Arkansas scientists have determined that spraying potassium on cotton foliage can correct late-season deficiencies of this important nutrient quickly and efficiently, if used correctly.

“Cotton appears to be more sensitive to low potassium availability than most other major field crops and often shows signs of potassium deficiency on soils not considered deficient,” said Derrick Oosterhuis, cotton physiologist at the Arkansas Agricultural Experiment Station. “Our research showed that properly timed foliar applications of potassium, at correct rates, can significantly increase yields.”

Oosterhuis began a comprehensive research program to study the response of cotton to potassium applied in the soil before planting and on the foliage of the plants during growth. The study looked at how potassium is taken up and distributed by the plant, optimum application rates and timing of foliar application, the best sources of potassium for foliar feeding, and the effects of drought.

A related three-year collaborative study was conducted in 12 Cotton Belt states to compare the benefits of foliar-applied potassium with increased soil-applied potassium.

“We learned the occurrence of potassium deficiency was related to contemporary varieties that have higher yields and faster fruiting, and decreased root growth after flowering,” Oosterhuis said.

The research also revealed that well-watered cotton responded better than dryland cotton to soil applications before planting. Oosterhuis said lack of soil water became more limiting than the availability of soil potassium beginning at early flowering and continuing through peak boll development.

“This is the stage where foliar application can make a difference,” he said.

The suggested rate of 4 pounds of potassium per acre and timing of four weekly applications after the start of flowering is now the standard method for foliar application throughout the Cotton Belt.

“Adequate availability of potassium during cotton boll development appears to be crucial for maximum lint yield,” Oosterhuis said. “Foliar applications can correct inadequate potassium, especially in late season when soil application may not be effective.”

Fred Miller is science editor for the Arkansas Agricultural Experiment Station. e-mail: [email protected].