Potassium Fertilization Influences Rice Growth, Yield, and Stem Rot Index.

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.