Upland Cotton

Upland cotton, Gossypium barbadense, and the two Old World diploids G. arboreum and G. herbaceum are all grown commercially, but they differ in fibre length, fineness and strength, and in the yarns they can be spun into. Upland is grown for volume and versatility; barbadense for the extra-long staple that fine-count yarns require.

Because "cotton" in trade statistics usually means upland unless stated otherwise, a figure for cotton production and a figure for upland production are close to the same number — but a specification written for one species does not transfer to another.

China, India, the United States, Brazil and Pakistan account for most of the crop, under strikingly different systems. Indian cotton is largely rainfed and smallholder-grown; Brazilian cotton is a large-scale second crop planted after soybean in the same season; irrigated production dominates in parts of China, Pakistan, Central Asia and the western United States.

These systems differ so much in planting date, plant population and harvest method that yield comparisons between them are rarely comparing the same thing.

The plant sets fruiting positions in a predictable sequence up the main stem and out along each fruiting branch, and it sheds squares and young bolls whenever the load exceeds what current photosynthesis can carry. Shedding is normal physiology rather than damage, and a plant that sheds nothing has usually set too little.

Management aims at cut-out — the point at which the plant stops initiating new fruiting positions and finishes the bolls it has — early enough for those bolls to mature before the season ends. Water, nitrogen and, in intensive systems, growth regulators are all used to bring that point forward or hold it back.

Cotton is comparatively tolerant of water deficit and comparatively intolerant of waterlogging, and it is grown across a wide moisture range. The sensitive window is flowering and early boll fill, when a deficit reduces boll retention directly.

Late-season irrigation is a common error: water applied after the useful bolls have set encourages regrowth, delays maturity and complicates defoliation without adding yield.

Bollworms boring into squares and bolls have historically been the defining pest problem, and insect-resistant cotton expressing Bacillus thuringiensis proteins changed the economics of the crop across most producing countries by suppressing them. The boll weevil was eliminated from large parts of North America through an area-wide eradication programme rather than by breeding.

Two consequences followed. Resistance to Bt proteins has emerged in several bollworm populations where refuge requirements were poorly observed, and sucking pests such as whitefly, jassids and mirids — untouched by Bt — have risen in relative importance as broad-spectrum sprays were withdrawn.

Verticillium and Fusarium wilts are the principal soilborne constraints and are managed largely through cultivar tolerance and rotation, since neither is treatable once a field is infested. Seedling damping-off is a routine early-season risk on cold, wet soils.

Cotton leaf curl virus, vectored by whitefly, has caused severe losses in South Asia and is a plant-health problem defined by vector management and resistant material rather than by direct treatment of the disease.

Mechanically harvested cotton is defoliated before picking so that leaf trash does not contaminate the lint. Timing is judged on the proportion of bolls open and on the maturity of the highest bolls worth keeping; defoliating early sacrifices immature bolls, defoliating late risks weather damage to open lint.

Hand-picked crops skip defoliation entirely and are picked over several passes, which yields cleaner lint at much higher labour cost. Which system is used is one of the strongest determinants of trash content in the bale.

Ginning separates lint from seed, and saw gins are used for upland where roller gins are used for longer-stapled cottons. Aggressive ginning and over-drying to speed the process both break fibre and cost length and strength that the field produced.

Bales are classed on measured fibre properties — length, uniformity, strength, micronaire, colour grade and trash — mostly by instrument. Micronaire, which conflates fineness with maturity, is the property most often penalised, and both immature and overly coarse fibre are discounted.

Every bale of lint comes with substantially more weight of seed, which is crushed for oil and meal or fed whole to ruminants. Cottonseed revenue is a real part of crop income rather than a by-product footnote.

Gossypol in the seed restricts its use in monogastric diets, which is why whole cottonseed goes principally to cattle and why the meal is used within defined inclusion limits.