C Corresponding author on soil and geomorphological issues; email: wverboom@agric.wa.gov.au D Corresponding author on botanical issues.Abstract. This communication presents the hypothesis that certain Australian lateritic and related oligotrophic soils may have been partly derived biotically from soluble iron-rich complexes generated following secretion of lowmolecular weight organic acids by phosphate-absorbing specialised proteoid (cluster) roots of proteaceous plants. Subsequent precipitation of the iron is then pictured as occurring onto the oxide rinds of developing laterite after consumption of the organic components of the complexes by soil bacteria. The hypothesis is first examined in relation to current theories of origins of laterites and the extent of the coincidences worldwide in past and present times between Proteaceae and oligotrophic soil types of lateritic character. The paper then provides more definitive lines of evidence supporting the hypothesis, based largely on recent studies by the authors in south-western Western Australia. This relates to (a) cases of definitive association in habitats rich in Proteaceae between zones of root proliferation and ferricrete layers in lateritic soils, (b) proximity in soil profiles between ferric deposits and current and ancestral root channels, (c) the recovery of citrate-consuming bacteria from soil profiles and specifically from ferricrete rinds and horizons accumulating sesquioxide organic matter and (d) distribution of iron and phosphorus within plant and soil profile components consistent with ferricrete rinds being generated by rhizosphere-mediated interactions of plants and microbes under conditions of severely limited availability of phosphorus. The mode of functioning of proteoid root clusters is then discussed, especially in relation to exudation of organic acid anions, uptake of phosphorus and the subsequent fate of organic anions and their metal ion complexes in the system. An empirically based scheme is presented indicating flow profiles for phosphorus and iron between soil, ferricrete rinds and bacterial and plant components. We then discuss possible carbon costs to proteaceous plant partners when accessing phosphorus under the nutrient-impoverished conditions typical of heathlands and open woodlands of Mediterranean-type ecosystems of Western Australia. The paper concludes with a critical overview of the hypothesis, particularly its implications regarding possible higher plant: microbial influences shaping soil and landscape evolution in the regions involved. J . S . P a t e , W . H . V e r b o o m a n d P . D . G a l l o w a y B T 0 0 0 8 6 I n t e r r e l a t i o n s h i p s b e t w e e n P r o t e a c e a e a n d l a t e r i t e s J . S . P a t e e t a l . e t a l .

A procedure for the rapid and accurate mapping of the depth to the texture contrast horizon of duplex soils was trialled. Data were collected using ground-penetrating radar with a 250 MHz antenna at 4 sites in the Esperance region of Western Australia. The contrast at the B horizon was identified using a ‘picking’ process similar to seismic surveys. The GPS data were integrated and depth to B horizon maps produced by kriging. The results were related to core data taken for sites and showed that GPR can provide accurate and detailed subsurface maps with ±0.1 m accuracy for B horizon depth. The influence of B horizon material composition on GPR response was also investigated using amplitude mapping. The spacing between GPR transects can affect map quality, particularly if the lateral variation in the B horizon depth is not adequately sampled by the line spacing selected. With further integration of the data collection and post-processing procedures, this would prove to be a useful tool for farmers and natural resource managers.

It appears from the tests performed that the first method given is the more sensitive and is less liable to interference from accelerators.