Abstract The effect of subsoil compaction on maize dry matter content and green tops yield was investigated in a lysimeter experiment. After labelling several layers of the soil profile with 45Ca the uptake of this isotope was determined. Maize green tops yield increased and dry matter content decreased with increasing subsoil bulk density. Total uptake of 45Ca had a minimum at 1.55 g cm −3 and was not different for 1.45 and 1.70 g cm −3. The concentration of 45Ca in the dry matter was higher at 1.70 g cm −3 than at 1.55 and 1.45 g cm −3, where it was similar.