Natural Topsoil Research Articles

Investigating the synergistic impact of ozonated water irrigation and organic fertilization on tomato growth

This study presents the outcomes of an experimental investigation aimed at evaluating the combined impact of irrigating tomatoes with ozonated water and applying organic fertilization. The experiment was conducted in a greenhouse equipped with an innovative ozonated water generation system. Tomato seeds were planted in 240 pots of 2-liter volume, arranged in 16 rows with 15 pots each. Alongside the native greenhouse topsoil, three distinct substrate mixtures incorporating compost compositions of 10%, 20%, and 40% were examined. Regular irrigation, twice a week, was implemented using three varying concentrations of dissolved ozone in water (1, 2, and 3 ppm). Results obtained after approximately three months of cultivation unveiled an almost twofold increase in plant productivity with ozonated water irrigation. This effect was notably pronounced when utilizing the native topsoil and a substrate containing 10% compost, coupled with an ozone concentration of 2 ppm. Intriguingly, the use of ozonated water facilitated enhanced development of both aerial and root components of the tomato plants. Moreover, the study suggests that organic fertilization may not be necessary when irrigating with ozonated water, as comparable productivity was observed for both fertilized and non-fertilized soil substrates. Although physicochemical analyses indicated minimal alterations, the noticeable improvement in plant vitality underscores the positive influence of ozone.

A survey of soil elemental variability in Singapore parks for forensic purposes

Soil, as a surviving trace after contact and transfer between contacting surfaces at a crime scene, can be recovered and analyzed to infer the presence of persons or tools at the scene and prior activity leading to its deposition. With its vast diversity and heterogeneity, it varies in composition from place to place, providing a basis for trace examiners to distinguish visually similar-colored soils. Unlike countries with native topsoil, Singapore’s urban lands are commonly filled with man-altered and man-transported soil, with relatively little known about the variations of soil’s characteristics within a small, localized area. The current study surveyed the soil’s elemental variability in Singapore parks, which are green spaces for public leisure use. Past installations of recreational facilities and landscaping with fast-growing vegetation in parks inevitably cause disturbance to the original natural soil and mixing with extraneous soil, further contributing to the heterogeneity of the park’s topsoil composition. In our sampling approach, visually similar-colored surface soils were collected from within a 1-m2 site, sites in proximity within a park, and parks across Singapore. The collected soils were dried and sieved into clay- and silt-size fractions for elemental analysis using WDXRF and SEM/EDS. To examine the extent of the spatial elemental variability, we adopted three-sigma interval match criteria and a discriminative model incorporating relative data, square root values and the Canberra distance measure for data processing and pairwise comparison of soil samples. The study also aimed to develop soil databases encompassing soils across Singapore with the intent of understanding the value of soil evidence within a local context.

Electrical resistivity tomography through reinforced concrete floor

AbstractThe electrical resistivity tomography (ERT) method is often challenged by the presence of reinforced concrete (RC) in urban and industrial environments, because the embedded metallic wire mesh can severely distort the distribution of subsurface currents. We investigate one typical scenario in real applications, in which an RC floor overlays the natural topsoil or rock. Our synthetic forward simulations show that the embedded wire mesh behaves like a local good conductor in data of small source‐receiver separations and acts like an equal‐potential object that keeps the potential from decaying at large source‐receiver separations. Routine ERT inversions that ignore the RC cannot work properly because the thin and highly conductive wire mesh may be manifested as large uninterpretable low‐resistivity anomalies in the imaging results. Two remedies are adopted to improve the ERT resolution in such cases. First, we find a top layer with high conductivity in our model to adequately represent the wire mesh; then, we initiate the inversion with the top‐layer model as the starting and reference model. This warm‐start approach overcomes the difficulty of recovering the large conductivity contrast between metallic objects and regular earth materials. Second, underground electrodes are added to the survey array, so more information from depth can be obtained to fight against the dominance of current channelling in the wire mesh. Finally, our strategies are used to invert a real ERT dataset from an indoor manufacturing plant, where RC covers the entire floor of the building and electrodes are in contact with the soil through open holes in the floor. Our simulation and field data inversion verify our findings and demonstrate the effectiveness of our solutions in improving the resolution of ERT when the survey is carried out over RC floor in urban and industrial environments.

Effect of long-term influx of tertiary treated wastewater on native bacterial communities in a dry valley topsoil: 16S rRNA gene-based metagenomic analysis of composition and functional profile.

Although dumping treated wastewater into soil might provide nutrients and organic matter, it can also expose the ecosystem to biological and chemical risks. A vital indication of soil health and quality is the soil microbial community. The current work used next-generation 16S rRNA gene amplicon sequencing to evaluate the effects of the long-term influx of tertiary treated wastewater (TWW) into Wadi Uranah, a dry valley in Makkah city, Saudi Arabia, on native topsoil bacterial community composition and predicted functions. The findings demonstrated that neither the compositions of microbial communities nor their predicted functions using PICRUSt2 differed significantly (p>0.05) between polluted valley soil (PolVS) and unpolluted valley soil (UPVS). Alpha and beta diversity, however, showed that the PolVS samples had a considerably higher level of diversity and variability. Firmicutes, Actinobacteria, Proteobacteria, and Bacteroidetes were the most prevalent phyla in both groups. Noticeable relative variations existed in some metabolic pathways such as cofactor, prosthetic group, electron carrier degradation, aldehyde degradation, and Entner-Doudoroff (ED) pathways. Overall, our findings suggest that because both groups have very similar core microbiomes and functions, the long-term disposal of tertiary TWW into Wadi Uranah may have little to no influence on the composition and function of soil bacterial communities. In addition, the long-term discharge of tertiary TWW after partially treated wastewater's initial disposal may have helped the native soil microbial community recover.

The effectiveness of use of water-saving technologies against erosion in hilly areas land

Reducing irrigation erosion is one of the major challenges in the world today. Particular attention is paid to the development and maintenance of soil fertility and the development of irrigation water-saving technologies. Soil erosion due to over-irrigation of arable land on farms leads to increased fertilizer consumption and decreased productivity. The washing of the fertile layer of soil not only affects the yield of crops but also affects the mechanical composition of the soil. Erosion destroys the natural topsoil, and a reduction in organic matter accompanies this. When erosion occurs, soil particles are lost, and organisms, mineral fertilizers, and nutrients are lost along with them. Currently, the average soil washing before irrigation in such an area is 51 t/ha per year, of which nutrients are: humus 590 kg/ha, nitrogen, and phosphorus -50 and 82 kg/ha, potassium 140 kg/ha, and small elements 33 kg/ha. e. Of these, 600 thousand are currently strongly washed soils - 39 thousand, average washed - 215 thousand, and weakly washed soils - 346 thousand. As a result of soil washing and lowering the quality of wetting of sloping lands, the gross yield of 28-47 % decreases in crop areas. Resolutions decree of the President-4919 of December 11, 2020, “On measures to further accelerate the introduction of water-saving technologies in agriculture”, as well as Resolution No. PF-6024 of July 10, 2020, of the President of the Republic of Uzbekistan The program of decrees “Concept for 2030” is being implemented. With economic irrigation technology using K-9 polymer in furrow irrigation, the water use coefficient in irrigation changed from 0.78 to 0.87 in furrows, from 0.7 to 0.76 under control. The water economy during the irrigation season is 400-878 m3/ha. Fuel economy in plowing was 3-4 liters per hectare. The number of swimmers has halved. K-9 polymer using furrow irrigation increased yields from 28.4 to 68.4 and 70 quintals per hectare.

Ecological homogenization of soil properties in the American residential macrosystem

AbstractThe conversion of native ecosystems to residential ecosystems dominated by lawns has been a prevailing land‐use change in the United States over the past 70 years. Similar development patterns and management of residential ecosystems cause many characteristics of residential ecosystems to be more similar to each other across broad continental gradients than that of former native ecosystems. For instance, similar lawn management by irrigation and fertilizer applications has the potential to influence soil carbon (C) and nitrogen (N) pools and processes. We evaluated the mean and variability of total soil C and N stocks, potential net N mineralization and nitrification, soil nitrite (NO2−)/nitrate (NO3−) and ammonium (NH4+) pools, microbial biomass C and N content, microbial respiration, bulk density, soil pH, and moisture content in residential lawns and native ecosystems in six metropolitan areas across a broad climatic gradient in the United States: Baltimore, MD (BAL); Boston, MA (BOS); Los Angeles, CA (LAX); Miami, FL (MIA); Minneapolis–St. Paul, MN (MSP); and Phoenix, AZ (PHX). We observed evidence of higher N cycling in lawn soils, including significant increases in soil NO2−/NO3−, microbial N pools, and potential net nitrification, and significant decreases in NH4+pools. Self‐reported yard fertilizer application in the previous year was linked with increased NO2−/ NO3−content and decreases in total soil N and C content. Self‐reported irrigation in the previous year was associated with decreases in potential net mineralization and potential net nitrification and with increases in bulk density and pH. Residential topsoil had higher total soil C than native topsoil, and microbial biomass C was markedly higher in residential topsoil in the two driest cities (LAX and PHX). Coefficients of variation for most biogeochemical metrics were higher in native soils than in residential soils across all cities, suggesting that residential development homogenizes soil properties and processes at the continental scale.

Evaluating biological properties of topsoil for post‐mining ecological restoration: different assessment methods give different results

Salvaged native topsoil is a scarce, highly valuable resource in post‐mining restoration, being the main source of organic matter and nutrients and a major repository of plant propagules and soil microbes. During the mining process, topsoil is often stockpiled, and factors such as stockpile depth, season of stripping, and storage time can adversely affect topsoil functionality. We aimed to determine if soil functionality differs between undisturbed native reference topsoils and stockpiled topsoils of various age and origin, and whether measures of soil microbial community composition, soil respiration, and plant growth provide comparable assessments of soil functionality. We investigated this using select biological assessments of undisturbed native reference topsoils and stockpiled topsoils collected from seven mine sites representing a range of climate, soil, commodity, and vegetation types across the major mining province of Western Australia. Biotic properties of stored topsoil were idiosyncratic and variable across mine sites, and results differed based on the biotic measure being assessed. Biomass was generally lower for plants grown in stockpiled topsoils than for plants grown in native reference topsoils across mine sites. However, no single biotic measure provided an accurate assessment of soil functionality as reflected in plant growth responses. Overall, stockpiling adversely affected soil functionality and further research is needed to improve topsoil management procedures that may be site‐ and biome‐specific.

Earthworms and soil mesofauna as early bioindicators for landfill restoration

Context Landfill activities physically disrupt soil habitats. When restoring landfill to ‘soft’ end uses such as woodland, the appropriate stockpiling and reapplication of native topsoil to provide suitable soil habitats may enhance soil fauna recolonisation and reduce restoration timeframes. Aims We studied the influence of reclamation practices on earthworm and mesofauna communities, and evaluated the role of earthworms and soil mesofauna as bioindicators of early landfill restoration success. Methods We investigated soil physico–chemical parameters, and earthworm and soil mesofauna communities at two restored landfill sites and the surrounding land uses. We also applied the QBS-collembola (QBS-c) and QBS-earthworm (QBS-e) index techniques in a reclaimed landfill setting. Results Natural colonisation of reclaimed landfill by earthworms occurred rapidly where original site topsoil was stockpiled, reapplied, and revegetated. QBS-e and QBS-c indices indicated that the most disturbed sites generally had the lowest soil biological quality. Mesofauna richness and abundance were generally higher in the low-disturbance sites. Conclusions and implications We demonstrate the value of recording a range of soil invertebrates during land reclamation, since different soil bioindicator groups respond differently to soil disturbance. QBS-c and QBS-e index techniques alongside traditional soil macro- and mesofauna assessments reinforced our observed soil fauna responses to reclamation practices. Thus, we encourage multitaxon soil monitoring during land reclamation. Where landfill restoration was carried out to a poor standard, results suggest that soil mesofauna are better indicators of soil status than earthworms. For future restoration schemes, best-practice methods are recommended to improve poor-quality reclaimed soil materials to facilitate rapid soil fauna recolonisation and soil structural development.

Evaluation of acid mine drainage sludge as soil substitute for the reclamation of mine solid wastes.

The reclamation of mine waste deposits is often hindered by the scarcity of natural topsoil. Acid mine drainage sludge (AMDS), as a mass-produced waste in metalliferous mines, is a potential topsoil substitute but had not been validated. In this study, a pot experiment with three plant species was conducted to evaluate the capacity of AMDS to support plant growth, buffer acidification, and immobilize heavy metal(loid)s when reclaiming mine waste rocks. Chemical fertilizer and compost chicken manure were applied to AMDS at different rates to explore their effects on plant growth and the physicochemical properties of AMDS. Results showed that all the plants could survive in AMDS even without fertilization. The contents of heavy metal(loid)s in rhizosphere remained almost unchanged over the experimental period, indicating low leachability of revegetated AMDS. Fertilizers enhanced macronutrients and soil enzyme activities, leading to significant increases in plant biomass. However, owing to manure composting and low richness and diversity of the bacterial community in AMDS, the NH4+-N and bioavailable phosphorus contents were extremely low. Bermuda grass was a suitable pioneer species for reclamation for its better adaptability to nutrient deficiency and heavy metal(loid) stress. Overall, AMDS is a viable soil substitute for mine reclamation due to its capability to support plant growth and environmental safety.

Long-term phytoremediation using the symbiotic Pongamia pinnata reshaped soil micro-ecological environment

Understanding the effects of phytoremediation on ecological environments is a core issue in soil bioremediation. However, the response of soil micro-ecological environment to long-term phytoremediation of symbiotic legume is still unknown. To address this issue, we focused on the changes of soil physicochemical properties, microbial communities, ecological functions, and correlation relationships of microbial populations in the VTi magnetite mine tailings subsoil and the natural topsoil after three years' in-situ phytoremediation using the symbiotic Pongamia pinnata. The results showed that the bioavailability of soil nutrients and metals had undergone different degrees of significant changes in the two different metallic soil types after phytoremediation. It was revealed by changes in alpha-diversity indices, relative microbial abundance, LEfSe scores, and the number of significant OTUs that long-term phytoremediation using P. pinnata significantly altered soil microbial communities. This shift further caused a significant change in soil ecological functions and microbial community correlations. All changes in ecological functions caused by P. pinnata were in different degrees in the two different soil types. The Bray-Curtis based redundancy analysis (bcRDA) indicated that the shift of microbial communities was driven by several bioavailable nutrients and metals. Therefore, this study proved that long-term phytoremediation of symbiotic legumes could reshape soil microbial communities, and implied that a dramatic change in soil micro-ecological environment and an improvement of soil quality were the results of following long-term phytoremediation using the symbiotic legume.

Crop production on heavily disturbed soils following crude oil remediation

AbstractCropland contaminated by crude oil typically requires remediation before it can meet pre‐contaminated productivity potentials. Remediation strategies focus on removing the contaminant, but they also often alter soil properties, which affects the capacity of the land to sustain agricultural production. This research describes crop production following the remediation of crude oil contaminated soil in North Dakota, USA using two different strategies, a modified land‐farming technique and ex situ thermal desorption. Wheat (Triticum aestivum L.) and field pea (Pisum sativum L.) were grown in soils treated by both of those techniques, as well as mixtures of each treated soil with native topsoil. Across three growing seasons of comparisons to native topsoil, crop production was 61 ± 20% lower in the modified land‐farm soils and 52 ± 25% lower in thermal desorption‐treated soils; these yield declines were likely associated with reduced soil organic carbon levels. Notably, the soil mixtures had higher soil organic carbon levels and matched the native topsoil in both yield and protein content, suggesting that soil mixing may be a promising tool in cropland soil reclamation. Overall, these findings reinforce that crop production on reclaimed land is linked with soil properties, so long‐term reclamation success requires a holistic approach to soil management.

Early Tree Growth in Reclaimed Mine Soils in Appalachia USA

Surface mining disturbs hundreds of hectares of land every year in many areas of the world, thereby altering valuable, ecologically-diverse forests. Reforestation of these areas after mining helps to restore ecosystem functions and land value. In Appalachia, native topsoil is normally replaced on the surface during reclamation, but waivers allow for brown and gray sandstone materials to be used as topsoil substitutes. Numerous studies report the growth of trees in these substitute mine soil materials, but few studies have compared the height of trees grown in reclaimed mine soils to the heights of trees grown in native soils. This study determined the growth of red oak (Q. rubra L.), white oak (Quercus alba L.), and tulip poplar (Liriodendron tulipifera L.) in two mine soil types which were compared to projected growth in native soils. Heights of tree seedlings in native soils at 11 years were estimated from site indices (SI) from USDA Soil Survey data. At the mine sites, areas with brown and gray mine soils (one site with a mulch treatment) had 12 tree species planted and growth was measured annually for 11 years. Mine soil pH after 11 years was 5.3 for brown mine soils, 6.6 for gray mine soils, 7.0 for mulched mine soils, and 4.1 to 5.2 for native forest soils. After 11 years, tree heights in gray mine soils were significantly lower (0.5 m) than tree heights in brown mine soils (2.8 to 4 m) for all three species. Trees in mulched mine soils were up to 0.7 m taller than trees in un-mulched brown mine soils. After 11 years, red oak height was 6.3 m in native soils and 3 m in brown and mulched mine soils (52% lower); white oak was 7.3 m tall in native soils compared to 3.6 m in brown mine soils (50% lower); and tulip poplar was 11.5 m tall in native soils and 3.5 to 4 m tall in brown and mulched mine soils (70% lower). In gray mine soils, trees were not growing at all. While the trees in brown mine soils are growing, tree growth has not reached projected levels of tree growth in native soils during the first 11 years after planting. The purpose of forestry reclamation is to restore ecosystem diversity and function. This study showed that one measure of ecosystem function, tree growth, was 50% lower on reclaimed mine soils than native forest soils. Maturing mine soils may develop properties over time that are similar to native soils and, with the increased rooting depth, may provide conditions where increased tree growth rates and height may be attained during the next several decades.

Nitrogen limitation and calcifuge plant strategies constrain the establishment of native vegetation on magnetite mine tailings

Mine tailings are challenging substrates for ecological restoration, as the establishment of diverse native plant communities can be constrained by a range of edaphic factors. Thus, the ability to restore native vegetation communities will depend upon developing a clear evidence-base as to what types of species and communities are likely sustainably reinstated on such altered substrates. As global tailings production and the cumulative footprint of tailings storage facilities continue to grow, understanding the effect of edaphic filters on community establishment is foundational for developing effective restoration solutions for tailings. We standardised growth rate estimates derived from nine root and shoot parameters for plants grown in magnetite tailings and natural topsoil, using crops (eight species) to characterise previously identified plant responses and native plants (40 species) to understand the impact of edaphic conditions on the species pool available for restoration. The edaphic conditions of unweathered magnetite tailings select against the majority of native plant species and nutrient-acquisition guilds (approximately 75% of reference floristic biodiversity), with plant development on tailings compared with natural topsoil compromised in a number of variables in all but six species. Plant growth on tailings was limited by a lack of available nitrogen (N) and high alkalinity (pH >9), and seedling growth and development was positively associated with seed N concentration. Calcicole species and species from N2-fixing and cluster root-producing strategies performed better on tailings than calcifuge species and species without specialised nutrient-acquisition strategy or those reliant upon mycorrhizal associations. The return of plant communities native to highly weathered, acidic soils on magnetite tailings is likely unsuccessful, unless strategies to ameliorate substrate hostility through acidification of the soil profile and improving N availability are prioritised.

Use of montmorillonite-enriched sandstone to remediate a sandy mined soil

Man-made soils (technosols) could be a practical alternative when the availability of suitable natural topsoil is limited in surface mine areas for reclamation. Screening potential topsoils is a necessary step to determine the suitability of materials for revegetation. This study aimed to obtain insights into the growth of alfalfa (Medicago sativa L.) on homogeneous and layered initial soils prepared with local natural materials (sandy soil and montmorillonite-enriched sandstone), before screening the optimal topsoil for alfalfa growth. Ten technosols were assessed in a growth study over 5 months by using the biomass production and root system as performance indicators. The shoot and root biomass production were highest in the treatment with a 20 cm montmorillonite-enriched sandstone layer at a depth of 20–40 cm, where the biomass production rate was approximately twice that in sandy soil. The root distribution according to the depth was more even in a homogeneous mixture of sandy soil combined with montmorillonite-enriched sandstone and the treatment with a 20 cm montmorillonite-enriched sandstone layer at a depth of 20–40 cm compared with the other eight options, possibly due to the higher water-holding capacity of the montmorillonite-enriched sandstone. The optimal technosol was determined as a 20 cm montmorillonite-enriched sandstone layer at a depth of 20–40 cm in a sandy matrix. The results of this study using locally sourced components for preparing topsoil could facilitate the development of strategies for mine reclamation.

Distribution of As and As(V) adsorption potential onto topsoil in the Datong Basin, northern China

Datong Basin is a typical groundwater irrigation area in northern China contaminated by As. In order to reveal the distribution of As and the adsorption behavior of As(V) onto topsoil in the Datong Basin, a total of 40 topsoil core samples were collected from a 2 m core. Samples were used for chemical composition analysis and an isothermal adsorption experiment. Results show that the collected samples are not contaminated. The adsorption capacity (Stot value) of topsoil for As(V) at the study site ranged from 257 to 1027 nmol/g with an average of 505.2 ± 200.2 nmol/g. Vertically, both Stot value and topsoil components exhibit a vertical zoning with a positive correlation between the Stot value and K2O, CaO, MgO, Al2O3, Fe2O3 contents while Na2O and SiO2 are inversely correlated. Fe2O3 content shows a strong positive correlation with As content while Al2O3 does not. Moreover, the correlation between Stot value and Al2O3 is much better than Fe2O3. These results indicate that Fe minerals are the main reservoirs of As in the natural topsoil at the study site. Furthermore, both Fe minerals and clay minerals can adsorb As(V), but clay minerals have a greater storage potential. This result indicate that a combined effect of Fe minerals and clay minerals for As(V) accumulation onto topsoil should be considered during geochemical modeling and further agricultural management.

Daytime Surface Energy Fluxes over Soil Material Remediated Using Thermal Desorption

Core Ideas Surface energy balance was quantified with micro‐Bowen ratio instrumentation. Surface energy balance was similar over native topsoil and soils treated with thermal desorption. Thermal desorption did not alter soil temperature dynamics or evaporation. A mix of topsoil and thermal desorption–treated soil matched surface energy balance of topsoil best. Remediation efforts to reduce contaminant concentrations in soils often alter soil properties. Since these alterations can affect the capacity of soil to function, their extent and magnitude may dictate future land use. This study addresses the suitability of soils for agricultural production after remediation of petroleum hydrocarbons using ex situ thermal desorption by quantifying the daytime surface energy balance prior to the growing season. The energy balance was quantified using micro‐Bowen ratio instrumentation to compare non‐contaminated topsoil (A) to both subsoil materials treated by thermal desorption (TD) and a 1:1 mixture (v/v) of TD and A (TDA). Despite differences in soil characteristics, the net radiation, soil heat flux, latent heat flux, and sensible heat flux were each similar among the three reclamation conditions over a period of 18 d. The fluctuations in these fluxes between the three conditions were attributed to natural variability, and they were not large enough to induce apparent inconsistencies in soil temperature dynamics or evaporative losses. Overall, these findings suggest the surface energy balance in thermal desorption–treated soils is similar to that of the native topsoil and that using a mixture of treated soils with native topsoil may even be a better representation of pre‐disturbance conditions.

Dye Tracer Visualization of Infiltration Patterns in Soils on Relict Charcoal Hearths

Anthropogenically modified soils are often characterized by a high heterogeneity of substrates and show unique patterns of water infiltration. Such effects are not limited to intensively used or disturbed agricultural and technogenic soils, but can also occur as legacies of former land use in forested areas. The remains of historic charcoal hearths represent a widespread legacy of historic land use. Soils at relict charcoal hearths (RCHs) are most prominently altered by the deposition of a layer of charcoal-rich substrate on top of the natural soil surface. The presence of such a technogenic layer can considerably influence infiltration and soil wetness patterns on the sites. This study describes the spatial patterns of infiltration and soil wetness at charcoal hearth sites compared with undisturbed sandy forest soils for a historic charcoal production area north of Cottbus, Germany. We characterized six plots on RCH and reference soils under pine, oak and mixed forest by visualizing preferential flow patterns of infiltrating water in dye tracer experiments. Additionally, we characterized bulk density, soil organic matter contents and water repellency, using water drop penetration time (wdpt) tests, of the RCH and reference soil horizons. The results reflect that the persistence of water repellency of both the technogenic substrates and the natural topsoils is extremely high under dry conditions, but is drastically reduced after wet antecedent conditions. The dye tracer experiments reflect increased preferential flow on the RCHs for dry soil conditions, for which infiltration is limited to very few flow paths in the technogenic substrate layer. Differences between RCH and reference soils are less clear for higher antecedent soil wetness, for which the results indicate more uniform wetting of the technogenic substrates. We conclude that the structural properties of the additional technogenic substrate layer of RCHs have characteristic effects on water infiltration, causing a high temporal variation of preferential flow in relation to antecedent soil moisture conditions. These effects can result in high heterogeneity of soil moisture for dry conditions, and generally in a high temporal variation of soil wetness in RCHs soils.

Does carbon limitation reduce nitrogen retention in soil?

Artificial soils made from waste materials offer an alternative to imported natural topsoils, notably in large-scale groundwork and reclamation projects. Benefits include diversion of waste from landfill and recycling. Nonetheless, there is limited information on the characteristics needed to support plant growth in the long term, particularly the existence of a sustainable nitrogen reservoir. Therefore, we assessed the efficacy of nitrogen cycling and retention within an artificial soil composed of 25% sand, 10% clay, 32.5% composted bark and 32.5% composted green waste over 52 weeks. Leachate was analysed for nitrogen species and nitrogen concentrations, and two of the soil columns had fertiliser added after 26 and 48 weeks. Results show that nitrate concentrations decreased from 6.73 to 0.36 mg N L−1 after 2 weeks, due to poor retention of this anion in soil, and remained low for 6 months, before increasing up to 5.87 mg N L−1 after week 26. This sharp increase in dissolved nitrate was preceded by a decrease in the ratio of dissolved organic carbon to dissolved organic nitrogen in the soil leachate. This finding indicates that the soil had become carbon-limited, leading to mineralisation of organic nitrogen by soil organisms and excretion of nitrogen. We also found that fertilisation of the soil did not alleviate carbon limitation and nitrogen loss was greater in fertilised soils, indicating nitrogen saturation. After the onset of carbon limitation, the dissolved nitrate concentrations in both the fertilised and unfertilised soils were close to exceeding the European Union threshold of concern for nitrate groundwater and river pollution. Thus, while the deployment of artificial soils is a viable option for landscaping projects, loss of nitrogen may be environmentally significant and soil management protocols must take account of both the carbon and nitrogen status of the substrate.

A large-scale soil-mixing process for reclamation of heavily disturbed soils

Soil excavation associated with energy production or mineral extraction results in heavily disturbed landscapes that must be reclaimed to avoid long-term economic and environmental losses. A common practice in reclamation of these sites is topsoil replacement across the disturbed area. In some instances, this process requires importing topsoil from another location, known as topsoil transfer, which can be expensive and introduce a new seedbank, insect community, or plant pathogens. This research describes a soil-mixing process for disturbed soils that may be used to reduce costs associated with topsoil transfer and accelerate the recovery of soil function following a large excavation. This process was applied to two disturbed soils: i) crude-oil contaminated subsoil material; and ii) crude-oil contaminated subsoil material that was remediated using ex-situ thermal desorption. These soils were separately mixed with native, non-contaminated agricultural topsoil at 1:1 ratio (by volume). The native, disturbed, and mixed soils were characterized for soil physical, chemical, and biological properties, and statistics indicated that the mixtures were homogenous both spatially and with depth. However, the mixtures were significantly different from both the disturbed materials and native topsoil, primarily driven by changes in soil organic carbon, plant available nutrients, and biological activity. These results suggest that this mixing process can be used for soil reclamation at large-scale excavation sites to both reduce project costs and enhance recovery of soil parameters.

Humusica 2, Article 14: Anthropogenic soils and humus systems, comparing classification systems

The aim of this article is to present a sort of state of the art from a soil classification point of view. How far are soils from their original natural state? A few years ago, the two most important soil classification systems added a classification of anthropogenic soils. Even so, the concept of anthropogenic soil differs slightly in the two systems, it is easy to recognize these soils all around us, in both urban and agricultural contexts. After presenting the main types of anthropogenic soil, using the WRB or Soil Taxonomy characteristics, we will focus on anthropogenic humipedons, presenting a table where they are subdivided into two new units called Agro (natural topsoils used for agricultural purposes) and Techno (human-made humus systems). This allows to conceptually compare soil and humipedon classifications, and prepares the field for further investigations on Agro (Humusica 2, art. 15) and Techno (Humusica 2, art. 16) humipedons.