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Soil composition can influence the chemical forms and bioavailability of soil mercury (Hg). However, previous studies have predominantly focused on the influence of individual components on the biogeochemical behavior of soil Hg, while the influence of various component interactions among several individual factors remain unclear. In this study, artificial soil was prepared by precisely regulating its components, and a controlled potted experiment was conducted to investigate the influence of various organic and inorganic constituents, as well as different soil textures resulting from their coupling, on soil Hg methylation and its bioavailability. Our findings show that inorganic components in the soils primarily exhibit adsorption and fixation effects on Hg, thereby reducing the accumulation of total mercury (THg) and methylmercury (MeHg) in plants. It is noteworthy that iron sulfide simultaneously resulted in an increase in soil MeHg concentration (277%). Concentrations of THg and MeHg in soil with peat were lower in rice but greater in spinach. A correlation analysis indicated that the size of soil particles was a crucial factor affecting the accumulation of Hg in plants. Consequently, even though fulvic acid activated soil Hg, it significantly increased the proportion of soil particles smaller than 100.8 μm, thus inhibiting the accumulation of Hg in plants, particularly reducing the concentration of THg (93%) and MeHg (85%) in water spinach. These results demonstrate that the interaction of organic and inorganic components can influence the biogeochemical behavior of soil Hg not only through their chemical properties, but also by altering the soil texture. [ABSTRACT FROM AUTHOR]

Soil composition can influence the chemical forms and bioavailability of soil mercury (Hg). However, previous studies have predominantly focused on the influence of individual components on the biogeochemical behavior of soil Hg, while the influence of various component interactions among several individual factors remain unclear. In this study, artificial soil was prepared by precisely regulating its components, and a controlled potted experiment was conducted to investigate the influence of various organic and inorganic constituents, as well as different soil textures resulting from their coupling, on soil Hg methylation and its bioavailability. Our findings show that inorganic components in the soils primarily exhibit adsorption and fixation effects on Hg, thereby reducing the accumulation of total mercury (THg) and methylmercury (MeHg) in plants. It is noteworthy that iron sulfide simultaneously resulted in an increase in soil MeHg concentration (277%). Concentrations of THg and MeHg in soil with peat were lower in rice but greater in spinach. A correlation analysis indicated that the size of soil particles was a crucial factor affecting the accumulation of Hg in plants. Consequently, even though fulvic acid activated soil Hg, it significantly increased the proportion of soil particles smaller than 100.8 μm, thus inhibiting the accumulation of Hg in plants, particularly reducing the concentration of THg (93%) and MeHg (85%) in water spinach. These results demonstrate that the interaction of organic and inorganic components can influence the biogeochemical behavior of soil Hg not only through their chemical properties, but also by altering the soil texture.

Spectroscopic measurements of soil samples are reliable because they are highly repeatable and reproducible. They characterise the samples' mineral–organic composition. Estimates of concentrations of soil constituents are inevitably less precise than estimates obtained conventionally by chemical analysis. But the cost of each spectroscopic estimate is at most one‐tenth of the cost of a chemical determination. Spectroscopy is cost‐effective when we need many data, despite the costs and errors of calibration. Soil spectroscopists understand the risks of over‐fitting models to highly dimensional multivariate spectra and have command of the mathematical and statistical methods to avoid them. Machine learning has fast become an algorithmic alternative to statistical analysis for estimating concentrations of soil constituents from reflectance spectra. As with any modelling, we need judicious implementation of machine learning as it also carries the risk of over‐fitting predictions to irrelevant elements of the spectra. To use the methods confidently, we need to validate the outcomes with appropriately sampled, independent data sets. Not all machine learning should be considered 'black boxes'. Their interpretability depends on the algorithm, and some are highly interpretable and explainable. Some are difficult to interpret because of complex transformations or their huge and complicated network of parameters. But there is rapidly advancing research on explainable machine learning, and these methods are finding applications in soil science and spectroscopy. In many parts of the world, soil and environmental scientists recognise the merits of soil spectroscopy. They are building spectral libraries on which they can draw to localise the modelling and derive soil information for new projects within their domains. We hope our article gives readers a more balanced and optimistic perspective of soil spectroscopy and its future. Highlights: Spectroscopy is reliable because it is a highly repeatable and reproducible analytical technique.Spectra are calibrated to estimate concentrations of soil properties with known error.Spectroscopy is cost‐effective for estimating soil properties.Machine learning is becoming ever more powerful for extracting accurate information from spectra, and methods for interpreting the models exist.Large libraries of soil spectra provide information that can be used locally to aid estimates from new samples. [ABSTRACT FROM AUTHOR]

Soil analysis to estimate soil fertility parameters is of great importance for precision agriculture but nowadays it still relies mainly on complex and time-consuming laboratory methods. Optical measurement techniques can provide a suitable alternative. Raman spectroscopy is of particular interest due to its ability to provide a molecular fingerprint of individual soil components. To overcome the major issue of strong fluorescence interference inherent to soil, we applied shifted excitation Raman difference spectroscopy (SERDS) using an in-house-developed dual-wavelength diode laser emitting at 785.2 and 784.6 nm. To account for the intrinsic heterogeneity of soil components at the millimeter scale, a raster scan with 100 individual measurement positions has been applied. Characteristic Raman signals of inorganic (quartz, feldspar, anatase, and calcite) and organic (amorphous carbon) constituents within the soil could be recovered from intense background interference. For the first time, the molecule-specific information derived by SERDS combined with partial least squares regression was demonstrated for the prediction of the soil organic matter content (coefficient of determination R2 = 0.82 and root mean square error of cross validation RMSECV = 0.41%) as important soil fertility parameter within a set of 33 soil specimens collected from an agricultural field in northeast Germany. Graphical Abstract [ABSTRACT FROM AUTHOR]

The sorption of heavy metals by soil constituents reduces the absorption of these pollutants by crops and vegetables, and thus limit food contamination. Low molecular weight anionic ligands are ubiquitous in soil and they influence the sorption of heavy metals. Here we review the influence of small anionic ligands on the sorption of heavy metals by soil constituents. We discuss the mechanisms of anionic ligand impact on heavy metal sorption by soil constituents; the influence of anionic ligands on heavy metal sorption by composites of soil constituents; and (4) the influence of mixed anionic ligands on heavy metal sorption. The information in this review will facilitate the assessment and control of heavy metal pollution in soils. [ABSTRACT FROM AUTHOR]

Abstract Once entering soil, carbon nanotubes (CNTs) can influence the fate of hydrophobic organic compounds (HOCs) in soil due to its strong adsorption capacity. This process may be influenced by the interactions between CNTs and soil constituents. The mechanisms therein were investigated in the present study by examining pyrene adsorption/desorption on one CNTs, two soils (black soil and paddy soil), and mixtures thereof. CNTs' amendment enhanced soil site heterogeneity and adsorption capacity of pyrene while it was less than that predicted by the sum of the individual adsorption on soils and CNTs, which was more obvious at low aqueous concentrations. This could be due to the interactions between soil constituents (dissolved organic matter (DOM) and clays) and CNTs. Modification of CNTs by DOM attenuated pyrene adsorption by 14.9%–66.1%, which was ascribed to occupying of surface adsorption sites, pore blockage of CNTs' aggregates, enhancement of surface polarity, and enhancement of pyrene solubility in aqueous phase. The coexistence of clay (kaolinite) also showed inhibition on pyrene adsorption onto CNTs with a reduction of 19.2% − 40.2%. This could be ascribed to that the attachment of clay particles on CNTs' aggregates could cover the surface adsorption sites and enhance the surface polarity of CNTs. The effect of CNTs amendment on pyrene desorption hysteresis differed among soils. The hysteresis index of the black soil doubled after CNTs' amendment while that of paddy soil remained unchanged. The results of this study provide insights into the possible effects of CNTs on the fate of HOCs in real soil environment. Highlights • CNTs exhibited strong, heterogeneous and reversible adsorption for pyrene. • Experimental K d of CNTs-soil was less than the sum of K d,soil and K d , CNTs. • The interaction of DOM with CNTs accounted for most of the difference. • The attachment of clay mineral (kaolinite) on CNTs also made contribution. • The effect of CNTs on the desorption hysteresis differed among soils. [ABSTRACT FROM AUTHOR]

Spectroscopy is the science concerned with the investigation and measurement of spectra produced when materials interacts with or emits electromagnetic radiation. Commercial infrared spectrometer were designed from the 1950’s onward and found their way into the pharmaceutical and chemical industries. In the 1970’s and 1980’s also natural sciences notably mineralogy and vegetation science started systematically to measure optical properties of leaves and minerals/rocks with spectrometers. In the last decade spectroscopy has made the step from qualitative observations of mineral classes, soil type and vegetation biomass to quantitative estimates of mineral, soil and vegetation chemistry. This resulted in geothermometers used to characterize metamorphic and hydrothermal systems and to the advent of foliar biochemistry. More research is still needed to bridge the gap between laboratory spectroscopy and field spectroscopy. Empirical studies of minerals either as soil or rock constituents (and vegetation parameters) derived from regression analysis of spectra against chemistry is important in understanding the physics of the interaction of electromagnetic radiation and matter which in turn is important in the design of future satellite missions. Physics based models and retrievals are needed to operationalize these relationships and implement them in future earth observation missions as these are more robust and easy to transfer to other areas and data sets. [ABSTRACT FROM AUTHOR]

Reflectance, emissivity and elevation data of the sensor ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer)/Terra were used to characterize soil composition variations according to the toposequence position. Normalized data of SWIR (shortwave infrared) reflectance and TIR (thermal infrared) emissivity, coupled to a soil-fraction image from a spectral mixture model, were evaluated to separate bare soils from nonphotosynthetic vegetation. Regression relationships of some soil properties with reflectance and emissivity data were then applied on the exposed soil pixels. The resulting estimated values were plotted on the ASTER-derived digital elevation model. Results showed that the SWIR bands 5 and 6 and the TIR bands 10 and 14 measured the clay mineral absorption band and the quartz emissivity feature, respectively. These bands improved also the discrimination between nonphotosynthetic vegetation and soils. Despite the differences in pixel size and field sampling size, some soil properties were correlated with reflectance (R² of 0.65 for Al2O3 in band 6; 0.61 for Fe2O3 in band 3) and emissivity (R² of 0.65 for total sand fraction in the 10/14 band ratio). The combined use of reflectance, emissivity and elevation data revealed variations in soil composition with topography in specific parts of the landscape. From higher to lower slope positions, a general decrease in Al2O3 and increase in total sand fraction was observed, due to the prevalence of Rhodic Acrustox at the top and its gradual transition to Typic Acrustox at the bottom.Dados de reflectância, emissividade e elevação do sensor ASTER (Advanced Spaceborne Thermal Emission and Reflection Radiometer)/Terra foram usados para caracterizar variações na composição dos solos com a posição em topossequências. Dados normalizados de reflectância do SWIR (shortwave infrared) e de emissividade do TIR (thermal infrared), integrados com a imagem fração-solo de um modelo de mistura espectral, foram avaliados para separar solos expostos de vegetação não fotossinteticamente ativa. Relações de regressão de alguns atributos dos solos com dados de reflectância e emissividade foram aplicadas sobre os pixels de solos expostos. Os valores estimados resultantes foram projetados sobre um modelo digital de elevação gerado a partir dos dados ASTER. Os resultados mostraram que as bandas 5 e 6 do SWIR e 10 e 14 do TIR mediram a feição de absorção das argilas e a de emissividade do quartzo, respectivamente. Essas bandas melhoraram também a discriminação entre vegetação não fotossinteticamente ativa e solos. Apesar das diferenças no tamanho dos pixels e dos locais de amostragem de campo, alguns atributos dos solos foram correlacionados com a reflectância (R² de 0,65 para Al2O3 na banda 6 e de 0,61 para Fe2O3 na banda 3) e a emissividade (R² de 0,65 para fração total de areia com a razão das bandas 10/14). O uso combinado dos dados de reflectância, emissividade e elevação revelou variações na composição dos solos com a topografia em porções específicas da cena. Das maiores para as menores elevações, um decréscimo no conteúdo de Al2O3 e aumento na fração total de areia foram geralmente observados. Isso ocorreu em razão do predomínio de Latossolo Vermelho-Escuro no topo e de sua gradual transição para Latossolo Vermelho-Amarelo na base.

Few studies have demonstrated the long-term effects of different tillage practices on changes of soil quality; however, understanding such effects is vital for the selection and establishment of appropriate soil conservation measures on steep hillslopes. This study was conducted at two adjacent sites in the Sichuan Basin, China, with one cultivated by traditional tillage (TT; i.e., hoeing starts at the bottom position and soil is moved downslope because of gravity and drag) and the other cultivated by conservation tillage (CT; i.e., hoeing is performed from hilltop to bottom, but soil is moved uphill because of drag). We used the Cesium-137 (137Cs) tracer technique to identify the pattern of soil constituent distribution and soil quality differences between the two tillage practices. The 137Cs residual rate for the CT practice ranged from -29.44% to 34.16% with an average of-8.56%, and the TT practice ranged from -57.12% to 4.63% with an average of--29.49%. A greater increase (ranging from 18.43% to 50.69%) in soil constituents (i.e., soil organic matter, total nitrogen [N], phosphorus [P], and potassium [K], available N, and extractable P and K) was found in the CT soils than in the TT soils. The CT treatment site exhibited markedly higher concentrations of soil constituents in each soil depth profile (0 to 40 cm [0 to 15.7 in] and each 5 cm [2 in] in length increment). The soil degradation index (SDI) for the CT practice significandy increased compared to the TT practice in the 0 to 15 cm (0 to 5.9 in) and 15 to 40 cm (5.9 to 15.7 in) depth of the profiles (p < 0.05). The greatest difference in SDI induced by these two till age practices occurred at the summit and toeslope positions, with an increase in SDI of 28.07% and 15.76% in the 0 to 15 cm (0 to 5.9 in) depth and of 49.16% and 31% in the 15 to 40 cm (5.9 to 15.7 in) depth, respectively. The 137Cs residual rate showed a corresponding relationship with the SDI changing trend, which implied that the 137Cs residual rate may be considered an indicator for appraising soil quality for eroding hillslopes. It is suggested that the long-term practice of CT largely diminishes soil degradation because of upslope soil translocation; therefore, it would also significantly improve soil quality in steeply sloping fields. [ABSTRACT FROM AUTHOR]

• The fate of P fertilizers in Alfisol is controlled by chemical adsorption reactions. • P is primarily immobilized by goethite, kaolinite, and illite in Alfisol. • P adsorbed by illite may serve as an indicator of P availability in Alfisol. Inorganic P is adsorbed by a variety of soil minerals. For acidic subtropical Alfisols with high contents of both (hydr)oxides and clay minerals, there is an underappreciated understanding of the importance of clay minerals to P species and availability varying with soil pH and P concentration. In this study, the rate and equilibrium of P adsorption in a subtropical Alfisol were investigated by combining soil incubation with three types of P fertilizer with multi-surface modelling. Phosphorus species analysis revealed that most of the P was present in the forms of Al-P and Fe-P in the subtropical Alfisol. The multi-surface model calculation showed that goethite, kaolinite, and illite were the most important soil constituents responsible for the immobilization of P. Clay minerals were as important as Al/Fe (hydr)oxides for P adsorption in the subtropical Alfisol. In addition, there was a highly positive linear correlation between P adsorbed by illite and Olsen P, with a slope of approximately to 1. The model analysis also showed that >99% of the P adsorbed by illite was in the form of - S O 2 P O 2 2 - . These results suggest the important role of illite in controlling P availability and that P adsorption by illite may serve as an indicator of P availability in the subtropical Alfisol. [ABSTRACT FROM AUTHOR]

A multi-compartment system was used to study the importance of microorganisms for Cd desorption from soil amended with sewage sludge and simultaneous resorption of the mobilized metal by soil constituents. Using this system made it possible to study the participation of microorganisms (Arthrobacter, Trichoderma), montmorillonite, humic acids, and iron oxides in resorption of the released Cd. A filter-sterilized water extract of root-free soil of pH 6.7 (RF) or RF supplemented with glucose (RFG) were used to mobilize Cd from soil at 14°C in 48h. Cadmium found in those extracts after 48-h incubation was recognized as bioavailable. Changes in pH values and enrichment of soil extracts with organic acids and siderophores resulted from microbial growth. RFG with lower pH and a higher content of ligands mobilized, on average, 40% of Cd introduced with sewage sludge amended soil, whereas RF mobilized only 20% of it. Sequential extractions of Cd at time 0 and Cd remaining in soil showed that RFG had mobilized Cd mostly from the fraction bound with Fe and Mn oxides. Microbial biomass accounted for only up to 3.4% (w/w) of the soil constituents used in the experiments but resorbed 25% of mobilized Cd. The chemical composition of mobilizing soil extracts and the solid-to-mobilizing-extracts volume ratio had a significant effect on the amount of bioavailable Cd. The results of the study suggest that microbial metabolites were involved in Cd mobilization, while the biomass of microorganisms was involved in Cd resorption as a biosorbent. [Copyright &y& Elsevier]