Silage maize grown in a four-crop rotation: Similar soil C4-stocks despite large fertilizer-induced differences in harvest yields

• Soil δ 13 C increased following introduction of maize in a four-course crop rotation. • Maize-derived C contributed about 1 % of the total SOC stock after 20 years. • The maize-derived SOC stock was independent of fertilizer-induced yield differences. Belowground crop residues are one primary source of C input in agricultural soils. Using changes in the natural abundance of 13 C, we quantified SOC derived from harvest residues of silage maize grown in a four-course crop rotation with different mineral fertilizer levels (UNF, ½, 1, and 1½NPK). After a period of two decades with five maize crops, maize-derived C accounted for 1 % (0.36 Mg C ha −1 ) of the total SOC stock in the 0–20 cm soil layer, irrespective of differences in aboveground harvest yields. This questions yield-dependent allometric functions for silage maize used in models simulating C turnover in agricultural soils.