Windblown soil crust formation under light rainfall in a semiarid region

Abstract

Many soils in arid and semi-arid regions of the world are affected by crusting, a process by which a compact layer or thin mantle of consolidated material is formed at the soil surface. Crusts can increase the resiliency of the soil to wind erosion, but characterization of soil crust formation to light precipitation events common to the Columbia Plateau region of the Inland Pacific Northwest is unknown. Our objective was to evaluate the effect of light rainfall events on crust formation of five soil types prominent in the Columbia Plateau. The five soils were Athena silt loam, Palouse silt loam, Ritzville silt loam, Walla Walla silt loam, and Warden sandy loam. Soil crusts were formed in the laboratory using a rainfall simulator that applied water at a rate of 2.5mm h−1 for various durations to achieve a total rainfall application of 0, 0.15, 0.30, 0.60 and 1.0mm. Crust strength was measured by a penetrometer while crust thickness was measured by a ruler. Silt and clay content of the five soils ranged from 23 to 66% and from 9 to 17%, respectively. An increase in crust thickness and strength was observed with an increase in rainfall for all soils. Crust thickness was similar among the soils whereas crust strength varied among soils at any given level of rainfall. For example, crust strength of soils when subject to 0.15–0.60mm of rainfall decreased in order of Walla Walla>Athena and Palouse>Ritzville and Warden. These results are consistent with a decreasing order of clay and silt contents. The strongest crust was formed on Palouse silt loam under the highest rainfall amount. A logarithm relationship adequately described the relationship between crust thickness and rainfall for the five soils (r2=1.00). This relationship over-predicted crust thickness based upon observations in the field, but performed better than the algorithm used by the Wind Erosion Prediction System.