In order to study the impacts of low nitrogen rate combined with high plant density on tillering, earbearing tiller percentage, dry matter accumulation, apparent transformation rate, N-use efficiency and grain yield, field experiments with three nitrogen rates (75, 150, and 225 kg N ha-1) and four plant densities (68, 40, 27, and 19 hill m-2) as well as with three levels of number of seedlings per hill (1, 2, and 3 seedling(s) hill-1) and four plant densities (40, 27, 19, and 14 hill m-2) were conducted using super rice cultivar Y-liangyou 1 at Changsha, Hunan Province and Chengmai, Hainan Province in 2012–2013. The results showed that when seedlings per unit area were the same or approximate in combination with reducing seedlings per hill and increasing density (RSID), the dry matter accumulated 10.5% and 5.2% more than those with increasing seedlings per hill and reducing density (ISRD) at heading and maturity, respectively. RSID also produced 2.9% higher grain yield than ISRD. Panicles m-2 had the highest and significant contribution to grain yield in RSID. Productive tillering stage was shorter by six days, and earbearing tiller percentage, apparent transformation rate (ATR), partial factor productivity of applied nitrogen (PEP) and internal utilization efficiency of nitrogen (IE) were respectively higher by 10.9%, 21.0%, 150.6%, and 19.6% under low nitrogen rate (75–150 kg N ha-1) combined with high plant density (40–68 hills m-2) than under higher nitrogen rate (225 kg N ha-1) combined with low plant density (19–27 hills m-2). The combination of applying 75 kg N ha-1 and transplanting 40–68 hills m-2 produced 3.2% and 7.5% biomass less than those of applying 150–225 kg N ha-1 and transplanting 19–27 hills m-2 at heading and maturity, respectively, but the differences were not significant. Meanwhile, the former combination decreased 1.2% and 5.2% grain yield at Changsha in two years and at Chengmai in 2012, respectively, while increased 9.1% at Chengmai in 2013, and the differences were significant at Chengmai. However, the combination of applying 150 kg N ha-1 and transplanting 40–68 hills m-2 produced 10.3% biomass and 3.3% grain yield more than that of applying 225 kg N ha-1 and transplanting 19–27 hills m-2, except for biomass decreased 1.7% at maturity. Therefore, the adoption of low nitrogen rate (100–150 kg N ha-1) combined with high planting density (40 hills m-2) would improve both grain yield and N-use efficiency for super rice due to reaching the projected tillers earlier, increasing panicles, improving earbearing tiller percentage and seed setting rate, and having suitable biomass and higher ATR at heading stage.
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