Effect of source and sink limitation on grain yield and yield components of three rice genotypes under levels of nitrogen fertilizer

To study the effect of source and sink limitation on grain yield and yield components of three genotypes of rice under different levels of nitrogen fertilizer a field experiment was conducted at Sari Agricultural and Natural Resources Sciences University, Sari, Iran, in 2009 growing season. Experiment was arranged as split-split-plot in randomized complete block design with three replications. Three levels of nitrogen fertilizer (0, 46 and 92 kg N.ha-1) were assigned to main plots; three rice genotypes (Jelodar, Danesh and Jahesh) as sub-plots and four levels of source-sink limitation (control, removal all leaves except flag leaf, flag leaf removal and removal of 1/3 end of panicle) in sub sub plots. Results showed that three genotypes had both source and sink limitations. Nitrogen fertilizer, however, could compensate sink limitation to some extent especially in optimum nitrogen level (46 kg N.ha-1) by increasing photosynthates remobilization. The findings of this research indicated that flag leaf contributed about 22.61% in grain weight. Flag leaf had the highest efficiency in 92 kg. N.ha-1, and other leaves had higher efficiency in 46 kg.N.ha-1 in grain yield improvement. Furthermore, by imposing source limitations (particularly removal all leaves except flag leaf) greater variation in 1000 grain weight was observed in genotypes which had greater grain size (e.g. Danesh). Nitrogen× genotype interaction indicated that Jelodar genotype had the lightest grain yield with 8478 kg.h-¹ in 92 kg.h-¹ of nitrogen fertilizer level. Nitrogen× genotype interaction was significant for harvest index and Danesh genotype showed the highest harvest index (57.8%) in 46 kg.h-¹ of nitrogen fertilizer level.