Reduced tillage and organic fertilizer application usually result in an increase in soil aggregate stability (AS). However, the magnitude of the effects can vary with soil properties and season. The aim of this study was to investigate AS dynamics over three seasons in a soil under various tillage and fertilization practices. The study was performed under three tillage practices (moldboard plowing (MP), surface tillage (ST) and no -tillage (NT)) and two types of fertilizer (poultry manure and mineral) seven and eight years after their establishment in Northwest France. AS was measured in three different seasons: spring, summer and winter. Soil properties that potentially influence AS such as organic carbon (OC), hot-water extractable carbohydrates (HWEC), water content (WC) and water repellency (WR) were also studied. On average, for all sampling dates, AS was 34% higher under NT than MP. Conversely, the effect of ST on AS varied with sampling date with values close to NT in mid -spring and summer, and values close to MP in early spring and winter. Poultry manure increased AS by an average of 12% regardless of sampling date or tillage practice. Variations in AS due to management practices were related to OC (r = 0.92) and HWEC (r= 0.88). Differences in AS between sampling dates were slightly greater than the effects of management practices. On average across management practices, AS increased by 47% from early spring to summer and decreased by 59% in winter. These variations were related to soil WC (r= -0.67) and WR (r= 0.72) at time of sampling. We suggest that seasonal variations in AS were at least partly due to variations in WC which acted physically by modifying the water entry rate into the aggregates and slaking effects. In contrast, the long-term AS dynamics were related to the organic matter dynamics, which are controlled by management practices. Because of the predominant effect of climate on AS, we suggest measuring AS in winter and summer to better estimate the effects of management practices on soil erodibility in this region. (C) 2017 Elsevier B.V. All rights reserved.

Several studies have emphasised the ability of Near Infrared Reflectance Spectroscopy (NIRS) to identify surface earthworm casts in the field. However, less is known about casts deposited within the soil, which usually represent the majority found in the field. This study tested the ability of NIRS to identify belowground casts in agricultural systems. Casts and surrounding soils were sampled at depths of 20-30 cm in a loamy soil under no tillage for 12 years. To distinguish different types of cast, sizes and orientations relative to the horizontal plane were measured. NIRS analyses and analyses of carbon and nitrogen content were also performed to compare casts to surrounding soils. Casts were classified into 4 size classes, with no preferential orientation. Cast carbon and nitrogen content were not influenced by their size and did not differ from surrounding soils. PCAs performed on the NIRS data did not allow casts to be differentiated from surrounding soils, regardless of size class. However, soil aggregates were clearly differentiated probably due to their spatial distribution in the soil. Although this study did not identify specific NIRS signatures for casts, it shows the utility of this method to investigate the origin of the soil consumed by earthworms. In our case, NIRS analyses suggest that the high bulk density of the soil (1.42 g cm(-3)) forced ingestion by endogeic earthworms, simply to move around, without preferential selection for organic matter. Consequently, their casts were deposited a few mm from where they had ingested soil with similar organic matter quality. (c) 2013 Elsevier B.V. All rights reserved.

We studied the combined effects of reduced tillage and animal manure on soil structure and hydraulic conductivity (K) in the 2-10 and 12-20cm layers in a loamy soil. The study was performed at the end of a 7-yr field trial and included three tillage treatments (mouldboard ploughing until 25cm depth: MP, shallow tillage until 12cm depth: ST, no-till: NT) and two fertilizer application treatments (mineral or poultry manure). Soil structure was assessed through bulk density ((b)), micromorphological and macropore-space characteristics. K was measured in situ at -0.6, -0.2 and -0.05kPa. Untilled layers had a vermicular microstructure resulting from earthworm activity, whereas tilled layers displayed a mixture of crumb and channel microstructures. Untilled layers had the highest (b) and twice as much lower total macroporosity area (pores>240m in equivalent diameter) than tilled layers, reflected by the smallest area of macropores 310-2000m in diameter and the smallest area of large complex macropores. K under untilled layers was 12-62% lower than that under tilled layers, but differences were statistically significant only at -0.05kPa in the 2-10cm. No significant interaction between tillage and nutrient application treatments was detected for all properties. Compared with mineral fertilizer, poultry manure resulted in a similar (b) but 20% greater total macroporosity area and 30% higher K at -0.2kPa. Overall, the sensitivity of soil structure and K to poultry manure were relatively small compared with tillage. We suggest that cultivation practices other than animal manure application are needed to improve physical properties under reduced tillage.

Processes and rate of macroporosity changes following heavy traffic in forest ecosystems are seldom studied. The aim of this study was to determine the ability of forest soils to regenerate their macroporosity naturally. The study was performed on 2 silty temperate-forest soils classified as sensitive to compaction located in north-eastern France. Macroporosity was measured in control and trafficked plots at 3 depths (0–7, 15–30 and 30–45cm) over 2–3years. Soil macroporosity characteristics (shape, size and orientation) were assessed on polished sections through 2D-image analysis and micromorphic observations. Immediately after heavy traffic, macroporosity decreased by 96 to 49% from 0 to 45cm in depth. Natural regeneration of macroporosity occurred in the upper 7cm of soil, while the soil below remained compacted. Small and medium macropores (0.05–0.8mm2) dominated by rounded and irregular pores regenerated completely. Large macropores (>0.8mm2) originally dominated by vughs, mammilated vughs and channels rarely regenerated and were gradually replaced by horizontally oriented planar pores. Our results suggest that initial stages of natural macroporosity recovery are likely due to plant-root penetration and physical processes (shrink–swell, freeze–thaw), whereas recovery due to fauna activities appears later.

Earthworm casts weathered by rainfall are difficult to differentiate from surrounding soil aggregates. We tested the hypothesis that morphological characterisation of soil aggregates by 2D-image analysis helps to perform this differentiation. Compact surface casts produced by Amynthas khami and surrounding aggregates lacking visible signs of biological activity (control) were left to disaggregate by natural rainfall and were separated into five size classes (10–5, 5–2, 2–0.5, 0.5–0.25 and <0.25 mm). The external shape and pore-space characteristics of aggregates were measured by image analysis. Casts >2 mm were characterised by less surface roughness and similar round shape than control aggregates. However, casts and control aggregates <2 mm had a similar external shape. The structural porosity of casts >0.25 mm was lower than that of control aggregates, whereas their textural porosity was similar. Therefore, this study demonstrates that measuring the porosity of soil aggregates by 2D-image analysis is a better indicator of earthworm-aggregate origin than external shapes.

In cultivated soils, Soil structure mainly results from climatic, anthropogenic and biological processes. Nevertheless, few field methods evaluating the quality of soil structure consider the contribution of biological processes. In order to include earthworm biostructures in the field description of soil-structure, an original method is proposed in this paper. Soil profiles under different agricultural practices were examined to distinguish soil-structure patterns, notably those resulting from earthworm bioturbation. The relevance of naked eye observation was tested by a micromorphological approach, using image analysis on thin sections. Then, the application of this method was illustrated by mapping soil profiles.Our study led to the creation of a typology (i.e. classification system) of eleven soil-structure patterns, taking into account anthropogenic processes (e.g. compaction, soil tillage), root activity and earthworm activity. Seven patterns were attributed to earthworm activity in the form of burrows or casts. Three burrow features were distinguished, differentiating between filled burrows, or empty burrows with a brown cutan or without visible cutan. Four patterns of cast packing were distinguished, differentiating between cast aggregates that were fresh, welded, compacted, or combined with burrow features. This typology appears relevant for developing a field tool to describe and spatially quantify soil structure. (C) 2011 Elsevier Masson SAS. All rights reserved.

In the French concept of deep nuclear waste repositories, the galleries should be backfilled with excavated argillite after the site has been filled. Some additives like lime could be used to improve the mechanical characteristics of the argillite. After thousands of years, the degradation of the concrete lining of the galleries will generate an alkaline solution (pH value > 12) that will diffuse through the backfill. This study presents the effect of a saturated Ca(OH)2 solution circulation through lime-treated sample at 60 °C for 3, 6 and 12 months, respectively. The effect of such circulation on the lime-treated Manois argillite (MA) was assessed by petrographical examination coupled to image analysis and scanning electron microscopy (SEM) equipped with energy dispersive X-ray (EDX) analyser of soil pieces. The objective of this study is to make the link among the mineralogical transformations, the textural and mechanical changes produced in the compacted clayey soil as a consequence of the alkaline solution circulation.

Endogeic earthworms significantly modify soil aggregation and porosity, which in turn control water flow in soil. This study aimed to determine how the earthworm casting activity influences soil porosity and its dynamics. The main hypothesis was that the deposition of belowground water-stable casts increases soil porosity and its water stability. First we quantified cast production by the endogeic earthworm species Metaphire posthuma under laboratory conditions for 15 days. Secondly, casts and the bulk soil were analysed for structural stability to water and were packed in soil and subjected to wetting under various conditions and energy levels. The shape and size of pores were measured by image analysis.Almost all casts (98%) were produced belowground. M. posthuma produced approximately five times its own weight per day. Casts were depleted in C and were more easily disaggregated by water than the bulk soil. Although casts initially led to larger soil porosity (on average 50%), their structure was unstable. As a consequence, water inputs led to a faster decrease in soil porosity in the presence of casts. Large pores in between casts were rapidly replaced by small elongated and rounded pores. These results suggest that cast lifespan and associated porosity are of primary importance in the regulation of soil porosity turnover and the ecological functions that are under its control. Our findings suggest that in the field, the low stability of casts is likely to lead to a rapid compaction of the soil after rainfall events. However, high levels of cast production may prevent soil porosity from being broken down. Soil structural porosity thus depends on the balance between the production and degradation of casts. Improvements to the soil structure will occur when the former predominates. (C) 2010 Elsevier B.V. All rights reserved.

In temperate soils, there has been little study of the abundance and water stability of belowground earthworm casts under different tillage systems and soil depths. The aim of this study was to determine the effects of earthworm activity on soil aggregate stability under various tillage systems. Three tillage treatments were compared (moldboard plowing (MP), surface tillage (ST) and no-tillage (NT)). We present here an original method by which earthworm casts were quantified via image analysis at 2- and 12-cm depths. In addition, soil aggregate stability expressed as the mean weight diameter (MWD) and factors involved in soil aggregate stabilization such as soil organic carbon, hot-water extractable carbohydrate content (HWEC) and water repellency (WR) of aggregates were measured in earthworm casts and bulk soil. In superficial soil layers, the relative cast abundance was small and more abundant under NT than the ST and MP treatments. At 12cm, the relative cast abundance doubled irrespective of the tillage treatment and tended to be higher with conservation tillage (i.e., NT and ST). Moreover, the MWD increased in casts compared to the bulk soil in this deeper layer. The increase in MWD in casts was explained in part by the increase in soil organic matter (carbon content and HWEC) and the WR. For the two depths, we found a positive relation between the MWD from the bulk soil and casts among the tillage treatments. We conclude from this study that casts located at a 2-cm depth did not participate in soil aggregate stabilization, while at 12cm the greatest structural stability observed under conservation tillage was explained in part by the production of casts.

In the sandy soils of northeast Thailand, root development is generally limited to the topsoil (0-20 cm depth) but a simple slotting intervention (20-40 cm) significantly increased the root frequency in the slotted material (E,It) compared with the undisturbed subsoil (E horizon). The aim of this study was to investigate the consequences of slotting on the soil structure by analysing at different scales the pore characteristics of the original soil profile and of the soil material inside the slot. These characteristics were studied using bulk density measurements, image analysis of thin sections and mercury porosimetry. Our results showed that the total porosity of the E horizon and E,,,, material was similar when measured in 100 cm 3 cylinders, but that the pore size distribution had been changed by slotting. The unaltered E horizon contained mainly small pores characterized by a narrow distribution related to close packing of the sand grains, associated with some biological macropores probably with poor continuity as they did not contain roots despite their size. On average, pores were larger in the E-slot material, with a broader distribution resulting from looser packing of the sand grains but with fewer biological macropores. Although slotting reduced the number of biological pores, the looser packing appeared to be more favourable to root development than the presence of macropores in the E horizon. Finally, the comparison of the porosity in the different horizons with the porosity of the E-slot material, indicated the significance of the closeness of the sand packing on root development.

We studied soil hydraulic conductivity (K) and porosity in five combinations of soil tillage and cover crop management systems. Treatments were winter wheat (Triticum aestivum L.) grown on a conventionally tilled soil (CT), on a no-till soil (NT), and on an NT with three different cover crops: red fescue (Festuca rubra L.; Fr), bird's-foot-trefoil (Lotus corniculatus L.; Lc) and alfalfa (Medicago sativa L.; Ms). Measurements were made on a loamy soil in Grignon, France, in November 2004, May 2005 and October 2005. K and mean size of hydraulically active pores were measured in situ at three water potentials (-0.6, -0.2 and -0.05 kPa) at the soil surface and at 10 cm depth. In November 2004 and May 2005, pore space was described using 2D image analysis of pores on undisturbed soil samples in the 0-10 cm layer and in the 10-20 cm layer. The major differences were caused by soil tillage that created two heterogeneous soil layers and increased K in the 0-10 cm layer relative to NT. The effects of cover crop on K and porosity were not affected by the root type: there were no major differences between the grass cover crop (fibrous-root type) and the leguminous ones (tap-root type). However, we recorded larger functional pores and more tubules in the no-till treatments with a cover crop, compared with the no-till treatment without cover crop; this was probably the result of root activity. Although these changes generally did not result in larger values of K, they participated in the maintenance of soil structure and K over time.

Selenium is an essential nutrient that is potentially toxic: one of its radio-elements is also a component of long-lived radioactive waste for which long-term deep geological storage is envisaged. The chemistry of Se in soils is complex and very sensitive to redox potential and microbial activity which largely determine its oxidation state and chemical form. The dynamics of Se have been extensively studied in soils where it is deficient, and even more so when concentrations are potentially toxic. In contrast, relatively little information is available on the fate of Se in soils at intermediate concentrations (1-5 mg kg(-1)). Some chemical reactions and biological processes that influence Se dynamics may be strongly concentration dependent. We have followed microbial activity by monitoring soil gas composition and Se volatilization and measured changes in Se fractionation using chemical extractions in a column of aggregated soil. A small proportion of soil Se was accumulated in the leaves, stems and fruits of tomato plants. Net Se volatilization losses were small (0.12% in a two-month period). There was a considerable upward movement of freshly added Se, but not of native soil Se. This vertical mobility was greater than that predicted from solute movement driven by evaporation. Selenium was strongly immobilized at the water-saturated, anoxic base of the soil columns. Straw amendment and the growth of a tomato plant did not lead to stronger association with soil organic matter. It was not possible to correlate changes in fractionation of Se between treatments and along a soil profile with the calculated fraction of anoxia, except in the completely anoxic zone. (C) 2007 Elsevier B.V. All rights reserved.

The evolution of clay soil porosity is currently demonstrated via the shrinkage curves in a large water content domain spreading from a shrinkage limit to a liquidity limit. In fact, the parallel between in situ profiles and the shrinkage curves in such a large water content range is difficult to obtain because of the lack of earth pressure in the laboratory tests and in situ limited water contents. The vertical distribution of porosity throughout a clay-rich marsh soil profile was studied in a grassland field with samples taken from the soil surface characterized by water contents near their shrinkage limit down to 2.00 m deep saturated sediments over their liquidity limit. The depth of the plasticity limit isolates a soil in a solid state characterized by a vertical prism-like structure from a plastic to pseudo-liquid state in depth. The porosity was calculated from the measurements of the density of intact samples by double weighing and image analysis of 100 cm(2) polished sections. The initial structure of clay soil was maintained by impregnation based on water-acetone-resin exchange. An ultraviolet photo luminescent pigment added to the resin allowed the capture of images from which shrinkage cracks and microporosity of the clay rnattix were easily separated. The distribution of porosity between the shrinkage crack mesoporosity and the clay matrix microporosity was evaluated after the mathematical decomposition of the grey level curves characteristic of each level. Vertical evolution of the porosity distribution from the soil surface in a solid state to the plastic and pseudo-liquid sediment in depth was presented on the shrinkage curve of the clay material. The measurements point out how the clay matrix microporosity and mesoporosity of shrinkage cracks are complementary and the role of the scale effect on the shrinkage curve. The analysis of images captured on an optical microscope under polarized and analyzed light and the SEM observation of freeze-dried samples demonstrated the isotropic arrangement of the clay particles in typical "honey-comb' architecture in the in situ plastic-to-liquid saturated domain. Eventually the distribution of porosity through the profile results from the evolution of the initial "honey-comb" microstructure of the sediment induced by the desiccation phenomenon. It is governed by the depth of plasticity limit of the clay material and by the depth of the water table. (c) 2007 Elsevier B.V. All rights reserved.

The aim of this work was to study the effects of soluble aluminium on the morphology and growth of the adventitious root system, aerial biomass and grain yield of maize (Zea mays). The analysis focuses on two hybrid cultivars (Al-sensitive HS7777 and Al-tolerant C525M). Experiments were carried out in the field and in a rhizotron in Curitiba, Paraná, Brazil. In the field, four levels of lime application were used: T0 = 0 t ha−1, T1 = 3.5 t ha−1, T2 = 7.0 t ha−1, and T3 = 10.5 t ha−1. Two levels were used in a rhizotron: T0 and T3. In the surface horizon (0–15 cm), the Al concentrations of the soil solution were: T0 = 15, T1 = 5.1, T2 = 4.4, and T3 = 3.1 μM. In the field, neither Al concentration in the soil solution nor cultivar affected the number of primary adventitious roots per internode or the total number of primary adventitious roots. However, root diameter, plant population and grain yield of the two cultivars confirmed the differences in Al tolerance between them. Al was observed to have an adverse effect on the grain yield from C525M, while low yields from HS7777, at all levels of Al, precluded any response to liming. In the rhizotron studies, Al concentration and cultivar affected the root branching and total root length. Cultivar C525M had more branches and total root length than HS7777, mainly at low concentrations of soil Al solution, leading to greater spatial colonization of the soil down to 0.9 m depth.

Earthworm activity produces changes at different scales of soil porosity, including the mesoporosity (between 1.000 and 30 mum eq. dia.) where both water retention and near-saturated infiltration take place. At this scale, the structural changes are poorly described in temperate agricultural systems, so we do not yet fully understand how these changes occur. The present study was conducted to determine the relationships between the morphology of the mesopores, which is mainly affected by earthworm activity, and the hydrodynamic behaviour (near-saturated infiltration) of topsoil under different agricultural managements inducing a large range of earthworm populations.Investigations were carried out at the soil surface in three fields under different management practices giving rise to three different earthworm populations: a continuous maize field where pig slurry was applied, a rye-grass/maize rotation (3/1 year, respectively) also with pig slurry, and an old pasture sown with white clover and rye-grass.Pore space was quantified using a morphological approach and 2D image analysis. Undisturbed soil samples were impregnated with polyester resin containing fluorescent pigment. The images were taken under UV light, yielding a spatial resolution of 42 gin pixel(-1). Pores were classified according to their size (which is a function of their area) and their shape. Hydraulic conductivity K(h) was measured using a disc infiltrometer at four water potentials: -0.05, -0.2, -0.6, and -1.5 kPa. The abundance and ecological categories groups of earthworms were also investigated. Continuous soil tillage causes a decrease in both abundance and functional diversity (cf. maize compared with old pasture) when soil tillage every 4 years causes only a decrease in abundance (cf rotation compared with old pasture). There were no relationships between total porosity and effective porosity at h = -0.05 kPa. Image analysis was useful in distinguishing the functional difference between the three managements. Fewer roots and anecic earthworms resulted in fewer effective tubular voids under maize. There were fewer packing voids in the old pasture due to cattle trampling. Greater hydraulic conductivity in the pasture phase of rotation may arise from a greater functional diversity than in the maize and absence of cattle trampling compared with the pasture. We point to some significant differences between the three types of agricultural management.A better understanding is required of the influence of agricultural management systems on pore morphology. This study provides a new methodology in which we consider the earthworm activity as well as community in order to assess the effects of agricultural management on soil structure and water movement. (C) 2003 Elsevier B.V. All rights reserved.

In a central Amazonian pasture, a single earthworm species, Pontoscolex corethrurus, becomes very abundant (400 ind. m(-2)) after forest clearing. Its casts form a compact, continuous and impermeable crust with a thickness of 20 cm. To analyze the structural modifications, we established a field experiment in which soil blocks from the forest were implanted in the pasture, and soil blocks from the pasture were implanted in the forest. The objectives were (1) to verify the formation of the compact crust at the soil surface in pasture environment, (2) to evaluate the time necessary for the formation and the destruction of this crust, and (3) to find out if the crust formation was a reversible process. We used quantitative morphology to identify the biogenic structures formed by different fauna groups and to quantify the modifications in the solid phase as well as the resulting porosity. For the soil depth 0-5 cm, the measured porosity was 48% in the forest and 16% in the pasture. After 1 year, the blocks of forest soil installed in the pasture presented a porosity of 26%, and the blocks of pasture soil installed in the forest presented a porosity of 34%. There were significant differences between the control blocks and the exchanged blocks. The results demonstrate that the processes of formation and destruction of the biogenic structures are reversible. Approximately 1 year is necessary to re-establish the equilibrium between the exchanged blocks and the control blocks.This experiment illustrates the compacting effect of P. colethrurus. In addition, the small millimetric pores, which are formed by termites in the blocks of pasture soil implanted in the forest, show the decompacting effect of certain termite groups. (C) 2001 Elsevier Science B.V. All rights reserved.

In the absence of irrigation, the cultivation of cereals in semi-arid zones provides a poor yield. To study the consequences of fallow tillage on the soil structure and hydraulic properties, we conducted an experiment from 1991/1992 to 1997/1998 using various techniques (chisel or disc plough, early or late tillage) on a calcisol of the high plateaus of eastern Algeria. In the middle of the tilled horizon (between 8 and 25cm depth), we measured the near-saturated hydraulic conductivity at four soil water tensions (or potentials) using multidisc infiltrometers, and quantified the morphology of the macropore space using image analysis. Results indicated that tillage increased soil conductivity mainly at low water potential (0.06 and 0.3kPa). This increase was more significant with the chisel (1.84×10−5ms−1 at 0.06kPa) than with the disc plough (1.25×10−5ms−1), but was attenuated during the crop cycle. Significant differences appeared between tillage treatments for surface macroporosity (5.1% for chisel, 1.1% for disc), pore-space morphology (thin cracks separating compact aggregates under disc, loose fine soil assemblage separating smaller aggregates under chisel) and porosity distribution pattern (equivalent diameter of the macropores varied from 1mm under disc to more than 2–3mm under chisel). Analyses of porosity distributions indicate a possible relationship between the structure of the surface horizon and soil hydraulic properties. Durum wheat grain yield varied from 1.08 to 2.85tha−1 during the 7-year trial. Grain yield under shallow tillage was significantly higher than under disc plough treatment during wet years. Tillage-date varied across seasons and early tillage effect was more apparent when the fallow season was less rainy.

Inoculation of Pontoscolex corethrurus (Glossoscolecidne, Oligochaeta) in a Peruvian ultisol under several treatments (without or with organic input) has been previously shown to increase macroaggregation and bulk density and to decrease water infiltration and soil moisture. In the present study, we used image analysis of thin sections of soil to understand the impact of earthworm on the structure of the upper layer of the soil. Morphological analysis allowed to quantify the abundance of casts, soil compactness, pore morphology and connections between different pore classes. This approach was applied to experiments carried out at Yurimaguas (Peru), in four plots. Two of them had been inoculated with Pontoscolex corethrurus. In each case, one control plot was conducted without organic input, the other with crop residues and legume green manure. Morphological parameters were measured in fourteen horizontal sections within the first 3 cm. They showed compaction of soil surface due to cast coalescence in plots with earthworms but without organic input and illustrated the typical crumb structure induced by earthworms in plots with organic input. (C) 2000 Editions scientifiques et medicales Elsevier SAS.