Abstract
Stabilization of soybean cultivation in rotational paddy fields is important issue for efficient utilization of Japanese arable land. The present study aimed to clarify the suitable condition of soybean planting for stable es-tablishment in clayey paddy fields by taking account the particularity of physical properties of clayey paddy soils. The effects of four experimental factors: intensity of com-pression, days after tillage, seeding depth, and tilth on the germination and growth of soybean, were investigated by field experiments following the randomized block design. The seeding depth and the timing of seeding after tillage were revealed to be the most influential factor while com-pression had supplementary role. Mean dimension of ag-gregates did not affect the germination and growth under the poor tilth condition. The results suggest that seed-ing should be conducted soon after tillage but the optimal depth depends on the expected weather in the following days. However if drainage efficiency of the field can be improved, seeding deeply supposed to be less risky unless enough rain is surely expected.
