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Water erosion on agricultural land preferentially carries away fine particles. Due to the generally high specific density of sorption sites of these particles, their displacement can be associated with substantial particle-bound transfer also of nutrients and pollutants with low solubility. Organic matter amendments can reduce soil erosion, but to what extent they affect the erosion-induced element losses has not been studied much. Here, we carried out field rainfall experiments on three pairs of soil plots (1.5 × 0.75 m) after incorporating a mixture of wheat straw and grass (2.12 g C per kg soil) as organic amendment into the topsoil (0–5 cm depth) of one plot in each pair (OI treatment). The other plot was prepared in the same way but without incorporation of the amendment (NI treatment). Artificial rainfall (49.1 mm h − 1 ) was simultaneously applied on each pair of plots for approximately 2 h, and sediment samples were collected at designated time steps for the analyses of C, N, P, Cu, Zn and stable carbon isotope ratios. The organic amendment substantially reduced element losses, but to a lesser extent than soil loss, as the element concentrations were higher in the exported sediments in the OI than in the NI treatment. With and without organic amendment, the concentrations of the studied elements were consistently higher in the exported sediments than in the bulk soil. They were always maximal at the onset of discharge and then continuously decreased towards the values of the bulk soil. The δ 13 C values revealed that the eroded C was preferentially derived from the fresh organic residue added to the soil. Pairwise correlations between elements and sediment size indicate that the export of N, Cu and Zn was primarily associated with soil organic matter loss, whereas P export was more associated with mineral fractions. [ABSTRACT FROM AUTHOR]

Abstract: An important aspect in risk assessment of nanoparticles (NPs) is to understand their environmental interactions. We used hydroponic plant cultures to study nanoparticle–plant-root interaction and translocation and exposed wheat and pumpkin to suspensions of uncoated CeO2–NP for 8d (primary particle size 17–100nm, 100mgL−1) in the absence and presence of fulvic acid (FA) and gum arabic (GA) as representatives of different types of natural organic matter. The behavior of CeO2–NPs in the hydroponic solution was monitored regarding agglomeration, sedimentation, particle size distribution, surface charge, amounts of root association, and translocation into shoots. NP-dispersions were stable over 8d in the presence of FA or GA, but with growing plants, changes in pH, particle agglomeration rate, and hydrodynamic diameter were observed. None of the plants exhibited reduced growth or any toxic response during the experiment. We found that CeO2–NPs translocated into pumpkin shoots, whereas this did not occur in wheat plants. The presence of FA and GA affected the amount of CeO2 associated with roots (pure>FA>GA) but did not affect the translocation factor. Additionally, we could confirm via TEM and SEM that CeO2–NPs adhered strongly to root surfaces of both plant species. [Copyright &y& Elsevier]

About 4 billion people will be added onto the present population by 2050. To meet further demand for food, agricultural production should increase on the existing land. Since the Green Revolution, higher crop production per unit area has resulted in greater depletion of soil phytoavailable micronutrients while less attention has been paid to micronutrients fertilization. Now, micronutrient deficiency has become a limiting factor for crop productivity in many agricultural lands worldwide. Furthermore, many food systems in developing countries can not provide sufficient micronutrient content to meet the demands of their citizens, especially low-income families. There are several solutions such as soil and foliar fertilization, crop systems, application of organic amendments to correct micronutrients deficiency and to increase their density in edible parts of plants. This review article presents (1) agronomic approaches to improve crop yield and micronutrient content of food crops, and (2) genotypic variation in uptake and accumulation of micronutrients. Considering ecological concerns, cultivation and breeding of micronutrient-efficient genotypes in combination with proper agronomic management practices appear as the most sustainable and cost-effective solution for alleviating food-chain micronutrient deficiency. Micronutrient-efficient genotypes could provide a number of benefits such as reductions in the use of fertilizers, improvements in seedling vigor, and resistance to abiotic and abiotic stresses. Using bioavailable micronutrient-dense staple crop cultivars can also be used to improve the micronutrient nutritional status of human. [ABSTRACT FROM AUTHOR]

Abstract: Abandoned industrial sites have traditionally constituted an important source of environmental problems. However, such sites are considered in many cases a historic heritage, and in this way, have been protected with different legal dispositions. Mining activities can be considered a special type of industrial site in that they encompass not only architectural but also landscape elements related to geology or topography. The necessity of developing new economic opportunities in these places, whose economy has been traditionally based on the “mining monoculture”, has resulted in the creation of a cultural revival in some mining sites. Nevertheless, these new economic potentials must be compatible with the obligation to maintain a low environmental risk in sites where the heavy metal concentrations are very high. The Cartagena–La Unión Mining District in Southern Spain is an example of such a case. This paper reviews the environmental situation in that area and the initiatives for establishing a cultural tourism. The goal of this paper is to incite the public debate about the balance between environmental risks, cultural safeguarding and economic development. [Copyright &y& Elsevier]

Abstract: Dissolved organic carbon (DOC) is a key component involved in metal displacement in soils. In this study, we investigated the concentration profiles of soil-borne DOC, Cu and Zn at various irrigation rates with synthetic rain water under quasi steady-state conditions, using repacked soil columns with a metal-polluted topsoil and two unpolluted subsoils. Soil solution was collected using suction cups installed at centimeter intervals over depth. In the topsoil the concentrations of DOC, dissolved metals (Zn and Cu), major cations (Ca2+ and Mg2+) and anions ( and ) increased with depth. In the subsoil, the Cu and Zn concentrations dropped to background levels within 2cm. All compounds were much faster mobilized in the first 4cm than in the rest of the topsoil. DOC and Cu concentrations were higher at higher flow rates for a given depth, whereas the concentrations of the other ions decreased with increasing flow rate. The decomposition of soil organic matter resulted in the formation of DOC, , and and was the main driver of the system. Regression analysis indicated that Cu mobilization was governed by DOC, whereas Zn mobilization was primarily determined by Ca and to a lesser extent by DOC. Labile Zn and Cu2+ concentrations were well predicted by the NICA-Donnan model. The results highlight the value of high-resolution in-situ measurements of DOC and metal mobilization in soil profiles. [Copyright &y& Elsevier]

Abstract: Based on previous preliminary survey results, elevated heavy metal concentrations of the agricultural soils of the villages of the Kremikovtzi region east of the Bulgarian capital Sofia were attributed to pollution from dusts emitted by the iron smelter in the centre of the region. Additional sampling in a test area indicated that high metal concentrations in this area could also be of geogenic origin. In order to test this hypothesis, we sampled a sequence of 14 soil profiles at increasing distance from the smelter along a 2 km transect through agricultural land outside the metallurgical complex of Kremikovtzi. The transect extended through two different units of soil types: Chromic Luvisols and Alluvial Fluvisols. Samples of the fine earth fraction (<2 mm grain size) from various depths were analysed for 19 elements by X-ray fluorescence spectroscopy (XRF). Maximum concentrations of the suspected main pollutants were approximately 170 mg/kg As, 185 mg/kg Pb, and 350 mg/kg Zn. Concentration profiles over depth were distinctly different between the two soil units for most elements and in comparison to this difference varied little within each unit. Within the two units there were no trends with distance to the smelter. The concentration profiles did not indicate any substantial contribution from atmospheric deposition. The enrichment of elemental concentrations relative to Zr did not provide sufficiently conclusive evidence to distinguish anthropogenic from geogenic metal sources. While the ratios of zinc, copper and arsenic to zirconium were almost constant, chromium, nickel and molybdenum ratios to zirconium varied between 2- and 5-fold (primarily showing a decrease) with depth in the majority of profiles, indicating gradients in the original deposition of the soil-forming parent material rather than an anthropogenic source. The study illustrates how important it can be in identifying the origin of soil pollution not only to look into areal distribution patterns of suspected contaminants, but also to investigate their depth profiles as well as that of other elements and to account for pedological factors and their variability. [Copyright &y& Elsevier]

Whereas metal effects on plants have been well studied, much less is known about plant effects on metal mobilization in soils. We investigated metal mobilization and speciation with a resolution of a few cm in soil columns planted with willows (Salix viminalis). In the presence of plants, the concentration profiles of dissolved organic carbon (DOC), major ions (e.g., Ca), Cu, and Zn exhibited more variation than in the absence of plants, and both smaller and larger concentrations were observed, indicative of strong local effects. The Cu concentration in the absence and presence of plants was controlled by DOC mobilization and could be described by the same relationship. Zn mobilization was controlled by DOC and Ca in the plant-free system and by pH and Ca in the presence of plants. Cu2+ and labile Zn were reasonably well predicted by the NICA-Donnan model and were influenced by the plant-induced changes of the soil solution composition. Plant uptake reduced the dissolved Zn concentration and transpiration reduced Cu and Zn leaching. [ABSTRACT FROM AUTHOR]

Chelant-enhanced phytoextraction has received a lot of attention in the past decade. In theory, this technique could cleanse metal polluted soils by solubilizing contaminating metals, allowing them to be taken up by plants that would subsequently be removed from the site. We review the processes of metal solubilization, uptake by plants, and leaching during chelant-enhanced phytoextraction. A large excess of chelant is required to solubilize the target metal due to the co-solubilization of Ca and Fe. Chelated metals are taken up via the apoplastic pathway. Disruption of the Casparian Band is required to achieve the high shoot concentrations needed for phytoextraction. Therefore, adding chelants to a soil increases not only the total dissolved metal concentration but also changes the primary route of plant metal-uptake from the symplastic to the apoplastic pathway. Depending on metal, plant species, and chelant concentration, significant increases in metal uptake are likely. Soil solution chelate concentrations of at least several mM are required to induce appreciable shoot concentrations. A simple calculation reveals that at such soil solution concentrations plants will remove only a small fraction of the solubilized metals. Leaching, exacerbated by preferential flow processes, is unavoidable. Chelant-enhanced phytoextraction is therefore limited to areas where the connection with groundwater has been broken, or where leaching is unimportant. Chelant-enhanced phytoextraction may nonetheless have a role in enhancing the uptake of essential trace metals. Such a role warrants further investigations into the use of biodegradable chelants such as ethylenediaminedisuccinic acid (EDDS). [ABSTRACT FROM AUTHOR]

Abstract: We report the application of an in situ method to obtain field dissolution rates of fine mineral particles in soils. Samples with different metal-containing mineral and slag particles (lead oxide, copper concentrate and copper slag) from the mining and smelting industry were buried in the topsoil of an acidic forest soil for up to 18 months. In addition we studied the dissolution of these particles in samples of the same soil, in a sand matrix and in acid solution under constant temperature and moisture conditions in the laboratory. Under field conditions the PbO particles dissolved quite rapidly (2.4±0.7×10−10 mol Pbm−2 s−1), whereas the copper concentrate (<1×10−11 mol Cum−2 s−1) and the copper slag particles (4.3±0.8×10−11 mol Cum−2 s−1) proved to be more resistant to weathering. In addition to qualitative information on dissolution features (SEM), the method yielded quantitative data on in situ dissolution rates. The dissolution rates followed the order: sand with acid percolation (pH 3.5; lab)

The use of chelants to enhance phytoextraction is one method being tested to make phytoextraction efficient enough to be used as a remediation technique for heavy metal pollution in the field. We performed pot experiments with sunflowers in order to investigate the use of the biodegradable chelating agent SS-EDDS for this purpose. We used singly and combined contaminated soils (Cu, Zn) and multimetal contaminated field soils (Cu, Zn, Cd, Pb). EDDS (10 mmol kg-1 soil)increased soil solution metals greatly for Cu (factor 840–4260) and Pb (factor 100–315), and to a lesser extent for Zn (factor 23–50). It was found that Zn (when present as the sole metal), Cu, and Pb uptake by sunflowers was increased by EDDS, but in multi-metal contaminated soil Zn and Cd were not. EDDS was observed in the sunflower roots and shoots at concentrations equal to metal uptake. The different metal uptake in the various soils can be related to a linear relationship between Cu and Zn in soil solution in the presence of EDDS and plant uptake, indicating the great importance of measuring and reporting soil solution metal concentrations in phytoextraction studies. [ABSTRACT FROM AUTHOR]

Abstract: Phytoextraction is an environmentally friendly in situ technique for cleaning up metal contaminated land. Unfortunately, efficient metal uptake by remediation plants is often limited by low phytoavailability of the targeted metals. Chelant assisted phytoextraction has been proposed to improve the efficiency of phytoextraction. Phytoremediation involves several subsequent steps: transfer of metals from the bulk soil to the root surfaces, uptake into the roots and translocation to the shoots. Nutrient solution experiments address the latter two steps. In this context we investigated the influence of the biodegradable chelating agent SS-EDDS on uptake of essential (Cu and Zn) and non-essential (Pb) metals by sunflowers from nutrient solution. EDDS was detected in shoots and xylem sap for the first time, proving that it is taken up into the above ground biomass of plants. The essential metals Cu and Zn were decreased in shoots in the presence of EDDS whereas uptake of the non-essential Pb was enhanced. We suggest that in the presence of EDDS all three metals were taken up by the non-selective apoplastic pathway as the EDDS complexes, whereas in the absence of EDDS essential metal uptake was primarily selective along the symplastic pathway. This shows that synthetic chelating agents do not necessarily increase uptake of heavy metals, when soluble concentrations are equal in the presence and absence of chelates. [Copyright &y& Elsevier]

Abstract: An immobilized metal-ion affinity chromatography (IMAC) method has been developed and validated for the separation of copper complexing ligands from soil solution. We first investigated the retention behavior of simple model ligands on the IMAC column and found that the ability to form ternary complexes of the structure Cu–IDA–ligand was the dominant factor influencing ligand retention on the IMAC column. The log K value of the Cu-complex was found to have only a minor influence on the retention. Legends containing only carboxylic acid functional groups were not retained on the column. To optimize reproducibility and quantitative recovery of copper ligands from soil solution, different composition and pH values of eluting buffer were tested. Soil solution chromatograms exhibited one non-retained fraction and two retained fractions. The elution times of the retained fractions were characteristic of peptides and proteins (first peak) and for compounds containing aromatic amines (second peak). The results show that IMAC is an effective tool for the fractionation of copper complexing ligands that are capable of forming ternary complexes. [Copyright &y& Elsevier]

Abstract: The paper describes a new HPLC method for the determination of ethylenediamine disuccinic acid (EDDS). EDDS is derivatized with FMOC reagent followed by HPLC separation on a reversed-phase column. The eluents consist of phosphate buffer at pH 6.8 and acetonitrile. Separation was carried out using gradient elution. The FMOC-EDDS derivative is detected with a fluorescence detector with an excitation wavelength of 265nm and an emission wavelength of 313nm. The detection limit is 0.01μM. The method is applicable to the determination of the compound in water, soil solution and plant material at trace levels. [Copyright &y& Elsevier]

We developed a simple method to monitor the transformation of particles in soils under in situ conditions. The particles were fixed on small polymer supports (2 cm × 2 cm) with a thin film of epoxy resin. Attached to these carriers, the particles could be put into close contact with soil at a chosen site and easily recovered after extended periods of time. The method was tested with lead oxide and copper concentrate in the field. Quartz and copper oxide particles were used in preliminary laboratory experiments. The used particles sizes ranged from 20 to 200 μm. Laboratory and field experiments with acidic and calcareous soils showed that the PbO and Cu concentrate coated polymer supports were stable under field conditions for at least one year. Nondestructive X-ray fluorescence spectroscopy was used to quantify the metals before and after exposure. Scanning electron microscopy combined with energy-dispersive X-ray spectroscopy as well as micro- Raman spectroscopy was used to identify signs of dissolution and newly formed mineral phases. The mineral dissolution rate could be determined under field conditions. The new method has the potential to be used in other environmental media such as sediments or water to study the reactions of a variety of particles larger than 20 μm. [ABSTRACT FROM AUTHOR]

• Organic amendment reduced the loss rates of dissolved elements in surface runoff. • Concentrations of dissolved elements were generally higher for the amended soils. • Surface runoff from amended soils contained more hydrophilic and low molecular weight DOC. • TDP and TDCu were closely correlated with DOC concentration regardless of the treatment. • TDCu was positively related to DOC aromaticity in runoff from the amended soils. Dissolved organic carbon (DOC) constitutes the largest carbon pool in surface waters, with soil being its main source via surface and subsurface runoff. Amendment with organic residues can reduce soil erosion and surface runoff, but little is known how this affects the amount and composition of DOC losses via surface runoff and the associated transfer of nutrients and pollutants. In this study, artificial rainfall experiments were conducted on three pairs of soil runoff plots with contrasting organic matter management. A mixture of grass and wheat straw residues was incorporated into the topsoil of one plot in each pair (OI treatment) but not into the other (control). Artificial rainfall was applied onto both treatments at an intensity of 49.1 mm h−1, and surface runoff samples were collected at designated time steps for analysis of DOC, total dissolved phosphorus (TDP), copper (TDCu) and zinc (TDZn) concentrations, as well as for characterization of DOC by UV–vis absorbance (SUVA 254 and E2:E3) and fluorescence spectroscopy (FI) indexes. The organic amendment reduced the loss rates of DOC, TDP, TDCu and TDZn by reducing surface runoff, although increasing the concentrations of DOC, TDP and TDCu. Regardless of the treatment, DOC, TDP and TDCu concentrations were always maximal at the onset of runoff and then continuously decreased after the initial flush. The observed relationships of TDP and TDCu concentrations with DOC indicate that the export of "dissolved" P and Cu primarily occurred in DOC-bound form, while the concentration of TDZn was not correlated with that of DOC. Surface runoff from the amended soils generally contained more hydrophilic and low molecular weight DOC (as indicated by low SUVA 254 and high E2:E3 and FI values), particularly at high DOC concentrations. The ratio between TDCu and DOC concentration showed a positive relationship to DOC aromaticity (as indicated by SUVA 254 values) in the OI treatment. The results indicate that organic amendment can reduce total rates of dissolved element losses with surface runoff, but attention should also be paid to the composition of lost DOC and the concentrations of DOC-associated solutes. [ABSTRACT FROM AUTHOR]

• Structural porosity and gravimetric air content are indicators of structure quality. • Gravimetric air content is the best simple, inexpensive and accessible indicator. • Target, trigger and remediation values for environmental legislation are provided. • Visual evaluation of soil structure was used as independent classification scheme. • More than 90% of the samples were correctly classed. Most soil functions, such as food production, carbon and nutrient cycling or water regulation and filtration strongly depend on soil structure quality (SSQ). But SSQ is increasingly threatened by compaction, carbon loss and erosion. SSQ should be protected by environmental regulations, however, reliable and easy methods for SSQ assessment are still missing. The aim of this study was to define a classification scheme and its indicators for soil structure protection regulation. Therefore, the physical properties of soil samples were determined with shrinkage analysis and their structure quality was scored with CoreVESS to provide a classification scheme independent from the indicators. We collected 185 undisturbed samples from the A horizon of Cambi-Luvisols across western Switzerland. CoreVESS score (Sq) 2 was used to identify the target value corresponding to good structure quality. Sq 3 was used to identify the trigger value, i.e. the limit between good and poor SSQ. Sq 4 was used to identify the remediation value. We found that structural porosity and gravimetric air content at −100 hPa (A −100) determined on undisturbed samples equilibrated free to swell in the laboratory were the best suited parameter to assess SSQ. They were correlated to SOC for soils with good SSQ, but not for soils with poor SSQ. As SOC was highly correlated to gravimetric water content at −100 hPa (W −100), it was possible to approximate SOC by W −100 in order to simplify the method for application. A −100 and W −100 are easy and inexpensive to determine and are therefore proposed as indicators. The limit values of A −100 were identified as following: target is 0.023 + 0.288 W −100 cm3g−1, trigger is 0.068 cm3g−1 and remediation is 0.045 cm3g−1. These values were designed to be useful to the Swiss environmental law. They apply to the Cambi-luvisol A horizons, and their applicability to subsoil or other soil types should be further studied. [ABSTRACT FROM AUTHOR]

Abstract Passive sampling (PS, equally used for passive sampler) methods have successfully been applied in situ to quantify the bioavailability of hydrophobic organic compounds in air, water and sediments. However, very little is known on the applicability of PS in unsaturated soils. Here, we present the results of a greenhouse experiment in which we applied in situ PS methods in pots. Low density polyethylene (LDPE) and polydimethylsiloxane (PDMS) fibres with a newly developed PS holder were used to analyse freely dissolved polycyclic aromatic hydrocarbon (PAH) concentrations (C free) in a skeet shooting range soil and an uncontaminated control soil under water saturated and unsaturated conditions for up to nine months. A short exposure time of three months was not sufficient for the PDMS samplers to reach distribution equilibrium with the surrounding soil. Under saturated water conditions, the in situ results agreed well with measurements obtained from the conventional ex situ soil suspension method. They were in accordance with similar comparisons made in previous studies on sediments, as well as with model predictions. However, for unsaturated water conditions, the results differed considerably from the ex situ C free values, in particular for the light molecular weight (LMW) PAHs such as phenanthrene, fluoranthene, and pyrene. The results of the two in situ PS methods were in good agreement with each other under both soil water conditions, indicating that dissipation mechanisms, such as degradation or volatilization, led to a substantial decrease in C free under unsaturated conditions, especially for the LMW PAHs (log 10 K OW < 5.85) over a period of six months or more. Thus, in their current state of development, in situ PS methods can be used in soils under water-saturated conditions. However, an adequate method to correct for non-equilibrium conditions needs to be developed before they can be applied to unsaturated conditions, mainly for LMW PAHs. Graphical abstract Unlabelled Image Highlights • In situ passive sampling methods agreed on freely dissolved concentrations, C free. • For saturated water conditions, in and ex situ methods agreed on C free results. • For unsaturated conditions, in situ C free results were lower than ex situ results. • Pros and cons of different methods and experimental conditions are given. • Water saturation impacted the C free of PAHs in soil. [ABSTRACT FROM AUTHOR]

Background and aims: Zinc (Zn) deficiency is a global problem in human nutrition due to imbalanced diets based on staple foods of low Zn contents. This study investigated the potential of using clover (Trifolium alexandrinum L.) and mustard (Sinapis alba L.) green manure crops to increase soil Zn uptake by wheat (Trifolium aestivum L.) without enhancing cadmium (Cd) accumulation.Methods: A factorial pot experiment with wheat was performed with three green manure treatments (clover, mustard or no green manure) and three soil treatments which were a high-Zn soil (FYM), a low-Zn soil (TURK) and the TURK soil with mineral Zn fertilization (TURK+ZN). Green manure crops were grown first and then incorporated into the soils before wheat.Results: In contrast to mustard, clover increased grain Zn concentrations in the FYM and TURK+ZN soils, but not in the TURK soil. The effect appeared to be due to high soil nitrogen inputs and concurrent pH decrease, root biomass increase, and the release of organic ligands mobilizing soil Zn and Cd. However, the high N inputs also induced Cd accumulation above critical thresholds.Conclusions: The study suggests that on Zn sufficient soils or in combination with Zn fertilizer, leguminous green manure can increase soil Zn accumulation by wheat. [ABSTRACT FROM AUTHOR]

Changes in soil fragment size distribution (FSD) under the impacts of successive rainfall events can have strong effects on sediment export during erosion events. However, field observations on the temporal dynamics of FSD under changing rainfall conditions are rare. In this study, we applied five successive artificial rainfall events with two different rainfall intensities (25.8 and 49.1 mm h − 1 ) on two replicated agricultural soil plots over a period of five weeks. Surface soil samples were taken immediately before and after each rainfall event and also in between the rainfall events in order to monitor surface aggregate stability and soil FSD. The FSDs resulting from rainfall-induced aggregate breakdown were used as inputs into a size-selective sediment transport model in order to assess how the variations in FSD would affect the concentration and size of exported sediments. Aggregate stability at first decreased due to generally wet conditions, but then increased with soil drying, until reaching a plateau towards the end of the experimental period. It did not fully recover to initial levels though, probably due to loss of stabilizing agents over time. Independent of soil moisture, notable re-aggregation occurred after each event but again did not reach the full restoration of the initial state even after up to 10 days of regeneration. In contrast to aggregate stability and irrespective of pre-event re-aggregation, the percentage of coarse fragments in post-event FSDs continued to decrease from event to event, suggesting that in addition to the previously re-formed aggregates also new coarse aggregates were broken down. The model simulations showed that the temporal variations in post-event FSD would have had as much influence on the amount and size distribution of sediments exported with surface runoff as a 3-fold variation in unit discharge, suggesting the importance of quantifying rainfall-induced FSD in soil erosion assessment. [ABSTRACT FROM AUTHOR]

Soil structure quality can be scored by visual examinations or measured with soil physical properties. To investigate the relationships between these two approaches, we adapted the VESS (Visual Evaluation of Soil Structure, Guimarães et al., 2011) to the scoring of cores (CoreVESS) on which shrinkage analysis was also performed. Scoring was performed blindly after equilibrating the samples at −100 hPa matric potential and was compared to soil texture, soil organic carbon content (SOC), soil hydrostructural stability, structural porosity, plasma porosity, bulk soil porosity or density, and water content at standard matric potential. A large geographical area of Cambi-Luvisols was sampled at 55 locations with different soil management in western Switzerland. VESS was performed on the pits and layers prior to sampling undisturbed cores. Sandy soils presented medium CoreVESS scores compared to clayey soils. Only soils with more than 20% clay content obtained good scores in this study. The relationships between CoreVESS scores, SOC and most physical properties followed a broken-stick regression, with most breaking points close to score 3. Most regressions were significant and highly determined with R 2 above 0.45. Linear decrease with CoreVESS scores was observed for total porosity and bulk density of air-dried soil and for water content at −10hPa. The underlying model of structural quality decrease can be summarized as follows. From score 1 to 3 the decrease in structure quality corresponds to a decrease in SOC. From score 1 to 2 occurs most of the decrease in coarse porosity volume. From score 3 to 5 the decrease of structure quality corresponds to a loss of structural porosity, which converges to 0 cm −3 g −1 for score 5, and to a collapse of the samples upon drying between scores 3 and 4, thus denoting a loss of hydrostructural stability. VESS scores of pits and layers were poorly correlated to CoreVESS scores and physical properties, probably due to local variability of the sampled layers. Our results suggest that the relation between visual scoring and physical properties is not site specific, and underline the need for standardizing the moisture conditions in soil structure quality assessment. [ABSTRACT FROM AUTHOR]

Most soil structure-related physical properties are correlated to soil organic carbon (SOC) content. Texture, mineralogy, and SOC:clay ratio are also acknowledged to affect physical properties, however there is no consensus or general conclusions in this respect. Against this background, the present study aims at determining objectives for the management of SOC in terms of structural quality of agricultural soils. The large area in which 161 free-to-swell undisturbed samples were obtained for this research represents a major part of the Swiss agricultural land and belongs to one broad soil group (Cambi-Luvisols). The structural quality was scored visually, and bulk volumes (inverse of bulk density) were measured at standard matric potentials. To define the effect of SOC without interference of soil mechanical degradation, soils with good structural quality scores were considered first in studying the relationship between SOC and soil pore volumes. Results suggest that the relationship is always linear, irrespective of the clay content of the soils. No optimum of SOC corresponding to a fraction of the clay content is found, contrary to the theory of “complexed organic carbon” (Dexter et al., 2008). However, the SOC:clay ratio decreases with decreasing soil structure quality. The SOC:clay ratio of 1:8 is the average for a very good structure quality. A SOC:clay ratio of 1:10 is the limit between good and medium structural quality, thus it constitutes a reasonable goal for soil management by farmers. A SOC:clay ratio of 1:8 or smaller leads to a high probability of poor structural state. These ratios can be used as criteria for soil structural quality and SOC management, and in that context, the concept of complexed organic carbon appears relevant. [ABSTRACT FROM AUTHOR]

Peatlands store large amounts of soil organic carbon (SOC). Drainage, required for agriculture, aerates these organic soils and triggers rapid peat decomposition. In turn, cultivation of organic soils is also accompanied by input of young organic carbon (YOC) from plant residues. The extent to which YOC inputs compensate for oxidative peat loss is unknown. Furthermore, the lability of YOC in organic soils introduced by cultivation has never been examined. Here we studied the amount and lability of YOC in two adjacent drained organic soils by a combined 13 C and 14 C approach. Soils have been under intensive arable use for several decades and were both cultivated, inter alia, with corn, a C4 plant. In 1995, one soil was converted from annual cropping to permanent cultivation with Miscanthus x giganteus , another C4 plant, while the other was converted to permanent C3 grassland in 2009. Using δ 13 C signatures, we analysed the fractions of C4 derived carbon in the soil and in CO 2 , during one month of soil incubation. This enabled us i) to estimate C4-C accumulation in both soils, and ii) to assess the lability of C4-C carbon that accumulated either at least five years prior to sampling (current grassland soil) or until sampling (current Miscanthus soil ). The fraction of C4-C derived SOC in the Miscanthus soil was 0.19 ± 0.024 in the top 30 cm, corresponding to an accumulation rate of 1.6 ± 0.2 t C4-C ha −1 yr −1 . This accumulation rate is in the range of rates found for fertile mineral soils cultivated with Miscanthus . Yet, this C4-C accumulation rate is below average C-losses of agriculturally used organic soils. The grassland soil contained a smaller fraction of 0.08 ± 0.002 C4-C in SOC. The rates of total CO 2 emitted from the two soils did not differ, but the fraction of CO 2 derived from C4-C was significantly higher in the Miscanthus soil (0.53 ± 0.05) than in the grassland (0.29 ± 0.04) soil. Hence, in both soils YOC was more labile than bulk SOC. The ratio between the fraction of decomposing C4-C and C4-C in SOC was the same for both soils indicating a similar lability of currently accumulated and aged C4-C. In both soils, the 14 C age of emitted CO 2 was younger than that of SOC, confirming an increased lability of YOC over old SOC. [ABSTRACT FROM AUTHOR]

Many plants have been found to show preferential root growth allocation to soil patches with locally increased nutrient availability. Little is known about the influence of the plants’ nutrient status on these responses. Addressing this question, we conducted a climate chamber experiment to investigate how foliar phosphorus (P) and zinc (Zn) application (alone or in combination) would affect root allocation and nutrient uptake by white lupin ( Lupinus albus L.) seedlings growing on soil with constructed heterogeneity in P and Zn distribution. The same soil packing was used in all pots. One quarter section of each packing was enriched with Zn, one with P, one with Zn and P, while neither Zn nor P was added to the fourth section (opposite to the section with the combined Zn and P amendment). Neither foliar P nor foliar Zn application had a fertilization effect on plant growth. The allocation of root length growth showed a clear preference for P-enriched soil sections, when no foliar fertilizer was applied. With foliar P or Zn application these preferences disappeared. Cluster root allocation and root P concentration showed a similar behavior. In the treatments with foliar Zn application, root length growth was also preferentially allocated in Zn-enriched soil, while without foliar Zn there was only a tendency for such a response. Root Zn concentrations were always much higher in soil sections with than without Zn amendment. The foliar treatments had no effect on root Zn concentration. While the responses to foliar P application can be understood in terms of an optimization strategy in root allocation for P foraging, the effects of foliar Zn application on root growth allocation cannot be interpreted in this way and require further investigation. [ABSTRACT FROM AUTHOR]

Shooting ranges are a source of environmental concern around the world as they are a source of toxic antimony (Sb) and lead (Pb). In-situ chemical stabilization is a strategy to reduce metal(loid) leaching and bioavailability. However it is difficult to find the right treatment due to the fact that Pb is a cation and Sb an anion, under oxidised conditions and they often show the opposite mobility in soil, on the application of amendments. A batch experiment was set up with two soils (slightly acidic and alkaline), two red mud based amendments (ViroSoil™ 1 and 2) alone and in combination with two reducing agents (zero valent iron and iron sulphate), to assess the effect of the treatments on metal(loid) leaching and compare it to unamended soil and soil amended with goethite, a known Sb adsorbent. Iron sulphate was effective at reducing Sb leaching due to the reduction of Sb V to Sb III which bound more strongly to iron (hyr)oxides in soil. However it had an adverse effect on the leaching of Pb due to its acidifying effect and reductive dissolution of manganese (hyd)roxides. Combining ViroSoil™ amendments with FeSO 4 still reduced Sb leaching but also Pb leaching and proved a suitable treatment. [ABSTRACT FROM AUTHOR]

Phytomanagement in terms of phytostabilisation has been proposed as a suitable technique to decrease the environmental risks of metal(loid) enriched mine tailings. Nevertheless, at these sites some issues must be solved to assure the long-term establishment of vegetation ( e.g. salinity, low fertility, metal(loid) phytotoxicity, etc.) The objective of this study was to assess the effects of the addition of a municipal solid waste on a mine tailings soil and on the growth and metal(loid) accumulation of a grass plant species ( Piptatherum miliaceum ). In addition, the effects of intra-specific interactions were evaluated. A pot experiment was performed during 8 months, including two soil treatments: the mine soil and its combination with municipal solid wastes. For each treatment, pots without plants, pots with one plant, and pots with two plants were arranged. The addition of municipal solid wastes improved the soil fertility and plant growth in the mine soil, but also increased the mobile fractions of Zn, Pb, Cd, Mn and Ni. Plants in the amended treatments showed better nutritional status (higher P and K). Stable isotope δ 15 N was associated to the better nutritional status, while δ 13 C and δ 18 O indicated higher photosynthetic efficiency and stomatal conductance in amended treatments. Although the accumulation in leaves of most metal(loid)s decreased with the municipal waste application, the concentrations in both treatments did not exceed toxic limits for fodder. There was an effect of intra-specific competition in plant growth, probably due to lack of nutrients in the mining soil or limited pots volume in the treatments with municipal waste. [ABSTRACT FROM AUTHOR]

Phage‐bacterium interactions influence soil microbial life and ecological functions, including microbial evolution, community patterns, and nutrient cycling. However, understanding of phage‐mediated soil bacterial lysis dynamics, and impacts on soil carbon (C) and nitrogen (N) cycling, remains elusive. Here, we used a short‐term laboratory incubation microcosm model system (which did not contain actual soil) consisting of a soil bacterium Bacillus cereus LB2 and an exclusive B. cereus phage SWEP1 to illustrate how a single soil phage manipulates bacterial lysis and the associated necromass formation under different nutrient conditions, and the associated changes on C and N dynamics. Results showed that the phage‐induced bacterial lysis significantly increased the total amounts of necromass C and N, which was correlated to nutrient conditions. Bacteria populations were effectively eliminated by phages under eutrophic conditions, whereas the lysis rate of SWEP1 slowed down under oligotrophic conditions. The presence of phage clearly stimulated necromass accumulation, albeit with a reduced proportion of dissolved NH4+‐N content from the supernatant. Therefore, phages may enhance microbial necromass formation, and actively contribute to soil organic matter (SOM) stabilisation and C and N cycling in soil ecosystem. Highlights: Phage‐mediated bacterial lysis increased C and N contents in necromassEutrophic conditions facilitate phage‐mediated bacteria eliminationThe lysis rate of phage slows down under oligotrophic conditionsThe contribution of bacterial necromass to SOM may be underestimated [ABSTRACT FROM AUTHOR]

Proper management of soil phosphorus (P) is essential to ensure sustainability in agriculture. To avoid excessive P accumulation in soil, a methodology for predicting long-term variations in soil P content is required. Using the Swiss Soil Monitoring Network (NABO) database, we tested the efficiency of the model EPIC to predict soil P temporal changes for typical Swiss arable and grassland sites. After performing a sensitivity analysis to identify the most influential model parameters for which calibration was needed, we calibrated the influential parameters on the available topsoil P data of 4 selected NABO sites and then we tested the calibrated model by comparison of predictions with data from a second set of 14 sites. We found that the model performance for grassland sites improved significantly when site-specific estimates of bioturbation depth were used. These site-specific estimates showed a close relationship to independently assessed subsoil hydromorphy. [ABSTRACT FROM AUTHOR]

Although soil compaction has become a common problem in forests nowadays, little is still known on the possibilities to promote the structural recovery of compacted forest soils. Here we examined how planting black alder into the ruts of skid lanes with and without application of compost would affect the regeneration of soil structure in a gleyic Cambisol on the Swiss Plateau. Seven years after planting, soil samples taken at three different depths next to the trees were analyzed for bulk density, total and coarse porosity, air permeability, precompression stress and root mass density and compared to samples from unplanted skid lanes and planted but non-trafficked reference plots. All four physical parameters showed strong compaction effects in the skid lanes. Coarse porosity was reduced down to 0.5 m depth, and air permeability even down to 0.7 m depth. In combination with compost application, the planting of black alders resulted in a significant regeneration of structure, although recovery was still far from complete compared to the untrafficked reference soil. Without compost, there was no significant treatment effect compared to the unplanted skid lanes, but a clear trend, as the differences in coarse porosity and precompression stress between the two alder treatments with and without compost were not significant either. Air permeability showed a significant effect of the alder treatment with compost that extended down to 0.7 m depth, but also reached values of the same magnitude as in the non-trafficked reference soil. Air permeability furthermore showed a very similar pattern of treatment effects to rooting density in the skid lane soils. The correlation between these two parameters increased with depth. These results suggest that the roots of the planted alder trees initiated structure recovery by generating air-conducting porosity and thereby promoted other biotic structure-formation processes. Our study highlights the fact that tree root growth may significantly contribute to soil structure recovery after compaction. [ABSTRACT FROM AUTHOR]

Soil compaction due to the use of heavy machinery for timber harvesting has become a widespread problem in forestry. However, only few studies deal with the regeneration of compacted forest soils. In the present study, we examined the potential of accelerating soil regeneration by planting black alder trees ( Alnus glutinosa (L.) Gaertn.) in skid lane tracks. In 2003, seedlings were planted into the rut beds of severely compacted skid lanes in two Swiss forest sites. In addition, some of the ruts were filled with compost. In 2009 and 2010, we assessed the success of these measures by analysing physical parameters of soil structure (bulk density, total and coarse porosity and air permeability), root densities and tree growth. Tree growth was exceptionally strong on the skid lanes. Total and coarse soil porosity and air permeability showed significant increase in planted skid lanes as compared to untreated control subplots, approaching values found for untrafficked soil in the immediate vicinity. All soil physical parameters were closely correlated to root mass density. Compost application enhanced tree growth and soil structure regeneration on one site, but had a retarding effect on the other site. Planting black alders has great potential as an environmentally friendly measure to accelerate the structural regeneration of compacted forest soils in temperate humid climates. [ABSTRACT FROM AUTHOR]

Aims and Background: Many plants preferentially grow roots into P-enriched soil patches, but little is known about how the presence of arbuscular mycorrhizal fungi (AMF) affects this response. Methods: Lotus japonicus (L.) was grown in a low-P soil with (a) no additional P, (b) homogeneous P (28 mg pot −1), (c) low heterogeneous P (9.3 mg pot −1), and (d) high heterogeneous P (28 mg pot −1). Each P treatment was combined with one of three mycorrhiza treatments: no mycorrhizae, Glomus intraradices, indigenous AMF. Real-time PCR was used to assess the abundance of G. intraradices and the indigeneous AMF G. mosseae and G. claroideum. Results: Mycorrhization and P fertilization strongly increased plant growth. Homogeneous P supply enhanced growth in both mycorrhizal treatments, while heterogeneous P fertilization increased biomass production only in treatments with indigenous AMF inoculation. Preferential root allocation into P-enriched soil was significant only in absence of AMF. The abundance of AMF species was similar in P-enriched and unfertilized soil patches. Conclusion: Mycorrhization may completely override preferential root growth responses of plants to P- patchiness in soil. The advantage of this effect for the plants is to give roots more freedom to forage for other resources in demand for growth and to adapt to variable soil conditions. [ABSTRACT FROM AUTHOR]

Highlights: [•] We spatially distribute agricultural land use types using newly available data. [•] The developed downscaling approach may be useful for a wide range of applications. [•] The very few simple rules applied to the data were shown to give accurate results. [Copyright &y& Elsevier]

Repeated application of Cd-rich phosphate fertilizers can lead to the accumulation of this nonessential element in soil. This can result in increased plant uptake, with possible breaches of food or feed safety standards. We aimed to determine whether lignite (brown coal) can reduce Cd solubility and plant uptake in New Zealand pasture soils. In batch sorption experiments, we tested the capacity of lignite and lignite-soil mixtures to sorb Cd at various soil pH and Cd loadings. Over a pH range of 4-7, Cd sorption by lignite was 1-2 orders of magnitude greater than by a typic immature pallic soil containing 2% carbon. The addition of S wt % lignite to a range of soils revealed that lignite addition was most effective in reducing soluble Cd in soils with low pH. In a greenhouse experiment, we tested the effect of lignite on the accumulation of Cd and other elements by perennial ryegrass, Lolium perenne (L.). The addition of just 1 wt % lignite to the aforementioned soil reduced plant Cd uptake by 30%, without adversely affecting biomass or the uptake of essential nutrient elements including copper and zinc. This may be due to preferential binding of Cd to organic sulfur in lignite. [ABSTRACT FROM AUTHOR]

Abstract: In most parts of Iran, water scarcity has been intensifying and posing a threat to the sustainability of agricultural production. Wheat is the dominant crop and the largest irrigation water user in Iran; hence, understanding of the crop yield–water relations in wheat across the country is essential for a sustainable production. Based on a previously calibrated hydrologic model, we modeled irrigated and rainfed wheat yield (Y) and consumptive water use (ET) with uncertainty analysis at a subbasin level in Iran. Simulated Y and ET were used to calculate crop water productivity (CWP). The model was then used to analyze the impact of several stated policies to improve the agricultural system in Iran. These included: increasing the quantity of cereal production through more efficient use of land and water resources, improving activities related to soil moisture conservation and retention, and optimizing fertilizer application. Our analysis of the ratio of water use to internal renewable water resources revealed that 23 out of 30 provinces were using more than 40% of their water resources for agriculture. Twelve provinces reached a ratio of 100% and even greater, indicating severe water scarcity and groundwater resource depletion. An analysis of Y-CWP relationship showed that one unit increase in rainfed wheat yield resulted in a lesser additional water requirement than irrigated wheat, leading to a larger improvement in CWP. The inference is that a better water management in rainfed wheat, where yield is currently small, will lead to a larger marginal return in the consumed water. An assessment of improvement in soil available water capacity (AWC) showed that 18 out of 30 provinces are more certain to save water while increasing AWC through proper soil management practices. As wheat self-sufficiency is a desired national objective, we estimated the water requirement of the year 2020 (keeping all factors except population constant) to fulfill the wheat demand. The results showed that 88% of the additional wheat production would need to be produced in the water scarce provinces. Therefore, a strategic planning in the national agricultural production and food trade to ensure sustainable water use is needed. This study lays the basis for a systematic analysis of the potentials for improving regional and national water use efficiency. The methodology used in this research, could be applied to other water scarce countries for policy impact analysis and the adoption of a sustainable agricultural strategy. [Copyright &y& Elsevier]

Abstract: Due to landscaping, mining and construction activities on previously cultivated land, more and more soils are excavated, translocated, deposited and restored. In many cases restored soils show signs of structural degradation such as overcompaction and water logging. There is a lack of methods to evaluate and assess the physical quality of restored soil. In this study a fuzzy logic expert system was developed which allows us to evaluate the potential plant productivity of restored soils based on measured physical soil parameters. The system is based on the statements of a group of soil experts relating physical soil quality to packing density, penetration resistance, air capacity and saturated hydraulic conductivity according to their personal experience or expertise. From these statements we derived fuzzy membership functions and inference rules. The expert system was applied to evaluate 10 restored sites in comparison to nearby non-restored reference soils. The physical soil quality had remained unchanged or decreased after restoration at most investigated sites. Only two horizons showed clearly improved soil conditions after restoration. The validity of the fuzzy logic expert system is demonstrated by comparing the results with evaluations of the same soils using two other indicators of the physical soil quality for plant production: the least limiting water range (LLWR) and the S-parameter (i.e. the slope of the water retention curve at the inflection point). The physical soil quality assessment with the fuzzy logic expert system was highly correlated with both the LLWR (r 2 =0.80) and the S-parameter (r 2 =0.70). These results show that fuzzy logic expert systems may provide a suitable tool to assess physical soil quality, taking proper account of the vagueness and ambiguity necessarily involved in this task. [Copyright &y& Elsevier]

Abstract: Soil restoration is the process by which a soil that has been disturbed by excavation and displacement or by degradation is returned to its original state by means of active treatment. At the beginning of the process, restored soils are mechanically labile and susceptible to compaction. In this study, we monitored the regeneration of some physical soil quality indicators (bulk density, coarse porosity, penetration resistance) and the development of indicators of mechanical stability (precompression stress, compression index) of a refilled sandy loam originating from an Eutric Cambisol. In particular, we derived multiple linear regression equations to correlate precompression stress and compression index to soil texture, gravel content, organic carbon content and void ratio. During the 3-year observation period after restoration, bulk density and penetration resistance increased significantly, while coarse porosity decreased significantly. Nonetheless, these parameters remained in a range, which is considered to indicate suitable physical soil conditions for root growth over the entire period of observation. Precompression stress increased significantly in the topsoil as well as in the subsoil. The compression index was significantly higher in the topsoil than the subsoil and stayed fairly constant over the observation period. Precompression stress was negatively and the compression index was positively correlated with initial void ratio and to coarse porosity. Taking additional parameters into account, such as gravel content, clay content, silt content and organic matter content, improved the correlation with precompression stress. The equations derived with multiple linear regression analysis from our data set gave a satisfactory coefficient of determination for the compression index (r 2 =0.81), but rather poor estimates for precompression stress (r 2 =0.50). [Copyright &y& Elsevier]

Organochlorine pesticides (OCP) are still found in food and feed crops although they were applied about 40 years ago. There is a considerable knowledge gap concerning the extent of soil and crop contamination by OCP. We performed two surveys in 2002 and 2005 to assess the loads of OCP in 41 Swiss horticultural fields under organic and conventional production and corresponding Cucurbitaceae fruits (cucumbers, zucchini, and pumpkin), whereas these fields stay for intensive agricultural production in Europe. In addition, soil organic carbon, texture, and pH were measured also. OCP were detected in 27 out of 41 fields (65.9%). The farming practice had no influence on the contamination or level of OCP in soil. The sum of OCP-loads per field ranged from <0.01 to 1.3mgkg−1 dry soil and pentachloroaniline (PCA, 2.1mgkg−1), p,p′-DDT (0.5mgkg−1), and p,p′-DDE and dieldrin (0.4mgkg−1) were the most detected pesticides over all investigated soils. PCA (up to 0.02mgkg−1), dieldrin (up to 0.04mgkg−1), α-chlordane and cis-heptachloroepoxide (<0.01mgkg−1) were detected in five cucumber samples out of 41 Cucurbitaceae samples. Statistical analysis revealed no significant influence of the measured soil properties on the OCP-load of soils and cucumbers, although there is evidence that the bioavailability of OCP in soils to Cucurbitaceae plants was influenced by the sorption of the compounds to soil organic matter and by the polarity of the pesticide molecules. It is suggested, that OCP contamination is widespread in all European regions with intensive plant production and associated pesticide use, and deserves more attention with respect to save food production. [Copyright &y& Elsevier]

Abstract: Mine tailings are ubiquitous in the landscapes of mined areas. Metal solubilities were compared in two chemically distinct mine tailings from the old Mining District of Cartagena-La Unión (SE Spain). One of the tailings was acidic (pH 3.0) with 5400mg/kg Zn, 1900mg/kg As and 7000mg/kg Pb. The other was neutral (pH 7.4) with 9100mg/kg Zn, 5200mg/kg Pb and 350mg/kg As. In samples from the acidic tailings, more than 15% of the Zn and 55% of the Cd were extractable with 0.1M NaNO3, and distilled water. In the neutral tailings, using the same reagents, less than 1% of the metals were extractable. A sequential extraction procedure revealed that the sum of the residual and the Fe oxide fractions of Cu, Zn and Pb comprised 80–95% in the acidic tailings and 70–90% in the neutral tailings. The acidic mine tailings had a higher metal solubility, resulting in more metal leaching in the short-term, but also a higher fraction of inert metal. In contrast, in the neutral tailings, the metals were evenly distributed between, oxides and the residual fraction. This implies lower metal mobility in the short-term, but that metal mobility may increase in the long-term. When applied to mine tailings, sequential extractions may provide misleading results because the strong cation exchange capacity of some extractants may induce pH changes and thereby significantly change metal solubility. [Copyright &y& Elsevier]

Abstract: Cationic surfactants have been found in previous studies to enhance the capacity of zeolites to bind organic compounds and oxyanions. In this study, we treated zeolite with hexadecyltrimethylammonium (HDTMA) and studied the sorption of antimonate by the modified zeolite. During the modification, the zeolite sorbed more than 94% of HDTMA initially present in different treatment solutions. Desorption of HDTMA from the zeolite was less than 15% in total after threefold washing with distilled water. Antimonate binding was most effective when the zeolite was treated with HDTMA solutions exceeding the zeolites external cation exchange capacity. A modified Langmuir-type isotherm was developed to describe HDTMA sorption onto zeolite. Antimonate sorption on modified zeolite was best described by Langmuir isotherms. HDTMA-zeolite in aqueous suspension (50g/l) sorbed up to 42% of antimonate from solutions containing from 0.09 to 2.15mmol/l Sb. [Copyright &y& Elsevier]

Root–soil interactions can strongly influence the soil solution chemistry in the rhizosphere. In the present study we propose a modification of the classical rhizobox/micro suction cup system to make it suitable for the collection and analysis of organic acids in the rhizosphere. In order to show the potential of the method, we tested the modified system with Lupinus albus L. as a model plant known to exude large amounts of citrate. The suction cups were installed through the transparent front plate of the rhizoboxes just after the emergence of cluster roots in order to allow optimal localized collection of soil solution. A small dead-volume allowed almost immediate stabilisation with formaldehyde of the sampled soil solutions in the collection container to prevent microbial degradation. The concentrations of organic acids were significantly larger in the rhizosphere soil solution of active cluster roots of Lupinus albus L. than in the bulk soil solution (about 400 µM of citrate versus <0.05 µM). We were able to follow the exudation process in-situ, which occurred during 2–3 days. Also the concentrations of other organic acids and inorganic anions differed between the bulk soil and the rhizosphere of cluster roots, normal roots, and nodules. [ABSTRACT FROM AUTHOR]

Owing to the lack of regulations limiting pollutant concentrations in sludge and rates of sludge application on agricultural lands, high loads of heavy metals are introduced into agricultural soils by the use of sewage sludge as fertilizer in Iran. In order to examine the risk of metal transfer into vegetables arising from this practice under the farming conditions of central Iran, we performed a four-year field experiment in which we investigated the uptake of heavy metals from a sludge-amended soil (fine loamy, mixed thermic Typic Haplarigid) by lettuce (Lactuca sativa L.) and spinach (Spinacia oleracea L.). Sludge application rates were 0, 22.5, and 45 Mg ha -1 . To determine the effect of repetitive sludge applications, applications were repeated on two-thirds of each plot in the second year and on one-half of these subplots again in the third year. Thus, total sludge amounts applied were 22.5 and 45 Mg ha -1 in plots that received one application, 45 and 90 Mg ha -1 in plots with two applications, and 67.5 and 135 Mg ha -1 in plots with three applications. Single applications increased the EDTA-extractable concentrations of copper (Cu), zinc (Zn), and lead (Pb). Cadmium (Cd) concentrations increased only after two or three consecutive applications. In subsequent years with no further sludge applications, EDTA-extractable metal concentrations in soil showed a decreasing trend but, even after four years EDTA extractable metal concentrations were still significantly higher in plots that had received more than 45 Mg ha -1 sludge than in control plots. Metal uptake by the plants also increased with sludge application and decreased again after applications stopped. Close correlation with the EDTA-extractable soil metal concentrations suggests that EDTA is an effective indicator of plant-available metal concentrations in the investigated soil. Lettuce and spinach yields both increased significantly with all sludge application rates and this fertilizer effect was still evident three years after a single sludge application, indicating that sewage sludge can improve fertility of arid soils in the region. [ABSTRACT FROM AUTHOR]

Phytoextraction has been proposed in recent years as an environmentally and cost-efficient treatment technique for the remediation of heavy-metal contaminated sites. In particular, plants that are fast growing, metal accumulating, and economically interesting, such as sunflowers or trees, recently became more important in research on phytoextraction. Heavy metal uptake of trees can be strongly influenced by ectomycorrhizal fungi. We investigated the possibility of enhancing phytoextraction of Cd by willows ( Salix viminalis) and poplars ( Populus canadensis) in association with three well known ectomycorrhizal fungi ( Hebeloma crustuliniforme, Paxillus involutus and Pisolithus tinctorius). A pot experiment was conducted using Cd polluted soil from a contaminated site. Four replicates of each combination of fungus and tree species, and controls without fungal inoculum, were set up. After a growth period of 11 weeks, yields and Cd concentrations in roots, stems, and leaves were measured. In addition, the total Cd uptake, the transfer to roots, and the translocation to stems and leaves were calculated. The association of P. canadensis with P. involutus led to a highly significant increase of Cd concentrations, in particular in the leaves, which contained 2.74 ± 0.34 mg Cd per kg dry matter. Compared to the control this is an enhancement of nearly 100%. The fungi also significantly enhanced the translocation from the roots to the leaves, leading to a concentration ratio (leaves/roots) of 0.32 ± 0.06 compared to 0.20 ± 0.02 of the control plants. Additionally, P. involutus significantly enhanced the total Cd extraction by P. canadensis. Similar effects were not observed by other fungi or in association with S. viminalis. [ABSTRACT FROM AUTHOR]

A possible remediation strategy for metal polluted soils is washing with chelants. Here, we compare the efficiency of batch and column extraction of Cu, Zn, and Pb from three soils using the biodegradable chelant EDDS. A total of 53-80% of Cu was extracted in batch and 18-26% in column extraction. For Zn, the extractability was 16-50% in batch and 20-64% in columns and for Pb 25-52 and 18- 91%, respectively. Column leaching was therefore equally or better suited for Zn and Pb removal. The longer extraction time in the column resulted in more formations of Fe(lll)EDDS by slow dissolution of iron oxides. Zn was uniformly washed from the column, while Cu and Pb were extracted in the top layers and deposited in the bottom layers, presumably by biodegradation of the metal-EDDS complexes and slow dissolution of iron oxides. Between 18 and 42% of the applied EDDS was lost through biodegradation after 7 weeks. In short time experiments, only 6% of EDDS was degraded. Using EDDS concentrations in excess of available heavy metals caused pronounced leaching of organic matter and clogging of the column. Our results prove that heap leaching using EDDS is a promising approach to reduce the heavy metal content of polluted soils. [ABSTRACT FROM AUTHOR]

A pot experiment was conducted to investigate the relationship between soluble concentrations of arsenic (As) in soil and its accumulation by maize (Zea mays), English ryegrass (Lolium perenne), rape (Brassica napus) and sunflower (Helianthus annuus) on two different soils: a calcareous Regosol (silty loam) and a non-calcareous Regosol (sandy loam). Arsenic (Na2HAsO4·7H2O) was applied to obtain comparable soluble As concentrations in the two soils. In both soils, soluble As concentrations, extracted with 0.1MNaNO3, were found to correlate better with As concentrations in plants after 4 month of growth than total soil concentrations, extracted with 2MHNO3. With all four plant species, the relationship between the soluble As concentration in the soil and As that in the plants was non- linear, following “Michaelis-Menten” kinetics. Similar soluble As concentrations in the two soils did not result in a similar As concentration in the plants. Except for maize, arsenic transport from roots to shoots was significant, resulting in As concentrations in the leaves and grains above the Swiss tolerance limits for fodder and food crops (4 and 0.2 mg As kg-1, respectively). Based on these results we suggest that beside As solubility, P availability and P demand, which are plant specific, have to be taken into account to predict the uptake of As by crop plants from As contaminated soils and to predict the risk of arsenic entering into the food chain. [ABSTRACT FROM AUTHOR]

The technique of diffusive gradients in thin films (DGT) has been shown to be a promising tool to assess metal bioavailability in soils under laboratory conditions. In this study we used DGT to investigate the resupply kinetics of Cu and Zn under in-situ conditions in a polluted lysimeter soil and compared the results with laboratory measurements using undisturbed soil cores at defined water contents as well as homogenized soil samples. Results differed considerably between these treatments, although the same soil material was used in all experiments. A small pool of rapidly available Zn was found in the field but not in the homogenized soil. Soil solution pH and dissolved metal concentrations also varied significantly between the soil treatments. In addition, we compared the DGT-measured effective concentration with the uptake of Cu and Zn into the shoots of Lolium perenne (Ryegrass) under the same three types of conditions, i.e., field, soil cores, and homogenized soil. A close relationship was found which was not linear but could be described by a saturation-type behavior. L. perenne is a metal excluder plant, and thus, metal accumulation is limited by translocation of metals from roots to shoots. DGT predicted plant metal uptake much better than the soil solution concentration or pH. The results of this study suggest that DGT may be successfully used under field conditions to study the kinetics of metal resupply. Plant metal concentrations were not well predicted in all cases by the effective concentration CE under field conditions. Some plants took up considerably more metals than estimated by CE. Variations in metal uptake independent of their bioavailability can be caused by local variations in microsite conditions, e.g. light, temperature, water, and nutrients. To some degree, such indetermination has to be expected as an inherent feature of the system and the concept of bioavailability. [ABSTRACT FROM AUTHOR]

This study investigated the effects of exogenous methionine (Met) and different phosphate (PO 4) concentrations on Cd uptake and translocation in Valeriana officinalis L. Seedlings were grown in nutrient solutions with three different concentrations of phosphate (900, 1200, and 1500 μM) for two weeks, then exposed for 4 days to 10 μM Cd, either in presence or absence of 400 μM methionine. The Met treatment decreased root Cd accumulation by up to 40%, while it enhanced Cd uptake into the shoots by 50%. In absence of Met, shoot Cd uptake was not affected by the level of phosphate application, although root Cd contents increased. The latter effect was entirely due to increased apoplastic Cd binding. In presence of Met, the Cd accumulation of both plant parts showed trends to increase with increasing phosphate level. In contrast to the treatments without Met, however, the phosphate effect on root Cd was due to increased symplastic root Cd allocation. The results suggest that the effects of Met on Cd uptake were due to the formation of mobile Cd-Met complexes, reducing phosphate-promoted Cd-retention in the apoplast and enhancing Cd transfer into the root symplast. Irrespective of the treatment, shoot Cd accumulation showed a close linear relationship to shoot mass, suggesting that convective transport with the transpirational water stream was the rate-governing uptake process. The results indicate that methionine supplementation could reduce Cd accumulation in valerian roots, which are the parts of this plant harvested for medicinal purposes, in Cd-contaminated soil, while phosphate would enhance it. • Methionine in nutrient solution increased shoot and root biomass of Cd-stressed Valerian plants. • Phosphate supply was less effective in promoting plant growth than methionine. • Methionine in nutrient solution reduced apoplastic but increased symplastic root Cd content. • Symplastic but not apoplastic root Cd responded to phosphate like shoot Cd accumulation. • Cadmium (Cd) uptake by Valerian shoots showed a close linear relationship to shoot biomass. [ABSTRACT FROM AUTHOR]

Cadmium (Cd) is a biologically non-essential heavy metal that can cause toxic effects in plants, animals and humans already at low concentrations compared to other metals. After Cd concentrations in cacao beans of various provenances, particularly from Latin America, were found to exceed the new regulations enforced by the European Union in 2019, there is an urgent need to find measures to lower Cd accumulation in cacao beans to acceptable values. In this research, the long-term cacao cultivar trial CEDEC-JAS in northern Honduras was used to investigate differences between 11 cultivars in Cd uptake and translocation. Sampling of various plant parts, including rootstocks, scions, leaves and beans, from three replicate trees per cultivar and the soil around each tree was conducted at this site. Results indicate that concentrations of available soil Cd were more closely correlated with Cd concentrations of the rootstocks (R2 = 0.56), scions (R2 = 0.59) and leaves (R2 = 0.46) than with bean Cd concentrations (R2 = 0.26). In addition, Cd concentrations of rootstocks, scions and leaves showed close relationships to available soil Cd concentrations, with no significant differences between the cultivars. In contrast, bean Cd concentrations showed only weak correlations to available soil Cd and Cd concentrations in the vegetative plant parts, but significant variation among cultivars. Three cultivars, which were analysed in more detail, showed significant differences in Cd concentrations of mature beans, but not of immature beans. These results suggest that cultivar-related differences in bean Cd concentrations primarily result from differences in Cd loading during bean maturation, possibly due to cultivar-specific differences in the xylem-to-phloem transfer of Cd. The results show that selection of cultivars with low Cd transfer from vegetative parts into the beans has high potential to keep Cd accumulation in cacao beans at levels that are safe for consumption. Unlabelled Image • Available soil Cd was closely related to Cd in vegetative parts but less to bean Cd. • Soil factors could not fully explain the variation in bean Cd. • Cd translocation into beans showed a significant influence of the cultivar. • Translocation of Cd into cacao beans could be limited by selecting appropriate cultivars. [ABSTRACT FROM AUTHOR]

Interactions between model parameters and low spatiotemporal resolution of available data mean that conventional soil organic carbon (SOC) models are often affected by equifinality, with consequent uncertainty in SOC forecasts. Estimation of belowground C inputs is another major source of uncertainty in SOC modelling. Models are usually calibrated on SOC stocks and fluxes from long‐term experiments (LTEs), whereas other point data are not used for constraining the model parameters. We used data from an agricultural long‐term (>65 years) fertilization experiment to test a multi‐objective parameter estimation approach on the RothC model, combining SOC data from different fertilization treatments with microbial biomass, basal respiration and Zimmermann's fractions data. We also compared two methods to estimate the belowground C inputs: a conventional scaling of belowground biomass from crop harvest yield and an alternative approach based on constant belowground C for cereals measured experimentally in the field. The resulting posterior parameter distributions still suffered from some equifinality; the most stable C pool kinetic constants and composition of exogenous organic matter were the most sensitive parameters. The use of fixed belowground C inputs for cereals improved the model performance, reducing the importance of treatment‐specific parameters and processes. The introduction of microbial biomass and basal respiration data was effective for increasing determination of the calibration, but also suggested a change in the model structure: the microbial biomass pool, which is proportional to the C inputs in the traditional models, could be represented by different microbial physiology functions. Highlights: Multi‐objective calibration with SOC and microbial or soil fractionation data can reduce model uncertainty.We compared different methods to estimate belowground C inputs on a long‐term trial in Switzerland.Fixed belowground C inputs measured in the field gave the best model performance.Microbial data can improve model calibration, but a change in model structure is suggested. [ABSTRACT FROM AUTHOR]

Abstract Wheat is a staple food crop and a major source of both the essential micronutrient zinc (Zn) and the toxic heavy metal cadmium (Cd) for humans. Since Zn and Cd are chemically similar, increasing Zn concentrations in wheat grains (biofortification), while preventing Cd accumulation, is an agronomic challenge. We used two Swiss agricultural long-term field trials, the "Dynamic-Organic-Conventional System Comparison Trial" (DOK) and the "Zurich Organic Fertilization Experiment" (ZOFE), to investigate the impact of long-term organic, mineral and combined fertilizer inputs on total and phytoavailable concentrations of soil Zn and Cd and their accumulation in winter wheat (Triticum aestivum L.). "Diffusive gradients in thin films" (DGT) and diethylene-triamine-pentaacetic acid (DTPA) extraction were used as proxies for plant available soil metals. Compared to unfertilized controls, long-term organic fertilization with composted manure or green waste compost led to higher soil organic carbon, cation exchange capacity and pH, while DGT-available Zn and Cd concentrations were reduced. The DGT method was a strong predictor of shoot and grain Cd, but not Zn concentrations. Shoot and grain Zn concentrations correlated with DTPA-extractable and total soil Zn concentrations in the ZOFE, but not the DOK trial. Long-term compost fertilization led to lower accumulation of Cd in wheat grains, but did not affect grain Zn. Therefore, Zn/Cd ratios in the grains increased. High Zn and Cd inputs with organic fertilizers and high Cd inputs with phosphate fertilizers led to positive Zn and Cd mass balances when taking into account atmospheric deposition and fertilizer inputs. On the other hand, mineral fertilization led to the depletion of soil Zn due to higher yields and thus higher Zn exports than under organic management. The study supports the use of organic fertilizers for reducing Cd concentrations of wheat grains in the long-term, given that the quality of the fertilizers is guaranteed. Graphical abstract Unlabelled Image Highlights • Impact of fertilization on Zn and Cd in wheat was studied in long-term field trials. • DGT and DTPA were used to measure plant-available soil metals. • DGT-available soil Cd positively correlated with wheat shoot and grain Cd. • Wheat grain Cd but not Zn was reduced by long-term organic fertilization. [ABSTRACT FROM AUTHOR]

Aims: The study investigated the growth and metal accumulation over time of young forest vegetation growing on metal-contaminated topsoil above either acidic or calcareous subsoil. Methods: A 4-year model ecosystem experiment was performed under quasi-natural conditions. The heavy metal (HM) contaminated topsoil contained around 3000 mg/kg Zn, 600 Cu, 100 Pb, 9 Cd. Results: Total biomass was 25.7% lower on the acidic than on the calcareous subsoil. The HM topsoil did not affect total understorey and Salix biomass, but decreased the growth of Populus, Betula and on the acidic subsoil also that of Picea. Leaf Cd and Zn concentrations were around 6 and 1000 mg/kg, respectively, in Populus and Salix on the HM topsoil, and 0.6 and 200 mg/kg in Picea and understorey. Leaf and wood HM concentrations, were lower in Populus and Salix on the calcareous than on the acidic subsoil. Temporal trends differed among the investigated metals. The HM-induced relative increases in leaf and wood metal concentrations were lower by at least an order of magnitude than in the respective soluble topsoil metal concentrations. Over the four years, Zn was increasingly accumulated in older twigs in Picea. Conclusions: The selected native trees are suited for phytomanagement of HM-contaminated topsoils. Subsoil acidity is a relevant factor. [ABSTRACT FROM AUTHOR]

Zinc (Zn) deficiency is a widespread problem in human nutrition and wheat grains are a major source of Zn intake in large parts of the population. It remains unclear to what extent organic and conventional farming practices, differing in organic matter management, influence Zn availability and uptake by wheat grains. Factors leading to an increased Zn uptake may also increase the Cd uptake in wheat grains, which can be harmful for humans. Here, we investigated the effects of different farming practices on Zn and Cd concentrations in wheat grains and their relationships with total and available soil Zn and Cd concentrations, and other soil properties. In northern Switzerland, 28 farms were sampled including 11 organic farms with compost use, 10 organic farms without compost use, and 7 conventional farms without compost use. Soil organic matter was a key factor for soil Zn and especially Cd concentrations across all three farming systems. Total and available soil Cd concentrations as well as soil organic carbon concentration (SOC) were significantly higher on the organic farms with compost use than on the conventional farms. However, only the compost farms with livestock showed significantly higher grain Cd concentrations in comparison to conventional and organic farms without compost use, although a nested effect of cultivar within the system also had an influence. In contrast to Cd, the soil and grain Zn concentrations showed no significant farming system effect although there was a correlation between total soil Zn and SOC when all farms were pooled. Grain Zn was decoupled from soil Zn indicating that under agricultural field conditions the farming systems are a minor factor in increasing grain Zn. Our study suggests that the Zn and Cd soil and grain concentrations were mediated by a combination of on-farm organic matter management, soil properties, cultivar, and livestock production. [ABSTRACT FROM AUTHOR]