Potential productivity of high-quality japonica rice in a ratoon rice system in a warm temperate climate in Japan

Midlatitude warm-temperate sites are suitable for ratoon rice systems. Compared with a single-crop system, annual productivity may increase greatly with the addition of a ratoon crop. Our objectives were to evaluate the annual productivity of promising japonica cultivars in a ratoon rice system under a warm temperate climate in Japan. Field experiments on ratoon cultivation were conducted at Kagoshima, southwestern Japan (31° N) in 2022 and 2023, using one indica check cultivar (‘Habataki’), one japonica check cultivar (‘Koshihikari’), and three japonica cultivars, with a stubble height of 10 cm. The high-quality japonica rice ‘Natsuhonoka’ achieved an annual yield of 14.8 t ha −1 yr −1 (unhusked grain) or 11.8 t ha −1 yr −1 (brown rice) in 2023, which was 68% higher than the annual yield of ‘Koshihikari’. The superior ratoon crop yield of ‘Natsuhonoka’ is attributable to its high regeneration capacity, supported by high nonstructural carbohydrate levels in the stubble. Similar to recent reports on ratoon rice from China, our findings showed that the ratoon rice system is much more productive than the single-crop system in southwestern Japan. Cultivar comparison suggested that crops with high stubble reserves allowed vigorous ratooning and high yield in japonica rice as well as in indica rice. • Ratoon-rice system doubled yield compared to single-rice in Southwest Japan. • Japonica cultivar 'Natsuhonoka' produced 14.8 t ha -1 yr -1 of unhusked grain. • High stubble reserves allowed vigorous ratooning and high ratoon crop yield.