A field experiment was carried out in an arable organic cropping system and included a sequence with sole cropped fababean (Vicia faba L), lupin (Lupinus angustifolius L), pea (Pisum sativum L), oat (Avena sativa L) and pea-oat intercropping with or without an undersown perennial ryegrass (Lolium perenne L) - white clover (Trifolium repens L) catch crop followed by a first crop of spring wheat (Triticum aestivum L) and second crop of winter triticale (Triticale hexaploide L). The rotation sequence was repeated twice. Natural N-15 abundance techniques were used to determine grain legume N-2 fixation and N-15 labeling technique to determine the fate of pea and oat residue N recovery in the subsequent crop. The subsequent spring wheat and winter triticale crop yields were not significantly affected by the previous main crop, but a significant effect of catch crop undersowing was observed. A higher soil mineral N content in the soil profile without undersown grass-clover increased the spring wheat yield. This effect was circumvented in the subsequent winter triticale, where yields in the treatments with catch crops undersown were significantly greater. The grass-clover catch crop after grain legumes had a higher grass proportion before incorporation as compared to grass-clover after oat, which had the greatest clover proportion. The dynamic response of interspecific interactions in the catch crop to the soil mineral N levels is moderating the preceding effect of main crops in the subsequent cereal - and sometimes to a higher degree than the main crop effect. For research involving rotation principles it is recommended to evaluate cumulative effects over several years and not only single seasons.