Abstract
It was recognized from surveys in 30 fields around Sapporo city that soil pH values were neutral (6.5-7.5) and nitrate nitrogen was deficient (less than 50ppm) in fields where Aphanomyces root rot of spinach was severe.
The effects of applied nitrate nitrogen and decreased pH on the root rot severity were examined. Disease severity was remarkably decreased at more than ca. 200ppm of nitrate nitrogen in soil solution. The effect of soil pH on the severity was not significant at high inoculum potential. It was elucidated from these results that nitrate nitrogen is more closely related to the outbreak than soil pH, and the severe outbreak occurs when nitrate nitrogen is deficient.
