<p>The measurement of aggregate stability is an important indicator of soil quality and is widely used for monitoring soil condition. The SLAKES mobile app is an alternative tool to laboratory-based methods to measure soil aggregate stability. It provides aggregate stability measurements through Slaking Index (SI) with SI close to 0 suggesting high stability and values above 7 suggesting minimum stability. As the duration of this low-cost experiment is only 10 minutes, SLAKES is very attractive for scientists and no-scientists. SLAKES was implemented in Australia and has proven its efficiency in several studies.</p><p>This study was conducted to determine whether the SLAKES mobile app could be adapted to French soils and then could be an alternative to the Mean Weight Diameter (MWD) method, normalized in France (ISO 10390). More specifically, the three main objectives were: (i) determining whether the aggregate stability measurements depend on the phones used for the experiment, (ii) estimating the number of measurements necessary to get reliable results, (iii) determining whether the app has the ability to detect the effect of contrasting soil managements previously shown using the MWD method.</p><p>The study was performed on silty loam soils from EFELE (Effluents d&#8217;Elevage et Environnement) experimental site at le Rheu (Brittany, France) which is part of the French &#8220;Organic Residues&#8221; research observatory (SOERE PRO). The experimental design combines two different tillage practices (conventional tillage and shallow tillage) with two fertilizer treatments (mineral and organic (cattle manure)) randomly replicated three times. Soil samples were collected in March 2017 at both 0-15 cm and 15-25 cm depth from the 12 plots.&#160;</p><p>The SI was measured on three aggregates simultaneously and this measurement was repeated 15 times for each sample which provided 45 SI per sample. Outliers above SI=11 were removed before statistical treatments. Four different phones of the same brand and generation were used to measure SI.</p><p>An analysis of variance showed that the effect of the smartphone on SI measurements was not significant (p-value = 0.73, 0.88, 0.067 for 3 different samples).&#160;The SLAKES results showed comparable significant separation of means (p < 0.0001) between each soil management than the MWD method. According to the results of an analysis of variance, SI was significantly lower in reduced tillage than in conventional tillage condition (p-value = 2.10<sup>-16</sup>). These results indicate a higher soil stability in reduced tillage. Yet, the analysis of variance did not underline any effect of fertilization on the SI (p-value = 0.28), as previously found with the MWD method.</p><p>This study proved that a relatively simple mobile app can detect the effect of soil management practices on aggregate stability with a similar performance than the MWD method. This conclusion was reinforced by the existing correlation between the SI and the MWD index (p-value = 0.00059, R<sup>2</sup> = 0.39). We recommend to perform similar experiments on other sampling campaigns or in other pedological and soil management contexts taking at least 15 measures per sample.</p>
Summary Soil interrill erodibility is a key component of soil erosion models. However, when using aggregate stability to assess soil erodibility, samples are usually collected from the plough layer, while soil erosion occurs at the soil surface. Hence, the potential changes in erodibility caused by crusting are ignored. Moreover, soil interrill erodibility is difficult to predict accurately. This lack of predictability means that current erosion models use a constant erodibility value for a given soil, and thus do not consider potential heterogeneity of erodibility. This study was conducted to (i) assess the heterogeneity of aggregate stability for a crusted soil and (ii) relate this heterogeneity to the aggregate stability of the underlying material (sub‐crust) and to standard soil properties. A field study was conducted in a small area of the L oess P lateau in C hina in which the crust and the sub‐crust soils were sampled. Standard soil properties (organic matter content, sand content, silt content, clay content, cation exchange capacity (CEC), pH in water, and water content at the time of sampling) were measured as potential explanatory factors of aggregate stability. The results showed a large heterogeneity in aggregate stability among the sites, even though the sites had the same soil type. The mean weight diameter ( MWD ) of the crust varied between 0.33 and 2.04 mm while the MWD of the sub‐crust varied between 0.23 and 1.42 mm. Soil texture and pH were uniform among the sampling sites, whereas water content, organic matter content and CEC varied more. Even though some correlations existed (for example r = 0.57 between MWD for the slow wetting test and organic matter content), none of the standard soil properties was able to predict aggregate stability accurately. The aggregate stability of the crust was significantly greater than that of the sub‐crust. The large differences in aggregate stability imply large differences in soil interrill erodibility. Because a single soil type was investigated, this finding proves that erodibility can vary greatly in space even for a given soil type. Soil interrill erodibility should be estimated from the exact material exposed to erosive forces, the soil surface material. Using the sub‐crust would have led to greatly over‐estimated erodibility and thus to a marked bias in erosion model predictions. Résumé La stabilité structurale d'un sol encroûté : différences entre la croûte et le matériau sous‐jacent, et conséquences pour l'estimation de l'érodabilité inter‐rigole. Un exemple dans le Plateau de Loess (Chine) L'érodabilité inter‐rigole est un paramètre clef des modèles d'érosion du sol. Cependant, lorsque des tests de stabilité structurale sont utilisés pour évaluer l'érodabilité, les mesures sont habituellement réalisées sur des échantillons prélevés dans l'horizon labouré alors que l'érosion a lieu à la surface du sol. Ainsi, les changements potentiels d'érodabilité causés par la formation de croûte sont ignorés. De plus, l'érodabilité inter‐rigole reste encore difficile à prédire avec précision. Ces difficultés conduisent les modèles d'érosion à utiliser une érodabilité constante pour un type de sol donné, et donc à ne pas considérer l'hétérogénéité potentielle de l'érodabilité. Cette étude a été conduite pour (i) évaluer l'hétérogénéité de la stabilité structurale pour un sol encroûté et (ii) relier cette hétérogénéité à la stabilité structurale du matériau sous‐jacent (sous‐croûte) et aux propriétés standards du sol. Une étude de terrain a été réalisée sur un secteur de surface limitée du P lateau de L œss ( C hine). Des échantillons provenant de la croûte et de la sous‐croûte ont été collectés. Les propriétés standards (teneur en carbone organique, teneurs en sable, limon et argile, CEC , pH , et teneur en eau au prélèvement), ont été mesurées en tant que facteurs explicatifs potentiels de la stabilité structurale. Les résultats ont montré une grande hétérogénéité de la stabilité structurale entre les différents sites alors que ces derniers présentaient le même type de sol. Le MWD de la croûte variait entre 0.33 et 2.04 mm tandis que le MWD de la sous‐croûte variait entre 0.23 et 1.42 mm. La texture du sol et le pH étaient très homogènes entre les sites étudiés, tandis que la teneur en eau, la teneur en matière organique et la CEC variaient plus fortement. Bien que certaines corrélations aient été identifiées (par exemple r = 0.57 entre le MWD du test à l'humectation lente et la teneur en carbone organique), aucune de ces propriétés n'a permis de prédire précisément la stabilité structurale. La stabilité structurale de la croûte était significativement supérieure à celle de la sous‐croûte. Les grandes différences de stabilité structurale mesurées impliquent des érodabilités très contrastées. Comme un seul type de sol a été étudié, ce résultat prouve que l'érodabilité peut être très variable spatialement pour un type de sol donné. L'érodabilité inter‐rigole du sol devrait être mesurée sur le matériau exact qui subit l'érosion, c'est‐à‐dire le matériau de surface. L'utilisation du matériau sous‐jacent aurait engendré une forte surestimation de l'érodabilité et donc un biais important dans les prédictions d'un modèle d'érosion.
Soil surface roughness plays an important role in determining how the soil will interact with its environment. Analysis of soil roughness at small scale matters both for preparation of soil in order to allow for plant emergence, and for decisions to favor soil conservation. Indeed, soil roughness may be shaped by tillage operations and then changes with time, under rainfall impact.
Soil surface roughness is usually estimated by various indices, computed on measured profiles or images of elevations. Another approach is focusing on soil cloddiness, either by sieving or by image segmentation. The objective of this study is to monitor the evolution of clods under rainfall with Digital Elevation Model (DEM) recording and image processing.
We prepared two trays of artificial soil surfaces in the laboratory with silt loam soil topped by pre-sieved clods. They were designed to look like a seedbed. Soil surface evolution was achieved by subjecting the trays to controlled artificial rainfalls, and DEM were recorded at each stage. We performed automatic clod segmentation and measurement of the volume of individual clods. Under rainfall impact, we could see smoothing and leveling of clods until disappearance of the smaller ones. We focused on the larger clods greater than 12 mm in diameter that remained till the last rainfall. They showed swelling (volume increase) followed by erosion (volume decrease), these two phenomena being size dependent. Clod volume decrease was modeled by an exponential function.
Now, the slope and the amplitude parameters decreased according to a power law, as a function of mean volume of clods. Monitoring of clod volume with cumulated precipitation with the help of DEM measurements is able to differentiate the dynamics of clod depending on their size. This technique improves the usual roughness description and allows for a better understanding of the processes.
Landuse organisation in Mediterranean France tends to follow a typical pattern where large flat coastal areas are densely urbanised and oriented toward summer tourism, inland alluvial plains are dedicated to vineyards for wine making, and hilly areas surrounding inland plains are occupied by forests and isolated housing. This spatial organisation reflects long term patterns of sediment redistribution where upslope geological substrates have provided sediments to downslope geomorphological units such as alluvial plains and colluvial deposits. Forest fires periodically destroy the forest canopy and litter layer and create conditions of aggravated erosion for a few years at a time. Typically, a forested area has probably undergone dozens of cycles of post-fire erosion and regrowth during the past millennia. The objective of this study was to analyse sediment dynamics for a burned forested area and compare these to erosion processes encountered in cultivated soils in the same catchment. The analysis was carried out in three steps. In the first, landuse was mapped using colour airphotos for a 230 km2 catchment in the ?Massif des Maures? in SE France. For each of the two major landuse classes of interest (forested, vineyard), slope distributions were calculated based on a 25 m DEM. Similarly, channel slopes were calculated for stream sections flowing through the two landuse classes. This initial survey was complemented by two field studies. In the first, zones of river bank erosion and sediment deposition in channels were mapped over a total length of about 40 km. This was carried out to identify critical slope thresholds for major sediment deposition. In the second, a North facing slope was sampled for litter layer depth, surface stone cover, soil depth, and textural and aggregate stability analyses for burned (August, 2003) and unburned forests and cultivated fields. The grainsize characteristics of slopes were compared to those of sediments trapped in stream channels. Almost three years after a forest fire in the Massif des Maures, the litter layer has only begun to recover and erosion processes are still active even though a substantial underbrush has developed and cork oak crowns have recovered. Runoff during post-fire rainfall events selectively removes the soil fraction finer than about 2 cm, leaving behind a stone lag on the surface. The steep slopes of the forested zone feed runoff directly into ephemeral streams, so there is virtually no deposition within the burned forested area. In addition, steep channel slopes eliminate the possibility of channel storage until the sediments have arrived well into the main river channel downstream. This indicates that delivery ratios are close to 100% for post-fire erosion in the burned Mediterranean catchments of SE France. The surface of the unburned forest is protected by a dense mat of litter, and the cultivated soils show some selective erosion depending on cultivation method. A comparison of erosion factors for forested and agricultural areas indicates that although both areas are sensitive to slope inclination, soil erodibility in the forested zone is dominated by the litter layer in the unburned forest, surface stone cover in the burned forest, and a combination of stone cover and aggregate stability in the agricultural soils.
We are interested in simulating overland flow on agricultural fields during rainfall events. In this context, we definitely have to cope with dry/wet interfaces and water inflow on dry soil. The model considered is the Shallow Water system (or Saint-Venant equations) without infiltration. Moreover, the model has to be completed with friction terms. It is numerically solved by a finite volume method. The topography and friction terms are treated by a well-balanced strategy with specific additional features to deal with dry/wet transitions. The method as well as the choice of the friction term are validated on both analytical solutions and experimental dataset produced by INRA-Orl´eans.
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