A greenhouse experiment was conducted to compare the effects of organic amendments differing in their C-to-N ratios or their physico-chemical structure e corn silage, hydrochar (produced from corn silage by Fa. CS Carbon Solutions, Kleinmachnow, Germany) and pyrochar (produced by the authors from corn silage) e on plant growth and soil properties. Chemical characteristics of the material. 54 pots with a diameter of 10 cm were filled with sandy soil, 54 potswere filled with calcareous soil (Table S1). Half of the pots of both soil types were planted with nine seeds of winter wheat (Triticum aestivum L., type “Bussard”, Bioland Jeebel, Germany) each; the other half was left without vegetation. The amount of added amendment increased the organic C content of the original soil by 30% and corresponded to 3.6, 3.5 and 2.0weight% for silage, hydrochar and pyrochar, respectively. All three types of additives were produced fromcorn silage, thus adding a d13C label to the soils (Table 1). Three different levels of N fertilizer were applied after germination: no fertilizer, 10 mg KNO3 eN per pot and 20 mg KNO3 eN per pot, corresponding to a fertilizer application of 0,