Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/12/2001
Publication Date: N/A
Interpretive Summary: Seal is formed during rainfall on the surface of the soil. It decreases soil water uptake. The decrease in water uptake causes loss of water, erosion or water logging - both environmental and agronomical problems. Chemical composition of the soil affects the extent of surface sealing. Magnesium (Mg) is a common soil constituent & it is often added to the soil las a part of dolomitic limestone. We believe that magnesium can increase when its amount is relatively large compared to calcium. The laboratory part of our study showed that large fractions of magnesium in soil caused destruction of soil structure. Under simulated rainfall, well-structured soils dominated by magnesium had only half as much water uptate as the same calcium-dominated soils. Even when water loss was the same, erosion was still larger for magnesium-saturated soil than calcium-saturated soil. This study questions the accepted theory that calcium and magnesium have the same effect on soil properties. It is possible that guidelines for liming have to reviewed taking into account results of this study. The impact of this work is that farmers should not only consider the acid neutralizng effect when choosing liming materials, but also should consider the Mg content of the soil and liming material.
Technical Abstract: Ca and Mg are often treated in agriculture as having the same influence on soil physical properties. However, there is a possibility of the adverse effect of Mg on soil structure and water intake rate. Less stable soil structure can lead to surface sealing, decreased infiltration, increased runoff and erosion during rainfall events. In this paper, we studied the influence of modified Ca/Mg ratio on surface sealing of four soils varying in organic matter content, clay content and mineralogy from the US Midwest. Part of the study was a laboratory experiment in which flocculation behaviors of soil clays were studied at different Ca/Mg ratios and solution electrolyte. A rainfall simulation study was conducted to examine differences in soil structure and consequently surface sealing and infiltration when soil Ca/Mg ratio was modified. It was found that Ca/Mg ration had a significant effect on clay dispersion and surface sealing. There was a linear relationship between Ca percentage in solution and optical transmittance of clay suspension as an indicator of clay flocculation. In rainfall experiments, Ca-treated well-structured soils had final infiltration rates twice that of Mg-treated soils, total infiltration was increased significantly as well. Ca saturation decreased soil losses to half of those from the Mg treatment. Ca/Mg exchange isotherms obtained in the course of modifying Ca/Mg ratio of the soils indicated a preference for Ca.