Estimation of nitrogen uptake of field vegetables

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).