Causes and Control Countermeasures of premature Senescence of Cotton under drip Irrigation

Since 2002, the 141 regiment has popularized the cotton drip irrigation planting technology in a large area, the per unit yield has been increased year by year, and the economic benefit is remarkable. However, in recent years, there are different degrees of premature senescence in cotton fields, resulting in poor bolting, shelling, stiff tip increase and lower quality.

1. Causes of premature senility

1. Continuous cropping for a long time

In the cotton fields with newly reclaimed and short cotton planting years, most of the cotton has green branches and green leaves. The old cotton field with continuous cropping for 10 years and more than 10 years grew well in the early stage, but once it encountered low temperature, overcast and rain in the middle and later stage, the symptoms of leaf red leaves occurred in a large area. The main reasons are as follows: ① due to long-term continuous cropping of cotton field, straw returning to the field, cotton Fusarium wilt and Verticillium wilt pathogens accumulated in the soil year after year, the number of antibiotic bacteria was less, resulting in increasingly serious diseases, resulting in premature senescence. Because of their different biological characteristics, ② crops have different kinds and amount of soil nutrient uptake; because of their root exudates, their effects on rhizosphere microflora and microbial energy substances are different; planting the same crop for a long time will make the soil ecosystem out of balance, greatly reduce soil fertility and cause premature senescence of cotton. ③ cotton field accumulates a lot of residual film, which is not conducive to cotton root growth and development, directly affects cotton root binding and extension, causes cotton root system deformity and distortion, is not conducive to root absorption of nutrients and water, and then affects the normal growth and development of cotton aboveground part, resulting in the increase of bud and boll shedding, resulting in cotton premature senescence.

two。 Shallow distribution of root system

Cotton drip irrigation has the characteristics of a small number of times, and the cotton root system has the characteristics of water and fertilizer, which makes the root distribution of drip irrigation cotton field relatively shallow, which is not conducive to cotton root absorption of deep soil water and nutrients, and drought resistance weakens. Once encountered with high temperature and drought, or insufficient water, it is easy to cause premature senescence. The investigation shows that early dripping at seedling stage and cotton fields with one film and three belts are more likely to cause premature senescence. The reasons are early water intake at seedling stage, short squatting time of cotton seedlings, poor root development, small and shallow root growth, poor stress resistance of cotton, and weak ability of absorbing nutrients and water at flowering and boll stage. The average dripping water of one film three belt cotton field is about 14 cubic meters less than that of one film and two tubes, the distribution of cotton root system is shallower, the drought resistance is worse, and it is easier to senescence prematurely.

3. Improper management of water and fertilizer

Cotton lasts 70-90 days from budding to boll-opening, accounting for more than 2% of the whole growth period. During this period, the distribution of nutrients in the plant is tight, and if the water and fertilizer are not managed properly, it will cause premature senescence of cotton. From the first ten days of June to the first ten days of July, cotton was mainly vegetative growth, and from mid-July to mid-August, cotton was mainly reproductive growth. more fertilizer was applied in the early stage of cotton growth and less in the middle and later stage, which led to excessive vegetative body in the aboveground part of cotton. there are many buds, flowers and bolls, but due to the lack of nutrients in the middle and later stage, a large number of buds and bolls fall off, and the reproductive organs of cotton plants are maldeveloped, resulting in premature senescence.

4. It's late to hit the top.

The topping time of our regiment is from June 25 to July 10, and the early flowering stage is the prosperous period of cotton vegetative growth and reproductive growth. the daily growth of the main stem reaches the maximum, and the cotton grows to a certain height without topping in time, which will make the reproductive growth lag behind. If the aboveground part of the nutrient body is too large, the leaf transpiration is relatively large, if it can not meet the water requirements of cotton in time, it is easy to suffer drought, resulting in premature senescence of cotton plants.

5. The chemical adjustment is unreasonable.

The top fruit branch was adjusted when the top fruit branch elongated to 8-10 cm at seedling stage, two-leaf stage and one week after topping, and the middle and upper fruit branches of cotton extended too long, affecting the air and light permeability of the lower fruit branches and the photosynthesis of leaves, resulting in the shedding of buds and bolls of the lower fruit branches, even if the bolls were not shedding, the bolls formed were smaller, and the weight of single boll was lighter, causing premature senescence of cotton.

6. The harm of insect pests

Cotton aphids and cotton leaf mites suck sap on the back of cotton leaves with piercing mouthparts, destroying leaf photosynthesis, discoloring, curling, and even shedding, resulting in premature senescence. Excessive concentration of pesticide and fertilizer spraying and more times of spraying will damage mesophyll cells and appear round or irregular water-stained patches on leaves, or leaves become red and scorched, resulting in serious bud and boll shedding and premature senility.

7.3 kinds of poor resistance

A wide variety of cotton, rapid renewal, cotton itself disease resistance, stress resistance is poor, will also cause premature senility. In 2007, Bianza No. 1, which was planted in a large area in our regiment, and precocious varieties planted in a small area, after continuous days of rainfall from August 12 to 14, 80% of the cotton fields had large area red leaves, which seriously affected the photosynthesis of the leaves and led to the premature senescence of cotton.

8. Climatic factors

The continuous rainfall and low temperature in the flower and boll stage caused a large area of red leaves of cotton, and even withered and shedded, resulting in premature senescence of cotton.

II. Prevention and control countermeasures

1. Rational crop rotation

Combined with the development of animal husbandry in the regiment farm, the planting structure should be adjusted, the planting area of grain and grass should be expanded, and the rotation of grain, cotton and grass should be carried out in order to maintain the long-term stable circulation of soil nutrients.

two。 Uncover the film in time

Opening the film at the end of June and the beginning of July in the early flowering stage of cotton can make the roots fall, improve the drought resistance of cotton, increase the recovery rate of residual film, and have no effect on the growth, development and yield of cotton.

3. Squatting seedlings properly

The first drip of cotton under drip irrigation was from the end of May to the beginning of June, when the cotton began to bud into the bud stage, and the bud stage was the fastest period of cotton root growth. the growth rate of main root was 2-3 times faster than that of main stem and about 1 times faster than that of lateral root. and there are a large number of new branch roots. At this time, the dripping delay is beneficial to the root system, and there is a certain amount of growth to ensure that the cotton has a large enough root system in the flowering and boll stage to meet the needs of growth and development in the middle and later stage.

4. Water and fertilizer management

Apply sufficient basal fertilizer at each growth stage, no or light application of bud fertilizer, adhere to one water and one fertilizer after entering the early flowering stage, heavy application of flower and boll fertilizer and top fertilizer to ensure uniform boll formation in the upper, middle and lower parts of cotton plants. The application of nitrogen fertilizer in the early stage should not be too large to avoid leading to vigorous growth and unstable peach growth. The mobility of phosphorus in the soil is poor and the utilization rate is low. If diammonium phosphate is applied as the base fertilizer, the whole growth period of cotton will be significantly improved, which is beneficial to the prevention and control of cotton premature senescence.

5. Control of diseases and insect pests

For cotton Fusarium wilt and Verticillium wilt, the diseased plants should be removed in light disease areas, the accumulation of bacteria should be reduced, and the rotation of gramineous crops such as corn and cotton could obviously reduce the disease in severe disease areas. the number of years of rotation should be increased, that is, at least 5 years. For insect pests to achieve early investigation, early control, and strive to eliminate the damage in the central strain or spot occurrence stage. In the prevention and control, it is necessary to achieve low concentration, large amount of water, and reduce the number of pesticide spraying. It is strictly forbidden to use pesticides that kill natural enemies to create a good ecological environment for natural enemies.

* * the frost-free period is short, and early-maturing varieties with strong disease and stress resistance and high yield should be planted. It is best to select the multi-resistant varieties approved by the relevant institutions, and it is strictly forbidden to transfer unquarantined seeds from seriously diseased areas, and carry out depilation and coating treatment.