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Abstract The hierarchical organization of aggregates in soil is responsible for the presence of inter and intra-aggregate pores. This research aimed to investigate effects of soil surface liming, considering lime rates of 0, 10 and 15 t ha−1, on the intra-aggregate porous system of soil aggregates with equivalent diameters of 2–4 and 1–2 mm, from 0 to 10 (A) and 10 to 20 cm (B) soil layers. These aggregates were selected by the wet sieving method carried out for determination of the mean weight diameter. Synchrotron-based computed microtomography (μCT) of aggregates was analyzed in terms of porosity, connectivity, tortuosity, and fractal dimension. Additionally, X-ray fluorescence was used to evaluate the elemental composition of the soil aggregates. All liming effects were concentrated at layer A, where calcium percentage was elevated in aggregates from 1–2 mm class as compared to those from 2–4 mm class. Accordingly, the physical parameters studied were generally more affected in the case of smaller aggregates (1–2 mm). Liming decreased total porosity, increased tortuosity of pores, and decreased fractal dimension for 1–2 mm aggregates, which was in line with the fact that larger pores were replaced by smaller ones in 1–2 mm aggregates, as found via both quantitative and qualitative analyses. On the other hand, liming did not affect pore connectivity under any of the circumstances. Highlights • Surface liming improved soil aggregation by increasing the mean weight diameter. • Smaller soil aggregates present higher percentage of calcium due to liming. • Liming effects on soil physical properties were stronger for smaller aggregates. • In these small aggregates, liming decreased porosity and increased tortuosity. • Liming provided a more homogeneous intra-aggregate pore space. [ABSTRACT FROM AUTHOR]

Abstract: Air-drying of soil samples is known to increase the exchangeable fraction of cadmium (Cd) in soil. Liming, on the other hand, reduces bioavailability of heavy metals in soil by metal hydrolysis reactions and/or coprecipitation with carbonate. However, due attention has not been paid to desorption and mobilization of Cd from air-dried and limed soils at realistic ionic strengths. We compared Cd desorption from moist and air-dried samples of two texture-contrasting soils which had been spiked with 3 or 30mg-Cd kg−1 after liming with 25mmolkg−1 of Ca(OH)2, or without prior liming. Repeated batch extraction with water and 1–10mM CaCl2 solutions was carried out, and chemical speciation of dissolved Cd performed using Visual MINTEQ. Desorption of Cd from the exchangeable pool in the soils was not exhaustive, with smaller fractions of Cd remaining after five extractions in the coarse-textured Chiba soil having lower CEC than the fine-textured Takada soil. Air-drying enhanced Cd desorption from the both soils particularly in the first extraction, with the cumulative Cd desorption after five extractions 1.5 times, on average, as large as that from the unlimed moist soils. Liming suppressed the Cd release, resulting in cumulative desorptions 0.14–0.19 times those from the unlimed counterparts. The air-drying and liming effects on Cd desorption were reflected in the apparent Cd2+/Ca2+ exchange selectivity coefficient, which was lowest in the first extraction upon air-drying, and significantly increased upon liming. Alternatively, assuming that constant Cd2+/Ca2+ exchange selectivities obtained from the moist unlimed soils apply, exchangeable Cd pools in the air-dried and limed soils were evaluated. The exchangeable pool was found to increase, on average, by 26% and 30% upon air-drying, and decrease by 79% and 86% upon liming in the Takada and Chiba soils, respectively. These results demonstrate that the size of exchangeable Cd in contaminated soils is prone to change upon drying and liming, and that the potentially desorbable Cd is only slowly mobilized under ionic strength conditions prevailing in the field. [Copyright &y& Elsevier]

Abstract: The aim of this study was to evaluate the effects of the particle size (2–4 mm, 0.5–2 mm, 0.25–0.5 mm and less than 0.25 mm) of magnesium limestone and the method of application (in a single dose or split in three yearly doses), on the forms of Al in the solid and liquid phases of an acid Galician soil destined for pasture production. Monitoring the experimental plots over a period of 3 years showed that the plots treated with a single application of the finest limestone (<0.25 mm) exhibited the highest pH and the lowest concentrations of exchangeable Al, with less than 10% Al saturation throughout the period of study. The average values of pH in water along the period of study were 5.30 in the most effective treatment and 5.06 in control plots. The average values of aluminium saturation were 6.5% in the most effective treatment and 16.9% in control plots. One year after liming, the plots treated with a single application of the finest limestone presented also the highest concentrations of weakly stable organo-aluminium complexes in the solid phase and of organically bound Al in the soil solution, as well as the lowest concentrations of labile Al, while no Al3+ (considered the most toxic Al species) was detected. Over time non-crystalline inorganic Al tended to precipitate, apparently at the expense of exchangeable Al and/or Al bound to the organic matter. The application of the finest limestone split in three doses (until completion of 3 t ha−1 in the third year of the study) was less effective than the application of a single dose. The plots treated with the coarsest limestone (between 2 and 4 mm) and the control plots provided similar results for all parameters throughout the three years of the study. In the former the exchangeable Al was higher than 20% and the concentration of labile Al was the highest of all plots. [Copyright &y& Elsevier]

Abstract: We studied soils exposed to emissions from the Ventanas copper smelter in central Chile. Values of pH, free Cu2+ activity, and total dissolved copper were determined in the saturated paste extracts and the soil solutions collected by means of perforated plastic bottles installed in situ. Soil solutions were collected based on the periodicity of the rain. The topsoils (up to 30 cm) exhibited pH values in the saturated paste extracts of 4.6–5.5 and total soil copper concentrations of 310–640 mg/kg. In contrast, subsoils exhibited pH values in the saturated paste extracts of 6.4–7.2 and total soil copper concentrations of 30–60 mg/kg. These data suggest that the anthropogenic inputs of the Ventanas smelter, with respect to increase in Cu concentrations and acidification, are restricted to the topsoil while the subsoil remains unaffected. The above observations are probably due to sandy loam texture of the topsoils that allowed rapid water infiltration that did not allow the equilibrium between the rain water and the soil constituents to be reached. Consistent with this argument, soil solutions were not as acid as saturated paste extracts. Likewise, free Cu2+ activities and total dissolved copper concentrations in the soil solutions were lower in the saturated paste extracts. Thus, saturated paste extracts were not a good proxy of soil solutions for short-duration and intense rain events. In situ soil solution sampling by simple and low-cost devices, such as perforated plastic bottles used in this study, is a better mean for assessment of metal mobility in contaminated soils than saturated paste extracts. In solutions percolating through the soil during rain events, dissolved organic carbon was the major factor controlling total dissolved copper concentrations while soil pH was the major factor controlling the free Cu2+ activity. [Copyright &y& Elsevier]