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

A pine tree fertilizer study was established in Twiggs County, Georgia in 2013. The thinned loblolly pine stand showed P and K deficiencies based on soil sampling in March 2013 and leaf area index (LAI) estimation in August 2013 appeared to indicate N needs. The fertilizer trial (with three replications in a randomized complete block design) consisted of four fertilizer treatments applied in Feb 2014 [i.e., full dose NP and NPK and ½ dose NP or NPK application with a second ½ dose to be applied in Feb 2017, a herbicide only treatment (all fertilized plots received a herbicide application in Oct 2013 prior to fertilizer treatments)], and an untreated control. The dominant soil series at the site is Eustis, which is an excessively drained loamy sand.

It is hypothesized that this soil series may not support good loblolly pine growth without NP or NPK fertilization as indicated by the current growth rate on the site through the early to mid 20-yr-old age class. The major objectives are to: 1) quantify the magnitude and duration of wood volume response to the fertilizer treatments, 2) determine changes in product class distribution, and 3) determine the cash flow and rate of return for each fertilizer combination compared to unfertilized control plots, and (4) discern if ½ dose applications of NP or NPK fertilizers, applied three years apart, enhance growth compared to a single NP or NPK treatment on these sandy somewhat excessively well drained soils.

Baseline soil, foliage, tree measurements and one year post-application soil and foliage samples were taken in Jan 2015. Third year tree measurements will be taken in Jan to Feb 2017.