Abstract
The correlation of root-system with yield components was investigated by using a leading variety "Onnemochi" grown on 21 different farmers' paddy fields in 1984. The results obtained were summarized as follows : 1. The highest value of grain yield was 649kg/10 a, and the lowest 496kg/10 a. The number of grains per square meter (N) varied from 27, 000 to 49, 000 ; the fertility percent (FP) from 76% to 95% and the percentage of fully ripened grains to fertilized grains (KP) from 81% to 96%. Yield significantly correlated with N (Fig. 1). 2. N showed highly positive correlation with crop growth rate (CGR) and mean leaf area index (MLAI) from the panicle formation stage to the heading stage. KP was significantly correlated with net assimilation rate (NAR) from the heading stage to the milk-ripening stage (Table 1). 3. The obvious differences in the vertical distribution of root were recognized among different farmers' fields (Fig. 2.). The percentage of root that distributed within 5cm from the ground surface to total root (the ratio of upper layer root) varied 55% to 87%. The ratio of upper layer root was significantly correlated with N (Fig. 3). Partial correlation coefficient of the percentage of root that distributed below 5cm from the ground surface to total root (the ratio of lower layer root) with KP was significant assuming that N was held constant (Fig. 4). The ratio of lower layer root was also significantly correlated with FP assuming that the nitrogen content in leaf blade at the heading stage was held constant (Fig. 5). 4. The correlation coefficient of the ratio of upper layer root with NH4-N mg/100g dry soil at the panicle formation stage was significant (Fig. 6). 5. These results indicate close correlations of root-system with the number of grains, the percentages of fertilization and ripening in rice plants which are grown in Hokkaido.
