Correct management of cabbage fertilization can be achieved by synchronizing the plant demand with N supply during the crop cycle. The objective of this study was to evaluate the evolution of nutritional parameters intensity of green color (SPAD index) taken on the fourth fully expanded leaf, N content, stem length, number of leaves, and fresh and dry matter weights to diagnose nitrogen status of cabbage and determine the critical value of each parameter at different assessment times. At 50, 64 and 78 days after sowing, the intensity of green color (SPAD index) measured on the fourth leaf, stem length, number of leaves, fresh and dry matter weights and N content in the leaf dry matter were determined. Five N rates (0, 75, 150, 300 and 450 kg ha-1) were evaluated. Treatments were arranged in a randomized block design with four replications. Last harvest of cabbage heads was at 103 days after sowing. Optimal values of variables over cabbage cycle depended on N rates and time of evaluation. Optimal SPAD values were 60.8, 58.4 and 53.5 at 50, 64 and 78 days after sowing respectively. Optimal values of N content were 62.9, 60.3 and 59.0 in the leaves, 48.6, 40.6 and 40.3 in the stem and 39.9, 36.9 and 20.1 in the roots.
Brassica oleracea L.; nutritional diagnosis; critical level
