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Field observations of no-till production plots in the southern semiarid pampas region of Argentina question the sustainability of this practice from the soil quality (SQ) standpoint when the amount of residues left by typical crop rotations is not taken into account. Our aim was to evaluate a set of management practices as they have been implemented on farm operations of the region on SQ parameters of the surface soil. The six production systems identified represent the combinations of tillage systems (no − till, NT and reduced till, RT), time since implementation (10 or 15 years), rotations (WW, winter crops; WF, winter crops with extended fallow; WS, winter and summer crops) and soil types (sandy loam or loam to clay loam) found in the agricultural operations of local producers. Composited soil samples at three successive depths (0–5 cm, 5–10 cm and 10–18 cm) were taken in 27 production plots of ∼50 ha in size each, and analyzed for soil chemical, physical and biological properties. Our results showed when including sunflower as summer crops on the dominant sandy loams, that NT production plots had the lowest total organic carbon (TOC) and total nitrogen (TN), and particulate organic carbon and nitrogen (POC, PN), and showed a three-fold decrease in structural stability when compared with NT of only winter crops or with RT managed plots. Furthermore, our canonical discriminant analysis (CDA) showed structural index (SI), TOC, change in the mean weight diameter of aggregates (CWMD), and biological activity (BA) as the best SQ indicators for the study area. The quantified degradation suggests the need to reassess NT implementation in order to make NT a sustainable option for the southern semiarid pampas region.

The reliance of current farming systems on synthetic fertilizers caused concerns about their sustainability, and alternatives to supply nitrogen through biological processes have to be adapted to practical conditions. The present study compared a pure legume and legume-grass biculture as cover crops for sorghum in their supply of nitrogen (N) to the cash crop and their N leaching losses during fallow. A three-year field experiment under no-till with sorghum (Sorghum bicolor Moench.) as main crop and cover crop treatments (C- control = bare fallow; R-rye Secale cereale L.; V-vetch Vicia villosa sp dasycarpa; VR-vetch-rye biculture) was established with a completely randomized block design (four replicates) in semiarid central Argentina. Aerial biomass (AB) and N contents were determined for all crops. Soil moisture to 1 m and nitrate-N to 0.60 m depth were determined. Water use- and nitrogen use efficiencies (WUE and NUE) were calculated and biological nitrogen fixation (BNF) estimated. BNF depended on nitrate-N contents of the soils; highest values (11 and 10 g BNF m−2 for V and VR respectively) were reached at 1.3 g N m−2. Sorghum responded to higher N availability with an average of +299 and +512 g AB m−2 for V and VR compared to C, with higher WUE. The relationship between WUE and nitrate-N was positive with an optimum of 0.048 g N m−2 mm −1 where WUE reached a maximum of 4.9 g AB m−2 mm−1. Potential N losses by leaching were highest in control, while all cover crop treatments had lower losses. Our results support the hypothesis that a legume-grass biculture was more efficient in the trade-off between nitrogen provision to the cash crop and prevention of N losses by leaching. Although the amount of BNF was lower in the biculture than in pure vetch, it covered sorghum N requirements with less potential leaching losses even in high rainfall fallows.

Soil depth has played a key role in the development of soil survey, implementation of soil-specific management and validation of hydrological models. Generally, soil depth at field scale is difficult to map due to complex interactions of factors of soil formation at field scale. As a result, the conventional sampling schemes to map soil depth are generally laborious, time consuming and expensive. In this study, we presented, tested and evaluated a method to optimize the sampling scheme to map soil depth to petrocalcic horizon at field scale. The method was tested with real data at four agricultural fields localized in the southeast Pampas plain of Argentina. The purpose of the method was to minimize the sample dataset size to map soil depth to petrocalcic horizon based on ordinary cokriging, five calibration sample sizes (returned by Conditioned Latin hypercube –cLHS-), and apparent electrical conductivity (ECa) or elevation as variables of auxiliary information. The results suggest that (i) only 30% of samples collected on a 30-m grid are required to provide high prediction accuracy (R2 > 0.95) to map soil depth to petrocalcic horizon; (ii) an independent validation dataset based on 50% of the samples on a 30-m grid is adequate to validate the most realistic accuracy estimate; and (iii) ECa and elevation, as variables of auxiliary information, are sufficient to map soil depth to petrocalcic horizon. The method proposed provides a significant improvement over conventional to map soil depth and allows reducing cost, time and field labour. Extrapolation of the results to other areas needs to be tested. Fil: Domenech, Marisa Beatriz. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Barrow; Argentina Fil: Castro Franco, Mauricio. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Costa, Jose Luis. Instituto Nacional de Tecnología Agropecuaria. Centro Regional Buenos Aires Sur. Estación Experimental Agropecuaria Balcarce; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Amiotti, Nilda Mabel. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

La región semiárida de Bahía Blanca -SO pampeano-, sufrió en años recientes una intensa sequía que determinó una reducción inusual del almacenamiento de agua en el dique Paso de las Piedras (mínimo: 154.1 m snm), fuente de abastecimiento de agua potable de las ciudades de Bahía Blanca y Punta Alta. Aunque esta emergencia ha finalizado, la población sin acceso a la red pública de agua potable utiliza el acuífero freático y el termal profundo. En ambos, se evaluó la calidad del agua (CAA, OMS, USEPA) determinando As, F, B y V. El As (18 - 500 µg L-1) alcanzó máximos en Gral. D. Cerri y Villa Aeropuerto, asociado a elevado F (2.500-3.500 µg L-1). En el sector Los Chañares, urbanización sin conexión a la red, la salinidad fue alta. El B fue

Designing and validating digital soil mapping (DSM) techniques can facilitate precision agriculture implementation. This study generates and validates a technique for the spatial prediction of soil properties based on C-band radar data. To this end, (i) we focused on working at farm-field scale and conditions, a fact scarcely reported; (ii) we validated the usefulness of Random Forest regression (RF) to predict soil properties based on C-band radar data; (iii) we validated the prediction accuracy of C-band radar data according to the coverage condition (for example: crop or fallow); and (iv) we aimed to find spatial relationship between soil apparent electrical conductivity and C-band radar. The experiment was conducted on two agricultural fields in the southern Argentine Pampas. Fifty one Sentinel 1 Level-1 GRD (Grid) products of C-band frequency (5.36 GHz) were processed. VH and VV polarizations and the dual polarization SAR vegetation index (DPSVI) were estimated. Soil information was obtained through regular-grid sample scheme and apparent soil electrical conductivity (ECa) measurements. Soil properties predicted were: texture, effective soil depth, ECa at 0-0.3m depth and ECa at 0-0.9m depth. The effect of water, vegetation and soil on the depolarization from SAR backscattering was analyzed. Complementary, spatial predictions of all soil properties from ordinary cokriging and Conditioned Latin hypercube sampling (cLHS) were evaluated using six different soil sample sizes: 20, 40, 60, 80, 100 and the total of the grid sampling scheme. The results demonstrate that the prediction accuracy of C-band SAR data for most of the soil properties evaluated varies considerably and is closely dependent on the coverage type and weather dynamics. The polarizations with high prediction accuracy of all soil properties showed low values of σVVo and σVHo, while those with low prediction accuracy showed high values of σVVo and low values of σVHo. The spatial patterns among maps of all soil properties using all samples and all sample sizes were similar. In conditions when summer crops demand large amount of water and there is soil water deficit backscattering showed higher prediction accuracy for most soil properties. During the fallow season, the prediction accuracy decreased and the spatial prediction accuracy was closely dependent on the number of validation samples. The findings of this study corroborates that DSM techniques at field scale can be achieved by using C-band SAR data. Extrapolation y applicability of this study to other areas remain to be tested. EEA Balcarce Fil: Domenech, Marisa. Universidad Nacional del Sur. Departamento de Agronomía; Argentina. Fil: Amiottia, Nilda. Universidad Nacional del Sur. Departamento de Agronomía; Argentina. Fil: Amiottia, Nilda. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Fil: Costa, José Luis. Instituto Nacional de Tecnología Agropecuaria (INTA). Estación Experimental Agropecuaria Balcarce; Argentina. Fil: Castro-Franco, Mauricio. Centro de Investigaciones de la Caña de Azúcar de Colombia. Estación Experimental Estación Experimental vía Cali-Florida; Colombia.

Changes in land-use systems such as the introduction of trees on agricultural land can give rise to changes in the physicochemical properties of the soils, also affecting the quantity and quality of organic matter incorporated into the system. The present study assesses humic substances (HS) in the soil such as humic acid (HA) and fulvic acid (FA) by looking at the relationship between the optic densities determined at 465 and 665 nm (E4/E6 ratio). Topsoil samples (0–20 cm) from pine woodlands 60 years of age were compared with agricultural soils of similar age in the central-south region of the Province of Buenos Aires, Argentina. The pH of the topsoil from beneath the pine trees was highly acidic (5.0 vs. 6.2) and a significant increase in the level of organic carbon (OC) was registered. The carbon to nitrogen (C/N) ratio was also higher (by one order of magnitude) beneath the pine trees, although the humification conditions of the soil organic matter (SOM) were good in the soils of both studied...

The interrelation between hydrochemistry and hydrodinamicswas analyzed in the basin of El Divisorio stream. Thiswas to gain undestanding in the magnitude, distribution of toxicions (As, F) and behaviour in the discharge of main nutrients (P,N) contributing to the eutrofication of Paso de las Piedras Dam.During two years, 47 sites were sampled determining several parameters:geographical position for each sampling point, phreaticlevel depth, and As, F, PO4 and N-NO3 concentrations. Repeatedmeasures, Fisher test, correlation and regression analysis were appliedto all variables. Highly significant space and time differences(P

Afforestation of grasslands can increase C sequestration and provide additional economic and environmental benefits. Pine plantations, however, have often been found to deplete soil organic C and trigger detrimental effects on soils. We examined soil characteristics under a 45-year-old Pinus radiata stand and under adjacent grassland on maritime dunes in temperate Argentina. Soil under the pine plantation had greater soil organic C (+93%), total N (+55%) and available P (+100%) concentrations than under grassland. Carbon was stored under the pinestand at an estimated mean accretion rate of 0.64 Mg ha−1 y−1. At 0- to 25-cm depth, soil C amounted to 61 Mg ha−1 under pine and 27 Mg ha−1 under grassland. Soil C accumulated more on dune slopes (35 Mg ha−1 y−1) than on ridges(29 Mg ha−1 y−1) and bottoms (12 Mg ha−1 y−1). Compared with the grassland, soil acidity, cation-exchange capacity, base losses (K > Ca = Mg) and C/N ratio increased under pine. Spatial heterogeneity in soil characteristics was greater unde...

We investigated the levels of F and its relationship with As, B and V in ground and surface waters of the southern Pampas, where cases of dental and skeletal fluorosis, and arsenic in hair and urine samples have been detected in the rural population. Eating vegetables and cereals grown in irrigated areas with excessive fluoride may increase the risk of fluorosis due to the addition of the extra F contributed from other sources such as drinking water. Moreover, if these elements exceed the tolerance of crops produce toxicity and, like salinity, they decrease the potential crop yield. Within an area of 2300 km2, 81 samples were taken from surface and groundwaters to determine F, As, B and V. Fluoride was detected in 86% of the sampled groundwaters, and in 65% of the surface waters reaching maximun concentrations of 7.12 mg/L and of 6.5 mg/L, respectively. Risk areas were determined based on the distribution of F in the unconfined aquifer; the highest concentrations were observed towards the S-SW, in the central and SE sectors. On he surface flow, the highest concentrations were found at the west with sampling points remarkably prominent. These waters are classified as sodium-sulfate, C3 and with high concentrations of F, B and V that could produce toxicity and reduce yields on irrigated crops. Fluoride correlated significantly (p

Surface and groundwaters of El Divisorio brook (Argentina) have excessive As (WHO, USEPA, CAA: > 10 μg L− 1). The rural population is at risk of arsenicism because groundwater is the only source of water for human consumption. We analyse geoavailability of As and other associated elements (Ba, Br, Co, Cr, Fe and Na) in the solid phase (INAA-Actlabs), determine the association between As and other elements in the mineral suite and in waters, quantify Fe oxides (Feox; Mehra and Jackson) and interpret their relationship with As, total Fe (Fetotal) and Na in the solid phase applying Principal Components (PC) to understand factors and processes that rule their incorporation into groundwaters and to identify areas at risk of elevated As in waters. Intrabasin variability of total As content (range 5.80–20.70 mg kg− 1) with the highest amounts towards the discharge areas and a more irregular vertical distribution, particularly in the alluvial plain, reflects differences in As-bearer frequencies. Arsenic is slightly lower in the Bw horizons compared with the A and C horizons and it increases in the Bt horizon through clay illuviation. More than 90% of sodium-bicarbonated surface and groundwaters showed As > 10 μg L− 1 (range: 10 to 114 μg L− 1) with the highest levels in the middle–lower basin. The highest contributions to PC1 were Br (0.673), Co (0.868) and Na (− 0.769); As (0.814) and Cr (0.686) were relevant to PC2 and Ba (0.501) and Fe (0.783) were relevant to PC3. In the upper basin, a greater amount of Na withheld in the solids promotes a less aggressive geochemical environment and prevents As from entering waters, thus yielding lower As levels in the aquifer compared with the middle–lower basin. Here, alkalinity (pH: 7 up to > 9) promotes weathering and liberation of As from volcanic glass and other carriers, formation of As oxyanion species together with As desorption from charged clays and Al–Fe–Mn sesquioxides and concentration up to unacceptable levels in solution. Landform configuration, climate and pedoclimate, the residence time of water and the local hydrogeochemical variables (pH, competition with other ions, adsorption–desorption) control mobility and concentration of As in a dynamic equilibrium with the local chemistry. Evaporation (subhumid to semiarid climate) and oxyion competition reinforce As accumulation in the shallow aquifers. Fil: Díaz, Silvana Letisia. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Agronomía. Laboratorio de Hidrología y Riego; Argentina Fil: Espósito, Martín Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Agronomía. Laboratorio de Hidrología y Riego; Argentina Fil: Blanco, María del Carmen. Universidad Nacional del Sur. Departamento de Agronomía. Laboratorio de Hidrología y Riego; Argentina Fil: Amiotti, Nilda Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Agronomía. Laboratorio de Hidrología y Riego; Argentina Fil: Schmidt, Erica Susana. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Agronomía. Laboratorio de Hidrología y Riego; Argentina Fil: Sequeira, Mario Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina. Universidad Nacional del Sur. Departamento de Agronomía. Laboratorio de Hidrología y Riego; Argentina Fil: Paoloni, Juan Dario. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Agronomía. Laboratorio de Hidrología y Riego; Argentina Fil: Nicolli, Hugo Benjamin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Ministerio de Defensa. Fuerza Aérea Argentina. Instituto de Geoquímica; Argentina

SSSAJ: Volume 76: Number 2 • March–April 2012 Soil Sci. Soc. Am. J. 76:558–568 Posted online 6 Feb. 2012 doi:10.2136/sssaj2011.0306 Received 7 Sept. 2011. *Corresponding author (villamil@illinois.edu). © Soil Science Society of America, 5585 Guilford Rd., Madison WI 53711 USA All rights reserved. No part of this periodical may be reproduced or transmitted in any form or by any means, electronic or mechanical, including photocopying, recording, or any information storage and retrieval system, without permission in writing from the publisher. Permission for printing and for reprinting the material contained herein has been obtained by the publisher. Agronomic and Taxonomic Consequences of Agricultural Use of Marginal Soils in Argentina Pedology

Resumen. La demanda de una mayor produccion bovina en la region del Caldenal en la zona centro de Argentina ha resultado en un sobrepastoreo continuo determinante de una estructura de la vegetacion en parches. Estos parches son claramente identificados en base a las especies dominantes resultantes de la historia de pastoreo. El objetivo principal del presente trabajo fue examinar la influencia de las plantas individuales sobre el patron multivariado de nutrientes del suelo en cada parche, evaluando asimismo la magnitud de la asociacion entre la concentracion de nutrientes en planta y suelo. El analisis discriminante canonico senalo a los contenidos de materia organica, fosforo disponible y zinc en el suelo como las variables de mayor impacto en la segregacion de los parches de vegetacion. El analisis de correlacion canonica entre las variables de suelo y planta indico una asociacion significativa entre ambos grupos (R2 0,97). Los parches con diferente historia de pastoreo pueden ser identificados no solo por las especies vegetales dominantes, sino tambien a traves del patron de atributos del suelo. Esta informacion puede contribuir al desarrollo de practicas de manejo orientadas a la recuperacion de los parches degradados por sobrepastoreo.

This research aims at making a diagnosis of the presence of arsenic, boron, fluorine and vanadium in the waters from the basin of El Divisorio stream, tributary of Paso de las Piedras reservoir, in the southwest of Buenos Aires Province. This storage is used to provide water to the cities of Bahia Blanca and Punta Alta with a population of approximately 400,000 inhabitants. A selective and specific sampling of wells, perforations and superficial watercourses was made in 46 points, in an area of nearly 400 km2. Groundwaters had arsenic (max. 0.114 mg/l) exceeding the reference guideline in 97.3% of the samples, boron (max. 1.42 mg/l), vanadium (max. 0.8 mg/l) and fluorine (max. 6.6 mg/l), being respect- tively, 91.9%, 82.9%, and 67.6%. Regarding the superficial flow, while arsenic concentrations were higher than the limit in 100% of the cases (max. 0.072 mg/l), 88.9% corresponded to elevated boron (max. 1 mg/l) and vanadium (max. 0.23 mg/l) and only 22.2% to fluorine (max. 3.18 mg/l) ones. In all these cases, concentrations exceed the reference guideline values suggested by the World Health Organization, the Argentine Food Code and the Environmental Protec- tion Agency. The presence of these contaminants that finally could determine the quality of the water resource entering the reservoir is attributed to the natural characteristics of the environment since contributions by anthropic actions have not been detected in the area. The most critical sectors in the basin were identified in order to stress the possible negative influence of consuming these waters on the community’s health, with the purpose of reporting the results to institutions, authorities and the population and applying them to preventive medicine.

Factors that determine the segregation of soils belonging to the Mollisol or Aridisol orders have been evaluated in the semiarid-arid transition region of Argentina. The influence of edaphic parameters and precipitation on the soil organic carbon content (SOC) and color of the surficial horizons were studied on a transect of 300 km length. Results indicate that the mean annual precipitation (MAP), the contents of clay (C), silt (Si), and their summation (C + Si), as well as the color attributes value (V), chroma (Ch) and their product (VCh) showed significant linear correlations with SOC ( r = 0.63, 0.55, 0.61, 0.65, − 0.71, − 0.45 and − 0.66 respectively, p r 2 = 0.20 to 0.50). A multiple regression model including the variables MAP and C + Si increased the explanation of the SOC variability up to 67% ( p 400 mm, epipedons are mainly mollic, between 400–300 mm, the mollic or ochric epipedons are closely related to its texture, and in areas with MAP − 1 , increasing with higher precipitation and finer textures.

The study was carried out in the zone corresponding to the Anzoátegui district (Province of La Pampa, Argentina), covering an area of 1600km2. This zone belongs to the Caldenal or Southern Espinal, an semi-arid region in central Argentina. The annual rainfall is 109/761 mm, but the annual evapo-transpiration is as high as 1220mm, so that the annual runoff is small compared with the annual rainfall. Since shallow ground-water is the principal source of water in the region, the hydrodynamics of the subterranean flow was evaluated and the depth variation of hydrostatic levels in relation to the surface was studied. Water quality was determined by hydrochemical analyses and classified for drinking water for cattle, human consumption and irrigation. It was found to be poor, 60·2% of the study area is affected by saline concentrations exceeds 5·0dSm−1. With respect to the ground-water-quality deterioration, reference was made to land use and management systems in the area, where the main economic activity is the cattle breeding, so that the vegetation has been degraded by overgrazing and deforestation for over 100 years. Fil: Paoloni, Juan Dario. Universidad Nacional del Sur. Departamento de Agronomia. Area Suelos y Aguas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Sequeira, Mario Eduardo. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca. Centro de Recursos Naturales Renovables de la Zona Semiárida. Universidad Nacional del Sur. Centro de Recursos Naturales Renovables de la Zona Semiárida; Argentina Fil: Fiorentino, C. E.. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Universidad Nacional del Sur. Departamento de Agronomia. Area Suelos y Aguas; Argentina Fil: Amiotti, Nilda Mabel. Universidad Nacional del Sur. Departamento de Agronomia. Area Suelos y Aguas; Argentina. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina Fil: Vazquez, Roberto Jose Luis. Provincia de Buenos Aires. Gobernación. Comisión de Investigaciones Científicas; Argentina. Universidad Nacional del Sur. Departamento de Agronomia. Area Suelos y Aguas; Argentina

The aim of the present study is to determine quantitatively the magnitude of the structural changes that occur in the soil during the degradation process affecting natural grassland in the semi-arid ecosystem of the southern area of the District of the Calden, Argentina. Topsoil horizons show a reduction in depth from 20 cm in ungrazed sites to 16 cm in grazed sites, mainly as a consequence of soil compression caused by animal hooves. Bulk density values in the first 5 cm of the profile in grazed sites are approximately 27% higher than those in ungrazed sites. Total porosity values in the top few centimeters are, on average, 17% lower in grazed sites, primarily due to the collapse of macropores (>50 μm) and larger mesopores (50-9 μm). Water retention curves for the three depths in the different patches reflect the changes in pore space distribution. Grazing causes a sharp increase in mechanical impedance-an average increment of 210% over ungrazed values in the first 10 cm of soil. There are marked differences in the degree of aggregation in grazed sites compared with ungrazed sites. The former show a lower quantity and density of roots in the top few centimeters of the profile. Changes are also evident in average root diameter as a result of vegetation substitution brought on by overgrazing. The lack of significant differences in soil physical properties in areas subject to different grazing intensities underscores the gravity of the problem caused by animal traffic, which poses a serious threat to the conservation and recovery of the grazed patches.

The aim of this paper is to explain soil genesis and spatial variability in the soil cover of a flat landscape in the southern part of Argentina's semiarid region. Soil survey data indicate random differences in the properties of soils lying within a few hundred meters of one another, as reflected in an intricate distribution pattern which cannot be explained by the climatic theory of soil genesis in a single pedogenetic cycle. This pattern is unrelated to the actual vegetation cover. The soil parent materials consist of a

The effect of single-tree influence areas on the physicochemical properties of the soil surface mineral horizon (0–18 cm) was studied in three stands of Pinus radiata D. Don introduced into Sierra de la Ventana, Argentina, grasslands 50 yr ago. Soil samples were taken at distances of 0, 1, and 2 m in transects from the tree to the periphery of the crown. Adjacent grassland soils with mollic epipedons were used as controls. Soil alteration was found to be highest near the trunk, with clear evidence of acid hydrolysis of primary silicates; the epipedon close to the trunk was classified as umbric rather than mollic. Decreasing values of pH, Ca, and exchangeable Mg, and increasing values of exchangeable H and Al, and also of fulvic acid-complexed Al, were registered from the grassland toward the axes of the trees. The soil properties analyzed fall into a distinctive spatial pattern of radial symmetry around each individual tree, with systematic and predictable variations, thus confirming the validity of the concept of “single-tree influence circles” for the study area. Each stand of P. radiata generates a patch of soil alteration within the undisturbed habitat matrix; the internal structure of these patches shows a radial pattern of different polypedons spatially and genetically associated with the inner ring of bark litter and the outer ring of leaf and twig litter. The present work shows that the introduction of P. radiata triggered changes in the evolutionary trend of the soils of such magnitude as to be reflected at the highest taxonomic level in soil taxonomy.

Concentraciones As >10 ug L-1 en aguas de bebida perjudican la salud humana y limitan la producción agrícola-ganadera ya que el As puede integrarse luego a las cadenas alimentarias. El objetivo de este trabajo es cuantificar los contenidos totales de As, Fe a Fe ox y Na en suelos-sedimentos a través de los que circula el agua de precipitación alimentando el acuífero freático en la cuenca del Arroyo El Divisorio. Se hipotetizó que el As total geodisponible y su distribución espacial responde a la dinámica sedimentaria. El Fe ox controla la As-transferencia y el Na determina pHs alcalinos que favorecen la movilidad y acumulación de As elevado (> 10 u,g L-1) en el agua. Se efectuó un Análisis de Componentes Principales (CP) en la fase sólida. En el agua freática se determinó As (u,g L-1) y otros elementos (F, B, V). La geodisponibilidad de As fue normal (5,10-20,7 mg kg-1) con máximos en la cuenca media-baja coincidentes con excesivo As (>10 u,g L-1) en las aguas freáticas. CP1 y CP2 explican el 60% de la variabilidad total. Na (-0,70) y As (0,72) contribuyen a CP1, el Fe total (0,81) fue más relevante para CP2 y Fe ox (0,71) aportó a CP3. Fe t l y Fe ox geodisponibles no correlacionaron significativamente (p>0,73). Fe ox funcionaría como fuente o como sumidero de As. El decrecimiento de Na geodisponible redundó en concentraciones de Na y pHs más elevados en el acuífero de la cuenca media-baja donde un 97,3% de las aguas tuvieron elevado As (10-110 ug L-1), B (120-1420 ug L-1), F (20-4880 ug L-1) y V (40800 u,g L-1). El As incrementó en el sentido del flujo hasta > 10 u,g L-1 en la descarga del acuífero y en la desembocadura del arroyo en el Embalse Paso de las Piedras.

The cation exchange capacity (CEC) and specific surface properties were investigated in four particle-size fractions