日本の寒地,北海道の稲作限界地帯におけるもち米の精米蛋白質含有率および米粒白度の年次間地域間差異とその発生要因(日语原文)

Variation of the Protein Content and Whiteness of Glutinous Rice Grains Among Years and Among Areas, and its Occurrence Factors in the Coldest Regions for Rice Cultivation in Hokkaido, Japan

北海道では,もち米は最も冷涼な稲作地帯で生産される。その作柄が大きく変動した4カ年の6栽培地域で,年次間では,障害型冷害危険期の気温が高く不稔歩合が低く,また出穂後40日間の日平均積算気温(登熟気温)が高く千粒重が重く多収なほど,低蛋白となり玄米と精米の白度は高くなった。一方,地域間では,これらの関係が概して明確ではなかった。このことは年次間の最小値最大値の差異および変動係数が地域間に比べ,精米蛋白質含有率(蛋白質)では1.0,1.3倍と同じかやや大きく,生育期別気温や生育特性では1.3~8.5倍,米粒の両白度でも1.6~2.6倍と大きいためであった。なお,蛋白質は登熟気温が年次地域込みで849℃で最低となる二次回帰を示した。また,年次と地域の各平均値が,障害型冷害危険期の平均気温で低く不稔歩合で高く,千粒重で軽く玄米収量で低く,蛋白質で高く米粒両白度で低く,すなわちそれらが不良なほど,年次では地域間,地域では年次間における変動係数が大きかった。さらに,米粒の両白度はいずれも1m~2の1籾当たりの登熟気温との間に正の相関関係を示し,目標の玄米白度を得るための同1籾当たり登熟気温および目的地域の平年の登熟気温からm~2当たりの籾数を求めることにより,目標の玄米白度を得るための施肥窒素量が算定できた。

Glutinous rice is produced in the coldest and the severest regions for rice cultivation in Hokkaido, Japan. The rice quality of four years and six cultivation areas with large fluctuation in yield and quality was investigated. Among years, the higher the temperature during the stage sensitive to sterile-type cool injury, the lower the sterility. Moreover, the higher the cumulative daily mean temperature during 40 days after heading(grain-filling temperature), the heavier the 1 000-kernel-weight, the higher the grain yield, the lower was the protein content and the higher were the whiteness of both brown and milled rice. However, the correlation among different planting areas was not clear. This was because, compared to the range of the regional variation(differences between the two extreme values and coefficients of variation), the range of the yearly variation in protein content was 1.0 and 1.3 times larger, the mean temperatures during some growth stages and growth characteristics like grain yield were 1.3~8.5 times higher, and the whiteness of both brown and milled rice were 1.6~2.6 times larger. It should be noted that the protein content was the lowest in the quadratic regression relationship at a grain-filling temperature of 849 ℃, among the 6 areas during the 4 years. In addition, concerning the mean values for year and area, the lower the temperature during the sensitive stage to sterile-type cool injury, the higher the sterility, the lighter the 1 000-kernel-weight, the lower the grain yield, the higher the protein content, the lower the whiteness of both brown and milled rice;namely, the worse these characteristics, the larger the coefficient of variation among areas and years. Moreover, the whiteness of both brown and milled rice showed positive relationships with grain-filling temperature per one unhulled rice in one square meter. Therefore, the number of unhulled rice in one square meter could be calculated from the grain-filling temperature per one unhulled rice to reach the target value of whiteness of brown rice and the grain-filling temperature in a normal year in the target area, and then the amount of nitrogen fertilizer application to obtain the target value of whiteness of brown rice could be determined.