Micromorphology and significance of the surface crusts of soils in rangelands near Cobar, Australia

• Published in: Geoderma Vol. 42; no. 3; pp. 227 - 244
• Main Authors: Mücher, H.J., Chartres, C.J., Tongway, D.J., Greene, R.S.B.
• Format: Journal Article
• Language: English
• Published: Amsterdam Elsevier B.V 01.08.1988; Elsevier
• Subjects: Agronomy. Soil science and plant productions; AUSTRALIA; AUSTRALIE; Biological and medical sciences; CARACT MORFOLOGICAS (SUELOS); Earth sciences; Earth, ocean, space; Exact sciences and technology; Fundamental and applied biological sciences. Psychology; General agronomy. Plant production; Soil erosion, conservation, land management and development; SOIL MORPHOLOGICAL FEATURES; Soil science; Soil-plant relationships. Soil fertility; Soil-plant relationships. Soil fertility. Fertilization. Amendments; Soils; Surficial geology; TRAIT MORPHOLOGIQUE DU SOL; Rain erosion; New South Wales; Soil erosion; Australasia; Calcrete; Horizons; Vegetation effect; Oceania; Bioturbation; Soils; Ground surface; Vegetation; Rangeland; Australia; Soil plant relation; Micromorphology
• ISSN: 0016-7061; 1872-6259
• DOI: 10.1016/0016-7061(88)90003-1

Micromorphological observations were made on thin sections of surface crusts from the uppermost 50 mm of red earths near Cobar, New South Wales. Samples were collected to represent six classes of surface conditions important to plant growth. The crusts consisted of an upper zone comprising cryptogamic mats, litter and transported soil aggregates, and a lower zone of layers of generally laminated sands, silts and clays. Crusts from class 1 surfaces which showed little evidence of erosion, were loosely structured, bioturbated and lacked sealing properties. Crusts from classes 2 to 4, in which erosion was increasingly evident, contained decreasing proportions of cryptogams, exhibited decreasing evidence of bioturbation and increasing proportions of platy and sealing structures. Crusts from class 5, found in areas of marked colluvial deposition, had a wide range of properties, whereas crusts from class 6 consisted primarily of litter deposited under trees. The major processes responsible for crust formation are considered to be a combination of erosion by raindrop impact, redeposition by rainwash and colonisation by cryptogams. Micromorphological properties of the crusts are believed to affect lodgement and germination of seeds and the infiltration and runoff of water, thereby influencing plant growth. Dry matter production ranged from 2.3 t ha −1 on soils with class 1 surfaces to 0.1 t ha −1 on soils with class 4 surfaces. Cryptogam mats also afford protection of the underlying materials from erosion and also promote aggregation. Cryptogams are therefore considered highly desirable components of the crusts.