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United States Department of Agriculture

Agricultural Research Service

Title: Crusts/structural

Authors
item Baumhardt, Roland
item Schwartz, Robert

Submitted to: Encyclopedia of Soils in the Environment
Publication Type: Other
Publication Acceptance Date: March 5, 2004
Publication Date: October 15, 2004
Citation: Baumhardt, R.L., Schwartz, R.C. 2004. Crusts/Structural. In: Hillel, D., editor. Encyclopedia of Soils in the Environment. Oxford, UK: Elsevier Press. p. 347-356.

Interpretive Summary: Many factors contributing to soil productivity such as supplying crop nutrient and water needs are governed at the soil surface. That is, movement of water and nutrients into the underlying bulk soil often must penetrate through a thin surface layer called a 'crust.' Crusts occur as biological or physical surface layers. Biotic, i.e., biological soil crusts are 10 to 100 mm thick microbial plant communities that develop on semiarid and arid soils, which remain undisturbed for decades. Physical soil crusts develop because of both raindrop impact and aggregate dispersion to form, in minutes, a 0.1 to 10 mm surface layer that is less porous or conductive than the underlying bulk soil. Soil crusts reduce infiltration that can cause runoff and water erosion of soil. Also, physical soil crusts impede emerging crop seedlings and reduce plant stand density and seedling vigor. The impact of this thin surface layer on hydrologic processes and agronomic practices has stimulated much research on physical soil crusts. These studies link soil mineralogy, physical properties, and the interacting soil and water chemical conditions to crust formation and effective management practices. One of the most practical and effective crust management strategies is to use crop residues to intercept raindrop impact.

Technical Abstract: Many of the processes defining soil productivity such as supplying crop nutrient and water needs are governed at the soil-atmosphere interface. That is, physical or transport limitations within a thin surface layer overlying the bulk soil govern various fundamental hydrologic and biologic processes. This modified surface layer is called a 'crust.' Soil crusts occur as physical or biological, 'Biotic', surface layers. Biotic soil crusts are 10 to 100 mm thick microbial plant communities that usually develop on semiarid and arid soils, which remain undisturbed for periods of decades. In contrast, physical soil crusts develop in response to a combination of raindrop impact and aggregate dispersion to rapidly form, in minutes, a 0.1 to 10 mm surface layer that is less porous or conductive than the underlying bulk soil. Soil crusts typically reduce infiltration, thus causing runoff and water erosion of soil. Additionally, physical soil crusts can impede emerging crop seedlings and reduce plant stand density and seedling vigor. The impact of this thin surface layer on hydrologic processes and agronomic practices has stimulated extensive investigation of physical soil crusts. These investigations link soil mineralogy, physical properties, and the interacting soil and water chemical conditions to formation and effective management practices. Physical crust formation is often reduced by management practices that retain crop residues at the soil surface to intercept raindrop impact.

Last Modified: 12/28/2014
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