ORGANIC-C AND NUTRIENTS IN SURFACE SOILS FROM SOME PRIMARY RAIN-FORESTS, DERIVED GRASSLANDS AND SECONDARY RAIN-FORESTS ON THE ATHERTON TABLELAND IN NORTH-EAST QUEENSLAND

Some long term effects of (a) converting rainforest to grassland, and (b) rainforest regeneration on cleared land were investigated by compa ring chemical properties of mineral soil (0-10 cm depth) from beneath primary rainforest, derived grassland and old secondary rainforest. Gr asslands and secondary rainforest. were on land cleared at least 50 ye ars ago. The study was undertaken on the Atherton Tableland in north e ast Queensland using soils formed on basalt, granite and metamorphic r ocks. Organic C, kjeldahl N and labile N were 15-50% lower (P < 0.05) beneath grassland than primary rainforest for all soils, and were high er beneath secondary rainforest than grassland. Exchangeable Ca varied in a similar way in basaltic soils but did not differ between vegetat ion types in the other soils. Extractable Al was lower under grassland than either forest type for soils formed on granite and metamorphic r ock. Total and organic P concentrations did not differ between primary forest and grassland, but were lowest under secondary rainforest for soils on metamorphic rock.