NITROGEN BALANCES DURING GROWTH OF BRUSSELS SPROUTS AND LEEKS

Abstract

The nitrogen balance at different N-application rates was determined in Brussels sprouts and leeks during growth of the crop in two field experiments on a sandy soil. The N-input (from fertilizer and mineralisation) and the N-output (N in the above-ground crop parts and the residual mineral N in the soil (Nmin)) were calculated. No deficit on the nitrogen balance was observed during crop growth of Brussels sprouts up to a fertilizer rate of 300 kg ha-1. In leeks no deficit was found when 125 kg ha-1 N was applied, but a deficit in the balance developed from 90 days after transplanting, when 250 kg ha-1 N was applied at the time of transplanting. In one year this deficit in leeks was 160 kg ha-1 N at the beginning of September. Based on a simulation study of the nitrate movement in the soil, it was concluded that the deficit in the balance in leeks was in fairly good agreement with the amount of nitrogen leached from the soil layer (0–60 cm) at the final harvest (November). At the final harvest the level of mineral nitrogen in the soil (0–60 cm) was less than 20 kg ha-1 N at all N-application rates in both crops. The uptake of nitrogen during the last part of the growing period of leeks played an important role in maintaining the green colour intensity. The results are discussed in view of the need for a mineral nitrogen buffer as prescribed in nitrogen management systems, based on KNS (Lorenz et al., 1989).