Yield and external quality of kohlrabi as affected by soil mineral nitrogen residue at harvest

Summary

Vegetable crops often leave large amounts of nitrogen (N) in the field after harvest, both in harvest residues and as residual mineral nitrogen (N_min) in the soil. If there is a risk of leaching after harvest, the residual N_min should not be higher than required to secure good yield and quality. To determine the required N_min residue for the vegetable crop kohlrabi (Brassica oleracea var. gongylodes L.), field experiments were carried out over two years with a range of nitrogen supplies, and yield and external quality (leaf colour and leaf fresh matter) were measured. The required N_min residue was estimated using the breakpoint of a linear response and plateau regression model. The breakpoints estimated (35.kg N ha^±1 for leaf colour, 35.kg N ha^±1 for leaf fresh matter and 28 kg N ha^±1 for total fresh matter yield) were similar, and agreed well both with breakpoints estimated from other published data and empirically derived values for kohlrabi.