EFFECTS OF NITROGEN AVAILABILITY ON THE BIOMASS AND NITROGEN PARTITIONING IN BRUSSELS-SPROUTS (BRASSICA-OLERACEA VAR GEMMIFERA)

The effect of rate and date of application of nitrogen fertilizer on t he partitioning of biomass and nitrogen in Brussels sprouts was studie d in held experiments. Growth of Brussels sprouts was in two phases: d uring the first phase mainly leaves and stem were produced and during the second phase mainly bud growth occurred. At the onset of bud growt h, 60-80% of the total biomass was produced and an equal proportion of nitrogen had been taken up. Final bud weight and bud nitrogen content correlated positively with the total biomass and nitrogen content at the onset of bud growth. Partitioning of biomass and nitrogen among th e different above-ground plant organs was hardly affected by the nitro gen availability and the time of the fertilizer application. Harvest i ndex at the final harvest was 0.25 for the biomass and 0.45 for nitrog en. During bud growth, leaf senesced at a high rate. Biomass and, espe cially, nitrogen was remobilized from the leaves before shedding. Duri ng bud growth the decrease in nitrogen content of the leaves was up to 50% of the nitrogen increase of the buds. When additional N was appli ed at the onset of bud growth, N remobilization decreased. An N applic ation at the onset of bud growth increased bud growth due to a delay o f leaf shedding. Nitrogen concentration in the buds increased due to a N application at the onset of bud growth, which resulted in a greener appearance. When a certain amount or nitrogen was split into two port ions (half at transplanting and half at the onset of bud growth) the n itrogen concentration of the buds was higher than when applied complet ely at transplanting only, but the partitioning of biomass and the bud yield was not affected.