Growth responses of loblolly pine plantations in East Tennessee to various fertilizer treatments

The objective of this study was to determine the growth effects that various fertilizer and cultural treatments had on loblolly pine plantations in East Tennessee. After the growth effects were determined, an economic was conducted to determine if the fertilizer treatments were economically feasible. Two study sites were established in East Tennessee. One site was on the Cumberland Plateau, and the other site was located in the Great Valley of East Tennessee. These two areas represented contrasting climates and stand characteristics. Sixteen treatments were replicated four times on the Plateau site, and 14 treatments were replicated four times on the Valley site. DBH and height were recorded for five years after fertilization. From these measurements, diameter, height, basal area, cubic volume and cords growth were computed. Diameter at 17.3 feet above ground was measured for four years following fertilization in order to determine if fertilization influenced stem-form. Soil textural analyses were made for each site. Tests on soil pH, phosphorus and potassium were conducted before and periodically after fertilization to determine how fertilization would effect the level of these soil properties. Fertilization made no significant difference in stem form although growth at 17.3 feet was greater than growth at 4.5 feet in 99.5 percent of treatment and control plots. K additions did not provide a growth stimulus over that provided by N and P. Nitrogen as urea gave the best results when compared to other N treatments. The urea-N also appeared to provide a stimulus for a longer period of time. It was found that fertilizer application on dry sites provided responses of short duration. Although the urea-N gave the best responses on the Plateau site, ammonium nitrate at the rate of 150 pounds of N per acre gave the best response at the Valley site. Results from thinning treatment at the Valley site indicate that fertilization can stimulate rapid recovery of the volume growth loss that usually follows thinning. An economic analysis was made using response data generated from the study and cost assumptions based on other company operatives and current market prices for fertilizers. At the Plateau site economic feasibility was highest where: (1) N was applied as urea, (2) N-levels were low (75 pounds per acre as ammonium nitrate), and (3) K was not included in the fertilizer application. At the Valley site, economic feasibility was highest where: (1) K was not applied, (2) N was applied at intermediate (150 pounds per acre) to low levels as ammonium nitrate, and (3) P was not included in the fertilizer application.