Articles
WATER REPELLENCY OF ORGANIC GROWING MEDIA AND ITS CONSEQUENCES ON HYSTERETIC BEHAVIOURS OF THE WATER RETENTION CURVE
Article number
819_33
Pages
287 – 296
Language
English
Abstract
In contrast to soils, most growing media can exhibit hysteresis during drying/wetting cycles, which greatly affects their hydraulic properties.
In the case of organic substrates, hydrophobicity during desiccation could be considered as one of the main factors leading to hysteretic behaviour.
The purpose of this study was to estimate the influence of changes in wettability on the water retention properties, Θ(Ψ), of peat and pine bark during a drying/wetting cycle.
Major differences in the hydraulic behaviour of the two organic materials studied were observed.
For peat, hysteresis was found in the water retention curve (21%) and also in the contact angle/water potential relationship, (
(Ψ), 20%), whereas in pine bark, this phenomenon was less pronounced in the water retention curve (10%) and even more limited in the (Ψ) curve (>5%). Water retention hysteresis was successfully modelled using a modified van Genuchten-Durner approach (VG model), which took into account the local hydrophobicity of each poral domain of the porous media, regardless of the extent of hysteresis.
Incorporating the parameters of the VG water retention model into a (Ψ) equation to characterize overall or average changes in the hydrophobicity of the material during desiccation resulted in values very similar to those of the contact angles calculated with the capillary rise method.
These results indicate that water retention properties of these organic substrates are strongly influenced by hydrophobicity.
In the case of organic substrates, hydrophobicity during desiccation could be considered as one of the main factors leading to hysteretic behaviour.
The purpose of this study was to estimate the influence of changes in wettability on the water retention properties, Θ(Ψ), of peat and pine bark during a drying/wetting cycle.
Major differences in the hydraulic behaviour of the two organic materials studied were observed.
For peat, hysteresis was found in the water retention curve (21%) and also in the contact angle/water potential relationship, (
(Ψ), 20%), whereas in pine bark, this phenomenon was less pronounced in the water retention curve (10%) and even more limited in the (Ψ) curve (>5%). Water retention hysteresis was successfully modelled using a modified van Genuchten-Durner approach (VG model), which took into account the local hydrophobicity of each poral domain of the porous media, regardless of the extent of hysteresis.Incorporating the parameters of the VG
water retention model into a (Ψ) equation to characterize overall or average changes in the hydrophobicity of the material during desiccation resulted in values very similar to those of the contact angles calculated with the capillary rise method.These results indicate that water retention properties of these organic substrates are strongly influenced by hydrophobicity.
Publication
Authors
R. Naasz, J.-C. Michel, S. Charpentier
Keywords
peat, pine bark, modelling, hydrophobicity
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