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Land capability and suitability maps are useful tools for soil resource conservation. This study aimed to build land capability and suitability maps using a multi-thematic approach by GIS in a salt-affected coastal area of Italy. Topographic, morphological, geological, pedological delineations and land cover maps, remote sensing image and climate data were acquired and the main physical and chemical properties, including electrical conductivity (EC) and available water capacity, were analysed on the soil samples collected in the study area. The acquired information were elaborated through QGIS software to obtain the land capability and suitability maps. The suitability map showed that most of the area (80%) is suitable for cultivation and, therefore, can be addressed for agricultural purposes without risk of degradation. In fact, the land capability map showed that 42% of the investigated area belongs to class I and II indicating that they can be used for a wide range of cultivations. While 44% of the investigated area clustered in class III and IV. In these latter the cultivation should be allowed to a limited range of crops due to the high sand content, which does not allow a good water retention, and due to a strong intrusion of sea water with consequent increase of the soil EC. In our study area, where agricultural productivity and environmental impact are in conflict, to classify the lands on base the land capability and suitability could help to define the best agricultural practices to apply in order to preserve soil functions.

Fragipan is a widely distributed subsoil horizon that induces severe limitations to plant growth and land use, mainly because of its high bulk density. In this work, we evaluated the poresize distribution through the analysis of the cumulative curve of intruded mercury volume in some soils with fragipan horizons. This approach provides information also about the arrangement of particles, thus we compared the results obtained for fragipan and nonfragipan horizons to relate porosity and particle arrangement with the specific physical properties of fragipans. The total volume of intruded mercury did not allow to discriminate between fragipan and nonfragipan horizons. However, from the variation of the pore volume as a function of the radius, two modal classes of pores were found, coarse and fine, respectively. The finepore class arose from the arrangement of clay particles, and its volume was correlated to clay contents r= 0.787 and to clay packing density r= –0.621. The clay fractions in fragipans were less densely packed than in the other B horizons, even if they had similar clay contents. The coarserpore modal class is known to arise from the interactions between clay, silt, and sand particles, and its volume was different among horizons. Fragipan had a low volume of this modal pore class. In addition, a packing density for the coarser phase of 0.74, corresponding to a rhombohedral packing, was found only in fragipans. Thus, the low permeability and high bulk density of fragipans are linked to specific arrangements of the particles: an open packing of the clay phase is associated to an extremely dense packing of silt and sand. This combination is not present in any other soil horizon.

Variations in soil-water and mineralogical composition of clay particles are important factors governing the formation and stabilization of soil aggregates. We evaluated the effects of these factors on aggregate genesis in two soils with different mineralogical compositions. One developed from chlorite-rich schists and the other from serpentinite, but they have similar organic matter and Fe oxides contents. The <2-mm fractions were submitted to one cycle of wetting and drying, producing two classes of newly formed aggregates (2-5 and >5 mm in diameter). The aggregates differed in water stability, with those from serpentinitic soil being more stable. The amounts of water-dispersible clay (WDC) were lower in the more stable aggregates than in the original <2 mm fraction, and the WDC showed more positive electrophoretic mobility values, indicating its stabilization during aggregation. In the aggregates obtained from chlorite-rich soil, the WDC amounts were similar to those of the <2-mm fractions, and the electrophoretic mobility values were more negative. The aggregation and stabilization processes differed in the two soils and were affected by the clay dispersion/flocculation behavior. The variations in aggregate stabilization were therefore attributed to different clay-clay and clay-sand interactions caused by the mineralogical differences in the clay fractions involved. No differences were found when comparing the two size classes of newly formed aggregates from the same soil. This indicates that the same mechanism produced aggregates of a variety of sizes.

Several mechanisms are responsible of the destabilization of soil aggregates in water slaking, swelling, and dispersion of the clay and mechanical breakdown by abrasion. The aggregate resistance differs in relation to the dominant disruptive phenomenon, and by applying different methods to assess aggregate stability, a specific physical susceptibility of different horizons may be evidenced. Therefore, we evaluated the relative importance of the mechanisms of breakdown in some Typic Fragiudalfs, taking into account the specific horizon characteristics, to understand if the fragipan brittleness is related to a specific mechanism, and how the soil properties affect the resistance to fast wetting. The standard wet sieving test, which evaluates all destabilization mechanisms together, indicated a clear role of soil organic matter in protecting the aggregates, with greater losses in the deeper horizons (about 70%), but did not allow us to discriminate between fragipans and other horizons. When the losses caused by water abrasion were separated from the breakdown due to wetting phase using a kinetic approach, a high breakdown caused by fast wetting was found in deep horizons, but still no difference between fragipan and non-fragipans were visible, even though fragipan clods are known to be particularly sensitive to fast wetting. By excluding the effect of organic matter and prewetting the samples with ethanol, differences between these horizons appeared within the water saturation phase and fragipans and non-fragipans were found to be sensitive to different mechanisms. In fragipans, the relative percentage of slaking was higher, always above 30%, whereas for non-fragipans clay dispersion and swelling weighted more heavily. The complexity of the clay fraction did not allow us to relate the mineralogy to swelling or dispersion, but slaking was instead clearly related to clay arrangement and the consequent porosity characteristics (r2= 0.62), and not to clay content only.