The Relationship between Soil Moisture and Soil Water Repellency Persistence in Hydrophobic Soils

Mohamed Bayad,Moussa Bouray,Stephen Trolove,Henry Wai Chau,Jim Moir,Leo Condron

doi:10.3390/w12092322

Mohamed Bayad, Moussa Bouray + Show 4 more

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https://doi.org/10.3390/w12092322

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Abstract

In this work, we modelled the response of soil water repellency (SWR) persistence to the decrease in moisture in drying soils, and we explored the implication of soil particle size distribution and specific surface area on the SWR severity and persistence. A new equation for the relationship between SWR persistence and soil moisture (θ) is described in this paper. The persistence of SWR was measured on ten different hydrophobic soils using water drop penetration time (WDPT) at decreasing levels of gravimetric water content. The actual repellency persistence showed a sigmoidal response to soil moisture decrease, where Ra(θ)=Rp/1+eδ(θ−θc). The suggested equation enables one to model the actual SWR persistence (Ra) using θ, the potential repellency (Rp) and two characteristic parameters related to the shape of the response curve. The two parameters are the critical soil moisture θc, where the Ra increase rate reaches its maximum, and the parameter δ affecting the steepness of the curve at the inflexion point of the sigmoidal curve. Data shows that both soil carbon and texture are controlling the potential SWR in New Zealand pastures.

Highlights

Soil water repellency refers to the inability of soils to absorb water
The potential water drop penetration time (WDPT) of air-dry soils varied between 38 and 8460 s (Rp from 1.57 to 4.2) (Table 1). This means that water repellency classes varied from strong to severe according to the classification suggested by Doerr [35]
All the studied samples representing different soil orders, textures and potential soil water repellency (SWR) represented a sigmoidal response to the decrease in soil moisture where WDPT attends a maximum for air-dry soils

Summary

Introduction

Soil water repellency refers to the inability of soils to absorb water. This phenomenon has been identified in different soils and climate combinations [1]. When the soil moisture becomes low enough during the drying process, their polar groups re-associate and interact through the hydrogen bonds, forcing the molecules back into position with the polar heads attached to the mineral surface and the non-polar tails orientated outwards resulting in the reestablishment of hydrophobicity [3,4,5,6,7,8]. Soils express water repellency when moisture drops below a critical water content. This issue has serious implications in decreasing water infiltration [9], inducing surface runoff, nutrient losses through runoff [10] and causing preferential flow [11]

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