Agronomic Principles

The family Gossypium has 39 species, whereas only few have economic importance: 

• - G. hirsutum L. – Upland cotton, constitutes 90% of total cultivated cotton
• - G. arboreum L. – India, Pakistan, China and Thailand
• - Others: G.barbadense L., G. aroboreum L. and G.herbaceum L

We will here concentrate our information on Gossypium hirsutum.

Cotton is grown for fiber and oil seed. The cotton plant is unique because it is a perennial with an indeterminate growth habit and has perhaps the most complex structure of any major field crop. Associated with this complex growth habit is an extreme sensitivity to adverse environmental conditions which is reflected in excess fruit abscission. A better understanding of cotton (Gossypium hirsutum L.) growth and development in commercial production is important in the continuing efforts of growers to produce lint and seed yield more efficiently. 

From emergence to appearance of the first flower bud, the shoot growth is slow. At this stage, the cotton establishes a vigorous root system. Upon the appearance of the first flower (white), a plant with good yield potential should have 9-10 knots above this flower. From the first flower buds, the goal is to obtain a plant with maximum possible number of knots, providing there is space for flowering and production.

Climate

Cotton needs a period of 140 the 160 predominantly sunny days. Temperature has a high influence on the development of the plant, it grows in tropical and sub-tropical warm humid climates. Annual requirements are 20 – 28 °C. After the 130 days, the time must be relatively dry to guarantee the opening of the fruits and the quality of the harvested cotton.

Water

Cotton respond to moisture and too little water can limit cotton yields. In the arid areas of the USA, irrigation is mandatory for production. In the humid south of the country, irrigation is critical for maintaining yields during drought. Cotton can adapt to semi-arid conditions. 

• In Brazil nearly all the cotton area is unirrigated
• In India 70% is rain fed 
• In China and Egypt it is irrigated (10 - 12 irrigations at 15 day intervals) 
• In USA (desert of Arizona, water equivalent to 1 040 mm is given)

Cotton is preferably grown on light to medium soils, pH 6 – 8, the plant is highly sensitive to soil acidity and water or soil salinity. With low pH, aluminum toxicity and low calcium content will give problems, hence acidity alleviation is essential to achieve high crop yields. Areas under risk of flooding are also unfavorable for cotton production, as cotton plants do not tolerate low oxygen in root environment.

Nutrients

Plant nutrition depends on an adequate supply of water for uptake, translocation and metabolic functions for growth. Therefore drought stress and irrigation strongly affect the efficiency of fertilization and the resulting growth and yield. Cotton exhibits a large degree of drought tolerance compared to other crops because of various mechanisms including root growth, osmotic adjustment and selective fruit shedding.