VARDAMAN VIRTUAL FORESTRY COMPANY

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FERTILIZING LOBLOLLY PINE PLANTATIONS

Everyone trying to make money growing trees has received a powerful tool from work done at Virginia Tech University and North Carolina State University. Researchers there have used data from the North Carolina State Forest Nutrition Cooperative plots to develop models for response in both height and basal area to mid-rotation fertilization with nitrogen (N) and phosphorus (P). We got a copy of their paper on the subject because JMV&CO is a member of the Loblolly Pine Growth and Yield Research Cooperative; it has been accepted for publication in Forestry Ecology and Management and will soon appear in print. We have begun work to add their models to PTAEDA2V so that we can predict the physical and financial responses to fertilization quickly and accurately, but the job may take several months. In the meantime we invite you to consider several aspects of their work with fertilizer response.

1. The plots used in their study were established in early-spring seasons of 1984-87. Average stand conditions in them then were age = 13, site index = 67, stems per acre = 468, and basal area = 91 square feet. Therefore, the heavy stand of trees took all of the fertilizer; none was captured by weeds or hardwoods on the sites.

2. They note some limitations in the study including a rather small sample size (13 installations) and narrow stand age at time of fertilization (11 to 14 years).

3. While the equations do a good job of modeling response to fertilization, there is still considerable variation due to soil, climatic and genetic conditions that the equations do not explain.

4. The equations were developed for a single fertilizer treament at one point in time. While the equations could be used for estimating response to multiple applications, it's uncertain how reliable they might be.

When it is published, we invite you to study the article. Meanwhile, we have space only to report these findings:

1. The greatest response comes from using N and P together, usually at per-acre rates of 200 pounds of N and 25 pounds of P.

2. The basal-area growth response peaks around two years after fertilization; for stand dominant height, growth response reaches its maximum level somewhat later, around two to four years after fertilization.

We intend to use fertilizer in accordance with these findings in managing all PPICs and to recommend it to everyone who asks us. We think that it should be applied immediately after the first thinning (usually at age 12) so that its maximum effect can be harvested about ten years later. Much of the fertilizer would be wasted if applied at the time of planting; it would increase herbaceous competition for the seedlings and be taken up by poor-quality stems. We will use other practices to bring seedlings to maximum size at age 12.

The profit potential of fertilization is large. It seems likely to increase IRRs from cultural treatments alone by at least 20%; therefore, it could compensate for over-estimates in the original timber-yield predictions. We'll go into this in great detail after PTAEDA2V is modified. For the time being, in a nearby article, we have used PTAEDA2V's current method of predicting fertilizer response to give you an idea of what's in store.