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Forest Fertilization Speakers Notes
Georgia Forestry Association Meeting - June 22, 1997

David J. Moorhead - Professor of Forestry, The University of Georgia

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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.


  • 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.

Source % N % P % K
Urea (46-0-0) 46 0 0
Ammonium Nitrate (33-0-0) 32.5 0 0
Diammonium Phosphate DAP (18-46-0) 18 20 0
Triple Super Phosphate TSP (0-46-0) 0 20 0
Ground Rock Phosphate GRP 0 11 - 13 0
Potassium Chloride (0-0-60) 0 0 50
Potassium Sulfate (0-0-53) (18% S) 0 0 44

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.

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Last updated on Wednesday, February 11, 2004 at 03:36 PM
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