Aust. J. Soil Res., 2001, 39, 1443–1451

The Australian soil texture boomerang: a comparison of the Australian and USDA/FAO soil particle-size classification systems Budiman Minasny and Alex. B. McBratney Department of Agricultural Chemistry and Soil Science, The University of Sydney, Ross St. Building A03, NSW 2006, Australia.

Abstract 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 µm, while the USDA/ FAO define it as 2–50 µm. 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. Additional keywords: particle size distribution, soil texture class, classification. BSR. M0ina6s5n,yA. B. McBrateny BSh. MrointaCsonmynaudicABaito.nMcBratney

Introduction Various pedotransfer functions for predicting soil physical and chemical properties have been developed. Cresswell and McKenzie (2000) developed a computer program for predicting soil hydraulic properties of Australian soil. However, 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. Nemes et al. (1999a) encountered this problem when evaluating different textural classes used in various European countries (Fig. 1). There are 2 major textural classifications used in the world—the International and the USDA/FAO systems. The particle-size limits are: International clay