Abstract
The purpose of this study is to clarify the contributions of dry matter production to the grain yield of soybean plants. The experimental design is the same as the previous report. The results were as follows : 1. The number of ovules per unit area increased with the accumulation of dry matter and the amount of absorbed nitrogen and phosphorus during the period from the date of flower-bud differention to flowering time. 2. The percentage of ripened seeds was mainly determined by the amount of dry matter distributed to each pod for about 3 weeks after flowering time. The number of these seeds per unit area increased with the dry matter distributed to the pods rather than the increment of total plant weight within about 4 weeks after flowering time. 3. The grain yield is composed of the duration of seed production and the crop growth rate in this duration, so increasing yield depends on the increase of these two components. The duration of seed production was mainly affected by the sowing date. The sowing date was the later, this duration was the shorter. Moreover, this duration was slightly prolonged by dense planting or heavy manuring. The change of crop growth rate was due mainly to NAR, when mean LAI was more than about 3.5. In late sowing, the leaf area was insufficient for increasing the crop growth rate. The increase of NAR under the large leaf area is important to obtain the high yield of soybean.
