Cotton Response to Surface Applications of Potassium Fertilizer: A 10-Year Summary

Abstract

Field studies were conducted for 10 yr on a Limestone Valley soil (Dewey silt loam, a fine, kaolinitic, thermic Typic Paleudults) in north Alabama to evaluate cotton (Gossypium hirsutum L.) yield and lint quality response to long-term surface applications of K. Potassium rates were 0, 60, 120, and 180 lb K 2 O/acre for the first 3 yr of the study. Fertilizer was broadcast in the spring or split applied in fall and spring. No K fertilizer was applied during the fourth year (1990). After the fourth year, half of the treatments were left in residual and remaining treatments continued to receive annual applications of K (1991-1996). The experiment was a split plot arrangement of a randomized complete block. From 1987 to 1989, two varieties were compared, which served as whole plots. From 1991 through 1996, one variety was grown and annual vs. residual K fertilization served as whole plots. Potassium treatments were used as subplots throughout the test. From 1987 to 1989 there were no differences between 'Stoneville 825' and 'Deltapine 50'. Lint yields were increased significantly by K fertilization in 6 of 9 yr that cotton was grown on this low K soil. Potassium fertilization increased lint yields by as much as 450 lb/acre in responsive years. From 1991 through 1996, residual K produced lesser yields than where K was applied annually. There were no differences in lint yield among split (fall-spring), fall, or spring applied K. In responsive years, micronaire increased with K rate. Our results support the calibration currently used by the Auburn University Soil Testing Lab for Limestone Valley soils.