Studies on some neutral red duplex soils (Dr 2.12) in north-eastern Queensland. 3. Availability of phosphorus in the C-horizon

Abstract

The C horizon phosphorus in neutral red duplex soils derived from granodiorite is shown by electron microprobe analysis to be present as coarse grains of apatite. Glasshouse experiments failed to show any contribution from this phosphorus to the nutrition of the test crops (Townsville stylo Stylosanthes humilis and green panic Panicum maximum). Since this phosphorus is soluble in 0.01 N H2SO4, this extractant grossly overestimated the available phosphorus status whereas extraction with 0.5 M NaHCO3 indicated the non-availability of the C horizon phosphorus in these soils.