Some fertilizer recommendation systems for field vegetables are based on es
timated nitrogen (N) uptake curves. The estimation of nitrogen uptake shoul
d be as accurate as possible, in order to avoid recommendations being too h
igh or too low. Therefore, the accuracy (standard error of difference betwe
en measured and estimated values, sd) of two estimation methods was compare
d. Comparison was carried out with measured nitrogen uptake curves of kohlr
abi (Brassica oleracea var. gongylodes L.) and white cabbage (Brassica oler
acea L, var, capitata f. alba).
For kohlrabi, the use of observed growth stages resulted in a small estimat
ion error (sd=14kg N ha(-1)). This method is recommended since it is accura
te and easy to use. The estimation that depended on time-after-planting, sh
owed a larger estimation error (sd=28kg N ha(-1)). For white cabbage, both
methods tested were not suitable because estimation errors were too high (6
3 and 51kg N ha(-1), respectively).