الفهرس 
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Abstract
A field experiment was carried out on the transplanted rice system at the Experimental Farm of the Rice Research and Training Center (RRTC) at Sakha, Kafr El-Sheikh, Egypt. The experiment was conducted during the two growing summer seasons of 2007 and 2008 to investigate the effects of nitrogen levels with different treatments of potassium on growth, yield, nutrient uptake, nutrients availability in flooded soil (NH4, NO3, K, P and Zn) and nitrogen use efficiency. A split plot design with four replications was used to carry at this experiment. The main plots were devoted to the three nitrogen levels were added as urea 46% N. where, N1: 0 kg N fed-1., N2: 69 kg N fed-1, N3: 92 kg N fed-1. where the sub plots were occupied by the eight treatments of potassium application at the rate of 24 kg K2O fed-1 as potassium sulphate form (50 kg. fed-1). where, K1: Zero potassium., K2: 50 kg as basal., K3: 25 kg as basal + 4 kg K2SO4/200Litter at P.I, K4: 25 kg as basal + 4 kg K2SO4/200 Litter at F, K5: 25 kg as basal + 4 kg K2SO4/200 Litter at P.I and F., K6: 4 kg K2SO4/200 Litter at P.I., K7: 4 kg K2SO4/200 Litter at F., K8: 4 kg K2SO4/200 Litter at P.I and F. The main results of this study can be summarized as follows: The highest values of dry matter, number of panicles per m2, heaviest panicles, maximum filled grains percentage, highest values of 1000- grain weight, grain yield and straw yield were recorded when hybrid rice plants were fertilized with either 92 Kg N fed-1 combined with half dose of potassium at transplanting (25 kg potassium sulphate) + spray with 4 kg potassium sulphate/200litter at both panicle initiation and flowering stage. Data showed also that maximum nitrogen potassium, phosphorus and zinc uptake values were found with increasing N-levels and potassium treatments. Results showed that, no significant differences in apparent recovery, partial factor productivity and internal nitrogen use in dry matter production among the different treatments. The highest values of agronomic efficiency were recorded when rice plants were fertilized with 69 kg N fed-1 combined with no potassium fertilizer. Data showed that highest values of available NH4-N, NO3-N, potassium, phosphorus available in soil were obtained when rice plants were fertilized with 92 kg N fed-1 with potassium treatments.