Forest trees require several soil-based elements to grow and maintain health. These include the "big three" macronutrients, nitrogen, phosphorus and potassium, as well as several important micronutrients. Many forest soils in North Carolina lack one or more nutrients in quantities sufficient for optimum tree growth. Adding these deficient nutrients through fertilization increases forest stand value by temporarily increasing tree growth, health and vigor and wood volume. Loblolly pine stands respond well to fertilization at mid-rotation age with increased growth. Landowners can use fertilization to increase financial return.

What the Research Tells Us

Make Fertilizers Work for You

Not all forest stands benefit from fertilization. To make fertilization work for you, be sure your stand is: 1) responsive to the nutrient amendments, 2) operable in size (greater than 40 acres), and most importantly, 3) nutrient deficient. Tree growth is often limited by soil conditions other than poor nutrition. NOTE: The cost of using fertilizer will not be cost effective where other factors limit tree growth (such as too little or too much moisture, or shallow topsoil). Carefully examine your site and soil to assess if the cost of fertilization is cost effective. Obtain the services of a forester to help you with this determination.

Know Your Soil

Visual Clues on When to Fertilize

Fertilizing Like the Professionals Do

  1. Soil nutrient tests can show what nutrients are immediately available to a stand of trees, but they do not measure how much nutrient a tree needs. The exception is phosphorus (P) deficiency, which can be identified from soil tests. A soil test with a P-index value of less than 3-to-5 ppm indicates phosphorus (P) deficiency.
  2. Foliar analysis provides the best information on what nutrients the tree is able to use from the soil. Foliage samples must be collected in the winter from the last foliage flush in the top one-third of the crown. Values shown in Table 1 indicate a nutrient deficiency.
Table 1. Critical values for foliar and soil nutrient content for loblolly pine. (expressed as % unless noted)
N P K Ca Mg S B Cu
Foliar 1.2 0.12 0.35 0.12 0.07 0.12 4–8 ppm 2–3 ppm
Soil (0–6 inches) <3–5 ppm <15 ppm

* Contact the N.C. Cooperative Extension Service or the N.C. Forest Service for information on how soil and foliar sampling is done.

When Fertilizer Pays the Biggest Dividend

Thinning and Fertilization

The Payoff

Volume gains vary and are hard to predict, but:

How Much and When to Apply

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Published in March 2009

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