2022 Volume 91 Issue 2 Pages 153-162
Three-year and two-year field experiments were conducted at the NARO Hokkaido Agricultural Research Center (NARO/HARC) (Sapporo) and its Bibai Experimental Station, respectively. Two rice cultivars, Yukigozen, bred in NARO/HARC and Nanatsuboshi, a common variety, were grown using a combination of two fertilization levels (standard fertilization and high fertilization) and two planting densities (standard density and low density). Yukigozen showed significantly higher grain yield in Sapporo in 2015, and significantly higher whole grain ratio in Sapporo in 2016 and in Bibai in 2018, than Nanatsuboshi. High fertilization gave a significantly higher grain yield only in Sapporo in 2015. In other years or in Bibai, fertilization rate affected neither grain yield due to lodging nor the trade-off between spikelet number per area and percentage of ripened grains nor grain weight. Low density resulted in significantly lower grain yield only in Bibai in 2018 with lower solar radiation. Yukigozen in standard density lodged with the nitrogen uptake at maturity more than 12 g m–2 or culm length longer than 80 cm, but that in low density had a lower lodging index. Yukigozen in low density tended to increase its grain yield by 28 g m–2 with high fertilization in Bibai in 2018. These results suggested that the combination of high fertilization and low density could reduce the risk of low grain yield under low solar radiation conditions and the risk of lodging caused by vigorous growth.
