Rice Response to the Time and Rate of Potassium Fertilization

Rice (Oryza sativa L.) requires adequate potassium (K) nutrition for optimal growth, grain yield, and disease resistance. Studies were conducted in 2001 and 2002 at the Pine Tree Branch Experiment Station (PTBS) to characterize K uptake by rice and investigate the effect of both K-fertilizer application rate and time on rice growth, K uptake, and grain yield. Potassium fertilizer was applied at rates of 0, 30, 60, 90, and 120 lb K2O/acre before rice emergence, preflood, panicle differentiation, and at the lateboot stage (LB). Potassium uptake was monitored through plant sampling every 14 d after flooding during the growing season. Potassium fertilization increased rice yields only in 2002. Rice yields tended to decrease as the time of K application was delayed, but small numerical yield increases occurred when K was applied shortly before heading. Rice uptake of K was greatest during vegetative growth and declined with time. Between 40 and 60% of fertilizer K applied before flooding was recovered by the earlyboot stage and then declined as rice progressed to heading and maturity. Potassium fertilizer applications made before flooding at the 5-leaf stage are the most efficient.