Loblolly Pine Stand Fertilization at Mid-rotation to Increase Small and Large Sawtimber Volume

Two fertilizer trials and an untreated control were established in 2004 near Bullard, Georgia, within a loblolly pine tree stand planted in 1978 and thinned in 2002-03. Fertilizer treatments examined NP, NPK and NPKSCu fertilization effects in one trial and NP, NPCu, NPKCu, and NPKSCu fertilization effects in a second trial. The one-time fertilizer applications were applied in February 2005. Fertilizer levels applied were 200 lb N, 50 lb P, 80 lb K, 60 lb S, and 5 lb Cu/A.

Six-year mean loblolly pine diameter increments measured at 4.5 feet above groundline (diameter at breast height or dbh) were greatest for the NP and NPKCu treatments with 27 and 28%, respectively, better dbh incremental growth than the control through six years. Six-year mean trees per acre (TPA) losses were greatest in the NPKCu treatment, which lost 8 TPA. The NPCu and NPKSCu treatments had the greatest six-year mean basal area growth (the combination of dbh and TPA) at 15 and 12% greater than the control, respectively. The NP and NPCu treatments 6-year height growth increments were 27 and 24% greater than the control, respectively, while the NP and NPKCu treatments six-year volume per tree increments were 35 and 37% greater than the control, respectively. Six-year mean volume per acre increments were 4.64 t/A/yr for the control, 4.78 t/A/yr for the NP, 5.55 t/A/yr for the NPCu, 4.72 t/A/yr for the NPKCu, and 5.07 t/A/yr for the NPKSCu treatment, resulting in the NPCu treatment growing 0.90 t/A/yr (19%) more wood than the control during the six year period. The six-year NPCu chip-n-saw + sawtimber volume per acre increment was 199 ft³/A (18.5%) greater than the control. GA-26F