To B and not B2 – the Australian soil horizon system: history and review

Abstract

Soil horizon designation plays a key role in the communication of information about soils – hence the need for uniformity, consistency and clarity in the way soil horizons are defined and designated. Since its establishment in the late 19th century, the A-B-C schema for soil horizons has evolved with the realisation that traditional concepts of soil genesis embedded in the original system do not fit the breadth of current knowledge regarding soil development. Along with a more objective approach, there has been progress toward harmonisation, with considerable agreement between the two major international systems: FAO and USDA. Both use an A-E-B-C-R schema for mineral soil horizons, coupled with the prescriptive use of alphabetic suffixes. This schema is now adopted almost universally – Australia alone has retained the once widespread system of numerically designated horizons, first codified in the USA in 1937. The A1-A2-A3-B1-B2-B3-C-D-R schema for mineral horizons can therefore be regarded as the ‘Australian system’. Australia is also unique in the way it designates organic soil horizons. This review summarises the history of soil horizon designation and critically appraises the Australian system. It identifies ambiguity and inconsistency in the definition and allocation of horizons, and demonstrates that soil horizon notation in Australia is convoluted and complex. Pedology in Australia would benefit by aligning with international approaches including a simpler set of objectively defined master horizons, rationalised intergrade horizons and the more rigorous application of alphabetic suffixes. This would improve both the communication of soil profile information and the utility of soil databases.