Farmers don't apply rock phosphate. They apply phosphorous in...

Farmers don't apply rock phosphate. They apply phosphorous in the form of MAP, DAP or superphosphate, or similar. They can apply reactive phosphate rock but this is only useful on acid soils so completely useless on the millions of ha of alkaline riverine soils in Australia. To my knowledge Wonarah doesn't have the solubility to be termed reactive so will be used to make conventional fertilisers like MAP and DAP.

The only way that P can be used in carbon trading is to increase soil organic carbon by improving productivity. The issue with that is that you need to add the additional emissions from legume residues and animals which means you get sweet FA in carbon credits. It isn't a profitable way of getting carbon credits.