ABSTRACT

Correcting subsoil nutrient deficiencies by deep banding low concentrations of potassium from 6"-15" deep in the drill takes a long term commitment by producers. In experiment 1, deep banded and split treatments of 160 lb K₂O/A significantly increased lint yield of DES 119 each year of a 4 year study. The deep banded 160 lb K₂O/A also increased lint yield of C-130 each year of the study. The split and deep banded 160 lb K₂O/A treatments produced significantly higher lint yields (averaged over varieties and years) than the currently recommended surface broadcast incorporated 80 lb K₂O/A rate. No differences in lint yield responses were found between varieties or rates of potassium with surface broadcast incorporated applications; however, with deep banded 160 lb K₂O/A potassium, DES 119 and C-130 produced higher lint responses than either DP 50 or St 453, and potassium rates produced different responses in DES 119, DP 50, and C-130. In experiment 2, potassium rates of 60, 120, and 180 lb K₂O/A increased first, second, and total lint harvested at each nitrogen rate (90, 120, and 150 lb N/A) compared to the control. The total lint yield was increased by 150 lb N/A rate in all split-surface and deep 60, 120, and 180 lb KO/A treatments, when compared to the 90 lb N/A rate over the 4-year study with DES 119. In experiment 3, the residual effect of 4-years of applications of potassium surface and/or deep were measured in 1992 (no additional potassium in 1992). All applied potassium treatment residuals increased 1992 lint yield over the check (no potassium in previous 4 years). However, lint yields were significantly higher from residuals when 100 lb K₂O/A was surface broadcast incorporated (1988-1991) plus 150 lb K₂O/A deep banded (1988-1991) than the residual effect of any surface only treatment (0, 50, or 100 lb K₂O/A). Deep banding of potassium can significantly increase lint yields when subsoils are deficient in K and other factors are not limiting yield. Additional studies are needed to determine how long residual subsoil potassium will last and how frequently deep banded K will be needed to maintain subsoil K levels.