Soil Solution Composition Research Articles

Tradeoffs between pH, dissolved organic carbon, and mineral ions regulate cadmium uptake by Solanum hyperaccumulators in calcareous soil

Soil solution pH and dissolved organic carbon (DOC) influence cadmium (Cd) uptake by hyperaccumulators but their tradeoff in calcareous soils is unclear. This study investigated the mechanisms of Solanum nigrum L. and Solanum alatum Moench in calcareous soil using a combination of concentration gradient experiments (0.6–100 mg Cd kg−1) and soil solution composition analysis. The results showed that the soil solution pH of S. nigrum remained stable despite Cd stress. On average, the soil solution pH of S. alatum was 0.23 units higher than that of S. nigrum, although pH decreased significantly under high Cd stress. In addition, the concentrations of potassium (K) and calcium (Ca) in the soil solution of S. nigrum increased and decreased under low and high levels of Cd stress, respectively. In S. alatum, the K and Ca concentrations in the soil solution generally increased with increasing Cd stress levels. Moreover, the level of DOC in the soil solution of both plants was higher under Cd stress compared to the control, and a gradually increasing trend with Cd stress level was observed in S. alatum. Consequently, the bioconcentration factors of the roots (2.62–19.35) and shoots (1.20–9.59) of both plants were >1, while the translocation factors were <1, showing an obstacle of Solanum hyperaccumulators in transferring Cd into their aboveground parts. Redundancy analysis revealed that the Cd concentration in S. nigrum roots was significantly negatively correlated with the soil solutions of K and Ca. In contrast, Cd concentrations in S. alatum roots and shoots were significantly positively correlated with soil solution DOC, K, and Ca but negatively correlated with pH. Our results suggest that calcareous soil neutralizes the acidity of released protons but does not affect cation exchange, inhibiting DOC in assisting the translocation of Cd within plants.

The osmotic potential of soil solutions in salt tolerance studies: Following M. Th. van Genuchten's innovation

AbstractThe osmotic potential in soil solutions decreases as salinity increases, and plants cannot take up enough soil water. Therefore, the osmotic potential of soil solutions can serve as an important metric of plant growth conditions in regions affected by soil salinization. Measurements of osmotic potential are labor and time consuming. This work aimed to determine more readily available soil salinity metrics to estimate the osmotic potential in soil solutions. A model to compute the osmotic potential from soil solution composition was developed and validated with data from the U.S. states of Washington, Oregon, Colorado, and Idaho. The mean relative error was 7%. Then, this model was applied to 230 datasets on soil solutions from various salinity‐affected regions of Eurasia. The correlation coefficient between logarithms of concentration of highly soluble (not including carbonates and sulfates of calcium and magnesium) in soil solutions at saturation and logarithms of osmotic potential values was above 0.99. The concentration of highly soluble salts in soil solution at saturation was chosen as the predictor of the osmotic potential. It was used to develop nomograms for evaluating the salinity‐related yield loss for major field crops, vegetables, and fruits. This work is a part of the Vadose Zone Journal tribute to the scientific legacy of Martinus van Genuchten, who championed the use of the osmotic potential for better quantification of crop salt tolerance at the macroscale and provided invaluable contributions to modeling soil salinity development and mitigation as a part of the global struggle for food security.

Changes in the composition and concentration of soil solutions in seasonal dynamics of irrigated agriculture

Changes in the composition and concentration of soil solutions in seasonal dynamics of irrigated agriculture

Transport and Model Calculation of Microplastics Under the Influence of Ionic Type, Strength, and Iron Oxide

Microplastics (MPs) in soil have attracted extensive attention as an emerging pollutant, and the transport of MPs is affected by their own physical and chemical properties, the chemical composition of soil solutions, and soil minerals. However, in the presence of oxides, the underlying mechanism for the transport of MPs in different ionic types and ionic strengths is still not fully understood. In this study, the effects of ionic type, ionic strength, and iron oxide on the transport of polystyrene microplastics (PSMPs) with different functional groups were investigated through stability experiments and transport experiments. The colloid transport model, CD-MUSIC model, and DLVO theory were used to explore the transport mechanism. The results showed that normalized concentrations (c/c0) of PSMPs were 0.99 in the NaH2PO4 background and 0.94 in the CaCl2 background, respectively, which indicated that the strongest stability of PSMPs was observed in the former and the weakest in the latter. Different ionic types had different effects on the transport of PSMPs. For the cations Na+ and Ca2+, Ca2+ strongly inhibited PSMPs transport in pure quartz sand because of the bridging effect and strong charge neutralization effect; the recovery rate of the PSMPs in the effluent was (43.83±1.71)%, and a first-order retention coefficient on the second kinetic Site-2 (k2a) was 1.54 min-1. The presence of iron oxide enhanced the inhibition, the recovery rate of the PSMPs in the effluent decreased to (6.04±0.40)%, and k2a increased to 5.33 min-1. For the anions Cl- and PO43-, the transport of PSMPs in pure quartz sand was dominated by surface electronegativity of PSMPs, and PSMPs exhibited lower electronegativity under Cl- background and thus showed higher recovery[(92.95±0.63)%] and lower k2a (0.19 min-1). However, in the presence of iron oxides, the Zeta potential of the quartz sand surface was the controlling factor for PSMPs transport. According to results of the CD-MUSIC model, PO43- could be easily adsorbed on the iron oxide surface to form innersphere complexes, which reduced the surface electronegativity of the iron-loaded quartz sand and enhanced the transport of PSMPs, higher recovery[(76.22±1.39)%], and lower k2a (0.66 min-1). Moreover, the species of the formed innersphere complex was controlled by the PO43- concentration, and different species of innersphere complexes had distinct negative surface charges. Higher surface electronegativity of the iron-loaded quartz sand was observed under higher PO43- concentration, which was not conducive to the transport of PSMPs. Further, the transport ability of PSMPs decreased with the increase in ionic strength. Finally, the Derjaguin-Landau-Verwey-Overbeek (DLVO) theory was used to calculate the variation in the primary barrier between PSMPs and the collector under the conducted experimental conditions, which helped better elucidate the transport behavior of PSMPs. The variation in the primary barrier was consistent with the transport ability of PSMPs, and a higher primary barrier indicated a larger repulsion between PSMPs and the collector, which was in favor of PSMPs transport.

Molecular membrane separation: plants inspire new technologies.

Plants draw up their surrounding soil solution to gain water and nutrients required for growth, development and reproduction. Obtaining adequate water and nutrients involves taking up both desired and undesired elements from the soil solution and separating resources from waste. Desirable and undesirable elements in the soil solution can share similar chemical properties, such as size and charge. Plants use membrane separation mechanisms to distinguish between different molecules that have similar chemical properties. Membrane separation enables distribution or retention of resources and efflux or compartmentation of waste. Plants use specialised membrane separation mechanisms to adapt to challenging soil solution compositions and distinguish between resources and waste. Coordination and regulation of these mechanisms between different tissues, cell types and subcellular membranes supports plant nutrition, environmental stress tolerance and energy management. This review considers membrane separation mechanisms in plants that contribute to specialised separation processes and highlights mechanisms of interest for engineering plants with enhanced performance in challenging conditions and for inspiring the development of novel industrial membrane separation technologies. Knowledge gained from studying plant membrane separation mechanisms can be applied to developing precision separation technologies. Separation technologies are needed for harvesting resources from industrial wastes and transitioning to a circular green economy.

Risk of Salinization in the Agricultural Soils of Semi-Arid Regions: A Case Study from Moldavian Plain (NE Romania)

In the present study, the salinization trends of different soil types from a small hydrographic basin situated in NE Romania (Roșior basin) are investigated. The climatic conditions are favorable for long dry summers and intensive evaporation. The soils are developed on immature evolved clay sediments, as revealed by geochemical analysis. The salinity varies among soil types, attaining maximum values for Solonetz with total dissolved salts (TDS) between 1165.75 to 1881.25 mg/L. The aqueous solutions are represented by natural water and soil solution. The hydrogeochemical facies of the natural waters change from HCO3−—Mg2+ in the upper basin to SO42−—Na+ in the middle or lower basin. The soil solution is moderately or strongly salinized and shows anionic variations from HCO3− to SO42− in the studied profiles, whereas Na+ is always the main cation. The concentrations of Na+ and SO42− evolve simultaneously. Raman spectroscopic exploration of the white efflorescences, which occur on topsoil, reveals the presence of thenardite as the dominant phase. The composition of soil solution results from both the ionic exchange and evaporation processes. The nature of soil solution mineralization and summer temperatures are two main factors that interact and promote the thenardite precipitation. The soil salinization induces negative effects on crop nutrition, impacting further the crop yields. The results of this study can be extrapolated to larger areas formed on Sarmatian sedimentary deposits affected by salinization processes.

Interactive effect of salinity and Ca to Mg ratio of irrigation water on pistachio growth parameters and its ionic composition in a calcareous soil

ABSTRACT This study investigated the effect of different salinity (EC≈6 and 9 dS/m) and Ca/Mg ratios (≈0.95,0.50, and 0.25) in irrigation water on the chemical composition of soil solution and growth of pistachio (Pistacia vera L.). The physiological, biochemical, and yield-related responses of pistachio seedlings were measured within ≈30 weeks in a greenhouse pot experiment. The EC of the soil solutions rapidly approached the one in the irrigation waters while the Ca/Mg ratios slowly altered, as such the final ratios were ≈50-100% larger than the one in the irrigation waters. The slower change in the Ca/Mg ratio is due to the fact that Ca concentration is dominantly controlled by the calcite solubility but the Mg concentration by the ion-exchange reaction. With increasing EC of the soil solution from 5.8–10.4 dS/m, we found 4-fold reduction in shoot dry weight and 62% increase in electrolyte leakage. In each salinity level, the highest yield and membrane stability were achieved at the Ca/Mg ratio of ≈1 in the soil solution. Overall, a Ca/Mg ratio < 1 in the irrigation water shifted the ionic composition of the soil solution, even in calcareous soil, towards a ratio < 1 and negatively affected pistachio growth.

Dispersion and transport of microplastics in three water-saturated coastal soils

The coastal area is one of the key zones for transport and fate of microplastics (MPs). This study investigated the transport behaviors of different sized MPs in three water-saturated coastal soils, with the aim to explore effects of properties of three different coastal soils on the dispersion and migration of three-sized MPs (0.3, 0.5, and 1 µm). All three-sized MPs had the strongest dispersion in Soil 3 solution, followed by that in Soil 1 solution and then that in Soil 2 solution. The strongest dispersion of MPs in Soil 3 solution was attributed to the lowest ionic strength. Such a high dispersion favored MPs movement in soil solution but readily be sorbed and fixed by rich Fe and Al oxides in Soil 3 solid through strong electrostatic attraction, leading to the lowest transport rate (20.5–41.2%). The high ionic strength in the Soil 1 solution decreased the dispersion of MPs, but the presence of high content of humic acid enhanced the electrostatic repulsion and steric hindrance between MPs and soil particles, resulting in the highest transport ability of MPs in Soil 1 (39.4–72.5%). The large amount of dissolved Ca2+ and Mg2+ in Soil 2 solution favored MPs bridged with fulvic acid, resulting in the highest aggregation of MPs and relatively lower transport ability (34.1–49.6%). Large-sized MPs had higher electrostatic repulsion between the particles, thus increasing the dispersion and transport capacity of MPs in soil. Modeling showed the experiment-consistent results that Soil 3 had the lowest MPs transport after 600 mm of heavy rainfall, with the maximum migration distance of 7.50–10.5 cm, which was smaller than that in Soil 2 (8.10–12.0 cm) and that in Soil 1 (9.00–18.3 cm). These results indicated that MPs transport in coastal soil is significant and soil solution and solid composition plays an important role in the dispersion and transport of MPs, respectively. These findings afforded a great basis for the assessment of the fate and risk of MPs in coastal areas.

Compositional constraints to identifying ternary interactions in ion‐exchange equilibria

AbstractCation exchange is one of the most important classes of reactions controlling the soil solution composition for major ions. Modeling ion‐exchange equilibria is complicated by ternary solid‐phase interactions. The present study alleges that spurious ternary‐interactions can be reported when dilution of the exchanging ions by other ions on the solid‐phase is not accounted for in models. Ion‐exchange equilibria data from the NH4+–Ca2+–K+–vermiculite system is used to demonstrate that previous reports of ternary interactions in this system are an artifact of how solid‐phase mole fractions are defined; what mathematicians call “compositional incoherence.” A graphical method to distinguish the effects of dilution from real chemical interactions is presented using mole fractions renormalizing in the ternary system so that they are defined the same way as they are in binary systems. Potassium was shown to not influence NH4+–Ca2+ exchange on vermiculite when these corrections for solid‐phase dilution were used.

Tolerance mechanisms and irrigation management to reduce iron stress in irrigated rice

Iron toxicity is a major nutritional disorder in rice plants, especially in flooded areas. The use of alternative crop management practices, such as soil drainage, may mitigate negative impacts of iron toxicity, since soil aeration that follows drainage can oxidize and precipitate potentially toxic Fe+2 into Fe3+. This study aimed to evaluate the impact of alternative water management on agronomical and physiological parameters in rice plants grown in a field location with iron toxicity history. Rice cultivars BR-IRGA 409 (sensitive) and IRGA 425 (resistant to iron toxicity) were tested. Irrigation management comprised three treatments: continuous irrigation, one cycle of water suppression (1S) and two cycles of water suppression (2S). Evaluations included the ionic composition of soil solution and leaf tissues, grain yield, antioxidant responses and gene expression. Permanent soil flooding resulted in higher grain yield in plants from the resistant than from the sensitive genotype, which had higher malondialdehyde (MDA) concentrations in leaves. In contrast, two cycles of alternate soil drying resulted in equivalent grain yield and MDA concentrations in both genotypes. Resistance to iron toxicity in IRGA 425 plants seems related to limited Fe translocation to shoots, increased tolerance to oxidative stress in leaves and higher expression of Ferritin, OsGAP1, OsWRKY80 and Oryzain-α genes. Plants from the BR-IRGA 409 cultivar (sensitive to Fe toxicity) improved growth and yield under the interrupted irrigation treatments, probably due to lower Fe availability in the soil solution. Management of water irrigation successfully alleviated Fe toxicity in rice plants cultivated in field conditions.

Modelling Salinity and Sodicity Risks of Long-Term Use of Recycled Water for Irrigation of Horticultural Crops

Long-term use of recycled water (RW) for irrigation in arid and semiarid regions usually changes the soil solution composition and soil exchange characteristics, enhancing the risk for salinity and sodicity hazards in soils. This modelling study focuses on developing alternative management options that can reduce the potentially harmful impacts of RW use on the irrigation of wine grapes and almonds. The multicomponent UNSATCHEM add-on module for HYDRUS-1D was used to evaluate the impact of long-term (2018–2050) use of irrigation waters of different compositions: good-quality low-salinity (175 mg/L) water (GW), recycled water with 1200 mg/L salinity (RW), blended water of GW and RW in the 1:1 proportion (B), and monthly (Alt1) and half-yearly (Alt6) alternate use of GW and RW. The management options include different levels of annual gypsum applications (0, 1.7, 4.3, and 8.6 t/ha soil) to the calcareous (Cal) and hard red-brown (HRB) soils occurring in the Northern Adelaide Plain (NAP) region, South Australia. Additional management scenarios involve considering different leaching fractions (LF) (0.2, 0.3, 0.4, and 0.5) to reduce the salinity build-up in the soil. A new routine in UNSATCHEM to simulate annual gypsum applications was developed and tested for its applicability for ameliorating irrigation-induced soil sodicity. The 1970–2017 period with GW irrigation was used as a warmup period for the model. The water quality was switched from 2018 onwards to reflect different irrigation water qualities, gypsum applications, and LF levels. The data showed that the GW, B, Alt1, and Alt6 irrigation scenarios resulted in lower soil solution salinity (ECsw) than the RW irrigation scenario, which led to increased ECsw values (4.1–6.6 dS/m) in the soil. Annual gypsum applications of 1.7, 4.3, and 8.6 t/ha reduced pH, SAR, and ESP in both soils and reduced the adverse impacts of irrigation, especially in surface soils. A combination of water blending or cyclic water use with 3.8 t/ha annual gypsum applications showed promise for the SAR and ESP control. Additionally, irrigation with RW, a 0.2 LF, and annual gypsum applications limited the harmful salinity impacts in the soils. However, in the RW irrigation scenario, ECsw and ESP at the bottom of the crop root zone (90–120 cm depth) in the HRB soil were still higher than the wine grape and almond salinity thresholds. Thus, annual amendment applications, combined with the long-term use of blended water or cyclic use of RW and GW, represent a sustainable management option for crop production at the calcareous and hard red-brown soils.

Development of functions to predict soil hydraulic properties that account for solution sodicity and salinity

Saturated soil hydraulic conductivity (Ksat) and the soil water characteristic curve have been predicted from soil texture, bulk density, and other soil physical properties. These previous functions do not account for soil clay mineralogy or soil solution composition. The objectives of this study were to: (1) analyze the performance of previously developed pedotransfer functions (PTFs) on saline and sodic soils, (2) predict hydraulic properties of saline and sodic soils with a range of clay mineralogy, and (3) develop PTFs that account for clay mineralogy and solution composition. Most PTFs do not perform well on soils with smectitic clay mineralogy and usually over-estimate Ksat and under-estimate soil water characteristic on smectite clay dominant soils. Accounting for soil cation exchange capacity (CEC) as an indicator of soil clay types and solution composition improved the prediction of Ksat which had a geometric root mean squared error of 3.28 cm day−1 compared to 6.04 cm day−1 for the best performing PTF from the literature. A PTF we developed to predict soil water characteristic curve was able to predict soil water characteristic curve with a root mean squared error of 0.032 g g−1 compared to 0.082 g g−1 for the best performing previously published PTF. The PTFs developed in this study improved prediction of soil hydraulic properties on salt affected soils by using soil CEC to account for soil clay behavior and responsiveness to the soil solution composition. The PTFs reported here can easily be used to predict the Ksat and the soil water characteristic curve of soils in response to changes in irrigation water quality.

Relation between soil solution composition and petiole cellular extract of crops in western Mexico

Crop fertilization greatly impacts food production. However, insufficient applications can lead to poor yields. On the other hand, an excessive application leads to soil and aquifers pollution. In this paper, field studies were carried out to determine the ranges of mineral concentration and the interaction of the ions in the soil solution (SS) and the petiole cellular extract (PCE) in several cultures established in the states of Guanajuato, Colima and Jalisco, Mexico. The hypothesis states that there is a causal relationship between the mineral composition of the soil solution (SS) and the minerals and total soluble solids (TSS) in petiole cellular extract (PCE). The following cultures were studied in this research: avocado, blueberry, broccoli, cauliflower, raspberry, strawberry, lettuce, cantaloupe, papaya, and pepper. For each culture, PCE samples and SS samples using a press to break tissue and ceramic tip lysimeters were obtained. The results were processed to obtain ranges of variation within 50% of the closest values to the median. Correlations between the several ion concentrations were analyzed using analysis of variance. The results showed values (mg L-1) of NO3- (40-620), PO43- (17-66), K+ (3-377), Ca2+ (27-582), Na+ (15.3-500), Mg2+ (10-53), Fe3+ (0.6‑1.8), and Zn2+ (2.8-7.4) in soil solution, which allowed obtaining values of NO3- (27-9225), K+ (820-9375), Ca2+ (1.0-650), Na+ (25-620) and TSS (2-13 °Brix) in petiole cellular extract of petiole. Statistically significant correlations were observed between the concentrations of the SS ions regarding the concentrations in PCE in crops suggesting a relationship between the plant nutritive assimilation and cations or anions present in soil solution. The conclusion derived from this study is that ionic concentration ranges registered in the SS and in the PCE provide an approximation to the ranges of nutritional sufficiency for the horticultural crops established in the summer-winter in western Mexico.

The capacity of ion adsorption and purification for coniferous forests is stronger than that of broad-leaved forests

In the past few decades, industrialization has caused a large number of pollutants to be released into the atmosphere. Forest ecosystems play an important function in regulating the biogeochemistry and the circulation of metal ions pollutants. Forest ecosystems affect the absorption of pollutants and dissolution of nutrients from the atmosphere and vegetation canopy, thereby influencing the content and composition of forest floor leachate and soil solution. This study examined changes in acid anions (NO3−, SO42−, Cl−) and metal cations (K+, Ca2+, Na2+, Mg2+, Fe3+, Pb2+, Cu2+, Cd2+) in rainfall, throughfall, stemflow, and forest floor leachate for five different forests (Larix principis-rupprechtii, Picea wilsonii, Picea crassifolia, Betula platyphylla and Rhododendron communities). The results showed that the enrichment capacity of acid anions and metal cations in the vegetation canopy of the coniferous forests (L. principis-rupprechtii, P. wilsonii, P. crassifolia) was stronger than that of the broad-leaved forests (B. platyphylla and Rhododendron communities). The content of acid anions and metal cations in stemflow of coniferous forests were 3.7–5.6 times and 0–9.3 times higher than those of broad-leaved forests, respectively. Corresponding values in throughfall were 1–1.4 times and 0.3–2.4 times, respectively. The contents of NO3−, Cl−, K+, Mg2+, Fe3+, Pb2+, Cu2+, and Cd2+ in leachate filtered from the soil layers that are deepening gradually showed consistent decreasing trend for all the forest stands. In addition, NO3−, Cl−, K+, Mg2+, Fe3+, and Pb2+ were also concentrated in the topsoil, except for Cu2+ and Cd2+. Nevertheless, SO42− and Na+ were concentrated in the subsoil, whereas Ca2+ was concentrated in the upper soil layers. Soil organic carbon (SOC) and total nitrogen (TN) contents in coniferous forest stands were 20–37% and 34–63% higher than those in broad-leaved forest stands, respectively. This results also shown that the contents of OC and TN has a strong correlation with the content of partial metal cations in soil and litter, indicating that coniferous forest stands had stronger ion scavenging and adsorption capacity in soil layer and litter layer than broad-leaved forest stands. Therefore, L. principis-rupprechtii, P. wilsonii, P. crassifolia had higher air pollutant adsorption and soil pollution remediation capacities than the other two forests. Thus, we recommend planting coniferous tree species (L. principis-rupprechtii, P. wilsonii and P. crassifolia) for eco-rehabilitation and water purification to improve the ecological service function of forest ecosystems.

Soil solution fluxes and composition trends reveal risks of nitrate leaching from forest soils of Italy

Although acidification is a natural soil formation process, atmospheric emissions of nitrogen and sulphur have exposed forest ecosystems to accelerated anthropogenic acidification for many decades. In Italy nitrogen deposition loads are high, and among the highest in Europe. Data from the Italian ICP-Forests monitoring network have shown that nitrogen deposition increases tree growth, and consequently the organic carbon sequestration. However, the accumulation of nitrogen in the ecosystem could cause nutrient imbalances and contribute to soil acidification. Within this context, we investigated the temporal changes of atmospheric deposition and soil solution concentration in the Italian ICP-Forests using the non-parametric Seasonal Mann Kendall (SMK) test. Further, we applied input–output models, to evaluate the capabilities of the soil-forest system to retain deposited nitrogen and thus protect underground waters.Increase of soil solution pH was observed in most of the sites, likely due to sulphate deposition decrease with a concomitant high and stable natural exchangeable base deposition. For the sites around the Po plain, however, high levels of nitrogen deposition impede pH increase. The site with the maximum mineral N deposition showed signs of active acidification. The analysis of the fluxes of nitrogen compounds demonstrates a complete retention of the ammonium forms, which further contribute to acidification through nitrification. Furthermore, the Italian monitoring network showed that the retention of nitrogen in the soil-forest system was effective since the observed N fluxes in mineral soil were strongly reduced compared to mineral N input in most of the plots. In spite of this, significant NO3- fluxes from the subsoil were observed in sites with high deposition, and also in the southernmost site which is exposed to relatively low mineral N loads. Drivers other than pollution should also be considered since N can follow different pathways at different time scales, influencing N leaching independently from the amount of deposition.

Assessment of the Tannery Wastes Impact in the Soil Properties of the disposal site In Sudan

The present study aims to examine chemical characteristics and heavy metal of tannery wastewater and sludge and to assess their influences on alterations in soil properties of disposal areas in terms of degree of heavy metal contamination and soil solution. Result revealed that soil layers exhibit greater values of soluble cations, anions, and electrical conductivity in tannery wastewater, sludge. Unlimited fluctuation in concentrations of heavy metals in soil profile was detected. Depending on estimated contamination factor (CF) and enrichment factor (EF), soil samples were found to be enriched and polluted with chromium. Simple correlation analysis showed significant progress between heavy metals and soil solution composition parameters. This proposes that both wastewater and sludge of tannery activities are accountable for altering properties of soil solution in term of chemistry and metal toxicity inducement into the soil atmosphere. Accordingly, tannery effluents, wastes, and sludge should not be allowed to be disposed into the environment without proper treatments.

Water-Soluble Components in Soils of Heterolithic Conjugate Landscapes in the Southern Taiga Subzone

This paper discusses the composition of soil–water extracts prepared from soils developing within a heterolithic geochemical landscape of the Klyazma River basin at the upper reaches of the river. The main factors determining the content of water-soluble components are the soil genesis and position in the series of elementary landscapes. The content of water-soluble macro- and microelements in soil profiles not affected by anthropogenic impacts is determined by the eluvial–illuvial structure of these soils. In a superaqual landscape withdrawn from the floodplain regime and featuring a complex soil cover, the distribution of water-soluble components in the soil profile is determined by calcareousness of soil–ground waters and their occurrence depth. Another factor affecting the soil solution composition is peat deposits underlying the soils. It is shown that calcium is one of the key elements determining the specificity of the studied heterolithic landscape. The performed cluster analysis confirms the identified differences in the composition of water-soluble components in each of the studied soils.

Effects of mound building Lasius flavus on organic carbon and nutrient fluxes in soils of temperate grassland ecosystems

Ants that build long-lasting mounds and move large amounts of mineral soil may influence the composition and fluxes of soil solutions, and thus soil nutrient cycling. However, studies quantifying such effects are scarce. In central Europe, the yellow meadow ant (Lasius flavus) is a common species that changes the character of extensively managed grasslands by its mound building activity.In total, sixteen mound-control pairs were selected within four plots on two grassland sites in Thuringia, Central Germany and monitored from 2013 to 2016. On each plot, bulk precipitation and soil solutions were collected via two open funnel samplers and eight suction plates to determine input and loss fluxes of dissolved organic carbon (DOC), nitrogen (DN), and base cations under L. flavus mounds and control locations. Effects of L. flavus mounds on soil microclimatic conditions were also investigated.In comparison to the controls, L. flavus mounds were characterised by slightly lower soil temperatures and always lower soil moisture. The main driver of lower fluxes of DOC and DN from mounds was related to the reduced seepage water flux under mounds compared to the adjacent grassland. Lasius flavus activity increased potassium (K) concentrations and fluxes in soil solutions from mounds in comparison to the controls, independent from plot-specific soil and seepage water flux variability. Increased concentrations of calcium (Ca) and magnesium (Mg) were measured in the soil solutions of the mounds but were generally not associated with higher Ca or Mg fluxes. In conclusion, L. flavus present unique micro-sites within grassland ecosystems by creating mounds that may function as ecosystem control points for the cycling of certain elements, such as K.

An algorithm to calculate the cationic composition of soil solutions. 1. Theory and structure

Difficulties forecasting cation exchange processes may limit the use of soil solution analyses in routine soil testing for agriculture. An important part of those difficulties is the need for much data and expertise to parameterise existing models that can be used for variable charge soils. This paper proposes an algorithm to simulate concentrations of the major nutrient cations in the soil solution. It is designed to have only modest data requirements, be applicable for variable charge soils, and be simple to implement in crop and environment simulation packages. It is based on a Gaines–Thomas type approach to cation exchange, adapted to allow for variations in cation exchange capacity. It includes interactions with anions and anion exchange, which may affect cation behaviour in variable charge soils. Assumptions and limitations of the approach are described, and some issues associated with parameterisation, implementation, and future extension are discussed.

An algorithm to calculate the cationic composition of soil solutions. 2. Parameterisation and test

This paper presents a parameterisation and test of an algorithm to calculate distributions of the major nutrient cations between the solution and exchangeable phases of soil when cation exchange capacity (c) may vary. Two contrasting soils were considered: a volcanic subsoil where c is dominated by variable-charge surfaces, and an alluvial silt loam topsoil with stable c. Experimental treatments consisted of applying either water or solutions of CaCl2, KCl, MgCl2, or NaCl. Solution concentrations of Ca2+, K+, Mg2+, and Na+ varied by up to two orders of magnitude, and were simulated well, particularly when using log10-transformed data. The ratios of the solution concentrations of K+, Mg2+, and Na+ to Ca2+ also were generally simulated well. However, the algorithm’s description of soil acidity needs further checking. For the variable-charge soil, cation concentrations were strongly influenced by fitted parameters associated with anion exchange. For the alluvial soil, fitted parameters had little influence, and the cation calculations were dominated by information gathered from the initial (equilibrium) distributions between phases. The algorithm has strong potential for forecasting changes in solution concentrations of the major nutrient cations, using relatively small amounts of fitting data.