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

Many private non-industrial forest (NIPF) landowners are seeking good economic returns to forest management and many loblolly and slash pine plantations in the South have nutrient limitations. A fertilizer trial was installed in a randomized complete block design in two Charlane Plantation thinned loblolly pine stands with marginal fertility (planted in 1978) in Twiggs County, Georgia, in 2004. One-time nitrogen (N), phosphorus (P), potassium (K), sulfur (S), and copper (Cu) fertilizer application levels were 200 lb N/A, 115 lb P₂O₅/A, 96 lb K₂O/A, 60 lb S/A, and 5 lb Cu/A. The Bullard Bluff East Tract has 8 plots with 2 replications of NP, NPK, NPKSCu, and a control. The Bullard Bluff West Tract has 15 plots with 3 replications of NP, NPCu, NPKCu, NPKCu, NPKSCu, and a control. Nutrient sources were urea, diammonium phosphate (DAP), potassium chloride (KCl), copper sulfate, and ammonium sulfate. The major objectives are: 1) quantify the magnitude and duration of the wood volume response to fertilization, 2) determine changes in product class distribution, 3) determine the cash flow and rate of return for each fertilizer combination compared to the unfertilized control plots, and 4) discern when fertilizers are to be re-applied to maintain wood volume gain. The funded project duration is 5 years.

The fertilizer materials were applied in mid-February 2005 to randomly-assigned plots. Rainfall patterns were good soon after application and remained relatively consistent through August 2005. Pre- and first-year post-treatment surface soil, foliage sampling, and leaf area index (LAI) estimations have been made. Gross treated plots are each one-half acre in size with the internal permanent measurement plots being one-quarter acre in size, centered within the gross treated plots, with 40 ft. of buffer between plots. All living loblolly pine trees were tagged with aluminum markers, numbered, and measured for dbh (diameter @ 4.5 ft.), total height, live crown ratio, height to fork, stem canker, or other defects, with each tree being merchandised into a product class (based on dbh and presence/absence of a visible defect). The same growth parameters will be re-measured every other winter (Jan-Feb 2007, 2009) to determine diameter class distribution, volume/tree, and volume/A by product class. GA-26F