In the winter and spring season, plastic greenhouses are not densely ventilated, and the high temperature and high humidity inside the plastic greenhouses make it very easy for the vegetables to be exposed to harmful gas, so that the plants will not grow well and will die when they die.

I. Harmful gas types and hazards

1. The two gases, ammonia and nitrous acid, mainly come from the nitrogen fertilizer and organic fertilizer applied to the soil. Especially in the case of over-fertilization and soil drought, the fertilizer will be decomposed in the short term if it encounters high temperatures in the greenhouse. A lot of ammonia. When the concentration of ammonia exceeds 5ppm, some sensitive vegetables, such as cucumbers, tomatoes, etc., will be damaged. At the beginning, the leaves will be burned like boiling water and become brown after drying. When the concentration of ammonia reaches 4%, the vegetables will be seedlings for 24 hours. It will die. When the content of nitrous acid gas in the air reaches 2-3ppm, it will cause damage to sensitive vegetables such as eggplant, tomato and pepper. The symptoms mainly occur on the leaves near the ground, rarely harm the new leaves, and start to be burned like boiling water. In the same way, due to the acidification of nitrous acid, the white veins gradually turned white. In severe cases, only the veins remained, and the leaves were bleached and withered.

2. When carbon monoxide and sulfur dioxide gas plastic greenhouses are heated by coal fire, they often produce large amounts of carbon monoxide and sulfur dioxide gas due to incomplete combustion or unsmooth flue. The hazards of these two gases can be divided into three types: First, hidden poisoning, the vegetables themselves have no obvious visible damage, but the reduction of assimilation performance, quality deterioration, generally have little effect on the yield; Second, chronic poisoning, gas Invade from the stomata on the back of the leaf, brown spots appear on the stomata and its surroundings, and the surface is yellow. Third, acute poisoning produces whitening symptoms similar to nitrous acid gas hazards.

3. Toxic gases emitted by the plastic film Some plastic films will generate volatile substances, such as ethylene and chlorine, which can invade the interior of the plant through the pores or water holes in the leaves, destroying the cell tissues and chloroplasts. Photosynthesis has been significantly weakened, seriously affecting the yield and quality of vegetables. According to data, the concentration of chlorine in the air reaches 0.1ppm. Exposure to radish can reach a concentration of 0.5-0.8ppm in 2 hours. It takes only 4 hours to injure most vegetables. It appears white or veins between veins. Light brown, irregular punctate or massive lesions, in which the entire leaf turns white or even falls off. When the concentration of ethylene gas in the protected area reaches more than 1 ppm, yellowing occurs between the leaf edges and veins of the vegetables, and then it turns white until Withered. According to the experimental observation, ethylene can also cause the leaves of many vegetables to droop and have an inhibitory effect on tomato seedlings; in the concentration range of 0.1-3ppm, flowers, buds, young fruits and leaves will appear in the range of 0.1-3ppm. Normally shedding.

In addition, when excessive aerosolized pesticides are used in greenhouses, they can also cause damage to vegetables.

Second, prevention and control measures

Harmful gases in greenhouses not only affect the growth and development of vegetables, but also directly harm the health of vegetable farmers. Therefore, we must actively take measures to prevent and control.

1, scientific fertilization greenhouse vegetable fertilization, should be high-quality soil miscellaneous fertilizer, appropriate application of phosphorus, potash fertilizer, appropriate amount of nitrogen fertilizer, and adhere to the base fertilizer-based, top dressing supplement. Topdressing must strictly follow the principle of “a small number of times” to prevent excessive fertilization. The topdressing method uses deep ditching, followed by soil tightness after application, and timely watering to dilute the fertilizer.

2, timely ventilation Ventilation utilization of high temperatures at noon, open the vents, so that air circulation; even in cloudy or snowy days, but also at noon for a short period of ventilation, in order to reduce the shed as much as possible harmful gases , reduce air humidity.

3. Reducing the source of toxic gas When the plastic greenhouse is heated by coal fire, it is necessary to make the fuel fully combust, install a chimney on the stove, and export the harmful gas out of the shed.

4. Non-toxic plastic film is not used as plastic film that incorporates more plasticizers.

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