First, the cause of cold damage to seedlings
(A), physiological drought caused by cold damage. Before the cold current occurred, the soil was dry and the water content in the plants was low. When the air suddenly becomes cold and cold winds blow, not only do the seedlings evaporate a lot of water, but because the soil temperature is lower, the root system cannot absorb water from the soil. This will cause the water supply of the seedlings to fall short of demand, dry shoots and death. This kind of chilling caused by physiological drought is the most common.
(b) Continuous cold temperatures cause chilling damage. The degree of lignification of the seedlings is not high. Once a continuous low temperature is encountered, the protoplasm of the cells will dehydrate and freeze, and the cells will be damaged. The seedlings cannot perform normal physiological activities and cause death. Some seedlings appear rotten roots, peeling branches, ulcers, etc. in the winter or early spring.
(c) The freezing of soil causes cold damage. After freezing occurred in winter, the roots of the seedlings were pulled out of the soil or broken due to the freezing and expansion of the soil, and were then blown by the wind to cause the seedlings to die.
Second, the main cold measures
(A) to improve the cold resistance of seedlings. The main ways are: 1, timely sowing, extend its growth period, so that the seedlings grow up long and thick. 2, in summer and autumn, shoot, let the seedlings stop growing, to promote its organization. 3, in the late growing season, more phosphorus, potassium fertilizer, less nitrogen fertilizer, so that the branches fully lignified. 4, after the fall to reduce irrigation, is conducive to lumber seedling lignification, improve its ability to resist cold. 5. Foliar fertilization (spraying 0.5% potassium dihydrogen phosphate liquid fertilizer 1 or 2 times) before freezing in early fall and winter can increase the cold resistance of seedlings.
(B), scaffolding insulation. Keeping seedlings warm with a plastic greenhouse or a plastic shed gives the best results. It can increase the soil temperature and increase the temperature.
(C), seedlings covered grass. Before the arrival of frost, the seedlings were completely covered with dry straw, deciduous, straw mats, drape, etc., and were removed in the following spring.
(D), root soil. Before the soil is frozen, in the roots of the seedlings, 5 to 10 cm thick soil is cultivated with loess or mycorrhizal soil, which can increase the ground temperature around the seedling root system and effectively reduce the degree of frost damage to the seedlings. After thawing in the spring, these soils are removed again. This method is not suitable for seedlings that are easy to break and perishable.
(E), irrigation antifreeze. Watering before the winter, so that the seedlings suck enough water, can effectively prevent the cold damage caused by physiological drought. When the temperature drops or before the freezing damage occurs, the characteristics of the specific heat of the water can be used to prevent the soil temperature from falling, and the soil temperature can be increased by more than 2°C.
(F), for the prevention of cold barriers. For some seedlings with large specifications and fear of cold wind, wind barriers can be established in the northwest direction of seedlings to reduce the degree of frost damage.
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