Here's a recent study on the use of Biochar in a category of tropical soils known as
Ferralsols in some quarters and
Oxisols elsewhere.
The results are mixed. Note that conclusions based on Ferralsols have little or no application to soils in the majority of the U.S. and Canada but might help some members in tropical regions.
Effect of biochar, lime, and compost application on phosphorus adsorption in a Ferralsol