Insight into the mechanisms of soilstructure formation: an experimentalapproach using soil micromorphology and image analysis.

The importance of soil structure for terrestrial ecosystems is well known. A large bulk of scientific literature addresses factors influencing soil structure and soil pore development, but little is still known concerning the underlying physical mechanisms of their action. The aim of this thesis was to investigate mechanisms of soil pore development by means an experimental approach using soil 2D image analysis and standard soil micromorphology. In this work the chapters are organized as collection of scientific papers. After the first introductory chapter, the second one investigates some problems related to the digital acquisition stage of soil image analysis in order to provide a contribution to the standardization of this procedure of soil structure study. The experimental work reported in the third chapter was performed by means of the addition of calcium carbonate and iron oxides on three simplified soil-like systems. The obtained results showed changes in the pore size distribution, in some cases very large, and allowed the identification of specific mechanisms of pore modification induced by iron oxides and micrite pedofeatures produced by the mobilization in suspension of iron oxides and calcium carbonate. The second experimental work, reported in the fourth chapter, was performed in order to investigate the effect of the interaction between different sizes and concentrations of rock fragments and soils with different shrinkage-swelling dynamics on the mechanisms of soil structure formation. The results obtained highlighted the contribution of rock fragments in soil pore development in two soils characterized respectively by high and low shrinkage dynamics. In the technical note reported in the fifth chapter was proposed a micromorphological image analysis approach that allow to discriminate the contribution of different biological activities to soil pore size distribution and aggregate size distribution. Overall the results of the thesis highlighted the potential of the experimental tests in pots combined with soil micromorphology and image analysis techniques for understanding the mechanisms of development of soil structure.