Recent interest in fertilization of forest soils has pointed up the need for improvements in investigational techniques in the field. Since methods developed for agronomic research often have little application to forestry, a series of experiments were conducted in slash pine plantations to check experimental technique. P32 measurements indicated 2-, 3-, and 5-year-old pine trees may feed out to about 19, 25 and 32 feet, respectively, on sandy soil. Root grafting, as determined by the use of P32, appeared to occur in trees 5 years or more in age. The size of plots depends upon the anticipated extent of the root system at the finish of the experiment. At least 30 trees should be included for measurements, with borders to prevent cross-feeding. Except for experiments to be conducted for short periods on young trees, individual plots should be about ¼ to ½ acre in size.
Depth of feeding, method of fertilizer application, and season of application are discussed. Care must be exercised when applying fertilizer at time of transplanting to prevent burn. Concentrations exceeding the equivalent of 300 pounds of soluble nitrogen (N) or potash (K2O) per acre may result in reduced growth and stand of newly planted pine on sandy soil. It appears that fertilization should be delayed at least 1 year after transplanting in order to reduce the danger of burning, leaching losses, and competition from weeds.