Studies on the Seed Production of Soybean. 3. Ar analytical study of dry matter Producion in the soybean Plant community

Abstract

This study was performed to analyze the characteristics of dry matter production in the soybean plant community on the field. Norin-No. 2 variety was grown under the different conditions, namely, sowing dates, amount of fertilizer and plant densities. The results were as follows : 1. The maximum crop growth rate (Cmax) was 100-120g/m2 of land area/week at about 530 ly/day in the middle stage of grawth, but it did not continue until the late stage. In the ripening period, crop growth rate rapidly decreased. 2. Maximum value of leaf area index was 6.5. The ratio of dry weight of non-photosynthetic system to leaf area (C/F ratio) rapidly increased with the development of seeds. 3. Net assimilation rate (NAR) showed the high value (50g/m2 of leaf area/week) in the early stage of growth. It gradually decreased with time and showed the low value below about 20g in the ripening period. The decrease of NAR are due to the mutual shading, the increase of C/F ratio and the decrease of nitrogen content in leaves. The decrease of solar radiation also caused the decrease of NAR.4. The optimum leaf area index (Lopt) is not a static value. It varies with light intensity, C/F ratio and nitrogen content in leaves. For example, Lopt and Cmax at 536 ly/day in three weeks after flowering time were 5.3 and 111g respectively, but in green pod stage at 502 ly/day, those were 4.7 and 80g as shown in table 1. These results indicate that the crop growth rate of the soybean plant commuties is lower than that of rice plant commuities. 5. The distribution ratio of increased dry matter to the leaves and roots was higher at early stage than that of other stages. The distribution ratio to the stems and petioles increased until 3 weeks after flowering time, then decreased with the development of seeds. The proportion of dry matter distributed to the pods was comparatively low for 3 weeks after flowering time, but after-wards, it became rapidly high. In each sowing date, the distribution ratio to the leaves and roots under the dense planting was lower than that under the thin planting. The same phenomenon was found in the pods for 3 weeks after flowering time. Reverse relationship, however, was found in the stems and petioles.