Potassium (K) needs for conventional spaced (30 to 40-inch row) cotton (Gossypium hirsutum L.) have been well researched and established, but there has been no published data on K requirements of ultra-narrow row (UNR) cotton. We conducted a replicated 3 year study on a Lucedale sandy loam (Rhodic Paleudults) in central AL to determine the potassium (K) need of cotton, as impacted by row spacing and tillage system. Treatments were a factorial arrangement of K fertilizer rate (long-term applications of 0, 30, or 60 lb K₂O/A), row spacing (8-inch UNR or 36-inch conventional), and tillage system (chisel disk or no- tillage). Cotton lint yields ranged from 142 to 1253 lb lint/acre during the 3 year study, depending on season and treatment combinations. Ultra-narrow row cotton consistently resulted in substantial yield increases compared to conventional row spacing (98% increase, averaged over tillage, K rates and years). Ultra-narrow row cotton yield response to K fertilizer was similar to that of cotton grown in conventional row widths and UNR spacing with adequate K fertilization (to 60 lb K₂0/A), consistently provided the highest yield. In two of three years, this row spacing-K fertilizer combination was optimized with no-tillage. Fiber quality, as determined from High Volume Instrumentation (HVI), varied with year, row spacing, tillage, and K fertilization. Adequate K (60 lb K₂O/acre on this soil) was required to maintain micronaire readings, especially with UNR cotton and/or no- tillage cotton. Although it remains to be seen whether UNR cotton will be accepted by the market, our results suggest that adequate K nutrition is critical to optimize yield levels and fiber quality of UNR cotton.