Abstract
The effects of draining after submerged direct seeding were investigated in pot experiments to improve emergence and establishment of rice seedlings in the new direct seeding method using a "shooting hill-seeder". By draining flooded water after sowing rice seeds coated with calcium peroxide into puddled soil, the paddy surface soil was contracted and the solid phase increased with the decrease in soil water (liquid phase) resulting in the change in soil structure, and thus the air permeability of the soil was increased due to the increased air phase. In the pots after draining coleoptiles and the first leaves (incomplete leaves) of rice seedlings stopped elongating soon after seedling emergence and the emergence and growth of the second leaves followed immediately. Dry weights of the shoots and roots in drained pots were higher than those in flooded pots. Under the flooded water condition, the soil structure and air permeability of the surface soil did not change, and the coleoptiles and the first leaves of seedlings continued to elongate after seedling emergence, resulting in delayed growth of the second leaves. These results suggest that the increase of air permeability in the surface soil after draining improved the early growth of rice seedlings. Drainage of flooded water, therefore, would contribute to stabilize emergence and establishment of seedlings in submerged direct seeding of rice.
