Soil Cation Exchange Capacity Research Articles

The Ameliorating Effect of Alkaline Industrial Byproducts in the Presence of Exogenous Low-Molecular-Weight Organic Acids on an Acidic Brown Soil from Jiaodong Peninsula of China

ABSTRACT It has been proposed that the quality of acidic soils can be improved in the presence of alkaline byproduct amendments containing silicon (Si), calcium (Ca), magnesium (Mg), and potassium (K). In the present study, we aimed to explore the effect of byproduct amendments on ameliorating acidic soil in Jiaodong Peninsula of China in the existence of different types of low-molecular-weight organic acids (LOAs, such as malic acid, citric acid, oxalic acid, and succinic acid) that are usually excreted by plant roots. Therefore, a 60-day incubation test was carried out to assess the effect of byproduct amendments and LOAs on soil physicochemical properties, soil available Mg and Ca, cation exchange capacity (CEC), soil respiration, and enzyme activities. The results showed that in the presence of LOAs, the byproduct amendments could still increased the soil pH and decreased the soil exchangeable acid and exchangeable Al3+. Compared with the control group (CK), all byproduct amendment-containing treatments could increase soil available Mg and Ca, soil CEC, soil respiration, and soil sucrase (S-SC) activity. The addition of byproduct amendments could significantly improve the chemical and biological properties of the acidic brown soils in Jiaodong Peninsula of China. However, LOAs, especially the LOAs that could precipitate with Ca in byproduct amendments, negatively impair the ameliorating effect on acidic soil compared with byproduct amendments alone treatment. When using byproduct amendments to ameliorate acidic soil, the type of LOAs secreted by plant roots was an influencing factor that must be considered.

Alkaline humic acid fertilizer alters the distribution, availability, and translocation of cadmium and zinc in the acidic soil–Sauropus androgynus system

Humic acids (HA) are a popular soil additive to reduce metal availability, but they have the drawbacks of reduced effectiveness over time and a significant reduction in soil pH. An alkaline humic acid fertilizer (AHAF) combining alkaline additives with HA was developed to overcome such drawbacks. A field experiment was conducted to investigate the effects of different AHAF application rates on the physicochemical properties, bioavailability, accumulation, and translocation of Cd and Zn heavy metals in Sauropus androgynus grown in acidic soil. Based on our results, the 100AF (100% AHAF) treatment significantly increased soil pH, cation exchange capacity (CEC), and organic matter content (OM) after one year of application. Compared with the control treatment (CK), the application of different rates of AHAF resulted in a 37.1–40.3% decrease in soil exchangeable Cd fractions (Exc-Cd) and an increase in the humic acid-bound Cd fractions (HA-Cd) Fe- and Mn-oxide-bound Cd fractions (OX-Cd), and organic matter-bound Cd fractions (OM-Cd) by 9.5–64.6%, 24.8–45.1%, and 158.8–191.2%, respectively (P < 0.05). The different AHAF treatments decreased the Res-Zn, Exc-Zn, and OM-Zn fractions by 69.6–73.0%, 7.4–23.9%, and 18.1–23.2%, respectively (P < 0.05), and increased the HA-Zn fraction by 8.4–28.1%. In the control treatment, the bioconcentration factors (BCFs) for Cd and Zn in different S. androgynus plant organs were in the following order: (Cd) Leaves > Stems > Branches > Roots > Edible branches; (Zn) Roots > Stems > Leaves > Branches > Edible branches. The transfer factors (TFs) of Cd and Zn in S. androgynus were classified as follows: TF2 > TF1 > TF3 > TF4. Thus, S. androgynus stems, and roots had a strong ability to transport Cd and Zn to the leaves. Compared with CK, the 100AF treatment significantly increased the BCFs for Zn in all plant parts (except BCFedible branches). In contrast, it significantly decreased all BCFs and TFs for Cd and the TF4 for Zn, effectively reducing Cd and Zn accumulation in the edible branches of S. androgynus. Soil pH, CEC, OM, and HA-M fraction were highly and significantly negatively correlated with Cd and Zn content in edible branches (P < 0.001). Stepwise multiple linear regression analysis revealed that the soil HA-M fraction was the key contributing factor for Zn accumulation and translocation in S. androgynus. Moreover, based on our findings, the absorption, uptake, and translocation of Cd and Zn were mainly determined by metal speciation and the pH in the soil. Moreover, the competitive antagonistic mechanisms between Zn and Cd absorption also affected their accumulation in S. androgynus. Thus, AHAF can be used as a soil amendment to sustainably improve acidic soils and effectively reduce Cd and Zn accumulation in edible branches of S. androgynus.

Effects of Feldspathic Sandstone Addition on Microbial Biomass, Soil Enzyme Activity, and Bacterial Community Structure of Sandy Soil

Desertification is a serious environmental problem worldwide. In this study, a long-term field experiment was conducted to investigate the effects of feldspathic sandstone on remediation of sandy soil. The results indicated that feldspathic sandstone addition increased the soil moisture, available N, P, K content, organic matter content, and cation exchange capacity of the sandy soil. The microbial biomass carbon increased 130.12%, 135.45%, and 120.34% in the compound soil with the feldspathic sandstone and sand mass ratio of 1:1, 1:2, 1:5, respectively, and the microbial biomass nitrogen increased 102.38%, 107.45%, and 81.69%, respectively. Meanwhile, soil urease, catalase and surface activity were significantly enhanced (p < 0.05). Illumina sequencing revealed the differences of bacterial community structure between compound soil and sandy soil. The Acidobacteriota was more abundant in sandy soil while Proteobacteria and Firmicutes were more abundant in compound soil. Proteobacteria and Firmicutes are involved in nutrient cycling and plant residues degradation, respectively. Their enrichment is beneficial for soil quality improvement. Redundancy analysis indicated that available N, K, organic matter and soil moisture content are key factors that involved in the assembly of bacterial community. Overall, adding feldspathic sandstone into sandy soil improved soil physiochemical properties, enhanced soil microbial activity and optimized the bacterial community, which would ultimately improve the quality and ecological function of the sandy soil.

Optimization of sample preparation and data evaluation techniques for X‐ray fluorescence prediction of soil texture, pH, and cation exchange capacity of loess soils

AbstractUse of X‐ray fluorescence (XRF) spectrometry for estimation of soil texture, pH, and cation exchange capacity (CEC) is desirable given the time‐consuming nature of traditional methods. Recent studies have shown promising results; however, further investigation is required to determine the effects of sample preparation and data evaluation techniques on accuracy. Our objective was to compare (I) a simple but well‐founded approach, combining measurement of powder samples and modeling with elemental contents as predictors in stepwise multiple linear regressions (MLR), with alternative approaches including (II) use of partial least squares regression (PLSR), (III) sample preparation as a pressed pellet, and (IV) spectral intensities as predictors (20 kV, 40 kV, and concatenated 20 + 40 kV). A total of 395 loess soils from three arable fields were used with a fivefold random training‐testing approach and a hold‐one‐site‐out training‐testing approach. With random partitioning, clay, silt, and sand accuracy with approach I was excellent (ratio of performance to interquartile distance in validation (RPIQv) = 8.5–12.9), while pH and CEC estimations were satisfactory to excellent (RPIQv = 2.0–2.5 and 2.2–3.3, respectively). Differences between MLR and PLSR were negligible. Increases in accuracy with pellet samples were 1%–13% of RPIQv for 20 kV intensities, but effects were inconsistent for other predictors. The optimal predictor varied by property, and differences ranged from 3% to 13% of RPIQv. Improvements to accuracy from Approach I to the best alternative were largest for texture (10%–15%) but may be superfluous given the excellent accuracy across all approaches. Although the leave‐one‐site‐out training resulted in variable performance, inclusion of soils from the target site in training assured reliable accuracy.

Simulated warming decreases acidity of forest topsoil under Norway spruce (Picea abies (L.) H.Karst.) stands in the Western Carpathians

Global warming is affecting the montane forests of the temperate zone, causing a number of changes in all elements of the ecosystem, including the soil. Norway spruce forests, weakened by ongoing decay over several decades, are likely particularly sensitive to climate-induced changes. The response of soil cation exchange capacity components of spruce stands to warming is not well understood. We have assumed that warming will cause significant changes in pH, disrupting ion-exchange relationships in the soil. To the best of our knowledge, the present study is the first devoted to examining the mechanisms of soil pH change in temperate forest under the influence of warming. The forest in-situ experiment, simulating the soil warming for 578 days, was performed. Laboratory analyses included measurements of pH, and concentrations of carbon and exchangeable forms of calcium, potassium, magnesium, sodium, and aluminum. Shortly after the beginning of simulated warming (84 days), we observed a significant increase in the pH of the topsoil horizons. On average, in the warmed organic (O) horizon, the pH increased by 0.21, and in the mineral (A) horizon by 0.29 pH units. Based on previous studies, the pH increase was most likely triggered by an increase in ammonium-nitrogen content in the warmed soil. Using the Henderson–Hasselbalch equation to model the pH revealed that, in the O horizon, the pH increase is a result of the presence of weaker organic acids, less able to release hydrogen ions during dissociation. In the A horizon, the increase in pH was explained by an increase in abundance of aluminum ions, probably migrating upward from deeper soil layers. We consider that the ion-exchange mechanisms described here will contribute to an improved understanding of the complex processes of spruce forest dieback in the context of climate warming.

Research Progress of Biochar and Pollution Control

In recent years, due to the impact of climate change caused by the emission of greenhouse gases such as carbon dioxide, nitrous oxide and methane, scientists have begun to pay attention to the use of biochar, because it helps to capture and remove greenhouse gases in the atmosphere by means of biochar storage, converting it into a very stable form and storing it in the soil for thousands of years. This paper focuses on the hazards of organic pollutants, the treatment of pollutants by biochar and the benefits of environmental remediation. Biochar is the product of biomass energy raw material after pyrolysis, and its main component is carbon molecule. In terms of pollution treatment, biochar has a strong adsorption capacity for organic pollutants such as phenol, and can also improve soil heavy metal pollution by increasing soil cation exchange capacity (CEC) and PH. In addition, biochar is also used in low-temperature NH3-SCR denitrification catalysts to deal with nitrogen oxides in atmospheric pollutants and other aspects. Biochar is easy to ignite, non-polluting, smokeless and tasteless, less residue after combustion, light weight and high calorific value, the use of performance is better than most similar materials, known as the main force of human new energy and future fuel. The purpose of this paper is to provide the basis and reference for the development of biochar basic science and application technology.

Biogeography and environmental preferences of Butia yatay (Mart.) Becc.

During the Quaternary, Chaco Phytogeographic Domain (Chaco) flora in subtropical South America experienced temperature and humidity fluctuations, primarily driven by wind dynamics, leading to significant shifts in species distribution. The palm Butia yatay is endemic to the Chaco and thrives in areas characterized by a warm-rainy climate and mostly restricted to sandy soils. To investigate the current geographic distribution of suitable habitat for B. yatay while assessing the significance of soil variables, we employed two distinct algorithms in species distribution modeling (SDM). We also determined whether the distribution of B. yatay has changed since the Pleistocene and whether these changes align with previously proposed Pleistocene refugia. In the present SDMs, we considered two separate sets of predictors, one set with bioclimatic variables only and the other set with bioclimatic topographic and soil variables. Additionally, we reconstructed the historical geographic distribution of suitable habitats using bioclimatic data. Our results suggested that the primary determinants of B. yatay's current distribution include precipitation and temperature of the driest month and soil cation exchange capacity. Incorporating soil variables affected the estimated size and range of suitable areas. Projections into the past indicated similar suitable habitat distributions during interglacial periods compared with the present. During the Last Glacial Maximum, climatically suitable habitat may have shifted northward, partially overlapping with previously suggested Pleistocene refugia located between the Paraná and Uruguay Rivers. These findings indicate the main factors driving the distribution and ecology of B. yatay and enhance understanding of subtropical flora shifts during the Quaternary. The approach also may prove valuable for other studies within the Chaco.

Soil-Derived Dust PM10 and PM2.5 Fractions in Southern Xinjiang, China, Using an Artificial Neural Network Model

Soil-derived dust emissions have been widely associated with health and environmental problems and should therefore be accurately and reliably estimated and assessed. Of these emissions, the inhalable PM10 and PM2.5 are difficult to estimate. Consequently, to calculate PM10 and PM2.5 emissions from soil erosion, an approach based on an artificial neural network (ANN) model which provides a multilayered, fully connected framework that relates input parameters and outcomes was proposed in this study. Owing to the difficulty in obtaining the actual emissions of soil-derived PM10 and PM2.5 over a broad area, the PM10 and PM2.5 simulated results of the ANN model were compared with the published results simulated by the widely used wind erosion prediction system (WEPS) model. The PM10 and PM2.5 emission results, based on the WEPS, agreed well with the field data, with R2 values of 0.93 and 0.97, respectively, indicating the potential for using the WEPS results as a reference for training the ANN model. The calculated r, RMSE and MAE for the results simulated by the WEPS and ANN were 0.78, 3.37 and 2.31 for PM10 and 0.79, 1.40 and 0.91 for PM2.5, respectively, throughout Southern Xinjiang. The uncertainty of the soil-derived PM10 and PM2.5 emissions at a 95% CI was (−66–106%) and (−75–108%), respectively, in 2016. The results indicated that by using parameters that affect soil erodibility, including the soil pH, soil cation exchange capacity, soil organic content, soil calcium carbonate, wind speed, precipitation and elevation as input factors, the ANN model could simulate soil-derived particle emissions in Southern Xinjiang. The results showed that when the study domain was reduced from the entire Southern Xinjiang region to its five administrative divisions, the performance of the ANN improved, producing average correlation coefficients of 0.88 and 0.87, respectively, for PM10 and PM2.5. The performances of the ANN differed by study period, with the best result obtained during the sand period (March to May) followed by the nonheating (June to October) and heating periods (November to February). Wind speed, precipitation and soil calcium carbonate were the predominant input factors affecting particle emissions from wind erosion sources. The results of this study can be used as a reference for the wind erosion prevention and soil conservation plans in Southern Xinjiang.

Biomonitoring of Potentially Toxic Elements in an Abandoned Mining Region Using Taraxacum officinale: A Case Study on the “Tsar Asen” Mine in Bulgaria

Mining is a significant industrial and economic activity, but it can also result in ore waste that contains several potentially toxic elements (PTEs). Furthermore, the wide range of observed transfer and accumulation factors suggests that not only the soil element concentrations but also the soil characteristics are important for uptake, which is recognized as a serious problem with potential impacts on human health and ecosystems. The aim of this study was to perform a pollution risk assessment of a region near an abandoned mine using suitable biomonitoring followed by multivariate statistical treatment of the obtained results. The content of PTEs in the soil and plant samples was determined to exceed the background concentrations typical for Bulgaria. The observed concentrations of copper in this study’s soil samples exceeded 2 to 16 times the maximum permissible values. The Taraxacum officinale concentrations for PTEs, particularly for Cd (5.13 mg/kg), were higher than the background levels. The obtained results for PTEs show significant TFs for Cd and Sn, while the AFs outline a significant accumulation of Cd and Sb. The applied multivariate statistical approaches revealed differences between the sampling locations and relationships between the elemental transfer/accumulation factors and soil cation exchange capacity. The outcomes from the statistical analysis confirm that the usage of both element factors and soil properties in biomonitoring studies are essential for reliable risk assessment.

Revitalizing the Biochemical Soil Properties of Degraded Coastal Soil Using Prosopis juliflora Biochar.

Biochar is an effective soil amendment with capabilities of boosting carbon sequestration and enhancing soil fertility, thus enhancing plant growth and productivity. While numerous studies have documented the positive effects of biochar on improving soil properties, a number of studies have reported conflicting results. Therefore, the current study was conducted to evaluate the impact of Prosopis juliflora biochar (0, 2.5, 5.0, and 7.5 t ha-1) on soil biochemical properties in Coastal Kenya to ascertain biochar's potential for soil fertility improvement. A randomized complete block design was used for setting up the experiment with three replicates, while Casuarina equisetifolia L. was planted as the test crop. Soil sampling for nutrient analysis was conducted quarterly for 12 months to assess nutrient dynamics under different biochar rates in the current study. Compared to soil untreated with Prosopis juliflora biochar, the results showed that there was a significant increase in soil pH by 21% following biochar utilization at the rate of 7.5 t ha-1. Total nitrogen was increased by 32% after the biochar application, whereas the total organic carbon was increased by four folds in comparison to biochar-untreated soil. Available phosphorus was increased by 264% following biochar application in comparison to the control treatment. In addition, the application of biochar resulted in an increment in the soil exchangeable cations (Ca2+, K+, Mg2+) across the assessment periods. Soil cation exchange capacity (CEC), bacteria and fungi were enhanced by 95, 33 and 48%, respectively, following biochar application at 7.5 t ha-1 in comparison to untreated soil. In conclusion, these results strongly suggest improvement of soil biochemical properties following Prosopis juliflora biochar application, thus providing potential for soil fertility improvement in regions such as the one in the study.

Kaolinite reduced Cd accumulation in peanut and remediate soil contaminated with both microplastics and cadmium

Microplastics (MPs) increase the effective state of heavy metals (HMs) in soil and seriously threaten the yield and quality of peanuts (Arachis Hypogea L.). Kaolinite (KL) has the potential to ameliorate MP- and HM- contaminated soils, but the mechanism of action between them is not well understood. Therefore, 60-day experiments were conducted, where KL (1 %, 2 %) and MPs (0.1 %, 1 %) were individually or jointly mixed into soils with different cadmium (Cd) concentrations (0.5, 2.5, and 5.0 mg·kg−1) to cultivate peanuts in a greenhouse. Finally, soil-bioavailable Cd, peanut dry weight, peanut Cd concentrations, the pH, cation exchange capacity (CEC), dissolved organic carbon (DOC), microbial biomass carbon (MBC) and microbial biomass nitrogen (MBN) were determined. It was shown that MPs negatively affected the peanut dry weight and increased the content of soil-bioavailable Cd and Cd concentration in peanut. In the MP- and Cd-contaminated soils, KL mitigated the negative influence of MPs by increasing the dry weight of peanuts by 8.40 %−40.59 %, decreasing the soil-bioavailable Cd by 23.70–35.74 %, and significantly decreasing peanut Cd concentrations by 9.65–30.86 %. The presence of MPs decreased soil pH (7.69–7.87) and the CEC (20.96–23.95 cmol·L−1) and increased the soil DOC (1.84–2.26 mg·kg−1). KL significantly increased soil pH (7.79–8.03) and the CEC (24.96–28.28 cmol·L−1) and mitigated the adverse influence of MPs on the pH and CEC of Cd-contaminated soils. A regression path analysis (RPA) evidenced that KL decreased Cd accumulation in plants by changing the properties of soil contaminated with MPs and Cd. The research results revealed the mechanism of KL on peanut growth and Cd absorption in MP- and Cd-contaminated soil. The results of this study provide a foundation to improve the quality of MP- and HM-contaminated soils and realize safe peanut production.

A novel iron-based composite modified by refinery sludge for fixing Pb, Zn, Cu, Cd, and As in heavy metal polluted soil: Preparation, remediation process and feasibility analysis

In this study, we prepared a novel iron-based composite (NIC) via a one-step reduction method utilizing refinery sludge (RS) as the reducing agent and iron ore (IO) as the iron source, allowing for the concurrent stabilization of multiple heavy metals (HMs) in soil. The loose, porous structure of NIC provided ample active sites, including Fe0, CaAl2Si2O8, fixed carbon, and a small amount of active amorphous substances. After 60 days of soil remediation using 5% NIC, the bioavailable content of HMs Cu, Zn, Pb, Cd, and As was reduced by 71.55%, 49.62%, 91.35%, 61.37%, and 41.45%, respectively. Upon magnetic recovery and analysis of NIC in soil, HMs were found to have been enriched in the material, forming new phases like FeAsO4, ZnFe2O4, among others. Thus, the immobilization mechanism of HMs included adsorption, co-precipitation and complexation etc. Furthermore, NIC enhanced soil pH and cation exchange capacity, elevating the soil's ability to retain heavy metal cations. Lastly, cost-benefit analysis revealed that RS as a reducing agent could lower the production cost of environmental remediation materials. Furthermore, HM leaching toxicity analysis verified the safety of its usage. Overall, our findings offer a promising procedure for both the resource utilization of refinery sludge and multi-metal co-contaminated soil remediation.

Soil properties change, and arbuscular mycorrhizal fungi associated with plants growing on the post-gold mining land of Bombana, Indonesia

&lt;p&gt;This study aimed to investigate the effect of gold mining on soil properties. Soil samples were taken from the post-gold mining land, the property of PT Panca Logam Nusantara and PT Alam Buana Indonesia, and a nearby natural forest in Bombana, Southeast Sulawesi Province. The next step focused on specifying soil pH, total nitrogen (TN) and carbon (TC) concentration, C/N ratio, available phosphorus (P) concentration, cation exchange capacity (CEC), and exchangeable K, Na, Mg, Ca, Fe, Mn, Cd and Pb concentration, texture and spore amount, AMF resource and AMF colonization. The result shows that the pH in post-gold mining soil was higher than that in natural forest soil. Meanwhile, TN, TC, available P, and CEC of post-gold mining soil got lower compared with these of natural forest soil. The texture in the post-mining soil was clay loam, while that in natural forest soil was clay. Total of 10 AMF species belonging to five genera and three families were found in a post-gold mining area. Soil pH, CEC, soil texture, Mn, and total Fe had a negative relation with AMF colonization and spore count, while organic C, total N, C/N ratio, P&lt;sub&gt;2&lt;/sub&gt;O&lt;sub&gt;5&lt;/sub&gt; and silt had a positive relation. Sand was proven to have a strong and positive correlation with the amount of AMF species. Adding organic matter and fertilization as well as applying mycorrhizal biofertilizers, were urgently required to support the effort in restoring post-gold mining soil.&lt;/p&gt;

The use of animal manure for improving chemical properties of degraded Ultisol, yield, and secondary metabolic of Zingiber montanum

Ultisols in Indonesia have the potential for agricultural development, but the soils have low pH and nutrient contents that hinder plant growth and yield. Using animal manure can be an alternative to improve soil productivity and crop yields. This study aimed to examine the effects of animal manure on the chemical properties of Ultisol, yield, and secondary metabolic of &lt;em&gt;Zingiber montanum&lt;/em&gt;. The treatments tested were combinations of types of manure (cow and chicken manure) and manure application levels, namely P0 (control), P1 (cow manure 20 t/ha), P2 (cow manure 40 t/ha), P3 (cow manure 60 t/ha), P4 (chicken manure 20 t/ha), P5 (chicken manure 40 t/ha), and P6 (chicken manure 60 t/ha). The results showed that the application of chicken manure of 60 t/ha increased N and P contents of the soil, and the application of cow manure of 60 t/ha increased soil cation exchange capacity. The application of cow manure of 60 t/ha gave the highest plant height, the number of leaves, and the number of at 18 weeks after planting, while the application of chicken manure dose of 60 t/ha produced the longest plant roots. The highest fresh and dry rhizome weight was observed for the 60 t/ha cow manure treatment. The highest secondary metabolic levels in each parameter were found in dry rhizomes (phenolic, flavonoid, and tannin) and fresh rhizomes (phenolic and flavonoid), with the highest tannin compound in the treatment of 40 t chicken manure/ha. The application of chicken manure at a dose of 60 t/ha resulted in a strong antioxidant yield in fresh and dry rhizomes.

Preparation of two types plant biochars and application in soil quality improvement

Soil degradation is a global problem that endangers sustainable development. Biochar is a solid, stable, carbon-rich, and highly aromatic material prepared using plant feedstock with a rich pore structure, high specific surface area, and high capacity for holding water and nutrients. This study selected two typical plant resource raw materials, Spartina alterniflora (P. australis) and Spartina alterniflora (S. alterniflora), to prepare biochar at different temperatures, and then investigated the effects of different raw materials and preparation temperatures on the biochar's characteristics. After re-activation treatment, soil improvement experiments were conducted under different carbon application rates. The prepared biochar was alkaline, and contained abundant oxygen-containing functional groups and nutrients (including C, N, Ca, Na, and Mg). Biochar addition had significant effects on the soil microbial community and soil enzyme activity. Finally, by calculating the membership function and factor weights, the various physicochemical and biological properties of the soil were quantified in the form of soil quality indices. The results showed that biochar application had a significant promoting effect on soil quality, mainly through providing rich nutrient sources, enhancing the soil cation exchange capacity and therefore the nutrient effectiveness, and increasing the ability of soil to retain nutrients. The application of biochar (different types) has changed the original nutrient composition, microbial community, and enzyme activity of the soil, and under the combined action of these factors, the soil quality index (SQI) has been improved. This study provides a feasible soil fertility improvement strategy.

Physicochemical properties of environmental media can affect the adsorption of arsenic (As) by microplastics

Microplastics are emerging pollutants that can adsorb heavy metals and threaten human health through food chain. Recently, there has been increasing interest in understanding the adsorption behavior of heavy metals by microplastics in farmland soil. In particular, arsenic (As), as a carcinogen, has the potential to be adsorbed by soil microplastics. However, the mechanisms and controlling factors of As adsorption by microplastics in farmland soil under natural conditions are still unknown. Here, microplastics and As were respectively added to farmland soils with different physicochemical properties from twelve provinces of China for adsorption experiment. We performed surface analysis of microplastics, quantified As accumulation through quasi-first-order kinetic equation and developed regression models to screen the factors controlling As adsorption. The results showed that the adsorption of As by soil microplastics was a chemical process accompanied by the loss of electrons from oxygen-containing functional groups. Soil cation exchange capacity (CEC) was the main factor controlling the adsorption rate, while soil organic matter (SOM), total nitrogen (TN) and CEC mainly influenced the equilibrium adsorption capacity. This is the first report on microplastic-As adsorption in natural soil, which allows deeper insights into risk assessment, prediction and control of microplastic-As pollution in agricultural soil.

Using the quantitative ion character-activity relationships (QICAR) model to predict the solid-liquid release of metals in soil

Dissolved metals in the soil’s liquid phase are more easily absorbed by biological tissues, thus posing potential risks to living organisms. Therefore, studying the solid-liquid partition coefficient (Kd) of metals in the soil helps understand their environmental risks. We collected 102 Kd data of metals in soil from the literature to build a quantitative ion character-activity relationship model (s-QICAR) based on the metals’ physicochemical properties. Correlation analysis showed ten elemental physicochemical properties related to Kd, including covalent bond index, atomic mass, and first hydrolysis constant, with R2 = 0.502–0.989. Through comparative screening, 39s-QICAR models were finally established, including covalent bond index and first hydrolysis constant. The established s-QICAR model predicted the Kd values of Mo, Sb, and La in the 39 soil samples, ranging from 21 to 19978. Finally, a coupling analysis was conducted between Kd-metal and soil physicochemical properties. The s-QICAR model with covalent bond index as the independent variable was mainly affected by soil pH and cation exchange capacity, while the s-QICAR model with first hydrolysis constant was influenced primarily by clay content. Therefore, this study established a predictive model for soil Kd, providing a basis for soil environmental risk assessment and management. Environmental ImplicationDissolved metals present in the soil liquid phase are more easily absorbed by biological tissues, thus posing potential risks to living organisms. Therefore, studying the solid-liquid partition coefficient (Kd) of metals in the soil helps understand their environmental risks. Common Kd values are obtained by measuring the content of soil solid and liquid phase metals. However, this method is time-material consuming. We study the relationship between element properties and their Kd, then establish a model that does not rely on measured data to predict Kd of soil elements, providing a basis for soil environmental risk assessment and management.

Effects of Soil and Water Conservation Practices and Slope Gradient on Selected Soil Physicochemical Properties in Ejersa Watershed, Toke Kutaye District, Ethiopia

This study was conducted to assess the effects of soil and water conservation practices and slope gradients on selected physicochemical properties of soil at Ejersa Watershed based on a total of 18 composite soil samples collected and analyzed using standard laboratory procedures. The values of pH, electrical conductivity, cation exchangeable capacity, organic carbon, organic matter, total nitrogen, and available phosphorus determined in soil samples collected from conserved and nonconserved plots were 6.4 and 6.16, 40.26 mS/m and 15.12 mS/m, 33.51 meq/100 g and 21.56 meq/100 g, 2.66% and 2.24%, 4.58% and 3.86%, 0.24% and 0.15%, and 29.45 ppm and 17.68 ppm, respectively. Soil pH, electrical conductivity, moisture, total nitrogen, and available phosphorus were significantly different ( p &lt; 0.01 ) between treated and untreated plots and among the slope classes. Values of soil organic carbon and organic matter showed significant differences ( p &lt; 0.05 ) between land types but not among the slope classes. Soil cation exchange capacity showed significant difference ( p &lt; 0.05 ) between land types as well as among the slope classes. Relatively, higher values of many of the physicochemical parameters were recorded in samples collected from the treated land and lower slopes which might be attributed to the deposition effects of the conservation practices and decline in the rate of soil erosion.

Key factors influencing arsenic phytotoxicity thresholds in south China acidic soils

Arsenic (As) toxicity threshold values (TTVs) for plants are fundamental to both establishing regional As reference values in soil and performing risk assessment. However, TTVs vary with plant species and soil types. In this study, a hydroponic experiment with 16 plant species was conducted to screen the most As-sensitive plant species. The results showed that the EC20 (available As concentration at which shoot biomass or height is inhibited by 20%) values were 1.38–104.4 mg L−1 for shoot height and 0.24–42.87 mg L−1 for shoot fresh biomass. Rice was more sensitive to As toxicity than the other species. Therefore, it was chosen as the ecological receptor in the pot experiment on As phytotoxicity in nine types of soils collected from Fujian Province in South China. The EC10 and EC20 with respect to rice shoot height were 3.72–29.11 mg kg−1 and 7.12–45.60 mg kg−1, respectively. Stepwise regression analysis indicated that free iron oxide concentration is the major factor that affects As bioavailability in soil, and ECx (x = 10, 20, and 50) of soil available As for shoot height was positively related to free iron oxide concentration in soil. In addition, soil cation exchange capacity, clay (<0.002 mm) content, and exchangeable magnesium content are also important factors influencing As phytotoxicity in acidic soils. The regression models can be used to predict As phytotoxicity in acidic soils.

Biological nitrogen fixation in rice paddy soils is driven by multiple edaphic factors and available phosphorus is the greatest contributor

Biological nitrogen fixation (BNF) is important for sustainable rice cultivation. Various edaphic factors have been individually evaluated for their effects on BNF in paddy soils. However, no single factor could fully explain the different soil outcomes. Paddy BNF is more likely to be simultaneously influenced to various degrees by combinations of several factors; however, the relative importance of the interaction of multiple edaphic factors on the regulation of BNF in rice soils is still unclear. Twenty-seven paddy soil samples with different soil properties were collected from major cropping areas in southwest and northeast China. Rice was transplanted into pots of these soils and grown in a 15N2 enriched airtight chamber. Estimation of BNF was based on measurements of 15N enrichment in the different soils and rice plants at the end of a 77-d incubation period. BNF amounts ranged from 0.66 to 12.3 kg ha−1. BNF had a significant positive relationship with available phosphorus (AP) and significant quadratic relationships with available molybdenum (AMo) and total soil nitrogen (TN). AP explained 42% of the observed variation in BNF, TN explained 17%, and AMo explained 13%. The specific interaction between the soil cation exchange capacity (CEC) and available soil N (ASN, as determined by rice N uptake) accounted for 28% of the variation. BNF was reduced when AP was < 14 mg kg−1, AMo < 0.09 mg kg−1, or when TN was > 3.2 g kg−1. These results provide valuable benchmarks that could be used to guide farmers in managing their soils to improve the potential contribution of paddy BNF to soil fertility.