Friday, 14 July 2006 - 2:25 PM

The Characterization of Soil Pore System for Water Movement Prediction.

Nadia Vignozzi, Sergio Pellegrini, and Marcello Pagliai. CRA-ISSDS, Piazza D'Azeglio 30, Florence, 50121, Italy

The most important modifications of soil structure mainly involve changes in soil porosity and, consequently, water movement. Therefore, measurements of this physical property can help to quantify the impact of management practices on soil. This is now possible because of the increasing use and availability of the technique of image analysis which makes possible the automated measurement of soil porosity on thin sections or impregnated soil blocks prepared from undisturbed soil samples. Soil porosity is, therefore, a very important indicator of soil structure quality. Quantification of the pore space in terms of shape, size, continuity, orientation and arrangement of pores in soil allows us to define the complexity of soil structure and to understand its modifications induced by management practices. In this way, we can identify those practices that are more compatible with environmental protection. Characterisation of the pore system provides a realistic basis for understanding the retention and movement of water in soil. Soil water retention curve, saturated and unsaturated hydraulic conductivity are basic hydraulic functions indispensable for the solution of all hydrologic problems related to tasks of sustainable soil management and environmental protection. Soil hydraulic functions are strongly dependent upon the soil porous system. Soil hydraulic functions are briefly discussed and the opportunity of physical interpretation of those functions by soil micromorphological parameters is shown, if the real pore size distribution is reflected by the soil water retention curve and by the unsaturated hydraulic conductivity. These assumptions are supported by results on a significant correlation between elongated continuous transmission pores and the saturated hydraulic conductivity, that can be useful in the development and improvement of models for predicting water movement. The micromorphological research shows as well that the shape of the walls of pores plays an important role upon the stability of pores. The formation and existence of vesicular pores is the main factor of substantial decrease in hydraulic conductivity. Further research should include all the existing information on pore micromorphology into physically based soil hydraulic functions. For a physically based formulation of soil hydraulic functions, the soil porous system characterisation is an indispensable basis. The development of models is characterized by the gradual transition from the simplest concepts up to the sophisticated approaches which should correspond to the reality studied by soil micromorphology. The problem is strongly related to pore scale, but the upscaling to representative elementary volume accompanies the studies as a necessity for applications of the results to the solution of practical problems. Key words: Soil structure; Soil porosity; Image analysis; Soil micromorphology; Hydraulic conductivity; Modeling.

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