N Accumulation and Translocation in Four Japonica Rice Cultivars at Different N Rates

<正>Developing high-yielding rice（Oryza sativa L.）cultivars depends on having a better understanding of nitrogen（N） accumulation and translocation to the ear during the reproductive stage.Field experiments were carried out to evaluate the genetic variation for N accumulation and translocation in different Japonica rice cultivars at different N rates and to identify any relationship to grain yield in southeast China.Four Japonica cultivars with similar agronomic characteristics were grown at two experimental sites in 2004 with three N rates of 0,60,and 180 kg N ha-1.Dry weights and N contents of rice plants were measured at tillering,initiation,anthesis,and maturity.Grain yields exhibited significant differences （P<0.05）among the cultivars and N application rates.Increasing N rates improved N uptake at anthesis and maturity in all four cultivars（P<0.05）.N translocation from vegetative organs to the grains increased with enhanced N rates （P<0.05）.N translocation to the grains ranged from 9 to 64 kg N ha-1and N-translocation efficiency from 33% to 68%. Grain yield was linear to N uptake at anthesis(r2=0.78**)and N translocation(r2=0.67**).Thus,cultivars with a high N uptake at anthesis,low residual N in the straw at maturity,and appropriate low N fertilizer supply in southeast China should efficiently increase N-recovery rate while maintaining grain yield and soil fertility.