Soil Solid Phase Research Articles

Responses of Cd Accumulation in Rice and Spectral Characteristics of Soil Dissolved Organic Matter Regulated by Soil Amendments

Studying the chemical composition and characteristic differences of soil dissolved organic matter (DOM) is significant for understanding the mechanism of Cd immobilization by soil amendments. Soil amendments have been widely applied to contaminated farmlands to reduce the accumulation of heavy metals in crops, but the spectral characteristics of DOM in soils under amendment regulation have rarely been studied. Typical Cd-contaminated paddy soil from South China was collected, three categories of amendments (organic-based, inorganic-based, and lime-based, a total of 11 types) were applied, rice planting pot trials were done, and the effects of different amendments on soil DOM were investigated. The spectral characteristics of rhizosphere soil DOM under the regulation of different amendments were comparatively analyzed using UV-Vis spectroscopy, 3D fluorescence spectroscopy, and parallel factor analysis (PARAFAC). The results showed that the lime-based amendments increased the soil pH and promoted the dissolution of organic matter from the soil solid phase, resulting in a significant increase in soil DOM content. Compared with that of the control, organic-based amendments increased the relative molecular weight and recent autochthonous origin contribution of soil DOM, inorganic-based amendments increased the aromatic content and hydrophobic components of soil DOM, and lime-based amendments increased the chromogenic components and the degree of humification of soil DOM. Four fluorescence components, C1 (255/465), C2 (325/400), C3 (275/390), and C4 (240/460), were identified using PARAFAC and verified with the OpenFluor database, all of which were humic-like. Two types of spectra corroborated with each other, indicating that soil DOM dominated by humus-like matter originated from terrestrial source input. The correlation analysis showed that the fluorescent component C4 of soil DOM could be used to predict Cd accumulation in brown rice in the red limestone soil-rice system. These results will provide a reference for the selection of the appropriate soil amendments.

Wheat yield prediction by zero sink and equilibrium-type soil phosphorus tests

Diffusive gradients in thin films (DGT) measurements have been shown to outperform other phosphorus (P) tests in soils with strong P sorption, but this has not been confirmed for moderately weathered European soils. We compared the performance of DGT in predicting wheat grain yield in Swedish long-term fertility experiments with those of standard intensity (water-extractable P (P-H 2 O)) and quantity (ammonium lactate-extractable P (P-AL)) tests. A Mitscherlich-type model was used to fit wheat yield response to P application rates (0, 15, 30 or 35, and 45 kg P ha -1 year -1 ) in each individual trial replicate to estimate the maximum yield. For trials with clear plateau-type yield responses and the goodness of fit ( R 2 ) > 0.75, relative yields (RYs) were calculated for each P treatment and plotted against the soil P test results ( n = 143). The goodness of the Mitscherlich-type fits decreased in the following order: DGT-measured P (P-DGT) ( R 2 = 0.35) > P-H 2 O ( R 2 = 0.18) > P-AL ( R 2 = 0.13). When excluding soils with P-AL:P-DGT ≥ 0.1 L g -1 , R 2 was considerably improved to 0.55 for P-AL, 0.46 for P-H 2 O, and 0.65 for P-DGT ( n = 61). At 95% of maximum yield, the upper limit of P deficiency for P-DGT was 44.8 (the soils with P-AL:P-DGT < 0.1 L g -1 ) and 61.9 μg L -1 (all soils), falling within the range reported for other European and Australian soils (6.0–142 μg L -1 ). We show that in the investigated Swedish soils, DGT performed better than the quantity and intensity tests, which is attributed to its ability to capture P diffusion and resupply from the soil solid phase, similar to plant roots in the rhizosphere.

Spatial and temporal variations of metal fractions in paddy soil flooding with acid mine drainage

Environmental release of acid mine drainage (AMD) poses a potential threat to the environment and human health due to its high content of heavy metals. The impact of AMD flooding on unpolluted soil leads to serious pollution over time via a complex process, related to the geochemical behavior of toxic metals that so far has only been partially investigated. Here, a soil column study was conducted to investigate the migration of Cu and Cd fractions in unpolluted paddy soil following treatment with AMD collected from the Dabaoshan Mining area. Tessier's sequential extraction was performed to fractionate the metals at various depths over time. After 160 days of experimental flooding, the soil pH stabilized at 2.52 at a column depth of 5 cm. The fractions of Cu and Cd that were highly mobile increased significantly during AMD flooding. For Cd, the latter already occurred on day 67. At a depth of 20 cm, the total content of Cu maximally increased from initially 26.89 mg kg−1 to 696.96 mg kg−1 on day 160, while the content of Cd maximally increased from 0.22 mg kg−1 to 391.30 mg kg−1 on day 67. Reduced partition index analysis conformed that the mobility of both Cu and Cd significantly increased in contaminated soil during continuous AMD flooding. Scanning electron microscopy coupled with energy dispersive spectroscopy (SEM-EDS) identified a changed distribution of the elements in the soil, with Fe appearing to have aggregated. The correlation analysis between Cu and Cd in pore water and in different fractions in the soil's solid phase identified a dynamic distribution of these metals in certain geochemical components during their migration. The results of this study contribute to a scientific foundation to describe the geochemical behavior of heavy metals in soil subject to AMD flooding.

Spatial distribution of soil phosphorus fractions in a clayey Oxisol submitted to long-term phosphate fertilization strategies

Due to the strong interaction of phosphorus (P) with soil constituents, P fertilizer placement can significantly affect how crops take up this nutrient. Nonetheless, few studies address the spatial distribution of P at the row-interrow scale according to management strategies. In a 16-yr no-tillage (NT) field experiment involving two different P fertilizer application methods (broadcast or band application) and two P sources (triple superphosphate – TSP or reactive Gafsa phosphate rock-RPR), plus a control treatment, the spatial distribution of P fractions was assessed in two occasions: after the 8th and the 16th crops. This was done vertically to a depth of 30 cm and horizontally from the crop row to the center of the interrows. Broadcast treatments showed total and Mehlich-1 P accumulation at the soil surface while for band application this accumulation was in the crop row region. A small P movement down the soil profile was observed from the 8th to the 16th crop with broadcast application, whereas with band fertilizer this effect was more noticeable, showing increased soil volume under P fertilizer influence even without soil tillage; it is likely that this was partly due to biological P turnover and application at depth. After 16 crops, the soil volume under the influence of P fertilizer was greater under band application while the volume above Mehlich-1 P critical levels for the 0–20 cm layer in regional studies was higher under broadcast application, independent of the P source. Soil organic carbon (SOC) contents were not affected by P placement or source. However, a significant accumulation of SOC was seen from the soil surface downwards after the last eight crops. The spatial distribution of P and SOC was better correlated under broadcast treatments, with high values for both variables at the soil surface; this may explain similar yields to those obtained with band application, where P fertilizer is placed near the main roots in an attempt to reduce P adsorption to the soil solid phase.

Biogeochemical features of soil formation without parent rock in natural conditions and in an urban environment

The aim of the present study is to establish the biogeochemical characteristics of the primary soil formation, separately for natural conditions (protected areas) and urban environment (with incoming technogenic aerosols) for pedogenesis models when there is no parent rock (“upward soil growth”). This makes it possible to assess the contribution of the still poorly studied pedogenesis factors that can form the specific geochemical features of the material composition of soils non-inherited from the parent rock, and without the involvement of biogenic bottom-up migration of elements. We have studied two contrasting regions to perform a comparative analysis of pedogenesis conditions. We have compared embryonic soils on megalithic gabbro-diabase blocks in a 17th century defence wall located on the territory of a natural reserve, 1 km away from the Black Sea coast (ecologically clean area) and a 45-year solid bitumen cover between a thermal power plant and a busy railway (an industrial zone in the central part of the city). In the natural reserve, the average dust deposition rate was 0.82 um yr1 (0.082 mm/100 yr) due to stardust, atmospheric aerosols and biogenic processes of pedogenesis. The mineral part of soils, which had formed on the solid bitumen in 45 years in the city’s industrial zone, differs from the soil developed in 320-350 years without the involvement of the parent rock in the protected area by higher content of V (9 times) and Cr (2 times), as well as CaO, SiO2 and Pb. In the industrial zone of the city, emission dust mostly contributes to the accumulation of V, Cr and Cu in comparison with the pedogenesis conditions in the ecologically clean area, where the rate of solid-phase soil matter accumulation is twice lower due to background aerosols and biogenic factors.

Simulated Bioavailability of Heavy Metals (Cd, Cr, Cu, Pb, Zn) in Contaminated Soil Amended with Natural Zeolite Using Diffusive Gradients in Thin-Films (DGT) Technique

The aim of this study was to investigate the effect of natural zeolite amendment to contaminated soil on the heavy metal (Cd, Cr, Cu, Pb and Zn) simulated bioavailability over a three-month period of storage. Two pot experiments were created by amending soil with two different amounts of natural zeolite (3 and 6 wt.%). During the experiment, pH level, metal concentrations in soil solution (Csol) and metal concentrations in soil by the diffusive gradients in thin-films technique (CDGT) were determined. When the zeolite was added to the soil, a significant decrease (p = 95%, n = 3) for Cd and Pb concentrations, both in Csol and in CDGT, was observed. The Cu, Cr and Zn concentrations also showed a decreasing trend, but the changes in their concentrations were not statistically significant. The R ratio between CDGT and Csol was calculated for each metal in order to assess the resupply of metals from the soil solid phase to soil solution. The R values significantly decreased for Cd and Pb, showing a low resupply from the solid phase in the samples with added zeolite.

Chemodiversity of dissolved organic matter in cadmium-contaminated paddy soil amended with different materials

Dissolved organic matter (DOM) in soil is a key factor affecting the bioavailability of heavy metals, but very few studies have focused on the role of DOM in the use of soil amendments to mitigate heavy metal accumulation in crops. Here, eleven materials were added to cadmium (Cd)-contaminated paddy soil in greenhouse pot trials; rice was grown and harvested, the chemodiversity of post-harvest soil DOM was characterized using Fourier-Transform Ion Cyclotron Resonance Mass Spectrometry, and the specific associations between soil DOM traits and water-extractable soil Cd concentration were identified at the molecular level. The results showed that the endogenous release caused by altering soil pH had a greater effect on soil DOM concentration than did the exogenous chemical input due to the application of organic amendments, which in turn contributed to the chemodiversity of DOM. After one season of rice cultivation, soil DOM molecules were mainly dominated by relatively low molecular weight heteroatom-free lignins. C/N, C/H ratios of organic materials influenced DOM molecular fingerprint patterns, and soil pH and redox potential were the main driving forces affecting the chemodiversity of DOM. Furthermore, the low molecular weight, high saturation, low aromaticity, and heteroatom-free DOM molecules are more likely to dissolve Cd from the soil solid phase, thus increasing the potential risk of Cd to the environment. The results provide critical information about amendments-induced changes in DOM chemodiversity and will inform the selection of appropriate soil amendments.

Effect of cyclodextrin on desorption of petroleum hydrocarbons in soil

The present study delineated to explore the possibility of using cyclodextrins as an environmentally friendly solubilizer for enhancing the desorption efficiency of petroleum hydrocarbons (PHs) in the contaminated soil. The results showed that cyclodextrins could promote the transfer of PHs from the soil solid phase to the aqueous phase. Through the batch desorption experiments, single-factors influencing the desorption efficiency, including desorption time, species of cyclodextrin, solid to liquid ratio (S/L ratio) of soil to solvent, concentrations of solubilizer and concentrations of the contaminated soil were investigated. In addition, the response surface methodology analysis were used to identify the optimal desorption conditions, and the optimal desorption parameters were concluded as the follows: desorption time of 34 h, S/L ratio of soil to solvent of 1:25, concentration of β-CD of 0.75 g/L (for PAHs), desorption time of 18 h, S/L ratio of soil to solvent of 1:5, concentration of β-CD of 4.8 g/L (for n-alkanes). The highest desorption efficiency of two representative PHs, polycyclic aromatic hydrocarbons (PAHs, phenanthrene, fluoranthene and pyrene) and n-alkane (C16, C20, C24, C28 and C32), were 63.0% and 61.7%, respectively. This study presented new-positive evidence of cyclodextrins for enhancing desorption of PHs, was of great importance for enhancement of bioavailability of PHs, and further revealed the great potential of cyclodextrins as a solubilizer in-situ assisting removal of PHs in the petroleum-contaminated sites.

Aqueous selenium removal and distribution in cattail and duckweed in constructed wetland microcosms

AbstractSelenium (Se)‐affected stormwater runoff raises concerns about potential downstream impact of Se on aquatic ecosystems. Unplanted (UNP) detention ponds augmented with cattail (Typha angustifolia L.; CAT) and duckweed (Lemna minor L.; DWD) may provide a solution for continuous, rapid abatement of Se‐affected runoff. This research was conducted to evaluate the efficacy of CAT or DWD and determining the distribution of Se within a continually flooded detain and drain system. Microcosms containing 3 kg of soil planted to either one CAT, 25 g fresh DWD, or left unplanted (UNP, control) were flooded with a 3‐L solution at 40 μg Se L−1, as sodium selenate (Na2SeO4), or a zero Se control. Over two 10‐d flood–discharge cycles (FDCs), plants in microcosms were evaluated in growth chambers maintained at 30 °C under a 12‐h photoperiod with 400 μmol m−2 s−1 irradiance. Initial and final water, soil, plant, and granular activated charcoal (GAC) were analyzed for total [Se] with inductively coupled plasma–mass spectroscopy (ICP–MS). Data were analyzed with PROC GLM (SAS EG 7.1) at α = .05. Within 10 d after Se application, CAT and DWD decreased aqueous Se from 40 μg Se L−1 to below the 11.8 μg Se L−1 threshold. Selenium recovery ranged between 75 and 100% of the applied Se. In continually flooded systems, the primary elimination pathway appears to be associated with the soil solid phase. Cattail and DWD are suitable species for constructed wetland phytoremediation of Se‐affected runoff. The microcosm design presented may be useful for future evaluations.

УПРАВЛЕНИЕ ЭКОЛОГИЧЕСКОЙ СОСТАВЛЯЮЩЕЙ ОРОШЕНИЯ С ПОМОЩЬЮ ИННОВАЦИОННЫХ АДАПТИВНЫХ ТЕХНОЛОГИЙ

Purpose: development of agricultural technologies that ensure soil fertility conservation by selecting (adaptation) special soil protection methods in relation to the actual energy indicators of solid runoff, a certain combination of which will allow maintaining soil fertility or keeping it at a scientifically based level under critical erosional conditions, with the creation of an innovative tool. Materials and methods. The value of solid soil phase washout during the studies conducted on corn crops under conditions of critical erosional slopes was determined on runoff sites, which are the field sections equipped with measuring devices (tanks) isolated from the surrounding area (with the help of metal frames). Results. An adaptive technology that combines the application of 60 t/ha of semi-decomposed manure, the implementation of operational planning and moling, the use of differentiated moistening of a soil layer of 0.4–0.7 m, depending on the development of the corn root system with irrigation rates respectively 360–500 cub. m has been selected. The technology provides an acceptable limit of soil solid washout, less than the set scientifically based value. To intercept surface (liquid and solid) runoff, both distributed and rill, an innovative drawn tool has been developed that forms the artificial “water-bearing” subsurface reservoirs and surface “mini-reservoirs” based on an intermittent furrow and intermittent slotting, created in the time of their joint trenching and providing the accumulation of the irrigation rate. Conclusions. The developed technology and tool design make it possible to implement erosion-preventive methods with a differentiated irrigation regime, which ensures the environmental safety and soil fertility conservation of irrigated lands.

Combining spectroscopic and flux measurement techniques to determine solid-phase speciation and solubility of phosphorus in agricultural soils

Soil solid-phase phosphorus (P) speciation and chemical conditions exert a crucial role in both aqueous P speciation and concentration—the most available and mobile pool for biota in environments. However, the interplay between solid-phase speciation and the aqueous phase of P in soil systems is unresolved. Herein, we investigated the speciation and solubility of P in tropical agricultural soils, which are often poor in P availability. Phosphorus K-edge X-ray absorption near edge structure (XANES) spectra of acidic soils identified dominant Al-hydroxide-phosphates (∼58%: P adsorbed to gibbsite 19%, P adsorbed to kaolinite 14%, and variscite 16%), followed by Fe-hydroxide-phosphates (∼36%: P adsorbed to ferrihydrite 14% and strengite 22%), and trace organic P (∼6%). Calcium phosphates (∼52%) prevailed in the alkaline/calcareous soils with moderate and minor contributions from Al-phosphates (∼37%: P adsorbed to kaolinite 28%, P adsorbed to gibbsite 1%, and variscite 7%) and Fe phosphate (∼11%), respectively. The time-averaged P concentration in the aqueous phase using diffusive gradients in thin films (CDGT) was highly variable from 4 to 123 μg P L–1, with the highest and the lowest values observed in acidic-coarse- and alkaline-fine-textured soils, respectively. The CDGT concentration was positively related to belowground P uptake. The CDGT concentration had negative relationships with pH, Ca-P XANES, and total and extractable Ca, indicating that Ca phosphates were the primary constituents decreasing the dissolvable P concentration. This study highlighted the importance of solid-phase P species in determining P fluxes and is relevant to diverse soils rich in Fe/Al/Ca compounds under extremely acidic to alkaline conditions.

Changes in hydrophobic-hydrophilic properties of chernozems under the influence of mineral fertilizers and their aftereffect

Soil samples and granulodensimetric fractions isolated from them ((silt particle size less than 1 µm, light fraction (LF) with a density of less than 2 g/cm3 and a fraction of the residues) of ordinary chernozem from experimental fields of the Kamennaya Steppe agricultural landscape of the Voronezh region were studied. The main differences between the variants of the experiment are introducing or stopping mineral fertilizers, and in the aftereffect of irrigation (13 years). There is an increase in the content of LF when using mineral fertilizers, as well as a change in the composition of sizedensity fractionations, expressed in different content of C and N and hydrophobic-hydrophilic components of humus substances (HS) of soils, silt and LF. The irrigation had practically no effect on the hydrophobichydrophilic composition of the initial soils, while the relative content of the hydrophilic components of the silt fraction of the soil increased, and the hydrophilic composition of HS LF decreased. The use of mineral fertilizers led to a significant variation in the degree of hydrophilicity of HS in silt and LF with a smaller change of this indicator for the HS of the soil as a whole. The abolition of fertilizers application, on the contrary, affected the hydrophobichydrophilic composition of the soil as a whole, and the composition of the soil silt and LF. The increase in the proportion of hydrophilic components in the composition of soil HS, as well as in the composition of HS silt and LF occurred simultaneously with an increase in the hydrophobicity of the surface of the solid phase of soil and with an increase in the carbon content in the soil, which indicates the stability of the system as a whole. Since the physical fractions of soils reacted more intensively to changes in the agrogenic load, compared with native soil samples, and changes in their qualitative composition were traced in two versions of the experiment, monitoring of hydrophobic-hydrophilic components of soil and soil granulodensimetric fractions is advisable to monitor and diagnose soil changes during agricultural use.

Organic matter of sod-podzolic soil after transition to a fallow state

Soil plays a crucial role in carbon sequestration in terrestrial ecosystems. It is known that the strengthening of carbon sequestration processes occurs with a decrease in the intensity of soil treatments. The study of changes in organic matter and physical properties of sod-podzolic soil 16 years after the transition from arable soils to a fallow state against the background of weak water erosion was carried out. A significant increase in the content and reserves of total carbon in fallow soil compared to arable soil was found, mainly due to carbon of the light fraction. On arable soil, the content of the light fraction in the lower part of the field was significantly higher than in the upper part, due to the washing away of light particles as a result of erosion, these differences were smoothed out on fallow soil. There are no significant changes in the density, density of the solid phase and total porosity in fallow soil at this stage of succession, compared with arable soil. In fallow soil, the content of macro-aggregates (including water-bearing ones) was noticeably higher, and the share of micro-aggregates was lower than in arable soil.

Adsorption of Fulvic Acid and Water Extractable Soil Organic Matter on Kaolinite and Muscovite

The interaction of organic matter with mineral components of the solid phase of soils is the most important process that regulates the cycle and balance of carbon in the biosphere. The adsorption of humic acids on minerals is accompanied by their fractionation in size, composition, and amphiphilicity, thus decreasing their heterogeneity. Despite a strong interest in studying the regularities and mechanisms of the interaction between natural organic matter and layered aluminosilicates, it is necessary to take into account the natural diversity of soil organic matter, adsorption conditions, and mineral composition. This study was designed to investigate the adsorption regularities of fulvic acid (FA) and water-extractable organic matter (WEOM) isolated from horizon H of peaty-podzolic-gleyic soil on kaolinite and muscovite. Sorbates and sorbents were examined by the following methods: high-pressure size exclusion chromatography (HPSEC), high-performance liquid chromatography (HPLC), and potentiometric titration. The specific surface areas of the sorbents were determined by the sorption of N2 molecules. We found that hydrophobic components of FA and WEOM are mainly adsorbed on mineral surfaces. The adsorption of FA and WEOM on kaolinite and muscovite is followed by decreased hydrophobicity of organic matter and decreased heterogeneity of its amphiphilic properties in an equilibrium solution. At pH levels around 6, sorption of organic matter from FA solution containing 19% and 81% hydrophilic and hydrophobic components, respectively, onto kaolinite and muscovite occurs mainly due to hydrophobic components. Hydrophobic interactions on siloxane surfaces are the main mechanism to fix FA on both minerals. Kaolinite adsorbs slightly more organic carbon per unit area than muscovite. The adsorption of WEOM from a solution with 41% hydrophilic and 59% hydrophobic components results not only from hydrophobic and hydrophilic components but also from hydrophobic and electrostatic interactions and depends on pH. The most hydrophobic fractions of organic matter are adsorbed from the hydrophobic components on the surface of both minerals. Under conditions of the performed experiments at pH &lt; 5, more WEOM is adsorbed on muscovite than on kaolinite.

1D_RnDPM: A freely available 222Rn production, diffusion, and partition model to evaluate confounding factors in the radon-deficit technique

The radon-deficit technique is a powerful tool to detect and delineate sub-surface accumulations of organic contaminants. Field measurements of 222Rn in soil air, however, are affected by several confounding factors that can lead to the misinterpretation of results. Among the most influential are: vertical and lateral changes of lithology, fluctuating contaminant saturations with depth, varying water saturation ratios along the soil profile and atmospheric (and, therefore, soil) thermal oscillations. To evaluate and minimize the effect of these confounding factors on the interpretation of the results of the Rn deficit technique, a Matlab® based multi-layer model of 222Rn production-partition-diffusion in unsaturated porous media (1D_RnDPM: One-Dimensional 222Rn Diffusion and Partition Model) has been developed and is freely available as Supplementary Material in this work. A laboratory protocol has also been proposed to obtain site-specific input parameters for the model, i.e., 222Rn equilibrium concentration (as determined by the accumulation chamber method), soil bulk density and soil solid-phase density. The model predictions have been contrasted with field information obtained from successive sampling campaigns in which 222Rn in soil air was measured at a site where the vadose zone, consisting of an anthropogenic backfill underlain by a silt layer, is affected by a complex mixture of benzene, phenol, (poly) chlorobenzenes, (poly) chlorophenols and hexachlorocyclohexane isomers, among other compounds. The model has successfully predicted the vertical profile of 222Rn concentrations in soil air, including the effect of the oscillations of the water table and of ground-level temperature. The results also underline that 222Rn measurements in subsoil air are representative only of local conditions around the sampling point, an expected result given that 222Rn maximum effective diffusion length is very limited. As a consequence, the influence of a highly fluctuating water table at the site goes undetected at the sampling depths used in the field campaigns. Main findingsThe combination of a numerical model and a laboratory protocol allows to predict the activity of 222Rn along the soil profile and to assess the influence of site-specific confounding factors.

Passive sampling of chlorophenols in water and soils using diffusive gradients in thin films based on β-cyclodextrin polymers

Chlorophenols (CPs) have been listed as priority control pollutants because of their high toxicity and wide range. An In-situ monitoring technique using diffusive gradients in thin films based on porous β-cyclodextrin polymers as binding materials (CDP-DGT), was established to monitor four typical CPs, namely, 4-Chlorophenol (4-CP), 2,4-Dichlorophenol (2,4-DCP), 2,4,5-Trichlorophenol (2,4,5-TCP), 2,4,6-Trichlorophenol (2,4,6-TCP) in water and soils. The performance of CDP-DGT are stable under the conditions of pH 3.5–9.3, ionic strength 0.001–0.500 mol L−1 and dissolved organic matter concentration 0–20 mol L−1. The adsorption capacities of CDP-DGT for 4-CP, 2,4-DCP, 2,4,5-TCP, 2,4,6-TCP were 57.80 μg cm−2, 98.82 μg cm−2, 95.69 μg cm−2 and 98.91 μg cm−2, respectively. The time-average weighted concentrations of four CPs determined by CDP-DGT at Sanjiangkou wharf (Yangtze river, China) were consistent with the results of grab sampling, indicating the feasibility of CDP-DGT application in actual water. In addition, the distribution of CPs in the red soil of Kunming and paddy soil of Yixing were also studied by CDP-DGT, and the desorption kinetics in the two soils were analyzed with the DIFS model. The higher the soil organic matter content is, the more CPs are distributed in the soil solid phase. CPs in both soils can be partially resupplied to soil solution from the soil solid phase and the higher the partition coefficient for labile CPs is, the stronger the supplement capacity is.

Post-agrogenic dynamics of soil properties of eroded agrochernozems in the forest-steppe zone of Western Siberia

Results of the study of a chronological series of post-agrogenic chernozems of slope lands of the forest-steppe zone of Western Siberia, characterised by a high degree of vertical and horizontal relief dissection, are presented. It was found that the rate of post-agrogenic transformation of abandoned soils depends on their regenerative features, the nature of the successional change of vegetation and the intensity of development of erosional processes. In the phytocenoses of young abandoned lands, 467.3 g/m2 of green phytomass and 114.9 g/m2 of aboveground mortmass are formed; in middle-aged fallows, the reserve of green phytomass is 511.2 g/m2 and aboveground mortmass is 632.7 g/m2. Total soil organic carbon accumulation in fallow soils occurs due to the formation of coarse (detrital) organic matter. No significant changes in particle size distribution as a result of the shift of arable soils to the fallow state were revealed. Bulk density was closely dependent on the structural organisation of the solid phase of soils, in which the content of macroaggregates, determining the ratio of volumes of aggregate and inter-aggregate porosity, water-holding capacity and water permeability of soils, increased. As a result of structural and functional changes in fertility indicators at the stages of young and middle-aged deposits, a high degree of recoverability was found for the content of labile humus, bulk density and aggregate composition.

Nano zero-valent iron-induced changes in soil iron species and soil bacterial communities contribute to the fate of Cd

Nano zero-valent iron (nZVI) is used for soil remediation; however, the impact of nZVI on soil solid iron phases and its interactions with soil microorganisms in relation to the fate of Cd in soil remains unclear. In the current study, we investigated the mechanisms underlying the change in mobility of Cd in exogenous Cd-contaminated soil with nZVI and γ radiation treatments. The results showed that nZVI treatment decreased Cd availability but also increased the soil pH and dissolved Mn and poorly crystalline Fe contents. However, the increased poorly crystalline Fe(II) levels contributed to a reduction in Cd availability in soils treated with nZVI by immobilizing Cd associated with Fe oxides, rather than by increasing pH or Mn oxide levels. Moreover, Cd stabilization efficiency was higher in γ-irradiated soils than in non-irradiated soils regardless of the Cd level, with noticeable differences in bacterial community composition between the non-irradiated and irradiated soils. The genera Bacillus, Pullulanibacillus, and Alicyclobacillus are important in the redox of poorly crystalline Fe(II)-containing minerals in non-irradiated soil. This research provides a new method for further improving the Cd stabilization efficiency of nZVI in combination with microbial iron oxidization inhibitors.

Using an improved Si-rich husk ash to decrease inorganic arsenic in rice grain

Paddy rice is efficient at arsenite accumulation by sharing the uptake and transport pathway for silicic acid. To limit As entry into rice by increasing soil Si availability, rice husk with concentrated Si deposition was subject to an ethanol-aided open combustion in this work to promote Si release from organic matrix. Compared to original husk, the content of amorphous silica was almost tripled in the resultant ash (Si-ash) with an apparent elimination of hydrocarbon groups. Following its incorporation into soil, 3.4-fold higher Si dissolution was maintained in rice rhizosphere compared to control, which was accompanied by 15.9–40.5% decrease in porewater As from tillering to harvest. Correspondingly, As sequestration in soil solid phase and root plaque increased by 8.0% and 26.9% with Si-ash, which could result from promoted FeAs co-precipitation by the liming effect of Si-ash and was linked to a notable decline in As transport through node I. Consequently, inorganic As (iAs) in white rice decreased from 0.36 mg kg−1 in control to 0.17 mg kg−1 with Si-ash, which is 15% lower than Chinese food safety standard. Results from this study highlight the advantage of Si-ash in securing rice production by mitigating iAs accumulation in white rice with fortified Si nutrition.

Limestone and gypsum reapplication in an oxisol under no-tillage promotes low soybean and corn yield increase under tropical conditions

Limestone and gypsum combined use in no-tillage (NT) systems can favor soil acidity correction and improve nutrient availability in-depth with positive effects on crop production. There are still doubts about the necessity to restart the NT when the soil’s natural acidity was not corrected properly. The study evaluated i) the changes in the vertical distribution of nutrients and the acidity attributes in the soil solid phase, ii) the crop yields resulting from limestone reapplication strategies, associated or not with superficial gypsum application, and iii) the need to restart the NT system, with limestone incorporation to correct the re-acidification of an Oxisol in the Cerrado biome. Six treatments were evaluated, following the NT maintenance: i) no limestone reapplication and no gypsum application (NL), ii) superficial gypsum application (NL+), iii) superficial limestone reapplication (SL), and iv) superficial limestone reapplication and superficial gypsum application (SL+); or restarting the NT: v) limestone reapplication and incorporation (IL), and vi) limestone reapplication and incorporation followed by superficial gypsum application (IL+). Seven years after the experiment implementation, the soil was sampled in eight stratified layers down to the 50 cm depth in the experimental plots and under the Cerrado natural vegetation (CNV). The chemical attributes related to soil acidity, nutrient availability, and the soybean and corn yields were evaluated. The soil under CNV has lower pH and greater aluminum saturation (Alsat) than the NL treatment, whose natural potential acidity was corrected 36 years ago and remained without limestone reapplication for 11 years. Such results indicate that the soil re-acidification process is slow. Superficial limestone reapplication (SL and SL+) reduced soil Alsat down to 25 cm but did not neutralize it completely. Limestone incorporation (IL and IL+) had little effect on Alsat distribution in-depth when compared to superficial limestone application. Gypsum application increased Ca content and lead to Mg displacement in soil depth, but did not affect Al dynamics, nor the crop yields. The effects of limestone and gypsum reapplication on the soil surface under NT provided a greater nutrient accumulation in the soil superficial layer, especially Ca and Mg. Soybean showed a low but positive yield response to the limestone reapplication, regardless of the method (average yield increase of 252 kg ha−1 year−1), but corn yield was less affected. There is no need to incorporate the limestone neither to apply gypsum in agricultural lands that had their natural acidity corrected properly in the past.