Abstract
Yields of winter wheat in Konan, Kiyosato-cho, were approximately 80-90% of the mean yield of the town, partly because of early die-off. This study assessed the factors affecting the low yields by examining the soil profile and root system in each field of that district. The results showed that pyroclastic flow deposits (Km-5a horizon) restricted root growth in the fields of the Konan area, and that shallow root systems have attracted a low yield in wheat yields. In Konan, significant correlations were observed between the grain yield and the root depth index. A survey of soil nitrate nitrogen also revealed that the soils of Konan fields tended to become severely nitrogen (NO3-N) -deficient. From these results, we suggest that shallow-rooted wheat and low nitrogen soil attracted a low yield.
