Effects of annual fertilization and complete competition control on current annual increment, foliar development, and growth efficiency of different aged Pinus taeda stands

Abstract

The effects that competing vegetation and nitrogen limitation have on the current annual increment (CAI), leaf biomass, and growth efficiency (GE) of different aged loblolly pine (Pinus taeda L.) stands planted on a Piedmont and lower Coastal Plain location in Georgia, U.S.A. were determined by measuring stands receiving a factorial combination of complete interspecific competition control and annual nitrogen fertilization. At the Piedmont location, CAI increased with age (5, 10, and 12 years) as well as fertilization (7.3–9.2 Mg·ha–1) and competition control (6.8–9.6 Mg·ha–1). The effects of fertilization on leaf biomass increased with stand age (no difference at age 5 to 1.5 Mg·ha–1 difference at age 12), while the effects of competition control on leaf biomass decreased with stand age (difference of 2.5 Mg·ha–1 at age 5 to difference of 1.6 Mg·ha–1 at age 12). At the Coastal Plain location, fertilization increased CAI from 10.3 to 14.8 Mg·ha–1. Leaf biomass increased with competition control (4.9–5.5 Mg·ha–1) and fertilization (4.4–6.0 Mg·ha–1). Leaf biomass increased with stand age for the fertilized stands (5.3–7.0 Mg·ha–1 between age 7 and 13) and decreased with stand age for nonfertilized stands (4.9–4.0 Mg·ha–1 between age 7 and 13). At the Coastal Plain location, fertilization increased the GE of the age-7 stands from 2.34 to 2.86 but decreased the GE of the age-13 stands from 2.32 to 2.14. In general, GE decreased as mean tree size increased indicating that changes in GE related to treatments may be confounded with changes in tree size. Results of this experiment emphasize the importance of nutrition on stand growth as fertilization increased leaf biomass and may increase stem production per unit of foliage at early stages of development.