Mollic Horizon Research Articles

Landscape-related transformation and differentiation of Chernozems – Catenary approach in the Silesian Lowland, SW Poland

The unfavourable environmental conditions to Chernozem development in Central Europe has led to questions regarding their origin and age, and conditions necessary for Chernozem persistence in Central Europe under a humid climate. This paper deals with Chernozem transformation during the Holocene period in SW Poland in relation to land morphology. The study was based on a catenary approach, with additional remarks on parent material homogeneity and soil classification. Based on textural and geochemical indices, the homogeneity of aeolian material (loess) was proven in the main part of the catena, which confirmed that the differentiation of “dry” and “wet” chernozemic soil across the catena did not result from the variability of parent material. No differences in morphological or physicochemical characteristics of mollic horizons were identified between the well-drained and wet sections of the catena. The strong redoximorphic features (manifested as stagnic or gleyic properties) in the lowermost part of catena are, therefore, secondary features, i.e. developed after the mollic horizon development, presumably in late Holocene period. Chernozems with chernic horizon, weakly developed subsurface argic horizon and free of redoximorphic features prevail in the central, well-drained and not eroded section of the catena. It has been hypothesized that the loess soils in the uppermost, more inclined part of the catena have been truncated by erosion during the first agricultural period, then afforested and transformed into Luvisols, probably due to temporary abandonment of those sites less favourable for farming. The soils in the transitional zone received the colluvial addition of humus material from the eroded hill summit; however, the colour of the humus layer has a chroma too high for a chernic horizon that surprisingly shifted these soils to the Kastanozems group. This study showed that the direction of transformation of native Chernozems in the Holocene period was strongly related to their position in the landscape, which affected the erosion/accumulation intensity and water drainage conditions (soil moisture regime). As a final result of these transformations, a relief-related zonality of soils has developed with Stagnic/Gleyic Chernozems – Luvic Chernozems – colluvial “Kastanozems” – Haplic Luvisols, in the lower (moist), middle (well-drained), and upper colluvial/eroded sections of the undulating loess plain, respectively.

Compositional variety of soil organic matter in mollic floodplain-soil profiles - Also an indicator of pedogenesis

Soils on riverine floodplains in Central Europe are commonly enriched in soil organic matter (SOM). We analyzed the quantity and qualitative aspects of SOM in three soil profiles with mollic horizons along the Elbe River (Germany) after physical fractionation by diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy to gain deeper insights into the composition of SOM and the formation of these soils. In all horizons, the majority of SOM was recovered in the fraction of particulate OM and in that of sand and aggregates, while SOM in the silt and clay fraction always made up <20% of soil organic carbon. The C:N ratios of most fractions did not decrease with depth, indicating less decomposed or pyrogenic OM or both. The presence of pyrogenic OM, as a characteristic feature of floodplain soils, was indicated in almost all physical fractions. As derived from DRIFT spectroscopy, SOM was less qualitatively differentiated among the fractions in the soil with the longest duration of flooding, while qualitative differences of SOM were more pronounced in the more aerated ones. The soils have developed from stratified fluviatile sediments and fulfil the criteria of a mollic horizon, irrespective of differences in the composition of SOM. From a soil-genetic point of view, we strongly suggest to classify these soils as Mollic Fluvisols instead of Fluvic Phaeozems, which would accord to the latest WRB classification.

Magnetic and pedological characterisation of a paleosol under aridic conditions in Spain

The systematic use of magnetic techniques for the characterization of soils is still scarce despite its great potential for the identification of pedogenetic processes. The main objective of this study is to analyze the magnetic properties of a soil profile with contrasting horizons and try to relate them to the properties determined through conventional techniques. The horizons of a soil profile located in a tectonic depression in Murcia, Spain are described and their physical, chemical, and mineralogical properties analyzed with conventional techniques. The following magnetic properties are included in the study: the mass-specific magnetic susceptibility, frequency-dependent susceptibility, continuous thermomagnetic curves at low field, isothermal remanent magnetization acquisition and the estimation of magnetic hardness (coercitivity) through the parameter S-200. Detailed description of the soil profile and the results of conventional analyses allowed the identification of a mollic horizon, an argic horizon, and a calcic horizon, as well as a textural discontinuity. Apparently, pedogenic magnetite occurs in the A horizon and is responsible for the magnetization in most cases. The magnetic carriers in the Bt horizons are superparamagnetic particles and they are related to the high percentage of clay. High coercivity minerals (hematite and probably goethite) were detected in different concentrations in all soil horizons. The amount of ferrimagnetic minerals decreases with depth. The magnetic properties allowed a better characterization of the diagnostic horizons. The results and information derived from the analysis of the magnetic properties could not be obtained using conventional soil analysis only.

Burn effects on soil properties associated to heat transfer under contrasting moisture content

The aim of this work is to investigate the topsoil thickness affected by burning under contrasting soil moisture content (field capacity versus air-dried conditions). A mollic horizon of an Aleppo pine forest was sampled and burned in the laboratory, recording the temperature continuously at the topsoil surface and at soil depths of 1, 2, and 3cm. Changes in soil properties were measured at 0–1, 1–2, 2–3, and 3–4cm.Both the maximum temperature and the charring intensities were significantly lower in wet soils than in air-dried soils up to 3cm in depth. Moreover, soil heating was slower and cooling faster in wet soils as compared to dry soils. Therefore, the heat capacity increase of the soil moistened at field capacity plays a more important role than the thermal conductivity increase on heat transfer on burned soils. Burning did not significantly modify the pH, the carbonate content and the chroma, for either wet or dry soil. Fire caused an immediate and significant decrease in water repellency in the air-dried soil, even at 3cm depth, whereas the wet soil remained hydrophilic throughout its thickness, without being affected by burning. Burning depleted 50% of the soil organic C (OC) content in the air-dried soil and 25% in the wet soil at the upper centimeter, which was blackened. Burning significantly decreased the total N (TN) content only in the dry soil (to one-third of the original value) through the first centimeter of soil depth. Soluble ions, measured by electrical conductivity (EC), increased after burning, although only significantly in the first centimeter of air-dried soils. Below 2cm, burning had no significant effects on the brightness, OC, TN, or EC, for either wet or dry soil.

Modelling the potential mobility of Cd, Cu, Ni, Pb and Zn in Mollic Fluvisols.

European floodplain soils are frequently contaminated with potentially toxic inorganic substances. We used a multi-surface model to estimate the aqueous concentrations of Cd, Cu, Ni, Pb and Zn in three Mollic Fluvisols from the Central Elbe River (Germany). The model considered complexation in solution and interactions with soil organic matter (SOM), a clay mineral and hydrous Al, Fe and Mn oxides. The amounts of reactive metals were derived from extraction with 0.43M HNO3. Modelling was carried out as a function of pH (soil pH±1.4) because it varies in floodplain soils owing to redox processes that consume or release protons. The fraction of reactive metals, which were dissolved according to the modelling, was predominantly <1%. Depending on soil properties, especially pH and contents of SOM and minerals of the clay fraction, the modelled concentrations partially exceeded the trigger values for the soil-groundwater pathway of the German soil legislation. This differentiation by soil properties was given for Ni, Pb and Zn. On the other hand, Cd was more mobile, i.e., the trigger values were mostly exceeded. Copper represented the opposite, as the modelling did not predict exceeding the trigger values in any horizon. Except for Pb and partially Zn (where oxides were more important), SOM was the most important adsorbent for metals. However, given the special composition and dynamics of SOM in mollic horizons, we suggest further quantitative and qualitative investigations on SOM and on its interaction with metals to improve the prediction of contaminant dynamics.

Magnetic properties as indicators of Chernozem soil development

A detailed magnetic study of four types of Chernozem profiles developed on the loess in the Homutovsky Steppe (Ukraine), Middle Poland and Moravia (Slovakia) was carried out. The magnetic methods were used to examine the subtle differences between four Chernozems, their pedogenic horizons and mechanism of soil formation. Loess of Ukrainian Chernozem (H2) revealed the greatest values of magnetic susceptibility (25 10−8m3kg−1) and frequency-dependence of susceptibility (6.5%), which indicates weathering processes responsible for loess alternation at the beginning of the soil formation. The advanced pedogenic processes in the mollic horizon resulted in the formation of superparamagnetic grains of pedogenic maghemite. The Chernozem from Middle Poland (MDZ) has the lowest values of all magnetic parameters but one of the highest intensities of pedogenesis expressed by the relative changes of frequency-dependence of susceptibility between top-soil and parent material. It could be the consequence of the short duration of pedogenic activity. The correlations between the organic matter content expressed by loss on ignition and magnetic parameters were found. For the mollic A-horizon the organic matter influences the magnetic enhancement (∆χ) and the production of SP grains through stimulation of pedogenesis. The correlation between mean annual rainfall – MAR and pedogenic component of susceptibility – magnetic enhancement gives the opportunity to look at the history of studied profiles. The data for studied Chernozems fit well with the relations between MAR and ∆χ for loessic soils from Russia, Ukraine and Europe.

Vertic properties and gilgai-related subsurface features in soils of south-western Poland

More than 650 subsurface concave structures (1–20m long, 0.5–7m wide, and 0.1–0.9m deep) were described in soils developed of clays overlain by loess in a large-scale archeological excavation in SW Poland. The structures are considered to be microlows and microhighs similar to those in gilgaied vertisols, which have never been reported in Central Europe until now. Soils do not have a clayey texture throughout the profile; however, the thick and humus-rich mollic horizons, as well as a clay-enriched argic layers, developed directly above vertic horizons have favored soil cracking and shrink–swell phenomena in the clayey subsoil. As a result, well developed wedge-shaped (lenticular) aggregates have formed in the clayey subsoil. Aggregates have grooved surfaces with an oriented matrix (slickensides) and are ordered under variable angles from 10 to 60°. A periglacial origin of these structures has been rejected and the mid- to late-Holocene period (since the Neolithic epoch) has been considered to be favorable for intense shrink–swell phenomena, vertic horizon development and clayey mass cycling responsible for the subsurface bowl and chimney structure development. A micro-mosaic of soil units related to these structures has been distinguished, including (non- or deep-vertic) Stagnic Chernozems/Phaeozems above the microlow centers, Mollic Planosols (Vertic) above the microslopes, and Mollic Planosols (Protovertic) over the microhighs (chimneys). It is concluded that a temperate climate (as in Central Europe) allows the formation of vertic properties and subsurface mass reorganization similar to those in soils with gilgai microrelief, if specific conditions – clayey substratum, position in landscape, soil moisture regime and the land use connected with vegetation type – support deep seasonal changes of soil moisture and shrink–swell phenomena in the subsoil.

Statistické zhodnocení aberací černozemí na území Moravy při komplexním průzkumu půd

In this paper, an attempt at measure formulation of aberation in the set of results of soil analyses observed on chernozems within Soil science is presented. The statistical evaluation was realized based on the report results from separate districts. The chernozem (regardless of subtype) were chosen as suitable for statistical evaluation. The analysis of one character was calculated for the set of results in topsoil (0–30 cm) and subsoil (30–60 cm). The comparison of average content in topsoil and subsoil was made by t-test. The significant difference is shown in content of humus (topsoil 2.61% and subsoil 1.86%), phosphorus (topsoil 8.31 mg/100 g, subsoil 4.75 mg/100 g) and kalium (topsoil 16.28 mg/100 g and subsoil 9.96 mg/100 g). There is no significant difference in other characters such as content of particles under 0,01 mm (topsoil 40.16% and subsoil 42.67%), exchange reaction (topsoil 7.03 and subsoil 7.00) and CEC – cation exchange kapacity (topsoil 23.74 mmol/100 g and subsoil 23.50 mmol/100 g). With respect to chernozems character it can be deduced, that in most of not anthropically influenced samples from mollic horizon the similar features were observed in both monitored depths. This presumption is supported also by observed differencies: humus content in topsoil was distinctly increased by addition of organic substances in organic fertilisers and by cultivation of perennial forage crops. The aberation was not observed in soil reaction. This fact could be interpreted by suppressor soil ability. Similarly, no aberation was documented in CEC. In view of quality/health of soils it is positive detection because both: exchange reaction and CEC are classified in basic soil characters. The maximal aberation was observed in phosphorous content in topsoil (with log-normal (extreme) distribution of results) and, somewhat less, in kalium content. Both characters are classified in most anthropically affected due to the addition of both components in fertilisers. Similar situation can be monitored also in the influence of humus content.

Soil organic matter of Chernozem in the part of Central Europe

In this study, we have tried to evaluate the current contents of Soil Organic Matter (SOM) in the Soil Type Chernozem for Central Europe and to determine the site specific level for the Czech Republic. In the past, the observed effect of SOM on the Agronomic characteristics in particular yields. Nowadays it means a very important influence on the Environment, particularly in the terms of ecological functions of soil (the influence of the filter function, sanitation function, protection against degradation etc.). The statistical analysis included data for all the Chernozems (N = 141) regardless of subtype derived from measurements from 2003 to 2006. Measurements were carried out at selected locations in the Czech Republic.Profiles at each site were divided into topsoil and subsoil and these were separately statistically processed. When evaluating the frequency distribution, we suppose that the anthropic un-affected Soils would be approximately equal to distribution Gauss normal distribution, and both frequency distribution (in topsoil and subsoil) will be similar (mollic horizon in this Soil Type on non-eroded land is relatively deep and homogeneous).Next from of the observed properties is relation between Content of Soil organic Matter and the texture, namely the content of particles smaller than 0.01 mm. The average SOM content is higher in clayey soil, clay-loam soil than in sandy soil. Differences between soil sandy-loam and clayey-loam are statistically significant. The paper also outlined the possible future development of SOM on Chernozem soils.

Changes in water repellency, aggregation and organic matter of a mollic horizon burned in laboratory: Soil depth affected by fire

High variability in the literature is reported on the soil depth affected by forest fires because many factors are involved. We study the fire-induced changes on properties related to soil erodibility as water repellency (WR), soil aggregate stability (SAS) and organic matter at topsoil centimeter-scale (O horizon, and Ah horizon at 1, 2 and 3cm depth). In order to achieve this aim, topsoil monoliths (Rendzic Phaeozem) were sampled from an Aleppo pine forest, with no recent history of forest fires and burned in an outdoor combustion tunnel.Fire caused an immediate and significant decrease in WR, total organic carbon (TOC) and pyrolyzed carbon (PyC) in the O horizon. The Ah horizon was also affected by burning but only up to 2cm soil depth and with a different intensity according to the soil property: TOC was not significantly affected; WR and PyC decreased up to the upper centimeter and SAS up to 2cm Ah horizon depth. Soil burning involved the loss of 2/3 of the pre-fire TOC of the O horizon and 1/3 of the TOC of the upper centimeter of the Ah horizon. Fire also modified the structural composition of organic matter, an effect that was apparent again only above 2cm depth. Specifically the relative abundance of typical vegetation markers (terpenes, resinic acids) and lignin markers (methoxyphenols) decreased. Fire fragmented the long-chain molecules of the alkylic series (n-alkanes, alkenes, fatty acids and methylated fatty acids). This observation, together with a conspicuous reduction in the amount of organic molecules with functional groups in the upper centimeters of the soil monoliths, may be related to the fire-induced decreases in WR and SAS. In conclusion, moderate burning of a mollic horizon in the laboratory produced changes in the hydrophobicity, aggregation, and organic matter only up to 2cm depth.

Chernozem properties of Black Soils in the Baltic region of Germany as revealed by mass-spectrometric fingerprinting of organic matter

Black Soils with dark-coloured, mollic horizons occur in the Baltic region of Germany and their classification as Chernozems was previously discussed. Mollic topsoil horizons are diagnostic for steppe soils. We therefore hypothesized that the molecular characterization of soil organic matter (SOM) by pyrolysis-field ionization-mass spectrometry (Py-FIMS) is suitable to identify similarities between the Black Soils and Chernozems as well as soils from other major soil groups with mollic horizons or otherwise high SOM content. Data were collected from a set of 341 topsoil samples and analysed based on 139 Py-FI mass spectra and thermograms. The OC content in Black Soils reached high values matching those of Haplic Chernozems from Germany and typical steppe climate ecosystems. Arable soil use converted Ah horizons to lighter-coloured Ap horizons that nonetheless had a similar or higher OC content than underlying Ah horizons. Arable soil use led to less stable SOM as indicated by a higher percentage of volatilized organic matter (VM) upon pyrolysis. Furthermore, VM was especially high (21–52%) for redoximorphic soils, whereas it ranged between 5.1 and 15% in the Black Soils, Chernozems and other steppe soils such as Phaeozems or Kastanozems. Assignment of marker signals from Py-FI mass spectra to the compound classes revealed that Black Soils, all Chernozems and other steppe soils had more phenols and N-containing compounds but less sterols and suberin than most of the other soil groups investigated. The percentage of volatilized organic matter (VM) – with low values hinting at SOM stabilization in soil – ranged from 5 to 52%. It was especially high for redoximorphic (21%) and organic soils (52%), whereas it ranged between 5.1 and 15% in the Black Soils, Chernozems and other steppe soils. Principal component analysis unravelled the SOM composition patterns of different soils and showed that the Black Soils clustered together with typical Chernozems, while soils of other units differed. This indicates that sources and especially humification pathways of SOM were different in these soils compared to Black Soils and Chernozems. Notably, this was the case for Colluvic soils (=Colluvic Regosols), redoximorphic soils (e.g. Gleysols, Stagnosols), Luvisols and Phaeozems, although colluviation, influence of ground- or stagnant water, and clay migration were found in several Black Soils as well. Our findings do not support a strong, direct influence of colluviation and perched water on the SOM composition in the mollic horizons of Black Soils. The data also show that the Chernozem-specific SOM formation and clay migration, as in Luvisols and Phaeozems, are temporally discrete processes. The results underline that Chernozem formation in Central Europe is a relic process and is not only due to steppe ecosystem conditions. Rather, it depends on parent substrate properties, especially clay and carbonate content, secondary carbonate input and anthropogenic soil use. These factors preserved or even regraded the relic Chernozems since the Atlantic stage.

Soil map update: Procedure and problems encountered for the island of Réunion

Many soil maps were drawn up after World War II with different soil classifications that have significantly evolved since. Updating such old maps with a new version or a new classification system is always complex: (i) we do not always possess all the original information; (ii) the criteria for determining references are often different, and (iii) on the most accurate scales, correlations come up against the complexity and specificities of each classification system. On Reunion, a volcanic tropical island in the Indian Ocean, we undertook a comprehensive overview of the old existing soil studies. This article describes (i) the procedure used to update the soil maps and the toposequence acquired with the old French Commission de Pédologie et de Cartographie des Sols (CPCS) classification system, without any new information, using the World Reference Base for soil resources (WRB); (ii) the construction of a new soil map drawn up with completely new information, and (iii) a comparison of these two approaches. At elevations below 350 m asl (above sea level), without any new pedological information, we updated Brown ferruginous soils, Reddish-brown ferrallitic soils, and Fersialitic soils into Haplic Nitisols (Humic, Eutric). The acquisition of new data showed that this update was incorrect because not all the diagnostic criteria of the Nitic horizons were met. The correct diagnostic horizons were a Mollic horizon when the thickness was 25 cm or more, or a Cambic horizon. Leptic Phaeozems and Leptic Cambisols were then the correct Reference Soil Group (RSG). At elevations from 350 to 900 m asl, without any new information, Brown and Reddish-brown ferrallitic soils, Andic ferrallitic soils, and Brown and Andic brown soils were updated into Haplic Nitisols (Humic, Dystric) and Andic Umbrisols (Humic). The acquisition of new data showed that this update was incorrect because Andic properties and the diagnostic criteria of the Nitic horizons were not met. Over 900 m asl, Pozols were correctly updated, as were the Andosols except from 900 to 1050 m asl where not all the Andic properties were met. Without any new information, incorrect updates were observed for both the determination of RSG and the qualifiers. Despite the field descriptions, the lack of any analytical determinations on the old soil studies was a source of updating errors for the more developed soils formerly qualified as ferrallitic. In order to update limits for Andic properties and Andosols, the systematic use of analytical determinations has to be considered for updating old soil maps, as the diagnostic criteria are more restrictive than in the past.

Influence of slope and parent rock on soil genesis and classification in semiarid mountainous environments

We investigate the effects of bedrock and slope position on soil diversity in a semiarid, wooded, mountainous environment, and we use these results to examine differences between the current diagnostic criteria of the Soil Taxonomy System (STS) and World Reference Base (WRB) classification systems. To achieve these objectives, we characterize a total of ten pedons occurring across representative catenas on limestone and gypsum bedrocks.Differing parent material causes the most variation among diagnostic horizons of the soils. In soils overlying limestone catena, a mollic horizon can be consistently defined according to STS criteria. But according to WRB criteria, a mollic definition can receive different interpretations due to differing color values associated with high lime content and its bleaching action, as well as the introduction of the concept “finely divided lime”. In soil classification, it is proposed to consider the concept “equivalent calcium carbonate”. Under these assumptions, soils in limestone catena are classified as Lithic Haploxerolls/Rendzic-Epileptic Phaeozems at the top, which transition into Pachic Haploxerolls/Rendzic Phaeozem at the mid-slope. The foot slope of the limestone catena also includes occasional Pachic Calcixerolls/Calcic Chernozems, through the presence of calcic horizons.Topography causes variations in soil depth and water retention, which tend to increase from the top of the hillslope to its base, and for this reason, the estimated soil moisture regime changes from aridic, at the top, to xeric along both catenas. This feature strongly influences soil classification, especially in gypsum catena because the soil moisture regime is used at first taxonomic level in STS. The STS soil classification is therefore tentative, given uncertainties concerning the exact soil climate regime. The soils of uppermost areas of gypsum catena are classified as Leptic Torriorthent/Haplic Leptosol (gypsiric) according to the STS and WRB while soils from the middle and lower slope, with prominent pedogenic gypsum accumulations, are classified as Gypsic Haploxerept by STS. These soils would correspond to different units (Hypergypsic, Haplic or Salic Gypsisols) according to the WRB, a level of specificity contributed to in part by mineralogical class in the STS. Similarly to the equivalent calcium carbonate, the term “equivalent gypsum” should be used. At the base of gypsum catena, a salic horizon is defined according to the WRB but not according to the STS due to differences in its definition, which should be standardized.This study shows that the current versions of the STS and WRB include certain inconsistencies that require clarification and standardization in order to serve as a foundation for a universal classification system and to improve the systems themselves.

Genesis and properties of black soils in Buryatia, southeastern Siberia, Russia

Soils with deep and dark brown to black humic surface horizons, derived from sandy-silty aeolian and alluvial sediments, are relatively fertile and store huge amounts of carbon. Globally, they mainly correlate with steppe ecosystems. Because their deep and dark epipedons are frequently rich in Black Carbon, it was recently suggested that they developed due to prevalent burning of the semiarid vegetation. This paper describes six soils with deep and dark humic surface horizons, located in catchments of the Selenga and Uda rivers in Buryatia, southeastern semiarid Siberia. The organic matter of most of these soils not only originates from grass steppe, but in addition from trees and shrubs. Five soils can be classified as Chernozems and Kastanozems ( WRB, 2006); one soil is a deep and black Anthrosol, occurring in patches in the region. All soils have calcic horizons below the mollic epipedon, some with cambic Bw horizons in between. As the parent material does not contain carbonates, aeolian input and hydrolysis of Ca-silicates contribute to the development of the secondary carbonate accumulation, which is frequently cryoturbated. All profiles are more or less stratified due to solifluction. Texture ratios (<6.3/63-2000 μm) show maxima in the dark A horizons, indicating advanced paedogenesis. This is supported by weathering proxies, including SiO 2/Al 2O 3 and Al 2O 3 × 100/Al 2O 3 + Na 2O. Increased concentrations of TiO 2, MgO and Fe 2O 3 presumably indicate advanced formation of chlorite. Radiocarbon analyses indicate that these deep and dark mollic horizons started to develop during the more humid-Holocene Climatic Optimum, ca. 7000–5000 BP. Palynological studies confirm expansion of forests in the Lake Baikal region in this period. This is in agreement with higher alkane ratios nC27/nC31 in most of the deep and dark A horizons, indicating that these epipedons, diagnostic for Chernozems and Kastanozems, did not develop exclusively under grass steppe, thus supporting the hypothesis that a significant part of the soil organic matter is inherited from trees and shrubs. This seems to be in contrast to Middle Europe and the Russian plain where Chernozems presumably developed during the early and mid-Holocene under grass steppe and subsequent degraded with increasing humidity and invasion of forests. High contents of Black Carbon in the Calcic Chernozem P4 and lower ones in the long-lasting occupied Hortic Anthrosol indicate that the deep and dark A horizons of Mollisols most likely do not result from frequent burning, but from biochemical processes.

Substâncias húmicas como suporte à classificação de solos brasileiros

As substâncias húmicas que compõem a matéria orgânica do solo participam de forma ativa dos processos pedogenéticos do solo, em especial dos horizontes diagnósticos O e H hístico, A chernozêmico, A húmico e B espódico. Este trabalho teve como objetivo determinar o teor de C orgânico das substâncias húmicas e avaliar sua influência na separação de horizontes diagnósticos. Foram utilizados 56 horizontes diagnósticos de diferentes regiões do Brasil, 52 superficiais (H hístico, A chernozêmico, A proeminente, A húmico e A moderado) e quatro subsuperficiais (B espódico). Nesses solos, foram feitas a caracterização química e física, e também de C orgânico, da fração ácidos fúlvicos (C-FAF), fração ácidos húmicos (C-FAH) e humina (C-HUM), as relações C-FAH/C-FAF e C-EA/C-HUM (C-EA = C-FAF + C-FAH) e a percentagem das frações em relação ao C orgânico total (COT), sendo as variáveis submetidas à avaliação por análises multivariadas. Nos horizontes orgânicos, o H hístico apresentou maiores valores e equilíbrio entre o C-HUM e o C-FAH. Na maioria dos horizontes minerais, observou-se predomínio do C-HUM, seguido pelo C-FAH nos horizontes A chernozêmico e A húmico e pelo C-FAF nos horizontes A proeminente e A moderado. Nos horizontes B espódico, foi observado predomínio variável de C-FAF e C-FAH. Com a análise de variáveis canônicas, identificaram-se as variáveis que poderiam ser utilizadas para a separação dos tipos de horizontes diagnósticos. Usando a análise de agrupamento, separaram-se os tipos de horizontes com menor influência da matéria orgânica. Pela análise discriminante, obtiveram-se resultados satisfatórios na classificação dos horizontes diagnósticos com base nas variáveis das substâncias húmicas, quando comparados à classificação original. Os resultados das análises multivariadas indicam que a distribuição do C das substâncias húmicas pode ser utilizada para separar os tipos de horizontes diagnósticos ricos em C orgânico.

Paleoenvironmental interpretation of multiple soil–loess sequence at Milford Reservoir, northeastern Kansas

Abstract A loess/soil section near the Republican River in northeastern Kansas includes three superposed soils/paleosols in at least three superposed loess units, including Peoria Loess (PL), the Gilman Canyon Formation (GCF), and Loveland Loess (LL), The GCF coincides with a composite soil with a 1.3 m thick, buried organic-rich (A) horizon that yields AMS radiocarbon ages from 30.3 to 22.4 ka (or 35.7 to 26.9 ka when calibrated) that overlies a 1.6 m oxidized B horizon complex. The B subhorizons stratigraphically and morphologically resemble the “reddish pedocomplex” described elsewhere in Kansas and Illinois that dates between about 69 and 35 ka. The upper LL yields a TL age of about 136 and 130 + 30 ka. Thus, PL, the GCF, and LL were probably deposited mainly during the late Wisconsinan, middle Wisconsinan, and Illinoian (∼ Oxygen Isotope Stages (OIS) 2, 3, and 6, or about 12 to 24, 24 to 60, and 130 to 188 ka, respectively). Soils 1, 2, and 3, then formed mainly during OIS stages 1, 3, and 5, respectively, or about 12 to 12, 60 to 60, and 73 to 130 ka. In comparison with other dated stratigraphic sections in the Great Plains, soils/paleosols have relatively simple, cumulic horizon sequences, as is typical at sites distal from principle loess source regions. Nonetheless, they record a complex pedosedimentary history that reflects climatically-driven variations in rates of sedimentation and pedogenesis. Soil 1 is an Udic Argiustoll with 21-cm A (mollic)/69-cm Bt (argillic)/60-cm Bk horizons, that formed under modern-type grassland and climate. Soil 3, the Sangamon paleosol, includes a 3-m thick, highly rubified and clay-rich argillic horizon that, based on its morphological properties, probably formed under a relatively warm, moist, equable climate and deciduous-type forest. Soil 2 coincides with the GCF, and as such is a pedolithostratigraphic unit that includes a 1.3-m mollic horizon and to 1.6-m oxidized 3Btb and 3BCb horizons. Whereas the oxidized B horizons apparently represent relatively warm, moist climatic conditions between about 65 to 35 ka, the upper cumulic (mollic) A horizons of the GCF probably formed under progressively cooling climate and grassland between about 35.7 and 26.9 (calibrated radiocarbon) ka. Estimated mean accumulation rates (MARs) of loess range from 0.12 m/k yr for the GCF to about 0.5 m/k yr for PL.

Morphological and physico-chemical characteristics of soils in a steppe region of the Kherlen River basin, Mongolia

Summary Morphological and physico-chemical characteristics of five soil profiles were studied at steppe sites in a vegetation transition zone of the Kherlen River basin, Mongolia. A vegetation survey showed differences in floristic compositions between southern and northern sites, and suggested a grazing effect and varying moisture conditions among the study locations. The presence of a mollic horizon and the accumulation of calcium carbonate (CaCO3) characterized the profile morphologies. The depths of the CaCO3 accumulation horizon differed among the study sites. The soils were classified as Calcic Kastanozems and Calcic Hyposodic Kastanozems, and soil physical properties showed high bulk density values and low hydraulic conductivity in the CaCO3 accumulation horizons. Regarding chemical properties, the organic carbon content was high in the A horizon then decreased rapidly with soil depth. The pH and electrical conductivity (EC) of the A horizon ranged from 6.3 to 7.2 and 0.29 to 0.95 dS m−1, respectively. The CaCO3 accumulation horizons of the five study sites showed distinct differences in pH and EC ranging from 8.6 to 10.0 and 1.25 to 4.70 dS m−1, respectively. Differences in the amounts of water soluble and exchangeable ions were remarkable, with sites in downstream areas of the Kherlen River basin tending to have higher Na+, SO 4 2 - , and Cl− ion values.

Variations in soil properties as affected by deforestation on loess-derived hillslopes of Golestan Province, northern Iran

Deforestation and shift of land use to agriculture, is of great concern in Golestan Province and has brought hazardous problems of flooding, landslide and soil loss. Soil organic carbon, total nitrogen content, available phosphorous and potassium, calcium carbonate content, thickness of A horizons and some important soil properties were studied on forested soils and compared with the adjacent deforested and cultivated soils. The studied soils were formed on a hillslope with parent material consisted mainly of loess deposits. Forested and deforested soils were classified as Calcic Hapludolls and Typic Hapludolls, respectively. The studied soils were all calcareous with the pH value of 7-7.9. The soil texture was silty clay loam with the silt content of 54-60%. The results revealed that the soil organic carbon, total nitrogen content and available potassium, were significantly lower in the deforestated soils. The thickness of mollic horizons was also reduced after deforestation in all studied pedons. While calcium carbonate contents of the subsurface horizon of the forested soils are significantly higher compared to the surface horizon due to the leaching processes, it is considerably high in the surface horizons of the deforested soils and does not change significantly with depth. This points to the effect of deforestation and cultivation practices which has led to soil erosion and the subsequent exposure of the highly calcareous subsurface horizon. Available soil phosphorous did not show any significant change by deforestation.

Hillslope Hydrology and Soil Morphology for a Wetland Basin in South‐Central Minnesota

Knowledge of soil and landscape hydrology is essential to evaluating the processes and quality of terrestrial ecosystems. Of particular interest in Southern Minnesota is the extensive Clarion–Nicollet–Webster catena, for which little quantitative work has been done in the region. The objective of this study was to investigate the relationship between soil hydrology and morphology for an undrained catena in south‐central Minnesota. Seven points along a 125‐m summit‐to‐wetland transect were instrumented with piezometers (25, 50, 100, and 200 cm), observation wells (300 cm), Pt electrodes (25, 50, 100 cm, footslope only), and thermocouples (10, 25, 50, 100 cm). Mollic epipedons were 77‐cm thick at the footslope (Cumulic Endoaquoll), thinning to 39 cm at the summit (Oxyaquic Hapludoll). The lower hillslope positions had low chroma colors below the mollic horizon, indicative of reducing conditions. The water table frequently was located in the mollic horizon for these soils and redox potentials at the footslope were frequently &lt;200 mV. Fe content decreased from summit to footslope, indicating the reduction and removal of Fe in the lower landscape positions. With the exception of the wetland, soils had equal piezometric head with depth, indicating lateral throughflow. The wetland had alternating recharge and discharge hydrology during the study. Profile Darkness Index (PDI) had strong correlation with the duration of saturation (r = 0.88, α = 0.05). Thickness and color of surface horizons in this landscape are strong indicators of landscape hydrology, especially when redoximorphic features associated with normal water table levels are masked by thick mollic epipedons.

Hillslope Hydrology and Soil Morphology for a Wetland Basin in South-Central Minnesota

Knowledge of soil and landscape hydrology is essential to evaluating the processes and quality of terrestrial ecosystems. Of particular interest in Southern Minnesota is the extensive Clarion–Nicollet–Webster catena, for which little quantitative work has been done in the region. The objective of this study was to investigate the relationship between soil hydrology and morphology for an undrained catena in south-central Minnesota. Seven points along a 125-m summit-to-wetland transect were instrumented with piezometers (25, 50, 100, and 200 cm), observation wells (300 cm), Pt electrodes (25, 50, 100 cm, footslope only), and thermocouples (10, 25, 50, 100 cm). Mollic epipedons were 77-cm thick at the footslope (Cumulic Endoaquoll), thinning to 39 cm at the summit (Oxyaquic Hapludoll). The lower hillslope positions had low chroma colors below the mollic horizon, indicative of reducing conditions. The water table frequently was located in the mollic horizon for these soils and redox potentials at the footslope were frequently <200 mV. Fe content decreased from summit to footslope, indicating the reduction and removal of Fe in the lower landscape positions. With the exception of the wetland, soils had equal piezometric head with depth, indicating lateral throughflow. The wetland had alternating recharge and discharge hydrology during the study. Profile Darkness Index (PDI) had strong correlation with the duration of saturation (r = 0.88, α = 0.05). Thickness and color of surface horizons in this landscape are strong indicators of landscape hydrology, especially when redoximorphic features associated with normal water table levels are masked by thick mollic epipedons.