Background and aims Quarrying causes severe degradation of soils and forest cover that can be recovered partially when the quarries are abandoned and re-colonised by plants. To understand the recovery of soil functionality and nutrient cycling, we studied the development of soil phosphorus pools during Scots pine (Pinus sylvestris) revegetation in a disused sand quarry in Northwestern Russia. Methods Sites that had been developing for different times since abandonment were compared to the parent sand and an adjacent undisturbed forest. Phosphorus speciation in genetic horizons of soil profiles was determined by sequential fractionation and solution phosphorus-31 nuclear magnetic resonance spectroscopy. Results Rapid transformations in soil properties occurred in 40 years, with a marked decline in pH and an accumulation of organic matter. Phosphorus transformations were shaped by geochemical processes, with a rapid release of inorganic phosphorus from primary minerals and accumulation of organic phosphorus to concentrations exceeding those found in the undisturbed site. Adsorbed and/or precipitated phosphorus increased rapidly, despite few reactive mineral colloidal surfaces. Conclusions Natural succession of Scots pine in post-mining landscapes promotes ecosystem restoration through the rapid re-establishment of the biogeochemical cycles of organic matter and phosphorus. This study also provides an important example of biogeochemical phosphorus cycling during the initial stages of pedogenesis.

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In the determination of the cation exchange capacity (CEC) by the NH 4 -acetate-NaCl method, the evaluation of the quantity of ammonium exchanged by the soil is often carried out by steam distillation and titration. While this procedure gives reliable results when applied to soils with medium to high amounts of available sites for exchange, in the case of sandy or desert soils it may not be as precise as required for a good interpretation of the results. Colorimetric methods are instead well known for their high sensitivity, although their application may require a more complicated procedure. The aim of this work was to assess the suitability of a well known colorimetric measurement of ammonium content for the determination of the CEC in sandy soils, to evaluate its range of applicability and to propose a standardized procedure. Eight sandy soils from Southern Africa were used for the evaluation of the method suitability. The procedure gave very acceptable results, with low internal 2519 ORDER REPRINTS variability and the data obtained were comparable to those obtained with the standard steam distillation procedure. However, its application requires certain precautions as the equilibrium for the reaction of color development is reached only after 90 minutes. With this method the determination of CEC values from as low as 1 cmol(+) Kg 21 to about 20 cmol(+) Kg 21 was possible using 0.1-0.5 mL of NaCl solution, but a wider range may be measured either by using lower sample weights or by diluting the NaCl solutions.

Eucalyptus stands in semi-arid areas may contribute to enhance carbon (C) stocks in both biomass and soil. However, the limited information available is mainly focused on short-rotation plantations. In this study, the aboveand below-ground C pools in five 50-year-old Eucalyptus camaldulensis Dehnh. stands planted on Miocenic evaporitic deposits in Sicily, Italy, with a xeric and thermic pedoclimate, were measured. Above-ground biomass was determined by partitioning and weighing branches, stem and leaves. Below-ground C pools included the determination of litter, root biomass, and soil organic and inorganic C. In terms of the above-ground biomass, the E. camaldulensis stand accumulated on average 116 Mg ha −1 corresponding to 55 Mg C ha −1 . Below-ground biomass consisted mainly of larger roots, followed by fine and medium roots (33 Mg ha −1 corresponding to 14 Mg C ha −1 ). Litter accumulation on the soil surface accounted for 13 Mg ha −1 corresponding to 5 Mg C ha −1 . The amount of C stored in soil was 554 Mg C ha −1 , of which 75% was in organic form. Although E. camaldulensis is planted extensively throughout the Southern Hemisphere and tropics where it is managed over short rotations (c. 2-4 years), the results obtained from this study make this species important in terms of future afforestation planning for longer rotations due to its potential to sequester C, particularly in the below-ground components.

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 typesalthough 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 ¼ 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.