Under field conditions a crop of Brussels sprouts (Brassica oleracea, var.gemmifera) usually utilises the plant-available nitrogen better than leeks (AlliumporrumL.). To investigate the role of the root system in nitrogen utilisation, the two crops were grown in the Wageningen Rhizolab, a new rhizotron facility. Large differences in rooting pattern were observed. Leeks had a relatively shallow rooting system with maximum root growth at a depth of 15 to 20 cm and a low rooting intensity. The rooting pattern of Brussels sprouts could explore the soil profile to a depth of one metre in a very short period. Large differences in nitrogen uptake pattern also showed up between the crops. Brussels sprouts depleted the entire rooted profile of nitrogen in a relatively short period (June to mid-August) whereas in leeks the nitrogen uptake was greatest in the second part of the season. The implications of these rooting and nitrogen uptake patterns for fertilisation management strategies to minimise N losses in ecological farming are discussed.