The Australian soil texture boomerang: a comparison of the Australian and USDA/FAO soil particle-size classification systems

The different classification of particle-size fractions used in Australia compared with other countries presents a problem for the immediate adoption of the exotic pedotransfer functions. Australia adopted the international system which defined silt as particles with diameters in the range 2–20 m, while the USDA/FAO define it as 2–50 m. We present empirical equations to convert between the two systems. The USDA/FAO textural classes were also plotted in the International system’s coordinate. The USDA/FAO classes in the International system had a ‘boomerang’ shape and only occupy 60% of the triangle. Particle-size data showed that the data are evenly distributed in the USDA/FAO triangle, while most data are concentrated in the boomerang in the International system. We therefore suggest that it would seem wise for most countries to consider adopting the particle-size limits and texture classes of the USDA/FAO system.