A four year field test was initiated in 1997 to evaluate potassium as a soil treatment on yield and fiber quality of cotton in Adana. Four rates of potassium as K2SO4 (0, 80, 160 and 240 kg/ha) were applied to C.1518 cotton in two splits with half the K applied at planting and half when the crop reached the first bloom stage. Yield, plant growth and development and High Volume Instrument quality evaluation were measured for each treatment. Averaged over all treatments, adding K produced significant seed-cotton and lint yield responses (P=0.01) compared with the untreated control. K treatments produced a significantly higher boll weight than the control. HVI lint quality values were not affected by any treatment.