Causes of death of overwintering seedlings of wheat

In recent years, winter wheat overwintering dead seedlings occur almost every year, due to the strong regulation of wheat population, the effect of seedling death rate below 10% is not significant, while higher than 20% will lead to a reduction in yield. the reasons are as follows:

1. Low temperature freezing injury. The main cause of wheat overwintering seedling death caused by low temperature. The weather is hot and cold from time to time, and the temperature changes greatly, fast and frequently. As a result, wheat seedlings freeze too quickly and thaw too fast. in this alternating change of freezing and thawing, wheat seedlings fail to adapt in time, resulting in the decrease of physiological function, resulting in the death of wheat seedlings. Winter wheat which has been hardened to resist cold before overwintering can generally endure a low temperature of-23 ℃. No matter how low the temperature is, the dead seedlings are serious. The ability of low temperature resistance of winter wheat without cold resistance training was obviously weakened. When the climate is cold in winter, the permafrost layer is very thick, the soil moisture is frozen, the root system can not absorb water from the soil, or the water absorption capacity is very weak, the stems and leaves of wheat seedlings still transpirate and lose water, resulting in the gradual dehydration and death of wheat.

two。 The soil is dry. The total annual precipitation, summer precipitation and winter precipitation have obvious effects on the dead seedlings. Due to the lack of soil moisture, wheat plants can not get sufficient water supply during the overwintering period, especially in the years with changeable climate, more wind and cold current, wheat seedlings die due to drought and lack of water. In the wheat field where straw is returned to the field, the soil is loose and the cold air is easy to enter, which is more likely to cause the freezing injury of wheat.

3. Weak seedlings survive the winter. Due to late sowing, poor fertility, excessive density, or weak seedlings caused by grazing. The individual growth of wheat seedlings is weak, the growth before winter is small, and the accumulated organic nutrients are less, which can not meet the needs of wheat overwintering. Winter cold can cause overwintering death of seedlings, and the weak winter varieties with poor frost resistance are more serious.

4. Winter irrigation is too late. Watering over the winter water is too late, first, the water content in the wheat body is high, and it is easy to cause the plant to freeze and die in the cold current; second, the permafrost ground cracks, the root system is broken, and the cold air enters the lower part of the soil layer and the seedlings die; third, the lower soil freezes, and the water cannot seep down after watering, the surface freezes, the soil suffocates for a long time, and the wheat suffocates to death. 5. Improper selection of varieties or soil preparation, sowing too shallow and so on.