Potassium deficiency of rice (Oryza sativa L.) has become an increasing problem due in part to inadequate fertilization and increasing yields. The objectives were to evaluate the influence of K-fertilizer rate on rice grain yield, whole-plant K concentrations at panicle differentiation (PD) and early heading (EH), and stem rot index (SRI) at maturity. A long-term K experiment was established in 2000, cropped to ‘Wells’ rice and soybean, and muriate of potash was applied annually at five rates (0-150 kg K/ha). This presentation will discuss data from 2006 and 2008 only. At maturity, grain yield was determined and SRI was assessed by examining rice stems collected from a 1-m section within each K rate and rated on a 1-5 scale (1 = healthy and 5 = dead culm). Data were analyzed as a randomized complete block with a split-plot treatment structure where K rate was the whole plot. Whole-plant K concentrations, averaged across years, showed rice receiving no K had deficient-K levels of 1.5% at PD and 0.99% at EH. A significant K rate × year interaction for rice grain yield showed rice receiving i) ?37 kg K/ha annually produced lower yields in 2008 than in 2006, ii) 75 kg K/ha annually produced equal yields each year, and iii) >75 kg K/ha produced significantly greater yields in 2008. The difference between the highest yield of rice receiving K and the no K control yield was 1512 and 4385 kg/ha in 2006 and 2008, respectively. The K rate × year interaction was also significant for SRI. The SRI was usually lower in 2008 (1.8-2.8) than 2006 (2.2-3.7) and, within each year, tended to increase significantly when annual K rate was <75 kg K/ha. Results suggest that long-term mismanagement of K fertilizer decreases rice yield potential and increases stem rot severity in rice.