NEEDLEFALL RETURNS AND RESORPTION RATES OF NUTRIENTS IN YOUNG INTENSIVELY MANAGED SLASH AND LOBLOLLY-PINE STANDS

Annual needlefall (NF) returns and resorption rates of nutrients in 6-yr-old slash (Pinus elliottii Engelm. var. elliottii) and loblolly (P. taeda L.) pine stands were investigated using a 2 x 2 x 2 factorial experiment (species, annual fertilization, sustained competition control) in north central Florida. Compared with the reference (untreated), the combination treatment (annual fertilizer plus competition control) increased NF N returns about 6.3-fold (from 2.5 to 15.8 kg ha(-1)) for slash pine and 13.3-fold (from 1.5 to 19.9 kg ha(-1)) for loblolly pine. Similar treatment effects were found for P, with recycling rates for loblolly pine greater than for slash pine. Absolute resorption rates of N (from 4.7 to 19.9 kg ha(-1) for slash pine; 2.5 to 21.1 kg ha(-1) for loblolly pine) and P (from 0.5 to 1.9 kg ha(-1) for slash pine; 0.2 to 2.4 kg ha(-1) for loblolly pine) increased for both species as management intensity increased (i.e., cultural treatments; reference vs. fertilizer plus competition control). However, specific resorption rates of N and P were lowest for fertilizer treatments. When averaged over all cultural treatments, slash pine resorbed more N (62 vs. 57%) and P (62 vs. 51%) than loblolly pine; approximately 26% of the annual P requirements for slash pine were met by reabsorption compared with 13% for loblolly pine. Nutrient pool size within the plant (uptake) and annual nutrient demands for growth were dominant factors influencing the nature and extent of N and P resorption for both pine species.