Influences of nitrogen and potassium top dressing on yield and yield components as well as their accumulation in rice (Oryza sativa)

This research was conducted to investigate the effects of different rates of nitrogen (N) and potassium (K) top dressing on grain yield and yield components of rice (Oryza sativa cv. Tarrom) and to investigate N and K content of upper leaves analyzed at ten different times. A pot experiment was carried out on a completely randomized design with seven replications under greenhouse conditions at the Experiment Station of Sari Agricultural Sciences and Natural Resources University, Iran, during the growing season in 2008. Nitrogen was applied in the form of urea (46% N) at the rates of 0, 23 and 46 kg N ha-1 and potassium in the form of potassium chloride (60% K2O) at the rates of 0, 30 and 60 kg K2O ha-1. Results indicated that panicle length, plant height, number of tiller, number of grain per panicle, hollow grain percentage, grain and biological yield were significantly affected by N and K fertilization. Maximum grain yield (75.46 g pot-1) occurred at 23 kg N ha-1 and 30 kg K2O ha-1. At flowering stage, K content of stems were higher than leaves, and N content in flag leaves was higher than other plant parts.   Key words: Leaf potassium concentration, potassium chloride, rice, top-dressing fertilization, urea and yield.