Influence of manure application method on veterinary medicine losses to water.

Veterinary medicines are routinely used within modern animal husbandry, which results in frequent detections within animal manures and slurries. The application of manures to land as a form of organic fertiliser presents a pathway by which these bioactive chemicals can enter the environment. However, to date, there is limited understanding regarding the influence of commonly used manure application methods on veterinary medicine fate in soil systems. To bridge this knowledge gap, a semi-field study was conducted to assess the influence of commonly used application methods such as, broadcast, chisel sweep, and incorporation on veterinary medicine losses to waters. A range of veterinary medicines were selected and applied as a mixture; these were enrofloxacin, florfenicol, lincomycin, meloxicam, oxytetracycline, sulfadiazine, trimethoprim and tylosin. All the assessed veterinary medicines were detected within surface runoff and leachates, and the concentrations generally decreased throughout the irrigation period. The surface runoff concentrations ranged from 0.49 to 183.47 µg/L and 2.26-236.83 µg/L for the bare soil and grass assessments respectively. The leachate concentrations ranged from 0.04 to 309.66 µg/L and 0.33-37.79 µg/L for the bare soil and grass assessments respectively. More advanced application methods (chisel sweep) were found to significantly reduce the mass loads of veterinary medicines transported to surface runoff and leachate by 13-56% and 49-88% over that of broadcast. Incorporating pig slurries reduced the losses further with surface runoff and leachate losses being 13-56% and 49-88% lower than broadcast. Our results show that manure application techniques have a significant effect on veterinary medicine fate in the environment and as such these effects should be considered in the decision-making processes for the management of manures as well as from a risk mitigation perspective for aquatic compartments.

Replacing chemical fertilizer with manure reduces N2O emissions in winter wheat - summer maize cropping system under limited irrigation.

Nitrous oxide (N2O) emissions from agroecosystems are a major contributor to global warming and stratospheric ozone depletion. However, knowledge concerning the hotspots and hot moments of soil N2O emissions with manure application and irrigation, as well as the underlying mechanisms remain incomplete. Here, a 3-year field experiment was conducted with the combination of fertilization (no fertilizer, F0; 100% chemical fertilizer N, Fc; 50% chemical N + 50% manure N, Fc + m; and 100% manure N, Fm) and irrigation (with irrigation, W1; and without irrigation, W0; at wheat jointing stage) for winter wheat - summer maize cropping system in the North China Plain. Results showed that irrigation did not affect annual N2O emissions of the wheat-maize system. Manure application (Fc + m and Fm) reduced annual N2O emissions by 25-51% compared with Fc, which mainly occurred during 2 weeks after fertilization combined with irrigation (or heavy rainfall). In particular, Fc + m reduced the cumulative N2O emissions during 2 weeks after winter wheat sowing and summer maize top dressing by 0.28 and 0.11 kg ha-1, respectively, compared with Fc. Meanwhile, Fm maintained the grain N yield and Fc + m increased grain N yield by 8% compared with Fc under W1. Overall, Fm maintained the annual grain N yield and lower N2O emissions compared to Fc under W0, and Fc + m increased the annual grain N yield and maintained N2O emissions compared with Fc under W1, respectively. Our results provide scientific support for using manure to minimize N2O emissions while maintaining crop N yield under optimal irrigation to support the green transition in agricultural production.

Spatial Distributions, Compositional Profiles, Potential Sources, and Intfluencing Factors of Microplastics in Soils from Different Agricultural Farmlands in China: A National Perspective.

More attention has been paid to ubiquitous microplastics (MPs). As a major food producer, the situation of MPs in China's farmland is of even greater concern. Spatial distributions, characteristics, and compositions of MPs in five types of agricultural lands with representative crops were investigated by collecting 477 soil samples from 109 cities in 31 administrative regions of mainland China. To better control MPs in farmland, nearly 400 field questionnaires were obtained, and meteorological conditions, soil properties, and other statistics were collected to quantify potential sources and determine influencing factors. The average abundances of MPs was 2462 ± 3767 items/kg in the agricultural soils, and MP abundance in the greenhouses, farmlands with film mulching, and blank farmlands from four integrated physical geographic regions were determined. The contributions of agricultural films, livestock and poultry manures, irrigation water, and air deposition to MPs in farmlands have been calculated. Influencing factors, such as recovery method, plowing frequency, meteorological conditions, and part of soil properties, were significantly correlated with the abundances of MPs in the agricultural soils (p < 0.05), while mulching age mainly affected MPs in the greenhouses (p < 0.05). This study provides basic scientific data for decision-making and further analysis.

A meta-analysis of arable soil phosphorus pools response to manure application as influenced by manure types, soil properties, and climate.

Manure amendments to agricultural soils is an excellent opportunity for sustainable utilization of agricultural waste while providing multiple benefits to improve soil quality and increase the availability of nutrients to plants, including phosphorus (P). In this study, a meta-analysis of published data from 411 independent observations based on 133 peer-reviewed papers was performed for an in depth understanding of various factors affecting the transformation of soil P pools with manure application. Manure application increased all soil inorganic P (Pi) by 58.0%-282% and organic P (Po) by 65.0%-105%, while decreasing Po/total P (TP), compared to those in unamended soils. Manure types, soil TP, and manure application rates were the important factors that influenced soil P fractions. Elevation of soil labile Pi was more pronounced with compost application, while poultry and pig manure were more beneficial for promoting soil Pi fractions and stable Po contents compared with other manure types. The manure application rate had pronounced effect on increasing the stable Po fractions. The effects of manure application on increasing soil P fractions were greater in soils with lower TP contents as compared to that in high TP soils. Manure effects on enhancing soil labile Pi and moderately labile Pi were greater in acidic soil than that in neutral and alkaline soils. In addition, soil P fractions showed significant correlation with latitude and mean annual precipitation (MAP). By integrating the impacts of manure types, soil properties, and climate, this meta-analysis would help to develop the management of manure application in a specific region of agriculture as well as promote the interpretation of the interfering factors on the soil P fractions changes in the manure-amended soils.

The Effect of Manure Application on Arsenic Mobilization and Methylation in Different Paddy Soils.

Organic matter plays an important role in controlling arsenic(As) release and transformation in soil, however, little is known about the effect of manure application on As behavior in soils with different As contents. In this study, waterlogged incubations using various As-contaminated paddy soils with manure amendment were conducted to investigate how manure application influence As mobilization and methylation in different paddy soils. The results indicated that manure application increased As release in paddy soils with high As (> 30 mg kg-1) contents. Moreover, our findings also showed that manure application increased the relative abundance of arsM-harboring Euryacheota and Planctomycetes at the phylum level and arsM-harbouring Methanocellaceae, Anaerolinea and Bellinea at genus level, thereby promoting As methylation. These results provide important insights for the significant variation in As mobilization and methylation in paddy soils amended with manure. Moreover, our results suggest that serious consideration should be given to the manure application in As-contaminated paddy soil.

Responses of soil organic carbon stock to animal manure application: A new global synthesis integrating the impacts of agricultural managements and environmental conditions.

Enhancing soil organic carbon (SOC) through applying animal manure is of interest for both sustaining cereal production and mitigating greenhouse gas (GHG) emissions. Previous syntheses showed that manuring-induced SOC changes varied substantially with agricultural managements and environmental conditions, while their significance and relative importance to such variability are still largely uncertain. Here, we presented a new synthesis using an updated and balanced database integrating the manuring-induced SOC stock changes and their plausible explanatory factors in 250 observations at global 120 sites. Manure application increased SOC stock by 7.41 ± 1.14 (95% confidence interval, CI) and 8.96 ± 1.83 (95% CI) Mg C ha-1 , respectively, compared to their mineral fertilized (REF-min) and unfertilized (REF-zero) references. Of which approx. 72% and 34% were directly contributed by manure-C input, respectively. Following the IPCC (Intergovernmental Panel on Climate Change) approach, these changes corresponded to the manuring-induced SOC change factors of 1.27 ± 0.04 (95% CI) and 1.40 ± 0.08 (95% CI), respectively. Basing on a balanced database, we identified the amount of manure-C input as the most important factor to the global variations in the resultant SOC stock changes. More importantly, our integrative analysis distinguished the significance of soil properties (e.g., soil pH and initial SOC content) in regulating the efficiency of manure application in enhancing SOC stock. These results indicate that, at the similar rate, applying manure could sequestrate much more carbon in alkaline soils than in neutral and acidic soils. By integrating the impacts of agricultural managements and environmental conditions, our findings would help to develop region-specific tailor-made manure application measures in agriculture and to refine the SOC change factors for regional GHG inventories.

Application of manure containing tetracyclines slowed down the dissipation of tet resistance genes and caused changes in the composition of soil bacteria.

Manure application contributes to the increased environmental burden of antibiotic resistance genes (ARGs). We investigated the response of tetracycline (tet) resistance genes and bacterial taxa to manure application amended with tetracyclines over two months. Representative tetracyclines (oxytetracycline, chlorotetracycline and doxycycline), tet resistance genes (tet(M), tet(O), tet(W), tet(S), tet(Q) and tet(X)) and bacterial taxa in the untreated soil, +manure, and +manure+tetracyclines groups were analyzed. The abundances of all tet resistance genes in the +manure group were significantly higher than those in the untreated soil group on day 1. The abundances of all tet resistance genes (except tet(Q) and tet(X)) were significantly lower in the +manure group than those in the +manure+tetracyclines group on day 30 and 60. The dissipation rates were higher in the +manure group than those in the +manure+tetracyclines group. Disturbance of soil bacterial community composition imposed by tetracyclines was also observed. The results indicated that tetracyclines slowed down the dissipation of tet resistance genes in arable soil after manure application. Application of manure amended with tetracyclines may provide a significant selective advantage for species affiliated to the taxonomical families of Micromonosporaceae, Propionibacteriaceae, Streptomycetaceae, Nitrospiraceae and Clostridiaceae.

Fate of metal resistance genes in arable soil after manure application in a microcosm study.

Manure application contributes to the spread and persistence of metal resistance genes (MRGs) in the environment. We investigated the fate of copper (Cu) and zinc (Zn) resistance genes (pcoA, pcoD and zntA) in arable soil after Cu/Zn-containing manure application. Manure with or without addition of metals (Cu/Zn) was added in a soil microcosm over 2 months. Soil samples were collected for analysis on day 0, 30 and 60. The abundances of all MRGs (pcoA, pcoD and zntA) in manure group were significantly higher than those in untreated soil and manure+metals groups. All MRGs dissipated 1.2-1.3 times faster in manure group (from -90 ± 8% to -93 ± 7%) than those in manure+metals group (from -68 ± 8% to -78 ± 5%). The results indicated that manure from healthy pigs contributed to the occurrence of metals (Cu/Zn) and MRGs (pcoA, pcoD and zntA) in arable soil. The significant effects of manure application on the accumulation of pcoA, pcoD and zntA lasted for 1-2 months. Cu/Zn can slow down the dissipation of pcoA, pcoD and zntA after manure application. This is the first report to investigate the fate of MRGs in soil after manure application.

The fate of 17ß-estradiol in snowmelt from a field with a history of manure application: A laboratory simulation and field study.

17ß-estradiol is a naturally occurring estrogen, and livestock manure applied to agricultural fields is a major source to the environment. Liquid swine manure is widely applied to agricultural fields in the Canadian Prairies, a region where the majority of the annual runoff occurs during a brief snowmelt period over frozen soil. Transport of estrogens from manure amendments to soil during this important hydrological period is not well understood but is critical to mitigating the snowmelt-driven offsite transport of estrogens. This study quantified the concentration and load of 17ß-estradiol in snowmelt from an agricultural field with a history of manure application under manure application methods: no manure applied, manure applied on the sub-surface, and on the surface, using a laboratory simulation study with flooded intact soil cores and a field study during snowmelt. A higher concentration of 17ß-estradiol was in the laboratory simulation than in the field (mean laboratory pore water = 1.65 ± 1.2 µg/L; mean laboratory flood water = 0.488 ± 0.58 µg/L; and mean field snowmelt = 0.0619 ± 0.048 µg/L). There were no significant differences among manure application methods for 17ß-estradiol concentration. Laboratory pore water concentrations significantly increased over time, corresponding with changes in pH. In contrast, there was no significant change in the field snowmelt concentrations of 17ß-estradiol over time. However, for both laboratory simulation experiments and field-based snowmelt experiments, mean concentrations of 17ß-estradiol were higher with subsurface than surface-applied manure, and the cumulative load of 17ß-estradiol was significantly higher in the sub-surface than in surface applied. The mean cumulative load from the field study across all treatments (6.91 ± 3.7 ng/m2) approximates the magnitude of 17ß-estradiol that could be mobilized from manured fields. The sub-surface application of manure seems to increase the persistence of 17ß-estradiol in soil, thus enhancing the potential loss to snowmelt runoff.

Manure application maintained the CO2 fixation activity of soil autotrophic bacteria but changed its ecological characteristics in an entisol of China.

The response of soil autotrophs to anthropogenic activities has attracted increasing attention against the background of global change. Here, three entisol plots under different fertilizing regimes, including no fertilization (CK), manure (M), and a combined application of chemical fertilizer and manure (NPKM) were selected, and then the soil RubisCO (ribulose-1,5-bisphosphate carboxylase/oxygenase) activity and cbbl (gene encoding the large subunit of RubisCO) composition were measured to indicate the activity and community of autotrophic bacteria, respectively. The results revealed that the RubisCO activity of CK showed no difference from that of M but was significantly higher than that of NPKM. The CK and M had the lowest and highest soil cbbl abundance, respectively. The α-diversity of soil cbbl-carrying bacteria showed no significant difference among these treatments, whereas they showed significantly different community structures of cbbl-carrying bacteria. Meanwhile, compared with CK, M had significantly lower abundances of bacterial species with the functions of nitrogen fixation (Azoarcus sp.KH32C) or detoxification (Methylibium petroleiphilum), indicating that manure application might have an inhibiting potential to some beneficial autotrophic bacterial species in this entisol.

Selective increase of antibiotic-resistant denitrifiers drives N2O production in ciprofloxacin-contaminated soils.

Agricultural systems significantly contribute to global N2O emissions, which is intensified by excessive fertilization and antibiotic residues, attracting global concerns. However, the dynamics and pathways of antibiotics-induced soil N2O production coupled with microbial metabolism remain controversial. Here, we explored the pathways of N2O production in agricultural soils exposed to ciprofloxacin (CIP), and revealed the underlying mechanisms of CIP degradation and the associated microbial metabolisms using 15N-isotope labeling and molecular techniques. CIP exposure significantly increases the total soil N2O production rate. This is attributed to an unexpected shift from heterotrophic and autotrophic nitrification to denitrification and an increased abundance of denitrifiers Methylobacillus members under CIP exposure. The most striking strain M. flagellatus KT is further discovered to harbor N2O-producing genes but lacks a N2O-reducing gene, thereby stimulating denitrification-based N2O production. Moreover, this denitrifying strain is probably capable of utilizing the byproducts of CIP as carbon sources, evidenced by genes associated with CIP resistance and degradation. Molecular docking further shows that CIP is well ordered in the catalytic active site of CotA laccase, thus affirming the potential for this strain to degrade CIP. These findings advance the mechanistic insights into N2O production within terrestrial ecosystems coupled with the organic contaminants degradation.

Investigating the effects of climate change and anthropogenic activities on SOC storage and cumulative CO2 emissions in forest soils across altitudinal gradients using the century model.

This study investigated the impact of climate change, grazing, manure application, and liming on soil organic carbon (SOC) stock and cumulative carbon dioxide (CO2) emissions in forest soils across different altitudes. Despite similar soil texture, acidity, and salinity across elevations, SOC stock significantly increased with altitude due to cooler temperatures and higher precipitation. The highest SOC stock (97.46 t ha-1) was observed at 2000-2500 m, compared to the lowest (44.23 t ha-1) at 500-1000 m. The Century C Model accurately predicted SOC stock, with correlation and determination coefficients exceeding 0.98. A climate change scenario projecting decreased precipitation (2.15 mm per decade) and increased temperature (0.4 °C) revealed potential SOC stock losses ranging from 28.36 to 36.35 %, particularly at higher altitudes. Grazing further decreased SOC stock, with a more pronounced effect at higher elevations. However, manure application (40 t ha-1 every four years) and liming (7-10 t ha-1 every three years) had positive effects on SOC stock, again amplified at higher altitudes and with an increase in lime application rate. In scenarios combining climate change with manure application and climate change with liming, manure application and liming mitigated some negative impacts of climate change, but could not fully offset them, resulting in 1.49-5.42 % and 0.39-4.07 % decreases respectively. Simulations of cumulative CO2 emissions mirrored the distribution of SOC stock, with higher emissions observed at higher altitudes and with management practices that increased SOC stock. This study emphasizes the critical role of conserving high-altitude forest soils and implementing optimal forest management strategies to combat climate change by minimizing SOC losses.

Nitrate in shallow groundwater after more than four decades of manure application.

Over-application of manure to agricultural fields can leach nitrogen below the root zone and contaminate groundwater. The goal of this study was to evaluate the factors affecting the spatial and temporal distribution of nitrate in shallow groundwater following 44 years of manure application to irrigated and non-irrigated long-term test plots. Sampling of 26 wells over an 18-month period revealed high spatial variability of groundwater nitrate concentrations, ranging from <0.1 mg-N/L to 1350 mg-N/L (mean = 118 mg-N/L). The highest concentrations were associated with the highest manure nitrogen loads, longer durations of manure application, and were generally located beneath irrigated land use. Regression modeling confirmed that cumulative manure loading had the greatest control on the spatial distribution of groundwater nitrate. A significant decreasing temporal trend was observed in selected wells downgradient of plots where manure application ceased more than a decade earlier. Isotopic analysis of 15N-NO3 and 18O-NO3 showed that denitrification occurred at 16 well locations, with evidence for dissolved organic carbon as the electron donor. The groundwater nitrate trends observed in this long-term study demonstrate that historical nutrient and water management practices will affect groundwater quality for many decades to come.

Dynamic characteristics of heavy metal accumulation in agricultural soils after continuous organic fertilizer application: Field-scale monitoring.

Manure has been considered as a source of soil heavy metal (HM) pollution. However, the long-term impact of manure application on soil HM accumulation have not been well studied. This study tracked the long-term cumulative trends of soil copper (Cu), zinc (Zn), arsenic (As), and lead (Pb) in three soil-crop systems over 5-8 years' application of commercial manure fertilizer. The contribution of different fertilization treatments (CF, chemical fertilizer; T1-T3, manure with different application dosages) to soil HMs pollution risk were assessed. There are accumulating tendencies for Cu, Zn, and Pb in paddy fields, Cu and As in orchard fields, and Zn, As, and Pb in vegetable fields, while the concentrations of As in paddy fields and Zn in orchard fields decreased over time. Manure application significantly influenced the accumulation of Cu, Zn, and As in soils rather than that of Pb. The modeling prediction subsequently revealed that the time required to reach the risk screening values (Cu: 50 mg kg-1; Zn: 200 mg kg-1) for HM content in paddy soil, according to GB15618-2018, decreased from 18.20 years to 7.20 years due to the introduction of Cu and Zn via manure use. Recommend annual manure application dosage was 7.73 t hm-2 y-1 to ensure a 20-year period of clean production in paddy soils, while it was 26.15 t hm-2 y-1 in the orchard soil and 16.23 t hm-2 y-1 in vegetable soil to ensure a 50-year period of clean production, respectively. Overall, the impacts of HMs input by manure application on soil HMs accumulation varied depending on the type of metal and the soil-crop system. The cumulative trends of HMs in soils play a crucial role in determining whether the input of HMs through manure application can lead to the risk of HM pollution.

Drive soil nitrogen transformation and improve crop nitrogen absorption and utilization - a review of green manure applications.

Green manure application presents a valuable strategy for enhancing soil fertility and promoting ecological sustainability. By leveraging green manures for effective nitrogen management in agricultural fields can significantly reduce the dependency of primary crops on chemical nitrogen fertilizers, thereby fostering resource efficiency. This review examines the current advancements in the green manure industry, focusing on the modulation of nitrogen transformation in soil and how crops absorb and utilize nitrogen after green manure application. Initially, the influence of green manure on soil nitrogen transformation is delineated, covering processes such as soil nitrogen immobilization, and mineralization, and losses including NH3, N2O, and NO3 --N leaching. The review then delves into the effects of green manure on the composition and function of soil microbial communities, highlighting their role in nitrogen transformation. It emphasizes the available nitrogen content in the soil, this article discussing nitrogen uptake and utilization by plants, including aspects such as nitrogen translocation, distribution, the root system, and the rhizosphere environment of primary crops. This provides insights into the mechanisms that enhance nitrogen uptake and utilization when green manures are reintroduced into fields. Finally, the review anticipates future research directions in modulating soil nitrogen dynamics and crop nitrogen uptake through green manure application, aiming to advance research and the development of the green manure sector.

Hypothetical scenarios estimating and simulating the fate of antibiotics: Implications for antibiotic environmental pollution caused by manure application.

The application of animal manure containing antibiotic residues as an organic fertilizer to farmlands, poses a major threat to the health of river basin ecosystems. Waste treatment processes can help reduce antibiotic pollution levels in river basins following manure application, but the overall influence of these processes remains unclear. This study evaluates the impact of manure treatment methods on the emission and subsequent river pollution caused by 14 frequently detected antibiotics in a typical pig breeding area in China, by using hypothetical scenarios method. Three scenarios were constructed based on possible fate pathways of antibiotics, representing in 47.0, 55.3, and 81.6 ton·yr-1 antibiotic emissions into the river basin. The soil and water assessment tool (SWAT) model successfully simulated the transport of antibiotics from farmland to surface water, with calibration and verification performed using hydrological station monthly data over 8 consecutive years. Field measured concentrations also verified the reliability of the model and were used to determine the most realistic scenario. In basins applied with manure, environmental antibiotic pollution is most affected by the wastewater treatment process and manure applied patterns, followed by changes in streamflow. The antibiotic pollution in manure applied areas showed significant spatial and temporal differences, resulting from the different manure application patterns. The simulated total outflow of antibiotics in the river basin accounted for 18.1% of the inflow, with the loss of target antibiotics by degradation, volatilization and sedimentation deposition in the river basin being 0.23, 0.01 and 33.2 ton·yr-1, respectively. This study can help to clarify the environmental fate of antibiotics in the basin following manure application, provide guidance for policy makers and help to design the effective corrective interventions for reducing the environmental pollution.

Manure applications alter the abundance, community structure and assembly process of diazotrophs in an acidic Ultisol.

The excessive usage of nitrogen (N) fertilizers can accelerate the tendency of global climate change. Biological N fixation by diazotrophs contributes substantially to N input and is a viable solution to sustainable agriculture via reducing inorganic N fertilization. However, how manure application influences the abundance, community structure and assembly process of diazotrophs in soil aggregates is not fully understood. Here, we investigated the effect of manure amendment on diazotrophic communities in soil aggregates of an arable soil. Manure application increased soil aggregation, crop yield and the abundance of nifH genes. The abundance of nifH genes increased with aggregate sizes, indicating that diazotrophs prefer to live in larger aggregates. The abundance of nifH genes in large macroaggregates, rather than in microaggregates and silt and clay, was positively associated with plant biomass and crop yield. Both manure application and aggregate size did not alter the Shannon diversity of diazotrophs but significantly changed the diazotrophic community structure. The variation of diazotrophic community structure explained by manure application was greater than that by aggregate size. Manure application promoted the relative abundance of Firmicutes but reduced that of α-Proteobacteria. Stochastic processes played a dominant role in the assembly of diazotrophs in the control treatment. Low-rate manure (9 Mg ha-1) application, rather than medium-rate (18 Mg ha-1) and high-rate (27 Mg ha-1) manure, significantly increased the relative importance of deterministic processes in diazotrophic community assembly. Taken together, our findings demonstrated that long-term manure application increased nifH gene abundance and altered the community structure and assembly process of diazotrophs in soil aggregates, which advanced our understanding of the ecophysiology and functionality of diazotrophs in acidic Ultisols.

Distinct aggregate stratification of antibiotic resistome in farmland soil with long-term manure application.

Agricultural soils, which are closely linked to human health via food supply, have been recognized as an important reservoir for antibiotic resistance genes (ARGs). However, there is still a lack of knowledge regarding the role of soil aggregates in shaping ARG profile. In this study, we collected soils from long-term experimental farmland plots receiving inorganic and/or organic fertilizers and examined the patterns of antibiotic resistome distribution among differently sized soil aggregates using high-throughput quantitative polymerase chain reaction (HT-qPCR). Our results showed that the distribution of soil ARGs could be affected by manure application and aggregate size individually but not interactively. More diverse and abundant ARGs were found in the manured soils, compared to the non-manured soils. The aggregate size fraction of <53 µm exhibited the highest diversity and abundance of ARGs. Variation partitioning analysis revealed that soil traits, mobile genetic elements, and bacterial community collectively contributed to the variation of soil antibiotic resistance. The knowledge about aggregation stratification of soil ARGs obtained in this study is fundamental and essential to understanding the fate of soil ARGs at the microscale.

Impacts of farmland application of antibiotic-contaminated manures on the occurrence of antibiotic residues and antibiotic resistance genes in soil: A meta-analysis study.

A meta-analysis of 94 published studies was conducted to explore the impacts of farmland application of antibiotic-contaminated manures on antibiotic concentrations and ARG abundances in manure-amended soil. Forty-nine antibiotics were reported, in which chlortetracycline, oxytetracycline, doxycycline, tetracycline, enrofloxacin, ciprofloxacin and norfloxacin were the most prevalent and had relatively high concentrations. The responses of ARG and mobile genetic element (MGE) abundances to farmland application of antibiotic-contaminated manures varied considerably under different management strategies and environmental settings. On average, compared to unamended treatments, farmland application of antibiotic-contaminated manures significantly increased the total ARG and MGE abundances by 591% and 351%, respectively (P < 0.05). Of all the included ARG classes, the largest increase was found for sulfonamide resistance genes (1121%), followed by aminoglycoside (852%) and tetracycline (763%) resistance genes. Correlation analysis suggested that soil organic carbon (SOC) was significantly negatively correlated with antibiotic concentrations in manured soil (P < 0.05) due to the formation of covalent bonds and nonextractable residues. Soil silt content was significantly positively correlated with antibiotic concentration (P < 0.05), which was attributed to greater sorption capacities. The ARG abundances were significantly positively correlated with soil silt content, antibiotic concentrations, mean annual temperature, SOC, MGEs and soil pH (P < 0.05), suggesting that changes in these factors may shape the ARG profiles. Collectively, these findings advanced our understanding of the occurrence of antibiotics and ARGs in manure-amended soil and potential factors affecting them and will contribute to better management of these contaminants in future agricultural production.

Microbial community composition and antimicrobial resistance in agricultural soils fertilized with livestock manure from conventional farming in Northern Italy.

Antimicrobials are commonly used in conventional livestock production and manure is widely applied to agricultural lands as fertilizer. This practice raises questions regarding the effects of fertilization on (i) soil microbiota composition and (ii) spread of antimicrobials and antimicrobial resistance (AMR) in the environment. This study was conducted in a high-density farming area of Northern Italy and aimed at assessing the impact of (dairy cattle, chickens and swine) manure application on soil microbiome, antimicrobial concentrations and antimicrobial resistance gene (ARG) abundance. We found the microbial community composition in manure to be different and less diverse than in soil, with manure application altering only marginally the soil microbiome. Exceptions were the phyla Firmicutes, Tenericutes and Cloacimonetes, which significantly enriched in fertilized soil. Of the antimicrobials investigated, only flumequine concentrations increased after manure application, albeit non-significantly. ARGs were more abundant in manure, with ermA, ermB, blaOXA-1 and oqxA being significantly enriched in fertilized soil. Positive correlations between oqxA and qnrS abundances and flumequine concentrations were observed, together with the co-occurrence of some ARGs and microbial taxa (e.g. oqxA correlated with Acidobacteria and Gemmatimonadetes). This study showed that manure application has little effect on soil microbiome but may contribute to the dissemination of specific ARGs into the environment. Moreover, flumequine residues seem to enhance the emergence of oqxA and qnrS in soil.