Key Technical Points and Correct Methods for Applying Boron to Cotton

In recent years, statistics from cotton boron fertilizer trials in various regions show that on boron-deficient soils (soil available boron below 0.5 mg/kg) and potentially boron-deficient soils (soil available boron below 0.8 mg/kg), applying boron fertilizer to cotton can achieve good yield increases.

1. Base fertilizer: Apply before cotton sowing or before transplanting nutrient (pot) seedlings, incorporated during land preparation. Apply about 0.5 kg of borax per mu, which can be mixed evenly with fertilizers such as nitrogen, phosphorus and potassium and applied together, or mixed with fine dry soil before application.

2. Seed fertilizer: At cotton sowing, apply boron fertilizer in a band in the sowing furrow or in spots in the sowing holes. Use about 0.5 kg of borax per mu, mixed evenly with fine dry soil. Special attention should be paid to avoiding contact between boron fertilizer and seeds; boron fertilizer should not be used for seed dressing nor for covering seeds, so as not to affect seed germination and seedling growth.

3. Foliar fertilizer: Boron fertilizer is mostly applied to cotton by foliar spraying. The advantages of spraying: first, because boron is not easily transferred from old tissues to new tissues within the plant, spraying boron fertilizer can promptly meet the needs of new growing tissues; second, pesticides and fertilizers can be sprayed together to save labor. In cases of severe boron deficiency, spraying should start from cotton bud stage, once every 10 days, for a total of 4 to 6 sprays, which can achieve good yield increases. In cases of mild boron deficiency, spray once each at cotton bud stage, early flowering stage and boll stage. A 0.2% borax solution gives better results as the spraying concentration. The amount of fertilizer solution to spray: 30 to 40 kg per mu at bud stage, 40 to 50 kg at early flowering stage, and about 60 kg per mu at boll stage.

For aerial spraying of boron fertilizer, use the Yunshu-5 aircraft, carrying conventional spraying equipment, to carry out conventional spraying operations. During operation, the airflow should be steady and the wind speed less than 4 m/s, the aircraft speed 160 km/h, the flight height 5 to 7 m above the cotton, the operation swath width 50 m, the aircraft carrying 1000 kg of solution, with 2.5 kg of liquid used per mu (containing 0.1 kg of borax), and 400 mu sprayed per sortie. For aerial boron spraying of cotton, the highest yields are also obtained by spraying once each at bud stage, flowering stage and boll stage.