An evaluation of the intrinsic sorptivity water repellency index on a range of New Zealand soils

Abstract

Undisturbed cores were removed from the surface of 14 New Zealand soils with a wide range of textures. The sorptivity to ethanol and water was measured with a 'sorptivity tube' to determine the repellency index (Rl) of each soil. Texture and gravimetric water content were measured, and the water drop penetration time (WDPT) and molarity of ethanol droplet (MED) tests for water repellency were conducted on the soils. The RI measured all soils water repellent (RI> 1.95) at field moisture conditions, and was more sensitive than the WDPT or MED tests. The RI was used to demonstrate that water repellency reduced short-time water infiltration of all soils by approximately an order of magnitude. Actual and 'potential' infiltration was then compared with rainfall and irrigation intensities. This illustrated the hydrological significance of the phenomenon, even in soils which appeared to wet normally (low WDPT). In all soils the curves of cumulative infiltration versus the square root of time for both water and ethanol stayed linear long enough for sorptivity evaluation. However, at longer times the slope of the curve tended to increase for water sorption in the more repellent soils, but decreased consistently for ethanol.

Modeling and field evidence of finger formation and finger recurrence in a water repellent sandy soil

“…Most field studies, even in sandy soils , have shown that preferential flow is more the rule than the exception, and may partly account for inaccuracies in the prediction of water and solute movement. Since water repellency is plant-induced and occurs often in field soils [Wallis et al, 1991;Wallis and Home, 1992], fingered flow may be more common than is presently thought. In our opinion, these models need to be adapted to account for the unstable flow phenomenon if they are to be employed to full benefit.…”

Soil Infrastructure, Interfaces & Translocation Processes in Inner Space ("Soil-it-is"): towards a road map for the constraints and crossroads of soil architecture and biophysical processes

“…But as for the effects of increased WR with increasing OC content and the possible resulting irregular water movement the positive role is less clear. Subcritical water repellency is a common feature of many soils (Wallis et al, 1991;Hallett and Young, 1999). It is a fundamental physical property of soil and has implications for the resistance of soil structure against disruption by wetting and bypass flow (Hallett et al, 2001).…”

Characterization of disaggregated nonwettable surface soils found at old crude oil spill sites

“…This simple and rapid method has been widely tested and is considered reliable when used on air-dried or oven-dried soil (King 1981;Karnok et al 1993). The MED test measures the molarity of ethanol in a droplet of water required for soil infiltration within 10 s. Ethanol lowers the surface tension of the liquid and thereby enables infiltration regardless of the soil contact angle (Wallis et al 1991). According to the interpretation guidelines provided by King (1981), soils with a MED index ≤1 are not significantly water-repellent, whereas soils with a MED index ≥2.2 are considered to be severely water-repellent.…”