Calcinated : SOM - , No-structure Undisturbed : SOM + , structure Sieved : SOM + , No-structure
1
WATER RETENTION OF A HYDROPHOBIC SOIL: DISENTANGLING THE EFFECT OF STRUCTURE, ORGANIC MATTER AND SOIL WATER REPELLENCY Carlos M. Regalado - Axel Ritter ([email protected]) Soil water retention is affected by hydrophobicity. Both soil organic matter content (SOM) and structure also affect water retention. However these three effects, hydrophobicity, SOM and structure, are coupled such that one may be affected by the others. Thus, for example, SOM contributes to soil structure but also to soil water repellency. We measured the water retention curve of a forest organic soil (48% SOM) under different treatments in order to evaluate in isolation the contribution of hydrophobicity, SOM and structure. We propose a mechanism to explain how the various components involved in the water 1.Calcinated: SOM - , No- structure 2.Undisturbed: SOM + , structure 3.Sieved: SOM + , No- structure Experiment I ( 3 soil treatments ) 1.Water: SOM + & Hydrophobic 2.Surfactant: SOM + & Wettable 3.Ethanol: SOM + & Wettable Experiment II ( 3 humectation liquids ) Determination of the drying water retention curve (0-90kPa) of the soil samples from experiments I & II Pressure cells Calcinated Sieved Undisturbed Water Surfactant Ethanol Water Surfactan t Ethanol Calcinated Sieved Undisturbed SOM - , S - , H - X X Experiment I Experiment II X X MATERIAL & METHODS: SOIL WATER RETENTION MODEL: RESULTS: Extended Young-Laplace equation: Ψ = cosβ(Ψ)/r ; Ψ= Soil suction cos β(Ψ)=a 1 exp(-a 2 Ψ); β=contact angle SOM + , S + , H + SOM + , S - , H + SOM + , S - , H - SOM + , S - , H - SOM: Soil organic matter S: Structure H: Hydrophobicity -/+: Absence/Presence Water retention model with log-normal pore radius (r) distribution + Effective saturation pF Wettabl e Air entry value Hydrophobic Air entry “like” value We studied the water retention curve of a forest organic soil. The experiments showed that the presence of organic matter increased the soil water retention capacity. This increase is due largely to a higher contact angle (hydrophobicity) provided by the soil organic matter, and more specifically to its effect on the value of the air entry point or bubbling pressure. Soil structure was also relevant, reducing the water retention in the range pF> 1 partly offsetting the hydrophobicity character of the soil, suggesting that previous results obtained from disturbed soil samples should be taken with caution when extrapolated to under field conditions. The data were fitted satisfactorily to the retention curve model originally developed by Kosugi (1994) and extended in this work in order to consider the case in which the contact angle varies with suction.
description
MATERIAL & METHODS:. Water. Surfactant. Ethanol. Calcinated. Undisturbed. Sieved. Calcinated : SOM - , No-structure Undisturbed : SOM + , structure Sieved : SOM + , No-structure. Water retention model with log-normal pore radius ( r ) distribution. SOIL WATER RETENTION MODEL:. - PowerPoint PPT Presentation
Transcript of Calcinated : SOM - , No-structure Undisturbed : SOM + , structure Sieved : SOM + , No-structure
WATER RETENTION OF A HYDROPHOBIC SOIL: DISENTANGLING THE EFFECT OF STRUCTURE,
ORGANIC MATTER AND SOIL WATER REPELLENCY
Carlos M. Regalado - Axel Ritter
([email protected])Soil water retention is affected by hydrophobicity. Both soil organic matter content (SOM) and structure also affect water retention. However these three effects, hydrophobicity, SOM and structure, are coupled such that one may be affected by the others. Thus, for example, SOM contributes to soil structure but also to soil water repellency. We measured the water retention curve of a forest organic soil (48% SOM) under different treatments in order to evaluate in isolation the contribution of hydrophobicity, SOM and structure. We propose a mechanism to explain how the various components involved in the water retention of the studied soil affect its moisture characteristic curve.
1.Calcinated: SOM-, No-structure
2.Undisturbed: SOM+, structure
3.Sieved: SOM+, No-structure
Experiment I( 3 soil treatments )
1.Water: SOM+ & Hydrophobic
2.Surfactant: SOM+ & Wettable
3.Ethanol: SOM+ & Wettable
Experiment II( 3 humectation
liquids )
Determination of the drying water retention curve (0-90kPa) of the soil samples from experiments I & II
Pressure cells
Calcinated SievedUndisturbed Water Surfactant Ethanol
Water Surfactant Ethanol
Calcinated
Sieved
Undisturbed
SOM-, S-, H-
X X
Experiment I
Experiment II
X X
MATERIAL & METHODS:
SOIL WATER RETENTION MODEL:
RESULTS:
Extended Young-Laplace equation:
Ψ = cosβ(Ψ)/r ; Ψ= Soil suction cos β(Ψ)=a1 exp(-a2Ψ); β=contact
angle
SOM+, S+, H+
SOM+, S-, H+SOM+, S-, H- SOM+, S-, H-
SOM: Soil organic matter S: StructureH: Hydrophobicity-/+: Absence/Presence
Water retention model with log-normal pore radius (r) distribution
+
Eff
ecti
ve
satu
rati
on
pF
Wettable
Air entry value
Hydrophobic
Air entry “like” value
We studied the water retention curve of a forest organic soil. The experiments showed that the presence of organic matter increased the soil water retention capacity. This increase is due largely to a higher contact angle (hydrophobicity) provided by the soil organic matter, and more specifically to its effect on the value of the air entry point or bubbling pressure. Soil structure was also relevant, reducing the water retention in the range pF> 1 partly offsetting the hydrophobicity character of the soil, suggesting that previous results obtained from disturbed soil samples should be taken with caution when extrapolated to under field conditions. The data were fitted satisfactorily to the retention curve model originally developed by Kosugi (1994) and extended in this work in order to consider the case in which the contact angle varies with suction.
We studied the water retention curve of a forest organic soil. The experiments showed that the presence of organic matter increased the soil water retention capacity. This increase is due largely to a higher contact angle (hydrophobicity) provided by the soil organic matter, and more specifically to its effect on the value of the air entry point or bubbling pressure. Soil structure was also relevant, reducing the water retention in the range pF> 1 partly offsetting the hydrophobicity character of the soil, suggesting that previous results obtained from disturbed soil samples should be taken with caution when extrapolated to under field conditions. The data were fitted satisfactorily to the retention curve model originally developed by Kosugi (1994) and extended in this work in order to consider the case in which the contact angle varies with suction.
