Impact of Rainfall On Crust Formation and Properties for Loamy Soils In a Semiarid Region.

Soil surface crusting due to the action of rainfall and rapid drying is a common process in many soils around the world, particularly in arid and semi-arid regions where soils are light, poorly structured and low in organic matter. Soil crust formation has both adverse and beneficial impacts on agricultural production and environmental quality. Crusts can impede seedling emergence, reduce infiltration, increase runoff and the potential for soil water erosion,  and reduce soil wind erosion. The objective of this study was to evaluate the effect of rainfall and soil properties on surface crust properties and characterize their quantitative relationships for loessial soils on the Columbia Plateau. A rainfall simulator that delivered rainfall at 2 mm/hr was used to simulate low-intensity, small-drop-size rains that are typical of the region. Soil samples from the upper 3 cm of the profile were collected from five major soil types across the region. Dispersed and nondispersed particle and aggregate size fractions of the samples were respectively measured using a laser diffraction instrument and sonic sieve. Soils were dried, passed through a 2-mm sieve and placed on four trays under the rainfall simulator. Crust thickness and strength as affected by 0.15, 0.3, 0.6 and 1 mm of cumulative rainfall were measured by the use of a ruler and penetrometer. Both crust thickness and strength of all soils increased with more rain.  Crust thickness was same for all soils for each rainfall treatment. . Crust strength varied by soil type and cumulative rainfall. Under low rainfall (0.15 to 0.3 mm), crust strength decreased in the following order: Walla Walla silt loam,  Athena and Palouse silt loam and Ritzville silt loam and Warden sandy loam. For a 1 mm rain, crust strength decreased in order: Palouse silt loam, Warden sandy loam, Walla Walla silt loam, Athena silt loam, and Ritzville silt loam. Crust strength was related to clay and silt content of the soils and appears to be dependent on the physico-chemical dispersion of fine particles that clog pores beneath the soil surface.