Detailed Explanation of Cotton Square and Boll Stage Management Techniques

    I. Square stage

After cotton enters the square stage, all regions should manage it according to the seedlings, with classified management. For first-class cotton fields, where cotton plants have vigorous vegetative growth, reasonable regulation should be carried out to shape an ideal plant form and promote early boll setting, more bolls, and large bolls; for second-class cotton fields, promotion and control should be combined to prompt the cotton plants to build a high-yield framework early; for third-class cotton fields, which develop late and grow weakly, the method of promoting both water and fertilizer should be adopted to prompt the cotton seedlings to grow early. Focus on the following aspects of work:

1. Grasp the "four rush" management. After wheat is harvested in wheat field intercropped cotton fields, promptly rush to irrigate, rush to clear stubble, rush to topdress, and rush to control pests, so as to provide a good environment for cotton seedling growth and development. The topdressing amount is generally about 5 kg of urea per mu; where base fertilizer is insufficient, 50 kg of cake fertilizer or 500-1000 kg of organic fertilizer may be applied; potassium-deficient plots may be topdressed with 10-20 kg of potassium sulfate. Focus on the control of cotton aphids, red spiders, and plant bugs. 

    2. Scientific fertilization. After cotton squares appear, fertilizer should be applied steadily and skillfully. According to the reality that cotton development is generally late this year, especially for second- and third-class cotton fields, action should be taken early, with promotion as the main approach and combining promotion with control. Generally, 10-15 kg of standard nitrogen fertilizer is topdressed per mu. For cotton fields with poor soil fertility, insufficient base fertilizer, and weak cotton seedling growth, apply earlier and more; for cotton that develops early or has sufficient seedling fertilizer and strong growth, apply later, less, or not at all. Potassium-deficient cotton fields may be topdressed with 10-20 kg of potassium sulfate per mu.
　　
    3. Timely watering. When the soil moisture content at 10-30 cm in the cotton field is less than 55%, water promptly, but each watering should not be excessive, with 20-30 cubic meters per mu being appropriate. After watering, promptly carry out intertillage and loosening of the soil to promote root penetration and enhance the cotton's drought resistance in the later stage.
　　
    4. Earthing up in cotton fields. After watering or thorough rain at the end of June and beginning of July, plastic-film-mulched cotton fields can have the film removed and be earthed up to prevent lodging, while also facilitating drainage and irrigation. Open-field direct-seeded and seedling-transplanted cotton fields can be earthed up directly. However, plastic-film-mulched cotton without irrigation conditions should not have the film removed and be earthed up before thorough rain.
　　
    5. Pest control. Focus on controlling second-generation cotton bollworm, red spiders, and plant bugs. When the number of larvae above the second instar reaches more than 20 per 100 cotton plants, chemical
　　
    control should be carried out promptly. For red spiders, when 20%-25% of cotton seedlings show yellow spots damaged by mites, control should be carried out promptly. The key to plant bug control lies in "early"; generally, when there is 1 insect per 100 plants in the field, or when small black spots appear on tender leaves or bract leaves of cotton plants, spraying should begin for control.
6. Chemical regulation. Mainly aimed at cotton fields with excessive growth and high density, use 0.5-1 g of mepiquat chloride per mu, or 2-4 mL of chlormequat, diluted in 10-15 kg of water for spraying. After applying growth regulators in cotton fields, management must be strengthened, with attention to watering and fertilizing, so as to promote below and control above. Prevent the situation where, after using regulators, because cotton leaves are dark green, no topdressing or watering is done and management is relaxed, causing premature senescence and yield reduction.
　　
    II. Flower and boll stage
　　
    The flower and boll stage is the key period determining cotton yield and quality. This period is when cotton needs the most nutrients in its entire life, and it is also a period when various natural disasters occur frequently. Strengthening management is very important for achieving a cotton harvest.
　　
    1. Heavily apply flower and boll fertilizer. According to the reproductive characteristics of insect-resistant cotton with many bolls set in the early stage, fertilization at the initial flowering stage is advocated, generally applying 15-20 kg of urea per mu. When fertilizing, flexibly control it according to cotton appearance and weather changes. For cotton fields with less base fertilizer and square fertilizer, relatively poor soil fertility, and weaker cotton plant growth, flower and boll fertilizer should be applied early and heavily, so as to "fertilize at flowering for use at boll setting." At the same time, in early August, supplement with topping fertilizer, 5 kg of urea per mu; for cotton fields with medium to high fertility, in order to strive for more bolls per plant, increase boll weight, and achieve higher yield, on the basis of topdressing at the initial flowering stage, 2.5-3 kg of urea per mu may be topdressed at the end of July and beginning of August; for cotton fields with a trend of premature senescence, topdress 5 kg of urea per mu; fertile cotton fields should only apply initial flowering fertilizer, and apply little or no topping fertilizer. Ordinary cotton fields may, in combination with pest control, begin foliar spraying from mid-August. Spray 0.5%-1% urea solution, 2%-3% superphosphate solution, or 800-1000 times monopotassium phosphate solution, once a week, for three consecutive sprays.
　　
    2. Topping and pruning. Topping should be flexibly controlled according to cotton field density and variety characteristics. Generally, conventional insect-resistant cotton sown in spring at a density of 3000-4000 plants/mu may retain 14-16 fruiting branches per plant; insect-resistant hybrid cotton at a density of 2000-2600 plants/mu may retain 16-18 fruiting branches per plant; summer cotton at a density of 6000-8000 plants/mu may retain 6-8 fruiting branches per plant. According to the principle of not waiting for branches when the time comes and not waiting for the time when branches come, the topping time for cotton fields with medium fertility is generally July 15-20, and late-developing cotton fields may be postponed to around July 25. The time for cotton edge-heart removal is generally before August 10. At the same time, promptly remove squares appearing after the Beginning of Autumn and after White Dew