Yield and Yield Components of three Rice (Oryza sativa L.)Cultivars in response to Source-Sink Limitations and Different Nitrogen Fertilizer

In order to study the effect of different nitrogen fertilizer rates and source-sink limitation treatments on yield and yield component of contrast rice (Oryza sativa L.) cultivars, a field experiment was carried out in the Rice Research Institute of Iran-Deputy of Mazandaran (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 100, 150 and 200 kg/ha from urea source) as main plots, rice cultivars in 3 levels (including Tarom, Shafagh and Bahar1 hybrid) as sub plots and source-sink limitation treatments in 4 levels (including cutting of flag leaf, cutting of leaves except flag leaf, cutting of 1/3 the end of panicle and control or without limitation) as sub sub plots were the treatments. Results showed that nitrogen rates had not significant effects on the studied traits expect on panicle length but cultivar and source-sink limitations significantly affect all studied traits such as grain number per panicle, 1000 grain weight, panicle length, panicle fertility percentage and unfilled grain number. Bahar1 hybrid had the highest grain yield, biomass, total grain number, unfilled grain and filled grain among cultivars. Among different source-sink limitation treatments, the lowest grain yield were observed when all leaves except flag leaf removed from plant probably because of induced source limitation. Also interaction effect of nitrogen fertilizer in source-sink limitation treatments showed that the highest yield was observed in 200 kg.ha-1 and control treatment. Among the mentioned traits, biomass (r=0.76**), harvest index (r=0.50**) had the highest positive and significant correlation with grain yield. In general, modern cultivars (Shafagh and Bahar1) had higher sink capacity than Tarom cultivar (traditional) that considered as a sink-limited cultivar.