Response of radiata pine to fertilisers containing N and P applied at planting

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Abstract
A field experiment is described which evaluates the early growth response of Pinus radiata to four levels each of N (as ammonium sulphate at 0, 34, 68 and 136 g/tree) and P (as superphosphate at 0, 113, 226 and 452 g/tree) applied at planting on sites prepared by ploughing followed by ripping. The experiment was undertaken at four sites which covered a wide range of native vegetation types within a 15 km2 area of the Neerim East plantation extension area located 100 km east of Melbourne. Each site was considered to be P deficient on the basis of soil tests. Early growth was found to be significantly affected by P, site and a P x site interaction. All sites were recolonised by a wide range of native species which had an above-ground biomass of 3720 to 6570 kg/ha depending on the site and contained only 1.3 to 2.6 kg/ha P three years after planting. Growth response to P was marked at two sites but only moderate at the others, despite the occurrence of P deficiency symptoms and low foliar P levels in unfertilised trees at all sites. Differences in P response between sites is likely to be due to the demand by weeds for soil moisture rather than demand for P. The work showed growth response to the application of P soon after planting but no response to N, indicating that the use of NP fertilisers cannot be justified in the absence of chemical weed control on sites similar to those investigated.