Horizons Of Soil Profiles Research Articles

Modeling and digital mapping of soil quality indicators in different land uses (a case study: Ravansar-Sanjabi Plain, Kermanshah).

Identifying the spatial variability of soil quality indices is necessary to manage soil resources on a watershed scale. This study aimed to identify suitable indices for soil quality assessment at the watershed scale using various soil characteristics and modeling approaches. Another objective was to map soil quality variability in a representative area in the Qarasu watershed in Kermanshah province, west of Iran. Latin hypercube sampling method using the auxiliary variables used to select 163 sampling points based on land use, soil, and topographical variability in an area of about 57 thousand hectares. In the field operations, soil profiles were described, and samples were taken from different soil profile horizons. Soil properties such as texture, pH, salinity, available water, equivalent calcium carbonate, saturation percentage, soil organic carbon, nitrogen, available phosphorous, potassium, Fe, Zn, Cu and Mn, and soil aggregate stability (mean weight diameter (MWD), geometric mean diametric (GMD), and stable aggregates larger than 0.25 mm (WAS)) measured in the laboratory. Soil quality indices (productivity index (PI), soil quality index (SQI) and reduced dimension soil quality index using principal component analysis (SQI-PCA)) were calculated for each point using the measured soil properties. Soil quality indices were simulated using modeling with the random forest and support vector machine methods and auxiliary variables. Results showed that the range of soil characteristics and integrated soil quality indices was very high across the study area. Soil organic carbon percent varied from about 0.19 to 8.44%. The range of changes in PI in the study area was more than SQI and SQI-PCA indices. Quantities of all soil quality indices were higher in forest and rangeland than in agricultural lands. The spatial estimation accuracy of the SQI-PCA was higher than other soil quality indices and converged well with land use changes compared to PI and SQI.

Content and Mobility Metals in Oligotrophic Peat Soils of the Cryolithozone of Western Siberia

The ongoing climatic changes have the greatest impact on natural ecosystems in high-latitude areas, as warming climate, as well as increasing anthropogenic load associated with the development of Arctic zone, contribute to the degradation of frozen peatlands and an increase in the thickness of seasonally thawed layer of soil. The relevance of studying peat oligotrophic soils (Cryic Histosols) of the northern territories of Western Siberia is associated with the fact that their degradation enriches natural waters by organomineral substances, which containing a large number of chemical elements, including heavy metals, contributing to changes in the hydrogeochemical properties of natural waters of the North. The article describes the main properties of peats sampled from different horizons of soil profiles laid down at key areas covering the territory of YNAO from north to south and from west to east. The chemical composition of soils was analyzed at the IPA SB RAS using standard methods. The concentrations of gross and mobile forms of metals (Fe, Ca, K, Na, Mg, Cd, Co, Cr, Cu, Mn, Ni, Pb, Zn) were investigated by optical atomic emission spectrometry and flame atomic absorption spectrometry, respectively. It has been determined that a characteristic feature of the distribution of concentrations of chemical elements in peat oligotrophic soils of the northern part of Western Siberia is the presence of two maxima within the soil profile. The first is confined to the upper horizons showing signs of degradation, while the second is confined to the upper part of the permafrost. Statistical analysis using principal component method showed that low ash content, pH and C/N ratio are associated with high mobility of K, Cu, Zn and Mg. The mobility of Fe, Mn, Pb, Cd, and Cr is associated with an increase in ash content, pH, and Ntotal in the upper part of permafrost organogenic rocks.

Evidence and mineralogical and physico-chemical properties of chernozem and chernozem-like soils in Croatia

The aim was to determine possible local differences between the parent materials of recent leoss-derived soils in eastern Croatia (Dalj, Zmajevac). Furthermore, it highlights the existence of chernozem and chernozem-like soils in Croatia and describes their basic physical, chemical and mineral properties. For this purpose, two soil profiles (P-3 and P-6) south of the Dalj settlement and one soil profile (P-10) near the Zmajevac settlement were excavated. The investigation included a detailed pedological analysis, a modal analysis of the heavy and light mineral fraction and a mineralogical analysis of bulk samples (the < 2 mm fraction) and the fraction < 2 μm. By comparing the obtained results with the criteria of the Croatian Soil Classification and the World Reference Base for Soil Resources, the soil profiles P-3 and P-6 can be defined as Chernozem on Loess or Hortic Calcic chernozem (Epiloamic, Endosiltic, Aric, Humic). The systematic unit for profile P-10 was defined as Rendzina according to the Croatian Soil Classification or Calcic Chernozem (Siltic) according to the WRB. Based on the results of the pedological analysis of the soil profile horizons, a gradual degradation of the chernozem was observed as a result of anthropogenic influence, but also due to recent climate change. The degradation is particularly evident in the form of a reduction in organic matter and the relocation of carbonates from the surface to deeper zones. Due to the increasing degree of weathering caused by recent climate changes, some differences in the mineralogical composition of the studied soils were also observed. The progressive degradation of the chernozem due to the effects of recent weathering processes is indicated mainly by the presence of goethite in the fraction < 2 μm as a weathering product of iron minerals (magnetite, pyroxenes…). Although the parent material of all three profiles is loess sediments, the reason why the soil material of profile P-10 has not developed a chernic horizon is the constant contribution of aeolian material and a short period of exposure to pedogenetic processes.

CHEMICAL COMPOSITION AND PEDOGENESIS OF SOILS OF AGRICULTURAL COLLEGE FARM, NAIRA, ANDHRA PRADESH

The study on elemental composition and pedogenesis of soils of Agricultural College farm, Naira of Srikakulam district was carried-out during 2021. The soils were developed from granite-gneiss parent material. Total silica (SiO2) content of soils ranged from 50.5 to 74.6 percentage. Silica content in general decreased with soil depth, while sesquioxides (R2O3), alumina (Al2O3), iron oxide (Fe2O3), CaO, K2O, Na2O, MnO were found increasing with depth. High silica/ sesquioxide ratio of soils indicated siliceous nature of soils. The aluminum oxide content of the profiles varied from 15.80% to 26.25%. Highest value was reported in lowland profile, whereas, the lowest value was recorded in rainfed upland profile. Iron oxide content varied from 5.04% to 8.50%. Iron oxide content showed slight variation within profiles. Among the other oxides, CaO > MgO > K2O > Na2O was of the order as the soils were developed under semi-arid climate, wherein, basic cations have accumulated in these soil profiles due to limited leaching. The molar concentration of silica (SiO2) ranged from 0.841 to 1.24 moles, and molar concentration of sesquioxide ranged from 0.191 to 0.313 moles. The molar ratio of SiO2 / R2O3 varied from 2.68 to 6.51 in different soil profiles. The SiO2 / Al2O3 ratio varied from 3.33 to 8.02. These wider molar ratios indicated salacious nature of parent material and due to dominance of silica among chemical fractions. Midland (P3) and lowland (P4) soil profiles showed silt/clay ratio of less than 0.45 and upland profiles showed more than 0.45 indicating relatively advanced weathering in mid and lowland profiles while it was moderate weathering in upland profiles. The Weathering Index of Parker (WIP) values of the soils of study area ranged between 2.8 and 32.4. The lower WIP values (2.8 to 8.1) were associated with rainfed uplands and higher values of 14.7- 32.4 with irrigated low lands. The PIA values ranged from 67 to 97 tend to decrease with the depth in all profiles. The profiles examined have the CIA values varied from 66 to 95 indicating high to intense weathering. The CIA values decreased with depth in all the profiles. The surface horizons of P1 and P2 soil profiles were classified as moderately weathered. On the other hand, all subsurface horizons of these two profiles were highly weathered. However, in profiles P3 and P4 the CIA values ranged between 68 to 90 indicating that these soils were highly weathered. CIW values closely followed the trend of CIA values. The bases/R2O3 values of all profiles ranged from 0.061 to 0.608 and found increased with soil depth in all the profiles. Relatively higher values of bases/R2O3 were found in P4 (low lands) indicating base rich character. Middle land and lowland black soil profiles showed silt/clay ratio of less than 0.45 and upland profiles showed morethan 0.45 indicating relatively advanced weathering in mid and lowland profiles while moderate weathering in upland profiles.

A Conceptual Approach to the Histosols Profile Morphology as a Risk Indicator in Assessing the Sustainability of Their Use and Impact on Climate Change

In the context of climate change, the questions of the sustainability of peat soil use are particularly relevant. The evaluation of changes in the properties of soils (including histosols) using chemical methods is expensive, thus, their application possibilities are limited. Analyzing the morphology of histosol profiles would provide effective spatial analysis opportunities for assessing the extent of their anthropogenic transformation and impact on climate change. The key diagnostic horizons and their sequences for the identification of the risk group are the main results of the study. The analysis included 12 soil profiles, whose morphological structure was characterized using the WRB 2022 system of master symbols and suffixes for soil profile horizon descriptions. The analyzed profiles were excavated in forested (relatively natural), agricultural (agrogenized) and peat mining (technogenized) areas. The insights of this article in the discussion are based on the chemical analyses (pH KCl, N, P and K, soil organic carbon, dissolved organic carbon, mobile humus substance, humic and fulvo acids, C:N ratio and humification degree) of three histosol profiles. The main discussion is based on the results of the morphological analysis of the profiles. The results of this research allowed for the identification of a different structure of the histosol profile. The upper part of the histosol profile, which consists of O–H(a,e,i) horizons, indicates its naturalness. The murshic horizon (Hap) is the classic top horizon of the agricultural histosol profile, which is most affected by mineralization. The technogenized histosols have a partially destroyed profile, which is represented by the Ahτ/Haτ or only Haτ horizons at the top. The morphology of the histosol profile and the identification of the relevant horizons (Hap, Haτ and Ahτ) indicate its risks and presuppose a usage optimization solution. The most dangerous in the context of sustainable land use principles and climate change is the murshic horizon (Hap), which is uncovered after removing the horizon O. The risks of sustainable use of histosol are caused by measures that promote its microbiological activity, which is the maintenance of a drained state and cultivation. In the context of GHG emissions and sustainable use, the most favorable means would be the formation of the horizon O by applying perennial plants. Rewetting should be applied to those histosols whose removal from the agricultural or mining balance would provide maximum ecological benefits.

Microbiocenosis of Cryofrost Soils in the South of the Vitim Plateau

The microbial communities in soils of cryomorphoses in the south of the Vitim Plateau have been studied. The objects of study were gley cryoturbated chernozems and humus-quasi-gley carbonated soils. In the course of the study, experimental sites with pronounced cryogenic phenomena were selected. The intensity of microbiological activity was determined by the carbon content of microbial biomass, the number of microorganisms in the dominant groups of microbial communities. Determination of the number of microorganisms in soils was carried out by direct microscopy, which makes it possible to carry out a more accurate count of bacteria in the soil, taking into account adsorbed cells. Cells were preliminarily desorbed on an ultrasonic disperser. The carbon of microbial biomass was determined by the rehydration method. Data were obtained characterizing the direction and intensity of microbiological processes along the horizons of soil profiles of heaving mounds and thermokarst depressions. The number of microorganisms and the dominant groups of bacterial communities of soils formed under the conditions of the ultracontinental climate of Buryatia and relatively close-lying permafrost are presented. It was revealed that bacterial microflora predominates in the soils of heaving mounds and thermokarst depressions. The intra-profile heterogeneity in the distribution of soil microorganisms indicates that, as a habitat, the soil is strongly differentiated in all directions. This differentiation along the vertical of heaving mound and thermokarst depression was reflected in the concept of soil horizons as special ecological niches and the possibility of using microbiological indications of heaving and subsidence occurring during heaving.

Changes of soil organic matter stock in meadow ecosystems in the south of Western Siberia

The study was conducted on the Baraba plain in the southern part of Western Siberia. Soil samples in meadow ecosystems that are at different stages of succession after drying of the lake bottom were analyzed. The conducted research allowed us to establish that the content of soil organic matter and microbial biomass (the active part of soil organic matter) in successional ecosystems formed in the floodplain of the drying salt lake gradually increases and in the last stages of development reaches the values of zonal chernozem soils. The process of accumulation of carbon stocks of humus and microbial biomass slows down against the background of a high concentration of salts in individual horizons of young soil profiles. This may be the reason for the revealed pattern, according to which the main carbon stock of humus and microbial biomass are concentrated in the upper (0-10 cm) layer of the emerging soils. This is especially noticeable at the very first initial stage of soil development and the next stage of the salicornia community (Salicornia perennans). In the last stages of succession, solonetz and chernozem-meadow soils are formed under meadow ecosystems. The carbon stock of humus and microbial biomass at these stages of soil development significantly increase against the background of active processes of reducing the amount of salts in the profiles of meadow soils. And only at these last stages there is a significant increase in carbon stocks of humus and microbial biomass in a layer of 10-20 cm.

Coupling changes of soil functional gene abundances and extracellular enzyme activities across the diagnostic horizons of agricultural Isohumosols

Soil functional microbial taxa and extracellular enzymes are involved in a variety of biogeochemical cycling processes. Although many studies have revealed the vertical change patterns of microbial communities along soil profile, the general understanding of the coupling changes in the functional gene abundances (FGAs) and extracellular enzyme activities (EEAs) in soil profiles is still limited, which hinders us from revealing soil ecosystem processes. Herein, we comparatively investigated the FGAs and EEAs in the diagnostic A, B, and C horizons of soil profiles obtained from two suborders of Isohumosols (Mollisols), Ustic and Udic Isohumosols, in Northeast China based on quantitative real-time polymerase chain reaction and standard fluorometric techniques, respectively. The distribution patterns of both FGAs and EEAs significantly distinguished by the two soil suborders and were also separated from A to C horizon. Additionally, the variations of EEAs and FGAs were greater in Udic Isohumosols compared to Ustic Isohumosols along soil profiles, and greater changes were observed in C horizon than in A horizon. Both FGAs and EEAs correspondently decreased along the soil profiles. However, when normalized by soil organic carbon, the specific EEAs significantly increased in deep soil horizons, suggesting that microorganisms will input more resources to the production of enzymes to ensure microbial nutrient requirements under resource scarcity. More importantly, we revealed that soil microbial nutrient demands were limited by carbon (C) and phosphorus (P), and the C and P limitations significantly increased along soil profiles with a greater C limitation observed in Ustic Isohumosols than in Udic Isohumosols. Overall, our findings provided solid evidence showing the links between FGAs, EEAs, and microbial nutrient limitations, which would be helpful for a better understanding of the ecosystem processes in soil profiles.

Horizontal Variation Characteristics of Alpine Grassland Soil Function and Vertical Changes Along Soil Genetic Horizons in the Three-River Headwaters Region

The Three-River Headwaters region is a hotspot for studying the response of soil function to climate change. To study the horizontal variation characteristics of alpine grassland soil function and vertical changes along soil genetic horizons, soil functional indicators (including respiration, nitrogen conversion rate, and enzymatic activity) of different genetic horizons in alpine grassland soil profiles and their correlations with environmental factors were analyzed. The results showed that there were no significant differences in soil functional characteristics between alpine meadows and steppes, and topsoil had higher respiration rates, nitrogen conversion rates, and enzymatic activities than those of subsoil. Total nitrogen was a key driver of soil functional characteristics in different genetic horizons, explaining 18.3%, 21.4%, and 27.5% of the horizontal variation in functional characteristics, respectively. Climate and vegetation factors mainly affected soil function indirectly by changing soil physicochemical properties in topsoil, but atmospheric nitrogen deposition still affected soil function in subsoil. These results indicate the significant nitrogen limitation of alpine grassland soil in the Three-River Headwaters region, and the findings provide a new insight into the maintenance of soil functional diversity and the response to climate change in the context of global climate change.

Response of heterotrophic respiration to vegetation restoration in a karst area of SW China

AbstractThe Grain‐for‐Green Program in China aims to restore sloping karst cropland severely degraded by intensive agriculture to secondary forest. Heterotrophic respiration (Rh) is a major process of carbon release from soils and is associated with the sequestration of soil organic carbon (SOC). However, we still do not have a comprehensive understanding of Rh and what drives it along soil profile horizons during the natural vegetative recovery process in typical karst soils. We investigated the responses of Rh (C release per gram of soil) and specific Rh (C release per gram of SOC) in soil horizons from the soil surface to bedrock at the different vegetation recovery stages in a karst region. Coincident soil microbial properties (e.g., bacterial and fungal abundance, total microbial biomass, potential enzyme activities) and physicochemical properties were quantified. Vegetation restoration after cropland abandonment significantly increased Rh rates due to increased soil nutrients and microbial biomass, bacterial abundances, and hydrolase activities (all, p < 0.05). The rates of Rh enhanced in sloping cropland (SC) from the soil surface to bedrock but reduced in the recovering stages (ASC: abandoned sloping cropland and SF: secondary forest) and primary forest (PF). The specific Rh between SF (1.34 mg CO2‐C g−1 SOC d−1) and PF (1.32 mg CO2‐C g−1 SOC d−1) were not significantly different but both of them were greater than those in SC (0.79 mg CO2‐C g−1 SOC d−1) and ASC (0.8 mg CO2‐C g−1 SOC d−1). Soil physicochemical properties and microbial properties explained approximately 48% and 22% of the variations in Rh along vegetation recovery, respectively. Nitrogen to phosphorus stoichiometry exerted the most direct and positive effects on Rh, suggesting the importance of managing soil nutrient status to regulate carbon decomposition during vegetation recovery in karst soils. The increased microbial biomass was the most important microbial factor regulating Rh in later vegetation recovery phases. Our results provide scientific insight into the impact of vegetation restoration on Rh in degraded ecosystems, which is important for reducing carbon loss in karst soils.

Soil Characteristics and Pedoclimatic Evaluation of Rainfed Sorghum (Sorghum bicolor (L.) Moench) in the Mayo-Lemié Division, South-Western Chad

In recent decades, many regions in the Chad Republic in Central Africa have experienced a continuous decline in agricultural yields. In order to determine the main factors leading to this decline in yields and mainly Sorghum yields, this study was conducted in South-Western Chad, in the Sudano-Sahelian environment. Three soil profiles of variable depths, namely, M1, M2, and M3, were dug along a toposequence, respectively, in the footslope, mid-slope, and the upslope. Soil samples collected from each horizon in the three soil profiles were labelled and sent to laboratories for mineralogical, geochemical, and physicochemical analyses. For land evaluation, climatic characteristics are divided into rating groups with respect to the crop and its climatic requirements. Parametric values were attributed to each soil characteristic for soil evaluation and the land index calculated. The main minerals identified in the studied soils are quartz, K-feldspars, plagioclase, kaolinite, smectite, illite, associated to traces of anatase, sepiolite, calcite, and interstratified minerals. In all the analyzed samples, silicon content is very high. It is closely followed by aluminum, iron, and potassium. The presence of kaolinite and smectite suggests that monosiallitisation is a crystallochemical processes acting at the bottom of profile towards bisiallitisation. All samples collected from the three soil profile horizons are mainly sandy and globally poor in nutrients. The pedoclimatic assessment of Sorghum cultivation reveals that the studied soils are marginally to moderately suitable for the production of Sorghum due to soil texture, wetness, and soil fertility. The decline in yields is related to low base saturation, in line with low exchange base content in the studied soils. These limitations could be solved by restoration of the cation balance through fertilization and liming, combining organic inputs with mineral fertilizer, and the realization of channels for the drainage of water at the base of the soil sequence.

Microbial communities in the diagnostic horizons of agricultural Isohumosols in northeast China reflect their soil classification

Soil depth greatly affects soil microorganisms due to the intensive changes in soil physical and chemical properties along soil profile. However, little is known about microbial communities in diagnostic horizons of soil profiles among different soil types, which is the key to understanding the biogeochemical cycling in deep soils. Herein, we collected soil samples from eight agricultural fields across Heilongjiang Province of China, which belong to two suborders of Isohumosols (Ustic and Udic), based on the diagnostic horizons. The microbial community abundances, diversities and structures were comparatively investigated using qPCR and high-throughput sequencing methods. Results showed that the abundances of bacteria, archaea, and fungi consistently decreased more than by 90% in C horizon (parent material horizons) compared with those in Ah horizons (humus horizons). In items of alpha diversity, the fungal diversity decreased by>50%, while archaeal diversity increased by more than two folds. The bacterial diversity varied along soil depths at different sites. In addition, all soil microbial community structures were obviously divided into Ustic and Udic groups, and a distinct succession of microbial communities was detected from Ah horizons to C horizons at individual sites. Moreover, compared to Ah horizons, the difference of microbial community structure between Ustic and Udic Isohumosols was greater in C horizons. Canonical correspondence analysis (CCA) and random forest (RF) analysis revealed that pH was the most important soil factor regulating the microbial communities among all tested edaphic variables. More importantly, using machine-learning methods, we found that soil microbial communities can be used to accurately predict two suborders of Isohumosols and diagnostic horizons. Overall, the findings of this study highlight that the microbial data of diagnostic horizons can be served as quantitative indices for the soil classification, and this conclusion needs to be verified in the future research using more soil types.

PEF-MODFLOW: A framework for preliminary soil profile horizon delineation based on soil color captured by smartphone images

Soil profile horizon delineation provides a vehicle for recording and communicating observations of soil profiles. A framework was developed to achieve soil profile horizon delineation based on soil color captured by smartphone images, consisting of a preprocessing module, an elbow method module, and a fuzzy c-means (FCM) algorithm module, referred to as PEF-MODFLOW. We have analyzed the effect of key parameters in PEF-MODFLOW on the results and demonstrate the high performance and interpretability of the PEF-MODFLOW in the ten validation profiles. This work shows that smartphones can be an effective tool for soil profile information collection. The results of soil profile horizon delineation are still preliminary due to the limitations of the information available in the soil profile images. The flexible adjustment capability of the input data gives the PEF-MODFLOW the potential for further improvement. The PEF-MODFLOW represents a key step towards smartphone-based access to soil profile information.

Organic Matter in Soils with Anthropic Horizons in The Eastern Amazon, Pará (Brazil)

The aim of this study was to evaluate the distribution of chemical and physical fractions of soil organic matter (SOM) in anthropic horizons of soil profiles in the west of Pará. The highest total organic carbon values were observed in the superficial horizons, especially in the antrópico LAd and antrópico CHd (45.0g kg-1). Were observed predominance of recalcitrant organic material. It appears that most of the C found in the SOM fractions is associated with C stabilization mechanisms such as the recalcitrance provided by the presence of pyrogenic coal, in addition to its ability to present carboxylic groups that increase its interaction with the mineral fraction of the soil, characterizing the mechanism of chemical protection. It is observed that the SOM fractions can function as indicators that contribute to better understanding of the soil carbon dynamics in soils with antrópico horizons.

Elemental and Molecular Composition of Humic Acids Isolated from Soils of Tallgrass Temperate Rainforests (Chernevaya taiga) by 1H-13C HECTCOR NMR Spectroscopy

The soils of Chernevaya taiga (tallgrass fir-aspen hemiboreal rainforest) have high fertility in comparison with oligotrophic analogs formed in boreal taiga. We have studied humic acids isolated from the soils of Chernevaya and oligotrophic taiga in the Novosibirsk, Tomsk, Kemerovo and the Altai regions of Russia and for the first time the structural and molecular composition of humic acids was determined using 13C CP/MAS and 1H-13C HETCOR NMR spectroscopy. According to data obtained in this study, up to 48% of aromatic compounds accumulate in the soils of Chernevaya taiga, which is higher than in the oligotrophic taiga and comparable with this rate of steppe Chernozems. In the course of active processes of transformation of organic matter, a significant number of aromatic fragments accumulates in the middle horizons of soil profiles. Using 13C CP/MAS spectroscopy, it was possible to identify the main structural fragments (aliphatic and aromatic) that formed in humic acids of the Chernevaya taiga. The HETCOR experiment made it possible to accurately determine the boundaries of chemical shifts of the main groups of structural fragments of humic acids. Our results demonstrate that the stabilization of organic compounds occurs in the soil of the Chernevaya taiga, which leads to the resistance of organic matter to biodegradation that is not typical for benchmark soils of boreal environments.

Digital soil morphometrics of coarse fragments and horizon delineation in soil profiles from Central Mexico

In this study, we developed a method that allows the delimitation of horizons and the quantification of coarse fragments in soil profiles from volcanic areas using digital images. The delineation of the soil profile horizons included the following phases: pre-processing of the digital image, extraction of color systems from the pre-processed image, k-means segmentation of the HSV and CIE L*a*b* color systems, delineation of the horizons, and determination of the horizon characteristics. The coarse fragments were quantified in the following three phases: superpixel analysis of the soil profile image, histogram classification of the image objects, and extraction and quantification of the coarse fragments. For horizon delineation, the HSV color system performed better for the Eutric Andic Cambisol (Loamic, Ochric), and the CIE L*a*b* system performed better for the Eutric Skeletic Mollic Silandic Andosol (Loamic). The RGB image and the S component of the HSV system demonstrated similar coarse fragment volume calculation performance for the Eutric Andic Cambisol (Loamic, Ochric), whereas the S component worked best for the Eutric Skeletic Mollic Silandic Andosol (Loamic). We created a graphic decision-making system for the delineation of soil horizons and for the quantification of coarse fragments in digital images of soil profiles.

Provenance, and environment context of pedogenic carbonates formation from MIS 3 to MIS 1 in the Teotihuacan Valley, Mexico

Pedogenic carbonates are considered important indicators of past climatic changes. Their formation is due to calcite accumulation through evaporation processes in arid or semi-arid regions. Over time, secondary carbonate accumulation results in the development of calcic and petrocalcic horizons in soil profiles. In this study, we conducted an analysis of pedogenic carbonates as records of paleoenvironmental characteristics in the Teotihuacan Valley, Basin of Mexico. Micromorphological, mineralogical, and geochemical characteristics of secondary carbonates from three paleosol profiles (Cerro Gordo 1, Cerro Gordo 2, and Maseca 1) were analyzed. Pedogenic carbonates were characterized by irregular and variable carbonate crystal sizes, inclusions of soil particles, and dark or light micrite and microsparite laminations. Micromorphology and scanning electron microscopy revealed weathered plagioclase minerals as a potential source of calcium for carbonate precipitation. The 87Sr/86Sr ratio of carbonate laminar crusts and nodules from the analyses pedons in the study area also indicated that rocks of the Transmexican Volcanic Belt were the principal source of Ca and Sr for carbonates, while contribution of a far-distance eolian input was minimal. The δ13C isotopic composition evidenced a mixture of C3 and C4 plants during the Pleistocene and a transition to a higher proportion of C4 vegetal cover during the Holocene. This agreed with an increase in modeled paleo-temperature from 10.9 °C to 13.7 °C based on 18O-temperature equations. Our results support those determined for the regional paleoenvironment during the Pleistocene, the Pleistocene-Holocene transition and Mid-Late Holocene.

Soil-site characterization on crop productivity in Alfisols of Eastern Ghats of Tamil Nadu, India

The effect of toposequence, crop cultivation, and soil conservation practices on runoff and soil loss was investigated in Alfisols of South-Eastern Ghats (SEG) of Tamil Nadu using large-scale soil mapping (1:10000 scale) information. Major landforms on peninsular granite gneiss are divided into hillside slope (P1), foothills (P2), upper pediment (P3), and lower pediment (P4). Major land uses are mango, ragi, pulses, groundnut, sorghum, little millet, and forest. A detailed soil survey was done undertaking a profile study in each landform. Soil samples were collected from different horizons of soil profiles and analyzed different soil properties. Soils were shallow (<50 cm) to deep (100–150 cm), well-drained, nongravelly to gravelly, slightly acidic to slightly alkaline (pH 5.71 to 8.29) in reaction and non-saline (EC 0.03 to 0.25 dS m−1). The soil texture varied from loamy sand to sandy clay loam with rich organic carbon in surface soils and decreasing with soil depth. Cation exchange capacity (CEC) and base saturation (BS) were ranged from 2.81 to 13.82 cmol (p+) kg−1 and 46 to 98% respectively. Soils are classified into Typic Haplustalfs (P1), Lithic Haplustalfs (P2), Kanhaplic Haplustalfs (P3), and Kanhaplic Rhodustalfs (P4) under different landforms. Results revealed that significant soil erosion was associated with slope position and crop management in SEG. Hence, adaptation of appropriate soil and water conservation measures and the land-use system could reduce soil erosion and ensure crop productivity.

Soil Quality Assessment of the Lower Niger River Plain Alluvial Soils in Bayelsa State, Nigeria, for Sustained Productivity

Floodplain soils worldwide are very useful for agricultural production and food security. But, the floodplains of Bayelsa State are under-utilized due to lack of technical information and knowledge on the nutrient status and other soil characteristics. This study therefore, assessed the soil quality of lower Niger River floodplain soils in Bayelsa State, Nigeria for sustained productivity and food security. Alluvial soils from different river plains in Bayelsa State, Southern Nigeria were characterized and fertility assessed. Pedogenic soil samples from the levee crest, middle slope, lower slope and recent alluvial soils from the channels of present active rivers were collected from identified genetic horizons of soil profiles and analyzed for physical and chemical properties using standard methods and the soils fertility status evaluated using Soil Fertility Index (SFI) and Soil Evaluation Factor (SEF). The soils were dominantly silt loam followed by silty clay loam and loam except Elemebiri 3 (ELM3) and Trofani 3 (TFN3), dominated by loamy sand and sandy loam. pH (5.31-7.00) was moderately acid to neutral and organic matter content, generally low to moderate, ranging from 0.19-3.88%. Total N values was also low while available P was low to moderate. The exchange complex was dominated by Ca²⁺ and ECEC values were low. The SFI values were higher than the SEF values in al the Soil Mapping Units (SMUs), contributed by pH, organic matter and phosphorus. Both SFI and SEF values decreased with increase in depth for all the soil mapping units except Trofani 1 (TFN1) where the bottom layers recorded higher SFI values and Elemebiri 3 (ELM3) for SEF. Though the soils nutrient concentration was generally low to moderate, both SFI and SEF evaluated the soils as fertile contributed mainly by organic matter, available P and pH. Since biomass accumulation contributed greatly to improvement of soil fertility and physical structure, soil organic matter maintenance should be given top priority in these soils for sustained productivity and food security.

Indexing the engineering properties of residual soils in the southern slopes of Mashhad, NE Iran

Residual soils are weathering products of rocks that are commonly found under unsaturated conditions. The properties of residual soils are a function of the degree of weathering. A series of index properties, engineering properties and geophysics survey examinations were performed on residual soils from two major geological formations in Iran. In the present research, the index properties of residual soils in the south of Mashhad city in Iran are investigated. Natural and artificial trenches were analyzed for evaluating the weathering profiles and collecting soil samples. Disturbed and undisturbed samples were obtained from each of the soil profile horizons resulting from weathering of different parent rocks. Subsequently, physical properties and mechanical properties of the soil samples were determined in accordance with ASTM standards. Also, the mineralogical composition, chemistry, and texture of the soil were evaluated in 51 profiles. The field observations showed the difference in the weathering profile of residual soils deposited on various rocks (igneous, sedimentary, and metamorphic). These profiles mainly consisted of two horizons including residual soil on top and saprolite at the bottom. The results of laboratory tests and geotechnical data showed that the properties of residual soil samples change by depth. Moreover, depending on the type of origin rock, the properties are different in various types of residual soils. In most of the samples, the moisture content of soil horizons was also increased by depth. Based on the unified soil classification (USCS), the soils of the upper horizons appeared to be classified as ML (Lean silt) and CL (Lean clay) while the soils of the lower horizons (saprolite zone) fall in SC (clayey sand), SM (silty sand), and SW (well-graded sand) classes. Moreover, the results demonstrated that the particle size of the soil was increased by depth. Comparison of results of the geotechnical tests showed that properties of residual soils are changed by variations of depth, weathering level, and type of parent rock. Considering the concentration of the number of lines and the concentration of the points of intersection, the length and dimension fractal of lineaments in the southeastern part of the study area, it is evident that this zone possesses weathering severity and soil thickness. Fieldwork data from this zone have also verified the severity of weathering conditions. The analysis of lineaments trends in different parts of the study area indicated that the lineaments with the NW-SE trend have a strong effect on weathering development. The weathering depth depends on the orientation of bedding joints with respect to the slope in the study area. Slope inclination and soil thickness are controlled by weathering and erosion processes.