An Examination of a Pinus radiata Phosphate Fertilizer Trial Fifteen Years after Treatment

An experiment testing equal rates of application of P from rock phosphate and superphosphate sources on an 8-year-old stand of Pinus radiata (D. Don), has been examined for its nutrient status at 23 years of age. P has been accounted by fractionation and shows that the distribution of Ca-, Al-, and Fe- phosphates has been influenced by the source material used. Superphosphate has shown a strong tendency to become Al- phosphate in the soil while Ca- phosphate has maintained its status in the rock phosphate treatments. The production of the forest stand has been equivalent from each source of P, and much superior to the control. Stand diameter distribution is not of the same type under the two P treatments. A highly significant correlation ( r = 0.75) exists between log. foliar P and sample tree height and a better correlation ( r = 0.91) between log, total foliar cations (Al 3+ , Ca 2+ , Mg 2+ , K + , N a+ , Fe 3+ ) and sample tree height. Exchangeable Al 2+ has been reduced significantly by both treatments.