Despite the available information, little is known about the effects that differences in C quality exert on the interaction between C-containing soil amendments and the N allocation between plants and soil organisms. A better understanding of the related interactions might offer the possibility to minimize the agricultural impact on ecosystems by using the gained knowledge to optimize agricultural management thus recommend research on the effects of various biochars on N transformations and especially on the fate of N additions to soils amended with char materials. The comparison of different materials offers insights into the interaction of C and N cycling in agricultural ecosystems and help to improve N use efficiency of agricultural crops.We expect that the differences in organic matter quality cause related variations in the allocation of N. We hypothesize (1) that soil amendments with a high C-to-N-ratio and a low condensation degree immobilise N thus causing N deficiency in plants if no N fertilizer is added to the system and (2) that soil microbes are progressively inhibited in the presence of materials with increasing structural organization of aromatic compounds. To test these hypotheses, we set up a pot experiment with winter wheat growing in soils amended with different organic materials all based on corn silage at various levels of 15N-labelled fertilizer.