Nitrogen fertilizer form may affect quality and yield of leafy vegetables. In the present study, the effect of ammonium nitrogen rates on yield and chemical composition of Cichorium spinosum L. was examined. Five fertilizer treatments with different amounts of ammonium nitrogen (F1: 14%, F2: 24%, F3: 34%, F4: 43% and F5: 53% NH 4 -0N of total N) were applied. Fertilizer treatments had a significant effect on both plant fresh weight and chemical composition, depending on growing period and harvest stage. For both harvests of the 1st growing period, yield was higher in treatments F4 (43% NH 4 -N) and F5 (53% NH 4 -N), whereas in the 2nd growing period yield was higher for treatments F1, F2 and F3. Moreover, the highest content of total phenolics were recorded in the 2nd growing period. Antioxidant properties were also affected by fertilization treatments and growing periods, with antioxidant potency being higher in the 2nd growing period and for treatments F1 and F2. According to the results of the present study, nitrogen fertilizer form should be considered together with growing period and harvest stage as a useful means towards increasing the quality of the final product without compromising total yield.
