ABSTRACT

Foliar-applied KNO₃ on cotton is becoming a widespread practice in parts of the Southeastern cotton belt. However, predicting the probability of a yield response to this practice is uncertain, in 1992, long-term soil fertility experiments at 5 Alabama locations were used to measure cotton yield response to foliar-applied KNO₃ and urea and plots where residual soil K variables exist. Foliar KNO₃ or urea was applied to split plots at a rate of 4.4 pounds K₂O per acre and 1.3 pounds N per acre 4 times, 7 to 16 days apart, beginning the first week after bloom initiation. Although cotton at all locations responded to increasing levels of residual, plow-layer K, foliar KNO₃ significantly increased yields at only 2 Central Alabama locations, both on Lucadale soils (fine-loamy, siliceous, thermic Rhodic Palaudults). At one of those locations, Prattville Experiment Field, dramatic yield responses to KNO₃ were also observed on N rate treatments where up to 150 pounds N per acre and 100 pounds K₂O per acre were applied to soils already testing "high" in extractable soil K. These results indicate that response to foliar-applied K appears to be soil related but not related to plow-layer extractable soil K. Other soil and physiological factors may influence the predictability of cotton yield response to foliar-applied K.