Causes of premature senescence in cotton field and its control countermeasures

With the planting of cotton in the field year by year, the phenomenon of premature senescence occurs from time to time, which has become an important reason for restricting the improvement of cotton yield and quality in the field.

1. Causes of premature senility

1. Leave seed cotton field for continuous cropping

The continuous cropping of cotton in the cotton planting area for many years leads to the lack of organic matter in the plough layer, which can not meet the effect of continuous soil fertilizer supply. At the same time, continuous cropping caused the accumulation of bacteria in the soil and the decrease of the number of insect-resistant bacteria, which hindered the normal growth of cotton roots, thus affecting the upper growth of cotton and leading to premature senescence.

two。 Premature senescence of cotton root system

The planting of wide film and ultra-wide film resulted in shallow distribution of main root, more lateral root and large root quantity of plastic film cotton. According to the survey, the root system in the 035 cm soil layer accounts for 85% of the total root, and the root in the 0cm soil layer accounts for 35% of the total root. In the later stage of cotton growth, the root quantity decreased rapidly, part of the roots gradually aged, the root-shoot ratio was small, the root activity decreased, the absorption fertility decreased, and was sensitive to the demand of water and fertilizer. At this stage, if the supply of water and fertilizer is insufficient, the root system will soon collapse. In particular, the drought or waterlogging at the bud and boll stage led to poor growth of cotton, resulting in root damage, resulting in premature senescence.

3. Imbalance between supply and demand of nutrition

Heavy application of chemical fertilizer, no application of organic fertilizer, heavy nitrogen fertilizer, light phosphate fertilizer, no application of farm fertilizer, potash fertilizer and micro-fertilizer, resulting in serious imbalance of soil nutrition. The lack of land stamina makes the nutrition supply of cotton plants unbalanced and the distribution of nutrients in different growth stages is uneven, resulting in the imbalance of plant nutrient absorption, obvious decline of disease resistance and premature senescence.

4. Extensive use of plastic film

The extensive use of plastic film year by year has seriously affected the habits of soil, decreased permeability and tillage, created a natural barrier to root absorption of nutrients and water, seriously affected the effect of fertilization and irrigation, and weakened the ability of stress resistance. as a result, full-layer fertilization is applied on the surface of plastic film, which affects the absorption of fertilizer by roots and reduces the utilization rate of fertilizer. At the same time, the residual film also affected the emergence and root system of cotton in the field.

5. The occurrence of diseases and insect pests

Fusarium wilt and Verticillium wilt are the main diseases in cotton field. After the disease of cotton, the nutrient supply is blocked, which affects the normal growth and development of cotton, resulting in the premature senescence of cotton in the later stage. In recent years, there are many varieties of cotton, and some varieties have poor disease resistance and premature senescence resistance, which is also one of the reasons for cotton premature senescence.

6. Improper management measures

In the suitable sowing time, the technical goal of uniform seedling, complete seedling, strong seedling, uniform seedling and early emergence of strong seedling can be achieved. If the sowing date of cotton is too early, the temperature is low, the root system grows slowly and the disease is serious. Early and more peach sitting in the early stage led to the lack of nutrition supply and premature senility in the middle and later stage. In the case of insufficient soil moisture at the seedling stage, the root system enters the soil shallowly and the distribution of lateral roots is less, but after budding, flowering and peach bearing, the vegetative growth and reproductive growth go hand in hand. Once there is enough water, the cotton will grow rapidly, resulting in greedy green late ripening and too many bolls. As a result, the cotton plant itself is malnourished and the plant resistance is reduced, coupled with the frequent occurrence of Fusarium and Verticillium wilt at this time, and the cotton field is prone to premature senescence.

7. Water shortage during irrigation period

The water requirement for cotton growth period is about 9.26% at seedling stage, 11.38% at bud stage, 56.4% at flower and boll stage, and 22.93% at boll opening stage. Cotton encountered dry weather in the middle and later stage, resulting in cotton plants can not carry out normal physiological metabolism, affecting the formation of yield and accelerating premature senescence. With the gradual decrease of irrigation area in autumn and winter and the use of drip irrigation technology, the amount of drip irrigation is small and the number of drip irrigation is more, which makes the root system distribute in a small range, the root system of cotton enters the soil shallowly, the distribution of lateral root is less, and the root system dependence is strong. Under unsuitable climatic conditions, cotton shows poor resistance and adaptability, resulting in cotton premature senescence.

II. Prevention and control countermeasures

1. Rotation and stubble

Cotton planting fields should be selected in fields with flat terrain, fertile soil, convenient drainage and irrigation, consistent previous crops and uniform soil fertility. The effect is obvious in 3 ~ 5 years, especially in grain-cotton rotation and alfalfa-cotton rotation, and intercropping and interplanting can be carried out properly to clean the cotton field and put an end to the residual film in the cotton field. At the same time, crop rotation and deep ploughing in cotton field can change the ecological conditions of cotton field, improve soil structure, reduce the source of bacteria, increase the accumulation of soil organic matter, improve the ability of soil water storage and fertilizer conservation, promote the deep root system, promote the plant to grow deeply and grow healthily, and prevent premature senility.

two。 Soil testing and fertilization

In order to achieve high quality, high yield and high efficiency of cotton, balanced fertilization and combined use of nitrogen and phosphorus were combined with the local situation of lack of nitrogen and phosphorus. The ratio of nitrogen to phosphorus in cotton field was 1 ∶ 0.3 ~ 0.7. Apply 45 tons of base fertilizer per hectare. Organic fertilizer has complete nutrients and decomposes slowly in the soil to supply the needs of cotton plants, while improving soil physical and chemical properties and soil structure, which is conducive to the root development of cotton plants and meet the needs of nutrients in the middle and later stages.

The application of chemical fertilizer should be in accordance with the principles of stabilizing nitrogen, increasing phosphorus, increasing potassium and replenishing. Each hectare is increased by 300 kg of potash fertilizer, 15 kg of zinc sulfate and 7.5 kg of borax. To achieve good seed fertilizer, steady application of bud fertilizer, re-application of flower and boll fertilizer, supplementary application of top fertilizer.

3. Residual film recovery

In the cotton field, the film should be uncovered in time during the growth period, and the work of cuddling and picking up film should be done before soil preparation in spring and ploughing in autumn. Gradually reduce the amount of residual film in the cotton field, reduce pollution, promote the root system of cotton, and prevent premature senescence of cotton.

4. Comprehensive prevention of diseases and insect pests

During the cotton growth period, we should strengthen the comprehensive control measures and do a good job in the prevention of Fusarium wilt and Verticillium wilt. Strengthen the investigation of diseases and pests, control the harm of its expansion and spread, and deal with the disease in time when it is found. Excessive spraying of powders and high concentrations of pesticides is prohibited to prevent damage to leaves and affect photosynthesis. Put an end to the use of organophosphorus pesticides and prolong the functional period of leaves. Especially in the middle and later stage of cotton, the comprehensive control of cotton aphid, cotton leaf mite and cotton bollworm can ensure the normal growth and development of cotton and slow down the senescence time.

5. Ploughing and loosening the soil

The cotton was ploughed twice in the seedling stage, the intertillage depth was 1416cm, the seedling belt was 810cm, and the intertillage depth was in place at one time. When ploughing, there is no partition wall, no clods, no trenches, no seedlings, no shovels, so as to meet the quality requirements of flat, loose and broken. For the land-consolidated cotton field, ploughing in time to break the hardening, enhance the permeability of the land, promote the root system, and ensure the steady growth of cotton. For the low-lying cotton fields, to achieve smooth drainage and irrigation, prevent water accumulation after rain, and timely ploughing and loosening the soil, so that the cotton roots grow in depth, so as to enhance the stress resistance of cotton.

6. Rational irrigation

The pressurized drip irrigation under plastic film provides a better land environment for the normal growth and development of cotton, which can not only avoid deep leakage, but also control and reduce crop root evaporation to the maximum extent, so that the soil is basically free of early waterlogging, and the shedding of buds and bolls is reduced to a great extent. In order to prevent the premature senescence of cotton in the later stage, the cotton should be dripped in time in case of drought in the flowering and boll stage from July to the middle of August, so as to shorten the irrigation period and enhance the ability of cotton to resist premature senescence. Cotton was dripped 8 times for 12 times during the whole growth period. Drip 225,375 cubic meters per hectare each time. According to the soil moisture and growth period, determine the appropriate water cut-off time to ensure that the cotton is not prosperous, green branches and green leaves spit white catkins.

7. Chemical adjustment branch

Cotton growth in the early stage is mainly to promote vegetative growth, to build a high-yield shelf, to promote controlled, strong but not prosperous, to avoid excessive vegetative growth, resulting in crazy growth. In the later stage, we should give priority to control and promote the combination of control, that is, to control vegetative growth, but also to control and promote in order to prevent premature senility. On the basis of water and fertilizer control, chemical control should be carried out timely and reasonably to make cotton prosperous and strong in the early stage and robust but not declining in the later stage, and adhere to the chemical regulation principle of "early, diligent and light". Hit the top in time and adhere to the principle of "when branches are not equal, time is not waiting for branches". When the number of fruit branches per plant is 8-9, it can be topped, and 7-9 fruit branches can be retained after topping. When topping, it is required to knock off the tops on both sides of the cotton plant. Timely pruning is generally required to take the flower as the boundary on August 10 to remove the excess part of the top of the cotton plant and end it all before August 15.