Topdressing of cotton at flowering and boll stage

At present, cotton fields are entering flowering period one after another, after which cotton will enter the flowering and boll period of more than 50 days, which is the peak period of fertilizer demand for cotton. Cotton flowers and bolls continuously during the flowering and bolling period of more than 50 days, and the demand for nutrients is continuous and uninterrupted, so in addition to particularly fertile soil, it must be supplemented by topdressing. Topdressing at flowering and boll stage is an important event in cotton management.

First, the lack of fertilizer plots to increase the amount of topdressing in the per capita cotton planting area more areas, some villages still maintain a low input, low output state, cotton planting benefits are very low. Some even apply only 10~15 kg urea or diammonium per mu (more than 150 kg seed cotton per mu all year round). Now cotton plants have shown serious fertilizer deficiency, especially in Nanpi County, where heavy rain has fallen, cotton fields have accumulated water, and few available nutrients in the soil have been leached and lost, so topdressing is urgently needed. If the amount of base fertilizer is small and the cotton field is not applied with potassium fertilizer, 10 kg urea and 7.5 kg high-quality potassium fertilizer should be applied per mu (potassium sulfate should be applied to saline-alkali land); if potassium fertilizer is applied in the base fertilizer, urea can be applied per mu of 10~15 kg. According to the experimental results of Soil and Fertilizer Institute of Hebei Province Academy of Agricultural Sciences, when the ratio of seed cotton to cotton straw is about 1∶1.5, every 100 kg seed cotton needs to absorb 4~5 kg nitrogen, 1.3~1.6 kg phosphorus pentoxide and 4~5 kg potassium oxide. High cotton yields cannot be obtained without applying a certain amount of fertilizer. Five kilograms of diammonium should also be added to the phosphorus deficient plots. Slow release coated urea (commonly known as controlled-release fertilizer) has a long fertilizer efficiency and high utilization rate, and can be mixed with ordinary urea according to 1:1, which not only ensures the present, but also takes care of the future. Flowering and boll stage topdressing should not be applied compound fertilizer, but urea, potassium sulfate and other quick-acting fertilizers should be applied to make cotton absorb and utilize as soon as possible.

II. In areas with large rainfall in the early stage of root fertilization, if the soil still has good moisture content, root fertilization should be carried out as soon as possible, and attention should be paid not to apply it between small rows. At present, most areas still adopt the planting mode of large and small rows. In many areas, the row spacing of small rows is only 40~42 cm, and many farmers have not broken the film so far. Small rows are the places where cotton roots are the least and weakest. If fertilizer is applied in small rows, if there is a little carelessness, such as large amount of fertilizer, uneven fertilizer, close to cotton trees, or light rain after application, it is easy to cause fertilizer damage to make cotton plants wilt. In many areas, improper selection or large amount of pre-emergence herbicides will weaken the roots, so it is strictly prohibited to apply fertilizer in small rows. At the beginning of flowering stage, topdressing should be applied in the middle of the big row. Most farmers worry unnecessarily about fertilizer being too far from the cotton plant. "Centralized fertilization" does not mean "near fertilization". According to the observation and measurement of researchers: the taproot depth of cotton at the initial flowering stage has exceeded 1 meter, the lateral extension length of lateral roots has exceeded 50 cm, and the extension speed of 0.5~1 cm can be maintained every day. Therefore, even if fertilizer is applied in the middle of a large row 1 meter wide, cotton on both sides can be utilized; moreover, cotton roots have chemotaxis, where there is fertilizer, where the roots are more prosperous. And topdressing the deeper the better, preferably up to 10 cm or more, so that fertilizer loss less, but also to induce roots under the tie.

Third, drought resistance watering must first fertilize after watering The author saw in the countryside that farmers in many areas did not fertilize when watering cotton, but after watering and then topdressing, so that the fertilizer efficiency was delayed for 5 to 7 days, once the rain was delayed, and the comprehensive effect of water and fertilizer could not be exerted. Therefore, when cotton is watered in the flowering and boll period, it is necessary to fertilize before watering. If the soil is too dry for root topdressing, sprinkle urea on the surface and water it (like@#@245@#@topdressing). Urea is very soluble in water, solubility at 20℃ is 105%, twice as high as ammonium sulfate, easy to move with water. Therefore, when urea meets water, it quickly dissolves into water and seeps into the soil with water for use by cotton roots. Although taboo by soil fertility experts and cultivationists, this method of surface application is still feasible when watering and soil is dry and hard, and it is simple, labor-saving and effective. Some people doubt that tilling and loosening after watering will cause urea loss in the upper layer of soil, but in contrast, the advantages of this combination of water and fertilizer far outweigh the disadvantages.

4. Urea and potassium sulfate are the best foliar fertilizer varieties for supplementing nitrogen and potassium for cotton fields that cannot be watered and fertilized at the roots. Spraying concentration is 2%, at least 0.5 kg fertilizer is sprayed on one mu at a time. Urea and potassium sulfate can be used alone, mixed or alternately, usually nitrogen first and potassium later. If mixed with pesticides spray, can appropriately reduce the amount of fertilizer, interval is shorter, spray several times. If combined with chemical control, chemical control should be given priority to, spraying more liquid at high positions of cotton plants and less at low positions.

Fish protein organic foliar fertilizer is a new type of foliar fertilizer, which 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 resistance, strengthen trees and promote roots, prolong leaf function, prevent premature senescence and control wilt. When spraying, depending on the size and nutritional status of cotton plants, 50~100 ml fertilizer is used per mu each time, and 3 times can be sprayed at the flowering and boll stage, once every 8~10 days. Other foliar fertilizers that have been tested by the masses and have obvious, reliable and economical effects can be applied.

5. High yield cotton field should be supplemented with fertilizer in the late flowering and boll stage. Whether cotton can produce high yield depends on the boll number and boll quality of the upper three fruit branches. In addition to climate and pest influences, nutrient availability still plays a decisive role. The root system of cotton in the later stage is aging day by day, and the absorption function is gradually decreasing; In addition, the boll in the middle and lower parts consumes a large amount of available nutrients in the soil; Moreover, after the rainy season, the available nutrients in the soil are subject to certain leaching loss, so the nutrient supply in the later stage generally cannot meet the needs of the upper boll, and it must be solved by foliar fertilizer spraying; Especially in the case of more bolls in the middle and lower parts, it is more important to spray fertilizer in the later stage.

Experience has shown that for most cotton fields at present, the most deficient nutrient element in the late stage is still available potassium. The typical symptoms of potassium deficiency are that the lower old leaves turn yellow or red first, while the veins remain green. Generally, potassium deficiency cotton fields begin to show after August 10, especially in rainy years. Therefore, most cotton fields should mainly supplement potassium in the later stage, and high-quality potassium sulfate is still the first choice for spraying potassium. No other foliar fertilizer contains as much potassium as potassium sulfate and is expensive. Potassium dihydrogen phosphate is a traditional foliar fertilizer for cotton, but it is not suitable for potassium supplement because it contains more phosphorus and less potassium. General cotton fields should be sprayed with potassium sulfate 2~3 times in the first and middle of August. If late August and early September found that cotton due to serious potassium deficiency and premature aging, potassium supplementation is too late.