Abstract
Effect of top-dressing of nitrogen fertilizer on the yield and ear number of rice (Oryza sativa) “Hoshimaru”, a representative variety for dry direct seeding in Hokkaido, was examined. Experiments were conducted in the paddy fields (soil type: Andosol) in Sapporo, Hokkaido from 2010 to 2012. Nitrogen fertilizer was top-dressed once a week from the 1.5-2.0 leaf stage to panicle formation stage of rice. Field water was drained to spray a herbicide at the 6.0 leaf stage of rice, i.e., 5.0-6.0 leaf stage of barnyard grass (Echinochloa crus-galli) in 2010 and 2012. Top-dressing of nitrogen fertilizer at the 5.0 leaf stage, 1-2 days before water drainage, had little effect on hulled grain yield or ear number of rice. In the same fields, top-dressing of nitrogen fertilizer at the panicle formation stage most effectively increased hulled grain yield and ear number of rice than that at the other stages. On the other hand, in the field with flooded water maintained, top-dressing of nitrogen fertilizer at the 6.5-7.5 leaf stage of rice, 1 week before the panicle formation stage, increased the grain yield and ear number of rice more effectively than at other stages.
