FORCE TO SHEAR THE STALK, STALK DIAMETER, AND YIELD OF BROCCOLI IN RESPONSE TO NITROGEN-FERTILIZATION AND WITHIN-ROW SPACING

Broccoli [Brassica oleracea L. (Italica Group)] crops may be rejected by wholesale buyers due to unacceptably tough stalks. Four experiments were conducted to examine the effects of various N levels and two within-row spacings (15 and 30 cm) on force to shear the stalk, stalk diameter, and yield of transplanted 'Premium Crop' broccoli. Shear was not affected by within-row spacing, and average stalk diameter was decreased only 3 mm by reducing spacing from 30 to 15 cm. Although the 15-cm spacing sometimes produced the greatest total number of marketable heads, this spacing resulted in higher cull head production, lower average marketable head weight, delayed maturity, and a lower percentage of field-planted transplants producing marketable heads than the 30-cm spacing. Increasing N fertilization decreased force to shear the stalk in only one experiment, when plants were exposed to water deficits and high temperatures. Nitrogen affected stalk diameter only when very low rates (37 and 74 kg.ha-1) were included. Yield of marketable-quality heads often showed no significant response to rates of applied N > 112 kg.ha-1, particularly at the 30-cm spacing. Hollow stem was negligible in all experiments.