Isabelle Cousin

Influence of rock fragments on the water retention and water percolation in a calcareous soil

Abstract The water retention properties of a calcareous soil containing rock fragments have been determined in the laboratory thanks to pressure plate measurements done on both the fine earth and the rock fragments from the soil. The available water content (AWC) has been calculated from these data. We have shown that when the rock fragments are neglected, the AWC can be overestimated by 39%. When we do not neglect their volume but when their hydraulic properties are not considered, the AWC can be underestimated by 34%. By using a reservoir model, we have also calculated the effect of rock fragments on water percolation to groundwater. Depending of the climatic characteristics of the year, the underestimation of percolation when we neglect the rock fragments can reach up to 14.9% and the overestimation when we neglect their hydraulic properties can be equal to 15.8%. These findings emphasise the role of the rock fragments on the water supply in stony soils.

Tillage and traffic effects on soil hydraulic properties and evaporation

Abstract Evaporation is a major component of the water loss from the soil whose structure is modified by traffic and tillage. This study was undertaken to analyse, in field conditions, the effect of tillage and traffic on soil structure and evaporation, and to determine the role of the change in hydraulic properties on soil drying using water transfer model. Three structures of the ploughed layer were formed in a loess soil (Luvisol Orthique) and a calcareous soil (Rendzina): a fragmentary structure created by deep soil tillage in autumn or in spring (rotary tiller at 30 cm depth), a compacted ploughed layer created by compaction under wet conditions. The bulk density varied from 1.16 to 1.63 Mg m−3 in the loess soil, from 1.00 to 1.45 Mg m−3 in the calcareous soil. Evaporation was calculated from the change in soil water content and matric water potential profiles measured during the spring season. Soil hydraulic properties were estimated using an inverse modelling method applied to field measurements of water content and water potential or the Wind method. Soil structure greatly affected the drying of the calcareous soil: the evaporation of the compacted plot was about two times that of the tilled plot. The compacted plot dried out homogeneously, with a soil surface which remained wet. Evaporation mainly concerned the first 15 cm of the ploughed layer created by autumn or spring tillage. This effect of soil structure on evaporation was not observed in the loess soil. The unsaturated hydraulic conductivity was higher in the compacted plot than in the tilled plots in the calcareous soil. It was similar in the three plots of the loess soil, because of the formation of relict structural pores by compaction. Experimental and numerical results showed that unsaturated hydraulic conductivity is of major concern in soil drying and that the albedo and surface roughness have minor effects if any. The possible relict structural pores have to be characterised in various soils, as a function of soil sensitivity to compaction, traffic and tillage conditions.

Soil drainage as an active agent of recent soil evolution: a review.

Abstract While research on pedogenesis mainly focuses on long-term soil formation and most often neglects recent soil evolution in response to human practices or climate changes, this article reviews the impact of artificial subsurface drainage on soil evolution. Artificial drainage is considered as an example of the impact of recent changes in water fluxes on soil evolution over time scales of decades to a century. Results from various classical studies on artificial drainage including hydrological and environmental studies are reviewed and collated with rare studies dealing explicitly with soil morphology changes, in response to artificial drainage. We deduce that soil should react to the perturbations associated with subsurface drainage over time scales that do not exceeding a few decades. Subsurface drainage decreases the intensity of erosion and must i) increase the intensity of the lixiviation and eluviation processes, ii) affect iron and manganese dynamics, and iii) induce heterogeneities in soil evolution at the ten meter scale. Such recent soil evolutions can no longer be neglected as they are mostly irreversible and will probably have unknown, but expectable, feedbacks on crucial soil functions such as the sequestration of soil organic matter or the water available capacity.

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 into 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...

DIGISOIL: an integrated system of data collection technologies for mapping soil properties

The multidisciplinary DIGISOIL consortium intends to integrate and improve in situ proximal measurement technologies for assessing soil properties and soil degradation indicators, moving from the sensing technologies themselves to their integration and application in (digital) soil mapping (DSM). The core objective of the project is to explore and exploit new capabilities of advanced geophysical technologies for answering this societal demand. To this aim, DIGISOIL addresses four issues covering technological, soil science, and economic aspects: (i) development and validation of hydrogeophysical technologies and integrated pedo-geophysical inversion techniques; (ii) the relation between geophysical parameters and soil properties; (iii) the integration of derived soil properties for mapping soil functions and soil threats; and (iv) the evaluation, standardisation, and industrialisation of the proposed methodologies, including technical and economic studies.

The role of pebbles in the water dynamics of a stony soil cultivated with young poplars

Background and aimsStony soils are widespread and often support plant production; nevertheless, their physical properties remain poorly understood, particularly regarding the role of rock fragments in plant water uptake. Understanding the hydric interactions between rock fragments and fine earth in stony soils remains central to water management in the context of climate change.MethodsA soil water retention curve of stony soil was developed based on a water retention curve for both rock fragments and fine earth. Water transfer between fine earth, rock fragment and plant roots was monitored during experiments under controlled evaporation conditions.ResultsDuring desiccation, the water retention curves for fine earth and rock fragments exhibited water movement from the rock fragment to the fine earth. During our evaporation experiment, fine earth water content decreased as soon as desiccation started, whereas the rock fragments released water after several days. We demonstrated that rock fragments are a water reservoir for plants; plants can uptake water directly from pebbles or after it is transferred into surrounding fine earth. However, this transfer could not be measured due to the non-equilibrium state between the two phases. Furthermore, we exhibited how the water potential dynamics in fine earth containers cultivated with poplar was not influenced by the rock fragments content.ConclusionWater in rock fragments can be directly released to plants or released through fine earth, thereby reducing plant water stress during moderate drought periods. Therefore, the assumption that rock fragments constitute an inert phase inhibiting ecological soil functions must be completely reconsidered.

Distribution Of Major And Trace Elements At The Aggregate Scale In A Soil Naturally Rich In Trace Elements: A Spatial Approach Using Electron Microprobe And X-ray Microfluorescence Analyses

Major and trace element concentrations have been determined from thin sections of an unpolluted and well-structured B horizon that presents macroscopic heterogeneous aggregates. Electron scanning microprobe and X-ray microfluorescence analyses have enabled the characterization of Fe, Si, Al, Ca, K, Cu, Cr, Co, Zn, and Ni concentrations. The structure of the aggregate was demonstrated as being complex, with an inner part richer in Fe and fine material and an outer part with abundant small quartz minerals. Iron, Cr, and Cu concentrations were much higher in the inner part of the soil aggregates, whereas Zn and Ni concentrations were not related to any location in the aggregate. Water logging during winter has been identified as the major process that modifies the spatial location of Fe in the aggregates. Swelling and shrinking caused by seasonal changes have been demonstrated as responsible for falls of allochthonous material from the upper part of the soil profile that results in modifications of trace elements concentrations in the outer part of the aggregates. This study showed the ability of quantitative microscopic techniques in describing the trace element spatial distribution at the aggregate scale in soils.

The benefit of using a covariate for minimizing the sample size needed to estimate mean value of a target variable at field scale

Two-phase sampling design with a covariate gives an unbiased mean value at field scale.Various second phase sampling strategies are easily implemented using R software.The precision of the estimates are assessed for the different sampling strategies.Accounting for a covariate in the second phase of the sampling improves the precision. The objective of this paper is to determine the mean value of Available Water Capacity (AWC) of a soil at field scale in the context of improving the water use efficiency in agriculture. The reasoning in this work consists in determining the minimum number of locations where AWC has to be measured in a 9ha field, using different two-phase sampling strategies, to obtain a mean AWC with an adequate precision. First, 44 locations spaced on a regular square grid were chosen by a systematic random sampling (first phase of the sampling). AWC and Soil Electric Resistivity (SER) were estimated at each location. The 44 locations were then subsampled using four sampling methods and by considering subsets of various sizes, from 1 to 10 (second phase of the sampling). For each combination involving one sampling method and one subset size, 10,000 subsets were generated independently. Each subset was used to estimate one value of the mean of AWC for the field and thus, the average value for the means of the 10,000 subsets. For each combination, we computed the range L of the interval containing 95% of the 10,000 estimated means. As the more precise, the smaller L was the correct estimation for the corresponding combination. One sampling method for the second phase was the simple random sampling, and the three other used the SER as a covariate. The latter led to more precise estimates of the mean AWC than the simple random sampling. A threshold of 30mm, corresponding to one irrigation period in the study area was chosen as the minimum precision required. This threshold was not exceeded for a subset of 5 locations in the cases of sampling methods accounting for the SER as a covariate whereas 8 locations were required for the sampling method that ignores covariate.

The « VSOIL » modeling platform

Human actions and climate change induce modifications in soils and hydrosystems that must be predicted and evaluated. The soil is a fragile component of the ecosystem and it plays an essential role for primary production and water quality. Modeling is a powerful tool to simulate physical, chemical and biological modifications of the soil. Comparing model outputs to long term experiments is absolutely necessary to evaluate our understanding of the soil plant atmosphere system functioning and thus our ability to predict its evolutions.

Soil Drainage as an Active Agent of Recent Soil Evolution

Abstract While research on pedogenesis mainly focuses on long-term soil formation and most often neglects recent soil evolution in response to human practices or climate changes, this article reviews the impact of artificial subsurface drainage on soil evolution. Artificial drainage is considered as an example of the impact of recent changes in water fluxes on soil evolution over time scales of decades to a century. Results from various classical studies on artificial drainage including hydrological and environmental studies are reviewed and collated with rare studies dealing explicitly with soil morphology changes, in response to artificial drainage. We deduce that soil should react to the perturbations associated with subsurface drainage over time scales that do not exceeding a few decades. Subsurface drainage decreases the intensity of erosion and must i) increase the intensity of the lixiviation and eluviation processes, ii) affect iron and manganese dynamics, and iii) induce heterogeneities in soil evolution at the ten meter scale. Such recent soil evolutions can no longer be neglected as they are mostly irreversible and will probably have unknown, but expectable, feedbacks on crucial soil functions such as the sequestration of soil organic matter or the water available capacity.