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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.

In the semiarid central region of Argentina the probability that rainfall meets crop requirements during growing season is less than 10%, therefore fallowing has been the most important practice to assure water availability during the growing season. Various site-specific and management factors have been identified as crucial for defining fallow efficiency (FE) and final available water contents (AW). The objective of the present study was to improve our knowledge about the interactions between residue cover, weed control, soil profile depth and water storage capacity (WSC) on FE. In 10 sites covering the environments of calcareous plains and sandy plains of the semiarid central region of Argentina and with different WSC, experiments with 3 different levels of residue cover (H, M, L) and with and without weed control (C and W respectively) during fallow were set up. A completely randomized block design with four repetitions and splits plots to consider weed control was used. Soil texture and organic matter were determined in samples of the A horizon (0.20 m). Bulk density, field capacity, permanent wilting point and soil water contents (monthly frequency) were measured at depth intervals of 0.20 m to the depth of the calcite layer or to 2.00 m depth. Soil temperature was taken in weekly intervals at 0.05 m depth and weed plants, separated by species, were counted at the end of fallow in 4 repetitions of 0.25 m2 in each treatment. An empirical model was developed to predict final AW under these experimental conditions. Model parameters were: Residue level, weed control, WSC, profile depth, and rainfall during fallow. Site-specific conditions (WSC and profile depth) affected water storage during fallow; soils with highest values for both parameters showed highest final AW. Weed density was the most important factor that controlled AW, with on average 35 mm less AW in W than in C treatments. Residue level had a positive effect on final AW in both C and W treatments, with a difference of 18.5 mm between H and L. An interaction between residue level and weed density was observed, indicating weed suppression in H treatments. This was also confirmed by correspondence analysis between residue level and weed species which revealed that different species were related to each level. High residue levels also decreased soil temperature, thus affecting germination of post-fallow crops. The empirical model had an overall average prediction error of 13.7% and the regression between measured and predicted values showed a determination coefficient of 0.77

The localization of two wild annual Helianthus species recently established in Argentina, H. annuus and H. petiolaris, were found to be connected with climate, soil, and agroecosystem variables. The habitats of both species, being mainly roadsides, were strongly related to disturbance, but they were also found in riparian areas and within crops. Microhabitat conditions allowed clear differentiation among the species’ preferences, H. petiolaris appeared associated with sandy soils with low organic matter content, while H. annuus showed preference for more fertile and fine textured soils. In the western region of the country, irrigation strongly modified the environment favoring H. annuus. No variables allowed characterization of the three sites, where both species grew together.

The fulvic acid fraction is considered an important constituent of soil organic matter and is sensitive to management regimes and tillage impact. Both humic acids (HA) and fulvic acids (FA) are able to form metal complexes which bind appreciable amounts of phosphate or phosphorus (P) species. The aim of the present study is to evaluate the fulvic acid carbon content of agricultural soils in Argentina and to explore the possible relationship between acid carbon (FC) content and the level of available P in the soil. A total of 74 surface samples of Hapludolls and Haplustolls covering areas with decreasing levels of annual rainfall were analyzed. It was found that soils with FC content >5.5 g kg−1 exhibited available P levels >30 mg kg−1, whereas available P levels

Laboratory experiments were conducted to study organic matter (OM) loss from soil columns with different clay mineral composition and treated with high sodium (Na) and potassium (K) saline solutions (SAR and Removal of organic and inorganic colloids was evaluated by determining organic matter content in the soil at the end of the trial and measuring absorbency of the percolated solutions. Though clay dispersion after magnesium (Mg) treatment was marked in the case of illitic and smectitic soils, little effect was detected in kaolinitic soil. For treatments with solutions containing Na, the highest removal of organic colloids was observed in illitic and kaolinitic soils. In smectitic soil this effect was more pronounced with calcium (Ca) in combination with Na and K. These findings have significance to explain differences in OM mobilization in salt affected depressions of different composition.

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 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.

To obtain information about the cation exchange capacity (CEC) of montmorillonite as affected by the sorption of charged organic molecules, montmorillonite samples were loaded with different amounts of positively charged molecules of safranin, toluidine blue, and negatively charged alizarin red S. Dye sorption by the clay was carried out by equilibrating samples with different concentrations of the dye. The adsorbed amounts were determined from initial and final dye concentrations using spectrophotometric methods. The CEC of the clay-organic complexes were determined by the BaCl{sub 2} base exchange capacity method. The CEC was found to decrease linearly with the increase in the amount of safranin and toluidine in the complex, giving rise to a 1:1 charge neutralization ratio. For alizarin the CEC increased linearly but was not in proportion to the amounts of alizarin in the complex. This noncumulative phenomenon was attributed to the hindering of free diffusion of exchanging cations by the adsorbed molecules.

We studied abundance as well as some morphological and physiological characteristics of six groups of bacteria (total aerobic, proteolytics, ammonifiers, nitrifiers, denitrifiers and bacteria from N-free medium) in six toposequences with salt-affected soils in the semiarid region of Argentina. Abundance of most groups of bacteria was positively related with soil organic matter content and inversely related with soil pH (within a pH range of 7 to 10.5), exchangeable sodium and soil depth. CaCO3 and electric conductivity were only related to the abundance of some bacterial groups in A and C horizons. Predictive equations for each toposequence explained between 31 and 89% of the variance in bacterial abundance. Multivariate relationships between bacterial groups and soil factors also indicated that organic matter content and pH were more important factors to influence microbial abundance than salt content in these soils. All the groups examined were present in the salt crusts which reached electric conductivity values of up to 216 dS/m. Bacillus spp. and coryneform bacteria prevailed among the 537 strains isolated from A to C horizons. Neither Azotobacter nor halophilic bacteria were found with the culture media utilized. One third of the 42 strains which grew in N-free medium utilized D-glucose and 55% did not use the sugars tested. All bacterial groups were more affected by NaCl than by Na2SO4 in laboratory tests with no groups surviving NaCl concentrations of 100 g/l.

Distribution and transformation of SOM in an Argentinian Hapludoll under arable land use and afforested with Pinus radiata was investigated by a combined approach using particle-size fractionation, wet-chemical analysis and 13C NMR spectroscopy. The soils showed thick mollic A horizons and had high organic carbon (OC) contents even in the subsoil, clay-sized separates having the highest OC concentrations. Under pine, a thick forest floor was built up. CuO oxidation data indicated low transformation of lignin in the forest floor, but advanced oxidative decomposition in the mineral soil horizon. In contrast, non-cellulosic carbohydrates, appeared to be stabilized in the mineral soil horizon against mineralization. Humic acids extracted from the mineral soil horizons showed an extremely high aromaticity. We assume that this was due to the production of pyrogenic aromatic moieties (black carbon) as a result of frequent fires in this ecosystem. No clear profile differentiation with respect to SOM quality was obtained. Composition of SOM in the mineral soil appeared not yet influenced from land use. Kennzeichnung der organischen Bodensubstanz argentinischer Schwarzerden Gegenstand dieser Studie war die Kennzeichnung der Verteilung und der Transformationsprozesse der organischen Bodensubstanz argentinischer Schwarzerden (Hapludolls) unter Acker und unter Pinus radiata mittels Korngrosenfraktionierung, naschemischer Analyseverfahren und 13C-NMR-Spektroskopie. Die Boden waren durch machtige Axh-Horizonte und hohe Gehalte an organischem Kohlenstoff (OC) auch im Unterboden charakterisiert, wobei Partikel der Tonfraktion die hochsten Konzentrationen an OC aufwiesen. Unter Kiefer kam es zur Ausbildung einer rohhumusartigen Auflage. Lignin war in den Auflagehorizonten nur schwach abgebaut, erfuhr jedoch einen intensiven Abbau im Mineralboden. Im Gegensatz hierzu erschienen nicht-cellulosische Kohlenhydrate im Mineralboden gegenuber Biodegradation stabilisiert. Die aus den Mineralbodenhorizonten extrahierten Huminsauren zeichneten sich durch eine extrem hohe Aromatizitat aus. Diese ist vermutlich das Ergebnis der Produktion signifikanter Mengen pyrogenen Kohlenstoffs durch die verbreiteten Feuer in diesem Okosystem. Es konnte keine ausreichende Profildifferenzierung mittels Charakterisierung der organischen Bodensubstanz nachgezeichent werden. Die unterschiedliche Landnutzung weist bisher keinen Einflus auf die strukturchemische Zusammensetzung der organischen Substanz im Mineralboden auf.

A simple method was developed for estimating the carbon concentration of fulvic acid from soil extracts at pH 2. Visible absorbance (410 nm) was measured in 20 samples of fulvic acids from different regions of Argentina. Linear regression analysis of absorbance as a function of carbon concentration yielded a high correlation coefficient (r = 0.983∗∗). The proposed method is expected to be useful in assessing changes in organic matter content as a result of different tillage systems, erosion, plant residues, etc.

Though it is commonly held that sodium (Na) rather than potassium (K) salts affect soil properties, in some treatmets the opposite has been found to be the case. The present paper describes soil trials carried out to determine changes in organic matter and colloidal content, pH, cation exchange capacity, and exchangeable cations as a consequence of leachings with Na and K salts. It was possible to classify salts into weakly and strongly alkaline according to their effect on soil properties. On the basis of the effect of K on soil properties, it is concluded that this salts should be included in soil salinity classifications.

[1] Black carbon (BC) is the product of incomplete burning processes and a significant component of the passive soil organic carbon (SOC) pool. The role of BC in the global carbon cycle is still unclear. This study aimed to quantify and characterize BC in major grassland ecosystems of the world. Twenty-eight representative soil profiles (mainly Mollisols) were sampled in the Russian Steppe, the U.S. Great Plains, the Argentinian Pampa, the Manchurian Plains in China, and the Chernozem region in central Germany. Black carbon contents were estimated using benzene polycarboxylic acids (BPCA) as a molecular marker, and indications about the origin of the BC were derived from bulk and compound-specific δ 13 C analyses and radiocarbon dating of bulk soil organic matter (SOM). Our findings suggest that between 5% and 30% of SOC stocks consist of BC. Maximum BC contributions to SOC frequently were found at deeper parts of the A horizon with 14 C ages younger than 7000 years BP; that is, incorporation of C as charred particles accompanied ecosystem development since the mid-Holocene. Most of this BC formed from local vegetation, as indicated by a 13 C isotope signature similar to that of bulk SOM. At some sites, also nonlocal sources contributed to soil BC, e.g., fossil fuel BC inputs at the German sites. Black carbon stocks were highest in Chernozems and lowest in Kastanozems. The Russian Steppe and Chinese Manchurian sites stored about 3-4 times more BC (around 3 kg m -2 ) than did the other sites because of thicker A horizons that were rich in BC. On a global scale, we estimate that steppe ecosystems contain between 4 and 17 Pg BC.

A study was conducted to determine the amounts and vertical distribution of fine roots −1 in high-growth stands and from 5400 to 40 700 kg•ha−1 in low-growth stands. Soil organic matter content provided the best correlation with root density. A possible practical implication would be the use of indices related to vertical distribution of organic matter, among other variables, as complementary estimators of effective depth of rooting. The results strongly suggest that trees maintain a large fine-root system in poor sites at the expense of aboveground growth.

Provisional forest site classes were established for the most widely planted conifers in a temperate, hilly zone of Argentina. Growth data were obtained from 72 unmanaged stands. Aleppo pine (Pinus halepensis Mill.) was studied on 22 sites, Monterey pine (Pinus radiata D. Don.) on 20 sites, and deodar (Cedrus deodara (Roxb) Loudon) and Italian or common cypress (Cupressus sempervirens f. hprizontalis (Mill.) Voos) on 15 sites each. Site index, regarded as the height of dominants at the base age of 25 years, was determined by using stem analysis. Site indices as well as yields were higher for the species of genus Pinus, particularly for P. radiata followed by Cedrus deodara and Cupressus sempervirens, respectively. Data from stem analysis pointed out that the mean annual increments in the stands did not culminate even at the age of 30 years.

Loess and palaeosols in the subtropical lowlands of South America (∼23-38°S) have a large potential to serve as archives of Late Quaternary environmental and climate changes. At present, mean annual precipitation generally decreases from N to S and from E to W, though with a complex seasonal pattern with austral summer rainfall related to the monsoonal circulation and with austral winter rainfall related to the SE-trades. In this paper, we present results of multiproxy geochemical analyses from three representative eolian/alluvial soil profiles along a S-N transect aiming at the reconstruction of past climate changes: (i) profile "Chasico" at the southern border of the subtropics (38°S), (ii) "D4" in Misiones at the northern border of the subtropics (27°S), and, for comparison, (iii) "Laguna Sucuara" in the savannas of the Bolivian lowlands (16°S). Our results show that before ∼16 ka BP, conditions were likely very cold and dry. Except for in "D4", loess or soils are not preserved due to rather scarce vegetation cover and resultant deflation. In "Chasico", accumulation of sands (directly overlying the Tertiary) starts only during the Late Glacial, indicating increasing temperatures and increased monsoonal precipitation (coinciding with the "Tauca" wet phase on the Altiplano). In "D4", a palaeosol is preserved below the Late Glacial sediments and the deflation hiatus. This palaeosol is dated to ∼40 ka BP and documents an earlier, but less intensive (southward reaching) phase of monsoonal precipitation ("Inca Huasi" on the Altiplano). Whereas the seasonality during the Late Glacial seems to have been very pronounced, conditions for organic matter production and preservation became much more favourable at "Chasico" and "D4" during the Early Holocene. We suggest that extra-tropical winter precipitation played a more important role than before and than today. Between ∼7.5 and 3 ka BP, the expansion of C4 plants along the S-N transect suggests increasing aridity, probably due to a weakening of the extra-tropical circulation in combination with a relatively weak monsoonal circulation. Only after ∼3 ka BP climate became more humid again due to the re-strengthening of the monsoon. Fil: Zech, W.. University of Bayreuth; Alemania Fil: Zech, M.. University of Bayreuth; Alemania Fil: Zech, R.. University of Bern; Suiza Fil: Peinemann, Norman. Universidad Nacional del Sur; Argentina Fil: Morrás, Héctor José María. Instituto Nacional de Tecnologıa Agropecuaria; Argentina Fil: Moretti, Lucas Martin. Consejo Nacional de Investigaciones Científicas y Técnicas; Argentina. Instituto Nacional de Tecnologıa Agropecuaria; Argentina Fil: Olge, N.. The Queens University of Belfast; Irlanda Fil: Kalim, R. M.. The Queens University of Belfast; Irlanda Fil: Fuchs, M.. University of Bayreuth; Alemania Fil: Schad, P.. Universitat Technical Zu Munich; Alemania Fil: Glaser, B.. University of Bayreuth; Alemania

Interactions between landscape position and the acidifying effect of trees planted into loess-derived grassland soils were studied in the Ventana region of Argentina. Forests of Pinus radiata planted at the end of 1940, were selected in two different positions from the landscape, plains and slopes. Samples of the soil surface mineral horizon were taken from landscape positions at four distances from the trees and compared with grassland soils. The values of the main soil chemical properties changed significantly with distance from trees, with a decrease in pH, base saturation, exchangeable Ca2+, Mg 2+ and K+, and increase in Na+, Al3+ and particularly H+ closer to the trees. This pattern confirms the prominent role of vegetation in bringing about changes in soil properties. Regression models showed high levels of explanation (r2 > 0.85) indicating that a high percentage of the spatial variability of soil chemical properties is systematic and predictable with distance from the trees. The pH in KCl proved an excellent tool for predicting the cationic composition of soils. Organic carbon and total nitrogen were significantly higher in the plains positions than in the slopes under the trees, whereas there was no difference under grassland. The slopes of the regression lines indicated that acidification is more intense in soils on the plains. Vegetation was the main factor influencing acidification of the studied soils. The landscape position regulates the bio-hydrological factor and thus the speed of acidification process. Fil: Amiotti, Nilda Mabel. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina Fil: Bravo, Oscar Abel. Universidad Nacional del Sur. Departamento de Agronomía; Argentina Fil: Zalba, Pablo. Universidad Nacional del Sur. Departamento de Agronomía; Argentina Fil: Peinemann, Norman. Consejo Nacional de Investigaciones Científicas y Técnicas. Centro Científico Tecnológico Conicet - Bahía Blanca; Argentina. Universidad Nacional del Sur. Departamento de Agronomía; Argentina

Zur Charakterisierung der Anteile von Lössen und Verwitterungsprodukten der liegenden Keuper- und Liasgesteine innerhalb kolluvialer Mischsedimente und holozäner Terrassenkörper erweisen sich in Oberfranken neben Korngrößenverteilungen insbesondere Quarz-Feldspat- und Albit-Mikroklin-Quotienten als geeignete Indizes. Danach sind an den untersuchten bodenerosiv überprägten Flachhängen bevorzugte Abtragung von Löß und Liegendmaterial an den Oberhängen, vorherrschender Durchtransport an den Mittelhängen und Ablagerung von Mischsedimenten an den Unterhängen zu erkennen. In den holozänen Sedimenten der Vorfluter sind Lößderivate demgegenüber nur gering vertreten, woraus auf vorherrschenden Durchtransport dieses Materials in den untersuchten Talstrecken und — im Vergleich mit niedersächsischen Beispielen entsprechender Größenordnung — auf eine regionale Differenzierung der holozänen fluvialen Dynamik geschlossen wird, die möglicherweise auf Unterschiede des Regionalklimas zurückzuführen ist., research

The chemisorption of phosphate on aluminium hydroxide (bayerite) and its kinetics were studied. A rate equation was derived on the basis that each phosphate molecule replaces a surface hydroxyl group and binds directly to an aluminium atom. The rate constants were evaluated and the free energy change of the sorption reaction was calculated as 20.4 KJ/mol. Phosphat-Sorption durch Bayerit Die Chemosorption von Phosphat an Bayerit wurde einschlieslich ihrer Kinetik untersucht. Eine kinetische Gleichung wurde auf der Grundlage abgeleitet, das jedes Phosphatmolekul eine Oberflachen-Hydroxylgruppe ersetzt und direkt an ein Aluminium-Atom gebunden wird. Die Geschwindigkeits-Konstanten wurden bestimmt und die freie Energie der Sorptionsreaktion wurde zu 20,4 KJ/mol berechnet.

Water evaporation measurements in small soil columns saturated with different salt solutions show that the surface salty crusts affect the water content as well as the water movement in the soils in the order: NaCl

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