Stimulating the biofilm formation of Bacillus populations to mitigate soil antibiotic resistome during insect fertilizer application

Inorganic and organic fertilizers application enhanced antibiotic resistome in greenhouse soils growing vegetables

Image courtesy of Flickr/Ravenz Shadow. Images (l to r) courtesy of Adobe Stock, USGS, USGS, NIAID, and Texas A&M AgriLife Research (photo by Kay Ledbette). Emerging contaminants include antibiotics, flame retardants, and personal care products. These compounds are commonly found in low concentrations in the wastewater, biosolids, and manure used in agricultural systems as irrigation and fertilizer. Emerging contaminants enter the environment as products that go down the drain in our homes, from industrial sources, and in the manure of livestock treated with antibiotics. Although increased monitoring has identified the presence of these compounds, little is known about how emerging contaminants move through the environment, or what impacts they may have over time. A special section recently published in the Journal of Environmental Quality (JEQ) titled, “Antibiotics in Agroecosystems: State of the Science,” summarized current knowledge, highlighted research gaps, and presented 16 research articles on this topic. Here we highlight three studies from this special section examining antibiotics. Although these papers are focused on antibiotics in agriculture, the questions and concerns over where these compounds are found, how they move through ecosystems, and what their impacts may be on plants, animals, and humans are relevant when evaluating the effects of emerging contaminants as a whole. Antibiotic resistance is commonly found in soil bacteria that live in feedlots and agricultural soils amended with manure, which is typically perceived to be the result of antibiotics used to treat livestock. However, antibiotic resistance does occur naturally in soils that have not been exposed to antibiotics, and determining these background levels could give researchers a baseline for comparison, according to ASA and SSSA member Lisa Durso, Research Microbiologist with USDA-ARS. “When you want to measure antibiotic resistance, [you're] generally measuring the drugs, the bugs, or the genes,” Durso explains. These three measures are used for both identifying the presence of antibiotic resistance and when thinking about ways to lower antibiotic resistance in agroecosystems, which is a common goal of researchers and farmers. But it is impossible to determine where antibiotic resistance is elevated or to set realistic targets for reduction without an understanding of the baseline antibiotic resistance in soils. In the article titled “Assessment of Selected Antibiotic Resistances in Ungrazed Native Nebraska Prairie Soils” (http://bit.ly/29EsXMG), Durso and colleagues were looking for the baseline “bugs” and “genes” in prairie soils. The first step was to find sites that had not been exposed to antibiotics through grazing or other agricultural practices. “I knew that prairies were the way to go,” Durso says, but finding ungrazed prairie sites in Nebraska took the researchers about a year. There is a long history of cattle grazing in the Great Plains, and even virgin prairies, which have never been plowed, have likely been grazed at some point in history. The time-consuming part of site selection was getting confirmation that prairie sites had not been grazed for the past 20 years. The team collected samples from 20 prairies across five counties in Nebraska. They analyzed the soil for standard physical and chemical properties, phenotypic resistance to selected antibiotics, and performed DNA isolations to serve as indicators for specific antibiotic resistance genes. Phenotypically, all 100 soil samples were resistant to tetracycline, a commonly used broad spectrum antibiotic, and cefotaximine, a third-generation cephalosporin antibiotic. Each bulk soil sample was also plated, and three isolates from each sample were subjected to disk diffusion assays of 12 antibiotic drugs. Durso and her colleagues found very few isolates resistant to ciprofloxacin (2% of isolates) and kanamycin (2% of isolates) while 43% of the isolates were resistant to ceftriazone. The phenotypic resistance to these 12 antibiotics was not statistically different when compared across all prairie sites, indicating that baseline antibiotic resistance is heterogeneous in this region. Test used by researchers to determine the number of generic bacteria in soil samples. Photo courtesy of the University of Nebraska. Taking samples from native prairie soils in Nebraska to isolate antibiotic-resistant bacteria. Photo courtesy of Lisa Durso. When looking at specific genes, antibiotic resistance genes were also common. Tetracycline genes (assays for 14 genes) were found at all sites, but not in all of the samples. The most common tetracycline genes were tet(D) and tet(A). Assays were also performed for two sulfonamide resistance genes; sul(I) was found at all 20 sites and sul(II) at 13 sites. This seeming abundance of resistance was not a surprise to the researchers. Durso's prior metagenomics research compared DNA in cattle fecal samples to DNA from a larger database, which included samples from the Sargasso Sea, Antarctic ice, and Kimchi fermentation. This earlier work revealed that all of the samples tested had antibiotic resistance in their genome. With researchers finding antibiotic resistance just about everywhere they look, it can be challenging to communicate their findings to a broad audience given the differences in the terminology between microbiologists and the medical community. “In human medicine, when you talk about resistance, you're talking about an infectious disease organism that's already making somebody sick, and then resistance is equivalent to treatment failure,” Durso says. “When you move into the environment, resistance isn't really defined in the soil…. Most of the organisms in the soil don't even have the capacity to be a pathogen to make people sick in the first place.” But the potential for increased antibiotic resistance in soil bacteria is still concerning from both a soil ecology and public health perspective. Understanding the background levels of antibiotic resistance is an important step in determining which types of resistance traits and genes are the result of agricultural practices and developing methods to reduce antibiotic resistance in agroecosystem soils. As Durso says, “There's lots of resistances out there, so let's prioritize those that are the most important.” Identifying the priorities and developing action plans will require the expertise of microbial, soil, and human health scientists. The methods used in this study are widely available, and Durso thinks that documenting baseline antibiotic resistance in conjunction with other soil research could advance the understanding of antibiotic resistance in soils. “We start to see correlations between soil physical and chemical parameters and types of antibiotic resistance bacteria or genes.” Suggesting that different soil types may influence the soil bacterial community present necessitate different methods to reduce elevated levels of antibiotic resistance and the best management practices to minimize antibiotic exposure. As the list of emerging contaminants grows and their presence in the environment increases, researchers need methods to identify which compounds are of greatest concern to human health. Kuldip Kumar, Senior Environmental Soil Scientist with Metropolitan Water Reclamation District of Chicago, became curious about plant uptake of emerging contaminants while investigating the fate and transport of antibiotics in soils from corn fields receiving swine manure as a source of nutrients. Finding that not all antibiotics were taken up by the corn, cabbage, and onion in a greenhouse study conducted at the University of Minnesota in Saint Paul, Kumar started reading medical and pharmaceutical literature about antibiotics. In his reading, Kumar found research describing how three properties—lipophilicity, polarity, and molecular weight—regulate the permeability of compounds across a lipid membrane in mammalian cells. Thinking these parameters made sense for uptake in plants too, where antibiotics and other emerging contaminants must also cross membranes, Kumar decided to investigate further. “Whenever you apply manure, biosolids, or recycled water to the soil, they have to go through the root membranes, and then they have to be transported aboveground,” Kumar notes. His investigation of this mechanism was the basis for the paper he was the lead author on titled, “A Framework to Predict Uptake of Trace Organic Compounds by Plants” (http://bit.ly/29Ez3LR), which can be used as a starting point for identifying emerging contaminants most likely to be taken up by plants exposed to manure, biosolids, or any industrial or agricultural by-product. Kumar found the existing model for mammalian tissues, known as the “Rule of 5,” which stated compounds with lipophilicity, polarity, and molecular weights less than specific factors of 5 (e.g., molecular weight < 500) were more permeable. Lipophilicity, or how well a compound will dissolve in fat or oil, is important because compounds with higher lipophilicity (measured as log Kow) are less likely to cross a lipid membrane. Polarity, expressed in terms of H-bonding, matters because a greater number of H-bond donors or acceptors impairs permeability of compounds. And compounds with a larger molecular weight (as a measure of molecular size) are less likely to pass through a membrane via diffusion. Kumar used the Rule of 5 as a starting point and reviewed the existing research on plant uptake of emerging contaminants. Based on the literature available at the time, he determined that a “Rule of 3” and “Rule of 3–5” were more appropriate for plant uptake of chemical compounds. The Rule of 3 states that uptake of a compound is more likely when the molecular weight < 300, log Kow < 3, the number of H-bond acceptors < 6, and H-bond donors < 3. The Rule of 3–5 suggests limited uptake by plants when the molecular weight is 300–500, log Kow 3–5, H-bond acceptors 6–10, and H-bond donors 3–5. Kumar points out that recent research on the uptake of emerging contaminants has supported this general rule. In developing this framework, the researchers were focused on the emerging contaminant compounds that are of greatest concern for human exposure via a plant-based diet. But there are broader ecological considerations, and Kumar points out that exposure levels and risk are different for other organisms exposed to wastewater, biosolids, and manure. To address this ecological question, Kumar says he's working on a similar framework looking at “what kind of properties the compounds will have that will accumulate more in aquatic organisms, or soil terrestrial organisms, like earthworms.” The issue of limiting exposure to emerging contaminants is much broader than evaluating uptake by food crops since emerging contaminants exist in many household products. The issue of limiting exposure to emerging contaminants is much broader than evaluating uptake by food crops since emerging contaminants can accumulate in other organisms (e.g., earthworms). Kumar also wonders about the risk of exposure to emerging contaminants via plant consumption compared with other sources of exposure. There are emerging contaminants in products we sometimes use on a daily basis like shampoo, toothpaste, plastic water bottles, and clothing treated with flame retardants. From this perspective, the issue of limiting exposure to emerging contaminants is much broader than evaluating uptake by food crops, but the questions of how low levels of emerging contaminants may effect human health and how to limit ecological impacts as these compounds enter aquatic and terrestrial systems remain the same. Alison Franklin, Ph.D. student in soil science and biogeochemistry at Penn State, collecting samples of wastewater treatment plant effluent that is being spray-irrigated at the university's Living Filter. Corn irrigation at Penn State's “Living Filter.” Photo by Emily Woodward/Penn State. by Joy Drohan If our food crops are spray-irrigated with treated wastewater, are we taking in minute doses of antibiotics and other emerging contaminants when we eat those crops? ASA, CSSA, and SSSA member Alison Franklin and her colleagues set out to answer that question in the article “Uptake of Three Antibiotics and an Antiepileptic Drug by Wheat Crops Spray Irrigated with Wastewater Treatment Plant Effluent” (http://bit.ly/29Fb01L). With antibiotic resistance much in the news, Franklin, a Ph.D. student in soil science and biogeochemistry at Penn State, wanted to begin to understand whether spray irrigation of crops with treated wastewater could be a problem long term. Her experiment is among the first to quantify the problem under field conditions using spray-irrigated effluent. Irrigation of croplands with treated effluent is increasing worldwide as water supplies tighten. In Israel, for instance, a significant amount of food crops are irrigated with wastewater. Forty-four percent of reclaimed wastewater projects in southern Europe have a predominantly agricultural use.1 Franklin's study examined uptake of three antibiotics and an anti-epileptic drug by wheat on the Living Filter, Penn State University's wastewater reuse system. The site receives about 5 cm of spray-irrigated effluent per week, at 12-hour intervals, year-round. The effluent first receives primary and secondary treatment at the University Park Wastewater Treatment Plant where the permitted capacity is 4 million gallons of influent per day. Spray irrigation provides tertiary treatment and recharges groundwater. Franklin chose four compounds to study that are meaningful to health after speaking with the pharmacy director at Penn State's University Health Services. Sulfamethoxazole and trimethoprim are typically prescribed together to treat ear or urinary tract infections or bronchitis. This combination, commonly known as Bactrim, is still generally effective against methicillin-resistant Staphylococcus aureus (MRSA), so doctors want to preserve its efficacy. Ofloxacin is a stronger version of the more commonly prescribed ciprofloxacin (Cipro). Carbamazepine is an antiepileptic drug that alters brain chemistry and persists in the environment. Although concentrations of carbamazepine in effluent were very low, its effects and behavior make it an important chemical to study. Franklin and her colleagues chose wheat as the study plant because it is the third most commonly grown cereal grain worldwide and the fourth most common agricultural crop in the United States. The wheat in this study was destined for animal consumption. The team sampled effluent in spring, summer, and fall to determine variation in the target compounds throughout the year. The population of University Park is highest in spring and fall, when classes are in session, and drops during the summer when most students leave. Concentrations of the target compounds reflected these population swings and the higher use of antibiotics in spring. Concentrations of sulfamethoxazole in spring were 22 µg/L, whereas in summer, they were only 580 ng/L. Maximum concentrations of trimethoprim and ofloxacin were much lower, 1 and 2.2 µg/L, respectively, in spring. The maximum concentration of carbamazepine was much lower still—23 ng/L. Wheat samples were collected three weeks before harvest and at harvest. Samples were rinsed with methanol to remove any of the target compounds adhering to the outside of the plant. Methanol was used because some of the compounds are not entirely water soluble. Straw and grain were extracted and analyzed separately via liquid chromatography–tandem mass spectrometry analysis. With spray irrigation of effluent, these pharmaceuticals and personal care products do cling to plant surfaces and are taken up by wheat. Ofloxacin was found at higher concentration in the straw (10 ng/g straw) than in the grain (2 ng/g). Trimethoprim was found only on the grain surface. Carbamazepine and sulfamethoxazole were concentrated in the grain (1.9 ng/g and 0.6 ng/g, respectively). The target compounds behaved differently because of their chemistry. The more hydrophobic a compound is, such as carbamazepine, the more likely it is to be bound with organic matter in wheat and soil. “The Living Filter is effective in trapping these compounds in soil,” says coauthor and ASA and SSSA member Clinton Williams, USDA soil scientist. This is important to know as land application of treated wastewater becomes more common. The concentrations in wheat are a million times lower than a typical adult dose (400–800 mg) of these drugs, assuming the USDA average daily wheat consumption of 166 g. To ingest the lowest typical dose of sulfamethoxazole, a person might have to consume 50–100 kg (100–200 lb) of this grain, says coauthor and SSSA member Jack Watson, a crop and soil scientist at Penn State. “But we don't know the long-term impacts,” Franklin cautions. “Could these compounds continue to accumulate in the environment and affect our health? We should either make sure they aren't getting into the environment or figure out the possible health effects of these low concentrations.” Still, Williams is encouraged that “the majority of the emerging contaminants are in a place where we can deal with them”—on the outside of the plants—and there was little contamination inside the plants. Franklin is continuing to explore this issue with investigations into whether microbial populations are affected by these compounds. She'll also look for antimicrobial resistance and, to help us decide whether effluent for irrigation of croplands requires additional treatment and/or testing, assess whether the compounds singly or in combination may produce negative biological impacts. J. Drohan, contributing writer for CSA News magazine View the articles from the special section in JEQ “Antibiotics in Agroecosystems: State of the Science” here: http://bit.ly/29wbOYF.

As an important grain production area in China, the Northeast Black Soil Region has experienced many problems, such as soil degradation, fertility decline, and grain yield reduction, in recent years. Optimizing fertilizer management is an important measure to maintain and enhance soil fertility. However, improper fertilizer application could aggravate nutrient losses and greenhouse gas N2O emissions, thus leading to soil degradation and environmental pollution. The objectives of the present study were to investigate the response of N2O emission from black soil to long-term application of organic and chemical fertilizers and the key controlling factors. Soil samples （0-20 cm） were collected from a total of nine treatments, including organic fertilizer as the primary treatment （M0- no organic fertilizer； M1- low organic fertilizer； M2- high organic fertilizer） and chemical fertilizer as the secondary treatment （CK- no fertilizer； N- chemical nitrogen fertilizer； NPK- chemical nitrogen, phosphorus, and potassium fertilizer）, in a long-term experiment （32 years） on the black soil of Gongzhuling, Jilin Province. The soil samples were incubated at 25℃ with 65% field water holding capacity for 21 days, and N2O emission and soil physico-chemical biological properties were determined. The results showed that long-term application of organic and chemical fertilizers notably increased N2O emissions from black soil. Compared to those from the M0CK treatment [（0.25±0.01） mg·kg-1, in terms of N, the same as below], the cumulative N2O emissions from the only organic fertilizer treatment significantly increased by 361%-456% [（1.17±0.02） mg·kg-1 and （1.41±0.02） mg·kg-1 for the M1CK and M2CK treatments, respectively]. Furthermore, the N2O emissions strongly increased with increasing organic fertilizer application amounts. Cumulative N2O emissions were significantly higher in the chemical fertilizer treatments by 96%-236% [（0.49±0.01） mg·kg-1 and （0.84±0.03） mg·kg-1 for the M0N and M0NPK treatments, respectively] compared to those in the M0CK treatments. Moreover, the increased N2O emissions due to fertilizers application were significantly larger in the M0NPK relative to M0N treatments. The positive effects of chemical fertilizer application on N2O emission decreased under organic fertilizer amendments （M1 and M2）, indicating that organic fertilizer application alleviated increased N2O emission because of chemical fertilization. The application of organic fertilizers significantly increased bulk soil, aggregate organic carbon （SOC）, total nitrogen （TN）, and soil microbial carbon and nitrogen contents. The application of organic combined with chemical fertilizers further increased SOC and TN contents in bulk soil and aggregates. Pearson correlation and path model analyses showed that the N2O emission was positively correlated with soil carbon and nitrogen fractions and microbial carbon and nitrogen contents among organic and chemical fertilizer treatments. Long-term application of organic and chemical fertilizers strongly regulated N2O emissions via affecting the distribution of carbon and nitrogen contents in soil fractions and changing microbial biomass and substrate availability. In conclusion, the application of organic fertilizers could significantly facilitate N2O emission by increasing the available soil carbon and nitrogen pools as well as microbial carbon and nitrogen contents. The application of organic fertilizers mitigated the positive effects of chemical fertilizers on N2O emissions. Appropriate amounts of organic fertilizers should be used when applying chemical fertilizers, in order to balance the comprehensive effects of fertility improvement with nitrogen loss and greenhouse gas emissions.

Antibiotic resistance in agricultural soils is a significant environmental and health challenge worldwide. To minimize the risk of antibiotic resistance, it is important to understand the fate and spread mechanism of antibiotics and antibiotic resistance genes (ARGs), and develop effective technologies to minimize their negative effects. In this work, we reviewed recent studies on the occurrence of antibiotic resistance in soil by different agricultural practices. The continuous land applications of manures and sewage sludge, and irrigation with wastewater contribute to the elevated antibiotic resistance in soil. The fate of antibiotic resistance from different interfaces are also discussed. In particular, the mechanisms of ARGs dissemination between bacteria are presented. Aerobic composting, and anaerobic and aerobic digestions of manure, sludge, or wastewater are found to be effective treatments to reduce antibiotic resistance into agricultural soils from the sources. Furthermore, strategies to alleviate antibiotic resistance in soil are proposed, and research directions on in-depth mechanisms are outlined to elucidate the antibiotic resistance decay in soil treatment processes. Although much progress has been made in understanding the links of antibiotic resistance between soil and human health, there are still many unknowns on the complex interactions between them.

From biowastes to risks? Impact of biosolids treatment and dose on antibiotic resistance in agricultural soils - A mesocosm study.

Impact of biochar on the antibiotic resistome and associated microbial functions in rhizosphere and bulk soil in water-saving and flooding irrigated paddy fields

Antibiotic resistance (AR) is a global phenomenon with severe epidemiological ramifications. Anthropogenically impacted natural aquatic and terrestrial environments can serve as reservoirs of antibiotic resistance genes (ARG), which can be horizontally transferred to human-associated bacteria through water and food webs, and thus contribute to AR proliferation. Treated-wastewater (TWW) irrigation is becoming increasingly prevalent in arid regions of the world, due to growing demand and decline in freshwater supplies. The release of residual antibiotic compounds, AR bacteria, and ARGs from wastewater effluent may result in proliferation of AR in irrigated soil microcosms. The aim of this study was to assess the impact of TWW-irrigation on soil AR bacterial and ARG reservoirs. Tetracycline, erythromycin, sulfonamide, and ciprofloxacin resistance in soil was assessed using standard culture-based isolation methods and culture-independent molecular analysis using quantitative real-time PCR (qPCR). High levels of bacterial antibiotic resistance were detected in both freshwater- and TWW-irrigated soils. Nonetheless, in most of the soils analyzed, AR bacteria and ARG levels in TWW-irrigated soils were on the whole identical (or sometimes even lower) than in the freshwater-irrigated soils, indicating that the high number of resistant bacteria that enter the soils from the TWW are not able to compete or survive in the soil environment and that they do not significantly contribute ARG to soil bacteria. This strongly suggests that the impact of the TWW-associated bacteria on the soil microbiome is on the whole negligible, and that the high levels of AR bacteria and ARGs in both the freshwater- and the TWW-irrigated soils are indicative of native AR associated with the natural soil microbiome.

The application of fertilizers is a key agronomic practice in the artificial cultivation of medicinal plants, aiming to boost yields and enhance the levels of their bioactive constituents. However, systematic investigations on the influence of various fertilizers on the concentration of active compounds in saponin-containing medicinal plants remain insufficient. In this study, 966 experimental outcomes from 29 papers were analyzed via meta-analysis to examine the effects of organic fertilizers, inorganic fertilizers, and their combined application on the levels of different saponin monomers in medicinal plants. The findings from the meta-analysis revealed that inorganic fertilizers contribute positively to the accumulation of saponins such as Rg1 in ginseng, Rb1, Rc, Rd, Re, and Rg1, in addition to the saponins from Paris polyphylla, Dioscorea, Panax quinquefolius, and Platycodon grandiflorus. Moreover, the application of organic fertilizers was found to markedly elevate the concentrations of Notoginsenoside R1, Ginsenoside Rb1, Ginsenoside Rb2, Re, and Rg1, along with Lancemasid saponins and Quinoa saponins. The combined use of both organic and inorganic fertilizers was shown to effectively increase the levels of Notoginsenoside R1 and Panax ginsenosides, encompassing Rb1, Rb2, Rc, Rd, Re, and Rg1. Overall, the results suggest that both individual and combined applications of organic and inorganic fertilizers have a positive impact on the enhancement of saponin monomers in medicinal plants. However, inorganic fertilizers promote the increase of saponin content, their prolonged use may lead to soil compaction and acidification, which could compromise the yield and quality of medicinal plants. On the other hand, organic fertilizers improve the soil environment and stimulate saponin accumulation, they do not supply all the nutrients required for the sustained growth of these plants. Therefore, a balanced fertilization strategy combining both organic and inorganic fertilizers is recommended as the optimal approach for cultivating saponin-rich medicinal plants.

Profiles of tetracycline resistance genes in paddy soils with three different organic fertilizer applications

To mitigate the issues of severe farmland soil salinization, the environmental degradation stemming from the overuse of chemical fertilizers, and suboptimal soil composition, a study was conducted to investigate the influence of different types and ratios of organic fertilizers on the physical and chemical attributes of saline–alkali soil. This study aimed to investigate the relationship between different types and proportions of organic fertilizers, soil moisture, organic fertilizer application rates, organic carbon molecular structure, and the soil environment in saline–alkali soils. Reducing the application of chemical fertilizers and substituting them with organic fertilizers can improve the soil quality of saline–alkali lands. The results indicated that replacing a part of the urea with organic fertilizer in saline–alkali farmland reduced the soil salinity by 11.1 to 22.8% in the 0–60 cm soil layer, decreased the soil pH by 0.11 to 1.52%, and increased the soil redox potential (Eh) values by 2.5 to 4.3% in the 0–20 cm layer of the mild and moderate saline–alkali soils. It also decreased the accumulation of the soil organic matter (OM) during the growing season. Compared to commercial organic fertilizers, natural organic fertilizers increased the accumulation of the soil soluble carbon (DOC) and nitrogen (DON), resulting in less soil salinity accumulation. When commercial organic fertilizer was applied in a 1:1 ratio with inorganic fertilizer, the salt accumulation was minimized. Compared to conventional fertilization, organic fertilizer reduced the accumulation of the NH4+-N (ammonium nitrogen) and NO3−-N (nitrate nitrogen) in the soil by 3.1 to 22.6%. In comparison to conventional chemical fertilizers, the application of organic fertilizer in the mild and moderate saline–alkali soils increased the accumulation of the DOC, DON, microbial biomass carbon (MBC), microbial biomass nitrogen (MBN), and microbial quotient during the grain-filling stage. Specifically, it increased the DOC, DON, and DOC/DON by 12.7 to 26.7%, 12 to 59.3%, and 15.2 to 35.5%, respectively. The application of commercial organic fertilizer in the mild saline–alkali soils increased the MBC, MBN, MBC/SOC, and MBN/TN by 37.1, 65.6, 36.7, and 4.7%, respectively. Through analyzing the relative proportions of soil surface organic carbon functional groups during the grain filling period, we observed that, after the application of organic fertilizer, the OM in the mildly salinized soils primarily originated from terrestrial plant litter, whereas, in moderately salinized soils, the OM was mainly derived from microbial sources.

Response of soil antibiotic resistance genes and bacterial communities to fresh cattle manure and organic fertilizer application

Organic and inorganic fertilizers play an important role in improving the nutritional quality of coriander plant (Coriandrum sativum L.). This study consists of 3 different fertilizer applications to coriander: Control-T0 (no fertilizer); organic fertilizer- T1 (300-600 mL/da); chemical fertilizer-T2 (2-3 L/da); vermicompost-T3 (1.5 L/da). It was conducted in three replicates in a randomized block design to evaluate the effect of different fertilizer applications on the morphological, biochemical and antioxidant potential of coriander plants. It has been observed that fertilizer applications have a significant effect on the morphological, biochemical and antioxidant properties of the plant, and especially in the coriander of seeds organic fertilizer and vermicompost applications have higher phenolic and flavonoid contents (1.82, 2.14 mg GAE/g DW and 2.57, 2.46 mg QE/g DW, respectively). In the GC-MS analysis, linalool was determined as the main compound and the highest concentration of 76.44% was obtained as a result of organic fertilizer application. Antioxidant potential was evaluated by DPPH radical-scavenging assay and the most effective antioxidant activity was determined from organic origin fertilizer (organic-IC50: 27.35±2.52 µg/mL, vermicompost-IC50: 29.42±2.41 µg/mL) applications.

High and sustainable crop yields in the tropics have been reported to be only possible with judicious combination of mineral fertilizers and organic amendments. Fertilizing croppings to achieve this has usually been a difficult task to achieve. The growth and yield of maize cultivated with a complementary application of organic and inorganic fertilizers was assessed compared with sole organic and sole inorganic fertilizers between April and July 2003 and 2004 at Ibadan, Nigeria, in the degraded tropicalrain forest zone. There was a no-fertilizer treatment as the control. The organic fertilizer was an equal mixture of composted domestic waste and stale cow dung, applied at 10 tonnes ha-1. Urea and Single super phosphate were applied as the inorganic fertilizer to supply 70 kg N and 13 kg P2O5 ha-1 respectively. The mixture of organic and inorganic fertilizer treatment consisted of half the rates used for sole organic and sole inorganic fertilizer treatments: 5 tonnes organic mixture was applied, with 35 kg N and 6.5 kg P2O5. Maize plant height at 8 weeks after planting washighest with inorganic fertilizer application while the leaf area was highest with organic fertilizer application. Stover yield and cob yields were also highest with inorganic fertilizer. Complementary application of organic and inorganic fertilizers however had similar plant heights; stover yield as well as cob yields with inorganic fertilizer. Nitrogen appeared chelated with organic fertilizer application. Plant ear – leaf Nitrogen was highest (1.68%) with inorganic fertilizer while the control plots had a Nitrogen content of 1.12% which was higher than 0.84% and 0.98% N from sole organic and a complementary application of organic and inorganic fertilizers, respectively. Plant P content was increased by 136% and 15% with organic and inorganic fertilizers, respectively, but was reduced by 15% with complementaryapplication of organic and inorganic fertilizers. The K content was highest with inorganic fertilizer (1.91%). Complementary application of organic and inorganic fertilizers had a K content of 1.70% while the organic – fertilized leaves had 1.53%. Stover nutrient uptake was highest for N and K with inorganic fertilizer while the P was highest with organic fertilizer application. Cultivating maize with complementary organic and inorganic fertilizers gives a comparable cob yield as inorganic fertilizer and has nutrients higher than from sole organic fertilizer application.Key words: Maize, Fertilizer type, Nutrient uptake

Impact of electrokinetic remediation of heavy metal contamination on antibiotic resistance in soil

Cyanobacteria plays an important role in other ecological processes in paddy soils, particularly in terms of nitrogen input to the ecosystem. Organic fertilizer and biochar are common soil amendment materials used to preserve soil health in agricultural intensification background. However, the consequent increase in soil nutrition may inhibit soil cyanobacteria, therefore decreasing nitrogen fixation and changes other soil processes. To test this hypothesis, we established a 2 × 2 full factorial experiment in a paddy field in South China, which included four treatments: Ctr (control, receiving no organic fertilization or biochar addition), +OF (organic fertilizer application only), +BC (biochar application only), and +Mix (organic fertilizer and biochar applications). The soil cyanobacterial community was analyzed using metagenomics technology, and 14 soil property variables were measured. The results suggested that organic fertilizer was effective in enhancing nutrient levels, leading to a significant increase in extractable and soluble nitrogen, phosphorus, and potassium. In contrast, biochar application had a stronger effect on total soil carbon, potassium, and soil pH. However, both organic fertilizer and biochar applications induced significant decreases in overall cyanobacterial abundance and species number. Dominant cyanobacterial organisms, particularly the two most abundant genera, Leptolyngbya and Phormidium, experienced a greater decrease compared to others. Canonical correlation analyses and structural equation models indicated that organic fertilizer and biochar applications affected soil cyanobacterial community mainly through soil available nitrogen and pH. In total, the present study highlighted that both organic fertilizer and biochar applications in paddy soils notably change soil physicochemical traits, inhibiting rather than benefiting cyanobacterial microorganisms, especially the dominant ones, and potentially reducing nitrogen input. Our study reveals the impacts of oragnic fertilizer and biochar applications in paddies on soil cyanobacteria and how the consequent changes in soil properties mediate this impact, thereby enhancing our understanding of the responses of different soil microbial groups to soil improvement measures.