Detailed Explanation of Key Points for Reasonable Fertilization Techniques for Cotton

Vigorously promoting scientific fertilization techniques for cotton is an important measure to increase the yield per unit area and product quality of cotton fields.

The demand of cotton for the three major elements of nitrogen, phosphorus, and potassium and fertilizer application techniques

Field fertilizer efficiency test results prove that for every 100 kg of seed cotton produced, 5.0 kg of pure nitrogen, 1.8 kg of phosphorus pentoxide, and 4.0 kg of potassium oxide are required, with the ratio of nitrogen : phosphorus pentoxide : potassium oxide being 1 : 0.36 : 0.8.

Reasonable application of base fertilizer. Base fertilizer should be mainly organic fertilizer, combined with a certain proportion of chemical fertilizer. Generally, per mu, use 2000 kg of pig and cattle manure or 5000 kg of farmyard manure. Since phosphorus is difficult to move in soil, and cotton is particularly sensitive to phosphorus in the early stages of growth and development, phosphorus fertilizer should all be applied as base fertilizer, generally 50 kg of superphosphate per mu. Superphosphate is best mixed evenly with organic fertilizer and applied deep to reduce contact with soil; calcium magnesium phosphate fertilizer should first be piled and composted with organic fertilizer or farmyard manure for 7-10 days before application.

Steady application of bud fertilizer. The principle of bud fertilizer application is to require cotton plants to grow steadily without excessive vegetative growth, so as to build a good high-yield framework, and also to promote early budding, early flowering, and early boll setting, laying a good foundation for high yield. Seedling fertilizer should be mainly organic fertilizer and phosphorus and potassium fertilizers, generally 1500 kg of pig and cattle manure or 100 kg of cake fertilizer per mu.

Heavy application of flower and boll fertilizer. Flower and boll fertilizer should account for about 50% of the total topdressing, generally 25-30 kg of 25% compound fertilizer per mu mixed evenly with 2000 kg of sieved farmyard manure or dry fine soil, applied in furrows from the initial flowering stage to when 1-2 large bolls have set on the lower part, then covered with soil to improve fertilizer utilization efficiency.

Boron physiological requirements of cotton and boron fertilizer application techniques

Available boron content in cultivated soil of our province. The results of the second soil survey show that the available boron content in cultivated soil of our province is seriously insufficient, with an average of only 0.26 mg of available boron per kg of soil. If the critical value for boron deficiency of 0.5 mg of available boron per kg of soil proposed by the Nanjing Institute of Soil Science, Chinese Academy of Sciences is used, then 94.3% of the province's soil has insufficient available boron supply.

Cotton is a dicotyledonous plant, and its boron requirement is greater than that of monocotyledonous plants. The boron content in the plant body is high, with normal plants containing 20-35 mg of boron per kg, and below 20 mg indicating boron deficiency. Cotton begins to absorb boron nutrition from the seedling stage, and the boron absorbed by the boll-setting stage accounts for 45.4% of the cumulative total for the entire growth period. Of the boron absorbed by cotton, 65.95% is distributed in the reproductive organs.

Boron fertilizer can promote root growth and development, improve root physiological functions, promote strong seedlings and early development, increase the speed of true leaf emergence, promote the transport of carbohydrates within the cotton plant, coordinate the balance of cotton plant growth and development, facilitate steady growth, early maturity, and prevention of premature senescence, effectively prevent the phenomenon of "budding without flowering" in cotton, reduce the rate of bud and boll shedding, increase the number of bolls per plant, single boll weight, and lint percentage, improve cotton quality, and increase fiber length and lint percentage.

When cotton is deficient in boron, root growth is impeded, lower leaves become larger, new leaves at the top become smaller, petioles have water-soaked ring bands, the growing point of the main stem is damaged, axillary buds proliferate, bud and boll shedding is excessive, the phenomenon of budding without flowering is severe, the corolla is shortened and difficult to extend, boll formation is very difficult, and cotton yield is seriously affected.

Boron fertilizer application techniques for cotton are as follows:

Boron fertilizer as base application. Per mu, use 0.5-1 kg of borax mixed evenly with 2000 kg of sieved farmyard manure or dry fine soil, then broadcast into the soil, followed by plowing and land preparation, then sowing or transplanting into nutritional pots.

As seed fertilizer. Per mu, use 0.5-1 kg of borax mixed evenly with 2000 kg of sieved farmyard manure or dry fine soil and apply in sowing or transplanting furrows and holes. Special attention must be paid to even application, avoiding contact with seeds, not mixing with seeds, not covering seeds, and not applying directly below the seeds, so as not to hinder seed germination and seedling growth.

Foliar spraying. Foliar spraying of boron fertilizer avoids both leaching loss and chemical fixation from direct contact of boron with soil, making it the most economical and effective application method. At the same time, split spraying better meets the boron needs of cotton at different growth stages.

Spraying period. The optimal periods for foliar spraying of boron fertilizer on cotton are the bud stage, initial flowering stage, and flower and boll stage.

Application rate. Generally, per mu, using 200 g of borax diluted in 100 kg of water for foliar spraying gives the best effect.