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

IPNI-2004-USA-GA26

05 Feb 2007

2006 Annual Interpretive Summary


The University of Georgia (UGA) Warnell School of Forestry and Natural Resources (WSFNR) installed a replicated fertilizer study on Chuck Leavell’s Charlane Plantation, located in Twiggs County, Georgia, in 2005. Seven of nine thinned loblolly pine stands showed NP, NPK, NPKS, and copper (Cu) deficiencies based on soil and foliar sampling on February 27, 2004. Leaf area index (LAI) estimation taken in July 2004 showed that these stands also had LAIs below optimal levels, indicating a good probability of response to N. Two fertilizer trials using fertilizer treatments and an untreated control (planted in 1978, thinned in 2002-03) were established February 15 and 16, 2005. One-time fertilizer application levels were 200 lb N/A + 50 lb P + 80 lb K + 60 lb S + 5 lb Cu/A. The Bullard Bluff East tract had 8 plots with two replications of NP, NPK, NPKSCu, and a control. The Bullard Bluff West tract had 15 plots with three replications of NP, NPCu, NPKCu, NPKCu, NPKSCu, and a control. The N and P sources were urea and diammonium phosphate (DAP), the K source was potassium chloride (KCl), the Cu source was copper sulfate, and the S source was ammonium sulfate. Untreated control plots will serve as reference plots.

The major objectives are: 1) quantify the magnitude and duration of wood volume response to the fertilizer combinations, 2) determine changes in product class distribution, 3) determine the cash flow and rate of return for each fertilizer combination compared to unfertilized control plots, and 4) discern when fertilizers are to be re-applied to maintain wood volume gain. Baseline soil (10 core samples to make a composite sample, with one composite sample/plot at 0 to 6 in. depth) were taken in each plot prior to treatment and annually post-treatment. All living crop trees in each plot were aluminum tagged, numbered, and measured for diameter at 4.5 ft. (dbh), total height, live crown length, and defect(s) prior to treatment (January 2005), with repeated measurements planned 2 and 4 years post-treatment. Rainfall patterns were excellent the year after fertilization, but there was drought in 2006. A low-cost ($15/A for product) foliar-active herbicide (glyphosate with a surfactant) was applied at a rate of 3 qts/A with an ATV and boomless sprayer at 15 gpa in August 2004 on BBE (pre-fertilization) and in August 2005 on BBW (post-fertilization). Plot LAI is being estimated annually, and foliage samples are being collected each dormant season for nutrient analyses. A field day is being planned for the fall of 2007 to share 2-year post fertilization findings and economic fertilization guidelines. It is anticipated that many forest landowners will be able to make educated and informed fertilization decisions in thinned loblolly pine plantations from this project. GA-26F