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【Objective】The research was conducted to explore the remediation effect of water regulation and biochar on farmland soil near mining areas and improve the safe use of farmland.【Method】Taking farmland soil near a lead-zinc mine in Yunnan as the research object, three water conditions: dry-wet alternation (G), flooding (Y) and natural moisture content (Z), and four biochar addition amounts of 0% (BC0, CK), 2.5% (BC1), 5.0% (BC2), and 7.5% (BC3) were set up. Through soil culture experiments, the effects of applying chicken manure biochar under different water regulation measures on the forms of Pb and Zn in heavy metal contaminated soil were studied.【Result】Under the three water conditions, the application of biochar could increase soil pH. The concentrations of water-soluble and exchangeable Pb and Zn in soil treated with biochar were significantly lower than that of CK, reducing the bioavailability of Pb and Zn. The mass fractions of oxidizable and residual Pb in soil treated with biochar increased, with ZBC2 treatment having the highest mass fractions of oxidizable and residual Pb, which were 64.58% and 25.06%, respectively. The mass fractions of residual Zn in soils under various treatments ranked as: dry-wet alternation > flooding > natural moisture content. Under different water conditions, the application of biochar significantly reduced the mass concentrations of TCLP-extracted Pb and Zn, both of which were far below the international limitation standards. Among them, the soil treated with GBC3 had the lowest concentration of TCLP-extracted Zn, which was 3.45 mg/L. The average mass fraction of Pb and Zn bioavailability by SGET method was lower than that by PBET method and SBET method, while the ZBC3 treatment by SGET method had the lowest mass fractions of Pb and Zn bioavailability, which were 0.43% and 0.27%.【Conclusion】The application of different amounts of biochar under three types of water regulation effectively passivated soil heavy metals Pb and Zn, reducing their harm to the soil environment. Under natural moisture content conditions, the application of high amounts of biochar (5.0%, 7.5%) had the best passivation effect on heavy metal Pb in soil; the optimal passivation effect of 7.5% biochar on heavy metal Zn in soil was observed under dry-wet alternation conditions.

Heavy metal(loid)s (HMs) contamination in farmland soils, an environmental issue of global concern, has undergone extensive research across local and regional scales in the Yellow River Basin (YRB), China, but comprehensive studies at the basin scale remain scarce. This study, utilizing published data from 2000 to 2023, analyzed the concentrations, distribution patterns, potential sources, probabilistic ecological risks, and source-specific health risks of eight HMs (As, Cd, Cr, Cu, Hg, Ni, Pb, and Zn) in farmland soils across the YRB. Results indicated that while most agricultural soils are safe, 21.7% of samples for Cd, 5.6% for As, and 1.2% for Zn exceed China’s risk screening levels for agricultural soil pollution, with Hg and Cd showing the highest pollution levels. Ecological risks were generally high, with Cd and Hg identified as primary risk factors. Correlation analysis and the positive matrix factorization model identified four potential origins, contributing in descending order: traffic-industrial atmospheric deposition (37.0%), mixed agricultural-natural sources (26.7%), industrial-natural sources (14.6%), and mixed agricultural-industrial sources (14.6%). The probabilistic health risk assessment identified negligible noncarcinogenic threats to the population; however, carcinogenic hazards were concerning, particularly due to industrial activities and As. Children are more vulnerable to hazards than adults. These findings enhance our insight into soil HM pollution risks in the YRB and offer a scientific foundation for targeted pollution management and control strategies at the basin scale.

The rise of microplastics (MPs) is a global concern jeopardizing environmental safety. Initial studies have extensively concentrated on aquatic ecosystems, leaving their presence in terrestrial environments unknown. Thus, this study was carried out to investigate the vertical distribution of MPs in farmland soils of Mabibo Bonde la Mchicha Farm (MBMF), Dar es Salaam. 39 soil samples collected from MBMF were investigated using a Stereomicroscope and QATR-S FTIR. Results herein showed that MPs were found in all soil samples in different depths up to 15 cm deep, ranging from 4.8 to 82.2 items g-1 dry weight (DW). There was a statistically significant difference in MP abundance in depths between 0–5, 5–10 and 10–15 cm layers (P = 0.033) at ὰ = 0.05. The observations were revealed by the observed colors, in which white (36.5 %) was the most frequently observed, followed by blue (21.4 %), brown (20.2 %), black (12.8 %) and red (9 %). Fibers (49.7 %), fragments (32.9 %) and films (17.3 %) were the dominant shapes. Polyethylene (PE) and polypropylene (PP) were the dominant polymers observed constituting 33 % each, polyethylene terephthalate (PET) 11 %, high-density polyethylene (HDPE) 8 %, polyester (PES) 7 %, polyamide (PA) 7 % and polyvinyl chloride (PVC) 1 %. It can be inferred that PE and PP exhibited greater vertical mobility. However, PA and PVC were only observed in the topsoil layer. This study reveals MPs' occurrence and vertical transfer in urban farmland soils of MBMF in Dar es Salaam.

Manure application is the primary input route for antibiotic resistance genes (ARGs) in farmland soil. This study investigated the effects of varying the rates of five chicken manure applications on the accumulation and distribution of ARGs across different soil depths (0–20, 20–40, and 40–60 cm) using metagenomic sequencing. The results revealed that the distribution of ARGs in farmland soil was closely linked to soil depth and influenced to some extent by the fertilizer quantity after 30 days of fertilization. ARGs were predominantly concentrated in the surface soil and exhibited a significant decrease in type and abundance with an increased soil depth. Compared with soil treated with chemical fertilizers alone, chicken manure-treated surface soil presented a higher diversity and abundance of ARGs. However, the diversity and abundance of ARGs did not increase proportionally with the increasing ratios of chicken manure application (0, 25, 50, 75, and 100%). ARGs in soil primarily conferred resistance to host bacteria through antibiotic efflux pumps (~33%), antibiotic target alteration (~31%), antibiotic inactivation (~20%), and antibiotic target protection (~8%). Correlation analysis involving ARGs and soil microorganisms revealed widespread multidrug resistance among soil microorganisms. Furthermore, two genera of human pathogenic bacteria (Pseudomonas sp. and Listeria sp.) were identified as potential microbial hosts of ARGs in all treatments. Correlation analysis involving ARGs and environmental factors indicated that soil ARGs are predominantly influenced by heavy metals and microorganisms. This paper offers valuable insights for environmental risk assessments regarding the utilization of livestock manure resources. Additionally, it furnishes a scientific foundation for farmland application strategies pertaining to livestock manure.

The spatial characteristics, pollution sources, and risks of soil heavy metals were analyzed on Hainan Island. The results showed that the heavily polluted points accounted for 0.56%, and the number of mildly and above polluted points accounted for 15.27%, respectively, which were mainly distributed in the northern part of the study area. The principal component analysis–absolute principal component score–multiple linear regression (APCS-MLR) and the positive matrix factorization (PMF) revealed four sources of heavy metals: agricultural pollution sources for cadmium, (Cd), industrial and mining pollution sources for arsenic, (As), transportation pollution sources for zinc and lead (Zn and Pb), and natural pollution sources for chromium, nickel, and copper (Cr, Ni, and Cu). The human health risk assessment indicated that the average non-carcinogenic risk (HI) for both adults and children was within the safe threshold (1, indicating a potential health risk above the safe threshold. Meanwhile, nearly 100% and 99.94% of the TCR values exceeded 1 × 10−4 for children and adults, indicating that Cr and Ni are priority heavy metals for control. The research results provide the necessary scientific basis for the prevention and control of heavy metals in agricultural soils.

Farmland soil quality is a crucial determinant for agricultural productivity, food safety, and human well-being. Among the various contaminants, heavy metals have emerged as pervasive factors significantly impacting farmland quality, attracting widespread societal concern. In this study, we systematically applied multivariate statistical analysis, geostatistical methods, and the positive matrix factorization (PMF) source apportionment technique to elucidate the sources and contributions of eight heavy metals (Cd, Hg, As, Pb, Cr, Cu, Zn, Ni) in farmland soils within an industrialized town. Our findings reveal that Cd, Hg, Pb, and Zn exhibit pollution or enrichment in farmland soils compared to natural background levels, with Hg and Cd surpassing 164.3% and 50.2%, respectively. Notably, Zn demonstrates discernible point-source pollution. Source apportionment results highlight industrial point sources, coal combustion, and agriculture as the primary anthropogenic contributors to heavy metal contamination, with zinc-plating enterprises being the predominant industrial point sources. Addressing the specific issue of point-source pollution from Zn in industrial activities, further analysis establishes a correlation between soil Zn content and the distance from zinc-plating enterprises. Utilizing an atmospheric transport model, we observe that the impact of industrial activities on soil Zn is limited when the distance exceeds 1.5 km, emphasizing the importance of monitoring Zn pollution within areas less than 1.5 km. This study pioneers a progressive source apportionment approach, considering the origins of different heavy metals, pollution levels, distance factors, and the cost-effectiveness of environmental measures. The insights gained provide scientifically sound strategies for future decision making in environmental protection.

IntroductionLead (Pb) pollution in agricultural soil has been accelerated by industrial development and human activities, and poses a major threat to agricultural ecosystems. Both biochar and arbuscular mycorrhiza (AM) fungi are considered to play an important role in remediation of Pb contaminated soil.MethodsThe combined remediation effects of introduced AM fungi and biochar on soil properties, Pb availability, microbial community and functional profiles were systematically investigated in unsterilized Pb-polluted agricultural soil.ResultsResults indicated that soil nutrients were significantly improved through the combined application of biochar and introduced AM fungi. The introduced AM fungi combined with biochar prepared at 400°C and 500°C promoted the transformation of Pb to a more stable state with low bioavailability. Moreover, the addition of AM fungi and biochar affected the relative abundances of dominant bacteria and fungi at the phylum and genus levels. Biochar mainly affected soil bacterial community and obviously increased the relative abundance of Actinobacteria and Blastococcus. The interactions between biochar and introduced AM fungi mainly affected fungal community, and increased the abundance of Ascomycota and Botryotrichum. Further, PICRUSt analysis indicated biochar amendment supported stronger bacterial metabolic functional potentials.DiscussionTherefore, the combined application of biochar and Therefore, the combined application of biochar and introduced AM fungi could improve soil nutrients, reduce Pb introduced AM fungi could improve soil nutrients, reduce Pb availability, availability, and show and show a positive effect on a positive effect on indigenous microbial communities and indigenous microbial communities and metabolic functions in metabolic functions in farmland soil.

BACKGROUND As the significant factor of the accumulation of heavy metals in farmland soils, mineral activities such as mining, traffic and mineral processing and smelting allow heavy metals to spread into the surrounding environment by water or atmospheric deposition, and finally collected into the soil, causing heavy metal pollution in the surrounding farmland soil. Heavy metals pollution in soils especially in farmland soils around the mining area thus has received great attention in the field of environmental pollution. Located in the middle reaches of the Yellow River watershed, the gold mining area in western Henan is an extremely important gold deposit area with great prospecting potential in China for the strong late Yanshan acidic magmatic activity and the extremely favorable metallogenic geological conditions, in which more than 40 large, medium or small gold deposits have been discovered. Under the background of ecological protection and high-quality development in the Yellow River watershed, the western Henan gold mining area, with a long history of gold mining development, lacks more attention to the accumulation, spatial distribution and ecological risk of heavy metals in farmland soil around the mining area during the years of mining, beneficiation and processing. It is particularly necessary to study the heavy metal pollution in soil, find out the impact of mining activities on heavy metals in surrounding farmland soil, and provide a scientific basis for prevention and control of heavy metal pollution in farmland soil. OBJECTIVES To clearly understand the impact of mining activities in the western Henan mining area on heavy metals in the surrounding farmland soil, provide necessary basic data for supporting the safe production of key mineral resources, the surrounding agricultural safety, and prevent and control heavy metal pollution in farmland soil. METHODS 375 topsoil samples from the farmland around the western Henan gold mining area at a depth of 0-20cm were systematically investigated and analyzed with reference to Code of Practice for Soil Geochemical Survey (DZ/T 0145—2017). The contents and spatial distribution characteristics of Cd, Cu, Zn, Pb, Hg, As, Cr, Ni were analyzed. The heavy metal pollution and ecological risk were evaluated by the geo-accumulation index method and potential ecological risk index method. RESULTS (1) The contents variation range of Cu, Pb, Zn, Ni, As, Hg, Cd, Cr are 1.00-71.72, 2.00-524.79, 8.00-320.37, 2.00-52.77, 2.29-24.64, 0.0067-0.268, 0.04-1.30, 28.20-107.93, respectively, and the average are 35.33, 74.43, 137.69, 31.60, 12.39, 0.064, 0.43, 76.27, respectively, showing significant differences between the 8 heavy metals. Compared with the soil background value in the middle reaches of the Yellow River, the average contents of Cu, Pb, Zn, Ni, As, Hg, Cd, Cr are 1.47, 3.24, 2.06, 1.05, 1.03, 1.52, 2.77 and 1.07 times of them, respectively, but lower than the value of risk screening values for soil contamination of agricultural land.(2) The characteristics of coefficients of variation show that Pb(90.72%)>Hg(85.25%)>Cd(65.65%)>Zn(44.0%)>Cu(33.66%)>As(31.72%)>Ni(24.23%)>Cr(13.61%), the Pb, Hg, Cd are the primary factors causing the soil pollution as the external input by mineral activities for the high coefficients of variation and special relation with mining. The main ore-forming elements in the gold deposit area are Au and Mo, and the associated elements are Cu, Pb, Zn, Ni, As, Hg, Cd, which may diffuse into the surrounding environment during ore transportation, waste rock and slag piling along the river, and processing. Alongside the Daping River, the two gold mining areas and concentrators are distributed around the farmland, and the gold ore heap leaching site on the east side is located at the top of the hillside and hill. The heavy metals produced by mining activities can diffuse in the downstream agricultural areas through atmospheric deposition, rainwater leaching, river drainage, and can accumulate in the surrounding agricultural soil, causing heavy metal pollution in the agricultural soil around the mining area.(3) The geo-accumulation index of 8 heavy metals is -0.1, 0.74, 0.33, -0.56, -0.60, -0.29, 0.62, -0.49 with the order Pb>Cd>Zn>Cu>Hg>Cr>Ni>As, in which Cu, Hg, Cr, Ni, As show no influence to the quality of soils for the average geo-accumulation index lower than 0, and Pb, Cd, Zn show moderate pollution for the average geo-accumulation index between 0-1. Among them, the proportion of samples with a Cd element of medium or higher impact grade is 20.27%, the proportion of samples with medium to strong impact grade is 7.73%, and the proportion of samples with strong impact grade is 1.07%. The proportion of samples with a Pb element above the moderate impact level is 18.93%, and the proportion of samples with moderate to strong impact level is 10.40%. Hg and Zn also have 7.46% and 13.33% of the samples reaching the moderate impact level, indicating that Hg, Cd and Pb in the soil at local sampling sites have different degrees of impact on farmland soil quality.(4) The average value of the single-factor potential ecological risk index of eight heavy metals is between 2.06 and 83.62, among which the single-factor potential ecological risk index of As, Cr, Ni, Cu and Zn is a slight potential ecological risk. Pb is mainly subject to slight potential ecological risks for 92% of samples, moderate potential ecological risks for 7.47% of samples and strong potential ecological risks for 0.53% of samples. Cd is dominated by moderate potential ecological risks, with 46.14% of samples, and there are 25.33% and 10.93% of samples reaching strong and very strong potential ecological risks respectively. For the ecological risk index of Hg, there are 35.47%, 11.46%, 4.27% and 3.20% of the samples that reach moderate, strong, very strong and very strong degree. The comprehensive potential ecological risk index (RI) ranges from 51.66 to 689.64, with an average of 192.07. The proportion of samples with slight, moderate, strong and very strong impact degree is 46.40%, 41.07%, 11.20% and 1.33%, respectively. The overall comprehensive potential ecological risk index shows moderate potential ecological risks. CONCLUSIONS Compared with the risk screening values for soil contamination of agricultural land, the contents of Cd, Cu, Zn, Pb, Cr, Ni, As, Hg are all lower than the standard, indicating low risk for the soil environment. There were different degrees of accumulation surrounding the intense mining area of Cd, Pb, and Zn by longtime mineral development. Cu, Ni, As, Hg, and Cr were influenced by the natural factor. The farmland area with strong and very strong comprehensive potential ecological risks is 349.4 hectares and 11.71 hectares, respectively. Cd and Hg are the main contributing elements, with higher risk to the soil ecology, which should be monitored and controlled from source to avoid the further accumulation of heavy metal elements in the soil.

To explore the short-term impact of uranium pollution on the microecology of farmland soil, this study investigated the activities of four enzymes involved in key soil processes (β-glucosidase, urease, phosphatase, and arylsulfatase) and analyzed the changes in microbial metabolic activity, carbon utilization capacity, and diversity using Biolog EcoPlate under short-term (3 d, 13 d, and 20 d) uranium treatments (0 mg/kg, 50 mg/kg, 200 mg/kg, and 500 mg/kg). The results showed that the activities of the three soil enzymes, except that of urease, were inhibited by uranium pollution, especially phosphatase activity, which was reduced by 75.9% in the 20-day U500 treatment group. In addition, microbial metabolic activity was inhibited by uranium pollution. However, the inhibition effect showed a downward trend with the extension of the treatment time. The carbon metabolism capacity of microorganisms was inhibited. By contrast, the ability of microorganisms to utilize amino acids, carbohydrates, and polymer carbon sources was positively correlated with time in the U50 treatment group. The results of diversity indices analysis and sho principal component analysis wed little effect on the microbial diversity of uranium contamination. Therefore, uranium pollution inhibited the metabolic activities of farmland soil microorganisms, especially the carbon, phosphorus, and sulfur cycles. This study provides a direction for the ecological restoration of farmland soil uranium pollution.

The depth of shallow groundwater significantly influences crop growth and yield by altering the physicochemical properties of farmland soil profiles. Concurrently, shallow groundwater is subject to various changes, and it remains unclear how alterations in shallow groundwater depth within field soil impact soil physicochemical properties, crop yields, and the overall dynamics of groundwater transformations. To address these uncertainties, this study utilized a sample plot equipped with a volume lysimeter and implemented four distinct groundwater depths as treatment conditions: G0 (no groundwater depth), G1 (a groundwater depth of 40 cm), G2 (a groundwater depth of 70 cm), G3 (a groundwater depth of 110 cm), and G4 (a groundwater depth of 150 cm). This study was carried out on a weekly basis to monitor fluctuations in ion content in shallow groundwater and soil moisture after the summer maize harvest, and special attention was afforded to non-irrigation conditions. This study also scrutinized the distribution of salt and nutrients in soil profiles and assessed changes in summer maize yield. Very interesting findings were obtained by conducting the study. Firstly, the shallower the groundwater depth, the higher the water and salt content of the soil surface. Small, frequent rainfall events (precipitation ≤ 25 mm) facilitated the effective removal of salt from the soil surface. Despite increased rainfall contributing to salt ion dilution in groundwater, the risk of soil surface salinization increased at the surface level. Secondly, a linear relationship existed between groundwater depth and surface soil moisture and salt content. With every 10 cm increase in groundwater depth, the surface soil moisture and salt content decreased by 0.56% and 0.06 g/kg, respectively. Soil nutrients tended to accumulate in the surface layer, with nutrient content increasing with depth. However, C/N was not notably affected by groundwater depth. Thirdly, Na+ and K+ consistently dominated the soil surface. As soil salinity increased, the prevalence of Cl− and SO42− increased, with the rate of SO42− increase surpassing that of chlorine. HCO3− altered by rainfall served as an indicator of soil alkalization characteristics, while Na+ and K+ in soil, along with Cl− and SO42− derived from groundwater, represented soil salt composition and salinization trends. Ultimately, under the conditions of this study, the most favorable groundwater depth for the growth of summer maize was determined to be 1.1 m. Analyzing the impact of different shallow groundwater depths on the physicochemical properties of farmland soil enhances our understanding of the mechanisms of interaction between groundwater and soil in agricultural ecosystems. This knowledge is instrumental in significantly improving the soil environment, thereby ensuring optimal crop yields.

The impacts of heavy metal pollution in arable soil on agricultural production, environmental health, and the wellbeing of urban and rural residents cannot be overlooked. It has become a significant bottleneck in achieving comprehensive rural revitalization. To accurately grasp the characteristics of heavy metal pollution in suburban cultivated soil, Tangwang Village (a suburb of Huainan City) was subjected to scrutiny. The contents of heavy metals (Hg, Cu, Hg, As, Pb, Cr, Cd, and Zn) in the topsoil of cultivated land in this area were detected, and their spatial distribution characteristics were analyzed using inverse distance spatial interpolation. (1) After conducting a comprehensive analysis and thorough examination of the PMF model sources, it was determined that Cu, Cd, and Zn exhibit a direct correlation with agricultural practices, collectively contributing to a cumulative percentage of 21.10%. Meanwhile, Cr is derived from a combination of sources, including both natural parent materials and human activities, accounting for a total proportion of 24.45%. Notably, lead emissions from automobile exhausts constitute a significant source, while arsenic is primarily associated with dispersed factories and their respective operations, contributing to respective proportions of 36.38% and 18.07%. It is evident that agricultural practices, transportation, and industrial activities are the main reasons for heavy metal pollution in arable soil. (2) The evaluation of geological accumulation indicators reveals that the level of soil arsenic accumulation pollution is mild to moderate (1.199). On the other hand, the cumulative pollution level of Cd, Hg, Cr, and Cu was relatively low (0.462→0.186), whereas the levels of Pb and Zn were below the threshold. (3) The assessment of the ecological risk index revealed that the predominant elements posing potential ecological risks in the investigated region were Hg, As, and Cd, with average Ei values of E(Hg) = 86.81, E(As) = 80.67, and E(Cd) = 67.83, respectively. (4) The human health risk assessment revealed significant differences in the single non-carcinogenic risk values of heavy metals generated by different exposure pathways, with oral ingestion > dermal contact > oral nasal inhalation. Children were more susceptible to the toxic effects of heavy metals compared to adults. Both As and Cr caused an increased risk of cancer in both children and adults, which is a matter of great concern. The results of this study contribute to a more accurate description of the sources of heavy metals in farmland soil. This study indicates that the application of PMF for soil source analysis yields clear results that can be further applied. This research also has potential policy significance as it can help to improve the sustainability of ecosystems by coordinating both environmental and human activities.

Heavy metals (HMs) in agricultural land have caused serious environmental problems, resulting in severe contamination of the food chain and posing potential health threats. This study aims to investigate the pollution levels and potential ecological risks of HMs in farmland soils in central China, taking into account atmospheric deposition. Several indices were used to assess the status of HMs and compare surface soil with deeper soil. Descriptive statistics, Pearson correlation, and UMAP clustering methods were utilized to identify the characteristics of HMs. Additionally, stepwise linear regression models were employed to quantify the contributions of different variables to the potential ecological risks of HMs. The results showed that the average content of Zn in surface soil (289.41 ± 87.72 mg/kg) was higher than in the deeper soil (207.62 ± 37.81 mg/kg), and similar differences were observed in the mean values of related Igeo (1.622 ± 0.453 in surface soil and 1.183 ± 0.259 in deeper soil) and PEI (0.965 ± 0.292 in surface soil and 0.692 ± 0.126 in deeper soil) indices. This indicates that surface soil is more heavily polluted. The UMAP results confirmed the high variability of HMs in the surface soil, while PCA results suggested the importance of pollution and ecological risk indices. The stepwise linear model revealed that different variable structures contribute differently to the risk. In conclusion, Cr and Zn were found to be the major contaminants in the local farmland soil, with higher concentrations in the surface soil. The geoaccumulation and total potential ecological risk were classified as low risk. High variability of HMs was observed in the surface soil. Therefore, HM-related pollution indices and ecological risk indices are important for assessing the contamination status of local HMs. The local potential ecological risk can be attributed to specific heavy metals, each of which can have different effects on the local ecological risk.

BackgroundWith the change of the national energy development layout, Qingyang has seen a situation where oil exploitation and agriculture go hand in hand, which may lead to local soil pollution if not taken seriously.ObjectiveTo evaluate the distribution characteristics, possible sources, and ecological risks of heavy metals in farmland soils around the main production areas of Changqing Oilfield.MethodsA total of 60 farmland soil samples were collected from Zhengning County, Zhenyuan County, and Qingcheng County of Qingyang City, and the contents of heavy metals such lead (Pb), mercury (Hg), chromium (Cr), cadmium (Cd), and arsenic (As) in farmland soil were detected according to GB 15618-2018 Soil environmental quality—Risk control standard for soil contamination of agricultural land (on trial). The soil background value of Gansu Province was used as the denominator in the calculation of pollution index, and the pollution characteristics and ecological characteristics of selected five heavy metals in farmland soil were evaluated by single-factor pollution index (Pi), Nemerow comprehensive pollution index (PN), and potential ecological risk index.ResultsThe levels of Pb, As, and Hg in farmland soils around Changqing Oilfield, the levels of Cr and Cd in Qingcheng County, and the level of Cd in Zhengning County were higher than the corresponding soil background values of Gansu Province, but lower than the national soil environmental quality standard. The single-factor pollution indexes (Pi) were: Hg, 2.14; Pb, 1.24; As, 1.13; Cr, 0.78; Cd, 0.67, which indicated that Hg were graded as moderate pollution, Pb and As were slight pollution, and Cd and Cr were not polluted. The Nemerow comprehensive pollution indexes (PN) were: Cr, 0.92; Cd, 1.08; As, 1.20; Pb, 1.68; Hg, 3.85, which indicated that Cr was graded as no pollution, Cd, Pb and As were mild pollution, and Hg was severe pollution. The variation coefficients of Hg and Cd in Zhenyuan County and that of Hg in Qingcheng County were 60.00%, 50.00%, and 50.00%, respectively, which were all greater than 50%, indicating that the pollution of above heavy metals in the location was subject to human activities. The potential ecological risk indexes (Er) of Pb, Cr, Cd, As, and Hg were 6.20, 1.55, 20.05, 11.28, and 81.64, respectively, indicating that Hg was graded as strong ecological risk, and the other four heavy metals were mild ecological risk. The comprehensive potential ecological risk index (RRI) was 124.48. Combined with the potential ecological risk index of Hg, the comprehensive potential ecological risk of the five heavy metals in local farmland soils was considered to be at a strong ecological risk level.ConclusionAlthough the average values of selected five heavy metals in farmland soils surrounding the main production areas of Changqing Oilfield are qualified with the national soil environmental quality standards, they exceed corresponding soil background values of Gansu Province, and there are signs of human influence and potential ecological risks of different degrees.

Converting biowaste into biochar and incorporating it into soil is recognized as an effective method for carbon (C) sequestration. However, biochar inevitably undergoes an aging process in soil, which influences its stability, and ultimately threatens its carbon sequestration ability. This study selected CaCl2 as an exogenous additive of sewage sludge and bone dreg for producing Ca-rich biochars, and both surface C and bulk C stability in them were investigated under three aging processes (dry–wet aging, freeze–thaw aging, and natural aging in farmland soil). The results showed that the above three aging processes resulted in oxidized surface C in Ca-rich biochar decreasing by 10~23%, 28~41%, and 0~74%, respectively, compared with that in pristine biochar, while oxidized bulk C decreased by 6~10%, 0~1%, and 0~35%, respectively. This was attributed to the “protective effect” of Ca-containing crystals on the biochar surface, including CaO, Ca5(PO4)3Cl, Ca5(PO4)3(OH), Ca8H2(PO4)6·H2O, and Ca10(PO4)6(OH)2, which intervened in the oxidation of C–C/C=C in biochar but also reduced the generation of a fragmented C structure. By comprehensively assessing surface C and bulk C stability under three aging processes, final C sequestration in Ca-rich biochar increased to 27~80%, compared to that in pristine biochar (23~74%). Therefore, Ca-rich biochar is more dominant than pristine biochar, considering C sequestration potential during long-term aging in soil.

The dissolved organic matter (DOM) is one of the most sensitive indicators of changes in the soil environment, and it is the most mobile and active soil component that serves as an easily available source of nutrients and energy for microbes and other living organisms. In this paper, DOM structural characteristics and main properties were investigated by three-dimensional fluorescence spectroscopy (EEM) and UV–visible spectrum technology in the farmland soils around Urumqi of China, and its possible sources and pathways were analyzed by spectroscopic indices. The results showed that humic-like substances were the main composition of the soil DOM, and its autogenesis characteristics were not obvious. Main DOM properties such as aromatability, hydrophobicity, molecular weight, molecular size, and humification degree in the southern region of Urumqi were higher than those of the northern region of Urumqi and Fukang in China, and higher on the upper layers of the soil (0–0.1 and 0.2 m) than in the deeper layer (0.2–0.3 m).This may be because the tilled layer is more subjected to fertilization and conducive to microbial activities. The spectroscopic analysis showed that the source of DOM of these regions is mainly from microbial metabolites. These results provide basic scientific data for the further research on the environmental chemical behavior of pollutants and pollution control in this region.

BACKGROUND The application of high frequency infrared carbon-sulfur analyzer to determine the organic matter in agricultural soil samples avoids the traditional method of sample liquid conversion. The method has a high measurement efficiency, but has problems such as low electromagnetic induction of soil samples and greater influence of the matrix. OBJECTIVES To solve the problems of low electromagnetic induction and large matrix effect in the determination of organic matter in agricultural soil samples. METHODS The iron and tungsten flux was optimized for the sample size. An accurate and efficient method for the determination of soil organic matter content was established by high frequency infrared carbon-sulfur analyzer. RESULTS When the conditions set for a sample size of 0.05g, the flux iron content was 0.40g, and the tungsten content was 1.50g, optimum results of organic content were obtained. The method was verified by soil standard materials. The detection limit of this method was 0.003%, the relative standard deviation (RSD, n=7) was less than 4%, and the error between the analytical result and the standard value was less than 5%. There was no significant difference between the results of different analytical staff. The proposed method and potassium dichromate volumetric method were used to analyze soil samples in farm land of Gansu Province. The absolute error ranges of this method and potassium dichromate volumetric method were from -0.25% to 0.28%. The positively linear correlation between the determination results (R2=0.9736) indicated that the two methods were in good agreement. CONCLUSIONS The detection limit, precision and accuracy of the established method meet the requirements of the soil samples of farm land.

As microplastics (MPs) are an emerging pollution to farmland ecosystems, the research into the ecological and environmental effects of MPs need to be clarified urgently. Available nitrogen is the determining factor for productivity in most terrestrial ecosystems, especially for the farmland ecosystems with a high productivity. To explore the effects of MPs on soil available nitrogen in farmland soil, an incubation experiment was conducted by adding polyethylene MPs with different concentrations to farmland soil, which was collected from farmland in Fuqing, Fujian Province. The contents of three different nitrogen forms (nitrate, ammonium, and dissolved organic nitrogen) and soil dissolved organic carbon were measured, and the soil mineralization rate was calculated. Bacteria was quantified and bacterial community diversity indexes were measured. The results showed that the MPs addition (T1 and T2) had no significant effect on soil ammonium, nitrate and soil nitrogen mineralization rate compared to the control (p > 0.05). However, a significant increase was observed in soil dissolved organic carbon and dissolved organic nitrogen content (p < 0.05). It can be seen that the influence of PE MPs on the soil dissolved organic nitrogen is greater than that of inorganic nitrogen. The results of this study showed no major detrimental effects of MPs on the abundance of some bacterial families, whereas a significant change in soil bacterial evenness index was observed in T2 treatment compared to the treatment without MPs addition. In the background of current MPs pollution, the research results can provide a scientific basis for reducing nitrogen loss in soil and protecting farmland soil safety.

High geological background and human activities are the two major pollution sources for soil potentially toxic elements (PTEs) accumulation around the world. Mining is the prime human activity that poses a serious threat to the farmland’s ecosystem safety. This study assesses the farmland safety in the typical high geological background area and the superimposed area of high background-mining activity in eastern Yunnan in China by systematic analysis of the accumulation and risk characteristics of seven PTEs such as arsenic (As), mercury (Hg), copper (Cu), zinc (Zn), lead (Pb), cadmium (Cd), and chromium (Cr). Furthermore, we used Cd as the characteristic element to establish a relationship model between crop PTEs accumulation and the physical and chemical characteristics of the soil. We find that in the farmland soil from the superimposed area, the accumulation point over-standard rate of seven PTEs is higher than in the typical high geological background area. The accumulation of Pb, Cd, Cu, and Zn is related to frequent man-made mining activities. The bioavailability relationship model, using Cd as the soil-crop characteristic element, reveals that only in the crops (cereals, vegetables) of the high geological background area; the Cd bio-concentration factor significantly correlate with the physical and chemical properties of the soil. This suggests that the PTEs contaminated farmland in high geological background areas can be concomitantly restored during usage by adjusting the soil’s physical and chemical properties, while in the superimposed area, the farmland area needs prior restoration by removing man-made mining activities.

In order to improve the energy efficiency of legged robots while walking on farmland, a simulation system of legged robot on farmland soil was put forward in this paper. Firstly, the finite element model of the interaction between the robot leg and the farmland soil was established, and the multi-body dynamics and the foot-ground interaction simulation were carried out in one gait cycle. Secondly, the orthogonal experiment with four factors was established to analyze the external energy required for the robot leg to walk in the soil. Then the range analysis and variance analysis of the results were carried out to optimize the energy consumption ratio. The influence of the four factors on the experimental results and the optimal gait parameters and foot structure were obtained subsequently. Finally, the no-load walking experiment in the self-developed soil-bin test-bed was carried out with the optimal gait and foot structure. The results demonstrate that the successive order of factors affecting the energy consumption ratio is foot structure, stride length, gait cycle time and stride height. The process of penetrating the soil consumes the most energy in a gait cycle. The optimization design of the foot structure and the penetration process is helpful to reduce the energy consumption of the farmland robot.

This study developed an analytical method to quantify glufosinate-P-ammonium (GLUF-P) in farmland soil using a reversed-phase high-performance liquid chromatography (HPLC) system with a fluorescence detector after derivatization. GLUF-P in farmland soil was extracted with a mixed alkaline solution and was further derivatized with 9-fluorenyl methyl chloroformate (FMOC) at 25 °C for 1 h. The derivatives were separated with an ACE-C18 column, gradient eluted with a mobile phase A of acetonitrile and a mobile phase B of 0.2% phosphoric acid solution, and finally determined by high-performance liquid chromatography (HPLC) with fluorescence detection at an excitation wavelength of 254 nm and an emission wavelength of 279.8 nm. The limits of detection (LODs) in the four types of soil ranged from 0.004 to 0.015 mg/kg, and the limits of quantification (LOQs) ranged from 0.0125 to 0.05 mg/kg. The mean recoveries of GLUF-P ranged from 94% to 119.8%, and the relative standard deviations (RSDs) varied between 2.8% and 9.0% when the spiked concentrations of GLUF-P were 0.1 mg/kg and 1.0 mg/kg, respectively. The coefficients of regression for the linearity equation were more than 0.99. The proposed method had high sensitivity and could be used for the determination of GLUF-P residues in farmland soil.

A total of 94 soil samples from different soil depths (0∼25 cm, 25∼50 cm) were collected of farmland soil around the plain of Beijing, and the concentrations of five heavy metal elements (Cd, Cr, Pb, As, and Hg) were measured using standard methods. The safety utilization evaluation method of heavy metals was based on three different evaluation methods. Then, the governance principles and specific management control strategy were determined in detail according to the core pollution source analysis of each safety grade zone. The results show that there are four different comprehensive safe utilization areas: safe, low-risk, medium-risk, and high-risk utilization. Among them, the study area was dominated by low-risk utilization areas, and the risk trend was gradually weakening from the center of the city to the periphery. Based on the characteristics of different security zones, this study puts on the governance principles of priority protection, long-term monitoring and moderate optimization, strengthens early warning, and cooperates with effective repair and priority governance. And then it puts forward practical control strategies according to the core pollution sources of each safety utilization zone. Our findings may provide a clear direction for rational utilization of land resources and renovation in the future.

Heavy metal elements in farmland soil can be absorbed by crops and endanger food security. To assess the risk of heavy metal elements in farmland soil to crops in Shaanxi Province, we collected 693 soil samples and analyzed the concentrations of nine heavy metals (As, Hg, Pb, Cd, Cr, Mn, Cu, Zn, and Ni). According to the National Standard (GB 15619-2018) of the People’s Republic of China, the proportions of soil sample points in which the concentration of heavy metals was higher than the risk screening value were 2.02% (Cd), 0.29% (Cr), 0.29% (Zn), 2.31% (Cu), 1.15% (Ni), and 0.14% (Pb). The proportions of areas in which the concentration of heavy metal was higher than the background value were as follows, from largest to smallest: Zn (53.20%) > Mn (49.86%) > Cd (29.51%) > Hg (26.77%) > As (26.58%) > Ni (14.95%) > Cu (13.90%) > Pb (6.49%) > Cr (1.40%). The assessment of the risk of heavy metal exposure (geo-accumulation index (Igeo), pollution load index (PLI), and potential ecological risk index (RI)) determined that Hg was the most concerning heavy metal in the farmland soil of Shaanxi Province. Moreover, 11.56% of these areas had Hg contamination, and they were mainly distributed in the western Guanzhong region. The farmland soil in the Guanzhong region was the most contaminated, followed by the southern Shaanxi region and then the northern Shaanxi region. The main sources of heavy metal contamination causing large-scale farmland soil pollution are agricultural production activities, transportation, and air pollution caused by coal combustion in Shaanxi Province. Therefore, sustainable strategies for the prevention and control of heavy metal pollution and agricultural development must be applied in different regions. Heavy metal pollution should be managed, and relevant policies should be created and enforced, such as the standardization of the use of qualified pesticides and fertilizers, improved treatment of livestock and poultry manure, development of the clean energy industry structure, and promotion of renewable energy vehicles. In terms of the high-quality development of agriculture, developing modern and local agriculture in different regions should be based on local geographical, climatic, and economic conditions.

Abstract Soil microorganisms are considered to be important indicators of soil fertility and soil quality. Most previous studies have focused solely on surface soil, but there were numerous active cells in deeper soil layers. However, studies regarding microbial communities in deeper soil layers were not comprehensive and sufficient. In this study, phylogenetic molecular ecological networks (pMENs) based on the 16S rRNA Miseq sequencing technique were applied to study the response of soil microbial communities to depth gradients and the changes of key genera along 3 meter depth gradients (0–0.2 m, 0.2–0.4 m 0.4–0.6 m, 0.6–0.8 m, 0.8–1.0 m, 1.0–1.3 m, 1.3–1.6 m, 1.6–2.0 m, 2.0–2.5 m, and 2.5–3.0 m). The results showed that the modularity of microbial communities was consistently high in all soil layers and each layer was similar, which indicated that microbial communities were more resistant to depth changes. The pMENs further demonstrated that microbial community interactions were stable as the depth increased and they cooperated well to adapt to changes in different soil gradients. This was evidenced by similar positive links, average degree, and average clustering coefficient. In addition, key genera were obtained by analyzing module hubs in the pMENs. There may be at least one dominant genus in each layer that adapted to and resisted changes in the soil environment. It seems microbial communities demonstrate a stable and strong adaptability to depth gradients in farmland soils.

Soil microorganisms play an important role in agricultural ecosystems, but their response to organic fertilizer application has not been thoroughly elucidated. Thus, high-throughput sequencing was used to investigate the responses of soil bacterial to organic fertilizer amendment (composted from pig manure) in the field during the entire growth cycle of maize plants. Four treatments were studied: treatment with 2 kg·m−2 organic fertilizer application (OF_2), treatment with 4 kg·m−2 organic fertilizer application (OF_4), treatment with 6 kg·m−2 organic fertilizer application (OF_6), and a controlled treatment (CK) without fertilization. The results revealed that the bacterial richness in OF_2 was significantly lower than that of CK (p < 0.05). Soil eutrophication bacteria Bacteroidetes increased effectively in all fertilized soils, relative abundance in OF_2, OF_4, and OF_6 for the entire maize growth cycle was 68.00%, 71.40%, and 77.93% higher than that in CK, respectively. In addition, soil nitrobacteria (Nitrospirae, Nitrospira), were markedly decreased (p < 0.05) with fertilization amount. The relative abundance of the nitrogen-fixing genus Adhaeribacter in OF_6 was 209.28%, 72.8% and 35.66% higher than that in CK, OF_2 and OF_4 at mature stage. The pathogenic genus Flavolibacterium was significantly increased (p < 0.05) in fertilized soil at the seeding stage. The driving factor governing the variations of bacterial community in CK, OF_2, OF_4 and OF_6 were pH value, available phosphorus, available phosphorus, and chromium, respectively. The findings highlight that part of the soil functional or pathogenic bacteria population was susceptible to organic fertilizer application; and the driving factor of bacterial composition change was associated with the rate of fertilization. More targeted experiments are needed to enhance the understanding of functional bacteria and the synergistic effect of soil physicochemical property physical on soil bacteria.

For the research on degradation and remediation of soil polycyclic aromatic hydrocarbons (PAHs) pollutants, researchers have been trying to find an effective method to quantize the dynamic processes. Many approaches have been designed, such as spiked experiment, concentrations comparison before and after the degradation, and modeling calculations. However, all of this culminates in contradictory results and lack of corroboration of the actual environment. Compound Specific Isotope Analysis (CSIA) technique is used in this study to investigate the phytodegradation process of soil PAHs with maize as the testing plant. Total concentrations of 16 PAHs in the bulk soil, rhizosphere soil and in the controlled soil samples were (299.8±37.9) ng/g, (272.2±11.6) ng/g, and (281.5±34.7) ng/g, respectively, all much lower than the original cultivating soil (380.8 ng/g). The soil PAHs concentrations did not show significant decline tendency during the maize growing period, except for 3-ring PAH compounds which was consistent with the accumulation effect of the 3-ring PAHs in maize roots and leaves. The δ13C value of 6 PAH compounds ranged from -34.31‰ to -23.95‰ with fluctuations between -0.6‰--9.0‰, and all δ13C values turned lighter with maize plants growing except that of Pyrene. No significant correlation between δ13C and the concentration of 4-, 5-ring PAHs was observed during the maize cultivating process. Most research indicates that PAHs and other macromolecular compounds strongly resist phytodegradation, which illustrates less obvious carbon isotope fractionation. PAH compounds below 3 rings would degrade more easily and the isotopes fractionate more significantly than those of other macromolecular compounds, thus maing the technique of CSIA more advantageous for understanding the transportation pathway of these compounds.

For the research on degradation and remediation of soil polycyclic aromatic hydrocarbons (PAHs) pollutants, researchers have been trying to find an effective method to quantize the dynamic processes. Many approaches have been designed, such as spiked experiment, concentrations comparison before and after the degradation, and modeling calculations. However, all of this culminates in contradictory results and lack of corroboration of the actual environment. Compound Specific Isotope Analysis (CSIA) technique is used in this study to investigate the phytodegradation process of soil PAHs with maize as the testing plant. Total concentrations of 16 PAHs in the bulk soil, rhizosphere soil and in the controlled soil samples were (299.8±37.9) ng/g, (272.2±11.6) ng/g, and (281.5±34.7) ng/g, respectively, all much lower than the original cultivating soil (380.8 ng/g). The soil PAHs concentrations did not show significant decline tendency during the maize growing period, except for 3-ring PAH compounds which was consistent with the accumulation effect of the 3-ring PAHs in maize roots and leaves. The δ13C value of 6 PAH compounds ranged from -34.31‰ to -23.95‰ with fluctuations between -0.6‰--9.0‰, and all δ13C values turned lighter with maize plants growing except that of Pyrene. No significant correlation between δ13C and the concentration of 4-, 5-ring PAHs was observed during the maize cultivating process. Most research indicates that PAHs and other macromolecular compounds strongly resist phytodegradation, which illustrates less obvious carbon isotope fractionation. PAH compounds below 3 rings would degrade more easily and the isotopes fractionate more significantly than those of other macromolecular compounds, thus maing the technique of CSIA more advantageous for understanding the transportation pathway of these compounds.