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 the partitioning of biomass and nitrogen in Brussels sprouts was studied in held experiments. Growth of Brussels sprouts was in two phases: during the first phase mainly leaves and stem were produced and during the second phase mainly bud growth occurred. At the onset of bud growth, 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 the different above-ground plant organs was hardly affected by the nitrogen availability and the time of the fertilizer application. Harvest index at the final harvest was 0.25 for the biomass and 0.45 for nitrogen. During bud growth, leaf senesced at a high rate. Biomass and, especially, nitrogen was remobilized from the leaves before shedding. During 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 applied at the onset of bud growth, N remobilization decreased. An N application at the onset of bud growth increased bud growth due to a delay of 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 portions (half at transplanting and half at the onset of bud growth) the nitrogen concentration of the buds was higher than when applied completely at transplanting only, but the partitioning of biomass and the bud yield was not affected.