Collards (Brassica oleracea L. Acephala Group) were grown in spring and fall to evaluate the effects of N fertilizer rate (0, 56, 112, 168, and 224 kg·ha -1), cultivar (Blue Max and Vates), and within-row spacing (15, 23, and 30 cm) on yield and leaf mineral nutrient concentrations. Season, cultivar, and N rate interacted in their effects on yield. In spring, `Blue Max' yield increased linearly with N rate to 10.4 t·ha-1, whereas the highest `Vates' yield (7.0 t·ha-1) was obtained with 112 kg N/ha, and yield remained similar with additional N. In fall, `Blue Max' and `Vates' yields were highest (14.5 and 9.9 t·ha -1, respectively) with 112 kg N/ha. Leaf N and P concentrations increased quadratically and linearly, respectively, in response to N rate. Maximum yields were obtained with the 15-cm within-row spacing. Leaf N concentration increased linearly with increased plant population. The adequacy of the present sufficiency range for leaf Ca concentrations of field-grown collards is discussed.
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