Abstract
The objective of this study is to establish a method of nitrogen fertilization suitable for growth and yield, particularly for dry matter production and nitrogen absorption in summer buckwheat (Fagopylum esculentum Moench, c.v. Kitawasesoba) cultivated in western Japan. Ammonium sulfate was applied as a basal dressing at the nitrogen rate of 0, 2, 4, and 10g/m2 in a drained paddy field. Dry weight and nitrogen absorption increased with increasing amount of nitrogen application. Seed yield was increased by nitrogen application up to 4g/m2 due to an increase in the number of seeds per plant. In the plot to which 10g/m2 nitrogen was applied (10g/m2 plot), the harvest index and nitrogen use efficiency of the seeds were low, and seed yield was almost the same as those in the 4g/m2 plot. In the 10g/m2 plot, the dry matter partitioning rate was still high in the stem during the late ripening period. Slow-release fertilizer (70 days type) as a basal dressing and ammonium sulfate as a topdressing at the flowering period were applied. However, they did not increase seed yield. It is thought that the promotion of initial growth by basal dressing is important for buckwheat cultivation in western Japan because seeds are sown in the spring when temperature is still low. The application of nitrogen fertilizer at the rate of 4g/m2 would be necessary even in drained paddy fields.
