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In order to study the physical properties of gypsiferous soils (Gypsic Xerochrepts and Typic Xerofluvents) from an irrigated semi-arid area in Catalonia (NE Spain) and their relationships to their pore characteristics, twenty horizons with gypsum contents ranging between 0 and 90% were sampled for micromorphological and physical analyses. The micromorphological study consisted of thin section description and of image analysis of uncovered thin sections of samples impregnated with a W-fluorescent dye. Eight fields of each horizon were studied. Two images were obtained from each field (2.1 x 3.1 cm(2)): one illuminated with incident W-light and the other with transmitted white Light. Image processing with an IBAS-system allowed measurement of the geometric characteristics of three types of objects: actual pores (eg. diam. > 100 mu m), transparent objects infilled or not with gypsum and pores located in these transparent objects. The physical characteristics of the same horizons considered in the study were the water-characteristic curves and the saturated hydraulic conductivity. Although differences in total porosity (between 6 and 16%) are not related to other properties, an increase of gypsum content leads in the studied horizons to the replacement of large pores by smaller packing pores between gypsum crystals in infillings, which are interconnected and do not reduce saturated hydraulic conductivity. Available water is affected by the degree of mixing of the gypsum infillings with the groundmass, besides the crystal size distribution. The results stress the importance of pore clogging by gypsum in these materials as a major constraint for root development, as well as the need of describing the type of gypsum accumulation when assessing the suitability of these soils for plant growth. (C) 1998 Elsevier Science B.V. All rights reserved.