Effect of pine needle removal and fertilization on tree growth and soil P availability in a Pinus elliottii Engelm. var. elliottii stand

Pine-needle raking and fertilization effects on tree growth nutrition and s oil inorganic phosphorus availability were examined in a 13-year-old slash pine (Pinus elliottii Engelm. var. elliottii) stand in Clay County, Florida . Fertilized and nonfertilized treatments were applied to main plots. Sixte en of the 32 plots were unfertilized, while the remaining 16 plots received fertilizer application with 280 kg ha diammonium phosphate (DAP) in August 1991 and again in September 1992. Four raking frequency treatments: no rak ing; rake-every-year; rake-every-2-years: and rake-every-4-years were appli ed to split-plots within these main plots. Diameter at breast height and tr ee heights were measured annually from 1991 to 1995. Raking every-year trea tment significantly reduced diameter growth by 5.2 mm. Fertilizer had a sig nificant negative effect on tree heights; nonfertilized trees in the stand grew more than fertilized trees in all diameter classes. Annual needlefall production rare was 8735 kg ha(-1) with a maximum of 50 kg N ha(-1) and 5 k g P ha(-1) removed through litter raking. During 1 year, a maximum yield of 737, 934, and 1093 bales/ha were produced in the rake-every-year, every-2, and every-4-year plots. N and P concentration in the raked needles was 0.5 9 and 0.052%. respectively. Needlefall P concentration was significantly lo wer among trees raked more frequently. Fertilizer significantly increased n eedlefall N concentration. Availability of soil inorganic phosphorus detect ed by anion-exchange membranes was significantly higher in the plots raked every-4-years followed by the control compared to the plots that were raked every-year. These results indicate that removal of pine needles does not h ave an immediate effect on old-field sites with high residual fertility, bu t removing 50 kg ha(-1) of N and 5 kg ha(-1) of P annually may eventually d eplete the site. (C) 2001 Elsevier Science B.V. All rights reserved.