The influence of Pinus radiata, Quercus suber, and improved pasture on soil chemical properties

Soil acidification and related land degradation issues are assumingincreasing importance in Australia and challenging the concept ofsustainability of current land management systems. In this study, theimpacts of tree plantations of 2 species and permanent pasture on soilchemical properties are compared. Soil samples were collected from thetop 50 cm (0-5, 5-10, 10-15, 15-20, 20-30, and 30-50 cm depths) from 3adjacent sites carrying pasture and monocultures of Pinus radiata(radiata pine) and Quercus suber (cork oak) on a deep-surfaced yellowpodzolic soil, and differences in soil pH and other soil chemicalproperties were examined. In the surface 0-5 cm, pH was similar at all 3sites. Below that depth, soil pH was significantly lower andexchangeable Al greater under the cork oak stand than at the other 2sites. Consistent with a decrease in soil pH there was significantlyless exchangeable Ca under cork oak. Also, less clay was observed underthe cork oak stand and this is taken as evidence of the degradationalimpact of soil acidification.An estimate of Ca in the top 50 cm of the soil implies considerable lossof Ca under oak, probably by leaching and loss of litter down the slope.Evidence is presented to show that there has been more Fe and Almovement under oak than under pasture and pine, this being ascribed inpart to the greater Al and Fe mobilising capacity of the water-solublecomponent extracted from freshly fallen leaf litter of oak. The Fe andAl composition of the oxalate extract from concretionary material at10-30 cm under oak is consistent with a process similar topodzolisation. Pseudogleying of Fe and Al may have accompanied theleaching of bases from the system and a reduction of pH.