What are the main measures for late-stage field management of cotton?
Cotton generally begins to open its bolls in late August and early September (from End of Heat to White Dew), and cotton management enters the late stage. The main tasks of late-stage field management of cotton are: preserving roots, preserving leaves, promoting early maturity, and preventing premature aging, so as to achieve high yield and quality and a bumper harvest.
1. Timely watering to prevent autumn drought: If soil moisture is insufficient in the late growth period of cotton, it will affect the absorption function of the root system, delay boll development, prevent fibers and seeds from maturing normally, and prevent soil nutrients from being used effectively. Therefore, if autumn drought occurs, water timely to prevent drought, give play to the role of water carrying fertilizer, maintain the vitality of the cotton plant, keep the leaves at a certain photosynthetic intensity, and increase dry matter accumulation. This has a clear effect on preventing premature aging, preserving autumn bolls, increasing boll weight, and improving seed plumpness and fiber quality.
During the boll-opening period of cotton, cotton fields are often rather compacted, water does not infiltrate easily, and the phenomenon of "water drying as soon as it passes the soil surface" often occurs, so watering must be thorough and even. General cotton fields usually need only 1 watering during drought in late August. If drought continues after autumn, for high-yield cotton fields and late-developing cotton fields with great yield-increasing potential, watering should continue into mid- and late September.
2. Apply foliar fertilizer reasonably to improve cotton plant nutrition: In the late stage of cotton, the absorption capacity of the root system declines, and because temperatures are relatively low in the late growth period, the effect of soil topdressing is poor. Therefore, timely spraying of foliar fertilizer plays an important role in improving the nutritional status of cotton plants, extending the functional period of leaves, preventing disease and strengthening the plant, preserving autumn bolls, increasing boll weight, promoting early maturity, and preventing premature aging. Foliar fertilizer is generally sprayed once every 7-10 days, and can be sprayed continuously 3-4 times. When spraying foliar fertilizer, the spray concentration of the foliar fertilizer must be strictly controlled to prevent fertilizer damage. On sunny days, it is best to spray in the afternoon; on cloudy days, foliar fertilizer can be sprayed all day.
3. Prune timely to improve ventilation and light conditions in the cotton field: For cotton fields that are late-maturing, excessive in vegetative growth, and shaded, late-stage pruning and training should be strengthened. Remove axillary buds and redundant buds timely. On the premise of ensuring three cotton leaves support one boll, empty branches may be appropriately cut, and 1-2 old leaves on the lower main stem that have basically lost function may be removed, so as to improve ventilation and light conditions in the cotton field, promote early maturity, and improve the quality of boll opening.
4. Use ethephon timely for ripening: Spraying cotton plants with ethephon can effectively prompt cotton plants to open bolls faster and increase the yield of pre-frost cotton. To use ethephon for ripening, the timing of ethephon use must first be well controlled. Spraying too early reduces boll weight, lowers lint percentage, and decreases quality; spraying too late, when temperatures are low, reduces the ripening effect and results in poor ripening. In the Yellow River cotton region, generally on October 1-5, use 100-150 ml of 40% ethephon, mix with 45-60 kg of water, and spray evenly on cotton plants. After cotton has set bolls for 30 to 40 days, if continuous rainy weather occurs, cotton field humidity is high, and cotton bolls are prone to rotting. In order to reduce losses from rotten bolls, cotton bolls that have been in the boll stage for more than 40 days, whose boll shells have faded and turned yellow, and on which black spots have begun to appear, can be picked timely before they rot. After the picked cotton bolls are dipped in a 1% ethephon solution, they are dried in the sun, and cotton with relatively good boll opening can be obtained.