Soil chemical properties under eucalypt forest and radiata pine plantations on coastal sands.  P. Hopmans, D. W. Flinn and R. O. Squire.  December 1977.  9 pp. (unpubl.)

SUMMARY

This study compares chemical properties of relatively infertile coastal sands under native eucalypt forest and mature plantations of Pinus radiata D. Don in south-western Victoria. Composite soil samples were collected from the A1, A2 and A3 horizons of six 0.65 ha plots established in 27 year-old P. radiata stands of low and high site quality and of eighteen 0.1 ha plots located in native forest. The soil samples were analysed for pH, organic matter, exchangeable cations, water soluble phosphorus, Kjeldahl nitrogen, and total phosphorus, aluminium and iron.

Soils under both eucalypt and pine were found to be extremely low in organic matter, Kjeldahl nitrogen and exchangeable cations with the exception of calcium. Total soil phosphorus under eucalypt was very low and predominantly present as calcium complexes; consequently the water soluble phosphorus fraction was relatively high. Soils under pine was significantly higher in Kjeldahl nitrogen, water soluble phosphorus and exchangeable aluminium, magnesium and potassium, and lower values for pH and total iron were found for the high quality sites compared with the low quality sites. Total soil phosphorus under pine was predominately present as aluminium complexes and this possibly accounted for the low levels of water soluble phosphorus found under pine.

Soils under pine were found to be higher in total phosphorus, aluminium and iron than those under eucalypt and this was attributed to natural soil variation. There was some evidence for depletion of phosphorus and exchangeable calcium and magnesium from the A1 horizon under pine. However, the influence of pines on soil properties after one rotation appeared to be slight and not detrimental to site productivity.

The infertile nature of these coastal sands combined with extremely low organic matter levels makes it imperative to conserve soil nutrients. Ideally, some of the nutrients removed in harvesting of the P. radiata should be replaced to ensure maintenance of long-term site productivity. In addition practises that destroy organic matter such as burning should be avoided.

Also published:

Hopmans, P., Flinn, D.W. and Squire, R.O. (1979)  Soil chemical properties under eucalypt forest and radiata pine plantations on coastal sands.  For. Comm. Vic., For. Tech. Pap. 27: 15-20.