Growth Characteristics to Achieve High Yield and High Palatability in a Rice Cultivar ‘Niji-no-kirameki’ in the Hokuriku Region

Abstract

‘Niji-no-kirameki’ is a Japanese cultivar with medium maturity, high-yield, and high-palatability cultivated in the Hokuriku region. The objectives of this study were (1) to clarify the relationship among grain yield, yield components, and palatability, (2) to calculate the shoot nitrogen content at the full heading stage to achieve the optimum spikelet number per square meter (SN) and (3) to determine the proper amount of nitrogen fertilizer as top dressing corresponding to the growth parameters at the panicle neck node differentiation stage in ‘Niji-no-kirameki’. Grain yield (y) had a positive relation with SN and panicle number per square meter (x),represented by a linear regression model. Top dressing of nitrogen fertilizer significantly increased grain yield when compared at the same amount level of nitrogen application. Grain protein content was negatively related with eating quality and grain thickness. Then to achieve a grain yield of at least 700 g m^–2 with SN of 37,500 and grain protein content of less than 6.5% (15% moisture basis), the shoot nitrogen content at the full heading stage was calculated as 13.2 g m^–2, the optimum value of growth index value (plant height cm × number of tillers per square meter × SPAD value) at the panicle neck node differentiation stage was in the range of 18.2-21.9. The amount of nitrogen fertilizer to give this growth index value would be 2-4 g m^–2 of nitrogen fertilizer. The optimum values of growth parameters at key developmental stages for achieving high-yield and high-palatability in ‘Niji-no-kirameki’ in the Hokuriku region were determined.