Potassium (K) deficiency symptoms in cotton are well known and have been described in many publications. Visible symptoms are traditionally characterized as interveinal and marginal chlorosis of leaf blades progressing to necrosis and, finally, to disintegration of leaf tissue beginning in the older (lower) leaves and advancing toward the top of the plant. With a few exceptions, that description fit the K deficiency symptoms observed in Arkansas prior to the 1980's.

In a series of cotton field studies conducted i Arkansas from 1982 through 1988, K deficiency symptom differed from those observed previously. In the earl stages of deficiency, leaves turned dark green, the developed bronzed mottling between the veins and around the margins and finally died. Bolls either shed o failed to develop fully where deficiency symptom occurred. Contrary to previously-observed patterns, the symptoms appeared first in the youngest fully expanded leaves and progressed down the canopy to the older tissue where K deficiency symptoms had usually been found.

We believe that the shift in the development of deficiency symptoms is a product of the high-yield, fast-fruiting capability of cotton cultivars that are currently grown in the mid-south.

Concentrations of K in the petioles of the youngest fully-expanded leaves (fourth leaf from the top of the plant) was closely related to the emergence of deficiency symptoms. The dark green color developed when K declined to 1.5% of dry matter, bronze mottling occurred at about 1.25% K and leaf tissue died when petiole K fell below 1.0%.