STUDIES IN PEDOGENESIS IN NEW SOUTH WALES

Abstract

Summary A field and laboratory examination has been made of the soils of the Pilliga district of New South Wales, with particular reference to those showing solonetzic morphology. The area consists largely of alluvium from the Jurassic sandstones of the Warrumbungle Range, and grading diagrams for the sandfraction suggest that distribution of the soils follows the changes in depositional pattern. It seems probable that a soil type can occur, morphologically and chemically similar to that which has been described as solodized-solonetz without ever having been through the stages of solontchak and solonetz. The conditions under which such a profile could develop are: (a) a semi-arid to sub-humid climate, where the mean soil temperature is too high to permit either accumulation of organic matter or the long persistence in the groundwater of organic compounds capable of chelation; (b) a parent material sufficiently coarse textured to allow movement of clay and of fine silt simply by the mechanical action of percolating water, but not so coarse that the clay is washed completely out of the column; (c) a parent material extremely low in calcium-bearing minerals. This condition would obviously be met when the parent material of the present soil was part of a fossil profile formed in a humid or strongly leaching environment; (d) the presence of vegetation capable of absorbing silica from the soil water and returning it to the surface in leaf fall in a sufficiently finely divided form; (e) a source of sodium ions. The solodized-solonetz could consequently be considered as the normal soil found on coarse-textured parent material in the semi-arid to sub-humid zone of the warm temperate and sub-tropical areas.