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New Zealand Journal of Forestry (1965) 10(1): 33–42
©New Zealand Institute of Forestry

Research article
Increased Phosphorus Uptake by Radiata Pine in Riverhead Forest following Superphosphate Applications

G.M. Will

One ton of superphosphate per acre applied to phosphate-deficient stands in Riverhead Forest resulted in higher concentrations of P in the foliage, bark, and sapwood. In the living bark, levels of N, K, and Mg also increased. Eight years after treatment the rejuvenated stand and litter layer contained an estimated extra 25 to 30 lb per acre of P (equivalent to 2Vi to 3 cwt of superphosphate).
Severely checked stands in this forest that are markedly deficient in phosphorus appear to require between a half and one ton of superphosphate per acre to enable them to make vigorous growth. Smaller amounts are probably sufficient where stands have not degenerated to the stage of dead tops and greatly reduced canopy.
The foliage P content of radiata pine is a good indicator of the adequacy of the P supply. Analyses of samples from a number of forests show that the critical level is about 0.11% of the oven-dry weight.

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