Abstract
In many districts in Japan, the soybean seeding time is the rainy season, which results in unstable seedling establishment. The use of a new system, farm-oriented enhancing aquatic system (FOEAS), consisting of a subsurface drainage system and a ground water level control system, can enhance soybean establishment. The percentage of seedling establishment of soybean, cv. Sachiyutaka, seeded in early July on an upland field converted from a paddy field with open ditch drainage was 44% on the average of 3 yr. The low emergence was probably attributable to high soil moisture contents and partial submergence by heavy rains. However, the percentage of soybean emergence was increased to 85% by effective draining by FOEAS. Seedling establishment of soybeans seeded in late July or early August was improved considerably by the temporary elevation of the ground water level for several days before seeding, even when soybean emergence was severely inhibited by soil drying. Later seeding reduced the period from seeding to flowering or initiation of pod elongation, and thus reduced the numbers of pods and grains, and grain yields. Compared with the early sowing under conventional conditions with open ditch drainage, sowing at the end of July reduced grain yields only about 10% FOEAS was adapted. Thus when using FOEAS, seeding in late July appears to be practicable to extend the soybean crop season.
