Recently, some Internet media reported that "this winter is cold, and wheat can be freeze-resistant for three days after sowing." I think this statement is unscientific. Wheat is best frost-resistant when it is sown properly, and early and late sowing have disadvantages.
What is a suitable seeding period? "Fit" is calculated according to the criteria for wheat to form strong seedlings before winter (5-7 leaves, 3 or more tillers), and is calculated from the effective accumulated temperature from wheat sowing to overwintering. This effective accumulated temperature is approximately 450 ~ 600 ° C. In other words, if the suitable sowing date stated in the cultivation guide of a variety is October 5-15, we will sow during this period. The accumulated temperature that does not grow before winter should be between 450 and 600 ° C. 5 to 7 leaves and 3 or more big tillers. At this time, the young wheat ears did not enter the two-edge period, and there was no sign of elongation in the first internode of the base, but the root depth at this time had been lowered to below tens of centimeters in soil, and even reached 1 meter. This type of wheat accumulates more nutrients and consumes less, laying a solid foundation for safe wintering. This kind of wheat seedlings are the most resistant to freezing.
The frost damage of cold winter wheat will be a little heavier. This is beyond doubt, but there are cold winters that occur in extremely cold or extremely cold weather. Most of the wheat that has been frozen to death or frostbite is wheat that has not been sown in an appropriate period. For example, wheat was planted during the National Day holiday in some growers in central and southern Henan in 2015. These "outrageous" early-seeding wheats encountered significant cooling and freezing, and even a large number of dead seedlings. As the sowing was premature, the winter wheat entered the two-edge stage or young ear development stage of wheat ear differentiation, and the internodes also showed signs of elongation. At this time, the cold resistance of wheat seedlings was greatly reduced, even if they were Freezing damage can also occur at low temperatures.
On the contrary, if it is planted late, the wheat does not form a strong seedling before winter, especially the wheat seedling that has just reached the 3-leaf stage, it is the wheat seedling "weaning period". Wheat in the "weaning period" is still weak in its ability to produce nutrients. The nutrients of the seeds have been used up, the root system is still shallower (the roots are slower when the temperature is lower), and the leaves are thinner and smaller. The color is lighter ... At this time, the wheat seedlings are the most vulnerable, and they can't withstand adversity such as severe cold and drought. In addition, late sowing will cause small spikes and small grains of wheat, which will threaten the yield. In areas or years with high incidence of scab, late sowing will cause the wheat flowering stage to shift backward, increase wheat field humidity during flowering, and give wheat scab disease. Favorable conditions for the occurrence of crops; late sowing and late maturity, the wheat harvest period is postponed, and there may be rain during the harvest period.
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