Soil Content Research Articles

Hybrid neuro-fuzzy models for assessing the optimum moisture content of lime cement-treated soil

Hybrid neuro-fuzzy models for assessing the optimum moisture content of lime cement-treated soil

Accumulation ability of trace metals by silver birch leaves in areas contaminated by Zn–Pb ore processing: Effects of excessive trace metal accumulation on specialized metabolism

The study was carried out in the most industrialised region of southern Poland. Four areas were selected for the study: the vicinity of the Miasteczko Śląskie Zn–Pb-works (ZW; with three transects selected: A, B, and C), and the metalliferous waste heaps (H1, H2, H3). Samples were taken from the surface soil layer, while only mature silver birch (Betula pendula Roth) trees (3–4 m high) growing spontaneously in the study area were selected for the collection of leaves. The analysis of metals including trace metals (TMs; Ag, Ca, Cd, Cr, Cu, Fe, K, Mg, Mn, Ni, Pb, Tl, and Zn) in the soil and leaves, as well as the contents of specialized leaf compounds belonging to polyphenols were performed. In general, the B. pendula trees in transects A and B located within 500 m of the furnaces exhibited 3–9 times higher content of TMs in their leaves compared to the plants located further away from the Zn smelter. In contrast, the quantity of TM in trees from transect C was independent of distance. The accumulation of TMs in the leaves was significantly lower in the metalliferous waste heap sites compared to the ZW area. It was hypothesised that the accumulation of TMs in B. pendula leaves would depend on the location and distance from the polluting source. It was demonstrated that TMs content in soil affects the accumulation of phenolic acids and flavonoids.

FLUOROSIS PREVALENCE AT DIFFERENT REGIONS OF THE EARTH (LITERATURE REVIEW)

The aim of the study is to analyze the literature about the fluorosis prevalence and the factors which lead to dental and bone fluorosis. The search for articles published in 2016-2023 was conducted by the authors in Scopus and Web of Science scientific data bases using the keywords “fluorosis”, “dental fluorosis”. To classify the severity of dental fluorosis, the index of developmental defects of enamel (DDE), the index of tooth surface fluorosis (TSIF), and mostly Dean’s index Thylstrup & Fejerskov Index (TFI) are used. The risk factors for dental fluorosis include living in regions with high level of fluoride, drinking water with high level of fluoride or salt fluoridation, drinking bottled water, use of fluoride toothpastes among preschool children, early weaning, and use of infant formula for long time, and, as well as, a hot climate and high fluoride content in soil and food. The studies from India and China demonstrated that the average concentration of dental fluorosis and skeletal fluorosis at fluoride contained 6 mg/l. The prevalence of dental fluorosis in NorthernTanzania, where the fluorine content in daily drinking water is 3.6 mg/l, reaches 75,22%. In Ethiopia, where fluorine content is 5.09 mg/l, the prevalence of skeletal fluorosis ranges from 55.1% to 72.4%. In Kenya, the fluoride content in drinking water reaches 72 mg/l, so the prevalence of dental fluorosis is 80%. The prevalence of dental fluorosis is lower in South Western Saudi Arabia and Iran where fluoride level is lower. In Jordan, the prevalence of dental fluorosis reaches 39.9% due to the high fluoride content in miner rocks. Skeletal fluorosis is wide spread in some areas of Pakistan due to the contamination of ground water by industrial production. The prevalence of mild dental fluorosis is 39% in New castle where water is fluoridated, and 24% in non-fluoridated Manchester in England. Dean’s index and TFI index are mostly used to classify these variety of fluorosis. Various factors affect the appearance of dental and bone fluorosis worldwide, so the prevalence of fluorosis varies from 11,1 up to 100%.

Cropping with Vicia villosa and native grass improves soil's bacterial structure and ecological network in a jujube orchard.

In a jujube orchard, cropping withgrass may influence bacterial diversity and ecological networks due to changes of physicochemical properties in soil, which has a serious effect on the stability of soil ecosystems. The aim of this study was to analyze the effects of different cultivation methods (CK: cleaning tillage; NG: cropping with native grass; VV: cropping with Vicia villosa) on the soil's bacterial structure and its co-occurrence network in a jujube orchard. The results showed that the highest moisture content, total nitrogen, and organic matter in the rhizosphere soil of a jujube orchard was found in the VV group. The soil's moisture content, total nitrogen, and organic matter in the VV group were 2.66%, 0.87 gkg-1, and 5.55 mgkg-1 higher than that found in the CK group. Compared to the CK group, the number of unique species in the rhizosphere soil in the NG and the VV groups increased by 7.33% and 21.44%. The PICRUSt and FAPROTAX analysis showed that sown grass had a greater influence on the ecological function of the soil's bacteria. Cropping with Vicia villosa and native grass significantly increased aerobic chemoheterotrophy, nitrogen respiration, nitrate reduction related to biochemical cycles, and the relative abundance of genes related to carbohydrate metabolism and the biodegradation of xenobiotics. The bacterial network complexity in the NG group was higher than that in the CK and VV groups and was greatest in the hub nodes (OTU42, Bacteroidota; OTU541, Nitrospiraceae). In this study, the ecological benefit seen in the soil's microbial function provides support to the theory that cropping with grass (Vicia villosa) increases the sustainable development of a jujube orchard.

Organic carbon as a factor of iodine differentiation of the soil cover in the Bryansk and Oryol regions by iodine availability

The distribution of stable iodine and humus in the upper horizon (0–20 cm) of various types of soils of the Bryansk and Oryol regions used as pastures has been studied. Soil sampling was carried out with a hand stick drill in layers in the depth interval: 0–5 cm, 5-10 cm and 10–20 cm. Iodine content was determined by kinetic rhodanide-nitrite method. Corg content was determined by the bichromate method of Tyurin. The work includes data from both long-term studies of the iodine content in the soil cover of the Bryansk region (2008–2020) and new data from expeditionary studies in the Oryol region (2022). It is shown that the soils of the Bryansk pastures are depleted of iodine and organic carbon (OC) in comparison with the Oryol region, which corresponds to the change of soil cover composition from west to east. The humus content in soils was determined and statistically significant correlation between iodine and C org. content in pasture soils were obtained (from r = 0.28 in Chernozems to r = 0.49 in Haplic Albeluvisols; in addition, for the whole sample (n = 48) the correlation coefficient ranged from 0.31 in the 0–5 cm layer to 0.43 in the 10–20 cm layer). The dependence of iodine accumulation on the OC content in different types of soils (Chernozems, Grey-Luvic Phaeozems, Umbric Albeluvisols, Haplic Albeluvisols) and their hydromorphism has been established. The identified differences in soil iodine fixation should be considered as they may influence iodine intake levels in pasture animal milk and local rations.

Bacillus B2 promotes root growth and enhances phosphorus absorption in apple rootstocks by affecting MhMYB15.

Due to the chelation of phosphorus in the soil, it becomes unavailable for plant growth and development. The mechanisms by which phosphorus-solubilizing bacteria activate immobilized phosphorus to promote the growth and development of woody plants, as well as the intrinsic molecular mechanisms, are not clear. Through the analysis of microbial communities in the rhizosphere 16S V3-V4 and a homologous gene encoding microbial alkaline phosphomonoesterase (phoD) in phosphate-efficient (PE) and phosphate-inefficient apple rootstocks, it was found that PE significantly enriched beneficial rhizobacteria. The best phosphorus-solubilizing bacteria, Bacillus sp. strain 7DB1 (B2), was isolated, purified, and identified from the rhizosphere soil of PE rootstocks. Incubatingwith Bacillus B2 into the rhizosphere of apple rootstocks significantly increased the soluble phosphorus and flavonoid content in the rhizosphere soil. Simultaneously, this process stimulates the root development of the rootstocks and enhances plant phosphorus uptake. After root transcriptome sequencing, candidate transcription factor MhMYB15, responsive to Bacillus B2, was identified through heatmap and co-expression network analysis. Yeast one-hybrid, electrophoretic mobility shift assay, and LUC assay confirmed that MhMYB15 can directly bind to the promoter regions of downstream functional genes, including chalcone synthase MhCHS2 and phosphate transporter MhPHT1;15. Transgenic experiments with MhMYB15 revealed that RNAi-MhMYB15 silenced lines failed to induce an increase in flavonoid content and phosphorus levels in the roots under the treatment of Bacillus B2, and plant growth was slower than the control. In conclusion, MhMYB15 actively responds to Bacillus B2, regulating the accumulation of flavonoids and the uptake of phosphorus, thereby influencing plant growth and development.

Comparison of Foundation by Direct Shear Test in Different Soil Condition

In this paper, we mainly focused on the comparison of foundation in two different locations. Size of foundation depends on bearing capacity of soil. Standard proctor test has been conducted to determine Optimum Moisture Content (OMC) of soil and Direct shear test has been conducted to determine the shear strength parameters in OMC. Bearing capacity of soil is calculated from shear strength parameters using Terzaghi’s equation. Area of foundation is calculated and it is found that area differ by 34.47% at two locations.

Comparison of various single-disc type furrow openers used in no-till seeders in terms of furrow properties and acting forces

The purpose of this study was to examine the impact of various single-disc type furrow openers used in no-till seeders on furrow aspects and forces acting on the discs at various soil moisture contents, soil compaction levels, and seeding depths in soil bin. Factors included plain, notched, wavy, concave, and fluted types of disc coulters, two soil moisture levels (12-18%), two soil compaction levels (2-3 MPa), and two seeding depths (50-75 mm). According to the results, the plain, notched, and fluted type discs had the lowest vertical, draft, and side force, while the wavy type disc had the maximum vertical force, draft force, and side force and the concave type disc had the highest side force. The vertical, draft, and side force requirements of all furrow openers were found to be lower in loose soils with low moisture content and greater in compacted soils with high moisture content. Fluted, concave, and wavy-type discs produced the best results in terms of the specific vertical, specific draft, and specific side forces, respectively. While the highest furrow cross-sectional area was obtained in the wavy disc, this furrow opener was followed by concave, notched, fluted, and plain-type furrow openers, respectively.

Quantifying the carbon sequestration potential of different soil management practices aimed at increasing organic content in soil and reducing the usage of chemical inputs

<p>The global imperative to address climate change and promote sustainable agriculture has underscored the critical role of soil management practices in enhancing carbon sequestration and reducing greenhouse gas emissions. This research focuses on quantifying the carbon sequestration potential of diverse soil management techniques aimed at increasing organic content in soil while minimizing the use of chemical inputs. It integrates a multidisciplinary approach, conducting field experiments across diverse agroecological regions with different soil types and cropping systems. Key practices under investigation include cover cropping, crop rotations, conservation tillage, compost application, organic amendments, integrated pest management (IPM), and precision agriculture. The study assesses their impact on soil organic carbon levels, greenhouse gas emissions, soil health indicators, and crop productivity through comprehensive data collection and analysis techniques. Statistical analyses and modeling are employed to quantify carbon sequestration rates, evaluate treatment effects, and assess environmental and agronomic benefits. These practices are implemented in controlled trials to assess their impact on soil organic carbon (SOC) levels, greenhouse gas emissions (CO2, CH4, N2O), soil health indicators (microbial biomass, nutrient cycling, soil structure), and crop productivity. Data collection and analysis techniques involve comprehensive soil sampling, greenhouse gas flux measurements, soil health assessments, and crop yield monitoring over multiple growing seasons. Statistical analyses and modeling approaches are employed to quantify the carbon sequestration rates, assess treatment effects on soil health and greenhouse gas emissions, and evaluate the overall environmental and agronomic benefits of the soil management practices. The study aims to contribute valuable insights into evidence-based strategies for promoting sustainable soil management practices that enhance carbon sequestration while maintaining or improving agricultural productivity. The findings will have implications for informing agricultural policies, guiding farm management decisions, and advancing research on climate-smart agriculture. By quantifying the carbon sequestration potential of different soil management practices, this research contributes to the broader goal of achieving climate resilience, environmental sustainability, and food security in agricultural systems.</p>

Effect of Soil pH on the Uptake of Essential Elements by Tea Plant and Subsequent Impact on Growth and Leaf Quality

Tea plant is an acidophilic plant, and soil pH has an important effect on the absorption and enrichment of elements, tea plant growth and quality. In this study, rhizosphere soils and leaves of tea plants from 30 tea plantations were collected to determine soil pH and multi-element content of soil and leaves of tea plants, to obtain and validate key elements that are enriched by pH affecting tea plants, and to analyze the effects of pH on the growth and quality of tea plants. The results showed that soil pH significantly affected the enrichment of 15 elements by tea plants, and the enrichment coefficients of 11 elements (C, Mg, Si, N, P, Mn, Sr, Cd, S, Ca and Sb) tended to increase significantly with the increase of soil pH, while the opposite was true for the other four elements (Cu, Rb, Ba and Al). TOPSIS analysis showed that soil pH had the greatest effect on tea plant enrichment of seven elements, namely N (100%), Mn (43.32%), C (39.22%), P (27.66%), Sr (15.30%), Mg (13.41%) and Ba (10.47%). Pot experiments with tea seedlings also verified that soil pH significantly affected the enrichment of tea leaves for seven key elements. Moreover, with the increase of soil pH, the growth indexes, photosynthesis indexes and quality indexes of tea seedlings showed a significant upward trend. Interaction analysis showed that the enhanced enrichment of N, Mn, C, P, Sr and Mg by tea plants was beneficial to increase the photosynthetic capacity of tea plants, promote the growth of tea plants and improve the quality of tea leaves. This study provides an important theoretical basis for the cultivation and management of tea plants.

Evaluation of electrical resistivity of cement-based materials using time domain reflectometry

Time domain reflectometry (TDR) is a widely used electromagnetic wave–based technique for evaluating the volumetric water content of soils, although its use for moisture measurement in cement-based materials is limited. This paper presents a comprehensive analysis of the electrical properties of cement pastes and cement paste–slime mixtures using TDR. Both TDR and electrical resistivity probes are used to estimate the electrical resistivities of various cement-based materials over their curing period. The study reveals that these properties are significantly influenced by curing time, water–cement ratio, and water–solid ratio. The experimental results demonstrate a consistent increase in electrical resistivity with curing time, underscoring the significant role of hydration-induced water evaporation and microstructural changes. Furthermore, the interpretation of characteristic voltages on the TDR waveform significantly influences resistivity estimates. Thus, this study highlights the potential of TDR in accurately evaluating the electrical resistivity of cement-based materials.

Evaluation of sand subgrade seepage erosion caused by buried pipeline leakage

Leakage from buried pipelines can lead to an increase in the water content of the subgrade soils and a rise in the water table, leading to soil loosening, erosion and ultimately the formation of hidden voids and roadway collapses. This study presents a discrete-element method and validates its accuracy by utilising cavity data from model experiments. It investigates the mechanism of seepage erosion resulting from pipe leakage and analyses the development of the soil arch effect. Furthermore, it discusses the influence of sand void ratio and particle size on sand seepage erosion. The results indicate that the erosion area is primarily affected by the void ratio and particle size. In comparison to soil particles ranging from 0.1 to 5 mm and from 2 to 5 mm, those with sizes between 0.1 mm and 2 mm generate areas of erosion and loosening that are approximately 40% larger. The proposed model offers a precise analysis of the developmental process and the extent of seepage erosion, thereby contributing to the prediction of potential road cavity areas based on dynamic changes in key factors such as subgrade soil type and groundwater level.

Effects of Substrate Composition on the Growth Traits of Grafted Seedling in Macadamia (Macadamia integrifolia) Nuts.

Macadamia nut plantings in China are expanding year by year. In order to breed and promote superior varieties, this study analyzed the effects of different rootstocks and scions on the survival rate of grafted seedlings, and then selected the best substrate composition for plant growth. The results showed that the survival rate of the HAES788 variety as rootstock and Guire No. 1 as scion was the highest, reaching 96%. The optimal grafting time in December was better than that in March. Furthermore, among 16 substrate formulations, T12, T13, T15, and T16 had advantages of agglomerated soil and more well-developed root systems compared to the CK made of loess. The plant height, stem diameter, leaf length, leaf width, and dry weight of the aboveground and underground parts of the grafted seedlings planted in these substrate formulations were significantly higher than those plants planted in the CK. In addition, the substrate formulations T12, T13, T15, and T16 significantly improved the organic matter, total nitrogen, and total potassium content of the substrate soils, but little improvement was observed for total phosphorus content after 13 months. Overall, macadamia grafting times are best in December, with HAES788 and Guire No. 1 being the best rootstock and scion. The optimal substrate formulations are T12, T13, T15, and T16. This study provides a solid foundation for the production of high-quality macadamia plants.

Accurate Quantification of 0–30 cm Soil Organic Carbon in Croplands over the Continental United States Using Machine Learning

Increases in organic carbon within agricultural soils are widely recognized as a “negative emission” that removes CO2 from the atmosphere. Accurate quantification of soil organic carbon (SOC) to a certain depth in the spatial domain is critical for the effective implementation of improved land management practices in croplands. Currently, there is a lack of understanding regarding what depth strategy should be used to estimate SOC at 0–30 cm when sample datasets come from multiple depths. Furthermore, few studies have examined depth strategies for mapping SOC at the agricultural management level (i.e., field level), opting instead for point-based analysis. Here, three types of approaches with different depth strategies were evaluated for their ability to quantify 0–30 cm SOC content based on soil samples from 0–5 (surface), 5–30 (subsurface), and 0–30 cm (full column). These approaches involved the generalized additive model and machine learning techniques, i.e., artificial neural networks, random forest, and XGBoost. The soil samples used for the model evaluation and selection consisted of the newly collected samples in 2020–2022 and the Rapid Carbon Assessment (RaCA) legacy samples collected in 2010–2011. Environmental covariates corresponding to these SOC measurements were used in model training, including long-term physical climate, short-term weather, topographic and edaphic, and remotely sensed variables. Among the models evaluated in this study, the XGB regression model with a full column depth assignment strategy yielded the best prediction performance for 0–30 cm SOC content, with an r2 (squared Pearson correlation coefficient) of 0.48, an RMSE (root mean square error) of 0.29%, an ME (mean error) of 0.06%, an MAE of 0.25%, and an MEC (modeling efficiency coefficient) of 0.36 at the pixel level and an r2 of 0.64, an RMSE of 0.32%, an ME of −0.20%, an MAE of 0.28%, and an MEC of 0.48 at the field level. This study highlights that machine learning models with a full column depth strategy should be used to quantify 0–30 cm SOC content in agricultural soils over the continental United States (CONUS).

Spatial patterns of organic matter content in the surface soil of the salt marshes of the Venice Lagoon (Italy)

Abstract. Salt marshes are crucial eco-geomorphic features of tidal environments as they provide important ecological functions and deliver a wide range of ecosystem services. Being controlled by the interplay between hydrodynamics, geomorphology, and vegetation, the contribution of both organic matter (OM) and inorganic sediments drives salt marsh vertical accretion. This allows marshes to keep pace with relative sea level rise and likewise capture and store carbon, making them valuable allies in climate mitigation strategies. Thus, soil organic matter (SOM), i.e. the organic component of the soil, plays a key role within salt marsh environments, directly contributing to soil formation and supporting carbon storage. This study aims at inspecting spatial patterns of OM in surface salt marsh soils (top 20 cm), providing further insights into the physical and biological factors driving OM dynamics that affect salt marsh survival and carbon sink potential. Our results reveal two scales of variations in SOM content in marsh environments. At the marsh scale, OM variability is influenced by the interplay between surface elevation and changes in sediment supply linked with the distance from the marsh edge. At the system scale, OM content distribution is dominated by the gradient generated by marine and fluvial influence. The observed variations in SOM are explained by the combination of inorganic and organic input, preservation conditions, and sediment grain size. Our results highlight the importance of marshes as carbon sink environments, further emphasising that environmental conditions within a tidal system may generate strongly variable and site-specific carbon accumulation patterns, enhancing blue carbon assessment complexity.

SCIENTIFIC SUBSTANTIATION OF THE MAXIMUM PERMISSIBLE CONCENTRATION OF OIL IN THE SOIL FOR THE TERRITORY OF THE INDUSTRIAL ZONE OF THE UZEN DEPOSIT IN THE MANGYSTAU REGION

The development and operation of an oil field is accompanied by an oil spill and the formation of oil-contaminated soils. The process of natural restoration of oil-contaminated soils is extremely slow. Therefore, among environmental protection measures, the rationing of oil content in soils is extremely important. The purpose of the work is to develop a standard for the maximum permissible concentration of oil in the soil for the industrial zone of the Uzen field.Methods. The basis for the development of the maximum permissible concentration of oil in the soils of the studied field is the "Methodological recommendations for the hygienic justification of the maximum permissible concentration of chemicals in the soil". The determination of the mass fraction of oil in the studied media was performed by gas-liquid chromatography. The chemical composition of the soil was determined by atomic absorption spectrometry. The determination of the specific activity of radionuclides was carried out by gamma-spectrometric method on the «MKS 01A Multirad» spectrometer. Results and discussion. During the work for the field, in accordance with the requirements for substantiating the maximum permissible concentration, an assessment was made on the physico-chemical and biological properties of soils and oils. Based on the experimental data obtained, the maximum permissible concentration of oil in the soil of the industrial zone of the Uzen field at the level of 3 g/kg is justified and reflects the real conditions in which oil intake in the soil will not cause harmful effects on human health and the environment.

Effect of Aminating Lignin Loading with Arbuscular Mycorrhizal Fungi on Soil Aggregate Structure Improvement.

Lignin is an important component of plant fiber raw materials, and is a three-dimensional network structure aromatic polymer with abundant resources and a complex structure in nature. Lignin is generally used as industrial waste, and its potential value has not been fully utilized. Modern agriculture extensively uses chemical fertilizers, leading to the gradual degradation of soil fertility and structure, which seriously affects crop growth, nutrient transport, and root respiration function. Based on soil bulk density, porosity, aggregates, and their stability indicators, this study analyzed the effects of aminated industrial lignin and its loading with arbuscular mycorrhizal fungi on soil structure improvement and plant growth. It was hoped that resource-rich lignin could play a beneficial role in improving soil structure and promoting crop growth. The phenolic hydroxyl group of lignin was epoxidized and further aminated to load with arbuscular mycorrhizal fungi. The results indicated that amine-modified lignin could effectively load with arbuscular mycorrhizal fungi. The application of arbuscular mycorrhizal fungi-supported aminated lignin to soil aggregate structure improvement greatly reduced the bulk density of soil, and increased the porosity of soil and the content of large granular soil. Compared with unmodified soil, soil bulk density decreased by 73.08%, the porosity of soil increased by 70.43%, and the content of large granular soil increased by 56.38%. Using the improved soil for corn cultivation efficiently increased the biomass of corn. The plant height was increased by 72.16%, the root-shoot ratio was increased by 156.25%, and other indexes were also improved to varying degrees. The experimental method provides an important basis for the effective utilization of lignin materials in agriculture in the future.

Study on synergistic and antagonistic interactions of P and Zn fertilization on sweet pepper

The present study was carried out to investigate the synergistic and antagonistic interactions of combined application of Phosphorus and Zinc fertilizers on sweet pepper in net house conditions. Pot experiment consists of thirteen treatments combinations set up in a completely randomized design. The treatment combinations comprising of four levels of phosphorus (0, 237.5, 355.5 and 475 kg Single Super Phosphate ha−1) and three levels of Zn (5, 7.5 and 10 kg Zinc Sulfate ha−1) including one control (100% NPK). The available macro and micronutrients content in potting mixture was confirmed in medium range before conducting the experiment. The results clearly demonstrate the treatment comprising 475 kg SSP ha−1 with 10 kg ZnSO4 ha−1 (T13) showed synergistic effects on vegetative characteristics, above and below ground nutrient content as well as nutrient uptake. When balanced phosphatic and zinc fertilizers (T13) are applied to soil, there is a low possibility of an antagonistic reaction. Antagonism problems arise most frequently when the soil’s Zn content is extremely low in combination with excess application of P fertilizer limiting their availability to plants. To avoid P-Zn antagonism in the soil system, utilization of appropriate fertilizer methods, supplies, and rates was done. As a result, the present study confirms that recommended fertilizer doses combined with phosphorus @ 475 kg SSP ha−1 and zinc @ 10 kg ZnSO4 ha−1, is the best nutrient combination for improving plant growth parameters; however, in terms of soil parameters, P and Zn fertilizers affected micronutrient content in soil, which further interacted antagonistically.

Comparative analysis of machine learning algorithms for identifying cobalt contamination in soil using spectroscopy

Cobalt (Co) has been recognized as one of the most hazardous elements by the United Nations Environmental Program; however, it has received limited attention in previous studies of identifying heavy metal contamination and has been limited to small, site-scale datasets and few machine learning algorithms. To fill this research gap, eight machine learning algorithms were combined with visible and near-infrared reflectance spectroscopy in this study to develop a large-scale model for classifying Co content in soil. In total, 18,675 topsoil samples were used to train and validate the models. Spectral preprocessing, principal component analysis, and hyper-parameter tuning were utilized to improve the tested models’ performance, which was evaluated using multiple indicators. The optimal model was then applied to the United States soil spectral dataset. The results show that the eXtreme Gradient Boosting (XGB) performed the best on both the training and testing sets, with an area under the curve value of 0.901 on the training set and 0.904 on the testing set. The application of XGB revealed that Utah, Arizona, New Mexico, North Dakota, Arkansas, Mississippi, and Alabama were at higher risk of Co contamination. In summary, XGB can be used to effectively identify areas of potential Co contamination. The approach presented here not only fills a gap in terms of large-scale identification of Co contamination but can also greatly assist environmental managers in risk assessment and reclamation strategies.

Effects of microplastics and cadmium co-contamination on soil properties, maize (Zea mays L.) growth characteristics, and cadmium accumulation in maize in loessial soil-maize systems

Microplastics (MPs) are pervasive pollutants found in agricultural soils, yet research on the combined impacts of MPs and heavy metals on soil-plant systems remains limited. This study investigates the combined impact of low-density polyethylene (LDPE) microplastics (L: 1 mm, S: 100 μm, 0.1%, 1%) and Cd on soil properties, available Cd content, maize growth, and Cd accumulation by mazie through pot experiments. The findings unveiled notable impacts of the treatment groups, namely MP-L0.1%, MP-S0.1%, MP-L1%, and MP-S1%, on soil organic carbon (SOC), maize height, and catalase (CAT) activity (P < 0.05). The dosage of MPs significantly influenced maize height, MP-S0.1% treatment resulted in a 5.6% reduction, while the other groups had insignificant effects. Particle size and dosage significantly affected SOC and CAT (P < 0.01). The MP-L1% and MP-S1% groups resulted in increases of SOC by 121.5% and 281.0%, respectively. CAT reductions were 32.6%, 62.8%, 41.9%, and 34.9% in MP-L0.1%, MP-S0.1%, MP-L1%, and MP-S1% groups, individually. The Cd treatment induced a significant decrease in soil cation exchange capacity (CEC), maize stem diameter, and root length, accompanied by significant increases in maize plant height, malondialdehyde (MDA), CAT, and superoxide dismutase (SOD) activities. Combined LDPE and Cd contamination had significant effects on maize height and Cd content in leaves. Specifically, MP-L0.1%+Cd, MP-S0.1%+Cd, MP-L1%+Cd, and MP-S1%+Cd reduced maize height by 4.1%, 4.5%, 8.7%, and 13.8%, respectively. The co-presence of LDPE and Cd increased available Cd content in soil while elevating Cd concentration in maize shoots and roots, with a notable 25.5% increase in Cd concentration in maize leaves in the MP-L1%+Cd group compared to the Cd group. Furthermore, LDPE effects on soil-plant systems varied depending on particle size and dosage. This research provides important perspectives on evaluating the concurrent contamination and potential dangers of MPs and toxic metals in soil-plant environments.