Soil Crusting and Some Factors Affecting It

Abstract

Physical studies were made of natural soil crusts and of the soils beneath them. Artificial crusts (briquets) were prepared by several methods and their modulus of rupture and bulk density were determined. The natural crusts had a much greater bulk density, a higher percentage of particles < 0.10 mm. in diameter, and a lower degree of aggregation than the underlying soil. The modulus of rupture of artificial crusts was increased by longer periods of drying at 105°C.; by slow drying (using lower temperatures); by compacting the dry soil in the briquet molds; by the beating effect of raindrops; and by puddling the soil before putting it into the molds. It was decreased by successive wetting and drying, but partial drying and rewetting gave results which varied with different soils. High modulus of rupture values were obtained with soils containing large amounts of soilt or total material < 0.10 mm. and, 2:1 type clay. Bulk densities were essentially the same: (a) for dry soil used in preparing briquets and the same type of soil beneath natural crusts in the field; and (b) for artificially prepared briquets and natural soil crusts.

Comparative Structure of Physical and Biological Soil Crusts

“…Compressional forces, such as those generated by machinery or hooves of grazing animals, can also destroy soil aggregate structure and cause a physical soil crust (Lemos and Lutz 1957). Trampling compacts the soil aggregates into a comparatively impermeable surface layer, especially when soils are moist.…”

“…Physical crusts may form on soils of almost any texture except coarse sandy soils that contain very low silt and clay (Lemos and Lutz 1957). Soils especially susceptible to physical crusting are those with low structural and aggregate stability, including those with low organic matter, high silt, and/or high salt (e.g., sodium or calcium carbonates).…”

Composition and Macrostructure of Biological Soil Crusts

“…There are three types of physical crusts: (1) structural crusts, formed by rearrangement of soil particles without lateral movement; (2) depositional crusts that develop as a consequence of lateral movement of sediment (Chen et al 1980); and (3) erosional crusts, which are comprised of only one thin, smooth surface layer that is enriched in fine soil particles and which results from the erosion of a structural crust (Valentin and Bresson 1992). While chemical crusts are restricted to areas with high evaporation, physical crusts can occur in various environments and in almost all textures, except on very coarse sandy soils (Lemos and Lutz 1957).…”

A Field Guide to Biological Soil Crusts of Western U.S. DrylandsA Field Guide to Biological Soil Crusts of Western U.S. Drylands

“…Physical crusts may form on soil of almost any texture except coarse sandy soils containing very low silt and clay (Lemos and Lutz 1957). Soils especially susceptible to crusting are those with low organic matter and high silt, sodium, or calcium carbonate content.…”