Nitrogen and Flowering Dogwood. II. Impact of Nitrogen Fertilization Rate on Flower Bud Set and Tree Growth

Abstract

Abstract Impact of nitrogen (N) fertilization rate on the growth of ‘Cloud 9’ and ‘Cherokee Chief’ flowering dogwood was assessed in a field planting from February 2001 until January 2006 in southwest Alabama (USDA Zone 8a). Starting at planting in 2001 and ending in 2005, ammonium nitrate was broadcast in a 0.3 m2 circle around the base of each tree at 4.1, 8.3, 16.5, 33.0 and 66.0 g N·m−2 (37.5, 75, 150, 300, 600 lb N·A−1) with the application of half of each N-rate in April and June of each year. In each year, disease control was maintained with approximately six applications of Heritage 50W fungicide made at 2-week intervals. Trunk diameter and tree height were recorded in early-winter from 2001 through 2006; flower bud counts were taken annually from 2003 to 2006. With the exception of 2004 when N rate had not influence on bud formation, highest flower bud counts were associated with elevated rates of 33 and 66 g N·m−2 (300 and 600 lb·N−2). Nitrogen rate had no influence on the height or trunk diameter of flowering dogwood until three and four years, respectively, after planting. Impact of N rates below 66.0 g N·m−2 (600 lb·A−1) per year on tree height was minimal. In 2005 and 2006, trunk diameter was greater for trees receiving the two highest than the two lowest N rates. Regression analysis was used to calculate optimum N rate for flower bud set, as well as change in trunk diameter and tree height.