After freezing, the young ears of the main stem and the big branch of the wheat plant in the wheat field with the symptoms of freezing injury were still able to head and seed normally, but the number of grains per spike was significantly reduced. When the freezing injury is heavy, the main stem, young branch panicles and heart leaves freeze to death, and the remaining parts can still grow. The wheat leaves and tips of wheat fields with severe freezing injury are hard and brittle like water scalding, and greenish or dry and blue green and blue. Stems and young ears shrink and die. SICHUAN UNIWELL BIOTECHNOLOGY CO.,LTD. , https://www.uniwellbio.com
During the 40 years from 1950 to 1990, the wheat in the suburbs of Beijing suffered from severe cold damage seven times, an average of 5-7 years. Since 1990, two more severe freezing injuries have occurred in 1993 and 1995. The characteristics of freezing injury in 1993 were dead seedlings, dead stems and serious frostbite. The dead seedling rate was 4.81%, the dead stem rate was 8.95%, and the frostbite rate was 100%. In 1995, frost damage was frost-freezing and thaw-thawing, and it was moderately heavy. It was characterized by severe blight, and the rate of dryness was close to 1005.
The cause of the first adverse weather conditions. In mid-November 1993, intense cooling weather suddenly appeared. The monthly average temperature dropped from 7°C on the 15th to -2°C on the 17th, and continued to cool down to 24th, including 4 days of daily average temperature below -5°C. Winter wheat had entered the overwintering stage more than 10 days earlier than normal in the absence of cold-resistant exercise. Physiologically, it did not undergo sugar accumulation and cell dehydration, resulting in severe frostbite in wheat. From December 20 to February 10, 1994, there was no rain for 50 days. In addition, with high temperature and large evaporation, the dry soil layer of most wheat fields was 3-4 cm thick, and the tillering festival was in dry soil for a long period of time. in. In the month of March, it did not rain, and the drought continued to increase, accelerating the degree of frostbite in wheat. The second is that the varieties cultivated in production are poor in cold resistance and are internal causes of frost damage. In the suburbs of Beijing in the 1990s, the 6th variety was upgraded, and a supporting system was established with Beijing 411 and Jingdong 6 and 8. In 1992, a series of dwarf big ear varieties such as Changfeng 10, Pin 9 and Nongda 92 were introduced. Apart from Beijing 411, these varieties have higher yield levels but have poorer cold resistance. Beijing 411 was cold-resistant, and the dead-stalk rate was 5.3%. As for Jingdong No. 6 and 8, the dead-stem rate was between 10% and 20%. The third is improper cultivation and management. Too deep or too shallow has a great impact on the emergence and post-emergence cold resistance of wheat. The normal sowing depth in the Beijing suburbs is 3-5 cm. In 1993, the dead seedling rate was 5.6%. The dead seedlings with a seeding depth less than 3cm were 22.9%, and the dead seedlings with a seeding depth greater than 6cm were 18.3%. The fourth is pouring frozen water. Pouring frozen water is an important measure for safe winter freezing and seedling protection. In 1993, the dead seedlings in the unfrozen waters were severe, the seedlings rate was 26.8%, and the dead seedlings with frozen water were only 7.3%.
The winter freezing injury of wheat is divided into two types: early spring freezing injury and late frost injury. The latter occurred more often in production, and the victims were heavier. Night frost damage is caused by the sudden cooling of night cream and low temperature damage to wheat. Especially in the warm winter years, early springing and sowing of spring varieties with high sowing rates are heavy. The freezing injury of wheat in the north is scheduled to occur from late March to mid-April. The degree of damage is related to the extent, duration, and steepness of cooling. The cooling rate and the degree of turbulence are large. The low temperature lasts long and the victim is heavy. There are three types of frost-shaping frost, radiation frost, and mixed frost on production. Advection frost refers to the dramatic cooling caused by the intrusion of northern cold air. High-lying, wind-slope wheat is a serious problem. Radiant frost is produced at night when there is no wind at night and when the ground radiation is strong, it is generated when the surface is rapidly cooled. It is harmful to low-lying, river valley, and basin wheat. Mixed frost is when the sky is dense clouds or dense water, under the circumstances of surface heat loss reflection, reduce the heat loss of the ground, when the weather turns fine, calm, night ground temperature suddenly dropped, easy to form a mixed frost. This frost has a wide range of invasiveness and occurs frequently, causing serious damage.
From the standpoint of wheat, the cold resistance significantly decreased after entering jointing. After sudden cooling, the body temperature of wheat dropped below 0°C, and the water in the intercellular space first freezes. If the temperature continues to decrease, the cells begin to freeze, causing the cells to dehydrate and coagulate and die. Shanghai, after December 27, 1991, suddenly fell heavy snow, the temperature dropped to -7.7 °C, so that wheat and rape have different degrees of frost damage. Applying nitrogen, phosphorus, and potassium compound fertilizers on January 7-8 will be light and light.
Prevention methods (1) Pay attention to the selection of cold-resistant wheat varieties suitable for the local spring wheat area can choose Ningchun No. 24, Liaochun No. 10, Mengmai No. 30, etc.; winter wheat area can choose Shumai No. 38, No. 40, No. 41, Jinmai 51, 52, 53, Wanmai 27, 25, Lumai 22, 23, 21, Yumai 38, Wanwan 41, Guifeng 1, Jinsong 49, Wheat No. 19, No. 8 Daimai, Xindong No. 18, No. 19, Wenmai No. 6, Buckwheat No. 38, No. 40, No. 41, Huamai No. 8 etc. (2) To improve the sowing quality, the sowing degree should be between 3 and 5cm. (3) timely pouring good wheat frozen water depends on the temperature: Daily average temperature of 3 - 10 °C began to pour. Prematurely due to high temperature and high evaporation, when winter wheat loses too much water, it loses the effect of pouring frozen water. If it is too late or the temperature is lower than 3°C, it will cause the ground temperature to drop, and the field will collect water or freeze, causing freezing damage. Dead seedlings; Second, look at the lyrics: When the sand has a relative humidity of less than 60%, sandy soil is less than 70%, clay land is less than 80%, and watering is required. When the soil moisture is higher than the above-mentioned indicators, the good-looking plots may not be poured or slowly poured; the third is to see the situation of the seedlings: the wheat seedlings grow well, the bottom-slow or slightly prosperous plots, can be suitable for late pouring or not pouring, to prevent the group from overheating ,is too big. For later sowing late winter wheat, because of the short growing time before winter, the leaves and roots are less, the seedlings are small and weak, and there are few tillers or no tillers. In order to obtain effective accumulated temperature, the growth and development of the wheat seedlings can be promoted. It is necessary to protect the crop in time to make it stronger and stronger; Fourth, it is appropriate: The amount of water should not be too large. Usually, the water is poured on the day, and there is no water on the ground. Make the soil water holding up to 80%. (4) Replenishment in early spring When the thickness of dry soil layer is greater than 3cm in the early spring, timely replenishment should be carried out to improve the soil moisture content, relieve the threat of dry soil layer, and reduce the freezing damage and reduce the dead seedling rate. 1 Cultivate pre-winter strong seedlings and suppress them in winter and spring. In the returning green period, 667 m2 was sprayed with paclobutrazol at a concentration of 200 mg/kg; in the jointing stage to the booting stage, watering or foliar spraying before the late frost came to increase the temperature of the leaf near the ground. Smoke will be smoked on the upcoming night of the frost to reduce ground radiation heat, increase the temperature of the near-ground and foliar surfaces, and prevent frost from occurring. 2 After wheat is frozen, take remedial measures and timely strengthen water and fertilizer management. For wheat fields where the leaves are frozen and young ears are not frozen, watering should be done early to prevent the dehydration of young ears. Young panicles have been frozen wheat, should be chasing nitrogen fertilizer, 667m2 chase ammonium nitrate 10-13kg or ammonium bicarbonate 20-30kg, combined with watering, cultivating loose soil, to promote the frozen wheat as soon as possible to restore growth. Generally do not destroy, castrate or grazing. Try to save. (5) Winter and spring wheat advocate the use of new technologies for mulching and mulching. Before wheat mulching, fine soil preparation is required. After the harvest, rotary ploughing as soon as possible after the harvest is performed to eliminate root boring, and then deep ploughing is adopted to achieve ground level, fine soil, and good quality. 667m2 organic fertilizer applied 4000-4500kg, urea 20-25kg, phosphate fertilizer 40-60kg, the above three fertilizers, with the cultivator once bottom. With a small four-wheel tractor traction mechanical coating, the best selection of 0.005mm, 1.4m wide super film. Then points, hole distance 10cm, 8-10 holes per hole, 667m2363 million points, basic seedlings 25-300000, sowing depth 4-5cm, sowing volume 8-10kg. After field Tian Qimiao, the first time the seedlings were planted under the membrane, and the second time before the soil was frozen, the dislocation of the membrane seedlings was completed. The use of wheat mulch film was the most promising new technology for the significant increase of wheat drought resistance during the current stage. (6) Advocate the application of Gamm harvesting plant to increase production regulators and multi-functional high-efficiency liquid fertilizer - Wanjiabao, as well as more rare earth pure nutrients. See methods for dry hot wind damage in wheat.