The potential of white clover to supply winter cereals with biologically fixed N was investigated in an experiment conducted on a loamy Cambisol. Spring barley, white clover as pure-sown crops, and clover with barley cover crops were established in the spring of the first experimental year. In the autumn, wheat was direct drilled into differently sown and managed clover to form a bi-cropping system. In other treatments wheat was conventionally sown after ploughing in of pre-crops. In the autumn of the second year, winter rye was conventionally drilled into the plots. The N content of pre-crop residues incorporated into the soil was higher in clover treatments with the barley cover crop. The wheat grain yield was higher (5.3-6.0 t ha -1) after ploughing in clover. The grain yield was significantly lower in the bi-cropping system and varied depending on the treatments (1.3-4.7 t ha -1); however, the yield was high for an organic crop rotation. The highest N concentrations in wheat grain yield were observed in bi-cropping. The winter rye grain yield was higher after differently direct drilled wheat (2.7-3.5 t ha -1) compared with that of conventionally drilled wheat (1.7-2.05 t ha -1). N concentration in rye grain was higher after a bi-cropping system had been used.
