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• Sorption behaviour of soil-oil mix was investigated using vis-NIR Spectroscopy. • A spectral index describes sorption of crude oil on soils. • The amount of clay and the clay mineralogy control sorption behaviour. • A model describes 4 stages of sorption behaviour at micro and macro levels. • Results suggest this technique can model sorption capacity of soils more rapidly. Theoretical models to describe and evaluate sorption of hydrocarbons on soil particles are well documented but experimental results in the literature are scarce. This study describes the use of a spectral index to evaluate sorption phenomena in oil-contaminated soils at micro and macro levels. Experiments involved oil-dosing from 0.25 mL to 4 mL and the application of a spectral index to estimate the sorption capacity of different soils based on change in statistically derived Critical Point (CP). Results show that sorption of oil varies with soil type, specifically the proportion of clay in a soil/sediment and the clay species, in the order smectite > illite > kaolinite. In support of theoretical models, this work proposes a model from experimental data that explains observed phenomena of soil-oil interaction with changing soil composition. The location and prominence of the CP is also strongly affected by soil moisture, particularly in coarse-grained soils, potentially providing insight to soil-oil–water interaction. The methods developed using a simple synthetic crude provide potential to explore other contamination scenarios including different soil compositions, types of petroleum products and different environmental controls. [ABSTRACT FROM AUTHOR]

Placic (Bsm) horizons are commonly found in different types of soils worldwide, but are very rare in Ultisols. The formation of Bsm horizon and podzolization are different processes in pedogenesis. This study collected five podzolic Ultisols containing Bsm horizons from the subalpine forests in Taiwan to illustrate the morphological characteristics and genesis of the Bsm horizons in these soils with both clay illuviation and podzolization. The distinctive Bsm horizons were 3 to 10 mm thick and had abrupt and wavy boundaries with overlying albic (E) and underlying argillic (Bt) horizons. All Bsm horizons contained over 35% of clay fraction which significantly increased from E horizon to B horizons in the pedons. The Bsm horizons showed much higher bulk density than adjacent horizons above or below them, elucidating that such iron pans were relatively impermeable to water and plant roots. The maximum contents of pedogenic Fe occurred in the Bsm horizons mainly cemented by poorly crystalline Fe oxides associated with high amounts of organic matter and epiaquic conditions. Pedogenic Al appeared to be accumulated in the Bt horizons where spodic materials were identified according to the oxalate-extractable amount of Fe and Al. The polygenetic processes of these podzolic Ultisols with Bsm horizons were proposed as three stages. Firstly, clay illuviation predominantly occurred to form Bt horizon in the interglacial periods during the mid to late Pleistocene. Then, podzolization gradually became a major process to accumulate spodic materials in the Bt horizon because of the coniferous forest formation under the cool and humid climates close to the late Pleistocene; however, water was perched at the soil surface due to poor drainage and abrupt textural change between E and Bt horizons after the Holocene. Eventually, the reduced iron from E horizon was gradually re-oxidized and precipitated on the top of Bt horizon where exhibited oxidizing condition to form Bsm horizon until today. Because of the occurrence of Bsm horizon in these Ultisols, a new subgroup Placic Epiaquults, was therefore proposed to the keys to Soil Taxonomy. • The pedons confirmed the existence of placic horizons in spodic Ultisols. • Clays and spodic materials were accumulated prior to the formation of Bsm horizon. • These polygenetic processes were corresponding to the paleoclimate changes. • Placic Epiaquults was proposed as a new subgroup in the keys to Soil Taxonomy. [ABSTRACT FROM AUTHOR]

Soil sodification and salinization present a global soil degradation risk to agricultural production since they affect soil hydraulic properties. Soils containing smectite clays have been found to be most sensitive to sodicity although little research exists directly relating sodicity to clay swelling under varying levels of salinity and Exchangeable Sodium Percentage (ESP). The goal of this study is to determine whether soil swelling related measurements can be a proxy to determine soil sensitivity to exchangeable sodium. This study examined the response of three smectitic soils treated with salt solutions having concentrations ranging between 5 and 40 mmol c dm−3 and ESP levels between 0 and 50% to create differing degrees of sodicity. Whole soil Atterberg limits and the coefficient of linear extensibility (COLE) were measured prior to and after treatments. Liquid limit, plasticity index and the coefficient of linear extensibility increased for all three soils after treatment with a salt concentration of 5 mmol c dm−3 at an ESP of 25 and 50% and 10 mmol c dm−3 at an ESP of 50%. Comparing liquid limit of low salinity treatment at 50% ESP to low salinity 0% ESP revealed the presence of swelling smectite clay and the sensitivity of the soils to sodicity and a soil measurement to identify soil sodicity risk. • High soil solution ESP and low soil salinity increases soil liquid limit and shrinkage. • Smectite in smectitic soils swell much less than Wyoming bentonite. • Liquid limit best identified smectite presence and soil sodicity sensitivity [ABSTRACT FROM AUTHOR]

Prairie, or mima, mound topography often exists in once-abundant, native tallgrass prairie ecosystems throughout North America west of the Mississippi River. However, the abundance of undisturbed prairie mounds is decreasing in many areas due to urbanization and agricultural disturbance. The objective of this study was to evaluate the variations in soil physical, chemical, and estimated hydraulic properties among mound positions (mound summit, backslope, toeslope, inter-mound), soil depths (10-cm intervals from 0 to 90 cm), and soil moisture regimes (udic and aquic) in a native tallgrass prairie in the Ozark Highlands region of northwest Arkansas. Soil samples were collected in mid-April 2017. Soil clay concentrations increased with depth (P < 0.01) at each site position in both soil moisture regimes. The clay concentrations in the mound summits roughly doubled from 0 to 90 cm, while the clay concentrations in the backslope, toeslope, and inter-mound increased by three to six times from 0 to 90 cm. Soil organic matter contents decreased (P < 0.01) with depth at all site positions within both soil moisture regimes and were generally at least numerically largest at respective depth intervals at the inter-mound within the udic soil and at the mound summit within the aquic soil. Estimated saturated hydraulic conductivity decreased (P < 0.05) with depth at each site position and was largest in the inter-mound from 0 to 10 cm (63.4 mm h−1) and numerically smallest at the inter-mound from 70 to 80 cm (4.6 mm h−1). Results clearly indicated that prairie restoration and management practices should consider mounded and inter-mound landscape positions separately to best restore and/or preserve the ecological functioning of the unique mound features in the sparsely remaining tallgrass prairies. • Soil organic matter contents were generally greatest at the inter-mound in the udic soil. • Extractable soil sodium content was greater in the aquic soil from 50 to 90 cm. • Soil texture was silt loam from 0 to 90 cm at the mound summit and backslope. • Total nitrogen content was unaffected by mound position and soil moisture regime. • Soil property results reflect the complexity of tallgrass prairie ecosystems. [ABSTRACT FROM AUTHOR]

Production of irrigated rice (Oryza sativa L.) without conventional soil submergence may increase water use efficiency but risk a decline in rice yield. Spatial variability in rice yield and relationships among yield and soil properties were examined across a 3.3-ha experimental site after uniform crop management. The site was initially consolidated from small, previously puddled parcels of land into eight laser-leveled plots across a 2.1-m elevation gradient in the Philippines. Six crops of rice in rotation with three crops of mungbean (Vigna radiata (L.) R. Wilczek) were then grown from January 2012 to March 2015. The four rice crops in the dry season (crops 1, 2, 4, and 6) were irrigated using an overhead sprinkler system to maintain soil water potential greater than −10 kPa without soil submergence. Soil was puddled and flooded with irrigation for only rice crop 5 grown in the wet season. Mean rice yield with full fertilization was 6.1 Mg ha−1 for crop 2 but only 3.6 Mg ha−1 for crop 6. Yield for rice crop 6 ranged from 1.6 to 5.4 Mg ha−1 across 36 locations in the 3.3-ha site. Rice yield for crop 6 was inversely related to soil bulk density (r = −0.72 and −0.80, P < 0.001), log 10 saturated hydraulic conductivity (K sat) (r = −0.71, P < 0.001), and sand content (r = −0.63, P < 0.001). Yield was directly related to water-filled pore space of soil (r = 0.61, P < 0.001). Field locations with large downward water movement and the correspondingly most aerobic soil conditions were most prone to low rice yields and large yield decline. Rice yield was directly related to anaerobic N mineralization (r = 0.72, P < 0.001) and soil ammonium-N (r = 0.54, P < 0.001) at 16 days after transplanting and to indigenous N supply (r = 0.83, P < 0.001), as determined from rice yield without application of fertilizer N. These relationships suggested lower net N mineralization at locations with the most aerobic soil conditions, as determined by water-filled pore space. Rice yield was, however, not limited by insufficient fertilizer N. Anaerobic N mineralization and indigenous N supply were unrelated to optimum fertilizer N rate calculated from yield gain with fertilizer N, which was determined at 36 locations using paired plots with and without added N. The long rainy season and clayey soil at the site limited triple-cropping systems to two rice crops and only one non-rice crop per year. In such environments where crop rotation is not an option to prevent yield decline for rice grown without soil submergence, periodic soil submergence to increase anaerobic soil conditions would be required to sustain rice yield. Our study suggested that soil bulk density and K sat , which can increase for successive rice crops grown without puddling and soil submergence, could serve as indicators of field locations prone to yield decline from factors other than water-deficit stress and requiring a period of soil submergence to sustain large rice yields. • Rice yield without soil submergence ranged from 1.6 to 5.4 Mg ha−1 across 3.3-ha site • Yield was inversely related to soil bulk density and saturated hydraulic conductivity • Rice yield was directly related to soil water-filled pore space and N mineralization • Low yield of N-fertilized aerobic rice was due to factors other than insufficient N • High bulk density and downward water flow may indicate need for soil submergence [ABSTRACT FROM AUTHOR]

Cation ratio of soil structural stability (CROSS) and exchangeable dispersive percentage (EDP) have been recently proposed to replace the traditional sodium absorption ratio (SAR) and exchangeable sodium percentage (ESP) for predicting soil structural stability, in conjunction with the electrolyte concentration. Both CROSS and EDP incorporate the dispersive effects as coefficients transforming K and Mg effects to equivalent Na, and flocculative coefficient transforming Mg effect to equivalent Ca. However, these coefficients are derived from the flocculating power of Na, K, Mg and Ca based on a limited number of soil clays. This study re-examines the flocculating power for a broad range of soil clays by analysing their critical flocculation concentrations (CFCs). Soil clays from 17 contrasting soils were separated and chemically treated into Na, K, Mg and Ca homoionic clays. Within the same cation treatment, there were significant differences among the measured CFC values, which can be related to their different clay mineralogy and co-existing materials in soil clays. The dispersive coefficients of K and Mg, as well as the flocculative coefficient of Mg, were seen to vary substantially in respect to the generalised values used in CROSS and EDP. The absolute errors between the specified CROSS and generalised CROSS as well as the specified EDP and generalised EDP have been calculated for the 95th percentile of possible cation concentrations. In terms of CROSS, the dispersive coefficient a [K] and flocculative coefficient b [Mg] both contribute to the absolute error, with a [K] having a greater influence than b [Mg]. In terms of EDP, the dispersive coefficient a [K] played the dominant role in causing absolute error between the specified EDP and generalised EDP, while the role of dispersive coefficient c [Mg] was not significant. The outcome of this work indicates that the soil-specific coefficients should be used to minimise the possibility of undue soil structural degradation, while the generalised coefficients are only applicable to a small range of outcomes. • CFC values of homoionic clays vary significantly among soils. • CFC of homoionic clays follows Na > K > Mg > Ca for each of the soil. • c [Mg] had negligible impact and can be dropped from EDP equation. [ABSTRACT FROM AUTHOR]

Ferrihydrite has been prevalently used in soil remediation as an effective amendment for in situ immobilization of arsenic (As). However, its poorly crystalline structure is unstable and can pose the risk of re-releasing As into soil. In this study, sequential extraction was coupled with a newly-established method, chelex-metsorb diffusive gradient in thin films (DGT), to study the ferrihydrite transformation/dissolution process and its effect on the mobility of arsenic in soil. Experiments in this work found that high soil moisture (70% SWHC) with a low soil redox potential (Eh) can significantly increase the rate of the ferrihydrite transformation/dissolution process compared to 30% SWHC. Soils with low pH and high available iron (Fe) content may also accelerate ferrihydrite transformation/dissolution, while soils with high clay fraction and high soil total organic matter (STOM) may inhibit the process. The amount of arsenic adsorption can also affect ferrihydrite transformation, even exceeding the effect of soil pH and dissolved Fe. Arsenic release was clearly observed in all three soils across all treatments, and it was also affected by changes in soil redox potential. More arsenic was released at high soil moisture (70% SWHC) roughly 7–15 d after the release of Fe. In addition, a partial arsenic fraction was transformed, along with ferrihydrite, from a combined As (F1 As) amorphous phase to combined As (F2 As) well-crystallized phase. These results suggested that ferrihydrite transformation/dissolution can affect the mobility of arsenic and that this phenomenon is more extreme at higher soil moisture levels. Unlabelled Image • Soil redox condition significantly regulated the ferrihydrite transformation/dissolution process. • Ferrihydrite transformation rate in soils was also controlled by the soil properties and amount of arsenic adsorption. • Ferrihydrite transformation/dissolution may lead to a short time release of the labile As. • Labile As release had a strong correlation with Fe(II) release. • Arsenic fractionation was also transformed with transformation of ferrihydite. [ABSTRACT FROM AUTHOR]

• Agroforestry complexity and soil texture influence ecosystem service provision. • P and Ca cycling through litter and stable soil carbon stocks are synergistic. • Sandy soils are most suited for complex agroforestry. • Agroforestry Complexity Index encompassing diversity, density and management. Agroforestry systems are often promoted as solutions to address land degradation and climate change. However, agroforestry is an umbrella term for a large variety of systems and it is not clear how their degree of complexity influences their provision of soil-based ecosystem services, such as soil organic carbon (SOC) storage and nutrient cycling. Furthermore, a knowledge gap remains whether agroforestry systems perform equally well on all soil types. The objectives of this study were 1) to assess the links between agroforestry complexity, nutrient cycling and SOC fractions, and 2) to assess how soil texture influences these relationships in Brazilian agroforestry systems. We sampled 59 agroforestry plots across 30 sites in Sao Paulo state, Brazil, and 8 monocrop sites (6 pastures and 2 crop monocultures). The 38 sites represented a soil textural gradient, ranging from very sandy to very clayey (clay content range 25 – 620 g kg−1). An Agroforestry Complexity Index (ACI) was defined based on tree species richness, stem density and pruning management. Nutrient (N, P, K, Ca, Mg) and C contents were determined in litter and soil (0–30 cm depth) samples, and mineral-associated organic C (MAOC) and particulate organic C (POC) in soil samples were assessed as well. ACI was positively associated with C, N, P, Ca and Mg stocks in litter, and these litter nutrients were in turn positively associated with the corresponding soil nutrient stocks. Associations between soil nutrients and MAOC were stronger on sandy soils than on clayey soils, particularly for P, Ca and Cation Exchange Capacity (CEC). For POC, robust relationships with nutrients were only found on sandy soils. Structural Equation Models indicated causal relationships between agroforestry complexity, P and Ca cycling, and MAOC and POC stocks in topsoils. Our results indicate that nutrients effectively cycle from in situ mulch into plant-available soil pools and highlight the synergies between nutrient cycling and stable C stocks that can be achieved in complex agroforestry systems. These synergies seem to be particularly strong on sandy soils (<15 % clay). [ABSTRACT FROM AUTHOR]

• Soil texture effect in temperate grassland region of China is examined. • A strong inverse soil texture effect on vegetation is evidenced. • Loam soil can be used as a benchmark to quantify effect of various textured soils. • Precipitation threshold for inverse texture effect increases with soil coarseness. The inverse texture effect of soil on vegetation has been reported in a few arid regions, but no information is available on the vast Chinese temperate grassland. In addition, no consistent criteria and approaches have been used to classify soil texture groups, determine the precipitation threshold (P θ) below which the inverse texture effect occurs, and quantify the effect size (Z), which has limited the generalization of the rules of the soil texture effect in different ecosystems. We analyzed the soil texture effect on vegetation using the remotely sensed vegetation data (MODIS/NDVI) and the Chinese soil profile texture data at 6851 sites in temperate grasslands of China. We found, first, a strong inverse texture effect, i.e., a higher NDVI on coarse- (>50 % sand) than fine-textured soil in low precipitation areas, and P θ was variable with annual precipitation and averaged 260 mm in the region. Second, we proposed a novel method to use the loam soil as a benchmark against which to quantify the effect of various textured soils, and determine P θ as the point on precipitation gradient where the soil texture effect shift from positive to negative or vice versa. As such, P θ decreased with soil coarseness, and increased with precipitation; and the texture effect decreased from positive to negative for sandy soils, whereas it increased from negative to positive for silt or clay soils, on the gradient of precipitation increase. Our results provide new insights into the relations of vegetation pattern and dynamics with precipitation and soil texture, and a method for quantifying and comparing soil texture effect across ecosystem types. [ABSTRACT FROM AUTHOR]

• Soil temperature temporal variations are in-phase with heat fluxes 10-cm deeper. • Moisture depression occurs in the seasonally frozen soil. • Spatiotemporal heterogeneity of moisture is stronger than that of temperature. • Strong thermohydraulic coupling exists in cold season, but not in warm season. • Zero curtain occurs in both dry and wet soils and varies from region to region. Frozen soil properties and thermohydraulic processes are still not fully understood due to lack of in-situ measurements, especially in the high altitudes and high latitudes (HAHL). Based on hourly measurements at 10, 40, 80 and 120 cm depths at 21 sites in the west, south and northeast regions of the Tibetan Plateau (TP) during July 2018 - July 2019, we examined soil particles, spatiotemporal variations of soil thermohydraulic processes and their connections with environmental factors to reveal the heterogenous frozen soil properties on the TP. Sand and silt are the dominant soil particles and clay is less than 10% at the sites. Existing and widely used soil products underestimates (significantly overestimates) sand (clay) content on the TP which raises the uncertainty in the thermohydraulic parameters derived from these products. Diurnal soil moisture and temperature variations are seen only above 40 cm, but seasonal variations occur down to 120 cm due to the soil memory effect. Seasonally frozen soil and permafrost soil show different freezing and melting processes. Dry soil features greater soil temperature temporal variability and deeper maximum frozen depth than wet soil. Zero curtain occurs in both dry and wet soil, and displays high (low) frequency but short (long) duration at 10 (80) cm that vary spatially. Moisture depression exists in seasonally frozen soil and is determined by the initial soil moisture and temperature gradient strength. The strong thermohydraulic coupling existed in cold season collapses in warm season. Soil moisture exhibits higher spatiotemporal variability than soil temperature. At daily time scale, the influences of precipitation, wind speed and relative humidity on soil moisture and temperature vary under different climate conditions. These findings fill the knowledge gaps in the soil thermohydraulic processes in the HAHL, and improve the understanding of frozen soil properties and heat-water coupling processes in soil in the HAHL. The study will benefit the Earth system model development and improve the quality of soil temperature and moisture assimilation and remote sensing products in the HAHL. [ABSTRACT FROM AUTHOR]

• Traditional methods for soil specific surface area (SSA) are costly and laborious. • We propose models to estimate SSA from a single hygroscopic water content (w h) • Separate SSA models are developed for soil samples grouped by clay mineralogy. • Considering soil clay mineralogy in SSA models significantly improved performance. • Models based on w h were superior to models based on texture, carbon or CEC. The soil specific surface area (SSA) is an important variable for soil science and geoenvironmental engineering applications, but traditional measurement methods are difficult and time-consuming. Regression models or pedotransfer functions are often used to estimate SSA from other soil properties (e.g., clay content and cation exchange capacity), but these models do not consider the impact of clay mineralogy. Hygroscopic water content (w h) is intimately linked to these soil properties, which suggests that w h may be a better parameter for SSA estimation. This study (i) proposes regression models that estimate SSA from w h at different relative humidity values (5 to 90%) for kaolinite-rich samples (KA), illite-rich or mixed clay samples (IL/MC), montmorillonite-rich samples (ML), and a combination of all samples (ALL) and (ii) compares the performance of the w h models to other published models that comprise clay, silt and soil organic carbon contents and cation exchange capacity. We found that the sample-specific w h regression models accurately estimated SSA for KA, IL/MC and ML samples. For KA and IL/MC samples, the performance of the KA model (e.g., for adsorption, average RMSE = 10.5 m2/g) and IL/MC model (average RMSE = 21.3 m2/g) were better than the ALL-calibration model (KA: average RMSE = 18.7 m2/g; ML: average RMSE = 22.4 m2/g). For ML samples, similar model performance between the ML-calibration model (average RMSE = 41.4 m2/g) and the ALL-calibration model (average RMSE = 41.1 m2/g) was observed. In addition, the model performance of regression models based on w h was superior to models published in the literature that are based on clay, silt and soil organic carbon contents and cation exchange capacity. Overall, this study confirms that a single measure of w h can provide reliable estimates of the SSA while revealing a significant impact of clay mineralogy on model performance. [ABSTRACT FROM AUTHOR]

Standard measurement methods for soil clay content, including the hydrometer and pipette methods, are laborious and difficult to repeat. This has motivated the application of proxy methods such as estimation of clay content from soil water vapor sorption isotherms. Previous studies have revealed that vapor sorption-based clay estimates are inaccurate for soils dominated by swelling or highly weathered non-swelling clays such as kaolinite. In this study, we evaluate an existing vapor sorption-based clay estimation model for soils dominated by either illite (IL), smectite (SM), or kaolinite (KA) clay minerals, and propose modifications to account for high SM and KA contents. Compared to the pipette method, the clay content obtained from the existing water sorption model at 50% relative humidity (RH) was accurate for the IL samples, but significantly overestimated (RMSE = 23.7%; ME = 19.7%) or underestimated (RMSE = 28.8%; ME = −17.0%) clay content for SM and KA rich soils, respectively. The proposed modification involves correcting the estimated clay content with a "slope factor", S for RH values ranging from 30 to 90% for both adsorption and desorption. For SM samples, S averaged 0.76 and 0.72 for adsorption and desorption, respectively, and for KA samples, S ranged from 2.26 to 1.19 and followed a polynomial relationship with RH. Comparison of the estimated clay content from the modified models showed markedly improved estimation of the measured clay content (for RH of 90%, RMSE = 8.0%; ME = 2.6% for SM samples and RMSE = 9.6%; ME = −5.7% for KA samples). • Model for estimating clay content from water content was evaluated for different soil types. • Model accurately estimated clay content for illite-rich samples. • Clay contents for samples rich in kaolinite and smectites were poorly estimated. • Model was improved by correcting for deviation of estimated clay content from measured data. • Improved model reduced average estimation errors by around a factor of two. [ABSTRACT FROM AUTHOR]

Irrigation water containing appreciable amount of magnesium (Mg) is increasingly used in farming. However, studies on the effect of Mg on soil permeability and structural stability are limited and the results are contradicting. In this study, four soils of different dominant clay mineralogy, specifically kaolinite, illite and montmorillonite, were used to investigate the effect of Mg on saturated hydraulic conductivity (K sat), interaction with organic carbon and soil clay dispersion and to compare to the effect of Ca. The soils were packed in columns and leached with four groups of either Ca-Ca, Ca-Mg, Mg-Mg or Mg-Ca solutions at the successive concentrations of 0.5, 0.25, 0.1, 0.05, 0.025, 0.01, 0.005, 0.001 and 0.0001 M, and finally with deionised water. K sat was measured and leachates were assessed for dissolved organic carbon (DOC) and dispersion as turbidity. The leached soils were tested for aggregate stability, mechanical dispersion and zeta potential. This study showed that Mg had a disaggregation effect on soil structural stability. As compared to Ca, K sat on Mg treated cores were lower over a wide range of concentrations, desorption of DOC and turbidity from Mg clay surface was higher, although the dispersion in leachates was insignificant under both Mg and Ca treatments. The effect of Mg treatment was more pronounced on smectic and illitic soils. The decrease in K sat was related to Mg induced disaggregation, due to intra-crystalline swelling and/or the inter-crystalline swelling in Mg treated soil clays. • Mg had a disaggregation effect on soil structural stability. • Mg reduces K sat as compared to Ca. • DOC from Mg leached samples is greater than that from Ca leached samples. [ABSTRACT FROM AUTHOR]

The acidic weathering process of soils is a worldwide problem. In this process, Al3+ is dissolved from silicates and intercalated into swellable clay minerals by replacing exchangeable cations such as Na+ or Ca2+. Al3+ polymerizes in the interlayer regions of the clay minerals to form fixed oligomers, which significantly reduces the clay minerals swellability and cation exchange, and hence, the soil fertility. The layer silicates with fixed (Al) oligomers in the interlayer are known as hydroxy-interlayered minerals, such as hydroxy-interlayered smectite (HIS), or hydroxy-interlayered vermiculite (HIV). These phases have been recognized for many years, but it is still problematic to adequately characterize the details of their structure and to determine their proportion in soils, based on X-ray diffraction (XRD), which is the most common method for mineral quantification. In the present study, two crystal structure models are used to allow characterization and quantitative determination of HIS in artificial and natural soils, using the Rietveld refinement technique based on XRD. Both models are identical regarding the 2:1 layer and the description of the hydroxy-interlayering, but differ in the effect imposed by environmental conditions. The first model describes the smectite in the ethylene glycol saturated state (≈17 Å), commonly used by clay scientists as a diagnostic intercalate for swellable smectitic or vermiculitic layers in pure smectite or vermiculite or interstratifications. The second model describes the smectite in the air-dried (AD) state including the collapsed state (≈10 Å), one-water layer state (≈12.5 Å), and two-water layer state (≈15 Å). Both models are used to fit XRD patterns obtained from samples with preferred orientation and from XRD random powder specimens, each including structural disorder effects. The models provide plausible refinement results with respect to crystallographic parameters and quantitative proportions. The degree of hydroxy-interlayering gives an estimate of how many exchangeable cations of the smectite were replaced by fixed Al oligomers that inhibit expandability. This value corresponds to calculated values within a range of precision of ≤15% mol/mol. Physical mixtures of HIS with clinochlore, muscovite, quartz, and albite were quantified using the proposed crystal structure model. Results showed that the HIS model delivers reliable quantification results (deviations from actual values ≤3% w/w) which may be applied also for natural soil. • Deeper understanding of HIM as typical soil minerals • Detailed structural characterization of HIMs in soils • Objective method for quantification of HIM • Rietveld refinement applicable to soils [ABSTRACT FROM AUTHOR]

During the acidic weathering of soils, aluminum (Al) is dissolved from primary silicates such as feldspars or chlorites and intercalated in layer silicates. Part of this Al polymerizes in the interlayer of former smectites or vermiculites and the resulting phases are called hydroxy-interlayered minerals. These phases are known for a long time but are still insufficiently understood in terms of chemical composition and crystallographical structure. In the present study a sample set consisting of a continuous series of hydroxy-interlayered smectite samples with different degrees of hydroxy-interlayering ranging from 0 to 96% mol/mol smectite/HIS was prepared from a bentonite sample by adding different amounts of a 0.1 mol/L AlCl 3 solution and different reaction times. The products were investigated by a multi-analytical approach using X-ray diffraction, Infrared spectroscopy, X-ray Fluorescence spectrometry, Fe2+:Fe total determination, Nuclear Magnetic Resonance spectroscopy, Simultaneous Thermal Analysis coupled with mass spectrometry and Cation Exchange Capacity to provide an in-depth characterization. X-ray diffraction indicated that the turbostratic disorder typical for smectite did not change during hydroxy-interlayering. Nuclear Magnetic Resonance spectroscopy proved the exclusive six-fold coordination of interlayer Al and based on chemical calculations the average size and charge of the interlayer structures were characterized. Hydroxy-interlayers evolved in-situ in the smectite interlayers by polymerization. These interlayer "polymers" were small oligomers, the average size of which increased from monomers to pentamers with increasing degree of hydroxy-interlayering while the average net charge of each oligomer decreased. An average structural formula of each interstratified smectite-hydroxy-interlayered smectite was calculated from X-ray Fluorescence data including Fe2+:Fe total ratios. If all exchangeable cations are attributed to smectite layers and all hydroxy-interlayers are attributed to hydroxy-interlayered smectite layers, the degree of hydroxy-interlayering ranged from 0 to 96% mol/mol smectite/HIS. The analysis provides an improved structural model of hydroxy-interlayered smectite suitable for Rietveld refinement which can be used to quantify the amounts of hydroxy-interlayered smectite in natural samples. • Synthesis of a HIS sample set with 0–96% mol/mol hydroxy-interlayering • Hydroxy-interlayers characterized as small oligomers (mono- to pentamers) • Oligomers evolved in-situ in the interlayers, no incorporation as such. • Turbostratic disorder of smectite did not change during hydroxy-interlayering. • Guide to characterize interlayer species in soils [ABSTRACT FROM AUTHOR]

Priming of soil organic carbon (SOC) is a crucial factor in ecosystem carbon balance. Despite its increasing importance in the changing global climate, the extent of influence of temperature and soil properties on the priming effect remains unclear. Here, soil priming was investigated using 13C labeled wheat residues in two cultivated, subtropical (Vertisol) and semi-arid (Luvisol), soils of Australia at four incubation temperatures (13, 23, 33 and 43 °C). The priming effect was computed from respired CO 2 and associated δ13C, which were measured periodically over the 52-day incubation period. Wheat residue addition resulted in greater priming effect in the Luvisol (1.17 to 2.37% of SOC) than the Vertisol (0.02 to 1.56% of SOC). The priming of SOC was the highest at 23 °C in the Luvisol, and at 43 °C in the Vertsiol, which indicates a variable positive priming effect of temperature in different soil types. Wheat residue addition significantly increased the temperature sensitivity (Q 10) of SOC mineralization in the Vertisol at temperature ranges below 33 °C (i.e., 13–23 and 23–33 °C) and had no significant effect in the Luvisol. A negative correlation was observed between temperature and the Q 10 values. Across soils, the Q 10 of residue C was lower than SOC suggesting that soil C is more vulnerable to climatic warming. This work demonstrates that the magnitude of SOC priming by wheat residue and Q 10 of SOC mineralization varied significantly with soil type (Luvsiol > Vertisol) and incubation conditions (temperature and time). Given the current trend towards increasing atmospheric temperatures, future studies should evaluate temperature effects on the priming of different pools of SOC induced by crop residue in different agro-ecosystems. • The wheat residue addition caused greater SOC priming in the sandy clay loam than clayey soil. • Temperature significantly influenced SOC priming but this differed by soil type. • The difference in SOC priming between sandy clay loam and clayey soil was greater at ≤23 °C temperatures. • Wheat residue significantly increased the Q 10 of SOC mineralization but only in clayey soil below 33 °C. [ABSTRACT FROM AUTHOR]

Soil physical and chemical properties are critical indicators for soil health assessment. It is important to understand how these qualities respond to different grazing intensities at different landscape slope positions. This study evaluated how soil physical and chemical properties respond to cattle grazing intensity and slope position on a rough fescue grassland. Cattle have been grazing at four stocking rates, 0, 1.2, 2.4 and 4.8 animal-unit-months (AUM) ha−1 since 1949 to simulate Control (CK), Light (L), Heavy (H), and Very Heavy (VH) grazing intensities. Surface soil penetration resistance was measured using a portable penetrometer and soil samples were taken from the top and bottom slope positions for each grazing paddock (but only from the top position for CK) in September 2016. Soil texture, aggregate stability, pH, available phosphorus (AP), water-soluble ions concentration and soil cation exchange capacity (CEC) were determined. Bulk density, porosity and hydraulic properties were measured using a HYPROP system. The S-index, the slope at the inflection point on the soil moisture retention curve, was calculated. Soil clay and silt contents were lower in VH than L treatments; total porosity, air capacity, and saturated water content followed the same pattern. However, the opposite was true for sand content, penetration resistance, and bulk density, with differences between the two grazing treatments greater at the top than the bottom slope position. Grazing changed the shape of soil moisture retention curve in both slope positions with the curve steeper in L than H and VH treatments. The S-index and saturated hydraulic conductivity were reduced by grazing but their responses to slope position and its interaction with grazing intensity were not significant. Soil pH, AP, and water-soluble Na+, K+, Mg2+, Ca2+ and SO 4 2− concentration increased with the animal stocking rate while Cl− and CEC were not affected. Similarly, greater increases in soil pH with increased animal stocking rates were observed in the top than bottom position, while AP, Na+, K+, and SO 4 2− increased with animal stocking rate only in the bottom position. Our results indicate that soil physical properties may be more sensitive to grazing at the top than bottom of a slope. Thus, slope should be considered when developing rangeland soil health assessment indices and grazing management strategies. • Heavy grazing decreased total porosity, air capacity and saturated moisture content. • Penetration resistance and bulk density were relatively higher under light grazing. • Grazing reduced the S-index and saturated hydraulic conductivity. • Grazing effects on soil physical properties differed with slope position. • Soil pH, AP, and Na+, K+, Mg2+, Ca2+ and SO 4 2− increased with animal stocking rate. [ABSTRACT FROM AUTHOR]

Abstract Precise and accurate measurement of soil water for monitoring crop water uptake, irrigation scheduling and management can be provided through continuous soil water monitoring, which is made possible with the aid of automated capacitance probes such as HydraScout. This study was carried out to develop HydraScout capacitance probe calibration equations for selected soil types and to evaluate the accuracy levels of the calibration equations for continuous measurement of soil water. The selected soil textural classes were sand, loamy fine sand, sandy loam, sandy clay loam, clay loam, sandy clay and clay. The volumetric water contents were plotted against the sensors readings to develop calibration equations. The best fit of the regression function was used on the basis of highest adjusted coefficient of determination (R2). Results indicated that calibration functions developed for the soils were linear (clay, clay loam and sandy soils) and polynomial (loamy fine sand, sandy loam, sandy clay loam, sandy clay soils). Volumetric water content was well predicted with the text-specific equation for clay loam (RMSE of 0.001 m3 m−3 and D-index of 0.99) and sandy loam (RMSE of 0.001 m3 m−3 and D-index of 0.99) soil textural classes. Prediction of volumetric water content for sandy clay produced the highest RMSE (0.009 m3 m−3) and lowest D-index (0.68) for all the soil textural classes. It was recommended that the text-specific laboratory calibration equations developed during this study should be used especially, for sandy loam soil type, in a situation where high numbers of the probes are in use. In the case where few of the probes are in use, each sensor must be calibrated. Highlights • The HydraScout capacitance probes can measure soil water continuously. • Calibrations equations developed were both linear and polynomials. • Each soil textural class has calibration equation peculiar for that specific soil. • Calibration equations were able to predict soil water with high accuracy. • The capacitance probe can be used on most of the soil textural classes in South Africa. [ABSTRACT FROM AUTHOR]

Abstract Various thermochemical conversion technologies can be applied in producing biochar from a wide range of raw materials. We studied the chemical quality of 10 different biochars produced via torrefaction (TOR), slow pyrolysis (SP), or hydrothermal carbonization (HTC), in order to assess their potential in improving clay soil aggregate stability and thus contribute to mitigation of erosion from agricultural soils. X-ray tomography was used to visualize soil aggregates in some selected biochar treatments. Feedstock type had a major influence on the properties of the biochar, but in general biochars derived through SP were alkaline and exhibited higher electrical conductivity and ash content and lower surface activity than acidic HTC and TOR biochars. Alkyl peak areas determined from FTIR spectra were higher in biochars produced by TOR and HTC than in SP biochars, which indicates a higher degree of hydrophobicity in the former. Significantly higher aggregate stability and reduced colloid detachment were achieved with HTC biochars, most likely due to hydrophobicity reducing wetting rate and aggregate slaking. When mixed with initially aggregated soil, the biochar particles settled in inter-aggregate voids. According to image analysis, the internal porosity of soil aggregates was not affected by biochar addition, i.e., biochar did not enter the aggregates during the short incubation period. Addition of hydrophobic HTC biochar decreased the soil water content at field capacity, whereas more inert SP chars tended to increase it. The overall effect of biochar hydrophobicity on soil functions needs to be explored prior to wider use of biochar as a soil amendment. Highlights • We studied the effects of 10 different biochars on clay soil aggregate stability. • Chemical composition of biochars varied greatly depending on the feedstock and process technology. • Only the hydrophobic hydrothermally carbonized biochars improved aggregate stability • Slow pyrolysis biochars increased the soil water content, whereas hydrothermally carbonized chars decreased it. [ABSTRACT FROM AUTHOR]

Abstract Local topography and elevation gradients can exert important influences on soil formation processes such as elemental migration, mineral weathering, and soil organic matter (SOM) accumulation, yet these influences remain insufficiently investigated to date, particularly in surface soils of subtropical monsoonal regions. Here, we report on an investigation of a series of surface soils collected from four different topographic locations across the subalpine Dajiuhu Critical Zone Observatory (CZO), representing hillslope (planar), swale and river channel (convergent), and bulge (divergent) microtopographic sites. Evidence provided by rare-earth element (REE) patterns, immobile element ratios, clay-mineral compositions, and particle-size distributions suggests that these soils have rather uniform parent materials. X-ray diffraction (XRD) analysis revealed that secondary clay minerals in these soils are complex, being dominated by various interstratified clays. Diffuse reflectance infrared Fourier transform (DRIFT) spectroscopy shows similar patterns among the swale, bulge, and river-channel soils that differ from those of the hillslope soils. Most soils at convergent sites with poor drainage contain more smectitic clays (interstratified illite/smectite and chlorite/smectite) and less vermiculitic clays (hydroxyl-interlayered vermiculite and interstratified illite/hydroxyl-interlayered vermiculite), and exhibit weaker chemical weathering and fewer elemental losses than those from non-convergent sites. The diversity of clay types can be ascribed to the complexity and heterogeneity, in particular of pH and hydrology, in these soil environments. Across the range of microtopographic sites investigated here, elemental migration and chemical weathering are generally coupled, with greater elemental losses associated with more intense chemical weathering. Soil organic carbon (SOC) content generally increases at higher elevations, which is attributable to lower temperatures and a consequent reduction of microbial remineralization, and under more reducing soil water conditions. Though influenced by eolian dust, variations in Fe/Mn, Ce anomaly, and C org /P can reflect redox conditions of different soils. SOC retention is also closely associated with soil redox status, with more reducing conditions being more conducive to SOC preservation. Highlights • Surface soils in a subalpine CZO of subtropical monsoonal China were studied. • Local topography strongly influences soil hydrology and soil formation processes. • The diversity of clay types ascribed to the heterogeneity of soil pH and hydrology. • Chemical weathering intensity generally increases with increasing elevation. • SOC storage in soils influenced by elevation gradients and soil redox conditions. [ABSTRACT FROM AUTHOR]

Abstract Proper characterization of saturated hydraulic conductivity, K s , of clay soils in a hillslope or a basin is still a challenge for soil science. In this investigation, the clay soils of the Maganoce (Sicily, Italy) basin were sampled at 19 sampling sites by the BEST procedure of soil hydraulic characterization. More OM implied less compact conditions (decreasing dry soil bulk density; coefficient of determination, R 2 = 0.67), more stability to water of the soil aggregates (increasing water stable aggregates; R 2 = 0.83) and, consequently, higher K s values (R 2 = 0.54). Variability of K s was lower in the steeper zones of the basin than in the flatter ones. A comparison with the K s data collected in the past with the Simplified Falling Head (SFH) technique at the same sampling points revealed a similarity between the two datasets but also a tendency of this last technique to yield some small K s values that were not obtained with BEST. Soil disturbance due to ring insertion that SFH requires and/or K s anisotropy likely contributed to explain this result. In conclusion, organic matter content and topographic attributes can help to plan an effective clay soil sampling strategy. High K s values are expected to be less uncertain than small values. Highlights • Hydraulic conductivity, K s , was measured for 19 clay soils of a Sicilian basin. • The BEST procedure of soil hydraulic characterization has been used. • Relationship between K s and organic matter content was detected. • Variability of K s was lower in the steeper zones than in the flatter ones. • K s data was compared with that collected in the past with the SFH technique. [ABSTRACT FROM AUTHOR]

Abstract Hard-setting soils become hard and compact during drying, and are therefore difficult or impossible to cultivate unless they are re-wetted. This study was done to quantify the hard-setting behavior on nine soils with a wide range of texture (from sandy loam to silty clay). Repacked soil cores were prepared with least disturbance of soil aggregates (05‒4 mm). Water retention curves of the soils were measured in the matric suction range 10–15,000 hPa in different bulk densities (1.20–1.70 Mg m−3). Single-porosity van Genuchten-Mualem and dual-porosity Dexter models were fitted to the water retention data. Dexter's indices of soil physical quality (S) and hard-setting (H Dexter) were calculated using the van Genuchten-Mualem parameters. Soil physical quality indices S 1 and S 2 (slopes of water retention curve at first and second inflection points, related to matrix and structural pore spaces, respectively) and new hard-setting indices (H 1 and H 2 related to matrix and structural pore spaces, respectively) were also calculated from the parameters of dual-porosity model. Tensile strength (Y) of the soil samples prepared at different bulk densities was also measured from near-saturation to oven-dry. Slopes of relationships between Y and water content were used as soil strength-based hard-setting indices. A larger slope means that the soil is more susceptible to hard-setting. The H Dexter , H 1 and H 2 increased with an increment in the bulk density, whereas the S , S 1 and S 2 decreased. Significant positive relationships between hard-setting indices (H Dexter and H 1) and calcium carbonate content were observed. Negative linear relations were derived between S , S 1 and S 2 , and bulk density and positive linear relations were obtained between H Dexter , H 1 and H 2 , and bulk density. Soil hard-setting and physical quality indices were significantly correlated with relative bulk density. Positive relationships were observed between soil strength-based hard-setting indices and relative bulk density, and the correlations between these indices and H 2 and S 1 were significantly positive and negative, respectively. These findings confirmed that the new proposed indices enable prediction of soil hard-setting behavior using only water retention data with no need to measure soil mechanical strength. Highlights • Hard-setting increased (physical quality decreased) with increment in bulk density. • Positive relation between soil hard-setting and calcium carbonate was observed. • Negative relations between hard-setting indices and clay content were obtained. • Structural pores (susceptible to compaction) mainly govern soil physical quality. • Significant correlations between strength-based and calculated hard-setting indices were obtained. [ABSTRACT FROM AUTHOR]

Abstract Soil water repellency affects vast regions of agricultural and native land across the globe. Sandy soils are most likely to develop non-wetting characteristics with susceptibility decreasing with clay content. This study uses molecular dynamics simulations combined with laboratory scale experiments to study the interactions and assembly of saturated C 16 straight chain alcohol and carboxylic acid molecules on a range of soil surfaces. The development of severe water repellency on sand at low loading levels of palmitic acid (0.75 × 10−6 mol g−1) is explained in terms of favourable H-bonding with silica surfaces and the development of 2–3 layers of lateral aligned organic molecules on the mineral surface. The efficacy of kaolinite in lowering soil water repellency is attributed to the higher surface area of this mineral and favourable surface chemistry, which hinders formation of persistent organic multilayers. Highlights • Molecular dynamics simulations identify interactions of fatty acids on sand and clay. • H-bonding interactions between the molecules and surfaces differ for clay and sand. • A parallel arrangement of molecules with the mineral surfaces is kinetically favourable. [ABSTRACT FROM AUTHOR]

Intense mechanization during forest harvesting and timber extraction degrades soil structure and affects pore functioning, but no studies have clearly distinguished the response of composition and functional soil properties to pine harvest in a subtropical environment. This paper describes the effect of mechanized harvesting of Pinus taeda L. on compaction and pore functioning of two subtropical Alfisols intensively used for commercial forest production in southern Brazil. The study was conducted in a 17-year old commercial forest of P. taeda on clay and sandy clay Hapludalf soils. Soil conditions tested were a control, i.e., before harvesting (BH); after tree felling (AF) in the full tree system; after timber dragging with one skidder pass (A1P); after timber dragging with three skidder passes (A3P); and after timber removal from stocking yard (TY). We evaluated composition (bulk density, degree-of-compactness, total porosity, and macroporosity) and functional (saturated hydraulic conductivity, precompression stress, compressibility coefficient, and penetration resistance) soil properties. The results show the upper soil layer is the most vulnerable to compaction, which significantly impairs pore functioning. Nevertheless, machine wheeling may affect subsurface layers (down to at least 0.40 m, as tested herein) depending on soil type, moisture and structure. Three passes of the skidder resulted in greatest degree-of-compactness, high bulk density, low macroporosity (below the critical level), reduced hydraulic conductivity (nearly water impermeable), and increased resistance to penetration (above the critical limit of 2 MPa). Pine harvest residues (9.8–15.6 Mg ha −1 , corresponding to 7.3–8.2 cm height) were insufficient to dissipate stress applied by skidder intense wheeling. We show planning of harvesting activities must consider reducing traffic intensity and/or establishing permanent traffic routes to ensure minimum damage on forest soils, particularly on their functional soil properties. [ABSTRACT FROM AUTHOR]

Multi-scale evidence of rapid, climate-induced soil structural changes occurring at yearly to decadal timescales is mounting. As a result, it has become increasingly important to identify the properties and mechanisms controlling the development and maintenance of soil structure and associated macroporosity. This is especially relevant since macroporosity has disproportionate effects on saturated hydraulic conductivity (K sat) which strongly influences water storage and flux, thus, affecting the water cycle. In this study, we use decision trees and piecewise linear regression to assess the influence of soil and climate properties on effective porosity (EP; a proxy of macroporosity) in both surface and subsurface horizons under varying land-use and management practices. Data from 1,491 pedons (3,679 horizons) spanning five ecoregions representing bioclimate (e.g., potential vegetation) across the conterminous US demonstrate that, at a continental scale, EP in surface (A) and subsurface (B) horizons is strongly dependent on the complexed fraction of the total mass of soil organic carbon (SOC) and clay; a combined fraction that we refer to as complexed organic carbon and clay (COCC). EP showed a slight positive response to COCC in A horizons but increased steeply with increasing COCC in B horizons. This is because the smaller values of COCC in B horizons reflect a larger pool of clay that has a greater potential to accommodate and complex additions of SOC promoting stronger organo-mineral bonds and the concomitant development and maintenance of soil structure in these horizons. In contrast, larger values of COCC in A horizons reflect conditions where all or most of the clay fraction is effectively complexed with SOC resulting in a larger pool of non-complexed soil organic matter with varying contrasting effects on macroporosity that ultimately mute the response of EP to increases in COCC. In surface horizons, indirect factors such as mean annual precipitation and land use were important predictors of EP, whereas COCC was more influential in controlling EP within the subsoil. The EP-COCC relationship also holds within ecoregions but its effect is mitigated by soil and climate interactions suggesting that the effect of climate on this relationship is indirect and complex. Plowed surface horizons and horizons underlying plowed layers showed greater homogenization (due to disturbance effects reducing heterogeneity in the soil) as well as a reduction in the magnitude and rate of change of EP as a function of COCC compared to undisturbed horizons. Our findings suggest that the complexed fraction of clay and SOC is important for controlling macroporosity and K sat at ecoregion scales and that the EP-COCC relationship may be an important framework for understanding and predicting future land use- and climate-induced changes in soil hydraulic properties. • Effective porosity (EP) depends on complexed organic carbon and clay (COCC). • The nature of the EP-COCC relationship changes for A and B horizons and land use. • Large A horizon SOC contents saturate clay sites muting the effect of COCC on EP. • B horizons contain more clay which is able to complex greater amounts of SOC. • EP and soil hydraulic properties are more impacted by SOC content in the subsurface. [ABSTRACT FROM AUTHOR]

• Nematode abundance increased with aggregate size. • Soil type shifted nematode community composition by aggregate size. • Clay soils fostered more k-strategist nematodes compared to silt-loam soils. • Tillage had no impact on nematode distribution by aggregate size. • Predator-prey dynamics drive soil C accumulation in larger aggregates. Soil aggregates are critical for soil carbon (C) sequestration and serve as a habitat for microorganisms, including free-living nematodes. Yet, the interactions between nematode community composition and soil C cycling across aggregate fractions is rarely assessed. The objectives of this study were to 1) determine how soil type alters nematode community dispersal across aggregate fractions, 2) understand how soil type may alter the relationship between nematode communities and labile C pools, and 3) assess the impact that tillage intensity has on nematode community assemblage across aggregate fractions. Soil cores were taken at two identical long-term trials located in Ohio (silt loam vs. clay). Each trial compared two different tillage intensities (chisel till vs. no-till). Soils were fractionated into three aggregate fractions (>2000 μm, 2000–250 μm, and <250 μm). For each fraction, nematode communities were identified to feeding group and permanganate oxidizable carbon (POXC) was measured. Results indicated that silt loam soils had greater bacterivore nematodes in the >250 μm aggregate fraction (p < 0.05) and relatively lower predator-omnivore nematode proportions when compared to clay soils. Tillage did not have a significant effect on nematode feeding groups. Correlation analyses revealed that predator-omnivore nematodes and POXC were positively correlated in clay soils, but only in the largest aggregate fraction (p < 0.05). Bacterivore nematodes were positively correlated with POXC in clay soils but negatively correlated in silt loam soils (p < 0.05). These findings reveal that predator-prey dynamics likely drive soil C accumulation in larger sized aggregates. Moreover, shifts in nematode community composition by soil type demonstrates how inherent properties influence soil food web structure and ultimately, soil C cycling. [ABSTRACT FROM AUTHOR]

• Weathering paths and soil depth serve as a first order control of soil organic carbon. • Soil deeper than 100 cm, can store significant portions of the total SOC stock. • SOC stock and poorly crystalline mineral concentrations peak in soil <30 cm at 30 kyr. Characterizing the distribution and dynamics of organic carbon in soil is critical for quantifying changes in the global carbon cycle. In particular, weathering controls on near-surface and deep (>1 m) soil organic carbon (SOC) dynamics have been proposed but limited data prevents us from predicting SOC over topographically complex landscapes and quantifying how changes in climate and perturbations, such as wildfire or land management, influence SOC stocks. To advance our understanding of how weathering alters soil geochemistry and influences SOC storage, we synthesize previous data with a new analysis of the Siuslaw River soil chronosequence from terraces in the Oregon Coast Range, a region that harbors the richest SOC inventories in the continental US. We analyze how the relationships between soil geochemistry, physical properties, and SOC storage vary with weathering status and pathways across soils that span 0.041 to 990 kyr and vary in depth from 1 m to >10 m. To distinguish the key properties and processes influencing SOC storage at different depths, we break our analysis into three depth intervals: 0–30, 30–100, and >100 cm. Our results suggest that the processes that control SOC stocks vary systematically with time and depth owing to weathering impacts on soil properties and pedogenic development. At 30 kyr we observe a peak in SOC stock in the top 100 cm coincident with a peak in oxalate extractable Al and Fe concentrations, representing secondary poorly crystalline minerals, which is consistent with previous studies. We also observe a decline in shallow SOC stock for >30 kyr soils as poorly crystalline minerals are replaced by more stable crystalline forms and soils become clay dominated. At 120 kyr, SOC below 100 cm starts to contribute significantly to the total SOC profile inventory and by 990 kyr, this fraction composes >40% of the total SOC stock. Taken together, our results indicate that total SOC stock increases with soil age as the increased intensity of bedrock weathering deepens the critical zone, creating accommodation space for deep SOC storage. These findings reveal the intimate link between poorly crystalline minerals and SOC and suggest that systematic analysis of soil development in the critical zone provides a first-order constraint on SOC stocks. [ABSTRACT FROM AUTHOR]

• Manure had little effect on water vapour sorption isotherms (WSIs) in clayey soil. • Improvement in soil WSIs by manure varied with crop type in silty and sandy soils. • Permanent grass had the most positive effect on soil WSIs. • Improvement in soil WSIs by crop rotation varied with soil texture. • Multiple linear regression models based on soil properties well estimated WSIs. Increasing studies indicate that long-term experiments (LTEs) involving manure application and optimal cropping systems can significantly improve soil physicochemical properties, which may also affect the soil water retention curve (WRC) in the wet region (pF < 4.2). However, few studies have explored the effect of long-term manure application and cropping systems on soil WRC in the dry region (water vapour sorption isotherms, WSIs) (pF > 4.2) as well as the associated soil physicochemical properties. To overcome this knowledge gap, we investigated the effect of long-term manure application (24 to 177 years) and different cropping systems (71 to 82 years) on soil organic carbon (SOC) content, WSIs, hysteresis, and specific surface area (SSA). Soil samples were collected from five long-term manure experiments in Sweden, the United Kingdom, Spain, Germany, and Denmark, and two long-term cropping systems experiments in the United Kingdom. The five manure LTEs comprised three soil textures (silty clay, silt loam, and sandy loam) with one to four crops grown in the fields, including wheat, barley, maize, and grass/clover. The cropping system LTEs comprised silt loam and sandy loam including bare fallow (BF), arable rotation, ley–arable rotation, and permanent grass. Results showed that long-term manure application increased SOC content in each site, but it had little effect on the soil WSIs, hysteresis, and SSA in silty clay soils. The changes of soil WSIs, hysteresis, and SSA in silt loam and sandy loam arising from manure application largely depend on the crops grown in the field. For the long-term cropping systems experiments, permanent grass had the most significant effect in increasing SOC content, soil WSIs in silt loam and sandy loam, and hysteresis and SSA in silt loam compared to other treatments. Compared to BF, arable rotation and ley-arable rotation had no effect on SOC and soil WSIs in silt loam, and on hysteresis and SSA in silt loam and sandy loam. Multiple linear regression models including SOC, clay, and silt contents sufficiently explained the variabilities observed in the soil WSIs, hysteresis, and SSA for both manure and cropping systems LTEs. [ABSTRACT FROM AUTHOR]

• We examine how sampling methods affect detecting inorganic N in 21 soils. • In situ microdialysis sampled proportionately less ammonium than soil extractions. • Ammonium was highest in salt extracts and correlated with soil properties. • Nitrate was correlated across methods implying minimal impact by disturbance. • Measurement of inorganic N is biased by methods-related soil disturbance. Measuring soil nitrogen (N) provides important information for ecosystem productivity and improving N use efficiency in agricultural systems. Conventional means of sampling N using soil extractions disturb soil structure and function, and likely distort accurate quantification. In situ microdialysis is a novel sampling method that generates differing N profiles compared to soil extractions. Here we test the hypothesis that differences observed between sampling methods are due to the minimal disturbance and sampling of a mobile N fraction when using microdialysis, with discernible patterns expected across soils with distinct clay and organic matter contents. In a short-term laboratory microcosm experiment with 21 sugarcane cropping soils, we compared salt (potassium chloride; KCl) or aqueous (H 2 O) extractants and microdialysis. KCl-extractable ammonium (NH 4 +) was highly correlated with the content of clay, total N and carbon, indicative of bound N being solubilised. In contrast, NH 4 + contributed significantly less to microdialysis fluxes and was not correlated with the measured soil properties, which we attribute to minimal disturbance of bound N·H 2 O extracts sampled proportionally more NH 4 + than microdialysis but were significantly correlated with fluxes. This suggests that while microdialysis and H 2 O extraction sample from a dissolved N pool, H 2 O extracts sample from an additional pool of loosely-bound NH 4 +. Nitrate (NO 3 −) measures were correlated between methods, but shared no relationship with the measured soil properties, indicating that NO 3 − sampling is less affected by the disturbance introduced by extractions. We conclude that sampling inorganic N is biased by the degree to which soil sampling methods disturb adsorbed N sources with implications for interpreting soil N measurements. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil sampling methods were assessed using 720 samples at two locations. • Calculated composite sampling decreased significant effects especially in sandy soils. • Sampling in-row resulted in greater crop effect on research results. • Soil enzyme activities required more samples compared to other soil properties. • A Monte Carlo simulation can be used to estimate needed sample size. A wide variety of soil sampling methods have been adopted, yet limited research has addressed how sampling methods can impact research results particularly for spatially variable soil properties. To address these concerns, we intensively sampled two existing soil health trials in Texas for analysis of soil extracellular enzymatic activities (EEAs), permanganate oxidizable C (POXC), soil organic C (SOC), and pH. The data generated was used to quantify the effect of composite sampling, sampling position (in-row vs between-row), and number of samples on statistical results. We compared a Monte Carlo simulation approach with a traditional power analysis to quantify the impact of the number of samples on our results. Calculated composite sampling resulted in lower statistically significant results compared to discrete sampling, demonstrating lower sensitivity of composite sampling. Sampling in-row resulted in greater values specifically for EEAs, pH, POXC, and SOC. Simulation generated estimated number of samples were mainly driven by the effect size and spatial variation. EEAs were highly variable, resulting in a higher estimated number of samples as compared to other soil properties such as POXC and SOC. In our study with two sites, soil with greater clay content resulted in overall lower estimated number of samples compared to a relatively sandy soil, demonstrating a greater sampling requirement for sandy soil. The simulation approach had a weak correlation with traditional power analysis. The simulation predicted lower estimated number of samples when compared to power analysis, which can help save cost in the long run. Overall, factors like composite sampling, sampling in-row vs between-row, and number of samples taken did impact research results. The impact of these sampling strategies on soil parameters of interest needs to be investigated to achieve the most accurate research results in soil science. [ABSTRACT FROM AUTHOR]

• Saltation bombardment is a main pattern of dust emission for compacted soils. • Wind tunnel was used to simulate the abrasion of compacted soils by blown sand. • Dust emission efficiency was positively correlated with the amount of abrader. • Clay and silt contents of soils had different influences on dust emission efficiency. • An integrated model of dust emission efficiency for compacted soils was established. Abrasion by blown sand is a main wind erosion process for compacted soils, such as dry lake basins and the undisturbed grassland that are widely distributed in arid land. Dust emission efficiency (δ) is defined as the ratio of the dust flux to the sediment transport rate from a soil surface. Previous studies mostly focused on the influence of wind velocity or soil properties on δ and rarely considered the amount of abrader in blown sand; furthermore, most of their experiments used loose soils involving three physical mechanisms of dust emission. In this study, we explored the mechanism of dust emission from compacted soils caused by saltation bombardment of the abrader making use of wind tunnel experiments and using the mass flux of the abrader (q) to represent the abrasion intensity of blown sand. The results showed that dust flux (F) generated from the compacted soil by abrasion and bombardment was linear with q , and δ was always positively correlated with q and with the silt and clay content in soils. Taking into account both the amount of abrader and the texture of the soil being abraded, we proposed and validated a model of dust emission efficiency for compacted soil. [ABSTRACT FROM AUTHOR]

One of the first soil forming processes in marine and fluviatile clay soils is ripening, the irreversible change of physical and chemical soil properties, especially consistency, under influence of air. We used Bayesian binomial logistic regression (BBLR) to update the map showing unripened subsoils for a reclamation area in the west of The Netherlands. Similar to conventional binomial logistic regression (BLR), in BBLR the binary target variable (the subsoil is ripened or unripened) is modelled by a Bernoulli distribution. The logit transform of the `probability of success' parameter of the Bernoulli distribution was modelled as a linear combination of the covariates soil type, freeboard (the desired water level in the ditches, compared to surface level) and mean lowest groundwater table. To capture all available information, Bayesian statistics combines legacy data summarized in a ‘prior’ probability distribution for the regression coefficients with actual observations. Our research focused on quantifying the influence of priors with different information levels, in combination with different sample sizes, on the resulting parameters and maps. We combined subsamples of different size (ranging from 5% to 50% of the original dataset of 676 observations) with priors representing different levels of trust in legacy data and investigated the effect of sample size and prior distribution on map accuracy. The resulting posterior parameter distributions, calculated by Markov chain Monte Carlo simulation, vary in centrality as well as in dispersion, especially for the smaller datasets. More informative priors decreased dispersion and pushed posterior central values towards prior central values. Interestingly, the resulting probability maps were almost similar. However, the associated uncertainty maps were different: a more informative prior decreased prediction uncertainty. When using the ‘overall accuracy’ validation metric, we found an optimal value for the prior information level, indicating that the standard deviation of the legacy data regression parameters should be multiplied by 10. This effect is only detectable for smaller datasets. The Area Under Curve validation statistic did not provide a meaningful optimal multiplier for the standard deviation. Bayesian binomial logistic regression proved to be a flexible mapping tool but the accuracy gain compared to conventional logistic regression was marginal and may not outweigh the extra modelling and computing effort. [ABSTRACT FROM AUTHOR]

We present a contextual spatial modelling (CSM) framework, as a methodology for multiscale, hierarchical mapping and analysis. The aim is to propose and evaluate a practical method that can account for the complex interactions of environmental covariates across multiple scales and their influence on soil formation. Here we derived common terrain attributes from multiscale versions of a DEM based on up-sampled octaves of the Gaussian pyramid. Because the CSM approach is based on a relatively small set of scales and terrain attributes it is efficient, and depending on the regression algorithm and the covariates used in the modelling, the results can be interpreted in terms of soil formation. Cross-validation coefficient of determination modelling (R 2 ), for predictions of clay and silt increased from 0.38 and 0.16 when using the covariates derived at the original DEM resolution to 0.68 and 0.63, respectively, when using CSM. These results are similar to those achieved with the hyperscale covariates of ConMap and ConStat. As with these hyperscale covariates, the multiscale covariates derived from the Gaussian scale space in CSM capture the observed spatial dependencies and interactions of the landscape and soil. However, some advantages of CSM approach compared to ConMap and ConStat are i) a reduced set of scales that still manage to represent the entire extent of the range of scales, ii) a reduced set of attributes at each scale, iii) more efficient computation, and iv) better interpretability of the important covariates used in the modelling and thus of the factors that affect soil formation. [ABSTRACT FROM AUTHOR]

To increase the analytical precision in identifying structural forms of heavy metals, it is necessary to refine the methodology for analysis of mineral crystals. The aim of this study was to characterize clay crystals in soils, and relate their mineralogy to the structural occurrence of Pb using scanning transmission electron microscopy (STEM) together with energy dispersive X-ray (EDX) spectrometry. We sampled soils from two areas naturally rich in heavy metals, with known occurrences of mineral deposits (PbS) in carbonate and phyllite/mica schist rocks. There was an association of P with Pb, and the main mineral phase containing Pb in the soil clay fractions was plumbogummite. No associations between Pb and Fe oxides were observed. Secondary phyllosilicate minerals, such as kaolinite and smectite, did not contain structural Pb. There was isomorphous substitution of Ti by Pb in an anatase crystal, despite the differences in ionic radii. The chemical analysis of individual crystals by STEM-EDX was hampered by the high occurrence of microaggregates of clay minerals. [ABSTRACT FROM AUTHOR]

Interactions of clay minerals with organic materials and the consequences of these interactions on dynamics of organic carbon (OC) have been reviewed in detail. However, the effects of exchangeable cations and clay types on the turnover rate of OC have not been given much attention. Appropriate amounts of homoionic Na-, Ca- and Al-clays from Georgia kaolinite, Illinois illite and Wyoming bentonite were mixed with pure sand to prepare artificial soils with different clay contents, exchange cations and clay types. Alfalfa plant residues were incorporated into the artificial soils and the soils were inoculated with microbes from a natural soil and incubated for 184 days to study the effects of clay contents, exchangeable cations and clay types on the mineralization of OC and plant residue derived microbial biomass. Mineralization of plant residue carbon was significantly ( ⁎⁎ p < 0.01) more rapid in pure sand than in soils containing 5 and 10% clay, indicating that clay contents influence the capacity of soils to protect and store OC. The amounts of biomass carbon were lowest in pure sand and highest in soils with 10% clay. There was a significant influence ( ⁎⁎ p < 0.01) of exchangeable cations on microbial biomass and hence the mineralization of OC over a period of 184 days. At 5 and 10% clay contents, the amounts of microbial biomass carbon and the mineralization of plant residue carbon were highest in Ca-soils and lowest in Al-soils. Statistical analysis of data showed a significant effect ( ⁎⁎ p < 0.01) of clay type on mineralization of plant residue carbon and microbial biomass. However, the effects of clay types on the mineralization of OC were much less than those of clay contents and exchangeable cations. The mineralization of plant residue carbon was highest in soils with Georgia kaolinite clay and lowest in soils with Wyoming bentonite clay. The amounts of biomass carbon were slightly lower in soils with Wyoming bentonite clay than soils with Georgia kaolinite and Illinois illite clay minerals. The results of this study indicate that OC and microbial biomass are stabilized in soils through the interaction with clay minerals and a small amount of clay (5%) slows OC decomposition significantly and reduces carbon dioxide emission from soils. Exchangeable cations exert their influence on microbial biomass and hence carbon dynamics by controlling the size and activity of the microbial population through modifying the physicochemical characteristics of microbial habitats. [ABSTRACT FROM AUTHOR]

• Sodicity was investigated in a semiarid Calcisol of the Great Konya Basin. • pH gradually increased while the EC decreased with irrigation water treatment. • Water quality strongly influenced ion concentrations in calcareous soils. • Short-term leaching with poor-quality waters restricts permeability. • Poor quality irrigation treatments increase the risk of secondary salinization. The often-indispensable use of poor-quality irrigation water in drylands instigates diverse physicochemical dynamics leading to soil salinization and sodicity which are recognized as major contributors to land degradation. This study aimed to examine the effects of water quality and irrigation mode on solute transport conditions in terms of ion exchange of colloidal particles. Laboratory studies with undisturbed soil columns were carried out with two water treatments - tap and sodic waters - as well as two water flow velocities: fast leaching which corresponds to Darcy velocity equal to the saturated hydraulic conductivity and slow leaching equal to half the fast-leaching case. Results indicated that the flow velocities did not significantly influence pH, EC and ion concentrations due to the high calcium carbonate and clay contents of the soil which make the soil less permeable. However, flow velocity rapidly decreased in the fast leaching compared to that in slow leaching as the sodic water was applied. This reveals the destructive effect of Na+ in the soil. The EC rapidly dropped at the beginning of leaching for both water qualities opposite to pH, then became steady. All sodic applications caused an increase in Na+ till the end of treatments. This also resulted in variations in measured soluble anions. In general, sharp decreases in highly soluble anions were observed in all treatments, leading to an increase in HCO 3 –, especially for sodic treatments. Overall, sodicity caused significant changes in flow dynamics and ion concentrations and created favorable conditions for secondary salinization in this low permeable soil system. [ABSTRACT FROM AUTHOR]

• Fe accumulates in decomposing litter within skid trail ruts. • Fine root biomass higher in uppermost 5 cm of skid trail ruts than forest controls. • Higher base saturation and pH in skid trails when compared to control. • Elevated levels of exchangeable Mn found throughout skid trails. • Soil compaction persists in skid trails 28 years after logging in a clay Ferralsol. The use of heavy machinery in logging operations leads to soil compaction, especially in highly used skid trails. In Amazonia, recovery of topsoil physical properties has been reported in skid trails. So, the present study sought to determine if this was a full recovery by investigating additional attributes, such as soil chemical properties and fine root biomass (FRB). In addition, forest floor litter was investigated to present a more complete view of soil recovery dynamics. To accomplish this, litter above sampling locations was collected, as well as soil samples below this in two depths. These depths represented the recovered topsoil layer (0–5 cm) and the still compacted soil layer (5–10 cm) below. Three areas were compared: control, middle of the skid trails, and skid trail ruts. Dry mass, C%, N% were determined for litter and FRB. Foliar nutrients (P, K, Ca, Mg, Fe, Zn, Mn) were also determined. Soil chemical properties such as pH, cation exchange capacity, base saturation, aluminum saturation, soil organic C and nutrients (total N, available P, exchangeable Ca, Mg, K, Na, Fe, Zn, Mn) were also assessed. The primary objective was to determine if there was a full recovery of properties evaluated in the topsoil, but also to determine if the compacted soil below acted as an effective hardpan that potentially exerted influence on the recovered topsoil. In the skid trail ruts, results revealed no significant differences with the controls in the recovered topsoil for FRB and all but one soil nutrient, Mn which was elevated. Additionally, the base saturation and volumetric water content of the ruts topsoil was significantly higher than the controls indicating a potential hardpan condition below. So, even though a topsoil may be considered fully recovered, the compacted soil below may still exert influence in the form of increased soil moisture and nutrient accumulation. Therefore, the key finding of this research is that for the first time a recovered topsoil in skid trails was demonstrated to be affected and influenced by the compacted soil below. This influence in the very clayey soils of Amazonia was observed after nearly-three decades. [ABSTRACT FROM AUTHOR]

[Display omitted] • Soil physical indicators were integrated into a soil physical quality index. • Uncontrolled traffic caused a reduction of 12% in the soil physical quality index. • Uncontrolled traffic increased bulk density, soil penetration resistance, and VESS. • Controlled traffic may be a strategy to reduce soil physical restrictions. The disorderly machinery traffic has been one of the main causes of soil physical degradation in sugarcane fields. In this sense, the adoption of strategies for machinery traffic control has been a viable alternative to reduce the risk of soil compaction and minimize physical restrictions to plant growth. However, the impact of traffic control on soil physical properties is still unknown in sugarcane fields. In this study, we investigated the impacts of machinery traffic control on soil physical properties and functions under contrasting soil textures (clayey and sandy clay), assessed at row and inter-row sugarcane planting positions. Bulk density, soil porosity, soil penetration resistance, the weighted average diameter of aggregates and visual assessment of soil structure (VESS) were measured. In addition, the soil physical quality index (SPQI) was assessed for the following soil functions: support root growth, ability to resist erosion and physical degradation, water supply for plants, edaphic fauna, and its relationship with the exchange of gases between soil and atmosphere. The results revealed that uncontrolled traffic farming increased bulk density, soil penetration resistance, and VESS scores as well as reduced total porosity mainly in the 0–10 cm soil layer. Controlled traffic farming supported soil functions in relation to uncontrolled traffic. Uncontrolled traffic caused a reduction by 12% on the SPQI at row position in both clayey and sandy clay soils, whereas for inter-row position, no difference was observed between the treatments. Controlled traffic in sugarcane fields was able to reduce soil physical degradation induced by agricultural machinery traffic, whose mitigation of compaction occurs mainly at row-position. These results suggest that controlled traffic farming may be a strategy to reduce soil physical restrictions for root growth in sugarcane fields. [ABSTRACT FROM AUTHOR]

• A regular evaluation of satellite soil moisture (SM) products was conducted. • Their accuracies in detecting SM anomalies and seasonality were identified. • l -band products can effectively capture SM seasonality over forest covers. • Products had difficulties in detecting SM variations over organic-rich soils. • AMSR2 showed higher accuracy to detect SM seasonality over arid areas. Satellite-based soil moisture (SM) products exhibit distinct error patterns at various timescales. Knowledge of their accuracy characteristics for capturing different SM signals is significant for many real-world applications in soil sciences. This study conducted a comprehensive evaluation of the following eight satellite-based SM products: the Soil Moisture and Ocean Salinity-Institut National de la Recherche Agronomique and Centre d'Etudes Spatiales de la BIOsphere version 2 (SMOS-IC-V2), the Level 3 (L3) Soil Moisture Active Passive V7 (SMAP-V7), the combined European Space Agency Climate Change Initiative V06.1 (ESA CCI-V06.1), the L3 SMOS V3, the L3 Advanced Microwave Scanning Radiometer (AMSR2) V3 from the Japan Aerospace Exploration Agency (JAXA), the L3 Land Parameter Retrieval Model (LPRM) C1- and X- band AMSR2 V001, and the Chinese FengYun-3B V1. By using >1,500 sites from the International Soil Moisture Network and triple collocation analysis, this study aimed to identify not only the relative strengths of the products for detecting original SM signals, short-term SM anomalies, and long-term SM seasonality, but also the impacts of land cover, soil organic carbon (SOC), and soil texture on their retrieval accuracy. In terms of capturing the temporal dynamics of SM anomalies, SMAP-V7 outperformed SMOS-IC-V2 and ESA CCI-V06.1. In arid and semi-arid areas, LPRM C1-band AMSR2 V001 outperformed SMOS-ICV2 and SMAP-V7, in terms of detecting SM seasonality. SMAP-V7, SMOS-ICV2, and ESA CCI-V06.1 effectively captured SM seasonality over most forest zones and effectively detected short-term SM anomalies over croplands and grasslands. The l -band products showed the highest accuracy in terms of capturing the temporal dynamics of all the SM signals when the clay fraction was in the range of 20 %–25 %. Most products had difficulties in detecting SM variations over bare deserts, sandy and clay soils, and soils rich in organic matter (SOC content > 8.72 %). [ABSTRACT FROM AUTHOR]

Among other driving forces, climate change may lead to significant modifications of soil properties through variations of the intensity and dynamics of a number of soil processes including the especially sensitive and ubiquitous processes of bioturbation and illuviation. Progress toward the quantification of these processes needs to be made as a first step in order to ascertain or predict the impact of climate change. In this study, we develop, and validate through an exhaustive accuracy assessment, a digital 2D image analysis method adapted to large soil thin sections, leading to the quantification, characterization and classification of pores and illuvial clay features considered diagnostic of bioturbation and illuviation, respectively. The need to consider large soil thin sections (14 x 6 cm) stems from observations that areas from 684 mm2 to more than 5 000 mm2 are needed to obtain representative measurements of fragments of illuvial clay (papules) and porosity associated with earthworms respectively. Whereas the soil heterogeneity in thin sections of such a large size prohibits the use of classical global and colorimetric image analysis procedures, we succeeded to quantify and characterize the porosity and illuvial clay features with accuracies as high as 96% for porosity and 92% for illuvial clay by carefully considering different levels of soil organization from aggregates to individual illuvial clay features. Quantification of the size and the shape of pores and of illuvial clay features makes it possible to develop morphological classifications distinguishing pores of biological origin (earthworms or roots) from others, or clay coatings and infillings from papules. All these data are particularly useful to better characterize underlying soil processes. Results suggest that the proposed methodology provides an accurate and representative quantification of biological porosity and illuvial clay features in large thin sections. We argue that the use of this approach could be extended to study and quantify bioturbation and illuviation intensities at the profile scale. [ABSTRACT FROM AUTHOR]

Dispersive clays are prone to erosion and could cause significant problems in geotechnical and geo-environmental projects. In this research, a new additive - the ZELIAC – was investigated for treating a Malaysian dispersive clay soil where an appreciable decrease in dispersivity was achieved due to treatment with 8% ZELIAC. The curing time was found to be significant that after 28 days, the initially dispersive samples became non-dispersive. Furthermore, due to the treatment, the samples had increased unconfined compressive strength (UCS), permeability, and optimum moisture content; and decreased fines content, plasticity index, maximum dry density, and compressibility index. The UCS increased nearly 7.3 times for sample treated with 8% ZELIAC and cured for 90 days. The X-ray fluorescence (XRF) results showed a cementitious structure with calcium content 10.8 times more in the treated sample than in the untreated one, reflecting the constructive cation exchange reaction taking place during the curing process. The sodium ion was noticeably replaced by calcium ion which resulted in a decreased thickness of the diffused double layer and the subsequent reduction in the dispersivity of the sample. These results were also reflected by the lower peak intensity as measured by the X-ray diffraction test (XRD) for the treated sample, as compared to the higher peak intensity for the un-treated sample. Finally, the SEM images indicate that the flocculated structures of the treated dispersive clay were surrounded by the ZELIAC particles. Thus, the ZELIAC was proven to be effective in improving the studied Malaysian dispersive clay. [ABSTRACT FROM AUTHOR]

• Contribution of organic carbon (OC) to total specific surface area (SA) is unclear. • EGME SA correlated with water sorption SA, except for OC-rich soils. • OC contribution to SA depended on clay mineralogy and OC content. • OC contribution ranged from 7.5 to 13.9 m2/g per %C depending on clay mineralogy. • For samples rich in montmorillonite, OC negatively contributed to total SA. Soil specific surface area (SA) reflects the quantity and quality of the soil mineral and organic fractions. For soil samples that have similar clay mineral types, clay content and or organic carbon (OC) contents are good predictors of SA. However, the magnitude of the OC contribution to SA for different soil types is unclear, particularly since SA varies depending on which method or probe molecule is used to measure it. Consequently, we set out to (i) quantify the contribution of soil OC to total SA for soils with varying clay mineralogy, and (ii) assess the effect of probe molecule (EGME or H 2 O) and water sorption direction on the contribution of OC to the total SA. We utilized 330 soil samples (clay = 1 to 89 %; silt = 2 to 78 %; OC = 0.03 to 34.9 %) that were grouped according to clay mineralogy and OC content. The total SA was measured using EGME adsorption (SA E) and water adsorption and desorption (SA H2O). The contribution of OC to SA was examined using regression and partial correlation analyses that combined clay, silt, and OC as explanatory variables. Results showed that SA E values were strongly correlated to SA H2O , except for OC-rich soils where SA E was significantly lower than SA H2O. Apart from montmorillonite-rich samples, OC contribution to SA E was smaller than for SA H2O. Organic carbon had a positive contribution to desorption SA H2O for all sample groups, except for montmorillonite-rich samples; OC contribution was 7.5, 10.7, and 13.9 m2/g per %C for illite-rich, kaolinite-rich and OC-rich samples, respectively. There was no significant effect of water sorption direction on the OC contribution to SA H2O. Partial correlation analyses that accounted for clay and silt contents confirmed a negative contribution of OC to SA E or SA H2O for soil samples dominated by montmorillonite clay minerals. We can conclude that for the soil types investigated here (except montmorillonitic soils), OC has a positive contribution to total SA, and the magnitude of the contribution depends on the clay type. [ABSTRACT FROM AUTHOR]

• Soil acidification rates and dissolved organic C fluxes were quantified on permafrost. • Fluxes of dissolved organic C were higher in clayey soils with shallow active layer. • Nitrate-N fluxes were higher at lower slope position even in arctic soils. • Cation uptake by lichen and moss as well as higher plants leads to soil acidification. • Climate warming has potential to increase active layer thickness and soil acidification. Climate warming is predicted to change the fluxes of dissolved organic matter and nitrate by increasing active layer thickness, plant productivity, and organic matter decomposition. These changes are hypothesized to increase mineral weathering and soil acidification rates. We investigated whether acidification rates and solute leaching fluxes are variable between permafrost-affected soils with different active layer thicknesses. We compared the fluxes of dissolved organic carbon (DOC) and total dissolved N and the ion fluxes associated with solute leaching and plant uptake to calculate proton budgets in the soils that differed in slope positions (upper slope and lower slope) and soil texture (clayey and sandy soils) in NW Canada. We found the wide variation in DOC and nitrate-N fluxes, depending on slope positions and soil texture. The nitrate-N fluxes were higher at the lower slope position of the sandy soil, compared to the upper slope position. Compared to sandy soils, the DOC fluxes from the organic horizons were higher in the clayey soils on shallower permafrost table. Organic acids were major proton sources in the organic horizons at all sites, but acidity was also contributed by nitrate (sandy and clayey soils at lower slope position) and carbonic acid (clayey soil at upper slope position). The weathering by carbonic acid lead to accumulation of short-range-order minerals in the clayey soils, while incipient podzolization of the sandy soils included the weathering of illite to vermiculite and the dissolution of short-range-order minerals. The shallower active layer thickness at the lower slope position resulted in lower plant productivity and acidification rates. In the permafrost-affected soils, the active layer thickness, the DOC and nitrate-N fluxes, and their contribution to acidification are dependent on the local variation in slope position and soil texture, as well as climate change. [ABSTRACT FROM AUTHOR]

• Na- and Ca-montmorillonite contents of the clay mixtures were estimated using visible-near-infrared (Vis-NIR) spectra. • Partial least square regression (PLSR) models well estimated Na- or Ca-montmorillonite contents of the clay mixtures. • PLSR models estimated Na- or Ca-montmorillonite content of bentonite samples. • PLSR models performed better than single regression (SLR) and multivariate (MLR) regression models. The aim of this study was to evaluate whether Na- and Ca-montmorillonite and the swell-indicating properties (i.e., free swell index, water uptake capacity, and cation exchange capacity (CEC)) of clay mineral mixtures can be estimated using visible-near-infrared (Vis-NIR) spectral features. The data regarding four types of reference clay minerals (KGa-1b, kaolinite; IYd, illite; SWy-3, Na-montmorillonite; STx-1b, Ca-montmorillonite) and binary and ternary mixtures of the reference clay minerals (SWy-3/KGa-1b/IYd, and STx-1b/KGa-1b/IYd) with specific mass percentage ratios were used as a calibration dataset. The absorption spectral features could be correlated well with changes in the clay mineral content of the mixtures. The leave-one-out cross-validation results showed that the partial least square regression (PLSR) calibration models produced the best prediction in the following order: Na or Ca-montmorillonite, kaolinite, and illite amounts in the mixtures. The calibration models produced better predictions in the ascending order of CEC, free swell index, and water uptake capacity, regardless of the multivariate statistical methods and type of exchangeable cations in montmorillonite. Validation using an independent dataset indicated that the PLSR model predicted the Na- and Ca-montmorillonite content in clay mineral mixtures and bentonite samples. The results of this study provide the possibility of using Vis-NIR absorption spectral features as a screening tool for predicting the montmorillonite content with different interlayer cations in relatively pure clay soils (e.g., bentonite), if the calibration model is developed using the specific montmorillonite contained in the clay soil of interest. [ABSTRACT FROM AUTHOR]

• Cover crop root-derived SOC influences aggregate stability in clayey red soil. • High root number and low lignin/cellulose result in high SOC and polysaccharides-C. • Fibrous root vetiver changes SOC and soil surface charge properties largely. • Lower repulsive soil net force leads to higher aggregate stability. Soil aggregate stability is influenced by soil organic carbon (SOC). However, the influence of SOC from different fall/winter cover crop roots (annual and perennial crops) on aggregate stability through soil internal forces (SIFs) (electrostatic repulsive force (P erf), van der Waals attractive force (P vdw), and surface hydration repulsive force (P h)) remains unclear. The objectives of this study were compare three fall/winter cover crops (lucerne, rapeseed, six-year-vetiver (Vet_6Y)) and two control (fallow and fallow with SOC removal (fallow-SOC-R)) to determine SOC effects red soil aggregation through SIFs. Plant root morphological and chemical traits, SOC properties, soil surface charge properties, soil internal forces and aggregate breakdown were all determined. The perennial crop (Vet_6Y) showed the highest root number density (0.21 counts cm−2), second highest root mass density (1.80 mg cm−3), and the lowest root lignin/cellulose ratio (0.69), and thus contributed to higher SOC content and SOC functional groups (mainly polysaccharide-C) than annual crops (rapeseed and lucerne). Such SOC traits in perennial vetiver resulted in a higher specific surface area (SSA), lower surface charge density and surface charge number (Q s) compared to annual crops (rapeseed and lucerne) and controls, and the relationship between the root, SOC and soil surface properties (i.e., SSA) was further confirmed by significant correlation (r ranging from 0.76 to 0.97). Ultimately, these soil surface charge properties after cover crops increased P vdw , decreased P erf , and thus decreased repulsive net force (P net) (the sum of P vdw , P erf , and P h) and the average repulsive net force displayed in order of fallow-SOC-R (2.77 MPa) > fallow (2.11 MPa) > lucerne (2.02 MPa) > rapeseed (1.78 MPa) > Vet_6Y (1.45 MPa) at a distance of 1 nm. This resulted in the mass percentage of released small particles (<20, <10, and <2 µm) w (< d) % from aggregate being reduced after cover crops compared to controls. Generally, clayey red soil aggregate stability can be improved by decreasing the repulsive soil P net through cover crop root contribution to SOC and SOC-functional groups. [ABSTRACT FROM AUTHOR]

• Soil erosion modulus of the large-scale gullies increased from north to south. • Hydraulic erosion dominated gully development during one-year monitoring period. • Contribution of gravity erosion to the gully was ascribed to hypsometric integral. • Clay in colluvial deposits contributed to regional difference of gully erosion. Gully erosion is the most serious threat to sustainable development of global ecosystem and economy, with declining soil productivity and fertility threatening agricultural production. However, due to limitations in quantifying gully erosion rate, origin of erosion could be hardly distinguished. This study aimed to figure out this problem by developing a soil erosion estimation method based on unmanned aerial vehicles (UAV) monitoring techniques. Specifically, 18 gullies with different terrain characteristics were selected across typical erosion regions in southeast China, and UAV low-altitude photography, weather station monitoring, and field sampling investigation were conducted from 2020 to 2021to monitor their total erosion volume (VE), collapse volume (VC), proportion of collapse volume to total erosion volume (VC%), morphological parameters (e.g., total length of scour channels, L; erosion area, A; residual volume, V; and hypsometric integral) and soil-environmental factors (rainfall, temperature, and soil properties). It showed that 92.65 % of VE was resulted from colluvial deposits, attributing to the variation of L. Additionally, VC quantifying the amount of gravity erosion was determined by soil clay content in the upper catchment (Clay1). And percentage of VC to VE, characterized by VC%, possessed a significant linear correlation with HI (R2 = 0.571, p < 0.001). Moreover, regional differences of VE and VC was mainly attributed to soil clay content in colluvial deposits (Clay3) and HI. Collectively, clay content in the gully system inhibited gully erosion, while all the morphologic factors facilitated the development of gully erosion. Meanwhile, rainfall and temperature had significant impacts on VE and the regional difference of VC, probably due to the limited monitoring period. [ABSTRACT FROM AUTHOR]

• Cover crop root-derived SOC influences aggregate stability in clayey red soil. • High root number and low lignin/cellulose result in high SOC and polysaccharides-C. • Fibrous root vetiver changes SOC and soil surface charge properties largely. • Lower repulsive soil net force leads to higher aggregate stability. Soil aggregate stability is influenced by soil organic carbon (SOC). However, the influence of SOC from different fall/winter cover crop roots (annual and perennial crops) on aggregate stability through soil internal forces (SIFs) (electrostatic repulsive force (P erf), van der Waals attractive force (P vdw), and surface hydration repulsive force (P h)) remains unclear. The objectives of this study were compare three fall/winter cover crops (lucerne, rapeseed, six-year-vetiver (Vet_6Y)) and two control (fallow and fallow with SOC removal (fallow-SOC-R)) to determine SOC effects red soil aggregation through SIFs. Plant root morphological and chemical traits, SOC properties, soil surface charge properties, soil internal forces and aggregate breakdown were all determined. The perennial crop (Vet_6Y) showed the highest root number density (0.21 counts cm−2), second highest root mass density (1.80 mg cm−3), and the lowest root lignin/cellulose ratio (0.69), and thus contributed to higher SOC content and SOC functional groups (mainly polysaccharide-C) than annual crops (rapeseed and lucerne). Such SOC traits in perennial vetiver resulted in a higher specific surface area (SSA), lower surface charge density and surface charge number (Q s) compared to annual crops (rapeseed and lucerne) and controls, and the relationship between the root, SOC and soil surface properties (i.e., SSA) was further confirmed by significant correlation (r ranging from 0.76 to 0.97). Ultimately, these soil surface charge properties after cover crops increased P vdw , decreased P erf , and thus decreased repulsive net force (P net) (the sum of P vdw , P erf , and P h) and the average repulsive net force displayed in order of fallow-SOC-R (2.77 MPa) > fallow (2.11 MPa) > lucerne (2.02 MPa) > rapeseed (1.78 MPa) > Vet_6Y (1.45 MPa) at a distance of 1 nm. This resulted in the mass percentage of released small particles (<20, <10, and <2 µm) w (< d) % from aggregate being reduced after cover crops compared to controls. Generally, clayey red soil aggregate stability can be improved by decreasing the repulsive soil P net through cover crop root contribution to SOC and SOC-functional groups. [ABSTRACT FROM AUTHOR]

• Soil erosion modulus of the large-scale gullies increased from north to south. • Hydraulic erosion dominated gully development during one-year monitoring period. • Contribution of gravity erosion to the gully was ascribed to hypsometric integral. • Clay in colluvial deposits contributed to regional difference of gully erosion. Gully erosion is the most serious threat to sustainable development of global ecosystem and economy, with declining soil productivity and fertility threatening agricultural production. However, due to limitations in quantifying gully erosion rate, origin of erosion could be hardly distinguished. This study aimed to figure out this problem by developing a soil erosion estimation method based on unmanned aerial vehicles (UAV) monitoring techniques. Specifically, 18 gullies with different terrain characteristics were selected across typical erosion regions in southeast China, and UAV low-altitude photography, weather station monitoring, and field sampling investigation were conducted from 2020 to 2021to monitor their total erosion volume (VE), collapse volume (VC), proportion of collapse volume to total erosion volume (VC%), morphological parameters (e.g., total length of scour channels, L; erosion area, A; residual volume, V; and hypsometric integral) and soil-environmental factors (rainfall, temperature, and soil properties). It showed that 92.65 % of VE was resulted from colluvial deposits, attributing to the variation of L. Additionally, VC quantifying the amount of gravity erosion was determined by soil clay content in the upper catchment (Clay1). And percentage of VC to VE, characterized by VC%, possessed a significant linear correlation with HI (R2 = 0.571, p < 0.001). Moreover, regional differences of VE and VC was mainly attributed to soil clay content in colluvial deposits (Clay3) and HI. Collectively, clay content in the gully system inhibited gully erosion, while all the morphologic factors facilitated the development of gully erosion. Meanwhile, rainfall and temperature had significant impacts on VE and the regional difference of VC, probably due to the limited monitoring period. [ABSTRACT FROM AUTHOR]

Pesticides in agriculture are commonly used to meet the growing food demand; however they compromise the quality of water and soil. The pesticide 2,4-D is one of the most widely used herbicides in the world, it belongs to the group of synthetic herbicides that control broadleaf weeds. In this paper the risk of groundwater contamination by 24-D and its major metabolite, 2,4-DCP, is studied in a context of high density of soil worms. We compared the adsorption, desorption, degradation and displacement of 2,4-D in soils from Tabasco Region having different properties: clay, organic matter, iron and aluminum oxides contents. In addition to the classical soil physicochemical characterizations, a 3D analysis of the soil structure and porosity was performed by analyzing images acquired by Computed Tomography. The objective was to evaluate the effect of soil properties and macroporosity produced by the macrofauna activity on solute movement. All the four soils studied sorbed the herbicides, more importantly 2,4-DCP, the metabolite, than 2,4-D itself. The distribution coefficients for 2,4-D sorption were linear and varied between 1 and 4 while those for 2,4-DCP were above 10. The contents of iron and aluminum have an important role in the adsorption of these two compounds. In aerobic conditions, the herbicides half-life was about 2 days. Water movement occurred in physical equilibrium in three of the four soils; soil dispersivity ranged from 1.2 to 7 cm, clay content being the main factor. After 20 to 60 days depending on the soil, no 2,4-D leaching was observed through the soil columns, except for one soil were there was preferential flow. Earthworms burrows were exhibited and quantified in the soils samples through the analysis of Computer Tomography (CT) images, they appeared as small, snail-shaped, rounded volume of 3 to 7 mm radius with a higher density with respect to the surrounding soil. They were extracted from the original data using a combination of image processing and mathematical morphology operators. Based on the results obtained, it can be concluded that preferential flow caused by both high clay content and the presence of macrofauna pores significantly reduces the buffering capacity of the soil, increasing the risk of contamination by herbicides of the underlying aquifer. [ABSTRACT FROM AUTHOR]

Abstract When making management decisions regarding the conditions of the Great Hungarian Plain, it is important to consider the soil clay content and soil salinity. Because the soil moisture conditions vary from extremely dry to extremely wet throughout the year, this limits the use of electric methods. In this study, we looked for fast, independent techniques to estimate soil clay content and soil salinity. Gamma dosimetry and X-ray fluorescence spectroscopy (XRF) were tested and showed consistent values. In two contrasting transects: one passing from top of the dune to the valley (Sanddune-Valley), and another passing from an elevated non-sodic grassland to low sodic patches (Sodic), the XRF-measured rubidium concentration proved to be the best overall predictor of both soil clay content and salinity as it provided better correlations than gamma dosimetry. Pearson correlation coefficients indicated opposing tendencies between the rubidium concentration and the soil clay content and salinity in the transects, owing to distinct differences in the soil formations inside the transects. We suggest using XRF and not gamma dosimetry for the field estimation of soil clay content and salinity with portable devices. Highlights • In dry soils electric methods are not good for predicting clay content and salinity. • Gamma dosimetry and X-ray fluorescence spectroscopy can help in dry soils. • XRF showed better correlation with lab measured parameters than gamma dosimetry. • Not XRF-K cc as expected, but XRF-Rb cc was best predictor of clay % and salinity. • The Sodic vs Sanddune-Valley transects showed very contrasting patterns. [ABSTRACT FROM AUTHOR]