N accumulation and translocation in four japonica rice cultivars at different N rates

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-1 and N-translocation efficiency from 33% to 68%. Grain yield was linear to N uptake at anthesis (r(2) = 0.78**) and N translocation (r(2) = 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.