Clay dispersion, infiltration, and erosion as influenced by exchangeable Ca and Mg

Soils of the US Corn Belt often experience surface sealing, low infiltration, and erosion under rainfall, all of which result in economic loss. This study seeks to establish if high Mg content in these soils can have an adverse effect on soil structure, clay dispersability, water intake rate, and erosion as a result of the greater hydration radius of Mg compared with Ca. The study modified the Ca/Mg ratio from four soils of the Midwestern United States that varied in organic matter (OM) content, clay content, and clay mineralogy. After that, flocculation behavior of the clay fraction as well as infiltration and erosion during simulated rainfall were examined. The Ca/Mg ratio had a significant effect on clay dispersion and surface sealing: for all soil clays, a negative linear relationship (R-2 = 0.82 to 0.99) was observed between the Mg percentage in solution and optical transmittance of clay suspension as an indicator of clay flocculation. In rainfall experiments, well structured Mg-treated soils registered final infiltration rates approximately half those of Ca-treated soils (2.7 mm h(-1) vs. 5.7 nun h(-1) for Blount loam soil and 16.8 m m h(-1) vs. 31.1 mm h(-1) for Catlin silt loam soil). Total infiltration decreased significantly as well. However, the effect was not significant for two less stable soils. Magnesium saturation increased final and total soil losses significantly for Blount loam and Fayette silty clay loam. Results indicate that high Mg can cause increased surface sealing and erosion in Midwestern soils.