The hazards of low temperature include two aspects. One is the low temperature hazard, also known as chilling damage, which mainly occurs in the middle and late stages of autumn cabbage. When the temperature is below 10 Â°C, the growth rate of Chinese cabbage is very slow, and when it is lower than 5 Â°C, the growth almost stops. In the northern region, due to the early cold current, the temperature drops rapidly, and the heat is insufficient, which often causes the ball to be unreal, and the yield and quality are not high.
The second is the freezing damage. The northern part of China is in the middle and the middle of November; the northeast and northwest alpine areas are in the middle and late October; the middle and lower reaches of the Yangtze River are in the middle and lower reaches of November to December, and two weeks before the harvest of autumn cabbage. Suddenly there is a cold current or snowfall, and the temperature drops to 0 Â°C ~ 3 Â°C. At this time, the cabbage has not yet been able to adapt, and the water content is higher. The lower temperature often causes the cell gap to freeze. When the temperature rises slowly, the water can return to the cytoplasm, allowing the cells to return to normal swell. If the temperature suddenly drops below 0 Â°C, the leaves are difficult to recover due to freezing, causing serious freezing damage.
In the middle and lower reaches of the Yangtze River, the cabbage can be exposed to winter. Due to the high humidity of the air and the small temperature variation, the degree of damage is often lighter than that of the north. Generally, the freezing damage is formed when the temperature drops to -8 Â°C.
The freeze damage performance of Chinese cabbage begins with the outer leaves, and gradually expands to the leaves as the temperature continues to decrease and the time prolongs. Because the cold wind can accelerate evaporation and take away a lot of heat, the freezing damage is aggravated and difficult to recover. The higher the sugar content of Chinese cabbage, the lower the freezing point. The measures to prevent freezing damage and low temperature are as follows:
1. In the spring seedling cultivation of seedling stage, after the seedlings are laid out, the seedbed should be ventilated, and the ventilation should be gradually increased with the warming of the weather. The seedlings should be kept at low temperature to improve the cold resistance of the seedlings and adapt to the outdoor low temperature environment.
2. Increasing the protection facilities First, the wind barrier is set up, and the wind barrier has a blocking effect on the cold air. In the wind barrier group, a special microclimate can be formed to prevent the surface from further cooling. The wind barrier should be kept at a relatively dense distance, generally about twice the height of the wind barrier. The second is to plant the ditch and cover the mulch. When planting the vegetables in early spring, the method of ditching can be used. The ditch depth is required to exceed the height of the vegetable seedlings, and then the mulch can be covered on the ditch, but it should be noted that the film should not be pressed against the vegetable seedlings, otherwise the top of the vegetable seedlings Still suffering from freezing damage. Third, straw, leaves, chaff, grass ash, etc. can be laid in the rows of Chinese cabbage or cover the soil 3 to 5 cm to cover the heart leaves, and the spring leaves.
3. Temporary heating and protection production. When the cold current comes, a simple coal stove can be built in the nursery shed or production shed to temporarily warm the shed to prevent freezing damage. However, you cannot use an open flame to avoid a fire.
4. Watering Generally, the North China region is in mid-November, the northeast and northwest regions are in the middle and late October, and the Yangtze River basin is from late November to mid-December. After strong cold air, the weather is fine and there is no wind or breeze at night. However, the temperature drops rapidly, especially when the local table temperature drops below 0 Â°C, and the well water can be poured on the ground to greatly increase the ground temperature. This method can raise the ground temperature from 0 Â°C to about 8 Â°C to avoid frost.
5. Applying the fertilizer to the fertilizer before the winter, apply 1000~2500 kg of pig manure or soil fertilizer to the cabbage line. The soil temperature will increase by 2 Â°C~3 Â°C, and it can also play the role of winter application spring.
6. Smoke on the frosty night, smoke in the field can effectively reduce or avoid frost disasters. However, it should be noted that the fireworks should be properly dense so that the smoke screen can cover the entire park. Second, the ignition time should be appropriate and should be in the upper hand. It ignites from midnight to 2 to 3 in the morning until there is still a smoke curtain covering the ground before sunrise.
7. Water spray Before the frost occurs, spraying the surface of the plant with a sprayer can slow down the temperature of the plant, and it can also increase the water vapor content in the atmosphere, and the water vapor condenses and releases heat to alleviate the frost damage.
8. Cultivating in the cultivating before the frost can reduce the degree of frost damage. Because the temperature in the spring gradually rises, the earth heat can be absorbed and stored better after the earthworms are loosened. Once frost damage has occurred, a portion of the heat has accumulated in the soil to alleviate the frost.
9. Spray anti-cold agent with plant anti-cold agent or anti-reverse stimulation agent 100~300 ml per acre, spray with water after dilution; or spray 27% high-fat film emulsion 80~100 times solution.
10. Timely harvesting and control of Chinese cabbage freeze damage mainly depends on the prediction of freezing damage before the harvest of Chinese cabbage, and it is detected whether there is strong cold air intrusion during the harvest of Chinese cabbage. When the temperature is likely to drop to -5 Â° C, prepare in advance and harvest in time.
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