Dry Matter and Nitrogen Partitioning in Rice Genotypes Varying in Different Nitrogen Harvest Index

To evaluate the contribution that dry matter and nitrogen (N) accumulation make when translocated to grain during the grain-filling period between genotypes with high and low N harvest index (NHI), a pot experiment was conducted in the greenhouse under a uniform environment. Three high-NHI rice varieties (Yangdao6, R26, and R138) and three low-NHI varieties (Ceysvonic, R44, and R98) were used in our experiment. Significant differences in dry matter and N accumulation, partitioning, and translocation were found between high- and low-NHI genotypes. Compared with low-NHI genotypes, high-NHI genotypes had greater amount of dry matter and N translocation to grain, and higher dry matter and N translocation efficiency, on the other hand, high-NHI genotypes had the lower contribution ratios of pre-anthesis assimilate and N to the grain. Regression analysis showed that grain yield was closely associated with dry matter and N accumulation at heading and maturity stage, N and dry matter translocation in high-NHI genotypes. On the other hand, grain yield was closely associated with the contribution of pre-anthesis assimilate and N to grain in low-NHI genotypes. These suggested that pre- and post-anthesis assimilate and N accumulations, including assimilate and N translocations, were very important in improving the grain yield in high-NHI genotypes.