Under the conditions of protected cultivation, the protection of flowers and plants is caused by unreasonable soil, fertilizer, gas, and temperature management, which leads to the production of some toxic gases. Because the enclosed gas in the environment is not easy to escape, it accumulates in the protected areas and endangers crop growth. Especially in the winter and spring season, the temperature is low, and the air permeability of the greenhouse is poor. In addition, the air is not released in time, and the internal and external gases cannot be exchanged in time, resulting in damage to the flowers in greenhouses. The light leaves are yellow, dry, and have poor growth. As the value is reduced and the plants in serious condition are dead, special attention should be paid to the occurrence and prevention of harmful gases in greenhouses and greenhouses. (1) Reasons for occurrence of flower damage in protected areas (1) Unreasonable use of fertilization Without the use of organic fertilizer without decomposition, no toxic gases such as nitrous acid gas, sulfur dioxide, and hydrogen sulfide will be generated during the fermentation without organic fertilizer. Excessive application of ammonium bicarbonate, ammonium sulfate, urea and other chemical fertilizers or fertilizer application is too shallow, applied to the topsoil, and watering after fertilization is not timely, will produce ammonia gas and nitrous acid. (2) Heating is not a scientific winter season. When the greenhouse is heated, the use of inferior coal, or incomplete combustion of coal, or unreasonable furnace design, rough installation, etc., can produce harmful gases such as carbon monoxide and sulfur dioxide. In addition, the quality of the film is poor, and excessive use of the drug can also cause damage to flowers. (2) The type of flower and gas damage in the protected land There are many hazards in the flower and gas hazards in the protected area. Nitrous acid gas poisoning and ammonia poisoning are the second most common sources, followed by carbon monoxide, sulfur dioxide, and poisonous gases volatilized from plastic films (such as o-phenylene). Diisobutyl formate, n-butyl ester, dioctyl adipate, etc.) and the like. (1) Nitric acid gas poisoning The main cause of nitrous acid gas is the decrease in the activity of nitrifying bacteria, the inhibition of the conversion of nitrite into nitrate, and the accumulation and decomposition of nitrous acid in the soil into nitric oxide gas, which is then oxidized by air. Nitric oxide, nitric acid, damages plants. The conditions for nitrite accumulation in soil are: a considerable amount of nitrogen is present: pH ≤ 5; soil temperature is low. The gasification of nitrous acid in the soil and the release of large amounts of nitrite gas is often caused by warming, so nitrous acid poisoning occurs when the temperature turns to sudden rise in temperature at low temperatures. The nitrogen fertilizer applied to the soil must go through the process of organic state ~ ammonium state ~ nitrite state ~ nitrate state, and finally use nitrate nitrogen for plant absorption and utilization. When the soil is acidic or the amount of nitrogen fertilization is too large, the above process is hindered, so that nitrous acid is not easily converted into nitric acid, and accumulates in the soil, resulting in the release of nitric acid and nitric oxide gas in the shed, if the ventilation is not timely, When the concentration reaches 2 ml per liter, poisoning symptoms occur. The victim's crop initially has water-soaked spots between the leaf margins or veins, and gradually loses greenness. After 1 to 2 days, it becomes yellowish-white or brownish and withered. There is a clear distinction between victimized organizations and sound organizations. The symptoms of victimization are usually the most severe in the median lobe, and new leaves near the growing point are generally not harmed. When the damage is severe, the leaves begin to wilt slowly after the morning air changes, and almost all of the flowers suffer the same symptoms. This situation mostly occurs 10 to 15 days after fertilization. Such as gerbera, starry sky and other prone to the above symptoms. (2) Ammonia poisoning Neutral to alkaline soils. When a large amount of ammonium nitrogen fertilizer is used, the ammonia produced by its decomposition will stagnate in the soil. When the temperature of strong light irradiation rises sharply, ammonia gas will escape; or it may be used. After ammonium nitrogen fertilizer, lime or alkaline fertilizer is applied to produce gaseous ammonia. Ammonia enters the plant through the stomata and damages the cells. The affected plants usually appear as water-soaked spots on the median lobe, yellowish-white or light-brown when dry, and can cause the whole plant to wither and die in severe cases. It is generally believed that when the concentration of ammonia in the air of the protected place reaches 5 ml per kilogram, vegetables will poison and die in only a few hours. When the concentration of ammonia reaches 4%, the plant will die within 24 hours. Such as cut roses often show the above symptoms. Ammonia harm occurs in the leaves on the outside of the plant, and the damage to new leaves is particularly serious. (3)Sulphur dioxide gas poisoning When using coal fire or sawdust combustion and heating in greenhouse heating, sulfur dioxide gas is decomposed and released due to insufficient combustion or unobstructed flue gas, and the presence of sulfur in the fuel or fertilizer that has not been completely decomposed. As a result, a large amount of sulfur dioxide is produced. The damage is generally the most vigorous leaf of the physiological activity, the whole leaf seems to burn like hot water, and gradually chlorosis. Sulfur dioxide generally invades from the stomata in the back of the leaf, destroys the chloroplasts, dehydrates the tissues, forms white spots in the affected part, and then dries up. In severe cases, the entire leaves turn green and the veins quickly dry up. If the stars, carnations, etc. are harmed, they show this symptom. (4) Diisobutyl phthalate poisoning Diisobutyl phthalate is an agricultural film plasticizer. It is covered with a plastic film containing this
Material in a greenhouse or a plastic product containing this material in a protective field. Use, easy to produce toxic gases, harmful to crops. For this kind of gas-sensitive flower seedlings, the victim's symptom is that the color of the leaves becomes lighter, gradually yellowing and turning white. Nearly two weeks or so, the whole plant withered, and the damage was aggravated when the temperature was high. The data shows that when the content of harmful substances such as 2-isobutyl phthalate in the water droplets reaches 10 to 20 mg per liter, the water droplets are atomized and absorbed through the roots or leaves, and they will have serious toxic effects. . (5) Ethylene and chlorine poisoning Polyvinyl chloride films will also volatilize some ethylene gas during use, thus endangering flower growth. When the ethylene concentration in the air reached 0.1 mg/l, the leaves of flowers sensitive to ethylene began to droop and the leaves turned green and yellow or white, and died severely. The plants that had blossomed resulted in falling and fruiting, and the young branches bent. In the polyvinyl chloride film, chlorine is volatilized due to impure raw materials. When the chlorine gas invades the leaf tissue, the chloroplast is first destroyed, and then the chloroplastic yellow, white, and severely die. When the concentration of chlorine in the air reaches 0.1 mg per liter, irregular brownish-brown spots appear on the leaves, and the leaves turn white or fall off in severe cases. When the ethylene content in the protected area reaches 1 mg/l, the yellow and white leaves of the flower will become yellow and dry. (6) Carbon monoxide greenhouses use coal fire to generate a large amount of harmful carbon monoxide when burned due to incomplete combustion or poor ventilation. When the concentration reaches 2 to 3 mg per litre, it will cause harm to some herbaceous flowers. At the beginning of the victim's leaf, the leaf surface and vein tissues become stain-like, and then turn white and yellow, eventually becoming irregular necrotic lesions. (7) Excessive use of aerosols (such as chlorothalonil and sirolimus) or excessive use of fumigant (dichlorvos) and unreasonable use of fumigants (such as formalin and methyl bromide can only be used in vacancies in plants. It is easy to produce phytotoxicity during the growing season. It will also cause yellowing and dryness of the leaves in flower plants. Especially in high temperature and high humidity conditions, the damage is more serious. (C) the simple diagnosis of flower damage in protected areas (1) the appearance of the diagnosis based on the various greenhouse gas flower damage hazards to determine, in particular, pay attention to observe the occurrence of leaf damage, as well as the victim site and the normal site boundaries. (2) Detection of pH Drop at the Top of the Shelf The ammonia and nitrous acid gases in the plastic greenhouse are tested for excess. The simplest and most common method is to determine the pH of the water droplets that drip from the top of the greenhouse. Taste dewdrops, taste also helps to judge, tongue dripping, there is a slippery sense of ammonia, such as taste is nitrous acid. (4) Comprehensive Prevention and Control of Flower and Gas Harm in Protected Areas Harmful gases in greenhouses not only affect the growth and development of flowers, but also directly endanger the health of flower farmers, and must take active measures to prevent and control them. (1) Rational fertilization This is a fundamental measure to prevent gas hazards in protected areas. Greenhouse flowers and fertilizers should be dominated by high-quality soil-based miscellaneous fertilizers, and phosphorus and potassium fertilizers should be appropriately increased to minimize nitrogen fertilizer application. The application of nitrogen fertilizer is based on base fertilizers, supplemented by topdressing. Do not apply cake fat and human waste, in particular, do not apply chemical fertilizers containing nitrogen and sulfides. Avoid using ammonium bicarbonate. When fertilization is required, strictly follow the “small amount†method of top dressing. When urea and ammonium sulfate are used as top dressings, they should be applied sparingly, and it is best to dilute it with 500 times water and pour it; organic fertilizers must be fully cooked before they can be used. Greenhouses used for nursery, as long as the seedlings grow normally, do not top-dressing. When the seedlings grow weak, the leaves should be sprayed at 11 o'clock in the sunny morning in winter and sprayed in the spring after ventilation. (2) Ventilation and ventilation in time This is an important measure to prevent air pollution in protected areas. Every morning use a pH test strip to measure the dew on the film. Under normal conditions, the pH of the water droplets is 7.0 to 7.2, that is, neutral or slightly alkaline, such as water droplets are alkaline, indicating excessive ammonia; water droplets are acidic, nitrous acid gas is too much. A pH of 5.5 or less will cause harm. Must be promptly released. Without affecting the temperature, increase the ventilation time as much as possible to discharge toxic and harmful gases, so that the gas composition inside the shed is close to the gas composition outside the shed. The winter is usually open at 8 to 9 am. The ventilation time in spring is gradually extended. Do not forget to open the door for ventilation especially at noon. Try to ventilate at noon on cloudy days. Even in the rain and snow, take a short time of ventilation at noon in order to minimize toxic gas and reduce air humidity in the shed. . Appropriately increase the amount of ventilation after top-dressing in the cold season to eliminate toxic gases. In the event of a hazard, the sheds should be ventilated and fully irrigated. For nitrous acid poisoning, soil acidity should be promptly corrected by lime, and nitrosative bacterial inhibitors can also be used. (3) Careful management, safety heating furnace and flue design must be reasonable, installation should be sealed. It is not necessary to use low-quality coal with high sulfur content, but also to wait for the normal combustion of coal before moving the coal stove into the shed to prevent the incomplete combustion of fuel to produce toxic gases such as carbon monoxide and sulfur dioxide. The second day after warming at night requires ventilation, preferably using pipe heating or electric heating. (4) Select high-quality plastic film as far as possible without plasticizers and other additives PVC film to reduce the volatilization of agricultural film itself toxic gases. The use of a polyethylene non-drip film also helps to improve the lighting conditions and temperature and humidity conditions in the shed, so as to reduce the source of poison, prevent harm, and promote flower growth. (5) Correct and reasonable use of chemical agents, especially aerosols. (6) Remedial measures When the symptoms of poisoning appear in plants, the cause should be identified. In addition to taking targeted measures, watering, fertilizing, loosening soil, etc. should be performed to promote the recovery of the damaged plants. Suspended flowers are exposed to sulfur dioxide. Flowers such as barium carbonate, lime water, lime sulfur, or 0.5% synthetic detergent are promptly sprayed. When exposed to ammonia, spraying 1% vinegar on the opposite side of the leaves has obvious effects. (Author: Zhang Jianguo: Zhejiang Forestry College)
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