Mineralogical and organic carbon content of water-dispersible particles from conventional and no-tillage soils

Abstract

Soil erosion from agricultural lands causes loss of soil productivity, as well as environmental problems down stream due to sediment and contaminants sorbed on dispersed colloids. In order to estimate the potential effects of erosion and to describe the behavior of various inorganic and organic contaminants in agro-ecosystems, quantitative characterization of soil colloid dispersion is essential. The effect of long-term tillage management (conventional-tillage and no-tillage) on mineralogical and organic carbon content in both field- and laboratory-generated water dispersible particles (WDP) were studied. Field-WDP were collected during rainfall simulation. Laboratory-WDP were obtained by shaking soil for 16 hours (soil to water ratio of 1:10). Results demonstrate that laboratory- and field-WDP differ in organic carbon content, particle size distribution, and mineralogical concentrations, and are influenced by soil management. Soils under no-tillage produced much larger amounts of laboratory-WDP and smaller amounts of field-WDP than the soils under conventional-tillage. Field-WDP from both no-tillage and conventional-tillage fields were dominated by silt-sized particles, while laboratory-WDP dominated in the clay-sized fraction. Both organic carbon and dissolved organic carbon concentration in field-WDP runoff decreased with time during simulated rainfall events. The laboratory procedure used here for generating water-dispersible particles may not be suitable for studying runoff sediments in the field.

Acknowledgments

We gratefully acknowledge the planning and initiation of this study in 1983 by Dr. C. K. Mutchler, who was the Research Leader of the Sediment Yield Unit of the USDA National Sedimentation Laboratory. The main objective of this long-term study was to determine the long-term effects of no-tillage and conventional-tillage on soil erosion and crop productivity.