Cotton Cultivation Techniques: How to Apply Topdressing During the Flowering and Boll-setting Stage of Cotton?
How to apply topdressing during the flowering and boll-setting stage of cotton? Please provide guidance. During the flowering and boll-setting stage of cotton, the following methods can be referenced for topdressing: 1. For plots lacking fertilizer, increase the topdressing amount. In areas with a relatively large per capita cotton planting area, some villages still maintain a low-input, low-output state, and the cotton planting benefit is very low. Some even apply only 10-15 kg of urea or diammonium phosphate per mu (with an annual seed cotton yield of more than 150 kg per mu). Now the cotton plants have shown severe fertilizer deficiency, especially in Nanpi County, where heavy rainstorms have occurred, cotton fields have accumulated water, and the limited available nutrients in the soil have been leached and lost. Topdressing is urgently needed now.
How to apply topdressing during the flowering and boll-setting stage of cotton? Please provide guidance.
During the flowering and boll-setting stage of cotton, the following methods can be referenced for topdressing:
1. For plots lacking fertilizer, increase the topdressing amount. In areas with a relatively large per capita cotton planting area, some villages still maintain a low-input, low-output state, and the cotton planting benefit is very low. Some even apply only 10-15 kg of urea or diammonium phosphate per mu (with an annual seed cotton yield of more than 150 kg per mu). Now the cotton plants have shown severe fertilizer deficiency, especially in Nanpi County, where heavy rainstorms have occurred, cotton fields have accumulated water, and the limited available nutrients in the soil have been leached and lost. Topdressing is urgently needed now. For cotton fields with minimal base fertilizer application and no potassium fertilizer applied, 10 kg of urea plus 7.5 kg of high-quality potassium fertilizer should be applied per mu (potassium sulfate must be applied in saline-alkali land); if potassium fertilizer was applied in the base fertilizer, 10-15 kg of urea can be applied per mu. According to experiments: when the ratio of seed cotton to cotton stalks is about 1:1.5, every 100 kg of seed cotton produced requires the absorption of 4-5 kg of nitrogen, 1.3-1.6 kg of phosphorus pentoxide, and 4-5 kg of potassium oxide. Without applying a certain amount of fertilizer, high cotton yields cannot be achieved. For phosphorus-deficient plots, 5 kg of diammonium phosphate should also be added. Slow-release coated urea (commonly known as controlled-release fertilizer) has a long fertilizer effect period and high utilization rate. It can be mixed with ordinary urea at a 1:1 ratio for application, ensuring both current and future needs. During the flowering and boll-setting stage, topdressing should no longer use compound fertilizer, but should use quick-acting fertilizers such as urea and potassium sulfate, so that cotton can absorb and utilize them as quickly as possible.
2. For plots with good soil moisture, carry out root fertilization as soon as possible. In areas with heavy rainfall in the previous period, if the soil still has good moisture, root fertilization should be carried out as soon as possible. Be careful never to apply it between the small rows. The space between small rows is where cotton roots are fewest and weakest. If fertilizer is applied between small rows, slight carelessness, such as a large amount of fertilizer, uneven application, being too close to the cotton plants, or light rain after application, can easily cause fertilizer damage and make cotton plants wilt. Moreover, in many areas, improper selection or excessive use of pre-emergence herbicides has further weakened the root system, so fertilization between small rows must be strictly prohibited. At the early flowering stage, topdressing should be applied in a single row in the middle of the large rows. "Concentrated fertilization" does not equal "fertilizing close to the plant." According to measurements: at the early flowering stage of cotton, the main root has penetrated more than 1 m into the soil, and the lateral roots have extended more than 50 cm horizontally, and can still maintain an extension speed of 0.5-1 cm per day. Therefore, even if fertilizer is applied in the middle of a 1 m wide large row, the cotton on both sides can utilize it; moreover, cotton roots have chemotropism, and where there is fertilizer, the roots there will be more numerous and vigorous. Also, the deeper the topdressing, the better, preferably more than 10 cm, so that fertilizer loss is reduced and roots can be induced to grow downward.
3. When watering for drought resistance, fertilizer must be applied first and then water. In many areas, farmers do not apply fertilizer when watering cotton, but instead topdress after watering, which delays the exertion of fertilizer effect by 5-7 days. Once rain occurs after watering, it will be delayed even longer, and the comprehensive effect of water and fertilizer cannot be brought into play. Therefore, when cotton encounters drought during the flowering and boll-setting stage and needs watering, fertilizer should be applied before watering. If the land is already dry and hard and root topdressing cannot be carried out, urea can be broadcast on the soil surface followed by watering (just like topdressing wheat). Urea is very soluble in water, with a solubility of 105% at 20°C, twice that of ammonium sulfate, and it moves very easily with water. Therefore, when urea meets water, it quickly dissolves into the water and moves with the water into the soil for cotton roots to use. Although this surface application method is taboo among soil fertility scientists and cultivation scientists, it is still a feasible method when watering is needed and the land is dry and hard and furrow application is impossible. Moreover, this fertilization method is simple, saves labor, and has a quick fertilizer effect. Some people question whether intertillage and soil loosening after watering will cause loss of urea remaining in the upper soil layer, but comparatively speaking, the advantages of this water-fertilizer combined fertilization method far outweigh the disadvantages.
4. For cotton fields that cannot be watered and cannot have root fertilization, immediately apply foliar fertilizer. Urea and potassium sulfate are the best foliar fertilizer varieties for supplementing nitrogen and potassium in cotton. The spraying concentration is 2%, and at least 0.5 kg of fertilizer should be sprayed per mu each time. Urea and potassium sulfate can be used alone, mixed, or alternately, generally nitrogen first and then potassium. If mixed with pesticides for spraying, the fertilizer amount can be appropriately reduced, the interval shortened, and spraying done more times. If combined with chemical regulation, chemical regulation should be the main measure, spraying more liquid on taller cotton plants and less on shorter ones.
5. High-yield cotton fields also need supplementary fertilizer in the late flowering and boll-setting stage. Whether cotton can achieve high yield ultimately depends on the number of bolls set on the upper three fruiting branches and the quality of the bolls. In addition to the influence of climate, pests, and diseases, nutrient supply still plays a decisive role. In the later stage, cotton roots gradually age and their absorption function gradually declines; in addition, boll setting in the middle and lower parts consumes a large amount of available nutrients in the soil; and after the rainy season, the available nutrients in the soil suffer certain leaching losses. Therefore, nutrient supply in the later stage generally cannot meet the needs of upper boll setting, and foliar spraying must again be relied upon to solve this; especially when there are many bolls in the middle and lower parts, late-stage spraying is even more important.
Experience shows that at present, for most cotton fields, the nutrient element most lacking in the later stage is still available potassium. The typical symptom of potassium deficiency is that the lower old leaves first turn yellow or red, while the leaf veins remain green. Generally, potassium-deficient cotton fields begin to show symptoms after August 10, especially in rainy years. Therefore, most cotton fields should focus on potassium supplementation in the later stage, and high-quality potassium sulfate is still the first choice for potassium spraying. No other foliar fertilizer contains as much potassium as potassium sulfate, and their prices are higher. Potassium dihydrogen phosphate is a traditional foliar fertilizer for cotton, but because it contains more phosphorus and less potassium, it is not suitable for potassium supplementation. Generally, cotton fields should be sprayed with potassium sulfate 2-3 times in early to mid-August. If by late August and early September it is found that cotton fields are prematurely aging due to severe potassium deficiency, then supplementing potassium will be too late.
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