Effect of long term K fertilizer application together with rice straw on optimum K level in leaf and stem of rice plants was evaluated in a field experiment. No K fertilizer (T1), rice straw only (T2); 20 kg K₂O ha^–1 of K (both at basal dressing and panicle initiation) with rice straw (T3), 20 kg K₂O ha^–1 of K (at basal dressing) with rice straw (T4), 20 kg K₂O ha^–1of K (at panicle initiation) with rice straw (T5), and 20 kg K₂O ha^–1 of K (both at basal dressing and panicle initiation) (T6) were applied. Rice straw was amended at the rate of 5 t ha^–1. Soil samples were analysed for exchangeable K and non-exchangeable K during the growing season and plant samples were analysed for K content in leaf and stem at maturity (12 weeks after planting). At harvesting, total grain yield and number of panicles were recorded. Soil and plant K contents under no K fertilizer (T1) were significantly lower (P<0.05) throughout the cultivation period compared to all other treatments. However, shoot dry matter, number of panicles, and grain yield were not significantly different (P>0.05) among treatments. All K fertilizer applied plots depicted higher K content in leaves and stem of rice plants, compared to the no K fertilizer treated plots, irrespective of straw application. The highest exchangeable K and non-exchangeable K contents were recorded in the treatment received with K fertilizer at the rate of 20 kg K₂O ha^–1(at basal dressing and panicle initiation) with rice straw, T3). When consider plant K uptake in relation to the non-exchangeable K there was a positive relationship irrespective of the type of treatment and the number of weeks after planting. According to these results it can be concluded that to maintain optimum K content (1.5 %) in leaf and stem of rice plant, it is needed to apply K fertilizer together with rice straw.