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New Zealand Journal of Forestry (1968) 13(1): 50–65
©New Zealand Institute of Forestry

Research article
Pumice Soils as a medium for Tree Growth: Part 2 - Pot Trial Evaluation of Nutrient Supply

G.M. Will and P.J. Knight

In the six major layers of a pumice soil prople, crops of Pinus radiata seedlings were grown in each of four successive growing seasons. Each layer's ability to supply N, P, K, Mg, and Ca was evaluated by supplying the others in fertilizer additions. The roots and shoots of each crop were harvested and analysed to obtain nutrient concentrations and total uptake.

The uptakes of N and P were very small from all layers except the topsoil. While there was a steady supply of N from the topsoil, the uptake of P decreased with time. The three layers of Taupo pumice found immediately beneath the topsoil contained good supplies of K but only low levels of Mg. In contrast, a buried topsoil now found at a depth of 8 ft proved to have a limited supply of K but was a good source of Mg.

When the removal of nutrients in forest produce is considered in relation to the supplies available in the soil, it is apparent that supplies of K and Ca are ample for several crops but N, P and Mg deficiencies can be expected to restrict growth within the next two crops unless additional supplies become available from such sources as atmospheric precipitation, the fixation of nitrogen and soil weathering.

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