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

Private non-industrial forest landowners are very interested in fertilization of their pine plantations. Many own tractors and spreaders and are willing to apply fertilizers themselves. Very little information is available to NIPFLs on the magnitude and duration of response to NP, NPCu, NPKCu, or NPKSCu fertilization in thinned loblolly pine stands on marginal fertility cut-over sites. Current pine pulpwood versus chip and saw and small sawtimber price disparities (pulpwood is 1/5 chip and saw per cord and 1/8 sawtimber per cord) have many NIPF landowners wanting to shift wood to the more valuable product classes as well as grow more wood.


Justification

There are over 600,000 private non-industrial forest landowners (NIPFLs) in Georgia who own approximately 67% (24.3 million acres) of the state’s 36 million acres of forested land. The NIPFLs in the southeastern United States own from 49% (Florida) to almost 70% (South Carolina and Georgia) of the forestland in these states. Forest Industry has been fertilizing between 900,000 to 1.2 million loblolly and slash pine stand acres annually in the southeastern U.S. over the last 8 years. Fertilization on NIPFL acreage is well below that of Forest Industry. Yet, numerous loblolly and slash pine NIPFL stands are candidates for fertilization based on diagnostic tool use (leaf area index estimates or LAI, soil test-P, crown visual symptoms, and foliar N, P, K, Ca, Mg, S, Cu, Mn, and B concentrations). Financial returns ranging from 8% to 17% over an eight to twenty year period can be realized with each fertilizer application.

Private non-industrial forest landowners are very interested in fertilization of their pine plantations. Many own tractors and spreaders and are willing to apply fertilizers themselves. Very little information is available to NIPFLs on the magnitude and duration of response to NP, NPCu, NPKCu, or NPKSCu fertilization in thinned loblolly pine stands on marginal fertility cut-over sites. Current pine pulpwood versus chip and saw and small sawtimber price disparities (pulpwood is 1/5 chip and saw per cord and 1/8 sawtimber per cord) have many NIPF landowners wanting to shift wood to the more valuable product classes as well as grow more wood.


Methodology

This draft proposes that a fertilizer trial (3 to 4 replications in a randomized complete block design) using NP, NPCu, NPKCu, and NPKSCu and an untreated control be installed in one of Chuck Leavell's thinned loblolly pine stands that has marginal fertility. The major objectives: (1) quantify the magnitude and duration of wood volume response to the fertilizer combinations, (2) determine changes in product class distribution and (3) 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.

The proposed project duration is 5 years. Seven thinned loblolly pine stands have been located on Chuck Leavell's property that are NP, NPCu, NPKCu or NPKSCu deficient.

Gross treated plots (147.6 x 147.6 feet, or 0.5 acres) and internal permanent measurement plots (104.5 x 104.5 feet or 0.25 acres) will be installed in the delineated soil series area. Forty feet of untreated buffer will be between each gross treated plot. Replications (blocks) will be laid out on the contour to minimize soil moisture differences. Baseline soil (10 to 20 samples to make a composite sample, with one composite sample /plot @ 0-8") and foliar samples will be taken in each plot prior to treatment. Initial stand and plot leaf area index (LAI) will be estimated using the NCSU protocol in midsummer. Foliage samples (3 dominants/plot, upper 1/3 crown, south side, first flush of previous year’s growth to represent each composite sample/plot) will be taken each dormant season. Soil and foliage analysis will include N (foliage only), P, K, Ca, Mg, S, Cu, Mn, Zn, and B. Soil pH for each plot will also be determined. All living crop trees in each plot will be aluminum tagged, numbered and measured for dbh and total height prior to treatment. Live crown ratio of all living trees/plot will be measured prior to treatment.

Randomly assigned to each plot will be a NP, NPCu, NPKCu, or NPKSCu fertilizer treatment. Untreated control plots will serve reference plots. The one-time fertilizer application levels in the thinned loblolly pine stand will be 200 lbs N/acre + 40 lbs elemental-P + 80 lbs elemental-K + 60 lbs S and 5 lbs Cu/acre. Application timing of fertilization will be targeted for late winter (February-March) to minimize N losses. Forest soil and foliage sampling will occur each subsequent winter following treatment, and LAI estimated at peak expression in midsummer following treatment. Total height and dbh will be remeasured every other winter to determine diameter class distribution, volume/tree, and volume/acre by product class. Live crown ratio of all trees/plot will also be measured every other winter.