Soil Physical Theory and Heterogeneity

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Youngs E.G
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Continuum soil physical concepts and theories describe physical phenomena that occur in inherently heterogeneous systems of interconnecting pores. An essential part of these theories is the definition of a representative elementary volume that allows porous media to be considered as if they were continua. Larger scale heterogeneities at many scales that are superimposed on this micro-scale heterogeneity can take many forms and often pose difficulties in the development and use of predictive theories of soil-water behaviour. Examples are given of water movement in spatially varying soils that can be interpreted wrongly as flow in homogeneous soils. The analysis of water flow through soils that show deterministic heterogeneity is briefly considered. While additive soil physical properties, such as soil-water content, of a heterogeneous porous body are the weighted mean values of the properties of its constituent elemental volumes, transport coefficients, such as hydraulic conductivity, are generally not given simply by the arithmetic mean (or harmonic mean) values. Instead of considering point soil physical properties based on the continuum concept of soil physics, bulk properties of the whole system are for many purposes more useful.
Agricultural Water Management, 6, p. 145-159