Abstract
A 2 x 2 nutrient and water factorial experiment with four replications was installed in an 8-yr-old stand of loblolly pine (Pinus taeda L.) growing on an infertile, excessively drained sandy site in Scotland County, North Carolina. After the fourth year of treatment, estimated stem volume increment, total biomass production, and peak leaf area index (LAI) increased 152%, 99%, and 101%, respectively, with fertilization and 25%, 23%, 16%, respectively, with irrigation. Stem volume growth efficiency (growth per unit LAI) increased 21% with fertilization, 9% with irrigation, and 30% with both fertilization and irrigation. Total biomass production efficiency increased 91% with fertilization, 29% with irrigation, and 120% with both fertilization and irrigation. The observed increase in stem volume growth efficiency may have been due, in part, to changes in biomass partitioning. However, altered partitioning patterns alone did not explain the observed increase in total biomass production efficiency. We hypothesized that the change in total biomass production efficiency may have been a result of greater allocation to foliage (photosynthesizing tissue) and less allocation to fine roots (a high maintenance respiration tissue) under fertilization and irrigation treatments. For. Sci. 44(2):317-328.