Performances of grain-legume-based cropping systems were compared to those of cereal-based systems. Legumes reduced N fertilizer requirements without compromising subsequent cereal crop yield and grain quality. Water use efficiency decreased slightly when including grain legumes but not when including cover crops. Cover crops which reduced nitrate leaching but however induced preemptively competed for N, which required adaptation of N fertilization. Cropping systems must be designed with suitable decision rules as a key for yearly adaption of management to benefit from grain legumes and cover crops.