Soil Trays Research Articles

Development of Wood-Plastic Soil Tray Composite (WPSTC) Using Polymerized Coir-Wood Dust for Green Roof Structures

Development of Wood-Plastic Soil Tray Composite (WPSTC) Using Polymerized Coir-Wood Dust for Green Roof Structures

Mitigation of aeolian erosion of loess soil by Bio-Stimulated microbial induced calcite precipitation

Microbial-induced calcite precipitation (MICP) is a soil amelioration technique that addresses various environmental and engineering concerns. Here, we present a study focusing on aeolian erosion control of loess soil from the Negev Desert (Israel). Changes in the treated soil's chemical, physical, and microbial community (abundance and diversity) were characterized following bio-stimulation of native, urea-hydrolyzing soil bacteria to achieve MICP. Bio-stimulation of the loess soil was induced in liquid media (batch experiments) and by spraying soil trays with stimulation media (urea and yeast extract). These experiments showed that the Negev loess could be readily stimulated to induce bacterial urea hydrolysis. Three to four daily sprayings were sufficient to achieve effective bio-stimulation, evidenced by a high hydrolysis rate and an alkaline pH. Erodibility experiments on a decimeter scale (50 cm x 50 cm trays) were performed on loess sprayed with treatment media with varying concentrations of urea and CaCl2, with a constant 1:1 M ratio. The effectiveness of the treatments was studied in a wind tunnel and by image analysis of desiccation cracks. Upscaling of the experiments to the large trays revealed a more complicated reality with urease activity, community composition, and calcium carbonate precipitation depending on the concentration of the treatment medium. Specifically, we show that a twofold reduction in the area and length of the desiccation cracks can be achieved by spraying the soil with a 0.5 M solution, resulting in effective MICP or a high concentration treatment (>1M solution) without achieving MICP. Our results show that erosion mitigation in loess soil depends on an interplay between biotic and abiotic processes based on the treatment media concentration and provides a necessary step for upscaling the bio-stimulated MICP strategy for future field implementations.

Variable response of particles and inorganic carbon of two different soils during splash erosion

Splash erosion caused by raindrops is the first stage of water erosion that detaches and transports soil particles. As an important component of soil particles, soil inorganic carbon (SIC) contains little information on its redistribution during splash erosion. In this study, two soils, purple soil and loess, were selected and placed in a soil tray with a diameter of 20 cm at the center of a splash tray, and a rainfall simulator was used to simulate three raindrop energies in experiments to investigate the migration of soil particles and SIC. The results showed differences in the amount and selective migration of splashed material between the soils, which was evident in the obvious sorting of the particle size of purple soil with distance and the insignificant change of loess soil. The SIC sorting characteristic performed differently in the two soils, that is, the SIC content of purple soil increased with particle size, while that of loess was the opposite. The enrichment and depletion of SIC during splash erosion varied with soil type, and differed from the general enrichment of soil organic carbon (SOC). The SIC enrichment ratio (ERIC) of purple soil was generally > 1, whereas the ERIC values of loess were < 1. In addition, multiple linear regression (MLR) models were established to predict the SIC content of splashed material. Rainfall splash plays an important role in SIC migration and may further affect the carbon cycle. These preliminary results provide a basis for further study of SIC response to rainfall splash.

Natural Salicylaldehyde for Fungal and Pre- and Post-Emergent Weed Control

A sustainable, alternative weed control strategy is developed using salicylaldehyde (SA; 2-hydroxybenzaldehyde) as an active ingredient. SA is a natural, redox-active small molecule listed as a Generally Recognized As Safe food additive by the European Food Safety Authority and the United States Food and Drug Administration. The repurposing of SA determined that SA possesses both pre- and post-emergent herbicidal, fumigant activity, where the emitted SA from the source completely prevented the germination of plant seeds and/or the growth of the germinated plants. As a proof-of-concept, we developed agricultural byproducts (tree nutshell particles) as SA delivery vehicles to the soil, thus helping the growers’ sustainable byproduct recycling program, necessary for carbon sequestration. In plate assays, SA emitted from the nutshell vehicles (0.15 to 1.6 M) completely prevented the germination of six invasive or native weed seeds (monocots, dicots). In Magenta vessel assays, SA emitted from the nutshell vehicles (0.8 to 1.6 M) not only prevented the germination (pre-emergent) of Lagurus ovatus (Bunny Tails Grass) seeds but also inhibited the growth (post-emergent) of the germinated weeds. We determined further that soil covering (soil pasteurization) could be one of the practices to effectively deliver SA to the soil, whereby 1.6 M of SA emitted from the nutshell vehicles prevented the germination of the L. ovatus seeds maintained in soil trays covered with plastic tarp at 22 °C, while 0.8 M SA allowed partial (15%) germination of the weed seeds. Of note, SA also possesses an intrinsic antifungal activity that overcomes the tolerance of the stress signaling mutants of filamentous fungal pathogens (Aspergillus fumigatus, Penicillium expansum) to the phenylpyrrole fungicide fludioxonil. Environmental degradation data available in the public database indicate that, once released to the environment, SA will be broken down in the air by sunlight or microorganisms and, thus, is not built up in aquatic organisms. Altogether, SA can serve as a safe, potent pesticide (herbicidal, fungicidal) ingredient that promotes sustainable crop production by lowering the pesticide burden in fields.

Сomparative analysis of methods for calculating stamp modules of soil deformation

Introduction. The purpose of the article is a comparative analysis of methods for calculating stamp modules of soil deformation regulated by various standards of the Russian Federation.Materials and methods. The experimental determination of the deformation modules for the soil of the roadbed was performed using stamp tests. The tests were carried out in a soil tray by loading and unloading a soil base compacted to the required compaction coefficient of 0.98. The load was applied by steps, and the stamp draft was measured after completion of deformation stabilization from each step. The criterion for stabilizing the deformation was a decrease in the speed to 0.02 mm / min and the time of application of the load, which should be at least 120 s. After measuring the elasto-plastic draft of the soil, the model was unloaded. Unloading is also carried out by steps. As a result, the dependences of the elasto-plastic and elastic draft of the soil model of the roadbed from the pressure in the form of hysteresis loops are constructed.Results. The calculations of the soil deformation modulus were performed according to the various methods regulated by the standards of the Russian Federation. The calculation results are grouped into data samples that are processed by mathematical statistics methods. When processing data, each sample is checked for the presence of gross errors. The data samples are checked for belonging to one general population. To check whether three samples belong to one general population, the Kruskal W. H. and Wallis W. A. criterion was applied. Based on this comparison, we made judgments about the significance of differences in the samples.Discussion and conclusions. To determine the deformation modulus of soil and road pavements made of granular materials, a method for calculating the modulus of deformation using a method that assumes a nonlinear dependence of deformations on pressures, described by a second-degree polynomial is recommended.

Studying the impact of geosynthetic materials on the strain-stress state of soil structures applicable to the mechanics of granular media

In the modern construction industry, a solution being successfully proven is the use of geosynthetic materials, applied as semi-holders, to increase the reliability and stability of soil structures. In connection therewith, solving the issues of expanding the range of methods and approaches to predicting the behavior of such structures under the activity of surface loads is a relevant task, since this is a vital factor in evaluating the designing arrangements made, including the use of geosynthetic materials. The aim of the studies according to this paper is to expand the pertinence of the mechanics of granular media (MGM) in order to assess the reliability of decisions made in the design of soil structures from pitifully durable soils, supported with geosynthetic materials, by comparing the obtained values with the results of full-scale tests and the values obtained by the limited component strategy. For this purpose, the paper presents a comparative analysis for the results of determining vertical stresses under the bridge reinforced with geosynthetic materials and its displacement, obtained by the mechanics of granular media and the limited component strategy. The results of laboratory tests, performed in a soil tray, were taken as verification data. The actual values of vertical stresses were determined using soil pressure sensors, and the values of displacement were determined using the movement indicator of the clockwork installed on the deflection meter of a die unit. An approach to determining displacement of a reinforced bridge using the mechanics of granular media was presented for the first time. The newly presented approach to determining displacement of an bridge, reinforced at the base with geosynthetic materials, allows us to conclude on its reliability, which significantly expands the applicability of the MGM as an alternative to the use of the limited component strategy. The aftereffects of contrasting the upsides of vertical anxieties under the bridge reinforced with geosynthetic materials and its displacement, utilizing the Plaxis programming bundle and the MGM dependencies, counting when contrasted and the consequences of lab tests, are presented. Based on the results obtained, a general conclusion was made on the possibility to use the MGM dependencies in deciding the example of the pressure dispersion and the values of displacement of reinforced bridges under the action of surface loads. The paper also discloses the promising directions of research in this area of geotechnical engineering.

Discovering the wild side of urban plants through public engagement

Societal Impact StatementThe Anthropocene has seen declining biodiversity inextricably linked to our societies, values, and choices. This requires ecologists to engage with the public in ecosystems such as cities to learn from and help inform their values and experiences regarding their role in urban nature. This article presents a transdisciplinary citizen science project on spontaneous urban vegetation in the context of urban botany, art‐science, and participatory research that engages with the ecology of cities. We address the interdependence of ecological and social networks, suggesting how plant ecology can become more relevant for society in the Anthropocene, while presenting a specific methodology for engaging the public with urban botany.Summary Cities are socio‐ecological systems that require new ways of thinking and engagement to successfully conserve biodiversity. In this article, we present the citizen science project Where Seeds Fall which was undertaken in the city of Zurich, Switzerland. It was developed in an “ecology with” cities approach seeking to conduct research with the humans living in the ecosystem while learning from and helping inform their values. Our project brings together the perspectives of ecologists, artists, and planners on the three themes of urban wastelands, spontaneous vegetation, and ecological connectivity. It is placed in the context of urban botany, environmental arts and participatory research. Volunteers placed trays of bare soil (without seeds) in their gardens and balconies and monitored what plants arrived and germinated. They then were able to share information about their trays (images, species lists) with one another through a spatially explicit web platform. The project was accompanied by public outreach events and artistic interventions in public space. This article presents the methodology of the project so that it can be replicated elsewhere. Based on the experiences with the project we discuss evolving transdisciplinary perspectives on wild plant biodiversity in cities.

Моделирование резания грунта при различных углах атаки лемеха рабочего органа стоечного рыхлителя методами фрактального анализа

The level of soil compaction is influenced by physical and mechanical properties, climatic conditions, the amount of annual precipitation, the type of cultivated crops, and other factors. Excessive compaction of the soil impairs water permeability and air access to the roots, resulting in reduced crop yields, increased soil erosion, reduced fertilizer efficiency, which leads to an increase in the cost of material and technical resources for tillage. Therefore, it is important to solve this problem with minimal energy and material costs. Such a solution is the loosening of the soil, which can be done naturally and with the help of mechanical loosening. (Research purpose) The research purpose is in evaluating the effectiveness of loosening the soil with a U-shaped ripper at different angles of the ploughshare using fractal analysis methods, which is necessary to reduce additional loads during further soil treatment. (Materials and methods) A dirt channel with a special cart was used to consider physical models of meliorative machines and specialized working equipment. (Results and discussion) Author conducted six experiments in a soil tray for each corner of the ploughshare separately. Nineteen ground sections were made. The structure of the soil before and after treatment depends on the mode of operation of the ripper model and the design features of its working bodies. (Conclusions) The more energy is spent on the treatment of homogeneous areas, the more the soil structure changes. To quantify the structural changes in the nature of the cultivated soil, we used its fractal characteristics, in particular, the fractal dimension. The soil sections have fractal properties, and, accordingly, fractal methods can be used for their analysis. The article proves the applicability of fractal methods in the analysis of the quality of tillage and the degree of its loosening.

First Report of Verticillium Wilt Caused by Verticillium dahliae Infection on Chinese Cabbage in Korea.

Chinese cabbage (Brassica rapa L.) is one of the most important vegetables in Korea due to its role as the main ingredient for the making of Kimchi. In June 2014, disease symptoms of leaves wilt, dry, and drop off on Chinese cabbage were observed in a Chinese cabbage farm located at Taebeak (37°26'50.7"N 128°95'50.0"E), Gangwon province, Korea. This disease was observed on approximately 35% of the plants in the field, causing an almost 10% decrease in total production. At the early stage of infection, the color at the edge of the plant foliage changed from green to yellow. As the disease progressed, infected leaves wilted, dried off, and detached from the plant. Soft rot that occurred at the base of the leaf stem and root tissues caused the infected leaves to dry and fell off the plant. To identify the causal agent, a small piece of infected leaf tissues was sterilized with 1% sodium hypochlorite solution for 1 min and rinsed with sterile water before it was transferred onto potato dextrose agar (PDA) media. The plates were then incubated at 25°C for 10 days in the dark. Fungal colonies grown on PDA media were of white-creamy in color with an abundance of mycelia and later develop into black color due to the formation of microsclerotia embedded in the media. Microscopic examination showed conidiophores and phialides were both appeared in a verticillate arrangement, whereas conidia were hyaline, smooth-walled, and ellipsoidal to oval with average size 5.4×2.5 µm (n=100). Microsclerotia appeared in elongate to an irregularly spherical shape and greatly variable in size. The morphological attributes of the fungal isolate described above were comparable to the characteristics of Verticillium dahliae Kleb. (V. dahliae) described by Hawksworth and Talboys (1970), and V. dahliae isolated from Chinese cabbage in Japan reported in Kishi (1998). Pathogenicity test was performed by soaking twelve individual Chinese cabbage seedlings for 15 min into fungal pathogen conidial suspension (1x106 conidium/ml) before transferred into soil tray. The same number of non-inoculated seedlings on the soil tray was used as a control. Inoculated and control plants were then covered with a plastic bag for 24 hours to maintain high humidity before transferred into the greenhouse (25°C). Seven days post-inoculation (dpi), treated plant leaves turned yellow, and soft rot was observed. At 10-dpi, plant leaf tissues dried off and severe soft rot occurred. Pathogenicity test was repeated three times and consistent results were obtained. The re-isolated fungal pathogen from the inoculated plants showed identical morphological characteristics to the original isolates, thus fulfilling Koch's postulates. For further identification, PCR amplification targeting Internal Transcribed Spacer (ITS) and RNA polymerase II gene (RPB2) regions were performed (Liu et al., 1999; White et al., 1990). Each PCR product was sequenced and deposited in the GenBank under the accession LC549667 and LC061275, respectively. Sequence analysis using BLAST showed that the nucleotide sequences of ITS and RPB2 DNA fragments are 99-100% identical to the reference strain of V. dahliae available in the NCBI database (MG585719, HE972023, XM_009652520 and DQ522468, respectively). Therefore, based on the results of morphological and molecular analyses, the fungal pathogen isolated from Chinese cabbage in this study was identified as V. dahliae and deposited in the National Institute of Horticultural and Herbal Science germplasm collection (NIHHS 13-252). Recently, due to high demand and a more competitive price, more Chrysanthemum farmers in Korea switch their crops to Chinese cabbage. Interestingly, the occurrence of V. dahliae infection was also reported to occur in Chrysanthemum plants in Korea (Han et al. 2007), which indicates a serious problem ahead to these farmers. Therefore, in this current study, the identification of V. dahliae pathogenic to Chinese cabbage will provide vital knowledge for the development of disease management strategies to minimize the loss of crop production. To our knowledge, this is the first report that V. dahliae causes Verticillium wilt disease on Chinese cabbage in Korea.

Stabilizing sand from dried-up lakebeds against wind erosion by accelerating biological soil crust development

Land degradation and the resulting desertification often lead to sand flowing from deserts and/or dried-up lakebeds and into habitable zones; a problem that has intensified in recent decades. We cultivated locally collected biological soil crust (BSC) bacteria (Bacillus subtilis strain) and cyanobacteria (Nostoc sp. and Oscillatoria sp.) from the dried-up bed of Lake Urmia, northwest Iran. To evaluate the ability of BSC to stabilize the sandy lakebed soil, bacteria and cyanobacteria were used to inoculate experimental trays of sandy soil from the same area, under laboratory conditions. After 120 days, we simulated winds at a speed of 72 km h−1 for three 10-min intervals (30 min in overall) to measure the sand transport rate as well as the durability and fragility of the BSCs during the wind erosion process, using an open circuit wind tunnel. We found that the bacteria, cyanobacteria, and cyanobacteria + bacteria inoculation reduced the sand flowing by 42.3, 96.6, and 95.9%, respectively, as compared to the control. We found that in addition to creating a protective cover on the soil surface, cyanobacteria created a strong bond between the soil particles through their exudation of exopolysaccharides and network of filaments, increasing the ability of the sand to withstand wind forces. Our inoculation technique was an effective and natural way to stabilize moving sand. Future research should replicate our methods under natural conditions to evaluate the potential for large-scale restoration.

An experimental bench for studying the processes of freezing-thawing of soil in the laboratory

In the article, the authors consider the problem of building buildings and structures on permafrost soils, provides a brief overview of ways to preserve the frozen state of base soils. The analysis of scientific works devoted to the thermal interaction of an engineering structure with permafrost soils is given. Conducting full-scale experiments in the conditions of the spread of permafrost soils is a laborious and expensive undertaking, therefore, as part of the research, an experimental stand was developed that allows one to study the processes of freezing and thawing soils in laboratory conditions. The experimental stand is a soil tray with rigid walls and a bottom with overall dimensions in the plan of 1000x1000 mm and a height of 1000 mm. The open system was modeled by placing perforated pipes at the bottom of the tray with a heating cable installed inside the pipes, maintaining a positive water temperature. To ensure one-sided and plane-parallel freezing, the side surfaces and the bottom of the tray were glued with a heater. To fix the temperature of the soil in the experimental bench and the air temperature in the freezer, the TEREM 4-1 measuring complex with DTS 1-1 soil temperature sensors is used. To fix the movements of the soil base in the experimental bench, ICH-50 dial indicators with a division price of 0.01 mm on a telescopic magnetic stand are used. To study the processes of freezing thawing of soils, the authors propose a series of experimental studies on water-saturated loams in laboratory conditions. A description is given of an experimental bench with a model of a thermostabilizer for studying the processes of freezing-thawing of base soils in laboratory conditions, and a methodology for conducting experimental studies is described.

Development and Research of Constructive and Technological Solutions Driven Drop-In Piles with Increased Bearing Capacity

The article presents the results of the study of the effect of the amount of large-size filler (fraction 5.0-0.65 mm), introduced into the fine sand at its angle of “internal friction”; the design of the developed pile with “pockets” on the side surface, which are filled with filler from the collar (funnel) on the surface of the soil and allows you to change the granulometric composition of the soil around the perimeter of the pile. Experimental studies of the interaction of the side surface of the models developed piles with large-size filler in the process of their driving in a soil tray with fine sand are presented, which showed that the proposed design and technological solutions increase the bearing capacity of the piles by 25% compared to prismatic ones without the use of filler. It is established that in the process of hammering the contact plane of the filler with fine sand is inclined from the vertical by about 100, which allows us to consider the developed pile as pyramidal. The method of calculation of bearing capacity of piles taking into account the proposed design and technological solutions is proposed.

EXPERIMENTAL STUDIES OF PILE FOUNDATION GROUND BASE REINFORCED WITH HARD INCLUSIONS

Often in construction practice there is a need to strengthen the pile foundation of buildings and structures. The traditional methods include the implementation of additional, as a rule, bored piles with the subsequent erection of a grillage incorporating them into operation. Often, this work has to be done in the conditions of dense urban development, in cramped rooms of the basement, etc., which leads to significant technological difficulties. One of the alternative ways to strengthen pile foundations is the method of high-pressure group injection, which consists in injecting a movable cement-sand mortar into the soil under pressure that exceeds its structural strength. As a result, after its hardening, solid injection bodies are formed at the base, reinforcing the soil base. The article describes the results of experiments to assess the impact of the layout of hard inclusions on the deformability of the soil foundation of the pile foundation model. The experiments were carried out in a small soil tray, which was filled with medium-grained loose sand. The piles were modeled with metal rods, the pile grillage with a metal square stamp. The pile foundation model included 9 piles arranged in a square grid. As injection bodies, gravel grains of various sizes and shapes were used. The studies included 10 series of experiments (each experiment was repeated at least 3 times): the volume of the inclusions used, their sizes, the positioning step in the plan and in depth varied. As a result of the analysis of the performed experiments, conclusions were formulated regarding the purpose of the optimal layout of hard inclusions when strengthening the soil foundation of pile foundations by high-pressure injection of mobile cement-sand mixtures.

New approach to estimate the shear stress and the force of raindrops and their effect on erodibility of agricultural soils

The objective of this work was to the study the erosive force of raindrops and the shear stress on the soil erodibility of disturbed and saturated agricultural soil. A mathematical development was used to determine a new approach to the shear stress. The soil erodibility is calculated using the WEPP (water erosion prediction project) model. To realize this work, an experimental study was led in a laboratory using the rainfall simulator. The soil tray used in this study has a length of 2 m, width of 50 cm and a depth of 15 cm and the slope was adjusted with a system. The soils used were sandy and silty agricultural soils. The results show that the relationship between the erosive force of raindrops and the shear stress on the soil erodibility increased respectively as a power and linear function with an important coeffiient of determination. As regards the relationships between soil erodibility and the mean raindrop diameter, the evolution is represented by a power function with high coeffiient of determination.

Slow and Fast‐Release Boron Sources in Potash Fertilizers: Spatial Variability, Nutrient Dissolution and Plant Uptake

Core Ideas A dual‐release boron (B) fertilizer can reduce the risks of seedling toxicity and leaching. Muriate of potash (MOP) was co‐compacted with slow‐ and fast‐release B sources. MOP+B resulted in a more uniform B spatial distribution compared to traditional bulk‐blends. Incorporation of colemanite in the formulation slowed the release of B from the MOP+B fertilizers. This novel B fertilizer may improve the synchrony between nutrient availability and crop demand. Boron (B) supply to crops is a challenging fertilization practice, due to its high mobility in soil, its narrow window between deficiency and toxicity and the necessity to evenly apply this micronutrient to the soil. We aimed to increase B fertilizer efficacy through the use of slow‐ and fast‐release borate compounds in a macronutrient carrier fertilizer. Borax, ulexite, and colemanite (alone or combined) were compacted with muriate of potash (MOP) to produce B‐enriched fertilizers varying in proportion of water‐soluble B. One such fertilizer was assessed for spatial B distribution compared with a bulk blend equivalent in a soil tray, while others were assessed for nutrient release in a soil column, and canola (Brassica napus L.) growth in a leached and non‐leached pot trial. The compacted MOP+B fertilizer improved B distribution in soil compared to a simulated bulk blend. The release of B was fastest for borax (&gt;93% released within 2.5 pore volumes [PV]) and slowest for colemanite (&lt;20% released after 20 PV). The combination of slow‐ and fast‐release B sources resulted in initial fast‐release of B followed by a constant slower B release. In leached soil, the higher B losses (up to 80% of applied B) resulted in lower canola B uptake with increasing borax and decreasing colemanite in the formulation. In non‐leached soils, there was no difference in B uptake among fertilizer treatments. The use of dual release B sources in MOP+B fertilizer formulations effectively addresses the risk of B loss, and better matches crop B demands during growth.

Effects of vegetative filter strip on overland flow nitrogen and phosphorus intercepting under different inflow conditions.

The vegetative filter strips can effectively intercept erosion of water and sediment on the slope, with huge potential to prevent and control soil erosion and agricultural non-point source pollution. A series of muddy water scouring experiments under different inflow conditions in the indoor soil trays were conducted to investigate the effects of vegetative filter strip (VFS) on intercepting nitrogen (N) and phosphorus (P) under different inflow conditions and its internal hydrological responses. The results showed that the VFS could effectively intercept N and P in the runoff. When the inflow was 200, 400, 600 L·h-1, the intercepting rates were 74.9%, 62.0%, 58.3% for N and 85.0%, 75.6%, 72.0% for P, respectively. The best intercepting effect occurred at the lower inflow rates. Different inflow N and P concentrations had no significant effect on N and P interception efficiency. Under different inflow conditions, the intercepting rates of N and P by VFS increased with the increases of Froude value with a significant linear positive correlation. However, there were linear negative correlations between the intercepting rate and resistance coefficient, shear stress and stream power. The relationship between the N and P intercepting rates and shear stress was the best among others, and the N and P intercepting rates could be well predicted by a formula containing shear stress.

The relations between the rainfall erosivity index AI and the hydraulics of overland flow and sediment concentration in sandy soils

The purpose of this study is to investigate the effects of rainfall erosivity index AI on the hydraulics of overland flow parameters such as the flow velocity, the flow depth, the flow regime, overland flow power and on soil surface characteristics, such as surface roughness and sediment concentration. The erosivity index AI represents six rainfall intensities, 31.40 mm·h-1; 37.82 mm·h-1; 69.49 mm·h-1; 81.85 mm·h-1; 90.39 mm·h-1 and 101.94 mm·h-1 generated by a rainfall simulator. To simulate the soil plot, a soil tray was filled with remolded agricultural sandy soil. The results found have shown that the AI represents better the rainfall than rainfall intensity and related to drop diameter with a power function. Overland flow never exceeded the laminar and subcritical regime; the Reynolds number reacted differently with AI and rainfall intensity, whereas the Froude number has similar reaction with both parameters. Re, Fr and n follow with AI logarithmic, linear and power functions respectively. Finally, AI is a good predictor of soil erosion.

Impact of soil hydrological properties on the 7Be depth distribution and the spatial variation of 7Be inventories across a small catchment

The natural fallout radionuclide 7Be is used as a tracer allowing estimates of soil redistribution on an event-based time scale. The observed 7Be inventory in the soil is converted to soil redistribution by comparing the 7Be inventory at a stable reference site to the location of interest and taking the 7Be depth distribution in the surface soil into account. The relaxation mass depth (h0), describing this depth distribution, is assumed to be uniform across the study area, whereas the 7Be inventory at the reference site represents the balance of atmospheric 7Be input and radioactive decay. The 7Be reference inventory should, therefore, not be influenced by soil redistribution or by any variation in physico-chemical characteristics of the soil within the entire study area. Most studies to date use 7Be to monitor soil redistribution on the spatial scale of a hillslope. However, if the assumptions of spatially uniform fallout and rapid and irreversible sorption of 7Be to soil particles can be extended over a larger area, 7Be could be used to monitor soil redistribution at the catchment scale. In this paper, the variability in 7Be distribution in the soil at hillslope and catchment scales is explored and possible sources of this variability are identified. To assess the impact of variability in soil hydraulic conductivity on the depth penetration of 7Be in surface soil, a rainfall simulation experiment with 9Be spiked rainfall was performed on artificially compacted soil cores. These rainfall simulation experiments indicated a significant positive correlation between the saturated hydraulic conductivity (Ksat) and the relaxation mass depth and, thus, demonstrated that the assumption of a spatially constant relaxation mass depth is likely to be invalid. An empirical correction factor is proposed to circumvent this problem. This work demonstrates the importance of assessing variability in soil hydrological properties across a study area and is also relevant to studies concerning the vertical transport of fallout contaminants in surface soil. To assess spatial variability in fallout across a catchment and across soil types, soil trays containing different soil types were placed at three reference locations in a small catchment of 8km2 across a nine month period. The spatial variation in 7Be reference inventory between the sites in the catchment was not larger than the variation within one reference site (37% and 36% respectively), indicating that the uncertainty on the reference inventory will be similar over the small catchment. However, the different soil types displayed diverse 7Be depth profiles and total 7Be inventories, suggesting that a clear understanding of sorption behavior across the soil types present in a catchment is needed prior to the use of 7Be as a catchment-scale sediment tracer.

A study of clod evolution in simulated rain on the basis of digital elevation models

Soil roughness is a key parameter to our understanding of soil properties and soil-water interaction, most of which occur at millimeter scales. Soil irregularities, such as aggregates, clods and interrill depressions, influence water infiltration and overland flow. The objective of this study is to observe and quantify clod evolution under cumulated precipitation. We prepared two soil trays with loose silt soil and pre-sieved clods put on top, at low and high concentrations. These trays were then subjected to a set of five successive artificial rainfalls. The digital elevation models (DEM) were recorded for each tray, at millimetric resolution, at the initial stage and after each subsequent rainfall. The clods were automatically segmented on the DEM and the diameter, surface area and volume of these clods were measured by computer.The isolated clods showed comparable behavior on both trays. The small clods were almost always decreasing in volume until they disappeared. The other clods swelled during the first rain or the first two rains, and then decreased in area and volume. The decrease was faster for volume than for area. This probably reflected a soil detachment phenomenon, which mostly affected the heights of the clods. On the high concentration tray, the close inter-proximity of the clods induced merging and the formation of blocks.The rate of decrease of clod volume as a function of cumulative precipitation could be modeled using exponential and linear equations. Small and intermediate-sized clods showed an exponential decrease that was smoother as the clod size increased. Large clod volume decrease was almost linear. We were further able to model the trend of the slope parameter of the exponential decrease, as a function of clod size. Our study has shown how the DEM recording and image analysis can be used to quantify the evolution of clods under rainfall, improve our understanding of clod dynamics under rainfall and roughness parameterization. The size dependency of clod volume decrease is important for soil conservation decisions. This will obviously affect crust formation, surface armoring, soil erosion and surface permeability to water and gas.

Production and effects of volatile organic compounds during interspecific interactions

Competition between mycelia of saprotrophic cord-forming basidiomycetes occurs both within dead woody resources and in the soil-litter interface, and involves a variety of antagonistic mechanisms including the production of volatile organic compounds (VOCs). The antagonistic potential of VOC profiles from interactions in wood blocks and in soil microcosms was assessed using shared headspace experiments, and the profile of VOCs emitted over the course of interactions elucidated using solid phase microextraction (SPME) with gas chromatography-mass spectrometry (GC–MS). Quantitative and qualitative changes in VOC production occurred in interactions compared to self-pairing controls, with different VOC profiles from fungi growing in wood blocks compared to soil trays. There were both stimulatory and inhibitory effects of VOCs on target mycelial extension rate, hyphal coverage and fractal dimension. VOC-mediated effects were greater in self-pairing controls compared to interactions, and differed depending on the substratum in which the VOC-producing fungi were growing.