Crust Formation Effects on Soil Erosion Processes

Abstract

AbstractSoil seals and crusts reduce soil infiltration rates and increase soil strength. How they affect the erosion process is not entirely clear. Effects of soil crusts at different stages of formation on soil erosion processes were analyzed and presented within the context of a model that divides crust formation into pre‐runoff, increasing runoff, and steady‐state runoff stages. Soil detachment trends accompanying crusting were characterized for Capay silty clay loam (fine, montmorillonitic, thermic, Typic Chromoxerert), Jacinto loam (fine‐loamy, mixed, thermic Mollic Haploxeralf), and Gridley coarse sandy loam (Typic Argixeroll). Soils crusts were formed on 61 by 61 cm2 plots inclined at 9% slopes using simulated rainfall applied at 42.5 mm h−1 as 3.2‐mm‐diam. drops falling 2.5 m. Photographs of crust surfaces were taken at selected times to provide additional morphological evidence to support conclusions drawn from erosion data. Soil splash and runoff materials were collected at intervals, and selected samples were analyzed for particle size distribution. In all three soils, erosion rates reached maximums during the period of increasing runoff, then decreased and tended toward equilibrium levels during the final, steady‐state runoff period. This suggests that crust formation decreases soil erodibility under these steady erosivity conditions. Splash erosion rates peaked during the period of increasing runoff, while wash erosion rates displayed a gradual increase over the periods of increasing and steady‐state runoff. These trends are related to the decreasing size and degree of aggregation of surface material available for detachement, and the buildup of a layer of overland flow that appeared to enhance splash detachment while retarding splash transport. Between‐soil differences in the rate of soil crust development, as inferred from progression through the three runoff stages, suggest an interaction between initial soil texture and soil aggregate stability.