Investigating nitrogen remobilization in different rice (Oryza sativa L.) cultivars in different nitrogen fertilizer rates and top dressed

n order to investigate the effect of nitrogen fertilizer rates and top dressed on nitrogen remobilization in different rice cultivars, a field experiment was conducted in the Rice Research Institute of Iran (Amol) during 2006. A split split experiment in the basis of randomized complete block design with 3 replications and 3 factors were used in which fertilizer rates in 3 levels (including 46, 69 and 92 kg N ha1 from urea source), top dressed in the 3 levels (in variable ratios in transplanting, tillering and heading stages including S1(50, 25 and 25 percentage) S2 (25, 50 and 25 percentage) and S3 (25, 25 and 50 percentage)) and cultivar in 3 levels (including Tarom, Shafagh and Bahar 1) were considered as main plot, sub plot and sub sub plot, respectively. Results of variance analysis showed that cultivars and different organs of plant had different responses to nitrogen fertilizer rates and split application in terms of nitrogen remobilization, and traditional cultivar, Tarom, had the highest amount of nitrogen remobilization from shoot organs. Among nitrogen fertilizer levels, 69 kg.ha-1 caused the highest rate of nitrogen remobilization, although application of the second split application level (S2) (25, 50 and 25 percentage) increased this rate too. Moreover, Tarom cultivar had the highest rate of nitrogen remobilization from stem and other leaves that seems due to early maturity and increased senescence of leaves in this cultivar. Findings of this experiment showed that nitrogen remobilization had a significant and positive correlation with grain yield. Among shoot organs, stem nitrogen remobilization had the highest significant and positive correlation(r=0.65**) with grain yield.