Recently, information about the yellowing, drying, and death of wheat seedlings in wheat fields has been mentioned repeatedly.
1.Intrinsic factors refer to the ability of wheat plants to resist cold and drought damage. If wheat varieties with poor cold resistance are used during cultivation, they are prone to die seedlings in case of frost damage. Individual wheat seedlings sown too early and differentiated to the biangular stage before winter have weak cold tolerance, and often die seriously in case of frost damage. In addition, some late-sown weak seedlings are prone to death due to their own accumulation of less sugar, and they are also prone to death in case of cold damage and drought damage.
2.External factors refer to various factors other than the wheat plant itself, such as unfavorable climate, soil conditions and inappropriate cultivation practices. For example, less precipitation in summer and autumn, insufficient soil moisture, less rain and snow in winter and spring, and more cold winds will aggravate soil drought, so that the wheat tillering joint is in the soil layer of cold and warm abrupt changes, resulting in physiological dehydration and death of wheat.
For another example, if the varieties with weak winter and shallow tillering nodes are selected, the seedlings will also die when the ground temperature is greatly affected by the temperature difference. In addition, if the sowing is too late, too deep or too dense, it is easy to form weak seedlings, which is not conducive to the safe wintering of wheat, especially in the case of insufficient bottom moisture, it is more likely to lead to the death of seedlings due to cold and drought.
The wheat seedlings that appear dead can be divided into three symptoms:
The wheat is dry and yellowish as a whole, but the root system is normal.The overall growth of wheat seedlings in the field is not vigorous, and the yellowing phenomenon occurs in irregular flakes, and it is difficult to see the existence of green leaves when the yellowing is serious.
The tips or leaves are dry and dehydrated, but the overall yellowing symptoms are mild.
The yellowing of wheat seedlings in such a large area is rare even in the past 20 years.
Some people think that the problem is caused by wheat seeds, some people think that they have purchased fake fertilizers, and more people suspect that herbicides are causing the problem.
Agricultural material dealers blame this on straw returning and severe cold and frost damage.
The two completely different views have had a fierce response between agricultural material dealers and farmers.
What causes yellowing of wheat seedlings? How to remedy yellowing of wheat seedlings?
At the seedling stage of wheat, the leaves will turn yellow, the plant will grow slowly, and the plant will be emaciated. There are many reasons why wheat sprouts turn yellow.
1. Nitrogen deficiency type yellowing.
Nitrogen deficiency will cause wheat seedlings to be short and weak, tillers are few and weak, wheat seedling leaves lose green and yellow, chlorophyll decreases or disappears in severe cases, leaves are small, leaf tips wilt, and the lower leaves of the old leaves are yellow and withered.
Remedy:10-15 kg of urea or 7-12 kg of ammonium bicarbonate per mu. If there is still nitrogen deficiency after returning to green, about 15 kg of urea can be applied per mu, and 12-15 kg of urea per mu can be applied at the getting up or jointing stage. It can also be sprayed with 2% urea solution twice on the foliar surface when the wheat seedlings are yellow, with an interval of about 7 days each time.
2. Phosphorus deficiency type yellowing.
Lack of phosphorus in wheat seedlings, reduction of secondary roots, less tillers, dark green leaf color, yellow leaf tips, blue-green new leaves, purple red leaf tips, if not remedied in time, it will lead to less small grains, not full grains, and a decrease in 1000-grain weight.
Remedy:7-10 kg of diammonium phosphate or 10-20 kg of superphosphate can be applied per mu, and 80 kg of 3%-5% superphosphate aqueous solution can also be sprayed on the foliar surface of the mu, sprayed once every 7-10 days, and sprayed 2-3 times in a row.
3. Potassium deficiency type yellowing.
Wheat seedlings often start from the tip of the old leaves, and then extend down along the veins, and the macula part is obvious, and it is mosaic and yellowish. The yellow leaves are draped under the yellow leaves, and the stalks of the diseased seedlings are small and thin, and they are easy to senescence and lodging.
Remedy:In the wheat seedling stage, 5-10 kg of potassium chloride or potassium sulfate should be applied per mu of furrow, and 30-50 kg of grass ash can also be applied per mu. In the middle and late stages of wheat growth, 10% plant ash solution or 02%-0.60 kg of 3% potassium dihydrogen phosphate solution, spray 2-3 times, spray 1 time every 7-10 days.
Fourth, the deep sowing type is yellowing.
Due to the unreasonable modulation of sowing machinery, the sowing is too deep, resulting in too long stems in the ground, and excessive seed nutrient consumption when wheat emerges, resulting in slender seedling leaves, poor root development, and thin and yellow wheat seedlings.
Remedy:Part of the covering soil can be removed, so that the thickness of the tillering joint cover soil becomes thinner, and then combined with tillage, improve the soil aeration condition, promote the development of lateral roots, and make the wheat seedlings stronger.
Fifth, the over-dense type is yellow.
For wheat fields sown earlier and with a larger amount, wheat seedlings often grow too densely, and wheat seedlings turn yellow due to poor ventilation and light transmission, weak ontogeny.
Remedy:Artificial thinning should be carried out appropriately for plots with too many basic seedlings to increase the light transmittance and ventilation of wheat fields and slow down the growth rate. Deep ploughing and root breaking, reducing water and fertilizer absorption, controlling the increase of tillering and over-vigorous growth, and promoting the growth of strong seedlings.
6. Yellowing of the arid type.
Due to the dryness of the plot and the rush to plant, the main manifestations are yellowing of the leaves at the base of the wheat seedlings, gradually drying up, the heart leaves are not growing, the secondary roots are few, and the tillering is difficult.
Remedy:Watering in time to promote the normal growth of wheat seedlings.
7. Yellowing of the fertilizer type.
The application of organic fertilizers that are not well decomposed, such as sheep manure, chicken manure, etc., or the application of excessive seed fertilizer, seedlings and seeds are easy to be burned after coming into contact with these fertilizers, resulting in yellowing of leaves or leaf tips.
Remedy:Watering and leaching, watering once in 5-7 days, and watering 1-3 times according to the fertilizer damage.
8. Yellowing of the pesticide damage.
If the concentration of pesticide dressing is too large, the root tip will be injured and expanded, resulting in yellow seedlings.
Remedy:If the problem is not serious, you can leave it alone, and wait until the secondary roots grow, and the wheat seedlings will naturally turn from yellow to green. If the problem is severe, it should be remedied by watering, and the soil should be loosened after watering.
9. Disease-type yellowing.
The wheat seedling stage is mainly the occurrence of root rot, which will make the wheat seedlings yellow, and in severe cases, the wheat seedlings will die and the roots will rot.
Remedy:70% thiophanate-methyl wettable powder can be used 800-1000 times liquid to irrigate the roots along the ridge.
Wheat is a large area of yellow, who is the culprit?
Improper planting
For example, in the southern area of Huanghuai Winter Mai, all wheat sown before and after the cold dew showed varying degrees of vigorous growth due to the high temperature. Due to the failure to suppress or control the wheat fields in time, when the temperature drops sharply, it is easy to cause a large area of frost damage.
Under the influence of higher temperatures, some wheat fields with sufficient water and fertilizer are also the "hardest hit areas" for vigorous seedlings.
Wangchang wheat entered the jointing stage in advance before the winter dormancy, and after suffering frost damage, it could only rely on tillering to re-form tillering seedlings, which buried a large risk of yield reduction for the next year's wheat yield.
Therefore, farmers can refer to the practice of previous years when planting wheat, but also refer to the local climate conditions of the year, as well as the fertilizer and water conditions in the field, to determine the amount and sowing time of wheat, rather than following the trend and rushing to plant.
Straw returning to the field is not scientific
According to the survey, all corn stubble and soybean stubble of wheat, yellowing phenomenon is more serious, this is because the wheat root system is suspended, the root system adheres to the soil poorly, resulting in weak seedlings, when the temperature drops sharply (more than 10 cooling), it will aggravate the frost damage of wheat seedlings.
However, the wheat fields with relatively clean straw clearing, the wheat fields that have been suppressed after sowing and the wheat fields that are not straw returning to the field have almost no yellowing phenomenon except for the vigorous growth factor.
The susceptibility of the variety to temperature changes
It is undeniable that the cold tolerance of wheat varieties is not the same, due to the continuous warm winter, growers ignore the management of wheat overwintering frost damage, especially the short stem and large spike as the only criterion for seed selection, but ignore other factors.
Since sowing, wheat has been in a relatively arid state, coupled with the superposition of unfavorable factors such as straw returning and sudden drop in temperature, which aggravates the occurrence of frost damage of wheat seedlings, especially some wheat varieties that are not cold-tolerant.
How to alleviate the yellowing of wheat seedlings in a large area?
At present, wheat seedlings are in the hibernation period, and it is of little significance to take remedial measures such as spraying and fertilizing, but in areas with conditions, winter irrigation can be carried out in good weather.
After the Spring Festival, the temperature rises, wheat enters the green period, 8-15 kg of nitrogen fertilizer can be applied per mu, and after the new leaves grow, humic acid or seaweed fertilizer + amino-oligosaccharides can be used for leaf spraying, which has a very good auxiliary effect on the recovery of wheat growth.
In summary,At present, the phenomenon of large-scale yellowing of wheat seedlings is caused by many factors such as climate, straw and unsuitable sowing time.
Cultivation measures to reduce dead seedlings
1.The selection of cold-resistant varieties and the selection of varieties with strong winter and good cold resistance are effective measures to prevent frost damage and death of seedlings. When introducing seeds, it is necessary to understand the adaptability of the variety, and take into account its yield as well as its cold resistance, so that the selected varieties can safely overwinter at least most years in the local area.
2.Seedling irrigation for the early sowing wheat field with insufficient bottom moisture, can be watered at the tillering stage, if the soil fertility is insufficient, a small amount of chemical fertilizer can be appropriately applied to promote early emergence of seedlings, so as to facilitate the safe wintering of seedlings. The management of late-sown wheat field should be mainly to improve ground temperature and moisture preservation, and the soil can be loosened by cultivating, and watering should not be done at the seedling stage, otherwise the ground temperature will be reduced and the upgrading and transformation of seedlings will be affected.
3.Timely winter irrigation and winter irrigation can form a good soil moisture environment, adjust the soil nutrients in the cultivated layer, improve the heat capacity of the soil, promote the rooting and multi-tillering of plants, and raise strong seedlings. Watering winter water is not only conducive to overwintering and seedling preservation, but also can reduce the adverse effects of cold damage, drought damage and drastic temperature changes in early spring, which is an important measure to prevent wheat seedlings from dying in winter and spring.
Watering winter water should be appropriate, with night freezing and day dissipation, the temperature is appropriate at 4 o'clock, and winter irrigation is easy to occur when the temperature is lower than 4. Winter irrigation should be flexibly mastered according to soil quality, seedling condition and moisture condition. Clay soil should be watered appropriately early to avoid freezing due to the fact that the water cannot be completely infiltrated before freezing. Sandy land should be watered late, part of the wetland, rice stubble or wheat field with good bottom moisture can not be watered, but for the wheat field with a large amount of straw returned to the field, winter water must be watered to crush the soil mass and freeze the pests.
4.Timely suppression can break the soil mass, fill the cracks, and stabilize the soil, so that the wheat roots and the soil are tightly combined, and the root system development is promoted. In addition, the repression also has the effect of improving and protecting moisture.
5.Properly cover the sand and cover the wheat in winter, and break the soil to cover the wheatIt can deepen the depth of the tillering node into the soil and protect the leaves near the ground layer, reduce the evaporation of soil moisture, improve the water status at the tillering node, and play the role of heat preservation and anti-freezing. The wheat field covered with soil should be cleared in time in spring, and the soil should be cleared out of the ridge when the temperature reaches 5.
For varieties with poor cold resistance, wheat fields with shallow sowing and poor moisture should be covered as early as possible. Mulching during the overwintering period can increase temperature and moisture, effectively prevent frost damage, promote plant growth, thereby increasing plant tillering and promoting its development into large tillers, and improving the tillering and panicle formation rate. The cover time is suitable when the temperature drops to 3, the cover is easy to grow early, and the leaves are easy to freeze when the cover is late. Late-sown microphones can be covered immediately after sowing.
However, it is worth noting that where there is more serious frost damage in the wheat field, it is strictly forbidden to spray herbicides, as for whether the herbicides can be sprayed normally after the Spring Festival, everything depends on the recovery of wheat seedlings, blind spraying of herbicides in wheat fields, not only easy to cause herbicide damage, but also seriously affect the normal recovery of wheat seedlings.
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