ABSTRACT

A two-year experiment with foliar application of five potassium sources was conducted on Loring-Calloway silt loam in 1991 and 1992 at Marianna, Arkansas. Salts of K used were sulfate, chloride, thiosulfate, carbonate and nitrate. Solutions of these salts were applied four times in 1991 and five times in 1992 during the 2nd through the 8th weeks of flowering. Each application consisted of the equivalent of 10 lb K nitrate in 10 gals of solution /A. The check treatment and treatments other than K nitrate received N as urea at the rate supplied by the K nitrate treatment. A composite soil sample of the experimental site field showed Melich 3 test levels of 179 and 176 lb/A in the 0-6- and 7-12-in depth zones, respectively. These K levels are considered medium for cotton. The soil was fertilized with 60, 60 and 0 lb/A of K₂O in 1990, 1991 and 1992, respectively.

In 1991, none of the foliar K treatments significantly affected cotton yield, boll weight, petiole nitrate-N or soluble petiole K. In 1992, only the K nitrate treatment significantly increased the lint yield (83 lb/A) compared with the check. The % soluble K in petioles of the most recently mature leaves of check plots at 3-9 weeks of flowering ranged from a high of 6.0 to 3.7 in 1991 and 5.3 to 3.5 in 1992. At weeks 10 and I 1 in 1992, % petiole K dropped to 2.0 and 1.3, respectively. The 1992 lint yields in lb/A were: K nitrate 1122, K thiosulfate 1058, check 1039, K chloride 1027, K sulfate 1022 and K carbonate 978. The 1992 yield produced by the K carbonate treatment was significantly lower than those of the check and the K nitrate treatment. Extreme soil variation limited precision in measuring treatment effects in 1991 but not in 1992. Differences in seasonal conditions between the two years also may have contributed to the differing treatment responses. This study will be repeated in 1993 with additional physiological measurements aimed at explaining these differences.