Impacts of the dose of nitrogen fertilizer applied to rice plants as top dressing on sake brewing

Applying nitrogen (N) fertilizer as top dressing to rice plants at the panicle formation stage affects the quality of rice grains. Our previous indoor experiment showed that application of a higher dose of top dressing N fertilizer to rice plants negatively affected the alcohol fermentation and yield of sake brewed from the grains. To further clarify the impacts of the N fertilizer dose, we performed a 2-year rice cultivation test in outdoor-installed containers with different doses of N fertilizer [1 (N1), 6 (N6), or 12 g N m⁻² (N12)] applied as top dressing at the panicle formation stage. The frequency of grains with a white core and the protein content of the grains were 17%–26% lower and 8%–13% higher, respectively, in the N12 treatment than in the N1 treatment in both years. The yield of sake was consistently lower (1%–3%) from rice in the N12 treatment than from rice in the N1 treatment. The reduced sake yield and increased protein content in rice grains led to higher concentrations of amino acids in the sake brewed from rice in the N12 treatment. These results highlight the importance of fertilizer management in rice paddies for sake brewing.