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The existing models for estimating cation exchange capacity (CEC) from easy‐to‐measure hygroscopic water content (θh) were based on a single water activity (aw) value rather than on the processes that govern soil water vapor adsorption for a distinct aw range. Here, we present a new CEC estimation model based on θh data of 119 soils with different clay mineralogy (i.e., illitic [IL], montmorillonitic [ML], and kaolinitic [KA] samples) and organic carbon (OC) contents for the aw range from 0.23 to 0.57 (Δθ0.23–0.57) and validate its performance. Based on the hypothesis that multilayer adsorption exhibits a higher correlation with CEC than monolayer adsorption and capillary condensation, the aw range from 0.23 to 0.57 was chosen with CEC calculated as CEC = k × Δθ0.23–0.57. The performance of the new model is compared to the Arthur (2017) model and the Torrent (2015) model, which considers a single θh value. The average proportionality coefficient (k) varied with the dominant clay mineralogy of the investigated soils. For soils dominated by 2:1 clay minerals (i.e., IL and ML), the new model showed a good estimation accuracy (Nash‐Sutcliffe model efficiency [E] ≥ 0.85; root mean squared error [RMSE] ≤ 4.18 cmol(+) kg−1). The new model performed better for IL and ML samples than for KA samples, and yielded more accurate CEC estimations than the Arthur model and Torrent model for soils with 2:1 clay minerals. For soil with high OC content (>23.2 g kg−1), the new model slightly underestimated CEC (E = 0.66; RMSE = 5.87). [ABSTRACT FROM AUTHOR]

Soil shrinkage characteristic curves are used to describe the shrinkage behavior and hydraulic properties of unsaturated soils. To construct soil shrinkage characteristic curves, a high‐data‐density measurement method is needed that relates water content to soil volume changes. We present a fully automated soil shrinkage measurement setup, based on the simplified evaporation method, to characterize the shrinkage behavior of undisturbed natural expansive clay soils. The high data density creates the opportunity to produce soil shrinkage characteristic curves without the need for a mathematical model. The technique allows for resaturation of the samples after drying, enabling differentiation between reversible and irreversible shrinkage. The setup consists of the commercialized HYPROP2 apparatus combined with optical distance sensors to measure the horizontal and vertical dimensions of the samples, yielding data on the sample volume, weight, and soil water suction. The measurement frequency is once per 10 min, and the measurement period is up to 4 weeks, providing a detailed time series of the drying and shrinkage characteristics. The setup can capture the different shrinkage phases and offers the opportunity to relate the soil shrinkage characteristic curve to soil water suction. The measurement data acquisition rate and accuracy enable detailed interpretation of soil water retention curves for nonrigid soils and are shown to be essential for understanding and quantifying the shrinkage potential of several types of deposits. [ABSTRACT FROM AUTHOR]

Because of the importance of the Central Valley of California, USA, to shorebirds along the Pacific Flyway, conservation investments have been made in the area's agricultural fields and managed wetlands. Increasingly, landowner incentive programs are being used to deliver shorebird habitat, presenting opportunities to answer remaining questions about which implementation strategies and field management practices are most effective at attracting birds. To provide management guidance for these investments, we collected and analyzed 5 years of data (2014–2018) on shorebird abundance in flooded rice fields enrolled in a dynamic habitat incentive program. The program incentivized flooding in fallow and post‐harvest rice fields in seasons when habitat is relatively sparse, specifically the early fall and late spring. Across nearly 9,000 field observations over 5 years, we explored the relationship between abundance and density (birds/ha) of shorebirds and vegetation cover, soil clay, landscape‐level flooding, and local flood timing, duration, and depth. We observed more shorebirds in fields that were approximately 50% flooded, had water depths of 5–10 cm, and had minimal rice straw or stubble cover, with strong or very strong evidence for each of these relationships. We found that the timing of habitat provisioning was important, with moderate evidence that earlier fall flooding and strong evidence that the duration of fall flooding was associated with higher shorebird density. We observed lower shorebird densities in locations with ample flooded rice habitat in surrounding areas, potentially because shorebirds spread out across the landscape. We found very strong evidence that flooding consistency, either at a site that was continually flooded over many months or a site that had been flooded in previous years, was associated with higher shorebird density. Soil clay content was associated with decreased observed shorebird density, potentially through its influence on the ability of shorebirds to forage for invertebrate prey. These results suggest best practices for shorebird habitat creation in agricultural landscapes, providing important information for conservation and population recovery. [ABSTRACT FROM AUTHOR]

Conservation management practices often produced positive but limited desirable outcomes in US Southeast sandy soils, likely due to their intrinsically low clay contents that constrain the soil’s capacity to preserve organic carbon (C) and nutrients. In the field, we tested the effectiveness of a novel approach, that is, clay soil amendment, to improve sandy soils. In October 2017, clay-rich soils (25% clay) were spread at 25 metric tons ha−1 and tilled onto a sandy soil (1.9% clay) in the field, which was further mixed by light tillage at 0- to 15-cm depth, followed by planting winter cover crop mixtures (cereal rye, crimson clover, and winter pea). The crop rotation was cotton and corn with cover crop mixtures planted in the winter fallow season. Soils (0–15 cm) were collected in August 2021 and subjected to physiobiochemical analyses. Clay amendment increased soil clay content to 3.4%, which improved nitrogen (N) availability by 51% but inhibited the activities of C (β-Dcellubiosidase [CB]; β-xylosidase [BX]; N-acetyl-β-glucosaminidase [NAG]) and N (leucine aminopeptidase [LAP]) cycling enzymes, resulting in up to 78% reduction in microbial respiration. A follow-up kinetic study on BG and LAP enzymes suggested that clay addition can have different impacts on enzymes with diverse biological origins through distinct mechanisms. Clay addition can potentially improve sandy soils by stabilizing the organic inputs in soils. However, more research is required to understand its long-term impacts making this approach practical. [ABSTRACT FROM AUTHOR]

The soil mantle of the tropical karstic landscapes of Southern Mexico was shaped by specific processes of pedogenesis and long-term human impacts of ancient Maya agriculture. To understand the interaction between natural and human-induced soilforming processes in the calcareous mountains of Chiapas state, we studied soil toposequences around the Classic Maya site of Budsilhá and related them to the archaeological evidence of settlement and land-use distribution. Soil chemical analysis, micromorphological observations, and clay mineral identification were carried out in key soil profiles at the main geoforms. Limestone hills are occupied by shallow Rendolls which are usually perceived as incipient soils. However, high content of silicate clay composed of kaolinite and vermiculite and ferruginous clayey soil material observed at macro- and microscale backed the hypothesis that these soils were formed from the residues of thick Terra Rossa after their erosion. Swampy lowlands are occupied by thick clayey gleyic soils with clay mineral assemblages similar to those in the upland Rendolls. We suppose that the mineral matrix of the lowland soils is largely derived from the pedosediments of eroded upland Terra Rossa, which lost original ferruginous pigmentation and aggregation due to redoximorphic processes. Some wetland soils contain neoformed gypsum that is atypical for humid tropics; sulfidesulfate transformation under fluctuating redox conditions could promote gypsum synthesis. Ancient Maya land use was closely related to soil-geomorphic conditions: settlements with homegardens occupied calcareous hills, whereas the primary agricultural domain was developed on lowland soils after their drainage by artificial canals. [ABSTRACT FROM AUTHOR]

New soil organic carbon (SOC) formation in cropland from straw/stover or manure input is a vital source of SOC for climate change mitigation. However, location and variations in the efficiency, specifically the ratio of new SOC formation to organic C input (NCE), remain unquantified globally. In this study, the spatial variability of cropland NCE from straw/stover or manure input and explanatory factors were determined by analyzing 897 pairs of long‐term field measurements from 404 globally distributed sites and by mapping grid‐level cropland NCEs. The global NCE for paddy and upland averaged 13.8% (8.7%–25.1%, 5th–95th percentile) and 10.9% (6.8%–17.3%), respectively. The initial SOC and the clay content of soil, rather than temperature, were the most important factors regulating NCE. A parabola with an apex at approximately 17 g kg−1 between the initial SOC and NCE was resolved, and a positive correlation between soil clay content and NCE was observed. High‐resolution mapping of the global NCE derived from manure/straw and insight into NCE dynamics provide a benchmark for diagnosing cropland soil C dynamics under climate change and identifying priority regions and actions for C management. [ABSTRACT FROM AUTHOR]

This work focuses on archaeological analogues as a way of obtaining long‐term data for assessing the lifetime of a spent nuclear fuel canister. An analysis of the environment around the excavated artefacts is presented, followed by geochemical modelling of the likely corrosion products and subsequent comparison with real phases in the corrosion layer estimated by X‐ray diffraction. A total of 16 archaeological sites with fine clay soils and the potential for long‐term flooding were evaluated. Although the soil pore solution contained high levels of silicates, no such phases with iron in the corrosion products were confirmed. Carbonate corrosion products, typical of bentonite environments, were also not observed. Although oxygen access is very limited in the environments of all sites, even low concentrations shifted the equilibrium of corrosion products formed in favour of (hydroxy)oxides. [ABSTRACT FROM AUTHOR]

The electro‐osmosis approach efficiently facilitates the rapid dewatering of soil with high water content and contributes to reducing contaminant levels within the clay soil. However, the changes of chemical field caused by ion transport in the clay soil during electro‐osmosis process will also influence the clay soil consolidation effect. Existing theories predominantly tend to disregard this crucial physical process and its resultant effects, thereby restraining a comprehensive analysis of electro‐osmosis consolidation (EOC) behavior under intricate chemical conditions. This study introduces a concise model of EOC and ion transport considering chemical osmosis. The model considers the nonlinear variation of clay soil parameters such as compressibility, permeability, and effective diffusion coefficients, along with the interaction between EOC and ion transport. Meanwhile, the correctness of the model is verified from different aspects such as theoretical derivation and model comparison. Based on the proposed model, the impacts of the variation in electrical field intensity and chemical concentration on the coupled behaviors between EOC and ion transport are systematically investigated, with and without incorporating nonlinear consolidation characteristics. The results show that diffusion and electro‐migration exhibit a more pronounced effect on ion transport during EOC. Simultaneously, with the increase of ion concentration in clay soil pore solution, the effects of chemical osmosis become increasingly apparent, thereby enhancing clay soil settlement. [ABSTRACT FROM AUTHOR]

Understanding the factors affecting the total amount and distribution of soil organic carbon (OC) across different functional carbon pools is important to better define the future management of soil OC stocks. The interactions between soil management practices, local physicochemical soil properties and climate are essential for determining the OC content of the soil. Nevertheless, how these factors affect the total amount of OC and its distribution across carbon pools, i.e., more labile particulate (POC) and more stable mineral‐associated (MAOC) organic carbon, is only partly known. In this study, we assessed topsoil (0–20 cm) samples from 93 arable farms in the southern half of Finland to determine the total amount of OC, and its distribution in MAOC and POC, along with relevant soil properties (amount of clay and silt, aluminium and iron oxides and pH), climate (precipitation and temperature) and fertilization (mineral versus organic). The fertilization did not affect the total soil carbon content (12–58 g OC kg−1 soil). The share of OC in the MAOC fraction (on average 86% of total OC) was relatively stable across the large range of OC contents and clay contents (2%–68%). We assessed the highest feasible MAOC of the soils with boundary line analyses and their OC saturation state with Hassink's equation (Hassink, 1997). Only soils with the lowest clay content (<10% clay) were assumed to be carbon‐saturated, suggesting that most of the studied soils have a capacity to accrue more MAOC. Simple linear regression showed that clay, aluminium and iron oxides explained 9%, 21% and 22% of the variation in MAOC, respectively. Multiple regression analyses including the amount of clay, clay+silt, aluminium and iron oxides, pH, type of fertilization, precipitation and temperature as explanatory variables explained 33%–53% of the variation in OC and MAOC. In all soils, aluminium oxides were important explanatory variable for MAOC, whereas Fe oxides were significant only in soils with higher clay content (>30%). In soils with a low clay content (<30%), pH had added value in explaining MAOC. Altogether, it seems that various climatic, edaphic and soil management‐related factors are context‐dependently controlling OC and that soil textural information alone is not necessarily an adequate predictor to assess the MAOC saturation state of the soil. [ABSTRACT FROM AUTHOR]

The present study examined how the use of soil color can help build and evaluate clay content prediction models from laboratory visible and near infrared spectroscopic data. This study was based on a regional database containing 449 soil samples collected over Karnataka state in India, which has been divided into red soils (240 samples) and black soils (209 samples) based on their Munsell soil color. Partial least squares regression models were calibrated and validated from both the regional datasets and subsets stratified as red and black soils. In addition, a random forest model was used to classify the validation soil samples into black and red classes to evaluate models' performance. First, while the clay content predicted by the regression model built from regional data was evaluated as correct at regional scale (R2val of 0.75), this model was evaluated as more accurate over black (R2val of 0.8) than red (R2val of 0.63) soil samples. Second, the regression models built from subsets stratified per soil color provided different performances than the regression model built from the regional data, both at the regional scale and soil color scale. In conclusion, this study demonstrated that (1) predictions are highly dependent on calibration data, (2) the interpretation of prediction performances relies heavily on validation data, and (3) pedological knowledge, such as soil color, can be effectively employed as an encouraging covariate in both the construction and evaluation of regression models. Core Ideas: Prediction of clay from visible and near infrared spectroscopy was analyzed based on soil color.Models were calibrated from regional database and subsets stratified by soil color.Global model yielded over‐ and underestimation of accuracy over red and black soils, respectively.Predictions are highly dependent on the calibration dataset.Model performance evaluation is highly dependent on validation data stratification. [ABSTRACT FROM AUTHOR]

During undrained cyclic loading, clayey soils experience substantial stiffness and strength degradation when subjected to shear amplitudes exceeding a critical threshold. This paper presents an enhanced bounding surface rate‐independent plasticity model, an evolution of the previous SANICLAY model, tailored to capture this specific behavior during cyclic loading. A distinguishing feature of the proposed model is the introduction of an activation mechanism. This mechanism triggers degradation modeling based on the applied cyclic shear amplitude. To measure this amplitude, the activation mechanism incorporates a novel state variable that serves as a proxy for the applied cyclic stress. The effectiveness of the proposed model is demonstrated by comparing it to experimental data from various materials subjected to cyclic shearing under undrained conditions. The study encompasses a broad range of constant strain or stress amplitudes. Compared to the reference model, the proposed model exhibits improved predictive accuracy for the stress‐strain response of clays at small amplitudes of cyclic loading and large number of cycles. Furthermore, it accounts for strength degradation due to cyclic loading. [ABSTRACT FROM AUTHOR]

The microplastics (MPs) formed by broken plastic film may migrate in the soil under drip irrigation. To investigate the migration distribution of MPs in desert farmland soil under drip irrigation conditions, our study was conducted on farmland in Xinjiang (China). A MP drip irrigation penetration migration testing device was set up in combination with Xinjiang farmland irrigation methods to conduct a migration simulation experiment. The results showed that the migration amount of MPs in soil was significantly positively correlated with the amount of drip irrigation, and significantly negatively correlated with the soil depth; in addition, the relationship between the migration amount of MPs in different types of soil was: clay < sandy loam < sandy soil. Under drip irrigation conditions, the migration rates of MPs were 30.51%, 19.41%, and 10.29% in sandy soil, sandy loam soil, and clay, respectively. The migration ability of these three particle sizes of polyethylene MPs in soil was ranked as follows: 25 to 147 μm > 0 to 25 μm > 147 to 250 μm. When the drip irrigation volume was 2.6 to 3.2 L, horizontal migration distances of MPs exceeded 5 cm, and vertical migration distances reached more than 30 cm. Our findings provide reference data for the study of soil MP migration. Environ Toxicol Chem 2024;43:1250–1259. © 2024 SETAC [ABSTRACT FROM AUTHOR]

Crop N decision support tools are typically based on either empirical relationships that lack mechanistic underpinnings or simulation models that are too complex to use on farms with limited input data. We developed an N mineralization model for corn that lies between these endpoints; it includes a mechanistic model structure reflecting microbial and texture controls on N mineralization but requires just a few simple inputs: soil texture soil C and N concentration and cover crop N content and carbon to nitgrogen ratio (C/N). We evaluated a previous version of the model with an independent dataset to determine the accuracy in predictions of unfertilized corn (Zea mays L.) yield across a wider range of soil texture, cover crop, and growing season precipitation conditions. We tested three assumptions used in the original model: (1) soil C/N is equal to 10, (2) yield does not need to be adjusted for growing season precipitation, and (3) sand content controls humification efficiency (ε). The best new model used measured values for soil C/N, had a summertime precipitation adjustment, and included both sand and clay content as predictors of ε (root mean square error [RMSE] = 1.43 Mg ha−1; r2 = 0.69). In the new model, clay has a stronger influence than sand on ε, corresponding to lower predicted mineralization rates on fine‐textured soils. The new model had a reasonable validation fit (RMSE = 1.71 Mg ha−1; r2 = 0.56) using an independent dataset. Our results indicate the new model is an improvement over the previous version because it predicts unfertilized corn yield for a wider range of conditions. Core Ideas: An improved N mineralization model predicts unfertilized corn yield for a wide variety of conditions.The new model provides realistic estimates of microbial humification efficiency across a range of soil textures.Humification efficiency is affected more by soil clay content than sand content.The updated coefficients account for the influence of precipitation on corn yield.The improved model provides a foundation for site‐specific N fertilizer recommendations. [ABSTRACT FROM AUTHOR]

Plant metabolites significantly affect soil nitrogen (N) cycling, but their influence on nitrous oxide (N2O) emissions has not been quantitatively analyzed on a global scale. We conduct a comprehensive meta‐analysis of 173 observations from 42 articles to evaluate global patterns of and principal factors controlling N2O emissions in the presence of root exudates and extracts. Overall, plant metabolites promoted soil N2O emissions by about 10%. However, the effects of plant metabolites on N2O emissions from soils varied with experimental conditions and properties of both metabolites and soils. Primary metabolites, such as sugars, amino acids, and organic acids, strongly stimulated soil N2O emissions, by an average of 79%, while secondary metabolites, such as phenolics, terpenoids, and flavonoids, often characterized as both biological nitrification inhibitors (BNIs) and biological denitrification inhibitors (BDIs), reduced soil N2O emissions by an average of 41%. The emission mitigation effects of BNIs/BDIs were closely associated with soil texture and pH, increasing with increasing soil clay content and soil pH on acidic and neutral soils, and with decreasing soil pH on alkaline soils. We furthermore present soil incubation experiments that show that three secondary metabolite types act as BNIs to reduce N2O emissions by 32%–45%, while three primary metabolite classes possess a stimulatory effect of 56%–63%, confirming the results of the meta‐analysis. Our results highlight the potential role and application range of specific secondary metabolites in biomitigation of global N2O emissions and provide new biological parameters for N2O emission models that should help improve the accuracy of model predictions. [ABSTRACT FROM AUTHOR]

Cover crops (CC) offer numerous benefits to agroecosystems, particularly in the realm of soil organic carbon (SOC) accrual and loss mitigation. However, uncertainties persist regarding the extent to which CCs, in co‐occurrence with environmental factors, influence SOC responses and associated C pools. We therefore performed a weighted meta‐analysis on the effects of CCs on the mineral‐associated organic carbon (MAOC), the particulate organic carbon (POC) and the microbial biomass carbon (MBC) pool compared to no CC cultivation in arable cropland. Our study summarized global research of comparable management, with a focus on climatic zones representative of Europe, such as arid, temperate and boreal climates. In this meta‐analysis, we included 71 independent studies from 61 articles published between 1990 and June 2023 in several scientific and grey literature databases. Sensitivity analysis was conducted and did not identify any significant publication bias. The results revealed that CCs had an overall statistically significant positive effect on SOC pools, increasing MAOC by 4.8% (95% CI: 0.6%–9.4%, n = 16), POC by 23.2% (95% CI: 13.9%–34.4%, n = 39) and MBC by 20.2% (95% CI: 11.7%–30.7%, n = 30) in the top soil, compared to no CC cultivation. Thereby, CCs feed into the stable as well as the more labile C pools. The effect of CCs on MAOC was dependent on soil clay content and initial SOC concentration, whereas POC was influenced by moderators such as CC peak biomass and experiment duration. For MBC, for example, clay content, crop rotation duration and tillage depth were identified as important drivers. Based on our results on the effects of CCs on SOC pools and significant moderators, we identified several research needs. A pressing need for additional experiments exploring the effects of CCs on SOC pools was found, with a particular focus on MAOC and POC. Further, we emphasize the necessity for conducting European studies spanning the north–south gradient. In conclusion, our results show that CC cultivation is a key strategy to promote C accrual in different SOC pools. Additionally, this meta‐analysis provides new insights into the state of knowledge regarding SOC pool changes influenced by CCs, offering quantitative summary results and shedding light on the sources of heterogeneity affecting these findings. [ABSTRACT FROM AUTHOR]

Soil exchangeable acidity (EA) is an indicator of aluminium toxicity potential in acidic soils. Predicting the distribution and dynamics of EA is needed for the identification and management of acidic soils. In this study, we used datasets of 355 pedons from across Ghana and the Cubist rule‐based algorithm to generate pedotransfer functions (PTFs) of EA. Eight soil properties (pH, organic carbon, calcium, sodium, magnesium, total exchangeable bases, cation exchange capacity [CEC] to clay ratio and soil depth) were used to predict EA. We first used the whole dataset to construct generic PTFs and then stratified the dataset based on World Reference Base‐Reference Soil Groups (WRB‐RSGs) to generate soil‐specific PTFs. Goodness‐of‐fit statistics comprising the root mean squared error (RMSE), Lin's concordance correlation coefficient (ρC$$ {\rho}_C $$) and coefficient of determination (R2) were used to evaluate the prediction accuracy and reliability of the developed PTF models on both calibration and validation datasets. The Fluvisols EA‐PTF exhibited lower performance metrics in the validation (RMSE = 0.17 cmolc kg−1, ρC$$ {\rho}_C $$ = 0.19, R2 = 0.24), whereas the EA‐PTFs for all other WRB‐RSGs and whole dataset had above‐average performance metrics in the validation (0.05 ≤ RMSE ≤ 0.97 cmolc kg−1; 0.34 ≤ ρC$$ {\rho}_C $$ ≤ 0.94; 0.52 ≤ R2 ≤ 0.96). Soil pH sufficed for predicting EA in soils with pH above 5.0, but in soils with a pH < 5.0, the levels of exchangeable bases (e.g., Na+, K+, Mg2+, Ca2+), CEC to clay ratio (CCR) and soil depth improved the prediction of EA. The developed EA‐PTFs are useful for estimating the missing values of EA in soil databases. [ABSTRACT FROM AUTHOR]

The past decades have witnessed the increased applications of induced polarization (IP) method in the critical zone studies with ubiquitous clay minerals. Although IP outperforms traditional electrical and electromagnetic methods through its unique ability to measure quadrature conductivity, the nonlinearity that quadrature conductivity behaves with salinities and frequencies greatly tortures IP practitioners, as (a) salinity‐dependency makes the quadrature conductivity a varyingly unstable parameter to quantitatively estimate hydraulic properties and clay content; (b) frequency‐dependent Cole‐Cole and Debye/Warburg decomposition models, although mathematically sound, physically mingle the properties of pore water and clay minerals and are empirical in nature. From basic principles, we demonstrate that quadrature conductivity remains a hybrid property involving both clay and water, and develop relevant models to distinguish them. Our models are validated by theories, experiments, simulations, and comparisons, all of which proclaim considerable advantages over previous models and offer the prospect of quantitative applications. Plain Language Summary: As habitually appears in the first chapter of many geophysics textbooks, rock and soil models (i.e., petrophysics) lay the base for geophysical applications, bridging the gap between macro‐scale field and micro‐scale rock/soil parameters such as porosity and permeability. In contrast to "clean" rocks and soils where Archie's law is readily used, the additional interfacial conduction and polarization arising from the electrical double layer of "dirty" rocks and soils, especially clayey ones, greatly complicate this issue and bring both challenges and opportunities. On the one hand, this interfacial conduction nullifies Archie's law, making the porosity evaluation challenging, but, on the other hand, these interfacial properties provide an opportunity to assess the pore structure and clay properties, making the permeability estimation possible. Although IP is highly commendable to separate the interfacial attribution from the bulk water, complex conductivity models that can both physically and mathematically explain clayey rock/soil behaviors are lacking, which is the goal of our work. We expect our developed models to deepen the understanding of IP mechanisms and lead to more quantitative IP applications. Key Points: Salinity‐ and frequency‐dependent nonlinearities lie at the crux of induced polarization mechanismsQuadrature conductivity increases with salinity mainly by virtue of the coupling between electrical double layer (EDL) and waterFrequency dependency of clayey rocks and soils stems from the leaky‐capacitor behavior of the EDL [ABSTRACT FROM AUTHOR]

Saltmarshes are known for their ability to act as effective sinks of organic carbon (OC) and their protection and restoration could potentially slow down the pace of global warming. However, regional estimates of saltmarsh OC storage are often missing, including for the Nordic region. To address this knowledge gap, we assessed OC storage and accumulation rates in 17 saltmarshes distributed along the Danish coasts and investigated the main drivers of soil OC storage. Danish saltmarshes store a median of 10 kg OC m−2 (interquartile range, IQR: 13.5–7.6) in the top meter and sequester 31.5 g OC m−2 yr−1 (IQR: 41.6–15.7). In a global context, these values are comparatively low. Soils with abundant clay (> 20%), older and stable saltmarshes in mesohaline settings, and with low proportion of algal organic material showed higher OC densities, stocks, and accumulation rates. Grazing led to significantly higher OC stocks than neighboring ungrazed locations, likely due to trampling modifying soil abiotic conditions (higher erosion‐resistance and higher clay content) that slow carbon decay. Scaling up, Danish saltmarsh soils, comprising about 1% of the country's area, have the potential to yearly capture up to 0.1% of Denmark's annual consumption‐based CO2 emissions. Our research expands the baseline data needed to advance blue carbon research and management in the Nordic region while highlighting the need for a more comprehensive approach to saltmarsh management that considers the full range of services of these ecosystems and does not only focus on climate benefits. [ABSTRACT FROM AUTHOR]

Evidence is emerging that microbial products and residues (necromass) contribute greatly to stable soil organic matter (SOM), which calls for the necessity of separating the microbial necromass from other SOM pools in models. However, the understanding on how microbial necromass stabilizes in soil, especially the mineral protection mechanisms, is still lacking. Here, we incubated 13C‐ and 15N‐labelled microbial necromass in a series of artificial soils varying in clay minerals and metal oxides. We found the mineralization, adsorption and desorption rate constants of necromass nitrogen were higher than those of necromass carbon. The accumulation rates of necromass carbon and nitrogen in mineral‐associated SOM were positively correlated with the specific surface area of clay minerals. Our results provide direct evidence for the protection role of mineral in microbial necromass stabilization and provide a platform for simulating microbial necromass separately in SOM models. [ABSTRACT FROM AUTHOR]

Formation of mineral‐associated organic matter (MAOM) supports the accumulation and stabilization of carbon (C) in soil, and thus, is a key factor in the global C cycle. Little is known about the interplay of mineral type, land use and management intensity in MAOM formation, especially on subdecadal time scales. We exposed mineral containers with goethite or illite, the most abundant iron oxide and phyllosilicate clay in temperate soils, for 5 years in topsoils of 150 forest and 150 grassland sites in three regions across Germany. Results show that irrespective of land use and management intensity, more C accumulated on goethite than illite (on average 0.23 ± 0.10 and 0.06 ± 0.03 mg m−2 mineral surface respectively). Carbon accumulation across regions was consistently higher in coniferous forests than in deciduous forests and grasslands. Structural equation models further showed that thinning and harvesting reduced MAOM formation in forests. Formation of MAOM in grasslands was not affected by grazing. Fertilization had opposite effects on MAOM formation, with the positive effect being mediated by enhanced plant productivity and the negative effect by reduced plant species richness. This highlights the caveat of applying fertilizers as a strategy to increase soil C stocks in temperate grasslands. Overall, we demonstrate that the rate and amount of MAOM formation in soil is primarily driven by mineral type, and can be modulated by land use and management intensity even on subdecadal time scales. Our results suggest that temperate soils dominated by oxides have a higher capacity to accumulate and store C than those dominated by phyllosilicate clays, even under circumneutral pH conditions. Therefore, adopting land use and management practices that increase C inputs into oxide‐rich soils that are under their capacity to store C may offer great potential to enhance near‐term soil C sequestration. [ABSTRACT FROM AUTHOR]

Piles as onshore and offshore foundation structures are often horizontally loaded. The usual calculation method for the behaviour of piles under such loads is the p‐y method. For piles in cohesive soil, several p‐y methods are proposed in literature, leading in general to differing results. A finite element model dealing with the behaviour of horizontally loaded piles in clay soils was established and validated against field tests. Utilising the results of a vast number of numerical simulations, a new p‐y method was developed, which gives reasonable results over the entire range of possible loads for piles of almost arbitrary diameters and embedded lengths in clay soils of varying consistency. The method requires in total six soil parameters and accounts for the actual deflection of the pile and also the effect of pile tip shear resistance by iteratively adapted y‐multipliers which depend on the course of the deflection line and the distance of the considered point to the pile tip. The new method can be generally used for calculation of the bearing behaviour of piles in soft clay under monotonic loading and can serve as a reference for consideration of cyclic load effects or softening effects in stiff clays. [ABSTRACT FROM AUTHOR]

Termites contribute to the spatial heterogeneity of the ecological processes of the highly degraded lands called the bowé in West Africa, but the underlying determinants of the distribution of the mounds remain poorly understood. Thus, the study aims to determine the principal abiotic and biotic factors shaping mound densities on bowé in Benin, West Africa. A number of 64 plots were randomly sampled on sites with mounds and adjacent off‐mounds sites on bowé. Data were collected on abiotic (soil variables (pH, bulk density, particle sizes and soil organic carbon) and altitude) and biotic (the number of live termite mounds, plant richness and cover) factors. Correspondence analysis (CA) was applied to assess the pattern of vegetation and termite mounds on bowé; while principal component analysis (PCA) was used to assess the relationship between soil variables (pH, bulk density, particle size and soil organic carbon), altitude, number of mounds, plant richness and cover. Generalised mixed effects and linear mixed effects models with Poisson error distribution were used to analyse the variation in soil variables, number of mounds, species richness and cover between termite species. The findings revealed that the pattern of termite mounds on bowé was driven by altitude (topography) and soil clay content that contribute to termite activities as well as improving soil bulk density, plant species richness and cover. These factors were positively associated with all termite species considered, except for those belonging to the genus of Macrotermes. [ABSTRACT FROM AUTHOR]

In‐depth knowledge about the impact of organic matter (OM) on soil water vapor sorption (SWVS) and associated hysteresis related to various water activity (aw) levels is limited. The objective of this study was to elucidate the effect of OM on SWVS and sorption hysteresis for different aw levels. We measured water sorption isotherms and physicochemical properties of eight soils with varying clay (6%–47%) and OM (2.0%–7.8%) contents before and after OM removal. In general, OM increased SWVS, but the effect of OM on SWVS varied for different aw ranges. The presence of OM generally increased water vapor sorption during the adsorption process. For soils with OM content above 4.6%, the presence of OM decreased water vapor sorption during the condensation process. The local hysteresis (Hw) of soils with OM was higher than that of soils without OM for soils with OM contents above 3.4%. For aw < ∼0.75, the water vapor sorption hysteresis of soils with and without OM showed a significant correlation with cation exchange capacity (CEC), and the Hw values of soils with OM were lower than that of soils without OM for the same CEC. The OM can affect water vapor sorption and the associated hysteresis at low aw levels through adsorbed cations and organic functional groups, and at high aw levels through the structures of pores and OM. Core Ideas: An increase in water vapor sorption due to OM mainly occurred during adsorption.A decrease of water vapor condensation due to OM is caused by a reduced pore volume.The OM content affects water vapor sorption hysteresis.The CEC is a key factor affecting sorption and hysteresis in soils with and without OM. [ABSTRACT FROM AUTHOR]

Background: Particle size distribution (PSD) is a fundamental soil measurement that is crucial for agriculture, engineering, hydrological, and environmental applications as well as in basic research such as in developing water release curves in flow and transport modeling. The accurate determination of PSD, particularly clay content, is especially critical in ascertaining the magnitude and rates of many physical, chemical, and hydrological processes in soils. The accuracy of the hydrometer method for PSD, which relies on the settling velocity of soil particles in a soil suspension, could be affected by the density of the suspension, which in turn, depends on the initial sample mass, texture, and mineralogy of the soil. Aims: We hypothesized that (1) initial mass determines the concentration and the physical interaction of particles in a soil suspension and affects particle settlement, recovery, and the accuracy of the hydrometer method, and (2) the widely used initial air‐dry mass of 50 g underestimates the clay percentage of medium to heavy textured tropical soils. The objective of this study was to investigate the effect of mass and KCl on clay recovery in tropical soils with varying texture and mineralogy using the hydrometer method. Methods: The experiment comprised seven soils, four soil masses (10, 20, 30, 50 g), and two KCl treatments in a 7 × 4 × 2 factorial design replicated three times. Results: Results showed a general trend of increasing estimates of clay % as the soil mass decreased from 50 to 10 g and the KCl concentration increased from 0 to 0.0025 M. This implies that using an initial sample mass of 50 g in sedimentation methods, underestimates, and 10 g overestimates the clay % in predominantly medium to heavy textured tropical soils. Interestingly, there was a drastic change in texture for most of the soils as the sample mass decreased to 10 g. Conclusions: We conclude that the initial air‐dry mass affects the clay recovery of medium to heavy textured humid tropical soils. Results suggest that the ideal initial mass for these soils lies between 20 and 30 g. Furthermore, the mechanistic pathway that drives the observed decrease in clay recovery as soil sample mass increase could be due to the flocculating tendency of KCl. [ABSTRACT FROM AUTHOR]

In cold regions, the creep behavior of frozen soil is a crucial indicator for evaluating the stability of engineering foundations. The creep properties of frozen soil are more complex than unfrozen soil owing to its special cryogenic structures. In this research, a series of creep tests were conducted on the heterogeneous frozen clay soil under different deviatoric stresses, and the influence of deviatoric stress and structural features on its creep behaviors were analyzed. Based on the test results and fracture mechanics, the damage variable of heterogeneous frozen clay soil considering the effect of cryostructure was defined, and the sensitivity of parameters in damage variable were analyzed. By introducing the hardening variable and damage variable into the classical Nishihara model, a new creep constitutive model for heterogeneous frozen clay soil considering the fracture of cryostructure was established, the validity of the model was verified using test results, and the model parameters were analyzed. Highlights: Creep tests were conducted on different structural types of frozen clay soil under different deviatoric stresses.The damage variable considering propagation of cracks during creep process was defined.A creep constitutive model for frozen clay soil based on the hardening and damage effects was proposed.The rationality of the model was verified, and the sensitive of model parameters were analyzed. [ABSTRACT FROM AUTHOR]

Recent studies suggest that wild animals can promote ecosystem carbon sinks through their impacts on vegetation and soils. However, livestock studies show that intense levels of grazing reduce soil organic carbon (SOC), leading to concerns that rewilding with large grazers may compromise ecosystem carbon storage. Furthermore, wild grazers can both limit and promote woody plant recruitment and survival on savanna grasslands, with both positive and negative impacts on SOC, depending on the rainfall and soil texture contexts. We used grazing lawns in one of the few African protected savannas that are still dominated by megagrazers (> 1000 kg), namely white rhinoceros Ceratotherium simum, as a model to study the impact of prolonged and intense wild grazing on SOC stocks. We contrasted SOC stocks between patches of varying grazing intensity and woody plant encroachment in sites across different rhino habitat types. We found no differences in SOC stocks between the most‐ and least grazed plots in any of the habitats. Intermediately grazed plots, however, had higher SOC stocks in the top 5 cm compared to most and least grazed plots, but only in the closed‐canopy woodland habitat and not in the open habitats. Importantly, we found no evidence to support the hypothesis that wild grazing reduces SOC, even at high grazing intensities by the world's largest megagrazer. Compared to the non‐encroached reference plots, woody encroached plots had higher SOC stocks in soils with low clay content and lower SOC stocks in soils with high clay content, although only in the top 5 cm. Accordingly, our study highlights that wild grazers may influence SOC indirectly through their impact on tree‐grass ratios in grassy ecosystems. Our study thus provides important insights for future natural climate solutions that focus on wild grazer conservation and restoration. Keywords: fire, grazing impact, rewilding, soil carbon, white rhinoceros, woody encroachment [ABSTRACT FROM AUTHOR]

Understanding of factors governing soil structural features is necessary for managing key processes affecting crop productivity and environmental impacts of agriculture, for example, soil water balance, aeration, and root penetration. Organic matter is known to act as a major binding agent in soil aggregation and thus constitutes a central pillar in soil structure formation. However, knowledge of the structural role of organic matter or carbon (OC) in soils highly rich in clay‐sized particles (<0.002 mm) is limited. In this study, the effects of clay and OC contents on aggregate stability, water holding capacity, near‐saturated hydraulic conductivity, total porosity, and pore size distribution were assessed in cultivated fields with high clay content located in private crop production farms in southern Finland. Significant positive correlations were found between OC content and proportion of water stable aggregates and specific pore sizes from the range of 30 μm up to 1 mm diameter determined by image analysis. Porosities on a smaller size range derived from water retention measurements likewise showed a positive correlation with OC in <0.2 μm sizes. On the range of 0.2–1 μm, a negative relationship was observed, which induced a negative effect of OC on soil plant available water reserves. In line with the positive correlation between OC and larger soil pores, free water, representing the amount of water that can be drained by gravity, exhibited a positive relationship with OC suggesting that OC content can enhance aeration of soils with high clay content. Compared to OC, clay content tended to have an adverse effect on soil structural properties. Clay correlated negatively with pores larger than 30 μm, free water content, and extrapolated field saturated hydraulic conductivity. Further, our imaging results showed how saturated hydraulic conductivity was controlled by pore morphology, and there was a power law relationship between the conductivity and critical pore diameter. K∝dc2$$ K\propto {d}_c^2 $$ in agreement with the percolation theory. Overall, the structural impacts and hydrological implications of OC and clay in heavy clay soils vary by pore size ranges and their emergent practical impacts are thus not straightforward. [ABSTRACT FROM AUTHOR]

In this paper, a simplified chemo‐hydro‐mechanics (CHM) model, in which only solute concentration is considered in the aspect of chemistry, is proposed to reflect the viscoelastic deformation of clay soil. By using the proposed model, the responses of the excess pore‐fluid pressure, solute concentration, and displacement of the viscoelastic clay soil are derived through the Laplace transform method. Then, semi‐analytical solutions, in the time domain, are obtained via the inverse Laplace transform numerically. The influences of viscosity on excess pore‐fluid pressure, solute concentration, and displacement are investigated through an illustrative example. The results show that: (1) the clay soil in low viscosity can be simplified as an elastic model; (2) the higher viscosity not only accelerates the dissipation of excess pore‐fluid pressure, but also slows down the deformation of the clay soil; (3) the viscosity of clay soil poses little impact on the distribution of solute concentration. [ABSTRACT FROM AUTHOR]

Rationale: Steam equilibration overcomes the problem of the traditional measurements of H isotope compositions, which leave an arbitrary amount of adsorbed water in the sample, by controlling for the entire exchangeable H pool, including adsorbed water and hydroxyl‐H. However, the use of steam equilibration to determine nonexchangeable stable H isotope compositions in environmental media (expressed as δ2Hn values) by mathematically eliminating the influence of exchangeable H after sample equilibration with waters of known H‐isotopic composition requires the knowledge of the equilibrium isotope fractionation factor between steam‐H and exchangeable H of the sample (αex‐w), which is frequently unknown. Methods: We developed a new method to determine the αex‐w values for clay minerals, topsoil clay fractions, and mica by manipulating the contributions of exchangeable H to the total H pool via different degrees of post‐equilibration sample drying. We measured the δ2H values of steam‐equilibrated mineral and soil samples using elemental analyzer‐pyrolysis‐isotope ratio mass spectrometry. Results: The αex‐w values of seven clay minerals ranged from 1.071 to 1.140, and those of 19 topsoil clay fractions ranged from 0.885 to 1.216. The αex‐w value of USGS57 biotite, USGS58 muscovite, and of cellulose was 0.965, 0.871, and 1.175, respectively. The method did not work for kaolinite, because its small exchangeable H pool did not respond to the selected drying conditions. Structurally different mineral groups such as two‐ and three‐layer clay minerals or mica showed systematically different αex‐w values. The αex‐w value of the topsoil clay fractions correlated with the soil clay content (r = 0.63, P = 0.004), the local mean annual temperature (r = 0.68, P = 0.001), and the δ2H values of local precipitation (r = 0.72, P < 0.001), likely to reflect the different clay mineralogy under different weathering regimes. Conclusions: Our new αex‐w determination method yielded realistic results in line with the few previously published values for cellulose. The determined αex‐w values were similar to the widely assumed values of 1.00–1.08 in the literature, suggesting that the adoption of one of these values in steam equilibration approaches is appropriate. [ABSTRACT FROM AUTHOR]

Ground Penetrating Radar (GPR) survey was conducted to detect historic unmarked graves from the period of the Civil War (1861–1865) at the Fairlawn Cemetery in Stillwater, Oklahoma. The GPR survey at the Fairlawn Cemetery will help preserve the unmarked historic graves if they exist or clear sections of the cemetery for possible expansion. GPR detection of historic graves are often a challenge as these graves are made of wooden boxes, bones and coffins, with no metal caskets or concrete burial vaults. It was even more challenging to detect unmarked graves in this study as the cemetery is covered with iron‐rich silty clay soil, which attenuates the GPR signals. We conducted the GPR survey along a grid consisting of 44 parallel 30‐m‐long profiles spaced at 50‐cm intervals using the 400‐MHz antenna. The acquired GPR data were processed as 2D profiles and produced a pseudo‐3D GPR volume to resolve the unmarked graves. Multiple features extracted from the pseudo‐3D volume at depths ranging from 0.7 to 1.3 m aligned along three north–south rows. Based on the dimensions, orientation, distribution and depth of burial of the anomalous features relative to the recent graves, we interpreted these features as unmarked graves. This study has demonstrated the GPR as an effective non‐invasive technique in detecting historical unmarked graves that contain no metal caskets or concrete burial vaults. This work will contribute not only to the science of historical archaeology but also to prehistorical archaeology, as caskets were not typically part of the prehistorical burials, and the modern‐day archaeology, particularly in the cases of mass graves in recent conflicts. [ABSTRACT FROM AUTHOR]

BACKGROUND: There is an increasing understanding of the importance of biochar‐based fertilizers in agroecosystems. However, no research has evaluated the effects of partial substitution of urea with biochar‐based urea on rice yields and soil microbial communities. We therefore investigated the rice yields, bacterial communities, and gene abundance involved in nitrogen in silty clay and sandy loam soil paddy fields treated with urea (U), total substitution of urea with biochar‐based urea (BSU), partial substitution of urea with biochar‐based urea in basal and tillering fertilizers (BSU1), and partial substitution of urea with biochar‐based urea in panicle fertilizers (BSU2). RESULTS: Compared with U, applying biochar‐based urea increased rice yields, with BSU2 having the most notable effect. Principal coordinate analysis revealed that bacterial communities treated with BSU2 in both soils were significantly different from those treated with U and BSU, most probably due to the decrease in pH caused by the decrease in the concentration of ammonium. The relative abundance of Subdivision3_genera_incertae_sedis, Azotobacter, Geobacter, Buchnera, and Terrimonas in silty clay soils and Saccharibacteria_genera_incertae_sedis and Geobacter in sandy loam soils significantly increased when treated with BSU2 and was positively correlated with rice yields, indicating that the improvements in rice yield were associated with changes in bacterial communities. Based upon amoA/narG related to nitrate accumulation and norB/nosZ related to nitrous oxide emissions, BSU2 enabled a lower risk of nitrate leaching and nitrous oxide emissions in both soils, in comparison with the U and BSU treatments. CONCLUSION: The BSU2 treatment had a stronger yield‐increasing effect than biochar‐based urea alone and lowered the risk of nitrogen pollution, which is beneficial to the sustainable development of paddy fields. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

Background: Soil aggregation and organic carbon (OC) content are important indicators of soil quality that can be improved with plant residue amendments. The extent of the effects of plant residue amendments on soil aggregation and OC content across different plant residue and soil types is not fully understood. Aim: In this meta‐analysis, we evaluated the effects of plant residue amendments on soil aggregation and OC content for different plant residues (fresh, charred) and soil types varying in clay content, initial OC content, and pH. Methods: Our meta‐analysis included 50 published studies (total of 299 paired observations). We estimated the response ratios of mean weight diameter (MWD) and separate aggregate size classes, total soil OC (TSC), and aggregate‐associated OC. We also considered the effect of experimental factors (study duration, residue type, residue amount, initial soil OC, clay content, and pH). Results: The benefit of plant residue amendment on soil aggregation was larger in soils with initially low OC content and neutral pH. Initial soil OC content and pH were more important than soil clay content for OC storage in soil aggregates. Both fresh and charred plant residue amendments were effective in forming aggregates, whereas charred residues were more effective in increasing TSC. We found only a weak positive relationship between the response ratio of TSC and MWD indicating that other factors besides soil aggregation contributed to the increase in soil C storage. Conclusions: While plant residue amendments can enhance soil aggregation and TSC, these effects are likely governed by the type of plant residue and soil properties such as the initial soil pH and OC content. [ABSTRACT FROM AUTHOR]

Retrogressive failures occur in slopes consisting of sensitive materials such as snow or quick clay. They can be triggered by a small disturbance at the slope toe, but can cause propagated failure spreading miles away. Understanding the physical mechanism and predicting the retrogressive failure process are particularly important. Previous studies have discussed the failure criteria, the soil properties or the method of numerical modeling of retrogressive slope failure. However, little attention has been paid to the microscopic failure mechanism, especially relating to various possible failure patterns. In this study, multiscale modeling is incorporated to study the physical mechanism of different retrogressive failure patterns, including earth flow, flowslide and spread failure, within a unified framework. Utilizing multiscale analysis, we found that earth flow failure is related to the shear failure of granular materials. In contrast, the development of macroscopic shear bands is accompanied by tensile failure. As shear and tension failures are typical failure mechanisms of frictional and cohesive materials, it is deduced that friction and cohesion effects play key roles in different retrogressive failure patterns. Therefore, the distributions of attractive and repulsive contact forces are explored and a novel parameter η is proposed to quantify the interplay between friction and cohesion. Further analysis proves that η can capture the effect of friction and cohesion and distinguish different retrogressive failure patterns. Finally, a spectrum of retrogressive failures for a granular slope is established, in which the failure mechanism is explained by the changeable dominant effect, that is, frictional or cohesive in soil. Plain Language Summary: Slope failure is a common geo‐hazard that occurs in nature and engineering. For example, a sensitive clay consisted soil slope can easily propagate for miles, leading to catastrophic damage to human lives and properties. Previous researchers mainly study the slope failure processes/mechanisms on the scale of soil blocks, lacking observations at the soil particle scales. In this research, a hierarchical multiscale modeling is proposed, which enables the simulation of both the retrogressive slope failure process and interactions between soil particles. The mechanisms of various retrogressive failure patterns are thereby explored, including earth flow, flowslide, and spread failure. The earth flow tends to fail near the surface by shearing, where the shear strength is mainly determined by the friction between particles. The flowslide fails in a retrogressive pattern, shown as bulks of soils moving after bulks. The soil in shear bands fails under stretching mainly, where the strength is determined by the cohesion between particles. The spread failure is more complex, combining the influences of friction and cohesion. The friction effect controls the bottom of slopes, contributing to the translational shear band and spread failure of slopes. A spectrum to classify different failure patterns is established at the end. Key Points: Hierarchical multiscale modeling is carried out to explore the mechanism of various retrogressive failure modes in granular slopesThe interplay between friction and cohesion near the slope surface determines the development of earth flow or flowslide failure patternThe friction effect controls the bottom of slopes and contributes to the translational shear band and the spread failure of slopes [ABSTRACT FROM AUTHOR]

Soil particle density (ρs) is often assumed as 2.65 g cm−3 (density of quartz). The objectives of this study were to compare the use of different gases for determining ρs in a gas pycnometer and relate measured ρs to soil particle size distributions. The ρs of 36 natural soil samples representing 12 USDA textural classes, fine glass beads, crushed granite rock, kaolinite, and bentonite were measured by a commercial gas pycnometer using He, N2, and dry air. The ρs of 30 of the soil samples, glass beads, and crushed rock were also determined with a water pycnometer. The ρs of 36 soil samples determined by He and 30 samples determined by water had narrow ranges with averages of 2.65 and 2.59 g cm−3, respectively. The ρs determined by air and N2 had much wider ranges with averages of 2.93 and 2.97 g cm−3, respectively. There was a near 1:1 relationship between ρs of all samples determined by air and N2 with a highly significant (p <.001) correlation coefficient (r =.99). The average ratio of ρs determined by He and water was 1.03, but the correlation coefficient for their relationship was only.416. Although the relationship between ρs determined by He and either air or N2 was relatively strong (r <.61), the regression coefficient was <.17. There was a strong relationship between soil clay content and ρs determined by N2 or air but a weaker, yet statistically significant (p <.05) relationship when using He. Core Ideas: Average particle density of soils belonging to 12 textural classes determined by helium was 2.65 g cm−3.Average particle density measured by air and nitrogen were 2.93 and 2.97 g cm‐3, respectively.Helium, nitrogen, or air can be used to measure particle density of coarse‐textured soils.Only helium should be used to measure particle density of medium‐ and fine‐textured soils. [ABSTRACT FROM AUTHOR]

Background: Pelosols are the Soil of the Year 2022 in Germany, Austria and Switzerland. They represent soils with a high clay content (≥45%) in the diagnostic P horizon. Pelosols are nutrient‐rich, have a strong capacity for swelling and shrinking, have a challenging water balance with a high portion of nonplant available water and are affected by high traction. Such special characteristics make them challenging soils under agricultural management. Aims: The occurrence, land use management and soil erosion risk of Pelosols in Germany were investigated and compared to their clay‐rich soil counterparts on a global scale. Methods: We intersected soil maps of the German and international digital soil mapping with soil erosion data. Results: A high percentage (63%) of Pelosols in Germany are under agricultural use, from which two‐thirds are arable farming. Simultaneously, Pelosols have a high risk for soil erosion by water and are the fourth most endangered soil type compared to all soil types in Germany. The average soil erosion loss of Pelosols used for agricultural practices assessed by the Revised Universal Soil Loss Equation (RUSLE) is 2.24 t ha−1 year−1 compared to an average erosion loss of all agriculturally used soils in Germany of 1.65 t ha−1 year−1. From an international perspective, Pelosols in Germany are mostly mapped as haplic Cambisols or haplic Luvisols, as they do not necessarily meet the diagnostic properties of the clay‐rich Vertisol soil type. Most Vertisols are classified as Pelosols, but Pelosols do not necessarily fulfil the diagnostic criteria of Vertisols. Vertisols on a global scale have an even higher soil erosion risk than Pelosols in Germany (3.5 t ha−1 year−1). Conclusions: Pelosols and Vertisols, despite their high percentages for agricultural use, have a high soil erosion risk compared to other soil types and thus need special care under agricultural use and adapted protective land use management. [ABSTRACT FROM AUTHOR]

The sand‐filled nodular pile (SFNP) foundation is newly proposed to improve the bearing capacity and accelerate consolidation settlement of foundations installed in soft clay soil. By filling sand while driving the nodular pile into the soft clay soil, the SFNP foundation provides an extra drainage path with the aid of the nodular segment, while maintaining the high modulus reinforcement body at the core of the composite foundation. The performance of the SFNP foundation is greatly influenced by its consolidation behaviour. This study develops a generalized model for the SFNP foundation, and a closed‐form solution is then established considering the smear and well resistance effects. The developed model and the associated analytical solution are employed to investigate the consolidation rate and load distribution of the SFNP foundation. Finally, the analytical solution is utilized to evaluate the performance of SFNP foundation for an expressway project located in Zhejiang, China. The predicted dissipation of the excess pore water pressure employing the developed analytical solution agreed well with measured response from the field test, which further confirmed the advantages of the SFNP foundation and the reliability of the developed solution. [ABSTRACT FROM AUTHOR]

Soil erosion is a major constraint to agricultural sustainability. Land management that protects soil from water erosion can be assessed from the fraction of aggregates stable upon water immersion. Conservation management with minimal soil disturbance is known to enhance water‐stable aggregation, but how annual vs. perennial vegetative cover affects soil biological activity and aggregation from soils varying in texture remains relatively unexplored. This study assessed the effects of long‐term conventional‐till and no‐till cropland, grassland, and woodland on dry‐stable and water‐stable mean‐weight diameter (MWD) from 25 research stations across North Carolina. Soil clay concentration varied from 36 to 279 g kg–1 and sand concentration varied from 392 to 904 g kg–1 (5–95% distribution). Across locations, water‐stable MWD followed the order: conventional‐till cropland (0.64 mm) < no‐till cropland (0.87 mm) < woodland (1.12 mm) = grassland (1.15 mm). Soil stability index (i.e., water‐stable MWD/dry‐stable MWD) followed a similar order: conventional‐till cropland (0.59 mm mm–1) < no‐till cropland (0.76 mm mm–1) < grassland (0.92 mm mm–1) = woodland (0.96 mm mm–1). Although water‐stable MWD was positively associated with clay concentration (r =.50, p <.001, n = 310), soil‐test biological activity had the strongest association with water‐stable MWD (r =.80). Soil‐test biological activity reflected biological manipulation of surface‐concentrated organic matter, as mediated by conservation land uses. This study revealed the large impact of surface organic C and N resources on water‐stable aggregation through soil biological manipulations interacting across a textural gradient. Core Ideas: Conservation land uses of no‐till cropland, grassland, and woodland improved soil aggregation characteristics.Soil stability index discerned conservation land use impacts across a soil texture gradient.Soil aggregation characteristics were not different between grasslands and woodlands.Soil‐test biological activity and sand were strongly associated with soil aggregation characteristics. [ABSTRACT FROM AUTHOR]

This study developed a comprehensive database of soil physical properties to expand the potential applications of soil moisture observations across the Kansas Mesonet environmental monitoring network. The database comprises 14 site‐ and depth‐specific soil hydraulic properties for 40 stations monitoring soil water content. The measured soil hydraulic properties include sand, clay, and silt contents; bulk density; particle density; total porosity; effective saturation; saturated hydraulic conductivity; and water retention at six matric potentials. The soil database spans eight soil textural classes, with silty clay loam, silt loam, and silty clay soils dominating the fine‐textured soils, and sandy loam and sandy clay loam soils comprising the only coarse‐textured soils. All the measured soil hydraulic properties showed low coefficient of variation (CV ≤10%) within soil textural classes, except for the saturated hydraulic conductivity, which varied from a median of 0.520 ± 308 cm d–1 in the clay soils to 47.1 ± 119 cm d–1 in the sandy loam soils. The uncertainty of the Kansas Mesonet soil water content observations was reduced by at least 29% using laboratory sensor calibration equations instead of the factory default sensor equation. Our soil physical property database offers new prospects to use historical and near real‐time in situ soil water content observations across the Kansas Mesonet for diverse agricultural and hydrological applications, including drought monitoring, wildfire preparedness, and estimating potential drainage and groundwater recharge rates. Core Ideas: This study developed a comprehensive soil physical property database for the Kansas Mesonet.The database comprises 14 site‐ and depth‐specific soil hydraulic properties for 40 stations.The soil database is dominated by fine‐textured soils with 92% of the soils having >20% clay content.Laboratory sensor calibration equations reduced the uncertainty of the water content measurements by at least 29%. [ABSTRACT FROM AUTHOR]

Supplemental fertilizer N recommendations for flood‐irrigated rice (Oryza sativa L.) have been developed with tests that quantify plant‐available N within the effective rooting depth. Alkaline hydrolyzable‐nitrogen (AH‐N) soil test methods were recently used to successfully guide supplemental fertilizer‐N management decisions of drill‐seeded, delayed‐flood rice, stimulating interest in evaluating additional indicators of N availability such as soil total carbon (STC) and soil total nitrogen (STN). Our first objective was to evaluate the relationship among STC, STN, and AH‐N to a depth of 60 cm. Our second objective was to correlate STC and STN to rice N uptake and grain yield and develop calibration regression models that identified the yield maximizing N rate (FN 95%RGY). The STC and STN were significantly and positively related to AH‐N when clayey soils were sampled to >15‐cm depth and the coefficient of determination (r2) exhibited a range of.22–.70 for STN and.26–.75 for STC. Overall, STC and STN were significantly related to rice N uptake, unfertilized grain yield (Yield0N), or relative grain yield (RGY) and r2 values tended to be greatest at a 30‐cm depth or only nominally improve when sampling depth exceeded 30 cm. Calibration of STC and STN to predict FN 95%RGY was successfully completed, but all linear regressions had r2 <.40. The influence of sampling depth on the ability of STC and STN to serve as indicators of rice response to supplemental N fertilization demonstrates the utility of sampling within the rice plant's effective rooting depth. Core Ideas: Soil total C and N increased linearly with alkaline hydrolyzable‐N to a 60‐cm depth.Soil total C and N explained <40% of the variability exhibited by rice response parameters.Soil total C and N from >30‐cm depth did not improve prediction of the rice grain yield maximizing fertilizer N rate.Correlation and calibration of soil total C and N to fertilizer N response of rice should consider the extent of rooting depth. [ABSTRACT FROM AUTHOR]

BACKGROUND: The availability of soil nitrogen (N) decreases as the structure of agricultural soils degrades. Traditional methods focus on organic amendments that indirectly affect the porosity and N content of soil. Due to the low efficiency of such amendments, new materials, particularly highly porous materials, are needed to improve the quality of soil, which has opened new directions. RESULTS: The addition of 2 to 7 mm of porous clay ceramic (PLC) significantly increased the fresh weight of Brassica chinensis. The soil aeration porosity (>50 μm) increased by 0.69% on average in response to 1% PLC application. Soil NO3−‐N, NH4+‐N and mineral N increased by 3.3, 1.3 and 4.6 mg kg−1 on average, respectively, following a 1% PLC application rate. The initial N content of the high PLC treatments was the lowest in the incubation experiment. The parameters of soil N mineralization, i.e. potentially mineralizable N (N0), the first‐order rate constant (k) and the mineralization composite index (N0 × k), increased obviously as the amount of PLC increased. Porosities larger than 1000 μm were significantly more positively correlated with the parameters of soil N mineralization than those <500 μm. The Pearson correlation coefficients suggested that high porosity, mineral N and N0 values had significant positive relationships with the fresh weights in double seasons. CONCLUSION: The application of PLC increased soil aeration and enhanced the availability of soil N, which yielded large vegetable harvests in clayey soils in the short term. © 2022 Society of Chemical Industry. [ABSTRACT FROM AUTHOR]

In Ukraine, 6.5 million hectares of agricultural land characterized by heavy clay soil could be available for sustainable bioenergy crop cultivation because they are considered marginal for food crop cultivation. This study investigated the biomass dry matter yield (DMY) of willow (Salix triandra L. and Salix viminalis L.) and Miscanthus (Miscanthus × giganteus Greef et Deuter) at two experimental sites with heavy clay in Ukraine. To promote plant rooting and adaptation in the first year of cultivation under low‐input conditions, tillage, moisture‐retaining agents, foliar fertilization, planting density and row spacing were varied. Willow obtained notable DMY on hard clay soils (clay >50%). The variety 'Tora' revealed the best DMY performance, indicated by the highest increment (4.1–4.6 m) in the first year of the second cycle. The highest biomass DMY (28.8 Mg ha−1) was obtained at a planting density of 15 000 plants ha−1 and a row spacing of 0.75 × 1.50 m. However, neither willow nor Miscanthus allow for a feasible biomass production at clay contents above 64%, because the young roots are damaged and deprived of nutrients as the soil dries out. For Miscanthus, plowing provided better soil loosening and easier sprouting of rhizomes compared with mini‐till. The application of moisture‐retaining agent Aquasorb (200 kg ha−1) supported Miscanthus plants with moisture in the first year of vegetation, but it did not maintain soil moisture in the long term. Therefore, growing willow and Miscanthus on soils with clay contents above 64% is not feasible because the soil texture and tendency to crack significantly reduce the DMY. © 2022 The Authors. Biofuels, Bioproducts and Biorefining published by Society of Industrial Chemistry and John Wiley & Sons Ltd. [ABSTRACT FROM AUTHOR]

The determination of the coefficient of linear extensibility (COLE) of soils is crucial for enhancing structural stability in civil engineering applications. Traditional methods for measuring COLE have some practical limitations. In routine soil analyses, clay and soil organic carbon (OC) are often measured, while soil hygroscopic water content (wh) is easy to determine on several soil samples simultaneously. The aims of the study were to (1) utilise two data partitioning approaches to develop regression models that estimate the soil COLE from hygroscopic water content, clay and OC contents, and (2) compare the model performance of the developed regression models. We used two data partitioning approaches. First, the calibration models were developed on 53 soil samples from Slovakia and validated with 24 soil samples from the United States (country‐wise). Second, the calibration models were built from 67% of the entire dataset and validated with 33% (mixed data). Regression models based on hygroscopic water content accurately estimated COLE regardless of sorption direction or data partitioning approach (RMSE: 0.014–0.023 cm cm−1). The inclusion of OC in multiple linear regression models of clay only marginally improved COLE estimation compared to clay alone. For all models, the mixed data partitioning method showed better model validation performance than the country‐wise approach. The COLE classes derived from the estimated COLE values compared favourably (72%–94% accurate) to the measured data. Thus, there is a great potential to estimate the COLE from readily available (clay and OC) or easily measurable (hygroscopic water content) soil properties. Highlights: Hygroscopic water content (wh) is intimately linked to soil properties that determine COLE.Regression models based on wh or clay, and organic carbon content accurately estimated COLE.Data partitioning approach for modelling significantly impacted model performanceSamples with very high COLE were better estimated by wh‐based models than by other variables [ABSTRACT FROM AUTHOR]

Since the early 2000s, digital soil maps have been successfully used for various applications, including precision agriculture, environmental assessments and land use management. Globally, however, there are large disparities in the availability of soil data on which digital soil mapping (DSM) models can be fitted. Several studies attempted to transfer a DSM model fitted from an area with a well‐developed soil database to map the soil in areas with low sampling density. This usually is a challenging task because two areas have hardly ever the same soil‐forming factors in two different regions of the world. In this study, we aim to determine whether finding homosoils (i.e., locations sharing similar soil‐forming factors) can help transferring soil information by means of a DSM model extrapolation. We hypothesize that within areas in the world considered as homosoils, one can leverage on areas with high sampling density and fit a DSM model, which can then be extrapolated geographically to an area with little or no data. We collected publicly available soil data for clay, silt, sand, organic carbon (OC), pH and total nitrogen (N) within our study area in Mali, West Africa and its homosoils. We fitted a regression tree model between the soil properties and environmental covariates of the homosoils, and applied this model to our study area in Mali. Several calibration and validation strategies were explored. We also compared our approach with existing maps made at a global and a continental scale. We concluded that geographic model extrapolation within homosoils was possible, but that model accuracy dramatically improved when local data were included in the calibration dataset. The maps produced from models fitted with data from homosoils were more accurate than existing products for this study area, for three (silt, sand, pH) out of six soil properties. This study would be relevant to areas with very little or no soil data to carry critical soils and environmental risk assessments at a regional level. Highlights: Soil mapping models were fitted with soil data within the homosoils of Mali.The fitted models were applied to our study area.Model accuracy dramatically improved when including local data.Homosoil maps were more accurate for 3 out of 6 soil properties compared to global and continental maps.New opportunity to map the regional soil pattern of areas with limited soil data coverage. [ABSTRACT FROM AUTHOR]

Digital soil mapping provides estimates of soil properties and, in turn, an understanding of the spatial variation in soil across landscapes. In recent years, several digital soil mapping products have been released across the world. An end user in New South Wales (NSW), Australia, could choose between a global product (SoilGrids), a national product (Soil and Landscape Grid of Australia) and a state product (NSW digital soil maps). All predict at grid resolutions of 250 m or less, which approaches the required detail for within‐field site‐specific management such as variable‐rate application of agricultural inputs. In this study, the quality of clay and soil organic carbon (SOC) products (0–30 cm) from these three publicly available digital soil maps (DSM) were validated with an external dataset of 394 soil observations, collected from 14 farms across eastern Australia. Each farm was sampled using stratified random sampling, allowing for unbiased estimates of prediction quality at three spatial supports: point (soil core), strata (management zone) and farm. For the clay attribute, this study observed Lin's concordance correlation coefficient (LCCC) values of 0.22–0.37 at the point spatial support, far below reported values. This improved at the strata spatial support with LCCC values of 0.20–0.60 and the farm spatial support with values of 0.07–0.54. For SOC, LCCC values ranged from 0.25 to 0.45 for points, 0.31–0.55 for strata and 0.31–0.60 for farms. The grid resolution of DSMs depends largely on the resolution of the covariates used, and current efforts look to incorporate more recent, finer resolution covariates to create higher‐resolution soil maps. However, the results of this study suggest that both the grid resolution and spatial support used in DSMs need further consideration. Rather than letting the resolution of covariates determine the resolution of DSMs, this should also be determined by the number of soil observations available for modelling, their distribution in geographic and attribute space and the prediction quality. Highlights: DSM products do not meet published accuracies when assessed with an independent datasetThe large‐extent DSM products were unable to represent within‐farm variabilityAggregation of the DSM products over large spatial supports improved accuraciesDSM products should be created at different spatial supports, each with an associated uncertainty [ABSTRACT FROM AUTHOR]

Soils have distinctive chemical, physical, mineralogical and biological properties, which make it possible to differentiate them in different environments and also to test for an association of a particular questioned item with a crime scene. Mineral compositions and structures in the soil clay fraction can reflect a distinct characteristic when analyzed by powerful techniques. In this way, the aim of this study was to compare the discriminative power of Fe‐oxides concentrated clay samples from the same soil class with and without differences in parent material when analyzed using the Rietveld method and two sources of X‐ray diffraction: conventional and high‐resolution synchrotron radiations. Clay samples were Fe concentrated (kaolinite and gibbsite removal) to clarify mineralogical composition of 12 samples from three simulated crime scenes, developed under claystone and granite. By Rietveld refinement, detailed crystallographic data were obtained to discriminate samples according their provenance. By synchrotron radiation, mineral data demonstrated the power of quantitative (crystallite size and minerals contents) and qualitative (identification of majoritarian and accessory minerals) analysis by Rietveld refinement, which provides well‐resolved data able to discriminate samples from different and same geology. The techniques can be applied in other criminal investigations given their potential of discrimination. [ABSTRACT FROM AUTHOR]

Since the nuclear disaster in Fukushima, Japanese soil scientists have tackled soil contamination problems due to radioactive cesium. For the radiation education based on the research results and outreach activities, we published a comic book and developed a digital application using iOS Xcode for Apple iPhone and tablet devices. This allows students to quickly understand why clay soil absorbed cesium and how to remove contaminated soil using educational mini‐games. Through radiation education seminars and a conference, our application was evaluated and revised by school teachers. [ABSTRACT FROM AUTHOR]

It is generally assumed that the dependence of conventional agriculture on artificial fertilizers and pesticides strongly impacts the environment, while organic agriculture relying more on microbial functioning may mitigate these impacts. However, it is not well known how microbial diversity and community composition change in conventionally managed farmers' fields that are converted to organic management. Here, we sequenced bacterial and fungal communities of 34 organic fields on sand and marine clay soils in a time series (chronosequence) covering 25 years of conversion. Nearby conventional fields were used as references. We found that community composition of bacteria and fungi differed between organic and conventionally managed fields. In the organic fields, fungal diversity increased with time since conversion. However, this effect disappeared when the conventional paired fields were included. There was a relationship between pH and soil organic matter content and the diversity and community composition of bacteria and fungi. In marine clay soils, when time since organic management increased, fungal communities in organic fields became more dissimilar to those in conventional fields. We conclude that conversion to organic management in these Dutch farmers' fields did not increase microbial community diversity. Instead, we observed that in organic fields in marine clay when time since conversion increased soil fungal community composition became progressively dissimilar from that in conventional fields. Our results also showed that the paired sampling approach of organic and conventional fields was essential in order to control for environmental variation that was otherwise unaccounted for. [ABSTRACT FROM AUTHOR]

Turnip (Brassica rapa var. rapa L.) (syn. B. campestris L. ssp. rapifera Sinsk) is an important crop species belonging to the Brassicaceae family. The 185 accessions belonging to this crop were collected from several areas of Toodshak region in Isfahan province, Iran, and their tubers were cultivated under homogeneous conditions in loamy clay soil. The morphological traits of different organs of those accessions were evaluated. Significant variations were detected among the accessions studied based on the traits recorded. Tuber shape showed high variation and included globose, oblong, ovate, obovate, and fusiform. Also, tuber skin color was highly variable, including white, bicolor white–violet, light violet, and dark violet. Tuber weight ranged from 1.56 to 35.70 g, while total soluble solids (TSS) of tuber flesh ranged from 7.00 to 11.80%. Principal component analysis (PCA) showed that 18 components were extracted by explaining 74.88% of total variance. The dendrogram obtained based on all the characters measured clustered the accessions into two major clusters. Sixteen accessions were placed into the first cluster, while the remaining accessions were placed into the second cluster which was divided into six subclusters. High level of morphological variabilities was observed among the accessions, which is applicable and useful for B. rapa var. rapa breeding programs. Based on the commercial and quality traits, 17 accessions could be selected for direct cultivation. Also, the promising accessions identified here can be utilized directly in breeding programs for genetic enhancement of this crop. [ABSTRACT FROM AUTHOR]

This paper presents a combined experimental‐modeling effort to interpret the coupled thermo‐hydro‐mechanical behaviors of the freezing soil, where an unconfined, fully saturated clay is frozen due to a temperature gradient. By leveraging the rich experimental data from the microCT images and the measurements taken during the freezing process, we examine not only how the growth of ice induces volumetric changes of the soil in the fully saturated specimen but also how the presence and propagation of the freezing fringe front may evolve the anisotropy of the effective media of the soil–ice mixture that cannot be otherwise captured phenomenologically in the isotropic saturation‐dependent critical state models for plasticity. The resultant model is not only helpful for providing a qualitative description of how freezing affects the volumetric responses of the clayey material, but also provide a mean to generate more precise predictions for the heaving due to the freezing of the ground. [ABSTRACT FROM AUTHOR]

The structure of soil aggregates plays an important role for the turnover of particulate organic matter (POM) and vice versa. Analytical approaches usually do not disentangle the continuous re‐organization of soil aggregates, caught between disintegration and assemblage. This led to a lack of understanding of the mechanistic relationship between aggregation and organic matter dynamics in soils. In this study, we took advantage of a process‐based mechanistic model that describes the interaction between the dynamic (re‐)arrangement of soil aggregates, based on dynamic image analysis data of wet‐sieved aggregates, to analyze the turnover of POM, and simultaneous soil surface interactions in a spatially and temporally explicit way. Our novel modeling approach enabled us to unravel the temporal development of aggregate sizes, organic carbon (OC) turnover of POM, and surface coverage as affected by soil texture, POM input, and POM decomposition rate comparing a low and high clay soil (18% and 33% clay content). Our results reveal the importance of the dynamic re‐arrangement of soil structure on POM‐related turnover of OC in soils. Firstly, aggregation was largely determined by the POM input fostering aggregates through additional gluing joints outweighing soil texture at lower decomposition rate, whereas at higher decomposition rate, soil texture had a higher influence leading to larger aggregates in the high clay soil. Secondly, the POM storage increased with clay content, showing that surface interactions may delay the turnover of OC into CO2. Thirdly, we observed a structural priming effect in which the increased input of POM induced increased structural re‐arrangement stimulating the mineralization of old POM. This work highlights that the dynamic re‐arrangement of soil aggregates has important implications for OC turnover and is driven by underlying surface interactions where temporary gluing spots stabilize larger aggregates. [ABSTRACT FROM AUTHOR]