An ecological five-year rotation of potato - spring barley with undersown grass clover – grass clover – grass clover – winter wheat with cover crop and a conventional three-year rotation of winter rape – winter wheat – spring barley systems were compared for soil mineral nitrogen content in 0-90cm from 2000-2003. The research was conducted on a field trial located at the Experimental Station in Osiny (Lublin province, Poland) on grey brown podzolic soil. In the ecological rotation, mineral nitrogen contents increased over time while in the conventional system the contents were the same after three years. However, depending on the crop and year there were large losses. The largest potential for Nmin losses was observed after grass clover in the ecological, and after rape in the conventional system
