Gloria Falsone

Influence of serpentine abundance on the vertical distribution of available elements in soils

Background and AimBiotic and abiotic factors contribute in shaping the distribution through the soil profile of elements released by mineral weathering; among them, leaching and biocycling dominate in temperate environments. We evaluated if the intensity of leaching and biocycling of nutrients can be modulated by element deficiencies linked to the abundance of serpentine in the soil parent material, i.e. if the most deficient elements are more efficiently retained.MethodsWe selected twelve poorly developed soils from Northern Italian beech stands, with variable amounts of serpentinites in the parent material, and determined total and exchangeable Ca, Mg and K, as well as an index of abundance of serpentine minerals.ResultsThe total element content depended on the abundance of serpentines, while only exchangeable Mg was related to the parent material. The vertical trend of Ca and K indicated the role of biocycling in all soils, but the relative availability of Ca (ratio between exchangeable and total content) was much higher in the top horizons of serpentine-rich soils.ConclusionsThe different element availability among soils suggested that the vertical distribution of available elements was linked to the parent material and that losses were limited in serpentine-rich soils, probably because plants take up the deficient elements as soon as they are released from litter and thus limit their leaching in deeper soil horizons.

Wet Aggregate Stability of Some Botswana Soil Profiles

ABSTRACT During intense and short rainfall events, important losses of fertility are expected as a result of erosion in drylands because the nutrient pools are concentrated in the topsoil. Therefore, we evaluated the kinetics of aggregate stability in some Haplargids and Torripsamments in Botswana as it represents a resistance factor against losses of materials, measuring also the release of organic matter and phosphorus during wet sieving. We found very low contents of 1–2 mm aggregates in both soil types—although the Haplargids had higher levels of this size aggregate (19%) compared with the Torripsamments (10%)—and no differences between the topsoil and the deeper horizons. The total losses of aggregates were similar in topsoils and deep soil horizons and independent from soil order, but the Entisols had a greater proportion of aggregate breakdown, 38% on the average, when the sample was water-saturated. Only clay and silt content, and cation exchange capacity showed good correlations with aggregate stability. Organic matter or iron oxides had no effect, suggesting that aggregation is the result of cation bridging between mineral particles. Up to 97% of the organic matter released into water was lost at the beginning of the wet sieving, but the amounts were not related to aggregate breakdown, indicating that organic matter, besides not influencing the stability of macroaggregates, had little effect on the stabilization of microaggregates. Phosphorus was also released during the wet sieving, and was related to soil available P (r = 0.713 after 5 min). With no effect of organic matter on aggregate stability, and nutrients concentrated in the topsoil, the vulnerability of these soils to fertility losses is therefore extremely high.

Characteristics of fragipan B horizons developed on different parent material in North-Western Italy

ABSTRACT A Fragipan (Bx) is a soil horizon hard when dry and brittle when moist, that undergoes slaking upon water immersion, forming a barrier to roots and limiting land use. Brittleness and slaking depend on soil porosity and particle arrangement, but still no agreement exists on the inorganic components responsible for such arrangement. We hypothesized that the same kind of particle arrangement may originate from different soil components, ultimately depending on the lithology of parent material, and evaluated the soil and clay characteristics that best differentiate Bx from B horizons. Thirty-six samples were taken from Typic Fragiudalfs developed on the two sides of an alluvial fan characterized by different amounts of ultramafic materials. Discriminant Analysis evidenced that pedogenic Fe oxides were fundamental in discriminating Bx from B horizons on pure ultramafic parent material, while clay mineralogy was more important in soils with less ultramafic materials. In the first case, the association between clay minerals and self-assembling oxides systems may lead to brittleness, while in the second case the higher abundance of kaolinite may contribute to weak associations between pH-dependent sites and negatively charged surfaces. The only common feature to fragipans on both river sides was a higher degree of weathering.