Spring cold often appears in spring, how to deal with it?

Every year in March-April, the fruit farmers have butterflies in their stomach, hoping that the fruit trees will grow slowly, and they have taken many preventive measures, but the cold spring still makes people unprepared. Exploring the principle of late spring cold is nothing more than the influence of sudden drop of spring temperature on the growth of fruit trees, but this "temperature" is much more difficult. What is the temperature? Treating "cold spring" requires a more thorough understanding, knowing yourself, knowing yourself, and winning the battle! We can clearly understand the ins and outs of late spring cold, so as to effectively grasp the preventive measures: large temperature difference between day and night and rapid temperature change are the characteristics of spring temperature. It is common to wear cotton-padded jacket in the morning and short sleeves at noon. It is common to bask in the sun the day before and bake the oven the next day. After the spring warms up, the temperature suddenly drops, which is what we call cold in the spring.

Warm ducks in spring and warm trees in spring. As long as the temperature rises, the fruit trees that have been dormant for a whole winter will begin to sprout. When the temperature is high, it will grow wildly, and when the temperature is low, it will easily freeze to death. Most fruit trees need a dormant period. After the dormancy period, the fruit trees germinate again and spread their leaves in spring. New shoots, leaves and buds are tender growth points, which are very sensitive to low temperature (below 5℃, the critical value of impassable fruit trees is different) and have poor cold resistance. Low temperature has different effects on fruit trees in spring and winter. In winter, the fruit trees are dormant, the cells are inactive, the branches are protected by cuticle, and the cold resistance is strong; However, in spring, fruit tree cells enter an active peak, and young leaves and buds are not protected by cuticle, so they are more vulnerable to cold current frostbite. In March and April, fruit farmers must pay attention to the weather conditions in the next few days, pay attention to the lowest temperature in the weather forecast, then calculate or measure the actual temperature of the orchard and take preventive measures when necessary.

It should be noted that the lowest temperature in the orchard must not be taken as the lowest temperature in the weather forecast, because the monitoring position of the weather forecast data is generally in the city center. According to the principle of urban heat island effect, the temperature in suburbs is lower than that in urban areas. Fruit tree planting, due to land costs and other reasons, the orchard is generally located in the suburbs, with large vegetation coverage, and the temperature is generally 2~5℃ lower than that in the city center. The farther away from the city center, the greater the difference between the actual minimum temperature of the orchard and the minimum temperature of the weather forecast. In spring, the fruit trees are tender. For many fruit trees, when the actual temperature of the orchard is lower than 2℃, there is a danger of freezing injury. When the lowest temperature in the weather forecast reaches 5℃, we must pay attention to measuring the actual temperature of the orchard, calculating the temperature difference and taking preventive measures in advance. In addition, at normal sunrise and sunset, the lowest temperature in a day is before sunrise, but when cold air comes, the lowest temperature is when the cold air mass passes through the border. During the Qingming period of 20 18, a severe late spring cold occurred in Shaanxi. At that time, some fruit farmers were very worried about whether the roots of their fruit trees would freeze. If you have this problem, I can definitely tell you no.

Because the roots grow in the soil, the soil temperature is very different from the ground temperature near the orchard. Sunlight first reaches the air near the ground and then reaches the soil, and the change of soil temperature is "slower" than that near the ground. When the sun rises, the temperature rises first, and then the soil temperature, because the density of soil is much higher than that of near-surface air. When the temperature reaches the highest in a day, the soil temperature does not reach the highest. Similarly, when cold air strikes, the heat dissipation rate of soil will be much slower than that of air near the ground. Moreover, the residence time of cold air is short, and the soil temperature is almost unaffected. The cold in late spring is generally caused by the cold air flow invaded by Russia. At this time, the sun is moving towards the tropic of cancer, and the cold air won't last long. Therefore, the late spring cold has little effect on soil temperature and will not freeze the roots. It takes a long time for the soil to heat up and cool down; However, when the temperature near the ground meets cold air, it drops rapidly, which has a great influence on the aboveground parts of fruit trees. For example, 20 18, cold air only sweeps the atmosphere near the ground where the above-ground parts of fruit trees are located. The next day, the weather was fine and the soil temperature was almost unaffected.

Orchard topography is not a factor affecting the occurrence of late spring cold, but it is related to the severity of late spring cold. When late spring cold occurs, high altitude is more serious than low altitude. The late spring cold in the convex part is more serious than that in the lower part. The cold spring on windward slope is more serious than that on leeward slope. The topography of the orchard is not only related to the severity of cold in late spring, but also has a slight impact on the microclimate of the orchard, such as rainfall, sunshine hours and wind power. The principle of preventing late spring cold is to increase the microclimate temperature of the orchard or increase the frost resistance of the branches and leaves of fruit trees as much as possible within a few hours after the cold air passes. At present, the most effective way to improve the microclimate temperature of orchard is smoking. Before the invasion of cold air, prepare a pile of smoked materials (aerosol formulation: ammonium nitrate 20%, sawdust or broken grass leaves 70%, waste diesel oil 10%) in advance and put them at the windward entrance of the orchard or even in the garden. When the temperature of the orchard continues to drop below 5℃, it can be ignited and smoked. Then the orchard sprinkler irrigation method.

If the temperature is already high before the arrival of cold air, and the temperature of water is the same as that of soil, the temperature will be much slower. You can turn on the orchard sprinkler irrigation when cold air comes, and then whoever sprays it will release heat, so that the temperature of the orchard will not drop very low; It should be noted that drip irrigation and flood irrigation are useless at this time. In order to improve the frost resistance of branches and leaves of fruit trees, antifreeze, brassinolide and potassium dihydrogen phosphate can be sprayed on the whole garden 1~2 days before the cold air strikes, so as to improve the frost resistance and aging degree of branches and leaves, but the concentration should be controlled. In addition, in Guangxi, when the temperature is low in winter, citrus growers will cover their fruit trees with cold-proof cloth (film). Maybe you can learn from it. For the orchard area is not very large, you can try to cover the fruit trees with cold-proof cloth, which is enough to cope with the cold air for several hours, but the cost should be considered. In a word, what is directly related to the occurrence of late spring cold of fruit trees is the actual ground temperature of the orchard, that is, the actual temperature of the orchard. The principle of preventive skills is to change the microclimate temperature in the orchard when the cold comes in late spring, and improve the cold resistance of the growing points of fruit trees (leaves, buds, new buds and other tender parts).