Effect of Sink and Source Related Characteristics on Grain Weight and Grain Nitrogen Content in Rice

This experiment was conducted to clarify the effects of source and sink related characteristics on grain weight increase and grain nitrogen accumulation in rice. Source was modified by leaf removing treatment with no sink modification in 2002 and sink and source were modified at the same time by different sowing dates, N fertilization rates, row spacings, and thinning treatments at heading in 2007. Grain weight (GW) and grain assimilates produced by photosynthesis during grain-filling (GWP) in- creased with the increase of source, while the grain assi- milates retranslocated from leaf and stem (GWT) decreased. Among the source-related characters, shoot dry weight were most closely related with GW. GW was dependant on GWP rather than on GWT. Grain nitrogen content (GN) and grain nitrogen absorbed from soil during grain-filling (GNS) increased with the increase of source, while the grain nitro- gen retranslocated from leaf and stem (GNT) decreased. Shoot nitrogen content among the source-related characters was related most closely with GN. The contribution of GNT to GN was relatively large although GN depended more largely on GNS than GNT. In addition, GN was supplied firstly from GNS or from GNS and GNT at the same time.