This study discusses the soil surface conditions under which crusting and runoff are generated. A field survey was conducted in three agricultural districts in the province of A Coruña (Galicia, Spain), where the soils, developed over basic schists in a temperate-humid climate, are prone to crusting. A total of 168 freshly tilled surfaces and the cumulative natural rainfall since the last tillage operation were studied. The agricultural situations corresponded to primary and secondary tillage, crop seedbeds and pasture seedbeds. Stages of soil crusting were recorded by visual assessment, based on the estimation of the extent of structural, transitional and sedimentary crusting. The runoff was estimated by measuring the maximum distance reached by soil particles carried by the runoff and then deposited on the soil surface where there were no incisions on soil. Surface crusting was observed in all agricultural situations. The amount of accumulated rainfall required to form a fully sedimentary crust was variable, depending largely on the initial soil surface roughness. On average, 50, 150 and 350 mm of accumulated rainfall were required for soil surfaces with a low, medium and high roughness, respectively. The combination of three soil surface conditions (crusting stage, roughness and vegetation cover) was primarily responsible for the start of runoff formation.

The soil organic carbon content was analyzed in more than 7 000 soil samples under different land uses, climates and lithologies from northern Spain (Galicia, Asturias, Cantábria y País Vasco). GIS maps (1:50 000) were made of the % SOC and SOC stocks. The % SOC varies according to land use (higher in forest and scrub soils and lower in agricultural soils) and climate, and there is a highly significant correlation between SOC content and mean annual precipitation. There are significant differences between the soils of Galicia/Western Asturias (GA<sub>w</sub>) and those of the rest of the study area (Central and Eastern Asturias, Cantabria and País Vasco) (A<sub>ce</sub>CV), although these are neighbouring regions. In forest and/or scrub soils with a <em>udic</em> soil moisture regime, in GA<sub>w</sub>, the SOC is usually > 7% and the average stocks 260 t ha<sup> -1</sup> (0-30 cm), and >340 t ha<sup>-1</sup> (0-50 cm) in soils with thick organic matter rich horizons (> 40 cm); these values greatly exceed the average contents observed in forest soils from temperate zones. Under similar conditions of vegetation and climate in soils of A<sub>ce</sub>CV the SOC average is 3% and the mean stocks 90-100 t ha<sup>-1</sup> (0-30 cm). The <em>andic</em> character of acid forest soils in GA<sub>w</sub> and the formation of C-Al,Fe complexes are pointed out as the SOC stabilization mechanism, in contrast to the neutral and calcareous soils that predominate in A<sub>ce</sub>CV, where the main species of OC are easily biodegradable.

The sorption capacity for Ni, Pb and Zn of mine tailings soil with and without reclamation treatment (tree planting and waste amendment) was evaluated using the batch adsorption technique. It is important to determine the capacity of waste-amended soils to retain Ni, Pb and Zn, as the sludges used usually have high concentrations of these metals. The results obtained in the present study showed that the untreated mine tailings soil had a low capacity for Ni, Pb and Zn retention. The sorption capacity for Pb increased significantly in all of the treated soils, without any significant differences between them. The treatment that most increased the sorption capacity for Ni and Zn was planting with trees and amending with waste simultaneously, as this increased the concentration of both organic and inorganic carbon, exchangeable calcium, soil pH and effective cation exchange capacity

During the Late Pleistocene, Mexico had a richer fauna than today with many different forms of megafauna that are now extinct. However, the ecosystems they inhabited and the particular ecological niches that they occupied are still poorly understood. Most of the findings of Pleistocene megafauna have been in alluvial deposits that present rich opportunities for paleoecological studies using paleopedological records. Floodplain paleosols commonly are poorly developed. However, micromorphological analysis provides information about the grade of development of the soil at a microscale, discriminating between genetic and sedimentary processes; thus helping in the identification of the environmental setting in which they formed. We analyzed the micromorphology of six pedogenetic units in the sequences of Santa Cruz Nuevo and Axamilpa, in the south of Puebla, and Huexoyucan, in the state of Tlaxcala. These pedosequences correspond to the second half of marine isotopic stage 3 (MIS3), MIS2 and the early Holocene. All studied units are characterized by strong pigmentation with dark humus. The micromorphological analysis of MIS3 paleosols reveals aquatic conditions with evidence of freshwater biota and microlamination as well as pedogenetic features of hydrogenic carbonate precipitation and redoximorphic processes. The dark paleosols of MIS2 and the early Holocene demonstrate signs of stronger coprogenic aggregation, weathering and fewer gleyic features. Comparison with modern soils shows that the latter were formed under better-drained, aerated conditions that exclude redoximorphic processes. We conclude that the dark colored Pleistocene paleosol units are indicative of different paleo-landscapes: wetlands in the MIS3 and moist meadows in MIS2 – early Holocene. The swampy ecosystems could play an important role as a megafauna habitat.

The research was performed in the south-eastern part of Russia. Soils were formed on clayey parent materials under an extreme continental climate favorable for the deep freezing and maintenance of permafrost. Based on morphological, micromorphological, physical and chemical attributes, the soils represent a soil complex that includes Vertic Luvic Phaeozems (Clayic and Turbic) and Luvic Phaeozems (Clayic and Turbic). Decomposition, aggregation, eluviation, illuviation, pedoturbation, mineralization and hardening result from accumulation and transformation of organic matter, freeze-thaw, shrink-swell, and translocation processes, and cryoturbation. The soil complex is interpreted as polygenetic. Interpretations were made in order to differentiate modern soil processes from relict ones. The most ancient features correspond to the cold Pleistocene glacial period and include cryogenic wedges, permafrost involutions, disrupted soil horizons, cryogenic sorting of coarse material, and accumulation of the organic matter above the permafrost. A subsequent stage of pedogenesis under a warmer and wetter environment is reflected by black humus crack infillings, black humus aggregates deep in the subsoil, vertical translocation of mobile organic matter, and the formation of clay coatings. Finally, the current climate is a warmer but more arid pedoenvironment. It is recorded in the soil complex by brownish fulvic humus and the formation of vertic features. Even in this last relatively warm climatic stage, vertic features formed by shrinking and swelling processes co-exist with annual deep freezing of the soils and subsoil permafrost at a depth of about ~300 cm.

Two surface microhorizons – vesicular and platy – were found to be typical of the fabric of topsoil horizons in gravely loamy soils located along an arid/continental climatic gradient in the Subboreal zone of Central Asia (from southern Russia to Uzbekistan, Kazakhstan, and Mongolia). Their genesis is related to active vesiculation (for vesicular А<sub>1</sub> microhorizon) and cryogenesis (for platy А<sub>2</sub> microhorizon) against a background of high clay mobility and/or eolian accumulation of fine material. New mechanisms responsible for the formation of vesicular pores are suggested: (a) the leaching of dense complete crystal infillings (moldic voids) and (b) the development of biogenic capsules typical of iron bacteria that were diagnosed by the microbiological method of fouling Agar-covered glasses under natural conditions. In a series of studied soils, Yermic Regosols are characterized by additional specific microfeatures: (1) iron depletion from the material around the pores and formation of iron concentrations in the intrapedal mass owing to biogenic mobilization of iron with participation of sulfate- and iron-reducing bacteria and (2) the accumulation of organic matter (residues of microbial cells) in the vesicular pores.

The objective of this study was to analyse the influence of tillage on soil aggregate stability using the ultrasonic dispersion method with different levels of energy. Experiments are performed with self-developed equipment at low vibration amplitudes of 0.5 μm, 2 μm and 5 μm. Ultrasonic power is 0.7 W, 8.9 W and 22.3 W for the three amplitudes. Samples of aggregates 2 000 - 250 μm of a degraded loamy silt Chernozem, a loamy clay Cambisol and a loamy sand Cambisol from eastern Austria were collected under different tillage regimes: conventional tillage (CT) with mechanical weed control and no tillage (NT) with inter cropping in winter. Measuring Soil Aggregate Stability (SAS) according to DIN norm showed that the stability decreased in the sequence loamy clay Cambisol > loamy sand Cambisol > loamy silt Chernozem. Influences of tillage could be observed with SAS for the last two samples mentioned. Ultrasonic dispersion tests at vibration amplitude 0.5 μm and 2 μm show higher stability of the Cambisol soils. Significant influences of soil tillage on aggregate stability for the loamy clay Cambisol and the degraded Chernozem were observed after short ultrasonic dispersion times and absorbed energies of 1 - 1.7 J ml<sup>-1</sup>. The measured aggregate stability decreased in the following order: Cambisol NT > Cambisol CT > Chernozem NT > Chernozem CT. Differences in loamy sand Cambisol could not be detected with the ultrasonic method due to a low aggregation level of the macro aggregates. This study highlights the importance of quantifying the energy output of the ultrasonic equipment when analysing changes in soil aggregate stability, for the evaluation of tillage treatments. A more comprehensive analysis of aggregate stability can be obtained when using both, the wet-sieving SAS method and ultrasonic dispersion at low energy levels.

n the characterization of the initial state of a long-term experiment (ELD) under no-till, we hypothesized that there are horizontal and vertical fertility gradients in the topsoil. The objective of this paper is to describe and to quantify those variations in a block design wheat fertilization experiment in the field of the National University of the South (UNS), Argentina. In a slightly inclined field 4 blocks were located across the slope. Soil depth was 80 cm at the top and increased downward to 100 cm. The soil was classified as a Petrocalcic Paleustoll, thermic coarse loam. Composite samples of each block were taken at the depths of 0-6, 0-12, and 0-20 cm. They were air-dried and sieved through 2 000 µm. Determinations were: pH; electrical conductivity (CE); cation exchange capacity (CIC); exchangeable cations: calcium (Ca<sub>int</sub>), magnesium (Mg<sub>int</sub>), potassium (K<sub>int</sub>) and sodium (Na<sub>int</sub>); extractable nutrients: phosphorus (P<sub>BK</sub>), sulphur (S-SO<sub>4</sub><sup>2-</sup>), boron (B<sub>ext</sub>), iron (Fe<sub>ext</sub>), manganese (Mn<sub>ext</sub>), copper (Cu<sub>ext</sub>) and zinc (Zn<sub>ext</sub>). In samples sieved through 500 µm total organic carbon (COT) and nitrogen (N<sub>ot</sub>) were determined. Walkley & Black (W-B) was used for analysis of easily oxidizable organic carbon (COX<sub>24</sub>), lower H<sub>2</sub>SO<sub>4</sub> concentrations of 12 and 18 N were used for further determinations (COX<sub>12</sub> and COX<sub>18</sub>). Results were analyzed using descriptive statistics, t test for paired means and regressions. Soil organic carbon variables and oxidation factor for W-B were consistent with low intensity use of native grasses in the plot selected as a starting point for the ELD. The range of pH values (7.3-8.0) reflected base saturation, with ideal levels of Ca<sub>int</sub>, Mg<sub>int </sub>and K<sub>int</sub>. Nutrient availability was high for S-SO<sub>4</sub><sup>2-</sup>, B<sub>ext</sub>, Fe<sub>ext</sub> and Mn<sub>ext</sub>, moderate for Cu<sub>ext</sub> and Zn<sub>ext</sub> and low for P<sub>BK</sub>. The coefficient of variation (CV) was between 7 and 11 % for ten variables. The most stable were pH, Mg<sub>int</sub>, CIC, C:N and Cu<sub>ext</sub> (CV < 7 %). Others (COX<sub>12</sub>, N<sub>ot</sub>, Mn<sub>ext</sub> and Zn<sub>ext</sub>) showed greater variability (CV 11-20 %) and P<sub>BK</sub> (CV 33.9 %). The statistical treatment of the space variability was adapted to the block design and sampling depths. In 12 out of 20 parameters, sampling depth and/or the position of the blocks explained over 30 % of the observed variations. The changes in depth of P<sub>BK</sub>, K<sub>int</sub> and cation micronutrients (with the exception of the Cu<sub>ext</sub>) can be associated to their scarce mobility in the soil. The position in the slope with potential effects on available water and biomass production, would explain the gradients in CIC, Ca<sub>int</sub> and organic carbon. The opposite trend found for P<sub>BK</sub> is attributed to its negative non-significant relation with pH. This variability study approach can enhance monitoring of soil chemical properties in the ELD.