Abstract
The yielding performance of the first high-yielding rice variety for Hokkaido, Kita-aoba, after application of various amounts of nitrogen (9.0 to 23.7 g m-2 in 2008 and 10.5 to 16.5 g m-2 in 2010) and under various planting densities (13.2 to 33.2 hills m-2 in 2008 and 17.5 to 36.8 hills m-2 in 2010) was examined in comparison with that of the common variety, Kirara397. Kita-aoba had higher grain yield than Kirara397 owing to its large sink capacity through larger sink capacity per unit biomass at heading. Kita-aoba had a high yield potential (the maximum grain yield of 1081 g m-2), and achieved a high grain yield even in Hokkaido where the rice-growing season is short. Kita-aoba had a large sink size, but, judging from the relationship between sink capacity and percentage of sink filled, further increase of sink size might not result in increase of grain yield. Kita-aoba showed a great increase in shoot dry matter from heading to maturity, but it was not enough to fill its large sink.
