Abstract
Dry matter and seed productivity of Sachiyutaka, an early maturing soybean (Glycine max Merr.) cultivar with a short stem, were investigated under four kinds of interrow spacing (30, 40, 60 and 80 cm) compared with a cultivar, Fukuyutaka under 80 cm of interrow spacing as the conventional culture in south-western Japan. In Sachiyutaka, the numbers of pod and seed per square meter increased by narrow row spaceing of 30 and 40 cm, and consequently, the seed yield was increased by 30 g m-2 compared with Fukuyutaka under conventional culture. The leaf area index (LAI) at flowering time and that at the seed-filling stage greater under narrow-row-dense-planting culture in Sachiyutaka, were as large as 5.0—4.4, which were approximately equivalent to those in Fukuyutaka under conventional culture. In addition, the light extinction coefficient of 50-cm upper layer was low at the seed-filling stage in narrow-row-dense-planting culture, showing excellent light-intercepting characteristics. As a result, maintaining a sufficient level of LAI at the seed-filling stage under the narrow-row-dense-planting condition in Sachiyutaka was considered as a factor to obtain a high seed yield equal to or superior to that in Fukuyutaka under the conventional culture.
