Topdressing Methods and Technical Key Points for Cotton During the Flowering and Boll Stage

Cotton fields are currently entering the flowering stage one after another. After this, cotton will enter the flower and boll stage lasting more than 50 days, which is the peak period of fertilizer demand for cotton. During the more than 50 days of the flower and boll stage, cotton continuously flowers and sets bolls, and its demand for nutrients is continuous and uninterrupted. Therefore, except for particularly fertile soil, topdressing is necessary to supplement nutrients. Topdressing during the flower and boll stage is an important task in the management of cotton during the flower and boll stage.

1. For plots short of fertilizer, increase the amount of topdressing. In areas where the per capita cotton planting area is relatively large, some villages still maintain a state of low input and low output, and the efficiency of cotton planting is very low. In some cases, only 10-15 kg of urea or diammonium phosphate is applied per mu (with an annual seed cotton yield of more than 150 kg per mu). Now the cotton plants have shown severe fertilizer deficiency. In particular, Nanpi County has experienced heavy rainstorms, cotton fields have accumulated water, and the limited available nutrients in the soil have been leached and lost. Topdressing is urgently needed now. If the base fertilizer application rate is small and no potassium fertilizer was 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 the test results of the Institute of Soil and Fertilizer of the Hebei Academy of Agriculture and Forestry Sciences: 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 obtained. In 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 1:1 for application, which not only ensures the current demand but also takes care of later needs. During the flower and boll stage, compound fertilizer should no longer be used for topdressing. Instead, quick-acting fertilizers such as urea and potassium sulfate should be applied so that cotton can absorb and utilize them as quickly as possible.

2. In plots with 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, and care must be taken never to apply it between the narrow rows. At present, most areas still use the planting method of wide and narrow rows. In many areas, the narrow row spacing is only 40-42 cm, and many farmers have still not removed or broken the plastic film. The narrow rows are where cotton roots are fewest and weakest. If fertilizer is applied between the narrow 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 very easily cause fertilizer damage and make the 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 the narrow rows must be strictly prohibited. At the early flowering stage, topdressing should be applied in 1 row in the middle of the wide row. Most farmers worry that if the fertilizer is too far from the cotton plants, it will not work, but this worry is completely unnecessary. "Concentrated fertilization" is not equal to "fertilizing close to the plants." According to researchers' observations and measurements: at the early flowering stage of cotton, the main root has already penetrated more than 1 m into the soil, and the lateral roots have already extended horizontally more than 50 cm, and can still maintain an extension speed of 0.5-1 cm per day. Therefore, even if the fertilizer is applied in the middle of a 1 m wide row, the cotton on both sides can use 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. The author has seen in rural areas that many farmers do not apply fertilizer when watering cotton, but instead topdress after watering, which delays the exertion of fertilizer efficiency 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 flower and boll stage and is watered, 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 and then watered (as in @#@245@#@ topdressing). Urea is very easily 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 use by cotton roots. Although this surface application method is taboo among soil fertilizer scientists and cultivation scientists, it is still a feasible method when watering is needed and the land is dry and hard so that furrow application cannot be done. Moreover, this fertilization method is simple, saves labor, and has a quick fertilizer effect. Some people question that intertillage and loosening the soil after watering will cause the urea remaining in the upper soil layer to be lost, but comparatively speaking, the benefits of this method of combining water and fertilizer far outweigh the disadvantages.

4. For cotton fields that cannot be watered and cannot be root-fertilized, immediately spray fertilizer on the leaves. 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 potassium later. If mixed with pesticides for spraying, the fertilizer amount can be appropriately reduced, the interval can be shorter, and it can be sprayed several more times. If combined with chemical regulation, chemical regulation should be the main focus, spraying more liquid on taller cotton plants and less liquid on shorter ones.

Fish protein organic foliar fertilizer is a new type of foliar fertilizer and is very suitable for cotton application. It can not only provide a certain amount of nitrogen, phosphorus, potassium, and trace element nutrition, but also improve cotton stress resistance, strengthen plants and promote roots, prolong leaf function, prevent premature aging, and control Fusarium and Verticillium wilt. When spraying, depending on the size and nutritional status of the cotton plants, use 50-100 mL of fertilizer per mu each time. It can be sprayed 3 times during the flower and boll stage, once every 8-10 days. Other foliar fertilizers that have shown obvious, reliable, and economical effects after trial use by the public can also be applied.

5. High-yield cotton fields also need supplemental fertilizer in the late flower and boll 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 and pests and diseases, nutrient supply still plays a decisive role. In the later stage, the cotton root system gradually ages, and its 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 a certain amount of leaching loss. Therefore, nutrient supply in the later stage generally cannot meet the needs of boll setting in the upper part, and foliar spraying must again be relied upon to solve this; especially when many bolls are set in the middle and lower parts, foliar spraying in the later stage is even more important.

Experience shows that, for most cotton fields at present, the nutrient 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 this after August 10, especially in rainy years. Therefore, in most cotton fields, the later stage should focus mainly on potassium supplementation, 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 the price is high. 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 premature aging is found in cotton fields due to severe potassium deficiency in late August and early September, it will be too late to supplement potassium.