Fertiliser application strategies for cotton

The sowing is normally in rows, and the plant density depends on the spacing of the rows and spacing between plants in the row. 

Examples of densities

• 55 000 plants/ha (India),
• 45 000 - 67 500 plants/ha (China/Yellow and Yangtze River) to
• 120 000 - 150 000 plants/ha (North China, short season)
• 60 000 - 90 000 plants/ha (USA)
• 100 000 – 200 000 plants/ha (Brazil) and
• from 100 000 (Egypt, traditional) to
• 168 000 plants/ha (intensive, recommended).

The nutrient requirement of cotton is directly related to the accumulation of dry matter determined by supplies of water and nutrients, temperature and radiation. In the hottest month of the growing period, the uptake is larger than during the cooler months. A proper redistribution of nutrients from vegetative to reproductive parts of the plant is an important component of the cotton plant nutrition, concerning particularly N and P. 

The cotton plant’s deep taproot is capable of reaching mobile nutrients in the soil like nitrate nitrogen from greater depths than many other plants. Cotton also has the possibility to store nitrogen in the leaves during periods of adequacy for later use during the boll fill period. Nitrogen is an important nutrient for development of all plant organs as it is a part of the plant’s proteins. The major part of N is absorbed after the first bloom and peaks at 2 to 3,5 kg/ha/day during fruiting. 10 to 20 percent of the total N requirements of the crop should be supplied to the plant prior to flowering, the remainder should be available during the boll development period. Split application improves the possibility of meeting crop needs when required.

Potassium is a nutrient of great important to the cotton crop. It has direct effect on fiber properties, i.e. micronaire, length and strength and is a component in enzyme systems. It can reduce the incidence and severity of wilt diseases and increases water use efficiency. Potassium is very important for maintaining water pressure within bolls for the fiber elongation, this indicates that there is an increase in K requirements in the period when this elongation occurs. 70 percent of K uptake occurs after first bloom, and the uptake peaks at about 2 to 3,5 kg/ha/day.

Shortage of potassium reduces fiber quality and yield, and results in more drought susceptible plants and diseases. Preplant applications can help avoid deficiencies, as well as correcting foliar applications during the growth season. Soil application must be the foundation of K management in the crop. The actual needs should be assessed with soil and tissue tests.

The nutritional benefits of a better fertilization scheme is in general associated with a prolonged period of fill of the boll. This effect are sometimes confounded with a delay in maturity, but it should be considered a prevention of a reduction in the filling period.