The impact of compaction by traffic on agricultural soils is not strict and irreversible. After compaction by machine traffic, soil structure changes both spatially and temporally as different generative processes occur. These are generally well-described in the literature. However, the preferential periods of occurrence and the soil depths affected by changes - thus, the characteristic scales of soil structural recovery - remain hypothetical. Further investigation through precise spatial and temporal monitoring under real in-field soil conditions is needed.In this paper, the structural changes of a locally trafficked silt-loam soil were assessed under both cropped and bare areas conventionally tilled from one-year soil monitoring. The monitoring was performed in-field by three methods at a low temporal resolution with the standard methods of visual description and soil coring in pits, and at a high temporal resolution with the non-destructive Electrical Resistivity Tomography (ERT) method. The specific use of ERT for this purpose is discussed.Compaction by traffic affected the overall tilled soil layer and was shown to be time-persistent. This suggested a characteristic time-scale of a complete structural recovery longer than one year, regardless of soil management. At the finest temporal scale, the results also highlighted some seasonal processes that potentially affect the long-term recovery, such as bio-drilling and soil cracking. The processes were related to the soil management, the wetting/drying cycles and the freeze/thaw effect. They likewise induced the start of structure fragmentation in the first centimetres of the soil and acted abruptly in the dry period, preferentially under the area initially cropped, with persistent effects on the soil structure in the rainy and cool season. (C) 2013 Elsevier B.V. All rights reserved.

Analysing the properties and functional characteristics of heterogeneous soils containing several phases requires a correct estimation of the volume proportion of each phase. In the case of stony soils, the volume percentage of the content of rock fragments remains difficult to estimate in situ. This paper presents a method that uses field spatial electrical resistivity measurements to determine the volume proportion of rock fragments. Based on the hypothesis that the electrical resistivity signal noise increases as the proportion of rock fragments increases, a model was developed that uses the standard deviation of the apparent electrical resistivity measurements over a small area as an indicator of rock fragment contents. The model was tested on three study areas of several hectares containing soil units with varying quantities of rock fragments. The estimation of the rock fragment content was accurate, and the error estimation of about 6% was the same order of magnitude as the Bussian model (1983). The developed model strongly depends on the water content in the soil and the rock type and must be calibrated in each context. Nevertheless, estimations of the rock fragment content in stony soils can be performed efficiently in the surface horizon as well as all along the soil profile.

Recently, geophysical methods have been developed that can monitor soil characteristics spatially at high resolution. However, interpreting electrical measurements is difficult because geophysical data can be influenced by many soil variables, some of which vary over time. Our objective here was to use spatial measurements of electrical resistivity to define zones of homogeneity, to interpret them in terms of changing water contents, and to compare them with a soil map. Our underlying assumption was that the time variation of electrical resistivity at the field scale was only due to the dynamics of soil moisture in our studied field. Monitoring of soil electrical resistivity and soil moisture was performed at four dates during 2006 by two methods: by the use of the MUCEP (Multi Continuous Electrical Profiling) device, which gives measurements over a whole field, and by local gravimetric measurement of soil water content. Homogeneous zones were defined directly from measurements of the electrical resistivity and after ordinary kriging of the water content. Our analysis of spatial and temporal variability has permitted us to discriminate three temporally homogeneous zones, in terms of both electrical resistivity and water content, which were broadly related to the soil map. The use of electrical measurements enabled us to directly describe spatial and temporal changes in soil water content at the field scale and to describe some hydraulic processes, like lateral flows or upward capillary flows, that would be difficult to derive from soil maps.

Soil tillage practices can affect water flow and solute transport processes dynamically in space and in time. However, the relationship between tillage practices and flow and transport in soils is not yet well understood. Within this paper, we analyze the short term impact of the conversion from conventional mouldboard ploughing (CT) to reduced disc harrowing (RI) on the solute transport process within a loamy soil. Solute breakthrough experiments at two flow rates were performed on 2 undisturbed lysimeter collected in a CT and RI field plot. Solute transport parameters were estimated using transfer function theory. Important differences in solute transport were observed between the RI and the CT treatments. The CT treatment exhibited a rapid, more homogeneous and less dispersive solute transport as compared to the RI treatment. These results are explained by the changes in soil structure due to tillage and compaction. The dominant transport was identified as being a stochastic-convective process in both lysimeters. The similarity of the mixing regime for the two soil columns can be explained by preferential solute trajectories activated within structural macropores as a result of the high flow rates applied. We show that the relationship between tillage practices and transport is complex, not only scale and time dependent but also influenced by the boundary conditions and tillage practices. (c) 2010 Elsevier B.V. All rights reserved.

HAL is a multi-disciplinary open access archive for the deposit and dissemination of scientific research documents, whether they are published or not. The documents may come from teaching and research institutions in France or abroad, or from public or private research centers. L’archive ouverte pluridisciplinaire HAL, est destinée au dépôt et à la diffusion de documents scientifiques de niveau recherche, publiés ou non, émanant des établissements d’enseignement et de recherche français ou étrangers, des laboratoires publics ou privés. Report of calibration of the tested technologies integrated in the DIGISOIL mapping tool Maud Seger, Isabelle Cousin, Arlène Besson, Raluca Maftei, Frédéric Andre, Sébastien Lambot, Julien Thiesson, Francesca Garfagnoli, Sandro Moretti, Antoine Stevens, et al.

Characterizing water processes at the field scale requires an accurate and high‐resolution description of the variability of representative state variables, such as water content. Obtaining these data, however, is unrealistic with conventional soil water sensors; we therefore propose an empirical approach to measure water content based on electrical resistivity. This geophysical method provides exhaustive and time‐repetitive information on the resistivity of a DC signal. Resistivity can be used to estimate water content, although the interpretation is not straightforward. As the approach is inexpensive and allows for repeated high‐resolution measurements, its potential benefits for the monitoring of soil water processes at the field scale warrant greater investigation. Soil electrical resistivity and soil water content were monitored at the field scale on four dates in 2006, by MuCEP (MultiContinous Electrical Profiling), which gives measurements at high spatial resolution, and by precise measurements of soil water content. The spatial organization of soil water dynamics was extrapolated from the geostatistical analysis of the spatial and temporal variability of electrical resistivity, and then improved data were obtained for the whole of the studied area. Homogeneous zones were then delineated and compared with soil units defined on a soil map. We demonstrated that the zones that had less than average soil water content over time for the whole area corresponded to those zones that had greater than average electrical resistivity values over time. The spatial similarity between these zones and the soil units defined on the soil map suggested that water flows were mainly vertical in the field. Nevertheless, our method could be used to characterize some specific hydrodynamic processes, such as lateral flows or upward capillary flows, that are usually difficult to characterize from the information derived from the soil map.

The aim of this article is to present a strategy to interpret the hydraulic functioning of a small field area by using measurements of the soil electrical resistivity. The spatial soil electrical resistivity was recorded at a high resolution on a 2 ha area by the MultiContinous Electrical Profiling (MuCEP) device at two dates. These apparent electrical resistivity measurements were firstly interpreted in terms of local electrical resistivity by I D inverse modelling to estimate the real resistivity of the soil. These interpreted electrical resistivity data were then transformed into soil water content values and soil water potential values by the use of independent punctual data of water content and the use of the water retention curve determined by laboratory data. Our analysis has permitted us to describe the spatial variability and temporal evolution of the hydraulic functioning at high resolution from electrical resistivity data. The interpretation of the water content and matric potential maps demonstrated that some soil hydraulic processes, such as lateral overland flow, can occur in the studied zone. They would never have been detected by local measurements of soil characteristics or by the use of the soil map. To cite this article: L Cousin et al., C R. Geoscience 341(2009). (C) 2009 Academie des sciences. Published by Elsevier Masson SAS. All rights reserved.

One of the challenges in soil science is to understand the relationships between electrical resistivity and other soil properties. Indeed, electrical resistivity is a complex soil electrical property that is affected by various soil parameters that can interact. Soil temperature plays a central role among all of the factors that significantly influence electrical conductivity. To determine the effect of the other soil parameters, the effect of temperature is commonly corrected on the experimental data using conversion models. These models have been developed from specific experimental data (usually measurements on soil solutions) but are extensively used not only on solutions, but also on disturbed or undisturbed samples or even on field experiments. We review several existing conversion models described in the literature and test their limits of validity on results of laboratory experiments on undisturbed soil samples at various water contents, clay contents, and temperatures. Our study shows that the models are reliable for correction of the effect of temperature when the volumetric soil water content is high, that is, near saturation. To better correct the temperature influence on the electrical resistivity measured on undisturbed soil samples with varying water content or clay content, a new conversion model dependent on only one parameter was developed. This useful tool still has to be confirmed over a large range of soils and for temperatures greater than 20 °C.

One of the challenges in soil science is to understand the relationships between electrical resistivity and other soil properties. Indeed, electrical resistivity is a complex soil electrical property that is affected by various soil parameters that can interact. Soil temperature plays a central role among all of the factors that significantly influence electrical conductivity. To determine the effect of the other soil parameters, the effect of temperature is commonly corrected on the experimental data using conversion models. These models have been developed from specific experimental data (usually measurements on soil solutions) but are extensively used not only on solutions, but also on disturbed or undisturbed samples or even on field experiments. We review several existing conversion models described in the literature and test their limits of validity on results of laboratory experiments on undisturbed soil samples at various water contents, clay contents, and temperatures. Our study shows that the models are reliable for correction of the effect of temperature when the volumetric soil water content is high, that is, near saturation. To better correct the temperature influence on the electrical resistivity measured on undisturbed soil samples with varying water content or clay content, a new conversion model dependent on only one parameter was developed. This useful tool still has to be confirmed over a large range of soils and for temperatures greater than 20 °C.