Nitrogen (N) is essential for the development of all plant organs including shoots, buds, leaves, roots, and bolls.
Phosphorus (P) is important in early root development, photosynthesis, cell division, energy transfer, early boll development, and hastening of maturity.
Potassium (K) is an extremely important nutrient in cotton production. It affects fiber properties such as micronaire, length and strength and functions in enzyme systems. It is important in reducing the incidence and severity of wilt diseases and increases water use efficiency. Bolls are major sinks for K. It is important in maintaining sufficient water pressure within bolls for fiber elongation. Thus, the need for K increases dramatically during early boll set. About 70 percent of uptake occurs after first bloom according to US Research. A shortage of K reduces fiber quality and yield and results in plants that are more susceptible to drought stress and disease.
Secondary nutrients and micronutrients are also critical to profitable cotton production.
A high yielding cotton crop can take up more than 30 lb each of Sulphur (S) and magnesium (Mg). Cotton responds to micronutrients like boron (B), zinc (Zn) and manganese (Mn) where they are deficient. Micronutrient availability, except for molybdenum (Mo) and chloride (Cl), is generally reduced in alkaline and calcareous soils.
In West Texas, Zn is commonly the most limiting nutrient after N and P. Soil tests, plant analyses and field history should be used to establish the need for these nutrients.
A complete fertility program is essential to attaining maximum profit in cotton production. Furthermore, balancing nutrient inputs with other management inputs like water, variety, tillage, and rotation helps ensure that maximum efficiency of production and profit are achieved.
Cotton fertilisation practices in West Africa
The cotton-producing countries of West and Central Africa produce high quality cotton. They account for 15% of global exports, placing them second behind the United States!
Cotton, which supports more than 10 million people in these African countries, is a major source of foreign currency and rural employment.
It is quite common that cotton is grown in the same areas year after year, and chronic soil mineral deficits can lead to the depletion of soil reserves of some minerals, especially potassium and magnesium. Crops may then show visible signs of nutrient deficiency disorders – magnesium and potassium deficiency symptoms are very common in regions with a long history of cotton growing.
In these areas, the formula of compound fertilizers commonly used in cotton crop fields (NPK 14-23-14+5S+1B2O3) should thus be modified by reducing the phosphorus concentration, increasing that of potassium and adding magnesium. (Source: CIRAD -Centre de coopération internationale en recherche agronomique pour le développement. Fertilization of cotton crops in sub-Saharan Africa).
East African Cotton
Cotton in East and North Africa is as important as it is in West Africa particularly in those regions (Sudan, Egypt, Tanzania, Ethiopia etc) where cotton has been grown commercially for decades. Nutricare has run an interesting trial some years ago in Tanzania, and the idea behind NPK was in fact quite similar to Cirad’s findings in West Africa, i.e. reduce P2O5 and add more K2O.
Results of the trial were quite interesting, and it proved that the above nutrient hypothesis was correct. In the near future, however, more emphasis should be put in micro nutrients like Boron.