Greenhouse Vegetables and Their Prevention and Control Measures

In winter, plastic greenhouses are not densely ventilated. Inside, the temperature is high and the humidity is high. Vegetables that thrive are vulnerable to harmful gases, causing poor plant growth and development, and can cause death and death when severe.

Harmful gas types and their hazards

The two gases, ammonia and nitrous acid, mainly come from the nitrogen fertilizers and organic fertilizers applied to the soil. In particular, when fertilizers are applied excessively and in the case of soil drought, the fertilizers encounter high temperatures in the greenhouse and will be in the short term (usually Decomposition produces a large amount of ammonia 3-4 days after fertilization. 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 vegetable seedlings 24 hours will die. When nitrite gas reaches 2-3ppm in air, it will cause damage to susceptible vegetables such as eggplant, tomato, and pepper. Symptoms mainly occur on the leaves near the ground, rarely harm the new leaves, and start to be burned like boiling water. 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 died. This situation mostly occurs 10-15 days after fertilization.

The simplest and most commonly used method to check whether ammonia gas and nitrous acid gas are excessive in plastic greenhouses (or greenhouses) is to determine the pH of the water droplets that drip from the top of the greenhouse, that is, the pH value. Under normal conditions, the pH of the water droplets is 7.0-7.2, that is, neutral or slightly alkaline, such as water droplets are alkaline, indicating excessive ammonia; water droplets are acidic, the nitrite gas is too much, the pH value is Below 5.5, it will cause harm.

When carbon monoxide and sulfur dioxide gas plastic greenhouses are heated by coal fire, they often produce large amounts of carbon monoxide and carbon dioxide gas due to incomplete combustion or unsmooth flue gas. 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 assimilation function is reduced, the quality is deteriorated, and the impact on the yield is not significant; second, chronic poisoning, gas From the intrusion of stomata on the back of the leaves, brown spots appear on the stomata and its surroundings, and the surface is yellowed. Third, acute poisoning produces whitening symptoms similar to nitrous acid gas.

The toxic gas emitted by the plastic film itself. Some plastic films will produce some volatile substances, such as ethylene, chlorine, isobutyl ester, etc., and can invade the interior of the plant through the pores or water holes in the leaves, destroying the cell tissues and chloroplasts. , Photosynthesis significantly weakened, seriously affecting the yield and quality of vegetables. Some data indicate that when the amount of isobutyl ester dissolved in the film water droplets reaches 10-20 ppm, the water droplets will be seriously poisoned after being atomized or absorbed by the roots and leaves of the vegetables; the concentration of chlorine in the air will reach O. At .lppm, most vegetables are injured in only 4 hours of exposure. Initially, white or light brown irregular punctate or massive lesions appear between the veins. In severe cases, the entire leaf turns white or even falls off; When the concentration of ethylene gas is more than lppm, yellowing may occur between the leaf edges and veins of vegetables, and then it turns white until it dies. 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 tomato, eggplant, etc. Normal shedding.

In addition, excessive use of aerosol pesticides in greenhouses (or greenhouses) can also cause damage to vegetables. Excessive use of chlorothalonil fumigant may cause wilting and death of the top leaf and edge tissues of vegetables, especially in high temperature and high humidity conditions.

Prevention

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 based on high-quality soil miscellaneous fertilizer, appropriate application of phosphorus, potassium fertilizer, minimize the use of nitrogen fertilizer, do not apply cake fat and human waste, 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. When urea is generally topdressed, it should not exceed 0.6 kg per 10 square meters. The topdressing method uses deep ditching. After the application, it is covered with soil and watered in time to dilute the fertilizer.

2. Prompt ventilation Ventilation Use open air vents at noon to allow air to circulate. Even in cloudy or snowy days, ventilate at short noon for short periods of time to minimize harmful gases in the shed. , reduce air humidity.

3. Reducing toxic gas sources When using coal fire to warm the plastic greenhouses, it is necessary to make the fuels burn as much as possible, and install chimneys on the stoves to export harmful gases out of the shed.

4. Use of non-toxic plastic film does not use plastic film incorporating more plasticizers as a film.

5. Remedial measures When greenhouse vegetables are exposed to the hazard of sulfur dioxide, spray cesium carbonate, lime water, lime sulfur or 0.5% synthetic detergent solution in time. Cucumber suffers from ammonia hazards. Spraying a 1% vinegar solution on the opposite side of the leaves all has the effect of significantly reducing the hazard.

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