In the cold season of winter and spring, crops cultivated in greenhouses, such as vegetables, fruit trees, flowers, etc., often suffer from harmful gases due to high temperature, high humidity and poor ventilation, which cause plant growth and development, and die in severe cases. .
First, the types and hazards of harmful gases
1. Ammonia. Ammonia gas mainly comes from nitrogen fertilizer applied to the soil and organic fertilizer that has not been fully decomposed. Especially in the case of excessive fertilization and soil drought, the fertilizer will decompose and produce a large amount of ammonia gas in a short period of time when it encounters high temperature in the shed. When the concentration of ammonia exceeds 5 μg/mg, some sensitive crops, such as cucumber and tomato, will be harmed, and will be damaged, causing water-spotted spots on the leaves, yellowing and browning of the leaves, and then the leaves will dry up; The ammonia hazard occurs mostly on the leaves on the outside of the plant, and the new leaves are particularly affected.
2. Nitrous acid gas. Excessive application of nitrate-nitrogen fertilizer in the shed hindered soil nitrification and caused a large accumulation of nitrous acid gas. When the concentration reached 2 μg/mg, the plant showed symptoms of poisoning, which often occurred on the middle leaves of the plant, and the affected leaves were irregularly green. White spots, when the concentration is too high, the whole plant dies.
3. Sulfur dioxide. The greenhouse uses sulfur dioxide gas generated when coal fire is heated. Generally, it invades cells from the pores on the back of the blade, destroys the chloroplast tissue, produces dehydration, and the white leaves and dryness appear in the damaged leaves. In severe cases, the whole plant leaves become green and the veins dry. Turn brown.
4. Carbon monoxide. When the greenhouse is heated, it is easy to produce a large amount of carbon monoxide due to incomplete combustion or poor ventilation. It will cause damage to some herbaceous flowers; the damaged leaves will fade, and the leaf veins on the surface of the leaves will first become water-stained, then turn white and yellow. Eventually it becomes an irregular necrotic lesion.
5. The toxic gas emitted by the shed film itself. Some plastic films will produce some volatile substances, such as ethylene, chlorine, 2-isobutyl phthalate, etc., and can invade the inside of the plant through the pores or water holes in the leaves, destroying the cell tissues and The chloroplast makes the photosynthesis significantly weakened, and the leaves are chlorotic, wrinkled and even dried. It has been reported that when the amount of 2-isobutyl phthalate dissolved in the water droplets of the shed film reaches 10-30 μg/mg, the water droplets will be seriously poisoned after being atomized or absorbed by the roots and leaves through the vegetables. The concentration of chlorine gas reaches 0.1 μg/mg, and the radish can be harmed by exposure for 2 hours. The concentration reaches 0.5-0.8 μg/mg. Only 4 hours of exposure can damage most crops; When the concentration of the gas reaches 1 μg/mg or more, the leaf margin and the veins of the vegetables are yellowed, and then whitened until they die.
Second, prevention measures
1. Rational fertilization. Fertilization of greenhouse crops should be based on high-quality soil and mixed fertilizers. Phosphorus and potassium fertilizer should be added as appropriate, nitrogen fertilizer should be applied as little as possible, no fertilizer and human waste should be applied, and the base fertilizer should be adhered to, and topdressing should be supplemented. Topdressing should be strictly in accordance with the principle of “small number of times†to prevent excessive fertilization. For greenhouse cultivation, as long as the seedlings grow normally, they may not be topdressed; if the seedlings are weak, the winter leaves may be sprayed at high temperature during noon, and the springs may be sprayed after ventilation.
2, ventilation and ventilation. If the temperature is not affected, the ventilation and ventilation time should be extended as much as possible to discharge the toxic and harmful gas in the shed, and the fresh air is exchanged to make the gas component in the shed close to the gas component outside the shed. In the winter, the door is generally open at 8-9 am. In the spring, with the temperature rising, the ventilation time is gradually extended. On cloudy days, the ventilation should be carried out at a high temperature at noon. Even in rainy and snowy days, a short ventilation should be carried out at noon to reduce the harmful gases in the shed as much as possible. Reduce air humidity.
3. Reduce the source of poison gas. When the shed is heated by coal fire, the fuel should be fully burned as much as possible, and the chimney should be installed on the stove to discharge harmful gases out of the shed.
4. Use a non-toxic shed film. Try not to use a film with a plasticizer or stabilizer as a film.
5. Remedy. It was found that the crop was damaged by sulfur dioxide, spraying strontium carbonate, lime water, stone sulphur or 0.5% synthetic detergent solution in time; and suffering from ammonia hazard, spraying 1% vinegar solution on the opposite side of the leaf.
First, the types and hazards of harmful gases
1. Ammonia. Ammonia gas mainly comes from nitrogen fertilizer applied to the soil and organic fertilizer that has not been fully decomposed. Especially in the case of excessive fertilization and soil drought, the fertilizer will decompose and produce a large amount of ammonia gas in a short period of time when it encounters high temperature in the shed. When the concentration of ammonia exceeds 5 μg/mg, some sensitive crops, such as cucumber and tomato, will be harmed, and will be damaged, causing water-spotted spots on the leaves, yellowing and browning of the leaves, and then the leaves will dry up; The ammonia hazard occurs mostly on the leaves on the outside of the plant, and the new leaves are particularly affected.
2. Nitrous acid gas. Excessive application of nitrate-nitrogen fertilizer in the shed hindered soil nitrification and caused a large accumulation of nitrous acid gas. When the concentration reached 2 μg/mg, the plant showed symptoms of poisoning, which often occurred on the middle leaves of the plant, and the affected leaves were irregularly green. White spots, when the concentration is too high, the whole plant dies.
3. Sulfur dioxide. The greenhouse uses sulfur dioxide gas generated when coal fire is heated. Generally, it invades cells from the pores on the back of the blade, destroys the chloroplast tissue, produces dehydration, and the white leaves and dryness appear in the damaged leaves. In severe cases, the whole plant leaves become green and the veins dry. Turn brown.
4. Carbon monoxide. When the greenhouse is heated, it is easy to produce a large amount of carbon monoxide due to incomplete combustion or poor ventilation. It will cause damage to some herbaceous flowers; the damaged leaves will fade, and the leaf veins on the surface of the leaves will first become water-stained, then turn white and yellow. Eventually it becomes an irregular necrotic lesion.
5. The toxic gas emitted by the shed film itself. Some plastic films will produce some volatile substances, such as ethylene, chlorine, 2-isobutyl phthalate, etc., and can invade the inside of the plant through the pores or water holes in the leaves, destroying the cell tissues and The chloroplast makes the photosynthesis significantly weakened, and the leaves are chlorotic, wrinkled and even dried. It has been reported that when the amount of 2-isobutyl phthalate dissolved in the water droplets of the shed film reaches 10-30 μg/mg, the water droplets will be seriously poisoned after being atomized or absorbed by the roots and leaves through the vegetables. The concentration of chlorine gas reaches 0.1 μg/mg, and the radish can be harmed by exposure for 2 hours. The concentration reaches 0.5-0.8 μg/mg. Only 4 hours of exposure can damage most crops; When the concentration of the gas reaches 1 μg/mg or more, the leaf margin and the veins of the vegetables are yellowed, and then whitened until they die.
Second, prevention measures
1. Rational fertilization. Fertilization of greenhouse crops should be based on high-quality soil and mixed fertilizers. Phosphorus and potassium fertilizer should be added as appropriate, nitrogen fertilizer should be applied as little as possible, no fertilizer and human waste should be applied, and the base fertilizer should be adhered to, and topdressing should be supplemented. Topdressing should be strictly in accordance with the principle of “small number of times†to prevent excessive fertilization. For greenhouse cultivation, as long as the seedlings grow normally, they may not be topdressed; if the seedlings are weak, the winter leaves may be sprayed at high temperature during noon, and the springs may be sprayed after ventilation.
2, ventilation and ventilation. If the temperature is not affected, the ventilation and ventilation time should be extended as much as possible to discharge the toxic and harmful gas in the shed, and the fresh air is exchanged to make the gas component in the shed close to the gas component outside the shed. In the winter, the door is generally open at 8-9 am. In the spring, with the temperature rising, the ventilation time is gradually extended. On cloudy days, the ventilation should be carried out at a high temperature at noon. Even in rainy and snowy days, a short ventilation should be carried out at noon to reduce the harmful gases in the shed as much as possible. Reduce air humidity.
3. Reduce the source of poison gas. When the shed is heated by coal fire, the fuel should be fully burned as much as possible, and the chimney should be installed on the stove to discharge harmful gases out of the shed.
4. Use a non-toxic shed film. Try not to use a film with a plasticizer or stabilizer as a film.
5. Remedy. It was found that the crop was damaged by sulfur dioxide, spraying strontium carbonate, lime water, stone sulphur or 0.5% synthetic detergent solution in time; and suffering from ammonia hazard, spraying 1% vinegar solution on the opposite side of the leaf.
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