Response of Nine-Year-Old Plantation Sweetgum to Nitrogen Fertilization in Mississippi
Abstract Nine-year-old planted sweetgum (Liquidambar styraciflua L.) consisting of four half-sib seed sources were refertilized with nitrogen in 1981 at the beginning of the tenth field-growing season. Increases in periodic annual height, diameter at breast height, basal area, stem volume (ob),and woody biomass increments of all four half-sib seed sources from applied nitrogen were observed during the 9 years following application. Periodic annual stem volume (ob) increments averaged over all half-sib seed sources were 120, 152, 192, and 266 ft³/ac/yr for the 0, 89, 178, and356 lb/ac N rates, respectively. The half-sib seed sources from alluvial sites were superior to those from upland sites in terms of productivity and response to N. The response of all half-sibs to N was immediate, occurring during the year of application; however, the increased growth ratesdue to N persisted for only 3 years. This suggests that on responsive sites, applications of N may be necessary every fourth year to maintain maximum growth rates. South. J. Appl. For. 16(3):146-150.