| Potassium deficiency of rice grown on silt loam soils in Arkansas has increased during the past 20 years, highlighting the need to better understand rice K uptake, soil-K availability and develop efficient fertilization strategies. The research objective was to characterize growth, uptake and partitioning of K by rice, and to characterize soil solution K and Mehlich-3 K throughout the growing season as affected by K rate. Field studies were conducted in 2001 and 2002 to model seasonal dry matter accumulation, K concentration, K uptake, soil solution K, and Mehlich-3 extractable K in a K-sufficient Dewitt silt loam amended with 0, 112, and 224 kg K ha-1. Potassium fertilizer rate had no influence on rice grain yield in either year. At maturity, rice straw and panicles each accounted for about 50% of the aboveground plant biomass. The proportion of K in grain at harvest was 20% of total plant K. Potassium fertilizer rate increased uptake and plant K concentrations across time, with plant K concentrations peaking about 16 to 18 days after flooding (DAF). Mehlich-3 soil K and soil solution K were greatest within 1 wk of flooding. Potassium availability is high immediately after flooding and increases from K fertilization. However, soil K concentrations decline rapidly reaching near minimum concentrations by panicle differentiation and then remain relatively constant for the duration of the growing season, regardless of K-fertilizer rate. Potassium uptake is most rapid during the vegetative and early reproductive growth stages, and little or no K is taken up during grain fill. Trends suggest that plant uptake of K fertilizer would be the most efficient when applied before the onset of tillering. |
