MINERALOGICAL AND ORGANIC CARBON CONTENT OF WATER-DISPERSIBLE PARTICLES FROM CONVENTIONAL AND NO-TILLAGE SOILS

Authors: KINGERY, W. - MISSISSIPPI STATE UNIV.; HAN, F. - MISSISSIPPI STATE UNIV.; SHAW, D. - MISSISSIPPI STATE UNIV.; GERARD, P. - MISSISSIPPI STATE UNIV.; McGregor, Keith

Submitted to: Communications in Soil Science and Plant Analysis
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/31/2001
Publication Date: N/A
Citation: N/A

Interpretive Summary: Various nutrients and pollutants attached to eroded sediment particles are transported downstream in the runoff. Improvements are needed in predicting and understanding the behavior of sediment and associated contaminants suspended in runoff. Soil samples collected in the field from plots with no-till and conventional-till management were suspended in water by shaking for 16 hours. Sediments remaining in suspension two hours after shaking were designated as the laboratory measured water-dispersible particles (Laboratory WDP). Samples of laboratory WDP were compared to sediments suspended in runoff occurring in the field (field WDP) under simulated rainfall on plots with no-till and conventional-till management. Soils under no-till produced much larger amounts of laboratory-WDP and smaller amounts of field WDP than the soils under conventional-till. Clay-sized mineral compositions were different in field WDP compared to laboratory WDP. The organic carbon content, particle size distribution, and mineralogical concentrations generated in the laboratory and in the field were different. In this study, the laboratory WDP could not be used to predict the field WDP under simulated rainfall. Results of this study will be of interest to scientists trying to predict and understand the behavior of sediment particles in runoff.

Technical 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 no-till 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.