Soil hydraulic properties as related to soil structure

Abstract

Soil structure is one of the main attributes of soil quality. It influences the soil pore system and through it all parameters of equations describing the transport processes in soil. Soil pore size distribution is either log-normal, or the log-normal distribution is an acceptable approximation. Kosugi [Water Resour. Res. 30 (1994) 891] has applied the log-normal distribution to data on the soil water retention curve and has replaced the empirical equation by the physically-based model. Log-normal pore size distributions were used for the estimation of the unsaturated hydraulic conductivity function. This paper deals with the application of Kosugi's model to the description of the retention curve and of the unsaturated conductivity function in soils exhibiting a bi-modal distribution of pores, typical for all soil horizons having a certain type of structure. The domain of structural pores and the domain of matrix pores are defined in these structured soils. Results from this study show that two hydraulic functions, the retention curve and the unsaturated conductivity are well described by models based on a log-normal distribution of pores in both the structural and the matrix domains of the soil porous system. The exponents α, β defined as parameters of the unsaturated conductivity are different for the structural and matrix domains. It is therefore, assumed that the configuration of soil pores including the tortuosity differs in these domains. The destruction of soil structure changes distinctly the configuration of soil pores which is demonstrated by the change of parameters α, β Consequently, the saturated and unsaturated conductivity is changed, too.