Studies on Ripening of Rice Varieties Grown under Low Temperature : I. Varietal differences in weather-dependent characteristics of ripening

[摘要] In this paper, the varietal differences in the weather-dependent characteristics of ripening were analized for the data taken during 12 years from 1973 to 1984 at Hokkaido Prefectural Kitami Agricultural Experiment Station. The main results are summarized as follows: 1. The significant multiple correlation coefficients of ln (1-percentage of ripening grains, R) with the number of grains per square meter (N), mean temperature for 25 days before the heading date (TI) and mean temperature for 40 days after the heading date (T2) were obtained in all varieties (Table 1). Therefore, the relation between R and these 3 factors for "Onnemochi" was shown by the next formula; R=1-39.23 exp (0.3447N-0.1454T1-0.1524T2 ) The relation for "Hayakogane" was shown by the next formula; R=1-2.05 exp (0.3727N-0.027T1-0.1321T2) 2. The contribution ratios of N, T1 and T2 to R differed between varieties (Fig. 2 ). It was presumed that the contribution ratio of N was associated with the plant type and the efficiency for dry matter production. The contribution ratio of T1 was correlated with the average value of fertility percent, and that of T2 was correlated with the average value of heading date. 3. By using the above formula, the optimum number of grains to obtain the highest yield was estimated (Fig. 3). It was more than 40, 000 grains/m2 under high temperature, but less than 30, 000 grins/m2 under low temperature. From the these results, it could be concluded that the sufficient number of grains for the stable rice culture were approximate 35, 000 grains/m2 in Abashiri District. 4. The suitable heading time was earlier about 1 week as compared with the average value of heading date in all varieties (Fig. 5). This may suggest that the qualitative improvement of seedling was very important to hasten the heading and to improve the percentage of ripening grains.

[学科分类] 农业科学（综合）