Kitagenki, a high-yielding rice variety, exhibits a high yield potential under optimum crop management practices

In the Hokkaido region of Japan, a new japonica-type high-yielding rice variety (HYV), Kitagenki, demonstrated higher grain yield than the early developed japonica-type HYVs; however, its yield potential is unknown. Therefore, a four-year (2015-2018) field study was conducted to elucidate the (1) yield potential of Kitagenki, (2) effect of early and late nitrogen (N) applications on the grain yield of Kitagenki, and (3) effect of early N application and planting density on the grain yield of Kitagenki. Experiment 1 consisted of three early N (10.5 N: basal 10.5 g N m- 2, 16.5 N: basal 16.5 g N m- 2, and 10.5 N + T1: basal 10.5 g N m- 2 with topdressing of 6 g N m- 2 at the panicle formation stage) combined with two late N (-T2: no topdressing at the full-heading stage, and + T2: topdressing of 6 g N m- 2 at the full-heading stage) applications. Experiment 2 consisted of two early N (10.5 N and 16.5 N) applications combined with two planting densities (standard planting: 22.8-23.0 hill m- 2 and sparse planting: 11.4-11.5 hill m-2). The yield potential of Kitagenki was approximately 1200 g m- 2 of gross hulled grain, which is the highest yield recorded among japonica-type HYVs cultivated in Japan. In experiment 1, the grain yield of Kitagenki was improved by both early N (16.5 N, 10.5 N + T1 > 10.5 N) and late N (+ T2 > -T2) applications owing to the improved sink capacity and source ability. We suggest 10.5 N + T1 + T2 and 16.5 N + T2 as the optimum combination of early and late N applications to stably maximize the grain yield of KG. In experiment 2, the grain yield of KG was significantly improved by early N (16.5 N > 10.5 N) application but not significantly by planting density. In 16.5 N, sparse planting tended to produce a higher grain yield by lowering the lodging scores and increasing the source-sink ratio compared to those obtained with standard planting. Therefore, we suggest 16.5 N sparse planting as the optimum combination of early N application and planting density to stably maximize the grain yield of Kitagenki.