AN EMPIRICAL-MODEL FOR DESCRIBING GROWTH AND NITROGEN UPTAKE OF WHITECABBAGE (BRASSICA-OLERACEA VAR. CAPITATA)

Field experiments with white cabbage crops (Brassica oleracea var. cap ilata) showed large variation in nitrogen uptake, dependent on differe nt local climate conditions, cultivars and growing practices. Proper f ertiliser recommendations should allow for these differences. For advi sory purposes, a simple model for nitrogen uptake was developed that c an be adapted to farm specific growing conditions. Model validation wa s carried out with 21 data sets obtained from experiments, grower's fi elds and the literature. Using expected yield, expected duration of cr op growth and planting date as input the model generated good fits to measured nitrogen uptake curves. In 56% of all measurements, the estim ation error was within the range of +/-25 kg nitrogen ha(-1) and in 90 % within +/-50 kg nitrogen ha(-1). (C) 1998 Elsevier Science B.V.