After wheat returns to green, yellowing often occurs. The main causes of this phenomenon are drought, large amount of straw returned to the field, lack of fertilizer, diseases, pests and freezing damage.
drought. The yellowing of wheat caused by drought means that when the water absorbed from the soil from the soil of the wheat is difficult to compensate for the transpiration, the moisture balance of the wheat is imbalanced, and the growth and development of the wheat is affected by yellowing, and it is severe when it dies. The performance of the field is that the whole wheat field is yellowish, the birth is slow, the leaves are grayish green, the growth is slow or stagnant, the new leaves are short and the roots are small and fine. This type of wheat is often found in the bottom pods, looting seeds, running through the wind, and not pouring frozen water in the field.
Corn stalks return to the field. The return of corn stalks to the field can help fertilize fertility and improve the soil. However, the requirement for returning stalks to fields is one acre or two acres, with a combination of nitrogen fertilizer and deep plowing 25 cm. Now, the returning stalks to farmers is actually an acre. One acre or plough layer is less than 20 centimeters, and some are not suitable for applying nitrogenous fertilizer. In this way, some roots of wheat in the field are tied up on loose stalks after the emergence of the wheat, and it is difficult to absorb nutrients from the soil, resulting in maturity of the stalks and competition for the growth of the wheat seedlings. After the spring wheat was returned to water, the soil was solid, and the wheat seedlings became yellow and even died.
Lack of fat. Insufficient nitrogen fertilizer or insufficient phosphorus fertilizer can cause yellowing of wheat. The lack of nitrogen in yellow wheat is due to the early sowing of seeds, prolonged growth before winter, underutilization of basal fertilizer or low nitrogen content in base fertilizer, and poor fertility, resulting in yellowing of wheat. The performance in the field was as follows: the plants were small and weak, and the tillers were small and weak. The leaves of the seedlings were yellow and the tips of the leaves were withered. The old leaves in the lower part of the leaves were yellow and withered. In this case, it is necessary to apply about 5 kg of urea per acre in the returning green period, and then apply 12-15 kg of urea per acre in the jointing or jointing period, and if necessary, it may also be combined with foliar spray fertilizer, with a concentration of 2% for spraying. The urea solution 30-50 kg, spray again about 7 days. There is no application of phosphate fertilizer in wheat base fertilizers, insufficient application of phosphate fertilizers, or lack of phosphorus in soil, often causing yellow phosphorus deficiency in wheat. The field performance was as follows: very few secondary roots, few tillers, dark green leaves, yellow tips, new leaves blue-green, and purple tips. The lack of phosphorus yellowing in wheat can lead to small spikelets, insufficient grain, and a decrease in grain weight, which will seriously affect the yield. When the wheat seedlings are deficient in phosphorus, they can apply 10 kg of diammonium or 45-50 kg of superphosphate per acre. If necessary, they can also use foliar fertilizer to spray 3 kg of superphosphate solution 60 kg per acre. -10 days, spray 2-3 times
Disease. According to field observations, the diseases causing yellowing of wheat are mainly wheat root rot and sheath blight. The main symptoms of wheat root rot are: root rot, lesions on leaves, dead stems, and withered neck. In the spring after the onset of wheat turning green, the field showed yellowing of seedlings, uneven plant height. In the case of wheat sheath blight disease at the seedling stage, the diseased part showed dark green patches at the beginning of the disease, and gradually became large mottled patches. In the early stage after the jointing of wheat, the edge of the leaf sheath of the plant near the surface of the ground first appears pale brown with a gray mottled lesion in the middle, and the lesion can be expanded to form a "flower stalk", which seriously causes the base. Black and even rot cause dead plants. Root rot in wheat can be used at the beginning of the disease, with 12.5% ​​wolfberry fruit 20-30 grams or 20% triadimefon 40-50 grams of water 50-60 kilograms, pull the sprayer to spray on the wheat stem base, 15 days, once twice. Wheat sheath blight can be sprayed with 5% Jinggangmycin water solution 7.5 g water 100 kg or 12.5% ​​water chestnut fruit 20-30 g water 50 kg. Severely affected fields are controlled once every 7-10 days.
Freezing damage. After spring wheat returns to spring, the ability to resist coldness is reduced. Especially after jointing, it is very sensitive to low temperatures. When encountering severe cold weather, when the temperature falls to normal plants can not afford it, it is vulnerable to freezing injury. After freezing damage to wheat, the symptoms are generally manifested in the growth cone, and the frozen growth cone shows an opacity in the initial stage. Afterwards, the disintegration of the cells is atrophic. The field showed dark green leaves and the leaves were burned with boiled water. The tip of the leaves were chlorotic and yellow, and then dried. In severe cases, the aboveground part was dry or the whole plant died.
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