NITROGEN RATE, CULTIVAR, AND WITHIN-ROW SPACING AFFECT COLLARD YIELD AND LEAF NUTRIENT CONCENTRATION

Collards (Brassica oleracea L. Acephala Group) were grown in spring an d fall to evaluate the effects of N fertilizer rate (0, 56,112,168, an d 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, respective ly) with 112 kg N/ha. Leaf N and P concentrations increased quadratica lly 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 th e present sufficiency range for leaf Ca concentrations of field-grown collards is discussed.