Forest Fertilization Speakers Notes Georgia Forestry Association Meeting - June 22, 1997 David J. Moorhead - Professor of Forestry, The University of Georgia

1997. Forest Fertilization Speakers Notes. Georgia Cooperative Extension Service, Warnell School of Forest Resources, The University of Georgia, Athens, GA 30602 U.S.A.

Comments on Forest Fertilization

• Fertilization has dramatically increased with more than 1.5 million acres of loblolly pine and 1 million acres of slash pine receiving fertilizer treatments.
• Fertilization can allow pine stands to dramatically increase productivity as part of a comprehensive management plan.
• Phosphorus is often critical for seedling establishment & growth on wet flatwoods sites.
• Nitrogen can become a limiting when tree crowns are rapidly expanding at ages ranging from 5 to 10 depending on management.

Fertilization at time of planting

• P most commonly applied to poorly drained soils, although some Upper Coastal Plain loam and clay soils are P deficient.
• Average response of 50 cubic feet per acre per year (90 cubic feet to a cord).
• Apply 40 to 50 lbs of elemental P at planting.
• Time of application is not critical, but generally done when beds are prepared.
• P may be broadcast, side dressed, or banded.
• Triple Super Phosphate (TSP) which has 20 % P is most commonly applied.

Mid-rotation fertilization

• N or N + P applied to stands beginning at age 5 in intensive management, or following thinnings.
• Common treatment is 200 lbs of N + 25 lbs of P, when P is low in foliage (<0.09%) or soil (< 3 ppm; or <3 lbs/ac) & foliage has a high N to P ratio (>11).
• Use 150 to 200 lbs of N alone if foliar N is low (<1.0%) but P is adequate, & the foliar N/P ratio is low (<10.5).
• Apply 25 lbs of P alone if foliar P is <0.085% and the foliar N/P ratio is high (>13).  200 lbs of DAP is a good treatment here as well.
• Timing of N is in the spring or fall. N applied in the summer may be leached out of the rooting zone by summer rains or be volatilized by dry soil conditions & high temperatures.
• Pine straw production (needle yield)can be increased 40 to 50% two years following fertilization

Impacts on wood quality

• Generally, specific gravity is not affected by fertilization.
• Most intensive management aimed at short-rotation fiber production.
• Rapid growth leads to large juvenile core & fewer rings per inch which may limit some solid wood product applications.

Fertilizers

• Phosphorus - Triple Super Phosphate (TSP) & Ground Rock Phosphate (GRP) most commonly used at planting. Diammonium Phosphate (DAP) at planting makes weed control essential.
• Nitrogen - Urea & Ammonium Nitrate.
• Nitrogen + Phosphorus - Diammonium Phosphate (DAP) at mid-rotation.
• Overall, little differences in fertilizer sources.  Cost is generally the overriding consideration.
• Chicken litter - perhaps difficult to uniformly apply, but a good option.
  One dry ton of litter supplies:56 lbs of N, 17 lbs of P, 40 lbs of K

Fertilizer sources for forestry use.

Foliar Sampling

• Take samples from December through February
• Collect needles from a primary lateral branch in the upper 1/3 of the crown.
• Pull foliage (include needle fascicles or sheaths) from the first growth flush of the season.
• Make a composite sample from 6 to 7 trees.
• Keep samples on ice until the are sent for analysis.
• The University of Georgia (check with your county extension agent) or private labs can run foliar analyses.