LEACHING OF INORGANIC PHOSPHORUS FROM LITTER OF SOUTHERN PINE PLANTATIONS

A study was conducted to quantify leachable nutrients in needles of the litter layer of intensively managed southern pine plantations. The study site used for sampling of litter was a 2 x 2 x 2 factorial (three replicates) of species (slash [Pinus elliottii Engelm. var elliottii] and loblolly [P. taeda L.] pines), weed control (with or without complete and sustained weed control) and fertilizer application (with or without annual applications of essential elements). Fresh, intact needles collected in September and December 1989 and in March 1990 were soaked in distilled water (4-degrees-C, pH 4.9) for 5 d and measured for pools of soluble inorganic and organic P and N. Of these nutrients, only inorganic P (P(i)) was detected in leachates. About 5 and 15% of the total P content was leached from Oi horizon needles in nonfertilized and fertilized plots, respectively. Because fertilizer application also doubled the total P content of Oi horizon needles, direct leaching losses will be important only in plots amended by fertilizer. A 5-d time-course experiment demonstrated that P(i) was continuously leached from Oi horizon needles of the combination treatment, whereas the small amounts of P(i) available for leaching in the Oe1 and Oe2 horizon needles were extracted immediately. In fertilizer-amended plots, at least, the Oi horizon provides the majority of potentially leachable P(i).