I、Types and hazards of harmful gases

1、Ammonia(NH3) and nitrous acid gas

These two gases mainly come from the application of nitrogen fertilizer and organic fertilizer in the soil. Especially in the case of excessive fertilization and soil drought, fertilizer encountered indoor high temperature, it will produce a large number of ammonia decomposition in the short term. When the ammonia concentration was more than 5ppm, some sensitive vegetables, such as cucumber, tomato and so on will be hurt, like boiling water burns first leaves, dried brown; ammonia concentration reached 4%, vegetable seedlings after 24 hours will be dead. The content of nitrite in gases in the air at 2-3ppm, the eggplant, tomato and pepper and other sensitive vegetables suffer symptoms occurred mainly in the leaves near the ground, little harm new leaves, also began to like boiling water burns, due to the subsequent acidification of nitrite, the interveinal gradually turned white, serious when leaving only mesophyll veins, bleaching and die.

2、Carbon monoxide(CO) and sulfur dioxide(SO2)

The greenhouse heating coal, because of incomplete combustion flue or not smooth, tend to produce large amounts of carbon monoxide and sulfur dioxide gas. The harm of these two gases can be divided into three types: First is the recessive poisoning, vegetable itself has no visible damage characters, only assimilation function is reduced, the quality, the general has little effect on yield; Second chronic poisoning, gas from the back of the blade stomata invasion, brown spots, in the hole and the surrounding gas the surface is yellow; Third acute poisoning, and nitrite gas hazards similar whitening symptoms.

3、Toxic gas emitted by plastic film

Data show that the concentration of chlorine gas in the air reaches 0.1ppm, 2 hours contact can make the radish suffer concentration reached 0.5-0.8ppm, only need to contact 4 hours can make the most of the vegetables were hurt, the first between the veins appear irregular white or pale brown punctate or massive injury spot, serious when the whole leaf white or even fall off; the concentration of ethylene gas in the protected area reached above 1ppm, the yellow leaf margin between vegetable and leaf, and white until dead. According to the experimental observation, ethylene can make a variety of vegetables have drooping leaves, and has inhibitory effect on tomato seedlings; in the concentration range of 0.1-3ppm, tomato, eggplant and so there will be flowers, buds and young fruit and leaf abnormal shedding. In addition, in the greenhouse when the use of aerosol pesticides excessive, it will cause harm to vegetables.

 

II、 Prevention and control measures

The harmful gas in the greenhouse, not only affects the growth and development of vegetables, but also directly threatens the health of farmers. Therefore, we must actively take measures to prevent and control.

1、Scientific fertilization

The fertilization of greenhouse vegetables, should be high-quality manure, phosphorus and potassium fertilizer increasing, little amount of nitrogen, and adhere to the base fertilizer, topdressing. Topdressing should be strictly in accordance with the principle of "a few times" to prevent excessive fertilization. The method of top dressing was made by deep furrow irrigation, and then covered with soil cover.

2、Timely ventilation

Use at higher temperature, open vents, air circulation; even in cloudy or snow, ventilation should be short time at noon, to minimize the harmful gases, reduce air humidity.

3、Reduce toxic gas source

Plastic greenhouse by coal-fired heating, make full combustion of fuel and chimney installation on the fire, harmful gases to the outside.

4、Non toxic plastic film

Do not use plastic film by incorporation of more agents for plastic films.

Oceanus recommends the use of a fixed gas detector in the greenhouse, at any time to detect the concentration of gas to ensure the growth of crops in a suitable environment.