Krasnozems - a profile

Abstract

Since the first soil map of Australia by Prescott in 1931, acid red soils developed from basalt have been specifically recognized in spite of their very limited area of occurrence in eastern Australia from North Queensland to Tasmania in a rainfall zone of about 1000 to 4000 mm. Until the early 1950s these soils were known as red loams, but the term krasnozem became formalised in 1953 with the publication of Stephen's Manual of Australian Soils. Over the past 40 years, these soils have been extensively studied because their favourable agronomic properties have led to intensive land use. The krasnozems are red to brown, acid, strongly structured clay soils (50-70% clay) ranging in depth from less than 1 m to over 7 m. Their clay mineralogy is dominated by kaolin and iron and aluminium oxides, and this ensures that the soils have variable charge properties with low cation exchange capacity and usually a significant anion exchange capacity. Free iron oxide contents range from about 7 to 18% Fe. Red basalt-derived soils occur in a number of other countries, and the 'typical' Russian krasnozems appear to have similar mineralogical and chemical properties but apparently lack the characteristic strong polyhedral structure of the Australian soils and are only about one metre deep. The Australian krasnozems are mostly classified as Oxisols in Soil Taxonomy and Ferralsols in the FAO-Unesco scheme. In the new Australian classification they are classed as Ferrosols and a more specific definition and subdivision of this class into lower categories is given, together with their relationship to morphologically similar soils.