Response of Semimature Slash and Loblolly Pine Plantations to Fertilization with Nitrogen and Phosphorus

Field trials to measure the response of semimature slash pine ( Pinus elliottii var. elliottii Engelm. ) and loblolly pine ( Pinus taeda L.) in the southeastern U. S. lower coastal plain were established between 1968 and 1970 at 32 locations. Treatments consisted of N at 0, 55, 110, and 220 kg/ha, and P at 0 and 55 kg/ha in a complete factorial arrangement. Grouping sites on the basis of soil drainage class and depth to and nature of the B horizon served as an efficient way to interpret response to fertilization. After 8 years stands on most soils exhibited moderate to large volume gains when fertilized with N and P. Stands on wet soils with clay near the surface responded favorably to the addition of P alone.