Equilibrium, non-equilibrium and residual water: Consequences for soil water retention

Dexter, A. R.; Czyż, Ewa A.; Richard, Guy

doi:10.1016/j.geoderma.2012.01.029

Cited by 33 publications

(34 citation statements)

References 21 publications

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“…2012; Dexter et al, 2012) that this is not true in general. These quantities are equal only when thermodynamic equilibrium has been achieved in the pressure cell ie all the water has the same value of free energy, and this occurs only along the curve section WX in Fig.…”

Section: Resultsmentioning

confidence: 99%

“…In contrast, when it is not in thermodynamic equilibrium, different 'packets' of water within the soil can have different values of specific free energy: for example, they can have different values of pore water pressure or suction. Dexter et al (2012) concluded that for every drying soil, two different water retention curves are needed: one for cases where de-watering occurs by immiscible displacement and one for cases where de-watering occurs by diffusion. Another curve is needed for soil wetting because of the hysteresis effect, but this case is not considered here.…”

Section: Introductionmentioning

confidence: 99%

“…The subject of water retention curves was discussed in detail by Fredlund and Xing (1994), however those authors did not distinguish between the above two physical processes of de-watering. Here, we follow Dexter et al (2012) The Dexter et al (2008) equation is based on the concept of a bi-modal pore size distribution as described by Monnier et al (1973) andStengel (1979). In this model, the pore space is divided into two parts: the textural porosity which occurs between the primary mineral particles; and the structural porosity which occurs between micro-aggregates and/or any other compound particles.…”

Section: Introductionmentioning

confidence: 99%

“…The subject of water retention curves was discussed in detail by Fredlund and Xing (1994), however those authors did not distinguish between the above two physical processes of de-watering. Here, we follow Dexter et al (2012) by using the Dexter et al (2008) double-exponential (DE) water retention equation for immiscible displacement and the Groenevelt and Grant (2004) water retention equation (GG) for cases where equilibrium has been attained by diffusion.…”

Section: Introductionmentioning

confidence: 99%

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Influence of soil type on the wilting of plants

Czyż¹,

Dexter²

2013

International Agrophysics

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A b s t r a c t. It has been shown that the water remaining in soil when plants wilt due to soil limitations and the residual water content as observed when soils are de-watered in pressure cell apparatus are essentially the same. Both are produced by immiscible displacement of water by air, and this leads to the water remaining in soil not being in thermodynamic equilibrium. Water removal by immiscible displacement ceases when hydraulic cut-off is reached. The point of hydraulic cut-off may be calculated by fitting waterretention data to equations for both the non-equilibrium case and the equilibrium case, and then solving these simultaneously. This has been done for water retention data for 52 soil horizons in Poland. These results are used to obtain a pedotransfer function for the permanent wilting point due to soil limitations and the results are presented for the different soil texture classes. The pore water suction when wilting occurs is estimated to be 1.0 MPa. The methods and findings in this paper are used to explain a range of published results on plant wilting. K e y w o r d s: hydraulic cut-off, pedotransfer function, permanent wilting point, residual water content, water retention INTRODUCTIONThe de-watering of moist soil by transpiring plants and the de-watering of soil samples in a pressure plate apparatus both occur by the physical process of convective movement of water in the soil by immiscible displacement ie air displaces the water . This explains why the water remaining in soil when plants of many species wilt is very close to the amount of water remaining in soil samples when they are de-watered in a ceramic pressure plate extractor with an applied air pressure of P a = 1.5 MPa (Richards and Weaver, 1943). This convective movement is completely different from the movement of water by diffusion. Whereas diffusion leads to water in thermodynamic equilibrium, immiscible displacement can lead to systems not in thermodynamic equilibrium. When a system is in thermodynamic equilibrium, all the water has the same specific free energy. In contrast, when it is not in thermodynamic equilibrium, different 'packets' of water within the soil can have different values of specific free energy: for example, they can have different values of pore water pressure or suction. Dexter et al. (2012) concluded that for every drying soil, two different water retention curves are needed: one for cases where de-watering occurs by immiscible displacement and one for cases where de-watering occurs by diffusion. Another curve is needed for soil wetting because of the hysteresis effect, but this case is not considered here.A water retention curve for a soil shows how the water content decreases with increasing pore water suction. The subject of water retention curves was discussed in detail by Fredlund and Xing (1994), however those authors did not distinguish between the above two physical processes of de-watering. Here, we follow Dexter et al. (2012) The Dexter et al. (2008) equation is based on the concept of a bi-mo...

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

“…The subject of water retention curves was discussed in detail by Fredlund and Xing (1994), however those authors did not distinguish between the above two physical processes of de-watering. Here, we follow Dexter et al (2012) by using the Dexter et al (2008) double-exponential (DE) water retention equation for immiscible displacement and the Groenevelt and Grant (2004) water retention equation (GG) for cases where equilibrium has been attained by diffusion.…”

Section: Introductionmentioning

confidence: 99%

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Influence of soil type on the wilting of plants

Czyż¹,

Dexter²

2013

International Agrophysics

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“…A sucção matricial no corte hidráulico foi calculada por dois métodos, conforme descrito em Dexter et al (2012). O primeiro método foi baseado no valor de h correspondente ao final do fluxo convectivo, calculado pelo ponto de máxima curvatura da CRA ajustada ao modelo DE (h maxc ), conforme a equação 9:…”

Section: Cálculo Do Valor De Sucção Em Que Ocorre O Corte Hidráulico unclassified

O conceito de equilíbrio hidráulico e termodinâmico da água no solo aplicado ao estudo da curva de retenção e murchamento de plantas

Torres¹

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Corn seedling root growth response to soil physical quality

et al. 2021

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Plant available water content or matric potential, particle size (texture), aeration, and penetration resistance are soil physical properties that influence soil structure, bulk density, aggregation, and several metabolic plant processes. Collectively they influence productivity and sustainability of agricultural practices, primarily through their impact on root development and growth. To simplify use of these parameters for assessing soil physical condition, the least limiting water range (LLWR) was developed as an integrated, comprehensive soil physical quality indicator. Our objective was to use the LLWR to evaluate corn (Zea mays L.) seedling root growth in soils with clay, sandy clay loam, or sand texture. Overall, root growth was affected by soil water content, aeration, and penetration resistance. Upper and lower LLWR boundaries were defined by a minimum air‐filled porosity and maximum soil penetration resistance for water contents between field capacity and permanent wilting point. Herein, the LLWR was calculated using a range of minimum air‐filled porosity (0.117–0.146 m3 m−3), field capacity (–2.2 to –5.3 kPa), and permanent wilting point or matric potential values (–461 to –6,516 kPa), and a restrictive penetration resistance value of 1.6 MPa as boundaries. The LLWR was sensitive to soil texture, decreasing from fine to coarse soils. The highest and lowest relative root growth measurements fell inside and outside the LLWR boundaries, proving that this index can successfully predict the optimum soil physical conditions for seedlings root growth and can therefore be used as a sensitive soil physical quality.

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Equilibrium, non-equilibrium and residual water: Consequences for soil water retention

Cited by 33 publications

References 21 publications

Influence of soil type on the wilting of plants

Influence of soil type on the wilting of plants

O conceito de equilíbrio hidráulico e termodinâmico da água no solo aplicado ao estudo da curva de retenção e murchamento de plantas

Corn seedling root growth response to soil physical quality

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