Soil Nitrogen Depletion by Vegetable Crops with Variable Root Growth

The ability of carrot, leek and white cabbage to deplete the soil inorganic nitrogen (N) pool was studied. All three crops are late-harvested crops with a long growing season, but they have been found to have very different root growth. At their optimal N supply, carrot left 27 kg nitrate-N ha-1 in the top 100 cm of the soil, leek left 87 kg N ha-1 and white cabbage left only 11 kg N ha-1, in accordance with previously published differences in rooting depth among the three crops. Compared at a supply of 160 kg N ha-1, 52, 65 and 4 kg nitrate-N ha-1 was left in the soil by carrot, leek and white cabbage respectively. Apart from an extensive root system, white cabbage also had a much higher N-uptake capacity than the two other crops. The significance of differences in root growth, N-uptake capacity and other factors in determining the ability of the three crops to deplete the soil inorganic N pool is discussed.