Nitrogen Balance During Growth of Cauliflower and Leek.

Better knowledge of nitrogen uptake  helps to better match the supply of nitrogen to the demand of the crop and thus to improve nitrogen use efficiency.  In a cauliflower-leek rotation four nitrogen application rates were evaluated. Target values for mineral nitrogen in the soil  during the cauliflower growing season (March-June) were set  at 50, 100, 150, 200 kg N /ha at planting and 100, 150, 200, 250 kg N/ha 5 weeks after planting.  Application of nitrogen was done by subtracting the measured mineral nitrogen still present in the root zone from these target values. Beds of 1.75 m by 40 m were used. In order to control the balance, each bed had an impermeable foil at a depth of 90 cm and at the sides of the bed. On top of the foil a drainage tube was laid out to collect the leachate. Drainage water was collected in a container and its volume was measured via ultrasonic waves. Fresh biomass, dry biomass and nitrogen content (Dumas analysis)  of all components were measured 5 times during the growing season via destructive sampling. Mineral nitrogen  in the soil (Kjehldal-method)  and leachate were also measured at regular intervals. During the growing season of cauliflower an average of 15 kg N/ha was leached from every bed. Total uptake of nitrogen by the plant was 142, 165, 183 and 225 kg N/ha. A deficit of 95, 75, 60 and 80 kg N/ha was calculated, which is probably due to mineralization of organic matter. After the harvest of cauliflower, plant residues were incorporated. Leek was planted in July and harvested in November in the same setup as the cauliflower with target values of 150, 200, 250 and 300 kg/ha 5 weeks after planting. Similar results as with cauliflower were obtained.