The effect of survey density on the results of geopedological approach in soil mapping: A case study in the Borujen region, Central Iran

Landscapes are considered to be complex systems that are hierarchically structured and spatially scale-dependent. Geopedology allows a systematic approach in geomorphic analysis for soil mapping that extrapolates the results obtained at sample areas up to similar units. This paper examines the influence of sampling intervals on the accuracy of geopedological results in the Borujen region, Central Iran. After a primary interpretation of the study area on air photos (1:20 000), a geomorphic unit that encompassed the maximum surface of the sample area (and also the study area) was selected and was surveyed at three different scales: 500, 250 and 125 m intervals. The credibility of generalization of the results of the geopedological approach for the studied unit was tested by comparison with three profiles in a similar unit outside the sample area, named the validation area. Although the type of mapping unit in the sample area and the validation area was the same (complex) at the three different scales, the dominant soil in the validation area was different in comparison with the sample area at 125 and 250 m intervals. The results indicate that the geopedological approach to soil mapping is better carried out in reconnaissance or exploratory surveys. Comparison of soil types between the unit in the sample area and the validation area at three scales indicated that by increasing the taxonomic accuracy, the hidden aspects of the soils may be more identifiable. Therefore, although the geopedological approach tries to distinguish more homogeneous soil mapping units, it still is not able to fully define and represent the variability and apparent chaotic nature of the soils. We recommend further investigations on different techniques of stratifying the landscape in order to better analyze and understand the soil forming processes and soil variability and to improve sampling and mapping approaches.     

Estimation of comparative water transmission in two pairs of adjacent virgin and cultivated pedons in wisconsin

Hydraulic properties and soil morphology of principal soil horizons of paired virgin and cultivated pedons, each pair with identical soil classifications, were studied at two sites. The capacity of the two cultivated soils to transmit water under saturated conditions was reduced as compared with the virgin soil, whereas this capacity generally increased in unsaturated soil at corresponding moisture tensions. Compacted layers below the Ap had a drying effect on the overlying Ap at a wide range of flow rates, whereas a wetting effect resulted in Al horizons of the virgin pedons at similar flow rates, representing unsaturated flow. Extrapolation for interpretive purposes of hydraulic conductivity data measured in a representative pedon of a mapping unit to pedons in identical mapping units elsewhere has to proceed with care, as differences may be substantial.A rather wide range of physical properties is acceptable in a pedogenic soil unit when broad qualitative soil map interpretations are made. However, specific interpretations require more detailed data, as is illustrated with examples relating to soil suitability for on-site liquid waste disposal.     

Properties and classification of volcanic ash soils around Lake Kuwanuma on the eastern footslope of Mt. Funagata in Miyagi prefecture,northeastern Japan

One of the developments in recognition of soil properties and different soils is from morphological to analytical. With an incorporation of analytical data, transitional soils can be systematically named using a key-out order as well as typical soils. Our major objective was to evaluate soils with multiple forming processes such as andosolization, podzolization, etc., using soil analytical data, selecting a small area having different soil names based on soil morphological properties. According to a local soil map, Ando soils, Brown forest soils (Dark) and Wet and Dry podzols soils are adjacently distributed around Lake Kuwanuma on the eastern footslope of Mt. Funagata in Miyagi prefecture, northeastern Japan. We studied the morphological, chemical and mineralogical properties of these soils and classified them according to the recent Comprehensive Soil Classification System of Japan (CSCSJ), United States Department of Agriculture Soil Taxonomy (ST) and the World Reference Base for Soil Resources (WRB). The elevation of Lake Kuwanuma is 780 m above sea level and a plateau is located next to a steep slope on the western side of the lake. Three pedons were sampled from the northern side of Lake Kuwanuma, and 3 additional pedons were sampled from the plateau. The average difference in elevation between these two groups of pedons was 229 m. All 6 pedons were classified as Andosols in CSCSJ, Udands in ST and Andosols in WRB. Thus, andosolization was the dominant soil-forming process throughout the study area. The major modification of Andisols in the study area was caused by forest vegetation. Of the 6 pedons sampled, three were classified as Fulvudands in ST and had the Fulvic prefix qualifier in WRB. Furthermore, weak podzolization was suggested on the basis of soil profile observations. One pedon on the plateau had a Bs horizon, which satisfied the spodic horizon requirements of ST. Thus, weak podzolization, especially on the plateau, was another accessory characteristic in the present study area. The nearby distribution of Podzols soils and Ando soils in the local soil map may be explained by differences in temperature, leaching intensity and other factors. A podzolic subgroup of Andosols/Udands was desired to express the properties of pedons on the plateau in the lower categories of the recent soil classification systems.     

Erodibility of a soil drainage sequence in the loess uplands of Mississippi

The susceptibility of loess soils in the lower Mississippi to runoff and erosion losses varies as a function of landscape position and mapping units. This study was conducted to determine the effects of soil drainage on physical and chemical properties that influence erodibility through their control of aggregate stability. Soil samples were collected from the A- and B-horizons of the five representative pedons in the Memphis catena whose drainage class varied from well-drained to poorly-drained. The fine earth fraction (< 2 mm) of each soil was characterized for a range of basic soil physical and chemical properties. Additional sub-samples (< 8 mm) were placed in a rainfall simulator pan (0.6 m × 0.6 m test area) and subjected to simulated rainfall at an intensity of 64 mm h^− 1. Soil erodibility was assessed by the use of an aggregation index (AI) computed from water dispersible clay (WDC) relative to total clay contents. The data show that as soil drainage classes became wetter, the percentage of sediment < 53 µm increased with a decrease in soil AI resulting from a loss of Fe, Al, and Si oxide cementing agents. These results suggest that cementing agents responsible for soil aggregate stabilization are mobilized under conditions of relatively low redox potentials which increase soil erodibility.     

Sediment source identification in a semiarid watershed at soil mapping unit scales

Selective erosion and transport of silt and clay particles from watershed soil surfaces leads to enrichment of suspended sediments by size fractions that are the most effective scavengers of chemical pollutants. Thus, preferential transport of highly reactive size fractions represents a major problem relative to sediment/chemical transport in watersheds, and offsite water quality. The objective of this research was to develop an approach to identify sediment sources at a soil mapping unit scale for the purpose of designing site specific best management practices which affect greater reductions in runoff and erosion losses. Surface soil samples were collected along transects from each of the major 25 mapping units in six subwatersheds of the Walnut Gulch Experimental Watershed. Suspended sediments were collected from supercritical flumes at the mouth of each subwatershed. Laboratory analyses included basic soil/sediment physical and chemical properties, radioisotopes, and stable carbon isotopes, all by standard methods. Aggregation index (AI) values [100 · (1 − water dispersible clay / total clay)] were taken as an indicator of relative soil erodibility. Potential sediment yield index (PSYI) values were calculated by multiplying percent relative area for individual soil mapping units times (100 − AI). Particle size results indicated that suspended sediments were enriched in clay, relative to the watershed soils, by an average of 1.28. Clay enrichment ratios (ER) were significantly (P ≤ 0.01) and positively correlated with AI, an indication that these two parameters can be equated with erodibility and sediment yield. The PSYI values for the six subwatersheds ranged from 68.0 to 81.7. The stable carbon isotope data for the suspended sediments gave a C3 (shrubs) to C4 plant (grasses) ratio that ranged from 1.06 to 2.25, indicating greater erosion from the more highly erodible, shrub-dominated subwatersheds which also coincided with the highest PSYI values. Correlation coefficients determined individually for PSYI versus clay ER, C3/C4 plant ratios, and multivariate mixing model results were: 0.962 (P ≤ 0.01), 0.905 (P ≤ 0.01), and 0.816 (P ≤ 0.05), respectively. These statistically significant relationships support the accuracy of a potential sediment yield index approach for identifying suspended sediment sources at soil mapping unit scales.     

Genesis,Classification, and Management Requirements of Soils Formed in Windblown Material in the Guinea Savanna Area of Nigeria

Abstract

Eight pedons representing the major soils found within the Guinea Savanna region of northern Nigeria were studied with respect to their important morphological, physical, chemical, and other characteristics, and their suitability for sustainable agricultural production was evaluated. The most important soil characteristics observed for separating the soils into mapping units include presence or absence of petroferric contact, effective soil depth especially to hardpan layer, gravel and subsoil clay content. Dominant pedogenic processes, which influence the rate of soil development in the area, include plinthization, clay eluviation‐illuviation, iron (Fe)‐oxyhydroxide release (lateral movement and enrichment), eolian deposition, and leaching. According to the USDA system of classification, the soils (MU‐EDA) in the summit to upper slope are classified as Lithic Haplustepts, those (MU‐EDB) at the midslope are Typic Haplustepts, the MU‐EDC (lower slope soils) as Dystric Haplustepts, and the MU‐EDD (soils at the valley floors) as Oxyaquic Haplustepts. In the FAO/UNESCO system, a typical toposequence in the area consists of Dystric Cambisols (CMd) petroferric phase (MU–EDA and EDB), Dystric Cambisols (MU‐EDC), and Gleyic Cambisols (CMg) for the MU‐EDD mapping unit. The land capability and fertility capability classes of the soils were also established. The MU‐EDA, EDB, EDC, and EDD soil units were grouped into land capability class IVes, IIIes, IIs, and Vw and fertility capability class L”Rdk (6–8%), Ldehk (3–5%), Ldh, and Lgehk, respectively.     

A REAPPRAISAL OF SOIL MAPPING IN AN AREA OF SOUTHERN SCOTLAND. PART I THE RELIABILITY OF FOUR SOIL MAPPING UNITS AND THE MORPHOLOCICAL VARIABILITY OF THEIR DOMINANT TAXA

A two stage random sample survey was made to study the composition of four common soil mapping units already mapped in the Central Lowlands of Scotland. The four mapping units were sampled at densities proportional to their mapped area. In terms of their A horizon textures, the mapping units had percentage reliabilities of 84, 96, 93 and 97 and drainage class reliability scores of 70, 80, 72 and 70. On the basis of taxonomic units within the mapping units, percentage reliabilities ranged from 43–66 but no minor constituent soil exceeded 16 per cent in any of the units studied. Although complex according to currently accepted guidelines, such mapping units should be named according to the dominant taxonomic unit. Errors of identification due to inadequate definitions of taxonomic units have contributed to some of the low levels of reliability of taxonomic units within mapping units and soil taxa should be defined more precisely in Scotland. Means and variances of the taxonomic units, upon which the above named mapping units are based, indicate that the four taxonomic units (and hence also mapping units) under study are not equally variable in the area of investigation.     

Bodengesellschaften von geomorphen Einheiten unter Berücksichtigung des Gefügestils im Stormarner Jungmoränengebiet (Brandenburger Stadium) in Nordwestdeutschland

Soil associations of different geomorpholocical units of a younger‐moraine area in Schleswig‐Holstein (NW Germany) considering matter fluxes As result of a detailed mapping work, the soil association of different geomorpholocical units of a younger‐moraine area (“Stormarner Jungmoränengebiet”) in Schleswig‐Holstein (NW Germany) is analyzed taking into account soil development in vertical and horizontal direction. The consequences for classification of soil types and soil associations are discussed. We distinguished between different patterns of matter fluxes (unilateral coupling, mutual coupling, no coupling of soils). By morphometric analysis of the relief, five geomorpholocical units were distinguished: till‐plains with dead‐ice kettles (I), tongue‐like basin with moraine slopes (II), terminal‐push moraine (III), moraine slopes with gutter valley (IV), und terminal‐push moraine valley with steep slopes (V). In the examination area with its intense agricultural land use, the regular sequence of erosion and accumulation of soils is a typical consequence of unilateral water‐flow direction. Thus, the truncated Stagnic Luvisols/Anthrosols association is dominating. We suggest to classify the truncated Luvisol with a Bt horizon exposed directly to the surface at the level of soil subtypes in the German soil‐classification system. Additionally soils in depressions such as Calcic Gleysols, Histosols and “subhydric soils”, which are influenced by solute and solid‐matter input, are frequently encountered. Within the till‐plains, a compensation of the relief by (historical) soil erosion took place, recognizable by the high percentage of Anthrosols (20 %). Therefore, no recent lateral transport of solid material can be found. The steep moraine slopes partly already show Regosols, thus indicating a high erosion potential (erosion rate for geomorphical unit IV: 13 t ha^–1 y^–1). In the depressions intersected with small streams, the afflux caused by mills led to an additional peat development.     

An approach to landscape analysis with emphasis on soils

Principal components of landscape are defined. The soils portion is termed the landscape pedoplasma, distinct geographic subdivisions of which are called soilscapes. Some concepts of morphology and fabric of soil pedons are adapted for application to entire landscapes. Terminology and numerical indices are suggested for characterizing polypedons and multi-polypedonic units, including soilscapes, as to size, shape and arrangement of the geographic units, population density of polypedons per unit area, and pedologic diversity in terms of local relief, slope, and soil drainage conditions, and in taxonomic terms. Some results of application of specific methods of soilscape analysis to published soil and topographic maps are reported. Geographic trends in soilscape variability are found on a broad regional scale as well as in local landscapes. This approach to landscape analysis is deemed useful in systematizing the great volume of cartographic data of modern published soil surveys and may help in the location of sites for detailed pedogeomorphic and land use field studies.     

Use of Soil Survey Mapping and Sampling for Determining Geochemistry of Regions

Abstract

The U.S. National Cooperative Soil Survey (NCSS) information about geographic distribution of soils is based on landforms and soil‐forming factors. A recent effort was initiated to determine the geochemistry of soils that are sampled as part of the routine NCSS work. The objectives of this article are to describe the mapping and site selection procedures, utility of these procedures in the geochemical analysis of soils, and the work and future direction of the Soil Geochemistry Program that was developed for this effort. This program was created within the U.S. Department of Agriculture, Natural Resources Conservation Service (USDA‐NRCS), for the purposes of instituting and monitoring the quality of laboratory geochemical methods and data, investigating the distribution of natural elemental concentrations in soils, and providing leadership in the application of geochemical data for NRCS. The soil survey has typically used the representative pedon concept as a basis for site selection, determined from the evaluation of soil morphology and component landforms within mapping units. The intent of this concept is to extend limited point data to geographic coverage. A geospatial database was compiled, containing major and trace element data for selected NCSS pedons. These data are provided with depth for major diagnostic horizons. Although initial geochemistry efforts have concentrated on benchmark soils to facilitate evaluation of source factors and broaden the utility of the data, this dataset includes both anthropogenic and nonanthropogenic soils. Future efforts require the investigation of geochemical variability of mapping units and the pedogenic redistribution of trace elements within soil landscapes.     

Soil genesis along a chronosequence on marine terraces in eastern Taiwan

Soil chronosequences developed on elevated marine terraces are ideal for studying changes in soil-forming processes with time. The coastal range of eastern Taiwan is a product of active arc–continent collision. Vertisols, Mollisols and Entisols are generally found on the different levels of marine terraces herein, but no detailed investigations of soil chronosequence have been conducted by integrating field morphology, physio-chemical characterization, micromorphology and mass-balance interpretations. Five soil pedons were selected on the three marine terraces including Tt-1 and Tt-2 pedons (Typic Hapluderts) on the first higher level with the oldest soil age (9–10 ka), Tt-3 (Vertic Hapludolls) and Tt-4 pedons (Typic Hapludolls) on the second intermediate level (5–6 ka), and Tt-5 pedon (Typic Udipsamments) on the third lower level with the youngest soil age (≤ 3.5 ka). The morphological characteristics showed that strongly developed angular blocky structures, pressure faces and slickensides are more common in higher terrace soils than in lower terrace soils. In this study, depth to C horizon, solum thickness, and thickness of the clay-enriched zone increase with relative terrace age. Although only one to two profiles per terrace were characterized, the following soil analytical characterizations increase with time: the degree of sand grains weathering, pH (H₂O), organic carbon, CEC, contents of Fe_d, Fe_o and Mn_d. Based on X-ray diffraction analysis of the clay-size fraction, soils on all terraces have a mixed mineralogy. Mica, smectite, and kaolinite have slightly increased with increasing terrace age. Furthermore, the dominant processes identified with mass-balance analysis include loss of bases (Ca and Mg), iron, and clay with time. The soil properties, including analytical and mineralogical characterizations, which do not have notable changes with time are primarily due to relatively young soil age (< 10 ka).     

Accounting for variability within map units when linking a pesticide fate model to soil survey

The aim of this study was to estimate the probability of exceedance (POE) of the USEPA health advisory level for particular pesticides in groundwater beneath citrus groves in southwestern Florida. The approach included bootstrapping to assess the uncertainty of the model output due to the variability of soil input data; a weather generator to provide daily rainfall amounts; daily evapotranspiration by the Blaney-Criddle (FAO) method; and a program written to compute POE values. Bootstrapping enabled us to assess the uncertainty of soils inputs by generating pseudo-profiles of soils from pedon characterization data. These pseudo-profiles were used in Monte Carlo simulations that captured the variance of selected soil parameters within soil taxonomic units. Single-name map units (i.e., consociations) were represented by no fewer than three actual pedon characterization data sets for the named soil and/or closely similar soil(s). In the case of a multiple-name map unit (i.e., soil association or soil complex), no fewer than three actual pedons of named and/or similar soils were used to generate pseudo-profiles for each of the named soils in the map unit. Inputs were linked to the pesticide fate model Chemical Movement in Layered Soil, CMLS (Nofziger and Hornsby) to produce cumulative probability curves showing the fraction of applied pesticide leaching below the 1-m depth. This curve was then used to determine the POE for various soil delineations in the groves within the watershed. Multiple POEs were generated for multiple-named map units; the rule was to select the higher(est) POE value as an estimator of environmental risk for each such map unit. Thematic maps are then created using soil and land use coverages and POE's for various pesticides evaluated.

Our approach suggests that the use of cumulative probability functions and probabilities of exceedance of health standards (USEPA HAL) provides needed integration of the uncertainties associated with input parameters, the significance of which can be easily grasped by decision officials. The use of environmental fate models to predict pesticide behavior in soils throughout a landscape has brought about intense scrutiny of soil attribute data and map unit delineations far beyond that envisioned for the present progressive soil survey. The authors also recognize that uncertainties in model formulation, pesticide fate parameters and toxicity further complicate assessments of this nature.     

Genesis and micromorphology of loess-derived soils from central Kansas

The genesis and micromorphology of three Harney soils from different precipitation regions (from 540 mm to 715 mm) (fine, smectitic, mesic Typic Argiustolls) in the Smoky Hills of central Kansas were investigated. The objectives were to (1) examine the morphological, chemical, physical and mineralogical characteristics of Harney soils formed in loess; (2) determine the clay mineral distribution with depth and the origin of the clay minerals present; and (3) investigate the relationship between the clay mineralogy and other soil properties such as soil plasmic fabric, COLE values and fine clay/total clay ratios. Mineralogical and micromorphological techniques were used to evaluate the characteristics of the loess-derived soils. The first pedon was formed in 88 cm of Bignell loess over Peoria loess and the other two pedons were formed from Peoria loess. The chemical properties were similar for the pedons studied. Differences were observed in physical properties, especially in particle size distribution, oven-dry bulk density and coefficient of linear extensibility values. Although the soils were mapped in the same soil series, the geomorphic positions of the pedons and the nature of the parent material affected the characteristics of the soils. Smectite was the predominant clay mineral, especially in the fine clay fraction, regardless of the location in the precipitation gradient. The dominance of smectite increased in the C-horizons. This implies a detrital source of smectite in the B-horizons formed in both Bignell and Peoria loess units. The presence of randomly interstratified mica-smectite and the micromorphological observations of weathering biotite indicate that weathering also plays an important role in the mineralogy of Harney soils. The high content of clay mica in the surface horizons was caused by dust fall in the study area. Thick and continuous argillans were observed when FC/TC and COLE values were low and crystalline smectite was present. In the lower part of the soil profiles, the plasmic fabric was mostly ma-skelsepic (granostriated b-fabric) and smectite was more crystalline as indicated by sharper X-ray diffraction peaks.     

Estimating soil labile organic carbon and potential turnover rates using a sequential fumigation-incubation procedure

Labile carbon is the fraction of soil organic carbon with most rapid turnover times and its oxidation drives the flux of CO₂ between soils and atmosphere. Available chemical and physical fractionation methods for estimating soil labile organic carbon are indirect and lack a clear biological definition. We have modified the well-established Jenkinson and Powlson's fumigation-incubation technique to estimate soil labile organic carbon using a sequential fumigation-incubation procedure. We define soil labile organic carbon as the fraction of soil organic carbon degradable during microbial growth, assuming that labile organic carbon oxidizes according to a simple negative exponential model. We used five mineral soils and a forest Oa horizon to represent a wide range of organic carbon levels. Soil labile organic carbon varied from 0.8 mg/g in an Entisol to 17.3 mg/g in the Oa materials. Potential turnover time ranged from 24 days in an Alfisol to 102 days in an Ultisol. Soil labile organic carbon contributed from 4.8% in the Alfisol to 11.1% in the Ultisol to the total organic carbon. This new procedure is a relatively easy and simple method for obtaining indices for both the pool sizes and potential turnover rates of soil labile organic carbon and provides a new approach to studying soil organic carbon.     

Saturated hydraulic conductivity of soils in the Southern Piedmont of Georgia,USA: Field evaluation and relation to horizon and landscape properties

Saturated hydraulic conductivity (K_s) is one of the soil properties used most often to predict soil behavior and suitability for a variety of uses. Because of the difficulty in K_s measurement and its variability with depth and across the landscape, K_s is commonly predicted from other more easily evaluated properties including texture, clay mineralogy, bulk density, pedogenic structure and cementation. Of these, texture and pedogenic structure are most commonly used to estimate K_s, but the reliability of these estimates has not been evaluated for common soils in the Southern Piedmont of Georgia. Thus, the objectives of this study were to evaluate K_s for major horizons in soils and landscapes in the Georgia Piedmont and to relate K_s to morphological properties of these horizons. Ten sites across the region were selected, and 21 pedons arranged in three transects were described from auger holes and pits. For each pedon, K_s was measured in upper Bt horizons, at 140 cm below the surface (Bt, BC, or C horizon), and at a depth intermediate between the shallow and deep measurements (Bt, BC, or C horizon) with a constant head permeameter. The K_s of individual horizons ranged from 1 × 10^− 8 to 2 × 10^− 5 m s^− 1. At six of 10 sites evaluated, clayey upper Bt horizons had higher K_s than deeper horizons with less clay. This difference was attributed to weaker structure in the deeper BC horizons. Structural differences did not explain all variation in K_s with depth, however. Other soil and landscape properties including parent material composition, colluvium on lower slope positions, C horizon cementation, and depth of soil development also affected K_s of horizons in these soils and should be used to better estimate K_s.     

Description of Soil Evolution in Southern Mashhad City Using Jenny's and Johnson and Watson-Stegner's Conceptual Models

Conceptual models are suitable for describing internal relationships of complex systems, including soil. We used conceptual models, the Jenny's and Johnson and Watson-Stegner's models to understand the formation and evolution of soil. We studied 20 pedons in granitic hilly lands, loessial piedmont, and piedmont plain in southern Mashhad, northeast Iran. These soils were characterized by high levels of gypsum, especially in the granitic saprolites, which suggested the importance of the wind in shaping the soil structure. Jenny's model is a developmental and equilibrium model, which only describes the state of the soil formation factors and considers that each bioclimatic zone has a specific climax soil. It focuses on the genesis of the surface soil and is not suitable for buried soils and paleosols. Johnson and Watson-Stegner's model describes soil as a product of progressive and regressive processes due to horizonation or haploidization. Progressive processes during the last interglacial cycle created a well-developed paleosol with an argillic horizon in all landforms, except the piedmont plain. Developmental soil up-building by aeolian addition led to gypsum enrichment of the granitic saprolite. Erosion decreased soil thickness and exposed the argillic horizon. The Last Glacial Maximum led to greater deposition of loess, covering the paleosol. Humidity was higher during the early Holocene than today, leading to the development of a Bk horizon. This horizon was preserved in the stable surfaces of granitic hilly land and in the loessial piedmont, but buried on the piedmont plain via the deposition of alluvial sediments. Jenny's model could be used for current soil formation factors, whereas Johnson and Watson-Stegner's model required morphological characteristics of pedons for interpretation.     

Soil genesis along a chronosequence on marine terraces in eastern Taiwan

Soil chronosequences developed on elevated marine terraces are ideal for studying changes in soil-forming processes with time. The coastal range of eastern Taiwan is a product of active arc–continent collision. Vertisols, Mollisols and Entisols are generally found on the different levels of marine terraces herein, but no detailed investigations of soil chronosequence have been conducted by integrating field morphology, physio-chemical characterization, micromorphology and mass-balance interpretations. Five soil pedons were selected on the three marine terraces including Tt-1 and Tt-2 pedons (Typic Hapluderts) on the first higher level with the oldest soil age (9–10 ka), Tt-3 (Vertic Hapludolls) and Tt-4 pedons (Typic Hapludolls) on the second intermediate level (5–6 ka), and Tt-5 pedon (Typic Udipsamments) on the third lower level with the youngest soil age (≤ 3.5 ka). The morphological characteristics showed that strongly developed angular blocky structures, pressure faces and slickensides are more common in higher terrace soils than in lower terrace soils. In this study, depth to C horizon, solum thickness, and thickness of the clay-enriched zone increase with relative terrace age. Although only one to two profiles per terrace were characterized, the following soil analytical characterizations increase with time: the degree of sand grains weathering, pH (H₂O), organic carbon, CEC, contents of Fe_d, Fe_o and Mn_d. Based on X-ray diffraction analysis of the clay-size fraction, soils on all terraces have a mixed mineralogy. Mica, smectite, and kaolinite have slightly increased with increasing terrace age. Furthermore, the dominant processes identified with mass-balance analysis include loss of bases (Ca and Mg), iron, and clay with time. The soil properties, including analytical and mineralogical characterizations, which do not have notable changes with time are primarily due to relatively young soil age (< 10 ka).     

A strand plain soil development sequence in Northern Michigan,USA

A practical problem limiting the theoretical application of a soil chronosequence study lies in the difficulty of identifying an appropriate geomorphic age sequence with more than a few surfaces. A sequence of approximately 75 strand plain beach ridges located along the northern shore of Lake Michigan, USA, overcomes this problem, and was used to explore rates of soil development in the initial stages of podzolization. Well drained pedons were sampled on 24 of the ridges, with an age range of 10 to 5200 years. Chronofunctions were developed using statistical regression techniques. For most forms of extractable Fe and Al, both linear and log–linear functions adequately describe the changes in property with surface age. Dithionite–citrate extractable Fe content, however, shows little correlation with surface age. High r² values (>0.7) for chronofunctions representing most extractable sesquioxide forms suggest that B horizon sesquioxide content increases with surface age, as expected for soils undergoing podzolization. Visual inspection of chronofunction data suggests that scatter increases on surfaces older than 3000 years, possibly because soil spatial variability increases with surface age.Theory suggests that the log–linear form of chronofunctions may be preferable to the linear form for these pedons. In general, equation slopes are steeper for chronofunctions representing only the initial 1650 years of soil development than for those representing the entire 5200-year sequence, suggesting that initially rapid pedogenesis slows over time. Most chronofunctions for pH and weighted profile organic C are not statistically significant, possibly because the temporal resolution of the chronosequence is too coarse to detect valid trends for properties that rapidly approach a steady state.