Main causes and Preventive measures of premature Senescence of Cotton under drip Irrigation

I. the main causes of premature senescence in cotton planting with high density.

1. Variety factor

The variety is not resistant to premature senility. In recent years, there are many varieties of cotton, some varieties of aging, degradation, some varieties of their own disease resistance and early aging resistance is poor, or not suitable for high-density planting, resulting in premature senescence of cotton.

two。 Environmental factors

The suitable sowing time of precocious cotton in ① temperature is 5 cm ground temperature and 12 ℃. If sowing is too early or cold injury occurs in seedling stage, due to low air temperature, slow root growth and serious disease, it is easy to damage the function of cotton root system and cause premature senescence of cotton.

Cotton encounters chilling injury of lower than 15 ℃ for a long time during flowering and boll stage. Due to physiological imbalance and metabolic disorder, cotton growth function is weakened and cotton is easy to form premature senescence.

② soil moisture is insufficient, cotton head water or 2 water is affected by drought, which affects the absorption of roots and the normal metabolism of cotton plants, resulting in premature aging of cotton roots, decline of function, weakening of absorptive capacity, and premature senescence of cotton.

Excessive soil moisture or heavy rain after irrigation resulted in stagnant water in the field, anaerobic respiration of roots under anoxic conditions, poisoning due to the accumulation of alcohol, affecting the normal metabolism of cotton plants, resulting in damage and aging of cotton roots and weakening of root absorption function. leading to premature senescence of cotton.

The widespread use of chemical fertilizers in ③ soil, especially heavy nitrogen fertilizer, light phosphate fertilizer, no farm fertilizer, potash fertilizer and micro-fertilizer, can easily lead to soil nutrition imbalance and premature senescence of cotton plants.

When cotton is planted on too dense soil, the soil is slightly dry, it is difficult for cotton to take root, the root growth is blocked, and the nutrients and water absorbed by roots at flowering and boll stage can not meet the needs of cotton plants, which is easy to cause premature senescence of cotton.

Long-term continuous cropping of cotton with ④ diseases and insect pests resulted in an increase in the accumulation of soil Fusarium wilt and Verticillium wilt in cotton fields, damage in nutrient transport, and premature senescence of cotton.

After cotton is harmed by diseases and insect pests, the prevention and control of diseases and insect pests is not thorough or unscientific, resulting in damage to leaf function, leaf photosynthesis, short life span, early shedding, and easy to cause premature senescence of cotton.

⑤ special climate cotton after drought dripping too much or sudden heavy rain, easy to cause cotton physiological disorders, metabolic disorders, leading to premature senescence of cotton.

Cotton flower and boll period in case of continuous cloudy days or continuous heavy rain suddenly clear, easy to cause cotton physiological disorders, metabolic disorders, the formation of cotton premature senescence.

3. Management factor

① irrigation is not suitable for drip irrigation cotton without stubble irrigation or winter irrigation before winter, due to insufficient soil moisture, early water intake at seedling stage, short squatting time of cotton seedlings, small root growth and shallow distribution, resulting in poor stress resistance of cotton, nutrients and water absorbed by roots at flower and boll stage can not meet the needs and are prone to premature senescence.

In the hot summer weather, the soil temperature dropped suddenly, the root metabolism was disordered, and the absorption was blocked, which led to the premature senescence of cotton.

The root distribution of cotton under drip irrigation is shallow, and the dripping period at flower and boll stage is too long, which is easy to cause premature senescence of cotton due to drought.

Unreasonable ② fertilization has been adopted to plant cotton with high density in recent years. The harvest of cotton has reached 1.5 ~ 18000 plants per square meter, and the biological yield of cotton is also increasing, so the amount of fertilizer input needs to be increased. Insufficient fertilization or unreasonable ratio of phosphorus, nitrogen and potassium can easily lead to premature senescence of cotton.

The chemical control of ③ in the early and middle stages was light, the field was too shady, and the lower leaves of cotton received less light and produced less nutrients, which could not meet the needs of lower buds, bolls and roots, resulting in premature senescence of cotton roots due to malnutrition and premature aging.

Early cotton field, early peach early and more, concentrated boll carrying, heavy physiological load, too heavy chemical control or insufficient supply of water and fertilizer, prone to premature senility.

In the later stage, the chemical control of cotton is too heavy, the upper internodes are too tight, the leaves are small and flat, and the middle and lower parts are poorly ventilated and transparent, which is easy to cause premature senescence of cotton.

Second, the main countermeasures to prevent premature senescence of cotton under high-density drip irrigation.

1. Select improved varieties

The mid-early maturing varieties with high disease resistance, resistance to continuous cropping, strong leaf function in the later stage and suitable for close planting should be selected.

two。 Suitable time for sowing

The sowing date of cotton should be determined according to the climate, growth characteristics of varieties and dripping conditions and other comprehensive factors. Generally, the soil temperature of 5 cm in the film can be sown and dripped steadily through 12 ℃ for two consecutive days.

3. Timely ploughing

Cotton ploughing in time can break hardening, loosen soil, increase soil permeability and soil temperature, which is beneficial to the normal growth of root system.

4. Squat seedlings at the right time

Under high-density drip irrigation, cotton must be irrigated in winter or stubble irrigation to store sufficient soil moisture, and the squatting time of cotton seedlings in spring is not less than 35 days, so as to ensure that the root system of cotton is large enough to meet the needs of cotton growth and development in the middle and later stage.

5. Scientific fertilization

Cotton yield 120kg lint, 667m2 standard fertilizer 130kg, nitrogen ∶ phosphorus ∶ potassium = 1 ∶ 0.4 0.5 ∶ 0.1 0.15, 30% 40% nitrogen fertilizer, 50% phosphate fertilizer 60%, 50% potassium fertilizer should be deeply applied, no fertilizer could be applied at seedling stage and bud stage, and the remaining nitrogen, phosphorus and potassium fertilizer should be dripped with water in flower and boll stage.

6. Reasonable dripping

Head water can not be too early, autumn and winter irrigation cotton dripping in the first and middle of June. Cotton should not be affected by drought or flooding during the flowering and boll period, and it is best not to drip before and after heavy rain. Measures can be taken to reduce the amount of irrigation and shorten the irrigation cycle to prevent drought.

7. Scientific tone

In order to improve the ability of producing nutrients in leaves and create a good condition for root growth, cotton under high-density drip irrigation was sprayed with promethamine at the stage of 3 leaves and 5 leaves, and urea and potassium dihydrogen phosphate were added.

Adhere to the principle of water control as the main and chemical control as the auxiliary, achieve a small number of times to ensure the uniform distribution of internodes, the lower 1-4 Internode length 2-4 cm, 5-7 Internode length 4-5 cm, 8-10 Internode length 5-6 cm, 11-13 Internode length 6-7 cm, leaf lift, the angle between the lower 1-4 Internode and the main stem is 30-45 degrees.

When cotton encountered high temperature or low temperature weather during the growth period, cotton suddenly rained after dripping water, and when it suddenly cleared after continuous cloudy days or heavy rain during the flowering and boll period, foliar fertilizer containing biological regulators, organic substances and trace elements could be properly sprayed on the field cotton leaves, and urea and potassium dihydrogen phosphate could be added to prevent premature senility.

8. Pest control

Adjust the production layout and promote rational crop rotation. For the cotton fields with recurrent Fusarium wilt and Verticillium wilt, the rotation should be reasonable, and the rotation period is 3-5 years, which has a certain control effect.

Cotton fields with sporadic occurrence of Fusarium wilt and Verticillium wilt should be surveyed twice in June and August, and the diseased plants should be removed and burned outside the field. Foliar fertilizer containing biological regulators, organic substances and trace elements, such as Haizhuangyuan 818 and Lvfeng 95, was sprayed on the leaf, and potassium dihydrogen phosphate was added.

Strengthen the comprehensive prevention and control of insect pests to achieve early detection and early control. We should conscientiously implement the control policy of "checking, inserting, wiping, picking, pulling, painting and beating" for red spiders. On the basis of careful investigation of cotton bollworm and aphids, we should pay close attention to the number of natural enemies and the development of insect pests, and then administer drugs when they reach the target. Put an end to large areas and large doses of drugs to protect natural enemies.

9. Other measures

For the early cotton field or the cotton field with the tendency of premature senescence in the later stage, the full flower and boll stage fertilizer should be applied, combined with chemical regulation, foliar fertilizer containing biological regulators, organic matter and trace elements, urea and potassium dihydrogen phosphate should be sprayed for 2 times.

When cotton is in hot weather, don't drip at noon. The amount of water dripping for the first time in the cotton field affected by drought should not be too large, so as to alleviate the drought by reducing the amount of irrigation and shortening the period.