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Title:   Author  item
                                            Wuest, Stewart
  Submitted to: Vadose Zone Journal
                                    Publication Type: Peer Reviewed Journal
                                    Publication Acceptance Date: 4/8/2009
                                    Publication  Date: 8/1/2009
                                    Citation: Wuest, S.B. 2009. Comparison of Preferential Flow Paths to Bulk Soil in a Weakly Aggregated Silt Loam Soil. Vadose Zone J. 8:623-627.Interpretive Summary: Water flow is not uniform in soil, but the causes and characteristics of this are not well described or understood. We compared zones of preferential flow to non-preferential flow in both tilled and untilled soil. Small volumetric core samples were taken and analyzed for bulk density, water content, root mass, total carbon, and water-stable-aggregate size distribution. Preferential flow zones had a greater proportion of large aggregates and less small aggregates, greater water content, and lower bulk density. Root mass and carbon were not significantly different. Tilled soil had a greater proportion of un-aggregated soil, greater water content, lower bulk density, and greater root mass than un-tilled soil. These results confirm other data showing that infiltration rates in this silt-loam soil are largely controlled by surface aggregation, and while infiltration is not hampered by increases in bulk density developed under no-till, tillage in itself does not destroy preferential flow pathways.
                                Technical Abstract: Water flow velocity is not uniform in soil, but the characteristics and causes of preferential flow paths are not known. We compared zones of preferential flow to
bulk soil and looked for differences between tilled and untilled soil. We used a 10 min pulse of dye and Br- to mark preferential flow paths at the end of 2 h ponded infiltration. Small volumetric core samples were taken from dyed and un-dyed soil at 10- to 25-cm depth and analyzed for bulk density, water content, root mass, total C, and water-stable-aggregate size distribution. Compared to bulk soil, preferential flow zones had a greater proportion of large aggregates and less small aggregates, greater water content, and lower bulk density (1.20 vs. 1.23 Mg m^3). Root mass and C were not significantly different. In comparison to untilled soil, tilled soil had a greater proportion of un-aggregated soil, greater water content, lower bulk density (1.16 vs. 1.24 Mg m^3), and greater root mass. There were no interactions between the preferential flow zone/bulk soil factor and the tilled/untilled factor. Bulk density may be a useful characteristic, but it did not correlate to infiltration rate. The rate determining factor may have been above 10 cm or a combination of density, aggregation, and effective cross sectional area. These results did not indicate distinct differences in preferential flow zone development between tilled and untilled soil.


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