International Soil Classification Research Articles

CONSTRUCTION OF A DIAGNOSTIC ALGORITHM FOR SOIL IDENTIFICATION ACCORDING TO THE INTERNATIONAL SOIL CLASSIFICATION SYSTEM WRB

Topicality. In this article discusses the identification of soils according to the international soil classification World Reference Base for Soil Resources system (WRB). The World Reference Base for Soil Resources was developed to identify soils and use the obtained data in different areas of everyday life: agriculture, forestry, animal husbandry, etc. The purpose of the work Note that the WRB, developed by a group of soil scientists, is not meant to replace national classification systems. Besides this classification system, there are also different soil classifications designed by national soil science schools. The difference in the structures of these classifications necessitated the development of a diagnostic algorithm to correlate them with each other. Results Three options for determining whether a soil belongs to reference soil groups are considered, depending either on soil parameters only, or on a combination of diagnostic horizons and soil parameters, or only on diagnostic horizons. A group of scientists headed by M. Babayev also developed a national soil classification system for Azerbaijan. In order to compare these two systems, this study proposes a soil data structure, as well as an algorithm for soil identification according to the WRB classification on the basis of the proposed structure. Conclusion A soil diagnostic algorithm is developed, which will allow identifying any soil type with the corresponding WRB Reference Soil Group. Three variants of allocating soils to WRB Reference Soil Groups based only on soil parameters, or on the combination of diagnostic horizons and soil parameters, or only on diagnostic horizons are considered.

Classification of acid sulfate soils and soil materials in Finland and Sweden: Re-introduction of para-acid sulfate soils

Established international soil classification systems have not properly accommodated acid sulfate soils (ASS) and soil materials in Finland and Sweden because: (1) in these soils some diagnostic ASS properties are too deep to meet the depth requirements, and (2) there is a lack of defined diagnostic soil classification criteria for acidic and potentially acidic soil materials that do not completely fulfill the diagnostic pH-criterion of pH < 4.0. In this paper, two new ASS materials are introduced with the prefix “para” for parasulfuric material (oxidized material) and parahypersulfidic material (reduced material). These materials have diagnostic pH-criteria of pH 4.0–4.5 and 3.0–3.5 (field-pH for parasulfuric material and incubation-pH for parahypersulfidic material) for mineral and organic soil materials (here defined as > 20% organic matter; peat and gyttja), respectively. The term “para-acid sulfate soil (para-ASS) material” is introduced for soil materials which may have a considerable environmental impact due to mobilization of acidity and dissolved metals. Because organic acids may lower pH to values below the established pH-value of < 4.0 for ASS materials, a pH of < 3.0 is used in the Finnish-Swedish ASS classification for organic soil materials. These changes and new additions to existing diagnostic ASS materials have consequently also led to a slight modification of the required field-pH values of the existing terms “hypersulfidic material” and “sulfuric material”. The Finnish-Swedish ASS classification further includes a systematic way for classification of the entire soil profile and no depth requirements for diagnostic ASS materials are present; what matters is the current or potential environmental impact that the soil has or may have. It is proposed that the Finnish-Swedish ASS classification may serve as a framework for establishing a unified ASS classification globally and that the new diagnostic ASS materials are included in relevant international soil classification systems.

The Impact of Tillage and Crop Residue Incorporation Systems on Agrophysical Soil Properties.

A long-term field experiment has been ongoing since 1999 at the Experimental Station of Vytautas Magnus University's Agriculture Academy. According to the latest edition of the International Soil Classification System, the soil in the experimental field can be classified as Planosol, with a silty medium-loam texture at a depth of 0-20 cm and a silty light-loam texture at a depth of 20-40 cm. Studies were carried out on winter wheat crops in 2014, 2017, and 2023. This research aimed to assess how different long-term tillage systems impact soil shear strength and aggregate stability, their interconnection, and the effect of crop residues on soil stability. The treatments were arranged using a split-plot design. In a two-factor field experiment, straw was removed from one part of the experimental field, while the entire straw yield was chopped and spread at harvest in the other part (Factor A). The subplot factor (Factor B) included three different tillage systems: conventional deep ploughing, cover cropping for green manure with no tillage, and no tillage. The soil samples were analyzed at the Laboratory of Agrobiology at Vytautas Magnus University's Agriculture Academy. The findings indicated that the long-term application of reduced tillage significantly increased the soil shear strength. Shallower tillage depths led to a higher soil shear strength, while the effect of spreading plant residues was relatively lower. The long-term tillage of different intensities, spreading plant residues, and catch crop cultivation for green manure did not significantly affect the soil structure. However, the soil structural stability was found to be highly dependent on soil tillage. Cover cropping for green manure with no tillage and no tillage alone positively affected the soil aggregate stability in the upper 0-10 cm and 10-25 cm layers. The correlation-regression analysis showed that, in the top 0-10 cm and 10-25 soil layers, there were moderate to strong correlations between the soil structural stability, soil shear strength, and the effect of crop residues on soil stability.

Some Agrophysical and Physicochemical Properties of Irrigated Gray-Brown Soils of South Mugan

The article presents the results of research on the study of the current state of irrigated gray-brown soils of South Mugan. Morphogenetic diagnostics, physicochemical and agrophysical properties of irrigated gray-brown soils of South Mugan have been established. The classification is based on the international soil classification WRB.

World Reference Base for Soil Resources—Its fourth edition and its history

AbstractThe fourth edition of the international soil classification system World Reference Base for Soil Resources (WRB) was released in 2022. It maintains the 32 Reference Soil Groups at the first classification level. Most qualifiers (second level) and most diagnostic horizons, properties and materials were maintained but some were abolished and new ones introduced. The main part of the fourth edition is followed by six annexes, most of them are new. For the first time, the WRB has a Field Guide (Annex 1) to facilitate field survey and to assure that all field characteristics required in the classification are reported. The fourth edition also provides designations for horizons and layers (Annex 3), which was not the case in the second and the third edition. The wordings of the definitions were harmonized, and the same features are worded in the same way throughout the text (including the annexes). Ambiguities have been corrected and many definitions written in a more concise and a more didactical way. The WRB has a long history. Four editions have been published: 1998, 2006 (with update 2007), 2014 (with update 2015) and 2022. Editor is the Working Group WRB of the International Union of Soil Sciences. The WRB followed the Legend and the Revised Legend of the Soil Map of the World. This map was edited by FAO (Food and Agriculture Organization of the United Nations) and UNESCO, and the system is known as the FAO Soil Classification System. In addition, WRB incorporated ideas from the former Working Group International Reference Base for Soil Classification that existed from 1982 to 1994.

The diagnostic continua of the soils of Europe

Diagnostic horizons, properties and materials are commonly applied building units of national and international soil classification systems. The presence, depth or absence of diagnostic information supports the process of objective soil classification, such as the World Reference Base (WRB). While the diagnostic units and associated descriptive qualifiers convey information that reflect pedogenesis, they also indicate important, and often complex properties that are related to soil fertility and other soil functions. The spatial extent or the continuum of diagnostic information is often different from the spatial extent of the mapping units in general soil maps (mostly reflecting soil types). This paper presents the spatial distribution of selected diagnostic units and qualifiers for the European Union and describes their significance for key soil functions. The derivation of selected diagnostics was performed based on the information provided in the European Soil Database and by taking into consideration the definitions, rules and allocation procedure of soils to the appropriate Reference Soil Group (RSG) defined by the WRB key. The definition of the presence/absence of the diagnostic units were performed by extracting information related to the first level of the WRB classification and to the qualifiers provided by the ESDB on the Soil Taxonomic Units (STU) level. The areal percentage of the STUs (thus, the derived diagnostics) within Soil Mapping Units (SMUs) was calculated and was visualized on separate maps. The study demonstrated the importance of the spatial information that the diagnostic elements convey, especially related to soil functions.

Soil Water Capacity, Pore Size Distribution, and CO2 Emission in Different Soil Tillage Systems and Straw Retention.

The long-term implementation of crop rotation and tillage has an impact on the soil environment through inputs and soil disturbance, which in turn has an impact on soil quality. Tillage has a long-term impact on the agroecosystems. Since 1999, a long-term field experiment has been carried out at the Experimental Station of Vytautas Magnus University. The aim of this experiment is to investigate the effects of long-term various-intensity tillage and straw retention systems on soil physical properties. The results were obtained in 2013 and 2019 (spring rape was growing). According to the latest edition of the International Soil Classification System, the soil in the experimental field was classified as Endocalcaric Stagnosol (Aric, Drainic, Ruptic, and Amphisiltic). The treatments were arranged using a split-plot design. In a two-factor field experiment, the straw was removed from one part of the experimental field, and the entire straw yield was chopped and spread at harvest in the other part of the field (Factor A). There were three different tillage systems as a subplot (conventional deep ploughing, cover cropping with following shallow termination, and no-tillage) (Factor B). There were four replications. The long-term application of reduced tillage significantly increased soil water retention and improved the pore structure and CO2 emissions. Irrespective of the incorporation of straw, it was found that as the amount of water available to plants increases, CO2 emissions from the soil increase to some extent and then start to decrease. Simplified tillage and no-tillage in uncultivated soil reduce CO2 emissions by increasing the amount of water available to plants from 0.151 to 0.233 m3·m−3.

Redoksimorfne značajke kao pokazatelji režima vlaženja tla

Soil water regime, as one of the key components of soil fertility, refers to the quantity, retention, and movement of soil water. Rather than through expensive and/or time-consuming measurements, it can be assessed from the field-observable morphological properties in the soil profile. Excessively wetted soils have a specific morphology, and are therefore often referred to as hydromorphic. Their morphology is caused by various soil redoximorphic features (RMFs), resulting from the reduction, translocation, and oxidation of iron and manganese oxides. Hydromorphic soils largely comprise Gleysols and Stagnosols (along with Gleyic Fluvisols) that are excessively wetted by groundwater, precipitation and/or flooded water. Their morphology is often described/analyzed with different terms/criteria in line with their global distribution. This complicates the comparison and classification of such soils and thus their use or reclamation. This review paper describes and compares common RMFs and explains their formation. It then proposes the revised Croatian terms for these features, which are in line with the terms used in the international soil classification systems of WRB and/or Soil Taxonomy. Furthermore, the criteria/rules used for diagnosing RMFs when classifying hydromorphic soils are critically reviewed. Finally, it is shown that a methodologically sound RMFs description can provide a quick insight into the crucial soil water regime parameters, such as location and duration of soil saturation, the origin of the excess soil water, recentness of excessive soil wetting, etc. However, depending on the research objectives and/or actual soil conditions, field soil description cannot always fully replace continuous field monitoring of the soil water regime and/or laboratory and micromorphological soil analyses.

Soil formation in technogenic landscapes: trends, results, and representation in the current classifications (Review)

For hundreds of years, humans have been a soil formation factor. With the recent industrial development of vast territories, the formation of soils in technogenic and postanthropogenic conditions requires more attention. This study reviews the literature on the soils of human-transformed or human-made landscapes (technogenic landscapes), in which soil formation starts on a new technogenic substrate. Such soils may occur in different bioclimatic conditions. We focused on processes that govern soil morphology and the subsequent transformation of these soils. Often, the soils of technogenic landscapes are characterized by high bulk density values and by the presence of dense contact. Their properties are affected mainly by organic matter accumulation (humus, litter, and peat). The paper also covers approaches to the reclamation of technogenic landscapes, the main stages, and partly the reclamation options. It is noted that the efficiency of reclamation activities depends on the available resources and timely decision-making. We assessed the efficiency of soil reclamation methods and suggested technogenic landscape survey techniques. The major approaches to soil classification in technogenic landscapes in national and international soil classification systems are briefly discussed, and an approximate correlation of soil names used in different systems is suggested. All considered classifications provide the opportunity to assess the soil properties and specifics of soil formation in technogenic landscapes. However, in most studies, the soil diagnostics are limited to top-order taxa only. The paper contains 3 Figures, 2 Tables, and 140 References.

The correlation of Azerbaijan arid soils with WRB-2014

The geographical principles are used in grouping of the soils the highest taxonomic standards in the soviet soil scientists works concerning the classification. But the Azerbaijan soil classification is based on genetic profile. Traditionally – topographic, color, climate and so on names are used in this classification, which in the soils genetic types idea is assumed as a basis. The International classification system is identified on the basis of the diagnostic parameters in the field researches and specified as a result of the laboratory analyses. The Azerbaijan soil classification consists of eight taxonomic level and a high taxonomic level is considered- soil class, section, genetic soil type, low soil taxa - soil gender, sort, diversity, row, soil variants. Mainly used central taxon is soil type. An aim of the research is to determine correlative chances of WRB-2015 International soil classification system with the Azerbaijan soil classification. It was detected that a correlation of both soil classifications is possible. The correlation is taken place in different taxon levels. Therefore, the soils were analysed at a type and subtype standard besides high taxas when the soils were correlated. As a result of correlation, it was defined that irrigated meadow-grey soils should be correlated Anthrosols, but meadow-grey soils concerned Calcisols and Gleysols.

Agricultural potential and soil use based on the pedogenetic properties of soils from the cerrado-caatinga transition

The sustainable use of soil requires a broad knowledge of its genesis, morphology, properties, and distribution in the landscape. Thus, the objective of this study was to characterize the pedogenetic attributes of representative soils from the cerrado-caatinga transition of the Gurguéia river basin to indicate their agricultural potential and limitations for the implementation of agroforestry systems. National and international soil classification systems were used to define the soil classes. The limiting factors and agricultural potential were characterized following the evaluation system of the agricultural potential of Brazilian land. In general, profiles 1, 3, 5, and 6 had a low nutrient budget and a sandy to loam texture. Profiles 2, 4, and 7 showed high clay content and nutrient budget. The soil profiles were classified as Ustic Quartzipsamments, Udic Haplusterts, Xanthic Haplustox, Arenic Kanhaplustults, Typic Haplustox, and Aridic Dystrustept based on their pedogenetic characteristics. Udic Haplusterts and Arenic Kanhaplustults soils display restrictions regarding the planting of forests owing to oxygen and soil depth limitations. The other soil classes had adequate physical properties for the implementation of agricultural systems and pastures, including good drainage and medium texture; however, they had low natural fertility, and thus require technologies for soil acidity correction and fertilization. Ustic Quartzipsamments and Ustic soils require the implementation of conservation systems, such as agroforestry, to avoid degradation.

Infiltration into Frozen Silty Clay Loam Soil with Different Soil Water Contents in the Red River of the North Basin in the USA

Predicting surface runoff and flooding in seasonally frozen areas such as the Red River of the North Basin (RRB) in USA is a challenging task. It depends on the knowledge of the complex process of infiltration in frozen soil, such as phase changes of water, ice content and distribution in the infiltration zone (the top 0–30 cm of the soil profile), soil pore size distribution, soil temperature and freeze–thaw cycles. In this study, the infiltration rates into frozen soil (Colvin silty clay loam according to the United States Department of Agriculture (USDA) Classification, and Chernozem according to Food and Agriculture Organization of the United Nations (FAO) international soil Classification) were measured at three different initial water contents: permanent wilting point (PWP), θpwp; field capacity (FC), θfc; and between FC and PWP, θmid. Laboratory infiltration experiments were conducted using a Cornell sprinkle infiltrometer with three replications for each initial water content. Volumetric soil water content (θv) and soil temperature at three depths were also continuously monitored using sensors. The average infiltration rates were 0.66, 0.38, and 0.59 cm/min for three initial water contents (θpwp, θmid, and θfc, respectively). Initial infiltration into frozen soil occurred quickly in the soil with θpwp because the soil was dry. Melted ice water contributed to the total soil water content over time, so it made the initial infiltration comparatively slower in the soil with θmid. Initial infiltration was also slower in the soil with θfc because the wet soil had very small pore space, so the soil rapidly reached its saturation after the infiltration started. The Horton infiltration equation was fitted with the observed infiltration rates for the soils with three initial water contents, and the goodness of fit was evaluated by using the coefficient of determination (R2) and the root-mean-square error (RMSE). The final infiltration rates from the fitted Horton equations were 0.060, 0.010, and 0.027 cm/min for the initial water contents (θpwp, θmid, and θfc, respectively). The soil water content along the soil profile changed with the amount of infiltrating water over time. However, the initial soil water content and melt water from ice resulting from soil temperature rise regulated the change in soil water content. The amount of ice melt water contribution to soil water content change varied among the soils with different initial water contents (θpwp, θmid, and θfc, respectively). The θv changed gradually in the θpwp soil, rapidly at 0 °C in the θmid soil, and less in the θfc soil. The change in pore distribution due to freeze–thaw cycles and soil packing altered the soil hydraulic properties and the infiltration into the soil. This study can provide critical information for flood forecasting model and subsurface drainage design in the RRB.

A multivariate method for matching soil classification systems, with an Australian example

Differences between local systems of soil classification hinder the communication between pedologists from different countries. The FAO–UNESCO Soil Map of the World, as a fruit of world-wide collaboration between innumerable soil scientists, is recognised internationally. Ideally, pedologists should be able to match whole classes in their local systems to those in an international soil classification system. The Australian Soil Classification (ASC) system, created specifically for Australian soil, is widely used in Australia, and Australian pedologists wish to translate the orders they recognise into the FAO soil units when writing for readers elsewhere. We explored the feasibility of matching soil orders in the ASC to units in the FAO legend using a multivariate analysis. Twenty soil properties, variates, of 4927 profiles were estimated from their visible–near infrared reflectance (vis–NIR) spectra. We arranged the profiles in a Euclidean 20-dimensional orthogonal vector space defined by standardised variates. Class centroids were computed in that space, and the Euclidean distances between the centroids of the ASC orders and units in the FAO scheme were also computed. The shortest distance between a centroid of any ASC order and one of units in the FAO classification was treated as a best match. With only one exception the best matches were those that an experienced pedologist might expect. Second and third nearest neighbours in the vector space provided additional insight. We conclude that vis–NIR spectra represent sufficiently well the essential characters of the soil and so spectra could form the basis for the development of a universal soil classification system. In our case, we could assign with confidence the orders of the ASC to the units of the FAO scheme. A similar approach could be applied to link other national classification systems to one or other international systems of soil classification.

An application of a fuzzy classification routine suggested for fine grained soils

Soil classification is an important stage in preliminary studies for design applications in engineering geology. A few letters or numbers assigned to a soil provide rapidly an idea to engineers. The classification of fine grained soils in national and international soil classification systems is determined using plasticity chart. However, because of the factors affecting liquid and plastic limit tests, uncertainties can arise in classification of fine-grained soils when this approach is used. Furthermore, uncertainty level has increased in case points fall sometimes on the lines or near the lines. In this study, an application of a fuzzy classification routine which was suggested before to minimize these uncertainties was performed. In the suggested method, the spatial distances of the evaluation points on the chart from the lines were considered. The membership degrees that define the fuzzified soil and plasticity were determined by using sigmoid function. Finally, fuzzy soil classes were obtained by using fuzzy operators. The suggested fuzzy classification routine, was performed on classification of 100 fine-grained soil samples ad obtained fuzzy soil classes were compared with crisp soil classes.

Morphological diversity of chernozemic soils in south-western Poland

Abstract Diverse chernozemic soils featured by thick mollic horizon, rich in humus, dark-coloured, structural, and saturated with base cations are relatively common in the loess-belt of SW Poland. It is postulated, that most of these soils may have similar initial (chernozemic) history of thick humus horizon, related to climate conditions and vegetation in the Late Pleistocene and the Neolithic periods. However, these soils exist on various bedrocks and under different moisture conditions that led to the development accompanying features and variable classification of soils, both in Polish and international soil classifications. The aim of the paper is to presents the most important variants of loess-derived chernozemic soils of SW Poland, in relation to local conditions, which influenced soil transformation and present spatial diversification. ‘Typical’ chernozems (WRB: Calcic Chernozems), which have a mollic horizon and secondary carbonates, but are free of strong redoximorphic features, are rather uncommon in the region. Whereas, the black earths (WRB: Gleyic/Stagnic Chernozems/Phaeozems), featured by the presence of mollic horizon and strong gleyic or stagnic properties in the middle and bottom parts of the profiles, are predominant loess-derived chernozemic soils in SW Poland. Their most specific forms, developed on the clayey bedrock, are black earths with a vertic horizon (WRB: Vertic Stagnic Phaeozems). The strongly leached chernozemic soils developed over permeable subsoils, lacking carbonates and free of (strongly developed) stagnic/gleyic properties are called grey soils, often featured by the presence of subsurface diagnostic horizons cambic or luvic (WRB: Cambic/Luvic Phaeozems).

Chernozems of Lubelszczyzna (eastern Poland)

Abstract The purpose of the work was to characterize the variously used humus in the south-eastern part of the Lublin region. The basic research material were data taken from the literature on the subject. Standard soil science methods were used in the study. The humus level of humus varieties ranged from 30 to 80 cm. The researched molds were formed from loess deposits, which most often showed graining of clay dust. Organic carbon content in humus levels did not exceed 2.9%. The surface levels of the analyzed molds showed clear decalcification. The CaCO3 content in the loess mother rock was a maximum of 15.5%. These are soils with high saturation of the sorption complex with basic cations. The content of available phosphorus and potassium in humus levels was low and medium. According to Systematics of Poland’s soils (2019), the analyzed molds mainly represented leached molds and typical molds, while according to the international soil classification WRB (IUSS Working Group WRB 2015) they are primarily Phaeozems. All the analyzed humus plants belong to soils with the highest utility value. Phenomena lowering the quality of molds in the Lublin region related to human activity are the use of improper agrotechnics, and above all water surface erosion. The unfavorable processes are favored by the undulating terrain and the grain size of the soils studied, characteristic for this area.

Chernozem (czarnoziem) – soil of the year 2019 in Poland. Origin, classification and use of chernozems in Poland

Abstract The Soil Science Society of Poland has elected chernozem to be the Soil of the Year 2019. Although chernozems cover less than 2% of Poland, they have high importance for agriculture due to their productivity and play a specific scientific role for understanding of soil development and functioning in an environment. Chernozems are also crucial for the reconstruction of Neolithic agriculture development and human impacts on soil and landscape. This introductory paper presents (a) a specific definition of chernozem in Poland, connected with a separate distinction of black earths and colluvial chernozemic soils; (b) a review of the present and former classification schemes for chernozems in Poland and their correlation with international soil classification systems (WRB and Soil Taxonomy); (c) the spatial distribution of chernozems in Poland, their agricultural evaluation and threats for chernozems’ quality and future existence related to intense land use.

REFERENCE SOILS OF THE FENNOSCANDIAN GREEN BELT

The core elements of the Green Belt of Fennoscandia are protected areas of various ranks. Such cores in the Republic of Karelia are the operating national parks Paanajarvi, Kalevalsky, Ladoga Skerries, strict nature reserve Kostomukshsky. The article describes the soil cover in the protected areas of Karelia situated within the Green Belt of Fennoscandia. Reference soils have been identified for areas of similar natural conditions, their spatial shares have been determined. A distinguishing feature of soils in the north-taiga subzone of the Fennoscandian Green Belt is the prevalence of the podzol formation process, as opposed to soils of the Karelian Ladoga coast, where podburs and brown earths are widespread. Distinctive morphological and physical-chemical properties have been noted for the podzolic soils in the northern and middle taiga of the Green Belt of Fennoscandia. The classification positions of the reference soils of the Fennoscandian Green Belt were determined according to the regional, national and international soil classifications. The resultant data can be used for soil monitoring in natural and disturbed ecosystems, and serve as a basis for protected area planning and designation in Karelia.

Классификация почв Дагестана в системе российской и Международной классификации почв

Классификация почв Дагестана в системе российской и Международной классификации почв

Relationships between soil pH and base saturation – conclusions for Polish and international soil classifications

Abstract Taking into account the fact that (a) measurement of the cation exchange capacity and base saturation is practically unavailable in the field, that formally makes impossible the reliable field classification of many soils, (b) base saturation is measured or calculated by various methods those results significantly differ, (c) base saturation and soil pH are highly positively correlated, it is suggested to replace the base saturation with pHw (measured in distilled/deionized water suspension) in the classification criteria for diagnostic horizons and soil units/subunits, both in the Polish Soil Classification and FAO-WRB. Based on statistical analysis of 4500 soil samples, the following pHw values are recommended instead of 50% base saturation: pHw <5.5 for umbric and pHw ≥5.5 for the mollic horizon, and for Chernozems, Kastanozems, Phaeozems (directly) and Umbrisols (indirectly). Furthermore, the pHw <4.7 may feature the Dystric qualifier in mineral soils and respective Reference Soil Groups of WRB; while the pHw ≥4.7 may feature the Eutric qualifier. The distinction between subtypes of the brown soils in the Polish Soil Classification may base on the pHw 4.7 or 5.0, but using different requirements of pH distribution in the depth control section. The replacement of the base saturation with pH refers to the formal soil classification only, and does not exclude the use of base saturation for professional soil characteristics.