Frost is the phenomenon that the temperature drops below 0°C and is enough to cause plant damage or even death. When the ground temperature suddenly drops below 0°C and is below the minimum temperature that wheat can withstand during a certain developmental stage, wheat will suffer freezing damage. Especially after the jointing of wheat, the cold-resistant ability gradually weakens and is vulnerable to frost damage. Some of the wheat damaged by late frost had some damage to the stem from the external shape of the plant. Some of them were yellowed and distorted. In severe cases, the plants withered and the pistils and stamens in the panicle were frozen, and the seed setting rate decreased. Therefore, we must strengthen forecasting and take preventive measures before the onset of frost. The common defense methods are as follows: 1. The irrigation water temperature is higher than the soil temperature when the frost occurs, sometimes higher than 10°C. Therefore, the irrigation water before frost can add a lot of heat to the soil. The heat capacity of water is much larger than that of air and soil, and the thermal conductivity of soil moisture is strong. When the weather suddenly becomes cold, the heat in the lower layer of the soil can be transmitted upwards to avoid rapid temperature changes. After the irrigation, the water vapor in the near-surface water increases, and when the water vapor condenses, a large amount of heat is released. Therefore, areas with sprinkling irrigation can spray water in the event of frost, regulate the microclimate in the field, and prevent freezing damage in wheat. According to the survey, before the occurrence of frost, irrigation can increase the ground temperature by 1°C to 3°C, and the temperature of the leaf surface can be increased by 0.2°C to 0.7°C. The freezing damage to wheat is significantly reduced. Second, smog smoke around the application of firewood smoke anti-frost has a long history. CHN chemical smoke can be used in areas with insufficient fuel. This chemical smoke agent is a mixture of ammonium nitrate, oil residue and sawdust. When firewood or chemical smoke agents are burned, not only do they release heat, so that the temperature rises, but also the smoke screen formed in the field can absorb the radiant heat of the sun, reduce the heat radiation of the ground, and prevent the soil and plants from losing heat. In addition, when water vapor condenses on the smoke, it can also release a lot of heat and increase the temperature. Flue-curing time should be mastered, not too early or too late, and it is usually better to reduce the temperature of the leaf surface to 1°C higher than the frost index. When the smoke is smoked, the firewood or smoke agent in each smoked point in the field must be lit at the same time to improve the effect. Third, the use of frost-resistant varieties of frost-prone areas should be selected and matched with late-maturing joint-tolerance varieties. Early jointing varieties are susceptible to freezing damage, late jointing varieties have strong cold resistance, and night frosts are lightly damaged. Fourth, to strengthen the cultivation and management of timely sowing: Early sowing got up early jointing, vulnerable to frost damage. Before the jointing, repression can inhibit the growth of the above-ground part, promote root development, and reduce frost. Reasonable fertilization: Plants with excessive nitrogen fertilization tend to be prosperous and prone to frost damage. Applying more phosphate and potash fertilizers can increase the frost resistance of the plants and have a significant effect on defense against frost. In addition, the spraying of chlormequat and paclobutrazol solution on the jointing stage can inhibit plant growth and reduce plant height, and it can both prevent and freeze.
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