Vegetables are vulnerable to harmful gases and affect practical value. Therefore, the occurrence and prevention of harmful gases in greenhouses should be paid attention in the spring. First, common types of air 1. Ammonia poisoning Greenhouses that are not fully matured using organic fertilizers (such as compost, ring fertilizers, cakes, etc.) or using large amounts of inorganic fertilizers such as urea and ammonium bicarbonate will produce high temperatures in the fermentation process, resulting in ammonia production. Ammonia can invade cells from the leaves of vegetables and invade cells, destroy chlorophyll, cause water-stained spots on the affected leaf ends, yellowing and browning of leaf edges, and finally leaves dry. A high concentration of ammonia also decomposes the chlorophyll of vegetables, and there are spots between the veins, dark brown patches, and a clear boundary between normal tissue. In severe cases, the leaves droop and show a wilting state. 2. The excessive use of ammonium nitrate in the nitrous acid poisoning shed prevented the nitrification of the soil and caused a large amount of nitrous acid gas to accumulate. After accumulating to a certain extent, the plants exhibited symptoms of poisoning and irregular green-white spots on the damaged leaves. 3.Sulphur dioxide poisoning Sulfur dioxide gas is generated when greenhouses are heated. They invade through the stomata on the back of the leaves, destroying the chloroplast tissue of the vegetables, causing dehydration, forming white spots and dryness. In severe cases, the whole leaves turn green and the veins turn brown. 4. When the carbon monoxide poisoning greenhouse is heated by coal fire, the combustion is not complete or the ventilation is not smooth, resulting in a large amount of carbon monoxide. When the concentration reaches a certain level, the affected leaves begin to fade, and the leaf surface veins become water stains and then turn white and turn yellow. Becomes irregular necrotic spots. 5. In the sulfite poisoning shed, a large amount of ammonium sulfate, potassium sulfate, and unrefined cake fertilizers are used to decompose and produce sulfur dioxide gas. Water will turn into sulfite, destroying the chlorophyll in the leaves of the vegetables, acidifying the soil, and reducing soil fertility. After cell necrosis near the stomata of the poisoned leaves, they appeared round or rhombic white spots and gradually withered off. 6. Carbon dioxide poisoning The high concentration of carbon dioxide in the air inside the shed often causes the leaves of the vegetables to curl. The chloroplasts inside the leaf cells are seriously deformed due to excessive accumulation of starch, affecting the normal photosynthesis, and withering when severe. High carbon dioxide concentration will also affect the crop's absorption of oxygen, can not be normal respiratory metabolism and affect normal growth and development, and promote the aging process. In addition, when the greenhouse carbon dioxide concentration is too high, if not timely ventilation, so that the temperature within the greenhouse quickly increased, causing the high temperature hazards of vegetables. 7. Film gas poisoning Plastic film with diisobutyl phthalate or n-butyl ester as a plasticizer, volatile gases such as ethylene, propane, chloroform, and tetrapentenyl alcohol are easily volatilized under high temperature and accumulated to certain extent. When the degree, the leaves are chlorotic, yellow, white, and dry. Second, common gas diagnosis The detection of harmful gases in greenhouses and greenhouses in spring is generally judged by the detection of dewdrops in greenhouses. The dew formed by carbon dioxide is acidic, and the dew formed by ammonia is alkaline. The detection of pH of dew drops is usually performed before the morning ventilation. The detection method can use precise Ph Test Paper to determine the type of gas and the degree of injury according to the detection result of dew pH. If the pH is less than 4.6, ammonia, sulfur dioxide, carbon dioxide and other gases are harmful. Third, the common gas prevention and control 1. Reasonable fertilization Greenhouse vegetables in greenhouses should be dominated by high quality decomposing soil miscellaneous fertilizers and green manures. Appropriate application of P and K fertilizers should be carried out with as little or no nitrogen as possible. The application of ammonia nitrogen fertilizer is mainly based fertilizer, supplemented by topdressing, and the topdressing fertilizer concentration is reduced as much as possible. Do not use chemical fertilizers containing chlorine and sulphides. When chemical fertilisers are needed, they should be strictly followed in accordance with the principle of top dressing with “a small number of times and thin fertilizers.†It is best to use a combination of water and water. When fertilizing in spring, it is best to select the foliar dressing between 11 am and 2 pm on sunny days. 2. Prompt ventilation On the one hand, the temperature in the greenhouse must be guaranteed. On the other hand, the time for ventilation and ventilation should be increased as much as possible to exclude toxic and harmful gases in the greenhouse and to inhale fresh air. Open ventilation at 10 to 12 in the morning in spring. As the temperature rises, the ventilation time is gradually extended. In the sunny days, the ventilation at high noon temperature is as high as possible. Even if it is rain or snow, ventilation should be performed at noon for a short period of time to minimize harmful gases and reduce air humidity. 3. Reducing the use of coal fire for heating in poisonous greenhouses, it is necessary to ensure that the fuel is fully burned, and that chimneys are installed on the stove to direct the harmful gases out of the shed. At the same time, attention should be paid to ventilation to prevent carbon monoxide and carbon dioxide from causing damage. 4. Carefully select the membrane as much as possible without the use of toxic plastic films with plasticizers or stabilizers. Use vinyl synthetic resin plastic film to reduce the source of the poison and prevent damage. Urine Glucose Test Strips,Urine Test,Urine Test Paper,Protein Urine Strips Changchun Medicon Technology Development Co., Ltd , https://www.teststrip.pl