As early as the 1950s, there had already been reports on the δ 15N value of some chemical fertilizers (Hoering, 1955). Since Kohl and his co-workers (1971) published the report that attempt was made to distinguish the respective contribution of soil nitrogen and fertilizer nitrogen to the source of nitrates in surface water according to the differ- As early as the 1950s, there had been reports on the δ 15N value of some chemical fertilizers (Hoering, 1955). Since Kohl and his co-workers (1971) published the report that attempt was made to distinguish the differences contribution of soil nitrogen and fertilizer nitrogen to the source of nitrates in surface water according to the differ-