Fog weather frequently occurs in northern China in winter. As long as there is fog, the growth and development of vegetables in the greenhouse will be affected, especially continuous fog, which seriously affects the yield and quality of greenhouse vegetables. More than 10 consecutive days of heavy fog in the middle and late December resulted in the yellowing of tomato leaves in many greenhouses in Linyi County, Shandong Province, where the growth and development stagnated, and the yield dropped dramatically.
Effect of heavy fog on the growth and development of greenhouse vegetables
1. Low greenhouse temperature In the event of heavy fog, the light intensity will be weakened. Illumination is the main source of greenhouse heat in winter, so in heavy fog weather, the temperature in the greenhouse is generally low and it is not suitable for the growth of vegetables. In many greenhouses in Linyi in late December, the temperature during the day is less than 20Â°C. Vegetables such as cucumbers and tomatoes cannot be used for photosynthesis and no nutrient accumulation is possible. The nighttime temperature is often below 10Â°C, causing the tomatoes to not turn red and cold. The decrease in temperature also greatly reduces the temperature of the ground. The ground temperature is generally below 15 degrees. Too low ground temperature causes the growth of the root system to stagnate and the absorption function is extremely weakened.
2. Illumination Weak light intensity in winter is inherently weaker and lower in foggy days. In many cases, the light intensity is at the lowest level of the critical intensity of vegetables. As a result, the photosynthesis of the leaves is relatively weak, and it is impossible to produce much nutrients, and the yield is naturally not high.
3. Humidity In winter, the humidity in the greenhouse is inherently large and can only be reduced by ventilation. The humidity of the outside world is almost saturated and the ventilation will not reduce the humidity in the greenhouse. Therefore, the indoor humidity is often saturated. This environment has severely inhibited the transpiration of vegetables, which has caused the roots to absorb moisture and has stagnated their functions. The physiological activity of the entire vegetable has been severely weakened.
4. In the absence of foggy vegetation, the transpiration of vegetables is reduced, and the moisture absorbed by roots is reduced. Nitrogen, potassium, iron, calcium, and other fertilizer elements that are brought to the leaves through dissolving water will be greatly reduced. Symptoms; Therefore, despite the use of soil testing and formula fertilization techniques, the soil in a variety of fertilizer elements are very adequate, but the vegetable plants are still poor growth due to fertilizer elements and poor growth. Under low ground temperature conditions, microbial activity in the soil has changed greatly, and the low-temperature-resistant microorganisms are still active, and microorganisms that are not tolerant to cold temperatures stop or half stop activities. In this case, nitrogen is found in the soil from ammonium. The state-change nitrate, which is destroyed by the dynamic equilibrium cycle of nitrate-to-iron transformation, begins to accumulate a large amount of ammonium nitrogen in the soil. The excessive accumulation of ammonium nitrogen has an antagonistic effect on the absorption of potassium, calcium, magnesium, iron, zinc, and other fertilizer elements, resulting in the vegetable roots can not normally absorb the above elements, so the lack of the above-mentioned elements may occur, resulting in The growth and development of vegetables is not normal. With the exception of aquatic vegetables, most vegetables use and absorb nitrate-nitrogen, and they do not use or absorb ammonium nitrogen. The lack of nitrate nitrogen in soil in winter affects the nitrogen supply of vegetable plants, so some plants will show symptoms of lack of nitrogen fertilizer.
5. Disease Most bacterial and fungal diseases occur in environments with high air humidity. Due to the high humidity in the interior of the greenhouse with fog, greenhouses often cause some diseases such as gray mold, leaf mold, downy mildew, sclerotinia and other diseases.
Heavy fog affects the symptoms of vegetables
The low-temperature environment caused by heavy fog leads to sagging of the leaves of cucumbers, tomatoes and other vegetables, the whole leaves turn yellow, the growth of plants is slow, the cucumber flowers are topping, the tomato suffers from yellow top disease, the deformed fruit increases, the tomatoes have more empty fruit, the coloring is poor, and the flower face fruits increase. .
The lack of light causes yellowing, thinning of the leaves of the vegetables, premature debility, and increased flowering and fruiting.
As the plants lack nitrogen fertilizer, the leaves become smaller and yellow; due to the lack of potassium, the lower leaf margins form a wide yellow band with yellow ring leaves; due to the lack of calcium, tomato cracking increases, the umbilical rot is severe, cucumber Melted cucurbits, coke-like leaves, downwardly revolving, parachute-like; lack of magnesium, the middle of the leaves yellow, green ring; due to the lack of zinc, the leaves appear yellow spots.
Due to weak light and low temperature, bubble disease often occurs.
Continuous fog measures to be taken
1. Improve the greenhouse insulation performance, such as thickening the wall; dig the cold trench; increase the height of the greenhouse, increase the incident angle of sunlight, increase the incidence of sunlight, increase the utilization of sunlight; use of plastic film and so on. Use grasshoppers with good insulation properties. Non-woven fabrics are used for double coverage in the greenhouse. The north side of the greenhouse hangs a light curtain. Use the above method to increase the temperature environment in the solar greenhouse.
2. Improve lighting conditions. Use artificial light if possible. Due to heavy fog, scattered light is still available for vegetables, so as long as the temperature conditions permit, the grass must be uncovered and the vegetables should be exposed. Even when the temperature is low, it cannot be uncovered for a few days. It should be seen at noon for a short time. Prevent prolonged yellowing of leaves in a dark environment.
3. Spray pesticides in time to prevent diseases. During spraying, add 0.2% potassium dihydrogen phosphate solution and organic leaf calcium fertilizers such as calcium, zinc, and iron to supplement the supply of potassium, calcium, etc. to solve the root absorption disorder and prevent the plants from lacking the above-mentioned fertilizer elements. occur. At the same time, it can increase the concentration of the cell fluid and enhance the ability of the plants to resist cold.
4. In the winter, spraying 10000 times liquid of alfalfa-Shuofeng 481 once every 20 days to promote photosynthesis, enhance the cold resistance of plants, and promote the growth and development of roots.
5. After a sudden and hazy day of sudden haze, one should cover the grasshoppers every other day when the light intensity is strong at noon, and then uncover them in the afternoon to prevent the wilting of leaves and the occurrence of bubble disease.
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