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Berlin Brandenburg

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  • 1
    Language: English
    In: Geoderma, 01 April 2016, Vol.267, pp.58-64
    Description: Soil landscapes often exhibit complex spatial patterns, with some aspects of soil variation apparently unrelated to measurable variations in environmental controls. However, these local, contingent complexities are not truly random or intrinsically unknowable. The purpose of this work is to develop and apply a method for identifying or teasing out causes of soil landscape complexity. Soil spatial adjacency graphs (SAG) represent the geography of soil landscapes as a network that can be analyzed using algebraic graph theory. These SAGs include linear sequential subgraphs that represent sequences of soil forming factors. The number and length of these soil factor sequences (SFS), and their associated spectral radius values, determine whether the SFS are sufficient to explain the spatial pattern of soil adjacency. SAGs and associated graph theory methods provide useful tools for guiding pedological investigations and identifying gaps in knowledge. The methods also allow sources of soil landscape complexity and variability to be determined in a way that can help assess the underlying deterministic sources of chaos and dynamical instability in pedology. The approach is applied to a soil landscape in central Kentucky, producing a SAG with 13 nodes (soil types) and 36 links indicating whether the soils occur contiguously. Five SFS were identified, the sum of whose spectral radius values is 6.35. The spectral radius of the SAG is 6.56, indicating that the SFS can explain most, but not all, of the complexity of the soil relationships. The analysis also points to potential environmental controls that could potentially enable full explanation.
    Keywords: Soil Complexity ; Soil Variability ; Spatial Adjacency Graph ; Soil Factor Sequence ; Spectral Radius ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 2
    Language: English
    In: Geoderma, 2010, Vol.156(3), pp.389-398
    Description: Steady-state regolith or soil thickness (SSST), whereby surface removals are approximately balanced by production of new soil by bedrock weathering, is a common assumption in most models of hillslope and landscape evolution. SSST is also a fundamental assumption in the use of cosmogenic radionuclides (CRN) to estimate erosion and weathering rates. The steady-state concept is based on feedbacks between soil thickness and weathering at the base of the regolith, such that (sometimes after an optimal or threshold thickness is achieved), thicker soils lead to lower weathering rates (and vice versa). SSST is thus only applicable to soils formed chiefly from weathering of the underlying bedrock, where sufficient time has elapsed for regolith accumulation, and where effects of processes other than weathering and surface removals on thickness are negligible. Even within this domain, the widespread occurrence of deep weathering profiles, regolith stripping, and inherited regolith features makes SSST problematic as a conceptual model for pedogenesis or weathering profile development. The ratio of soil thickness to total weathering profile thickness is proposed as a simple index of steady state. Steady-state profiles formed on weathered bedrock should exhibit ratios close to unity. Data from the Cumberland Plateau region of eastern Kentucky show that soil/weathering profile ratios in shallow (〈 1.5 m) profiles formed on sandstone may reach or approach unity, but are generally 〈 1. Geotechnical core data show depths to bedrock of 2 to 〉 20 m, and generally significantly greater than soil thicknesses in the region, suggesting ratios 〈〈1. However, while evidence shows that SSST is likely rare and not a viable conceptual framework for assessing soil and weathering profile development, deviations from SSST may have limited influence on results of CRN-based estimates of erosion and weathering and simulation model results. This is because in the landscape settings where SSST is typically assumed, and over the customary time scales involved, rates of denudation and weathering are very small compared to regolith thickness, such that imbalances do not materially affect results of calculations. Steady-state in development of soil, regolith, or weathering profile development thus represents a facilitating the use of some models and tools. The potential pitfalls arise from the possibility that the utility of SSST as a convenient fiction in some contexts may be mistaken for a realistic representation of the dynamics of pedogenesis and weathering profile evolution.
    Keywords: Soil Thickness ; Steady-State ; Regolith ; Weathering Profile ; Soil Geomorphology ; Eastern Kentucky ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 3
    Language: English
    In: Geoderma, 2009, Vol.149(1), pp.143-151
    Description: Several recent theories and conceptual frameworks in pedology, ecology, geomorphology, and evolutionary biology, taken together, suggest the notion that earth's soils are not just strongly influenced by biota, but represent selective pressures. These ideas point in the direction of many aspects of soils as expressions of the effects of genes through the effects of organisms (i.e., extended phenotypes). The cumulative, interacting, overlapping effects of these extended phenotypes as manifested in the soil represent an . If this is the case, then we should expect major changes in biological evolution to be reflected in major changes in the types of soils. A brief review of paleopedology literature supports the notion of coevolution of soils and biota, not just in the sense of both responding to the same environmental forcings, but also with respect to explicit pedological expressions of biological change. The extended composite phenotype notion also suggests that significant biological changes should be reflected in significant qualitative pedological changes (i.e., fundamental changes in soil morphology beyond quantitative changes in specific short-lived soil properties). This is demonstrated via recent research in the Ouachita Mountains, Arkansas, where changes in selective pressures on trees associated with fire frequency are linked to changes in soil morphology. The concept of soils as extended composite phenotypes has repercussions for pedology, evolutionary biology, and interpretations of soils in other earth and environmental sciences. The notion of genetic signatures in soil morphology also has implications for the search for extraterrestrial life, and extends the notion of Earth as a set of tightly-coupled, densely interwoven systems.
    Keywords: Soils ; Extended Composite Phenotype ; Coevolution ; Biomantle, Ecosystem Engineers ; Niche Construction ; Pedology ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 4
    Language: English
    In: Geoderma, 2007, Vol.141(1), pp.89-97
    Description: The study of pedodiversity and soil richness depends on the notion of soils as discrete entities. Soil classifications are often criticized in this regard because they depend in part on arbitrary or subjective criteria. In this study soils were categorized on the basis of the presence or absence of six lithological and morphological characteristics. Richness vs. area relationships, and the general pattern of soil variability and diversity, were then compared to analyses of pedodiversity based on Soil Taxonomy. The study area consists of sixteen 0.13-ha plots on forested sideslopes of the Ouachita Mountains, Arkansas, with a minimum of 20 classified soil pits per plot. An classification was developed, from the standpoint of soil geomorphology and studies of the coevolution of soils and landscapes, and based on the regional environmental framework. Soils were classified based on (1) underlying geology (shale, sandstone bedrock, or transported sandstone rock fragments), and on the presence or absence of (2) texture contrast subsoils, (3) eluvial horizons, (4) surface and/or subsurface stone lines or zones, (5) lithological contrasts between soil and underlying geology, and (6) redoximorphic features. The soil geomorphic classification (SGC) yielded 40 different soil types (out of 288 possible different combinations of the criteria), compared to 19 different series or taxadjuncts identified by standard soil classification. However, 21 of the SGC soil types had only one or two representatives. Individual plots contained five to 11 different SGC soil types with extensive local variability. A standard power-function relationship between soil richness ( ) and area or number of samples ( ) provided the best fit for most plots ( = ). The exponent was slightly higher than for the taxonomy-based analysis, but in general the analyses lead to similar conclusions with respect to the relationship between richness and area, and the relative importance of local, within-plot versus regional, between-plot variability. Results support the view that soils can be viewed and treated as discrete entities, that richness assessments are not necessarily extremely sensitive to the classification used, and that highly localized variability may be critical to pedodiversity. The suggested criteria for identifying discrete soil types are given, based on qualitative morphological differences and state factor relations, contiguity, and connectivity.
    Keywords: Pedodiversity ; Soil Richness ; Soil Classification ; Soil Geomorphology Classification ; Richness-Area Relationship ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 5
    Language: English
    In: Geoderma, 2001, Vol.102(3), pp.347-370
    Description: Soils and landscapes are subject to historical and spatial contingency, leading to locally unique pedologic features. This can make broad-scale generalizations difficult, impractical, or even impossible. The development of vertical texture-contrast soils with argillic horizons, for example, is potentially subject to all general forms of spatial and historical contingency. A case study in east Texas shows evidence both supporting and refuting five general classes of explanation for the formation of vertical textural contrasts. Multiple causality is likely, and attempts to apply any single explanation to a county-size area (and sometimes to a pedon) are not likely to be successful. The implication is not that pedologists should abandon the search for generalizations, but that the context in which laws and generalizations are developed needs rethinking. Explanatory constructs should be formulated not with the notion that a single explanation is likely to be applicable to most soils, but with the idea that multiple causality and polygenesis are likely, and that location-specific characteristics cannot be ignored. The search is directed not toward a single principle to explain the majority of cases and against which exceptions can be judged, but toward a set of principles that define the possibilities (or probabilities). Two analogies that may be useful in addressing historical and spatial contingency in soils are proposed, based on demographic and synoptic metaphors.
    Keywords: Soils—Evolution ; Soils—Geography ; Historical Contingency ; Spatial Contingency ; Texture-Contrast Soils ; Bioturbation ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 6
    Language: English
    In: Geoderma, 2008, Vol.145(3), pp.419-425
    Description: The relationship between soil modeling and field pedology is recursive. Models should be firmly grounded in field observations. Field data are then used to test, calibrate, and refine models. One often-overlooked relationship between models and field studies is the use of models to generate field-testable hypotheses unrelated to the model itself—propositions derived from model outputs or implications, the testing of which provides pedologic insight independent of the model and its underlying assumptions. This paper provides an example using a model of soil thickness. The case study illustrates a stepwise, recursive relationship between field evidence and models. The relationship between bedrock weathering, soil thickness, and surface erosion used in most numerical models of soil and hillslope evolution was generalized into a qualitative nonlinear dynamical systems model, the interaction matrix of which is dynamically stable. This supports the notion of a steady-state equilibrium soil thickness where weathering is balanced by surface removal. However, empirical data in the Ouachita Mountains, Arkansas, USA, shows nonequilibrium soil thickness. This in turn indicates either recent and/or large disturbances or changes in boundary conditions, or that factors other than weathering and erosion play a significant role in determining thickness. The inconsistency between model results and field evidence led to further field investigations, suggesting that biomechanical effects of trees on soil depth are highly significant. A model devised to explore this notion showed that the interrelationships between individual trees and soil depth are dynamically unstable, leading to generation of a specific field-testable hypothesis, that soil should be systematically thicker under trees than in adjacent sites. This relationship was confirmed by augering to bedrock at 108 pairs of tree stumps and immediately adjacent sites. The recursive relations between soil modeling and field pedology thus led to specific findings regarding the influence of trees on soil thickness and nonequilibrium soil thickness that would not have arisen otherwise. Another key lesson is that field observations contrary to a model may be of greater importance in advancing pedology than those consistent with the model.
    Keywords: Soil Modeling ; Soil Thickness ; Field Pedology ; Biomechanical Effects ; Dynamical Stability ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
    Source: ScienceDirect Journals (Elsevier)
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  • 7
    Language: English
    In: Geoderma, 1998, Vol.86(1), pp.1-21
    Description: The application of nonlinear dynamical systems (NDS) theory to pedology involves the interaction of complex systems theory, which has not yet been widely applied to field-oriented sciences such as pedology and soil science, where applications of NDS theory are recent and relatively rare. The gap between pedologists and systems theorists can be narrowed by reconsidering Hans Jenny's factors of soil formation model. The latter is an inherently holistic, systems-oriented approach and evidences a concern (in common with NDS theory) with qualitative changes in (soil) system states. Jenny's own reformulation of the original state factor model assigns a strong role to initial conditions and historical contingency, implicitly recognizing the possibilities of self-organization and deterministic chaos. Many fundamental concepts from nonlinear dynamics are thus already embedded in familiar pedologic theory, making the former more accessible to pedologists. Similarly, the links between NDS and soil state factor theory should help nonlinear systems theorists conceptualize the real-world implications and limitations of NDS theory on and in the ground. Abstract Copyright (1998) Elsevier, B.V.
    Keywords: Soils-Genesis ; Soils-Evolution ; Soils-Geography ; Nonlinear Dynamical Systems ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 8
    Language: English
    In: Geoderma, 1993, Vol.58(1), pp.1-15
    Description: The dominant conceptual framework in pedology and soil geomorphology, the state factor model as exemplified by Jenny's "clorpt" equation, is reinterpreted as a nonlinear dynamical system. While the model in its most general form is insoluble, it may be solved with respect to the stability of the soil system for a particular soil property or phenomenon. A conceptual model of the degree of soil profile development in the context of the state factor model is shown to be asymptotically unstable and to have the potential to exhibit deterministic chaos. This suggests that spatial and temporal complexity in patterns of soil properties and soil development may be inherent in system dynamics, independently of any stochastic forcings or a priori variation in environmental controls.
    Keywords: Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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  • 9
    Language: English
    In: Geoderma, 2005, Vol.124(1), pp.73-89
    Description: A high degree of soil variability over short distances and small areas is common, particularly in forest soils. This variability is sometimes, but not always, related to readily apparent variations in the environmental factors that control soil formation. This study examines the potential role of biomechanical effects of trees and of lithological variations within the parent material in explaining soil diversity in the Ouachita Mountains of Arkansas. The diversity of soils on Ouachita sideslopes is high, and the soil series vary primarily with respect to morphological properties such as soil thickness and rock fragment content. Soils vary considerably within small more-or-less homogeneous areas, and richness–area analysis shows that the overall pattern of pedodiversity is dominated by local, intrinsic (within-plot) variability as opposed to between-plot variability. This is consistent with variation controlled mainly by individual trees and local lithological variations. Given the criteria used to distinguish among soil types, biomechanical as opposed to chemical and hydrological effects of trees are indicated. Results also suggest divergent evolution whereby the pedologic effects of trees are large and long-lived relative to the magnitude of the initial effects and lifespan of the plants.
    Keywords: Pedodiversity ; Spatial Variability ; Ouachita Mountains ; Biomechanical Effects ; Richness–Area Analysis ; Agriculture
    ISSN: 0016-7061
    E-ISSN: 1872-6259
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