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Title: USING RARE EARTH OXIDES AS TRACERS TO STUDY SOIL EROSION AND AGGREGATION

Author
item Zhang, Xunchang
item FRIEDRICH, JON - PURDUE UNIVERSITY
item Nearing, Mark
item Norton, Lloyd

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 5/11/2001
Publication Date: 9/5/2001
Citation: N/A

Interpretive Summary: Soil erosion by water is a worldwide problem and a threat to world food security and fiber production. It deteriorates land, soil, and water resources and therefore adversely affects agricultural production and environmental quality. To minimize the adverse effects and to promote agricultural productivity and sustainability, soil erosion has to be controlled. To control soil erosion, we must have the knowledge of where sediments come from and how soils are eroded. The purpose of this work is to test the feasibility of using non-hazard chemicals, called rare earth elements, for tracing soil movement along a hill slope or within a watershed. Results showed that those chemical elements were strongly bound with soil materials and were easy and inexpensive to measure. Those rare earth elements may be ideal tracers for tracking sediment movement in a field. This work provided soil erosion scientists and soil conservationists a new method for determining sediment source areas and fo quantifying spatial distribution of soil erosion patterns. This information is needed by scientists to calibrate soil erosion prediction tools. It can also be used by soil conservationists and farmers to lay out site-specific management practices to combat soil erosion.

Technical Abstract: Most existing soil loss data are spatially averaged, though various tracing techniques have been used for obtaining spatially distributed data. Spatially distributed soil erosion data are needed for validating physically based erosion prediction models and for better understanding soil erosion dynamics. The objectives of this study were to evaluate the feasibility of using rare earth element (REE) oxides directly as tracers for soil erosion studies by examining their binding ability with soil materials, and also to test a quick acid-extraction procedure. Five REE oxide powders were directly mixed with a Miami silt loam soil (fine-loamy, mixed, mesic Typic Hapludalfs) and then leached with deionized water in a soil box to evaluate the mobility of REEs. Following leaching, soil samples were collected in 25-mm increments and analyzed for REEs. The REE- tagged soil was wet sieved to obtain REE concentrations in each aggregate size group. A simple acid-leaching method was used to extract REEs from all soil samples. The extracts were analyzed by ICP-MS techniques. The data indicated that the maximum coefficient of variation was < 10% for all REEs. The REE oxides were uniformly incorporated into soil aggregates of different sizes (> 53 um) and were bound with silt-size particles. This finding shows that the direct use of REE oxides is feasible, which should be superior to other REE-tagged particulate tracers because it eliminates the needs of tagging exotic particles with REEs. Also, direct mixing of a trace amount of REEs does not substantially alter physicochemical properties of soil particles and aggregates. This work has shown that REE oxides may be ideal tracers for studying soil translocation at various scales.