Changes of soil pore system and pore functions following stress application Marcello Pagliai , Nadia Vignozzi, Sergio Pellegrini Istituto Sperimentale per lo Studio e la Difesa del Suolo, MiPAF, Piazza Massimo D’Azeglio 30 – 50121 Firenze, Italy. Tel: +39 055 2491255; Fax: +39 055 241485; e-mail pagliai@issds.it Abstract The main aspects of environmental degradation can be ascribed to soil (erosion, soil compaction, soil crusting, deterioration of soil structure, flooding, losses of organic matter, salinisation, onsite and offsite damages, etc.) following the impact of human activities. Since the increase of stress application to soil by the agricultural conventional production systems has resulted in excessive erosion and soil degradation, there is need to control and fight such degradation. Among the above mentioned aspects, soil compaction is surely one of the most important factors responsible for environmental degradation. In fact, stress application like compaction and shearing causes strong modifications to soil structure and reduces not only soil porosity but also pore functions. Therefore the measurements of such a physical property can help to quantify the effects of compaction. This is now possible because of the increasing use and availability of the technique of image analysis allowing the measurement of soil porosity on thin sections or impregnated soil blocks, prepared from undisturbed soil samples. Micro and macroporosity, pore shape and size distribution, penetration resistance, saturated hydraulic conductivity and water content were analysed in loam soils where long term field experiments were carried out to investigate different types of soil tillage and traffic for cereals and vineyard cultivation. Results showed that compaction caused by traffic, but overall by shearing of tillage implements, not only reduces total soil porosity but also modifies the pore system. In fact, the proportion of elongated pores, useful for water movement and root growth is strongly reduced in compacted soil. The modifications to the pore system also changes the type of soil structure: the massive platy structure are common feature in compacted soil. Results also showed that the reduction of porosity and of elongated pores following compaction and shearing, is strictly related to the decrease of hydraulic conductivity, thus indicating strong modifications of pore functions. This leads to a drastic reduction of water infiltration and drainage with consequent flooding in the plains and erosion, sometime catastrophic, in the hilly environment. The decrease of soil porosity is also related to the increase of penetration resistance and the reduction of root growth. Key words: Soil degradation, soil structure, soil pore system, soil pore function, image analysis Introduction Soil compaction is one of the most important factors responsible for environmental degradation. It causes strong modifications to soil structure and reduces soil porosity. Soil