Citrus requirements for environmental conditions - temperature
Temperature is the main factor affecting the growth and distribution of citrus. Citrus's temperature requirements vary depending on the species and variety. The optimum temperature for growth is 23-29°C, and the growth is stopped if the temperature is lower than 13°C and higher than 37°C. The average annual temperature of the broad-leaved oranges is 16.5-19°C, and the Satsuma oranges are more resistant to hypothermia in the broad-leaved citruses. To 15.5-17.5 °C is appropriate. The annual effective accumulated temperature is preferably above 300°C. If the annual average temperature and accumulated temperature are insufficient, it will affect the normal growth and results of citrus. Citrus prefers to be warm and not cold, when the absolute low temperature is below -5°C (when the rootstock is lower than minus 8 degrees). There is a threat to the overwintering of citrus and it is prone to freezing damage. The cold resistance of different citrus varieties and varieties is very different, but also affected by the physiological conditions, stock types, age, tree vigor, cultivation environment and the duration of low temperature and cold wind and other aspects. The more vigorous the general growth, the less cold-resistant, the deeper the degree of dormancy, the more cold-resistant. The lemon grows and blooms as a result. Therefore, the cold is the least, and kumquats and clams will enter a complete dormancy in the winter, so it is the most hardy. The stronger cold-resistant adult trees with sorghum as the rootstock had stronger cold-resistance, and the young trees or weak trees had weaker cold-resistance. If the cold temperature is coupled with extensive management, winter drought and cold wind, the frost damage will increase.
The level of temperature also affects the quality of citrus. Within a certain range, when the temperature rises, the peel becomes a book, the acid content decreases, the fruit color fades, and the storage property decreases. If the temperature is as high as about 40°C, the fruits and branches will be easily burned, causing sunburn and affecting the results of the current year or the next year. High temperatures can also cause June fruit drop and wilting.
Citrus antifreeze measures
The major natural disasters in the northern part of China's Orange region are the limiting factors for the development of citrus production. Preventing and reducing frost damage is one of the keys to the development of citrus production and the achievement of high and stable production.
The cause of frost damage in citrus is, in addition to the direct factor of low temperature, also determined by species, variety, tree age, tree vigor, rootstock, cultivation management level and site conditions. If you can choose cold-resistant varieties on the cultivation, use cold-resistant rootstocks, choose the site to avoid freezing, and set up shelterbelts, so that fine management can avoid or reduce freezing damage. Practice has proved that the same species, poor cultivation and management of severe cold injury, cultivation and management of a good frost damage is not or free from frost damage, so to strengthen the cultivation and management, enhance tree vigor, improve cold resistance, is an important way for citrus antifreeze, especially to strengthen Soil management, pest control, application of winter fertilizer, timely harvesting, proper pruning, and late autumn picking are all more important. In addition, the following anti-freeze measures can also be taken:
(1) Water spray before freezing or when spraying cold water during freezing: The principle of releasing a large amount of latent heat when the water is frozen and cooling, and irrigating before the occurrence of frost damage; or spraying cold water when frost damage occurs, has a certain effect. However, irrigation must be filled in order to receive good results.
(2) The trunk is covered with white, dry ground soil, saplings or scaffolding, and mulching.
(3) Smoke smoke: According to the weather forecast, 4-6 piles of grass are ignited at the same time in the citrus grove in the citrus garden before the frost comes, so that a dense smoke curtain covers the park to reduce the temperature of the ground and reduce the temperature, and increase the air Heat has a certain effect on preventing frost.
(4) Rolling thin snow and ice: Citrus trees do not fall off in winter. In case of heavy snow, the branches are easily broken and must be shaken in time. However, you must not injure the foliage when sowing.
(5) Spray-suppressing and heat-insulating agent: about 30 days before the cold or before the cold. Spraying 2-3% of the steam-inhibiting and heat-insulating agent on the canopy to cover the foliage with a layer of film to suppress moisture evapotranspiration, can play the role of anti-freezing, wind prevention and concurrent treatment of red spiders, but there is a slight defoliation phenomenon.
The Nursing Measure After Citrus's Freezing Injury
(1) Fertilization: Frozen trees, due to weakened transpiration, water and nutrient transport difficulties, so spring fertilizer should be carried out as early as possible after thawing in early spring, can be divided into two applications. Fertilizers should be based on available nitrogen fertilizers. For those who are slightly chilled and who have leaf curls, yellow leaves, and debilitating growth, 0.5% urea water should be sprayed immediately on the canopy. Once every 5 days, they should be sprayed about three times. For a large number of severed branches due to freezing, due to a small number of leaves, fertilizer and water is difficult to absorb, fertilization is easy to hurt the root, spring fertilizer should be less or not Shi, but we must pay attention to loose soil weeding work.
(2) Pruning: According to the different severity of freezing, it should be treated differently. If the shoots are intact and some of the leaves are slightly scorched but not shed, they should be removed as soon as possible so as not to continue to consume water and expand the frozen parts. For the plants that had been exposed to freezing, the dead parts were cut off after the shoots were budded. Post-freezing pruning is usually done early after the dividing line between life and death. For trees that are severely affected by freezing, the crowns and tree vigor are unlikely to be restored, and the park should be rebuilt.
(3) Pest control: Frozen plants are highly susceptible to pests and diseases (such as resinous diseases, skirt rot, and caries and fleas, crickets, aphids, wind butterflies, leaf miners, etc.) Should be prevented and treated early.
Citrus winter cold measures
The temperatures in winter and spring are low, and citrus trees are vulnerable to freezing injury. Light flower buds are frostbite, stems are drained dry, and fallen leaves are severe. The yield and quality of fruit trees are severely reduced. In severe cases, there will be freeze-cracking of branches and dried cortex, and even the phenomenon of whole-plant freezing and freezing. Now the following effective antifreeze measures are introduced. .
First, give full fruit fertilizer and winter fertilizer. Young trees should apply sufficient winter fertilizer before “small snow†and organic fertilizers should be used for wintering. Organic fertilizer not only helps increase soil temperature, protects the roots from frost damage, but also helps to supply nutrients to the tree in early spring and reduce frost damage. For the result tree, the heavy fertilizer is mainly applied before and after fruit picking, in order to supplement the nutrient consumed by the fruit, restore the tree vigor, promote flower bud differentiation, and enhance the overwintering ability. The combination of quick-acting fertilizer and delayed-effect fertilizer accounts for about 30% to 35% of the annual application amount. Before and after harvesting fruit, it should be applied to the late-maturing variety or the mountain drought or winter cold area in November.
Second, the orchard covered grass. Between the rows of fruit, straw, weeds, leaves, etc., can be preserved, and the ground temperature can be maintained and increased.
Third, antifreeze irrigation. 7-10 days before freezing, the citrus tree is irrigated to store temperature with water and reduce the temperature difference so that the ground temperature during the freezing period is relatively stable, thereby reducing the freezing injury. It is best to do it at noon during irrigation and it is appropriate to infiltrate in the evening.
Fourth, timely earth training. Combining fertilization and one-time soil cultivation before frost can effectively avoid the freezing damage to the root and the stem, and it is better to use turf soil or mixed soil. Each soil depends on the size of the crown. Earthworms should be pounded to the upper part of the root neck, usually about 15 cm. If it is covered with a plastic film, the film is compacted with soil compaction to prevent heat loss and wind blowing. After the low temperature, the soil above the root neck should be promptly opened in order to prevent rot roots and diseases and insect pests.
Fifth, the tree bandage. When the temperature is low, the main branch of the main stem is tightly wrapped with straw, which can effectively prevent the cold current from invading.
6. Protect the canopy and remove accumulated frost. After the “big snowfallâ€, fruit trees are often piled with accumulated frost, which not only breaks down the fruit trees, but also causes freezing damage. Therefore, the accumulation of frost on the branches should be promptly cleared. If conditional, cover the orange orchard canopy with bags, straw, etc.
Seven, trunk white. When the orchard cleans the garden in winter, the main branch of the fruit tree is painted white. The formulation of the whitening agent is: 2.5 kg of quicklime, 0.75 kg of sulfur powder, 1.25 kg of salt, 0.1 kg of vegetable oil, 0.05 kg of bean flour, and 18 kg of water. During the preparation, quicklime and salt are separately dissolved in water, fully stirred into a paste, then added with sulfur powder, vegetable oil, and bean flour. Finally, the water is used to separate and stir.
Eight, cut off late autumn shoots. In late autumn, the tip leaf is thin and pale, organic matter is less accumulated, and the nutrient concentration of the cell fluid is low, which is prone to freezing injury and leaves falling.
Nine, spraying hormones and oil to protect the leaves from freezing. In early and mid-December, spray 80 times of engine oil emulsion before cold wave arrives. Small citrus trees can be properly diluted oil to prevent phytotoxicity. Naphthalene acetic acid solution spraying in early spring can delay the flowering period of fruit trees, so that fruit trees avoid the harm of early spring low temperature. Concentration of pmm is appropriate, first dissolved with warm water, then use enough water and mix thoroughly.
Ten, smoke-free antifreeze. It is better to use sawdust and weeds to mix the fuel. When the cold wave is approaching, let the smoke cover the garden.
In addition, set up a windbreak to create a windbreak. Setting up windbreak forests around the citrus groves can also be used to plant peri-wine bamboo forests to reduce wind speed and achieve cold-resistance.
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