Long-Term Growth Responses To Phosphatic Fertilisers In A Pinus Radiata Plantation

The effects of phosphatic fertiliser on growth and nutrients in trials at different stages of stand development have been studied in second-rotation Pinus radiata plantation sites of Lidsdale State Forest, New South Wales. The sites were on phosphorus-deficient clay soils. High, early growth responses to phosphatic fertiliser occurred when applied to individual trees at the time of planting compared with slower initial growth when fertiliser was broadcast applied. There were long-term responses to broadcast treatments of phosphorus or nitrogen/phosphorus at time of planting, but it took several growing seasons for the trees to access the applied phosphorus. Later-age applications of phosphorus also gave significant responses with and without nitrogen and the level of response was related to the prior nutritional status of the stand. There were additional responses to high levels of nitrogen when the initial phosphorus deficiency was overcome. Application of phosphorus or nitrogen/phosphorus after thinning resulted in significant increases in growth. Combining trial results and assuming treatments were additive, it was concluded that productivity could be increased from 8m(3) ha(-1) y(-1) to about 16m(3) ha(-1) y(-1) over 24years. The trials show there could be a range of nutritional management strategies where fertilisers are applied at various times in the rotation process and the appropriate one would be selected in terms of management objective, the cost and outcomes.