New procedure for sampling infiltration to assess post-fire soil water repellency

Robichaud, P.R.; Lewis, S.A.; Ashmun, L.E. 2008. New procedure for sampling infiltration to assess post-fire soil water repellency. Res. Note. RMRS-RN-33. Fort Collins, CO: U.S. Department of Agriculture, Forest Service, Rocky Mountain Research Station. 14 p.

Keywords: water repellency

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Abstract: The Mini-disk Infiltrometer has been adapted for use as a field test of post-fire infiltration and soil water repellency. Although the Water Drop Penetration Time (WDPT) test is the common field test for soil water repellency, the Mini-disk Infiltrometer (MDI) test takes less time, is less subjective, and provides a relative infiltration rate. For each test, the porous base plate of the MDI is placed on the soil surface and the amount of water that passes into the soil in one minute is measured.

Thousands of paired WDPT and MDI tests were applied at burned sites throughout the western United States, and the data were significantly correlated (r = -0.64). A classification tree analysis was used to group the MDI test results into "degree of soil water repellency" categories (strong, weak, and none) that correspond to similar categories established for the WDPT test. Fire-induced soil water repellency has high spatial variability and requires a valid sampling method if the data are to be credible. The MDI test protocol and sampling method described in this Research Note were developed for post-fire assessment, and provide a practical evaluation of burned soil infiltration characteristics in a limited time.

Moscow FSL publication no. 2008a