Growth and nutrition response of young sweetgum plantations to repeated nitrogen fertilization on two site types

Short-rotation intensive tree culture is being investigated in the southern United States as a method of producing hardwood fiber, but little is known about the early productivity and nutritional needs of these systems, especially on different site types. We studied the growth and foliar nutrition response of two sweetgum (Liquidambar styraciflua L.) plantations on a converted agricultural field and a pine cutover site to biannual applications of three nitrogen (N) fertilizer rates: 0, 56, and 112 kg N ha(-1). The trees did not respond to treatment at any age on the agricultural field site, but the fertilized trees on the cutover site had about 60% greater biomass at ages 5 and 6. Fertilization doubled foliar biomass on the cutover site in the years fertilizer was applied. Stem biomass was directly related to foliar biomass, but the relationship was age-specific. at both sites. Stem biomass was also related to the foliar N concentration. Foliar critical values of N were about 18 g N(.)kg(-1). Foliage phosphorus (P) and potassium (K) contents were diluted by the N fertilization-induced growth responses at both sites. Fertilization of young intensive-culture sweetgum plantations is necessary for optimum foliar N concentrations and foliar and stem biomass production, but is site-specific. (C) 2004 Elsevier Ltd. All rights reserved.