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

Abstract

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.

Water Repellency of Two Forest Soils after Biochar Addition

“…Briggs et al (2012) observed extreme water repellency (water drop penetration test >2 h) for a freshly produced ponderosa pine (Pinus ponderosa) derived charcoal, but older carbon under forest floor layers was less water repellent. Unlike the hydrocarbons created during a fire, where extreme temperature gradients force hydrocarbons into the soil profile (Robichaud et al, 2008), biochar does not coat mineral soil particles but causes water repellency of the soil surface because it is a hydrophobic substance until it is sufficiently wetted. Biochar, coated particles, or charcoal from fire may alter water movement into the soil profile by preventing water infiltration into the mineral soil (DeBano, 2000).…”

“…Estimating changes in soil hydrologic processes after biochar additions is important because water-repellent soils have an impact on infiltration rates (Doerr et al, 2000Robichaud et al, 2008. Past studies have shown increased water retention of biochar-amended agricultural soils (Novak et al, 2009), and some infiltration research has been conducted on naturally occurring black C (Briggs et al, 2012).…”

“…Therefore, our primary objective was to conduct a laboratory assessment to evaluate the water repellency of biochar either added to the soil surface or mixed into the mineral soil for both fine and coarse textured soils. Our goal was to assess soil water infiltration rates changes using (1) tension infiltrometer tests (MDI; Lewis et al, 2006;Robichaud et al, 2008), (2) water drop penetration time (WDPT; DeBano, 2000; Letey et al, 2000), and (3) molarity of an ethanol drop (MED; Doerr, 1998) to develop some best application rates and methods for land managers.…”

Assessment of Site and Soil Characteristics of Rill Erosion Following the Lockheed Fire in the Little Creek Watershed, Swanton Pacific Ranch

“…The procedures used for these measurements were taken from Robichaud et al, 2008. The suction of the MDI was adjusted to 1cm, which is the suggested setting for post fire soil infiltration to provide capillarity suction and maintain a constant pressure while keeping the instrument from leaking (Decagon Devices, Inc., Pullman, WA).…”

“…A water drop was applied to the soil surface at 1 and 3 cm depth and the residence time of the water drop to infiltrate was recorded. The classification to determine the degree of water repellency was taken from the USFS BAER procedures, and threshold class of WDPT: <10 s (weak), 10-40 s (moderate), and >40 s (strong) (Robichaud et al, 2008).…”