Quantification of soil volumes in the Eg&Bt-horizon of an Albeluvisol using image analysis

In this study, we provide a strategy to quantify the effects on soil evolution of driving forces such as human activities or global change. This strategy was developed for situations in which soil evolution resulted in the formation of a complex juxtaposition of soil volumes with distinct properties including soil colours. It is based on image analysis. Our approach proceeds in two steps: (1) to find the minimum sample size over which the soil anisotropy can be neglected and (2) to define a Representative Elementary Volume (REV) of that sample. This approach was developed on the Eg&Bt horizon of a drained Albeluvisol in which three decimetric soil monoliths were sampled at 60, 110 and 210 cm from a drain. The monoliths were sliced in 1.5 cm horizontal layers. Each slice was photographed and studied by image analysis. At the monolith scale, there was neither lateral nor vertical anisotropy. The sampled monoliths were larger than the REV allowing quantification of the different soil volumes constituting this particular horizon. We quantified significant evolutions of the abundance of the different soil volumes characterized by their colour as a function of the distance to the drain. Such a quantification of the effects on soil evolution of human activities or global change equally applies for Podzols, Calcisols or Gleysols for which pedogenesis also resulted in contrasted soil colour evolutions

3D representation of soil distribution: An approach for understanding pedogenesis Représentation 3D des sols, apports à la compréhension de la pédogenèse

International audienceSoils are characterised by a spatial variability in the three dimensions (3D) of space. However, 3D studies remain scarce due to the qualitative nature of many soil horizon characteristics, notably the horizon designation. Indeed, existing 3D tools are mainly developed for quantitative data. To solve this difficulty, we propose a new approach based on the interpolation of the horizon thickness to derive digital elevation models for both the upper and the lower limits of each horizon. This approach was applied to Planosols previously extensively studied with 2D approaches. The pseudo 3D obtained representation evidences soil processes that were missed in 2D approaches. As an example, we evidence the impact of differential weathering, resulting from the mineralogical heterogeneity of the parent material, on the subsequent pedogenesis. Les sols sont des continuums tridimensionnels (3D), caractérisés par une variabilité spatiale dans l'ensemble des directions de l'espace, mais les études 3D demeurent rares. Une des difficultés majeures des approches 3D est due à la nature qualitative de nombreuses caractéristiques des horizons, dans la mesure où la plupart des outils 3D existants sont principalement développés pour l'interpolation 3D de données quantitatives. En substitution à l'interpolation directe de la variable « nom de l'horizon », nous proposons une approche basée sur l'interpolation de l'épaisseur des horizons pour calculer les modèles numériques d'altitude correspondant aux limites de chaque horizon, permettant ainsi une visualisation pseudo 3D. Cette étude, appliquée à des Planosols bien caractérisés en 2D par ailleurs, montre que la représentation 3D des sols permet de souligner des processus omis lors des approches précédentes, tels que l'impact de l'altération différentielle, résultant de l'hétérogénéité initiale du matériau parental, sur une pédogenèse ultérieure

Landscape design for soil conservation under land use and climate change

International audienceSoils and landscapes evolve simultaneously. Soil evolution is controlled by redistribution and transformation processes influenced by topographic and climatic parameters, with also a major contribution of management strategies. The perennial landscape features have a strong influence on soil spatial distribution (geometry) and soil genesis. Building landscapes which enhance soil resilience to degradation processes and increase soil services appears as a promising way to adapt to forthcoming climatic and land use evolutions. The presentation aims to synthetize major results from a research program nicknamed Landsoil which focused on the evolution of agricultural soils over medium time scales (decades to centuries) in relation to changing conditions of land use and climate. Precise study of the soil 3D organization in three contrasted landscapes (Brittany, Touraine, Languedoc-Roussillon) enabled to link soil redistribution in space to landscape components (field geometry, hedges or ditches network) and their past evolution. A dynamic and high resolution spatial modeling approach was developed coupling erosion processes and soil organic matter evolution and was calibrated over past evolution using dating techniques (Cs137, C14, OSL). The resulting Landsoil model was afterwards applied in a prospective manner under different scenarios of land use and climate change over the 21th century. Indicators of soil vulnerability and soil resilience were defined and tested by the comparison of several prospective scenarios applied on a same landscape and by comparison of the contrasted landscapes

L’évaluation des services écosystémiques auxquels contribuent les sols, dans le cadre de EFESE-EA

L’évaluation des services écosystémiques auxquels contribuent les sols, dans le cadre de EFESE-EA. Séminaire de lancement du projet ANR SoilServ

Using GIS to predict concentrated flow erosion in cultivated catchments

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Improving topsoil carbon storage prediction using a digital elevation model in temperate forest soils of France

International audienceSpatial distributions of C pools in forest soils are difficult to estimate because of their inherent spatial variability and because of lack of reliable data (C concentration and bulk density down to a sufficient depth). In southwest France, thick humic acid soils have developed from Quaternary silty alluvial deposits, Previous studies have shown that these soils have accumulated large amounts of organic C (OC) and that the regional distribution of C stores depends on both textural and climatic gradients. However, a significant part of C content variability still remained at a more detailed scale. The objective of this work was to determine if the topographic situation also influenced topsoil C storage, which would improve the accuracy of the prediction of organic pools in forest soils. This work uses a digital elevation model (100 x 100-m grid) to calculate topographic attributes on a 6000-ha area. The results suggest that slope is the main factor controlling variability in local C stores. This study shows that relating OC contents to spatial available landform parameters that might influence OC distribution, and combining them into spatial models, can provide a useful tool to improve geographical prediction of this characteristic

Modelling soil organic carbon fluxes attributable to conversion of forest to corn cropping in a landscape of southwest France

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