From Agronomists of the
Potash & Phosphate Institute
655 Engineering Drive, Suite 110
Norcross, Georgia 30092-2837
Phone (770) 447-0335

Summer 2002, No. 5


Potassium uptake demand by cotton is high,and is at its peak during flowering through boll filling. The top potassium uptake rate may exceed 4 pounds of K2O per acre each day, if the fertility program is adequate. Modern cotton cultivars accumulate potassium over a shorter time period than the older varieties, which means the newer cultivars might suffer more quickly under potassium stress. Any shortage of potassium during reproductive growth can lead to premature cutout (termination), decreased yields, and decreased fiber quality.

Potassium is an enzyme activator, increases photosynthesis, improves plant water uptake and use efficiency, increases the transfer of carbohydrates from leaves to cotton bolls, increases boll size and weight, increases the lint percentage, and helps reduce plant damage from diseases. During the last few years, many growers have learned (some the hard way) that high soil potassium fertility enables plants to withstand drought stress better. Research has shown that yield losses under drought stress are less severe when soil potassium is maintained at high levels through adequate fertilization.

Studies by the United States Department of Agriculture-Agricultural Research Service (USDA-ARS) in Stoneville, Mississippi, showed that potassium fertilization increased the efficiency of fertilizer nitrogen use by 19 percent and nitrogen utilization by 13 percent. That is, adequate potassium fertilization causes plants to produce more lint per pound of nitrogen applied.

Recent soil test summaries compiled by the Potash & Phosphate Institute show that about 52 percent of the soil samples from the southeastern U.S. had soil test potassium levels medium or lower. So, many cotton fields need potassium fertilization. According to the USDA-Economic Research Service (USDA-ERS), from 1990 to 1997 the average potassium rate applied to cotton was about 50 pounds of K2O per acre. To make a yield of two bales per acre, cotton will take up potassium at about 140 pounds of K2O per acre from the soil.

Potassium deficiency causes plants to prematurely cutout,the photosynthesis rate drops, carbohydrate transfer to developing bolls is short-circuited, and yield potential and fiber quality decline. Photosynthesis is one of the first critical physiological processes to suffer under inadequate potassium nutrition.

No matter how you look at it,inadequate potassium nutrition spells bad news for both cotton yield and quality. Since potassium is one of the least expensive plant nutrients and it does so many good things for the crop, there should be little reason not to apply appropriate potassium rates based on soil tests. If soil samples have not been taken recently, farmers should consider applying from 60 to 120 pounds of K2O per acre. Be sure that appropriate fertilizer rates are used this year to ensure that plants have the potassium they need to produce good yields and high quality fiber. Protect your crop from the ravages of drought stress and prevent premature cotton cutout with potassium.

For more information, contact Dr. Cliff S. Snyder, Midsouth Director, PPI, P.O. Drawer 2440, Conway, AR 72033-2440. Phone: (501) 336-8110. E-mail:
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