gas due to high temperature, high humidity, and poor ventilation, causing poor plant growth and development and severe death. .
I. Harmful gas types and hazards
1, ammonia. Ammonia comes mainly from nitrogen fertilizers applied to the soil and organic fertilizers that are not fully decomposed, especially in the case of over-fertilization and soil drought. Fertilizers encounter high temperatures in the greenhouse and will decompose in the short term to generate large amounts of ammonia. When the concentration of ammonia exceeds 5 μg/mg, some sensitive crops, such as cucumbers and tomatoes, will be damaged, and they will be harmed, causing water-stained spots on the leaf ends, yellowing and browning of leaf edges, and then the leaves will dry up; Ammonia hazards mostly occur on the leaves on the outside of plants, and the damage to new leaves is particularly serious.
2, nitrous acid gas. Excessive application of nitrate-nitrogen fertilizers in the shed impedes soil nitrification, causing a large accumulation of nitrous acid gas. When the concentration reaches 2 μg/mg, the plants appear to have symptoms of poisoning, which often occurs on the middle leaves of the plants. Irregular green leaves of the affected leaves occur. White spots, the whole plant died when the concentration was too high.
3, sulfur dioxide. The sulphur dioxide gas generated during the coal-fired heating of the greenhouses generally invades the cells from the stomata on the back of the leaves, destroys the chloroplast tissue, produces dehydration, and causes leukoplakia and dryness in the affected leaves; in severe cases, the leaves of the entire plant turn green and the veins dry up. Turn brown.
4, carbon monoxide. When the greenhouses are heated, they may cause damage to some herbaceous flowers due to incomplete combustion or poor ventilation, which may cause damage to some herbaceous flowers. The damaged leaves lose their color, and the veins on the surface of the leaves first become water stains and then turn white and turn yellow. Eventually become irregular necrotic lesions.
5. The poisonous gas emitted by the film itself. Some plastic films will generate some volatile substances, such as ethylene, chlorine, 2-isobutyl phthalate, etc., and they can invade the interior of plants through the pores or water holes in the leaves, destroying the cells and Chloroplasts significantly reduce photosynthesis, and the leaves lose chlorosis, shrinkage and even dryness. It has been reported that when 2-isobutyl phthalate is dissolved in the water droplets of the shed to reach 10-30 μg/mg, the water droplets will be seriously poisoned after being atomized or absorbed by the vegetables through the roots and leaves. Role; chlorine concentration of 0.1 micrograms / mg, exposure to 2 hours will be able to make radish victims, the concentration of 0.5-0.8 micrograms / mg, only need to contact 4 hours will be able to make most crops damage; ethylene When the concentration of gas reaches 1 μg/mg or more, yellowing occurs between the leaf edges and veins of the vegetables, and then it turns white until it dies.
Second, prevention and control measures
1, a reasonable fertilization. In greenhouse crops, fertilization should be based on high-quality soil-based miscellaneous fertilizers. Phosphorus and potassium fertilizers should be added appropriately. Nitrogen fertilizer should be minimized, and no cake fertilizer and human waste should be applied. Base fertilizer should be the mainstay, and top dressing should be supplemented. Topdressing must strictly follow the principle of “a small number of times†to prevent excessive fertilization. Greenhouses used for nursery, as long as the seedlings grow normally, do not top-dressing; seedlings grow weak, the winter can choose to sunny noon high temperature period foliar spray fertilizer, spring spraying fertilizer after ventilation.
2, ventilation. In the case of not affecting the temperature, extend the ventilation time as much as possible to discharge toxic and harmful gases inside the shed, exchange fresh air, so that the gas composition inside the shed is close to the gas composition outside the shed. The winter is usually open at 8-9 a.m. In spring, with the rise of temperature, the ventilation time is gradually extended. When the temperature is high at noon, ventilation is carried out on cloudy days. Even if it is rain and snow, it is necessary to conduct ventilation at short noon to reduce harmful gases in the shed as much as possible. Reduce air humidity.
3, reduce the gas source. When the shed is heated with coal fire, it is necessary to make the fuel as full as possible, and to install chimneys on the stove to export harmful gases out of the shed.
4, use non-toxic film. Try not to use films with plasticizers or stabilizers for the film.
5. Remedy. It was found that crops were exposed to sulfur dioxide hazards and sprayed with barium carbonate, lime water, lime sulfur or 0.5% synthetic detergent solution in time. If exposed to ammonia, a 1% vinegar solution could be sprayed on the opposite side of the leaves.
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