Continuing growth response to phosphate fertilizers by a Pinus radiata plantation over fifty years

The period of growth response of forest plantations to phosphate fertilizer applications has been variable and difficult to predict. Significant growth responses by Pinus radiata (D. Don) to two different phosphate fertilizers, superphosphate and rock phosphate applied at 96 kg P ha -1 (previously reported by the authors) have continued for the 50 yr period since the fertilizers were initially applied in 1947. There have been no further fertilizer applications. At the end of the second rotation of 33 yr (50 yr after the fertilizer was applied), the growth and biomass of the trees were determined, together with soil and foliage chemical analyses, and comparisons made with those obtained earlier. The standing volume of the phosphate treatments was 430 m 3 ha -1 , an increase of 50% over the 287 m 3 ha -1 in the untreated control. Soil total phosphorus concentrations were increased from 64 mg kg -1 in the control to 105 mg kg -1 and 134 mg kg -1 in the superphosphate and rock phosphate treatments, respectively, and have remained constant. The aboveground blomass of the treated plots was about 380 tonne ha -1 compared with 278 tonne ha -1 in the control. The single application of phosphorus has led to a significant change in site characteristics. The implications for forest management are that a relatively low application of fertilizer on some nutritionally poor sites changes the productive capacity of the site. For. Sci. 48(3):556-568.