Redoximorphic Features Research Articles

Loess Toposequences in the Lower Mississippi River Valley: I. Fragipan Morphology and Identification

AbstractDespite large acreages of agronomically important fragipan soils in the Lower Mississippi River Valley, relatively little information is available regarding their morphology, particularly in regard to fragipan definition and formation. This study was designed to evaluate morphological differences between nonfragipan (memphis [fine‐silty, mixed, thermic Typic Hapludalf]) and fragipan (Loring [fine‐silty, mixed, thermic Typic Fragiudalf] and Grenada [fine silty, mixed, thermic Glossic Fragiudalf]) soils occurring on the same landscape. A secondary objective was to determine if morphological characteristics of the Loring and Grenada pedons are consistent with taxonomic criteria. Five representative sites were selected based on published soil survey maps and landscape relations. Morphological characteristics associated with fragipans are present in all the Loring and Grenada pedons. The most obvious and consistent indicators of a fragipan are vertical gray seams and associated redoximorphic features. Because brittleness is subjective and a function of moisture content, it is not always a reliable indicator of fragipan occurrence. Likewise, root distribution is not particularly useful since deep‐rooted vegetation did not occur on these soils. Several Memphis pedons exhibit protofragipan development, but based primarily on the organization of gray seams, these should not be considered fragipan soils. Overall, the published criteria are adequate, with the notable exception of slaking, and the characteristics of the Loring and Grenada pedons are consistent with them. Greater relative root penetration and less brittleness also assist in differentiating between the nonfragipan horizons within the Memphis pedons and fragipan horizons of the other members of the toposequence, but these evaluations have to be made in detail from deep pits, particularly in borderline situations.

Redoximorphic Paleosols in Alluvial and Lacustrine Deposits, 1.8 Ga Lochness Formation, Mount Isa, Australia: Pedogenic Processes and Implications for Paleoclimate

ABSTRACT Paleosols in the Lochness Formation (1.8 Ga, Australia) include both rare, non-red and abundant, strongly reddened varieties that formed at subaerial exposure surfaces in both ephemeral-river and lacustrine settings. Physical processes dominated non-red paleosols, which were characterized by repeated episodes of desiccation, shrinking, and cracking alternating with wetting and introduction of sand, silt, clay, and iron oxyhydroxides into planar voids. Redoximorphic (oxidation-reduction) processes were especially intense for the red paleosols; redox depletions of Fe and Mn (hypoalbans) occur immediately adjacent to desiccation-related macropores and peds, whereas redox concentrations of Fe and Mn (quasi-coatings) occur within paleosol matrix adjacent to redox depletions. Illuviated cla and Fe-oxide coatings and hypocoatings are also common in planar macropores and on ped faces. Redoximorphic features indicate periodic water infiltration and saturation, accompanied by development of reducing conditions along planar macropores and ped surfaces in Lochness Formation paleosols. Variations in soil saturation were caused by seasonal fluctuations of lake level in lacustrine deposits, and by formation of perched saturation zones within floodplain deposits, respectively. Occurrences of red, hematitic paleosols in the Lochness Formation are compatible with previous interpretations of a weakly oxygenated 1.8 Ga paleoatmosphere. Redoximorphic features in the paleosols suggest a warm to cool temperate paleoclimate (mean annual soil temperature 5-20°C) characterized by seasonal saturation, by analogy with Quaternary redoximorphic soils. A minimal concentration of organic C (at least 1 wt %), possibly of microbial or bacterial origin, must have been present in these Proterozoic soils to allow for Fe reduction.

Formation of soils with plinthite on a toposequence in Maranha˜o State, Brazil

Soils with plinthite and ironstone concretions are extensive in Maranha˜o State, northeastern Brazil. They formed from the Fe-rich Itapecuru sandstone in a tropical subhumid climate with distinct wet and dry seasons. Most plinthic soils in Brazil have properties associated with low-activity clays, but these soils were reported to have properties associated with high-activity clays. The main objectives of this study were to characterize the chemical and mineralogical properties of the soils and to deduce the processes of their formation in relation to hillslope position. six soils were sampled, two each on summit, shoulder, and footslope positions. They were analyzed by standard characterization methods and by X-ray diffraction and infrared spectroscopy. The parent sandstone bedrock contained mainly quartz, feldspars, muscovite, biotite, and resistant minerals in the sand fraction, and smectite, mica and kaolinite in the clay fraction. The main Fe-oxide mineral was hematite. Most soil horizons had lower Fe concentrations than the sandstone parent material. Kaolinite, mica and quartz occurred in the coarse clay fraction of all pedons. Soils on the summit positions (Ustic Dystropept and Typic Ustorthent) lacked redoximorphic features, lacked plinthite, had the highest cation exchange capacity, and showed the weakest development. They were rich in smectite, probably inherited from the parent material, and goethite. soils on shoulder positions (Inceptic Plinthustult and Plinthic Dystropept) had the largest concentration of total Fe, mostly as goethite. Those on footslopes (Typic Plinthaquult and Plinthic Paleaquult) exhibited the most redoximorphic features and had horizons in which the Fe was strongly concentrated in ironstone and plinthite, mostly as lepidocrocite and goethite. The crystallinity of these minerals increased from non-plinthic material to plinthite to ironstone concretions. They formed as the hematite in the sandstone weathered. These soils are less weathered than most plinthic soils of Brazil. Diagnostic criteria for some subgroups of the Plinthustult and Dystropept great groups of soil Taxonomy and some new classes for the Brazilian soil Classification system were proposed.

Saturated Zones and Soil Morphology in a Mollisol Catena of Central Iowa

AbstractThe zone of saturation plays significant roles in decisions regarding soil classification systems and land use both present and potential. This study was conducted to determine the status of water tables, morphological features, and groundwater hydrology and to evaluate the zone of saturation on selected soils (Aquolls and Hapludolls) of a Mollisol catena. Water table depths and the amount of precipitation were measured for a 10‐year period on five soils formed in glacial till or till‐derived sediments in central Iowa. Results show that the depth of the water table, duration of saturation, morphological features, and recharge and discharge to groundwater varied with geomorphic position in the Mollisol catena. In general, soils on summit and shoulder positions (Hapludolls) are not saturated and have high chromas without redoximorphic features in the B horizon, have deeper water tables, and have maximum fluctuation of water table levels. The soils on toeslopes and depressions (Aquolls) have the shallowest water tables, have the longest time of saturation, and have B horizons with gray matrices, bright mottles, and Fe‐Mn concretions. Nicollet soils (fine‐loamy, mixed, mesic Aquic Hapludoll) on backslope positions have intermediate characteristics. Redoximorphic features present in these soils are correlated with the fluctuating depth of the present‐day water table. The extent of recharge and discharge and artificial the drainage are contributing factors to the water table level. Data for water table level and calcite/dolomite ratio indicate that ephemeral recharge and discharge of groundwater occur in the soils on lower landscape positions. Recharge is the dominant process in the soils of higher landscape. This study was designed to contribute to the understanding of drainage class‐water table‐morphological features of soils in this region. The apparent drainage conditions and the redoximorphic features contribute to the testing and clarification of soil classification and soil taxonomy.

Temporal and Spatial Patterns of Episaturation in a Fragixeralf Landscape

AbstractRelatively low saturated hydraulic conductivities associated with fragipans result in seasonal perched zones of saturation (episaturation). This study was conducted to monitor seasonal episaturation in a Fragixeralf landscape of northern Idaho. Perched zones of saturation above a fragipan in a 1.4‐ha field were monitored during a 2‐yr period using 64 piezometers arranged on a 15‐m grid spacing. During the winter of 1991–1992, relatively mild temperatures and high rainfall resulted in development of perched zones of saturation lasting from early December into May. Average quantities of perched water present within the landscape during the winter and early spring months ranged from 8.4 to 15.4 cm, representing between 34 and 43% of the seasonal precipitation that had been received at the study site. During the 1992–1993 winter, colder temperatures and relatively large quantities of snow delayed development of episaturation. When the snow pack began to melt in early March, an average of >20 cm of water was present in the saturated zone above the fragipan. This water represented 58% of the seasonal precipitation that had been received. Soil morphological characteristics and elevation were correlated with quantities of perched water present on sampling dates when potential evapotranspiration was low. For all sites, quantity of perched water was most strongly correlated with the thickness of the zone above the fragipan exhibiting redoximorphic features; depth to the fragipan was less strongly correlated. Elevation was generally a poor indicator of episaturation. Results of this study indicate that significant periods of episaturation occur in fragipan‐dominated landscapes under xeric moisture regimes.

Water table depths and color patterns in Spodosols of two hydrosequences in Northern Michigan, USA

Relationships between soil color patterns and depth and duration of water tables were studied using piezometers in two hydrosequences of Spodosols. Most mottles in E and B horizons appeared to reflect differences in eluviation and illuviation, respectively. Color indices developed for Udalfs, Aqualfs, Aquolls and Aquepts were not helpful in relating soil color patterns in these Spodosols to water saturation. Redoximorphic features were identified with difficulty in most saturated horizons. Low Fe content in spodic horizons was a good indicator of water saturation. Landscape position was also useful in ranking length of saturation in the soils of each hydrosequence. Water saturation appeared to hinder translocation of Al and Fe in these soils.

Strongly Contrasting Redoximorphic Patterns in Virginia Valley and Ridge Paleosols

AbstractSoils with bisequel morphology and classified as Typic or Plinthic Paleudults are common in the Virginia Valley and Ridge Province. Horizons in the older materials have redoximorphic features that are strongly contrasting with respect to color and distinctness of boundary. Research documenting these horizons is nonexistent. We examined the physical and chemical properties of these horizons to describe the strongly contrasting redoximorphic patterns (SCRP) and investigate their genesis. Two types of SCRP occur. In both types, redox concentrations have Munsell colors of 2.5 YR 3/6, 4/6, or 3/2. In one case, depletion features (10YR 5/6 or 6/2) are randomly distributed throughout the horizon. These horizons are dense (bulk density of 1.75 g cm−3), which restricts water movement and promotes Fe segregation. In the other type of SCRP, most Fe concentrations, depletions, and planar voids are oriented parallel to the soil surface. These soils have a fluctuating water table. Dithionite‐extractable Fe ranges from 70 g kg−1 in redox concentrations to 4 g kg−1 in adjacent depletion features. Goethite occurs in both redox concentration and depletion clay fractions. Hematite only occurs in the redox concentration clay fractions. Depletion features have lower coarse/fine ratios (separated at 20 µm), more oriented clay, and 10 to 20% more clay than associated redox concentrations. Horizons with SCRP are dominated by nodules and masses in ped interiors, and Fe depletion features along voids. Thus, Fe is primarily reduced along voids and moves into the matrix. Horizons with a fluctuating water table also contain Fe‐rich pore linings. Iron is concentrated on these surfaces because these pores are the first to drain as the water table recedes.

Morphological and Physical Properties of Selected Fragipan Soils in Massachusetts

Fragipans are no longer officially recognized in New England. Presently all dense layers found in the region are considered unaltered dense basal tills. Comparisons between morphological and physical properties of five pedons in Massachusetts previously classified as having fragipans and typical fragipan properties were undertaken to ascertain the possible existence of fragipans. Morphologically, the pans contained the typical fragipan features outlined in the soil taxonomy including bleached prism faces (BPF), lack of rooting in the pan, and the presence of an eluvial horizon just above the pan. Physically, the pans have a high bulk density and sometimes enough increase in clay content to meet the taxonomic criteria for an argillic horizon. Additionally, the pans show redoximorphic features and indications of lateral water movement across their upper surface. The argument that the pans that developed in dense basal till in Massachusetts are largely geogenic in origin does not appear valid.

Nutrient Elements in Some Benchmark Soil Pedons from the Ganges River Floodplain of Bangladesh

This paper presents the results of chemical analysis of seven selected nutrient elements in soil samples collected from four pedons representing four extensive benchmark soil series from the Ganges river floodplain of Bangladesh. The results of total and available N, P and K contents as well as DTPA (diethelene-triamine pentaacetic acid) -extractable and total Fe, Mn, Cu and Zn contents in the soils were reported. With respect to nutrient status, the soils were rated as fertile with reasonably high production potential under balanced fertilization. The nutrient contents are presumed to be renewed every year by fresh siltation during the monsoon floods. High contents of total iron and potassium in these soils are noteworthy features. Iron in these paddy soils forms redoximorphic features. The release mechanism of K+ from the potash bearing minerals needs further study to determine the need for K fertilization in these soils. The total quantities of the seven studied nutrients in these soils vary widely. In the same way the quantities of extractable (available) nutrients in the soils vary widely. For elements like P, K and Fe less than one percent of the total remain in the available forms. Soil characteristics like organic matter, clay content, cation exchange capacity, pH and lime content have important roles in the availability of nutrients in soils. Keywords: Ganges floodplain, Benchmark soil, DTPA-extractable micronutrients, Soil characteristics DOI: 10.3329/bjsir.v44i3.4411 Bangladesh J. Sci. Ind. Res. 44(3), 359-366, 2009

Characterization and classification of some intensively cultivated soils from the Ganges river floodplain of Bangladesh

Most of the soil samples from four pedons representing some extensive soil series from the Ganges river floodplain of Bangladesh found to be heavy textured with clay content averaging from 43 to 55 per cent up to a depth of one meter. The soils had neutral to alkaline reaction with high percentage of base saturation. Because of seasonal flooding ranging from two - three months the soils have developed redoximorphic features including redox concentration in the middle zone and a redox depletion in the lower zone of the profiles. The seasonal submergence and drying are the most active factors in developing the morphogenetic features in these soils. Smectite was the dominant clay mineral followed by mica and kaolinite with small quantities of vermiculites and interstratified minerals. The minerals in the clay fraction of the soils appear to be inherited from alluvial parent materials with very little in situ mineral transformation. The soils were characterized at the family categoric level of USDA soil taxonomy.Key words: Ganges river floodplain; Characterization; Classification; Cultivated soilsDOI: http://dx.doi.org/10.3329/dujbs.v20i1.8870Dhaka Univ. J. Biol. Sci. 20(1): 71-80, 2011 (January)