Freezing injury of overwintering crops, fruit trees and economic trees often occurs. Freezing injury is a great threat to agriculture. For example, citrus production in the United States, winter wheat and citrus production in China often suffer huge losses due to freezing injury.
Freezing injury mostly occurs in middle and high latitudes. The great plains of central and western North America, Eastern Europe and Central Europe are the main areas where winter wheat freeze injury occurs. China is most affected by the freezing damage in the northern winter wheat area, mainly in the northern Xinjiang on the southern margin of Junggar Basin, the Loess Plateau in eastern Gansu, northwestern Shaanxi and central Shanxi, the northern Shanxi, Yanshan Mountains and southern Liaoning, the Beijing-Tianjin-Hebei and the North China Plain in northern Shandong.
In the Yangtze River basin and South China, although the frequency of freezing injury is less, the blocking effect of hilly areas on cold air going south often causes cold air to accumulate, resulting in long-term low temperature, accompanied by snowfall and freezing rain, which seriously damages wheat, rape, broad beans, peas and citrus.
Extended data
Different crops have different freeze injury characteristics, such as winter wheat, which can be mainly divided into:
① Winter cold type. It is very fragile when there is no snow in winter or when the snow is unstable;
② The temperature drops sharply in winter. When the temperature drops suddenly before and after wheat seedlings stop growing, or when the temperature is too high and the growth of winter wheat is too strong in the early stage after sowing, it is easily affected by cold air;
③ Early spring thawing type. Early spring warms up and melts, and spring seedlings are easily affected by strong cold air when they begin to sprout, and so on. The freezing injury index of different crops and varieties is also different. For example, when plants die more than 50% in freezing, the lowest temperature of tillering nodes is often used as the critical temperature of freezing injury, which is an index to measure the cold resistance of plants.
The critical temperature of freezing injury of varieties with strong cold resistance is-17 ~- 19℃, and that of varieties with weak cold resistance is-15 ~- 18℃. The critical temperature of severe freezing injury of mature fruit trees is -7 ~-9℃ for citrus and-16 ~-20℃ for grape.
The causes of freezing injury are related to the speed of cooling, the intensity and duration of low temperature, the weather conditions before, after and during the occurrence of low temperature, the daily temperature difference and the cooperation of various meteorological factors.
When plant tissues are in a period of vigorous division and proliferation, even if the temperature drops briefly, it will suffer; On the contrary, plants in dormancy have strong frost resistance. The frost resistance of each development period generally decreases in the following order: bud coloring period → flowering period → fruit setting period.
Baidu encyclopedia-frostbite