ROOTING CHARACTERISTICS AND NITROGEN-UTILIZATION OF BRUSSELS-SPROUTS AND LEEKS

Under field conditions a crop of Brussels sprouts (Brassica oleracea, var. gemmifera) usually utilises the plant-available nitrogen better t han leeks (Allium porrum L.). To investigate the role of the root syst em in nitrogen utilisation, the two crops were grown in the Wageningen Rhizolab, a new rhizotron facility. Large differences in rooting patt ern 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 intens ity. The rooting pattern of Brussels sprouts could explore the soil pr ofile to a depth of one metre in a very short period. Large difference s in nitrogen uptake pattern also showed up between the crops. Brussel s sprouts depleted the entire rooted profile of nitrogen in a relative ly short period (June to mid-August) whereas in leeks the nitrogen upt ake was greatest in the second part of the season. The implications of these rooting and nitrogen uptake patterns for fertilisation manageme nt strategies to minimise N losses in ecological farming are discussed .