Late-rotation fertilization was studied over a 6 yr period in loblolly pine (Pinus taeda L.) plantations in north Louisiana. Fertilizer (150 lb/ac of nitrogen and 50 lb/ac of phosphorus) and herbicide (hexazinone, 2.5 lb ai/ac) were applied to five loblolly pine plantations in the 25-yr-old age class (25-26 yr), and five plantations in the 30-yr-old age class (30-32 yr). The study was established as a randomized block design with three blocks in each plantation. Three treatments studied were fertilizer (F), fertilizer+herbicide (FH), and herbicide (H), which were compared to a control. Diameter and volume growth responded significantly to treatments F and FH in both age classes. A greater per-tree response occurred in the 25-yr-old age class as a result of the additive effect of recent thinnings. The use of herbicide in treatments FH and H did not cause a significant increase in growth response. The growth response in treatment FH was not significantly different from the response in treatment F, nor was the growth response in treatment H significantly different from the control. In the 25-yr-old age class the response to fertilization (treatments F and FH) was allocated primarily to the larger trees. Treatments F and FH increased total volume growth (lb) by 48 and 55 ft³/ac/yr, respectively, over control plots while treatment H increased growth by 15 ft³/ac/yr. In the 30-yr-old age class, the response was distributed more evenly among all diameter classes. Treatments F and FH increased total volume growth on average of 58 and 60 ft³/ac/yr, respectively, over control plots while treatment H increased growth by 17 ft³/ac/yr. An economic analysis was performed using discount rates of 8% and 12%, and current prices and costs at the time of the study. Rates of return ranged from 29.6 to 38.8% under various economic scenarios (discount rates, prices and costs) in the 25-yr-old age class. The net present value equivalent to an annual income (EAI) gain for each of the 6 yr of the study ranged from $34.07-$60.54/ac/yr. These same economic scenarios produced rates of return of 23.3 to 31.9% in the 30-yr-old age class, with an EAI range of $18.98-$40.03/ac/yr. South. J. Appl. For. 24(3):166-175.
Document Type: Journal Article
Arthur Temple College of Forestry, P.O. Box 6109 SFA Station, Stephen F. Austin State University, Nacogdoches, TX 75962
Publication date: August 1, 2000
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Each regional journal of applied forestry focuses on research, practice, and techniques targeted to foresters and allied professionals in specific regions of the United States and Canada. The Southern Journal of Applied Forestry covers an area from Virginia and Kentucky south to as far west as Oklahoma and east Texas.