How To Use Chemical Fertilizers
- November 2, 2021
The term “chemical fertilizer” refers to any number of synthetic compound substances created specifically to increase crop yield.Complex (or blended) chemical fertilizers often contain a mix of ammonium phosphate, nitrophosphate, potassium, and other nutrients.Chemical fertilizers allow growers to maximize their crop yield on a specific piece of land — the more the plant grows, the better.As long as you know how to approach the use of chemical fertilizers, they can even make otherwise poor quality land produce significant yields.Make sure you choose a brand and type that aligns with your specific goals, or you might not see ideal results.On the other hand, a homeowner fertilizer blend is certainly not ideal for a bigger operation where crop yield and sustainability are important.Used correctly, chemical fertilizers can dramatically increase yield and turn otherwise poor soil into productive land.On top of that, chemical fertilizers provide exactly what plants need to grow with minimal filler, and they’re highly regulated.As a general rule of thumb, treat the use of chemical fertilizers as a valuable, important tool.Take the time to consult with professionals in your area to learn more about the importance of fertilizer and how to choose the right kind for your needs, and work from there. .
Chemical fertilizers are generally reported to account for from one-third to one-half of our total agricultural production.The major energy-consuming phases of the fertilizer system are production of ammonia (71% of total); distribution of products (11% of total); production of wet-process acid (8% of total); and drying of granular fertilizers based on ammonium phosphates (1% of total).Development and demonstration of more efficient U.S. technology should begin as soon as practical to provide for initiation of conversion of the U.S. ammonia industry to coal feedstock by about 1985.Studies of a high-temperature reaction system using U.S.
phosphate rock should receive research and development priority. .
China needs to cut use of chemical fertilizers: research
It also urged the government to reduce subsidies to fertilizer makers and called for more support for farmers who use animal waste. .
Traditional farming systems generally included a period of fallow in the cropping sequence to help restore soil fertility.Spreading animal manures in the field, as well as inclusion of leguminous crops, helped to add nitrogen, a principal nutrient, to the soil.In 1840, Justus von Liebig of Germany, called the “father” of soil chemistry, proved that treatment with strong acid increased the availability of bone nutrients to plants.Necessity impelled the development of artificial fertilizers, which are chemical substances containing, in forms readily available to plants, the elements that improve the growth and productivity of crops.Potash fertilizer could be extracted in readily soluble forms, such as potassium chloride, from geological deposits found in several countries, including Germany, France, the USA, Canada, and from the brine of the Dead Sea.The need to mine and transport these substances across the ocean, and the frequent disruption of international trade by wars in the twentieth century, made these fertilizer sources too expensive and insecure. .
The data from this research have shown that soil N storage change indicating soil fertility/productivity can be different significantly for fertilization treatments (Table 3).Our results showed that the average total N loss to the environment from the manure incorporation treatments (NPKM or 1.5NPKM) was 20–24% of total N applied while it was 43% from the commonly used balanced NPK fertilization treatment (Table 3).Although there were no apparent differences in plant uptake, soil N from the NPKM treatment increased ~7 times or higher significantly than the NPK treatment.The 1.5NPKM treatment resulted in relatively higher N loss than NPKM, most likely due to the unnecessarily higher total N amount applied because a lower NUE for the 1.5NPKM and similar grain yield were observed12.Although many studies indicate manure application could increase the risk of N leaching, our study demonstrated that a combination of manure and chemical fertilizer as 70% and 30% N resulted in not only the lowest N loss, but also with either higher or similar NUEs than those from 100% chemical fertilizer N (Table 3).The results imply that when applied properly, combination of manure with chemical fertilizer is an effective management strategy in agricultural production to significantly improve soil fertility (indicated by N storage increase), increase NUE or yield, and minimize N loss in the rain-fed annual cropping system in both alkaline (Urumqi and Zhengzhou) and acidic (Qiyang) soils.Future research should strengthen the understanding on the mechanisms, especially the response of N transformation microorganisms to application of manure and crop residue that are associated with N availability to plants.The estimated total N loss to the environment varied from average 20% for the NPKM treatment to 63% for the N treatment from this long-term study.By taking the NH 3 loss into account, the N loss would be in the range of 16–38% for all the chemical fertilization treatments including the NPKS but little leaching from the NPKM treatments based on the data in Table 3.Our study results indicate that the total N loss can be reduced to ave. 20% or lower by simply incorporating manure in the fertilization regime that reduced the loss more than 50% from chemical fertilizations (Table 3).In the highly weathered acidic red soil in south region of China, all fertilization treatments increased the N content as well as downward movement in soil profile suggesting a higher leaching risk.At all study sites, manure application resulted in a lower total N loss to the environment (ave.
≤24% vs. >35% from all other chemical fertilization treatments). .
How Fertilizers Harm Earth More Than Help Your Lawn
Dear EarthTalk: What effects do fertilizers, pesticides and herbicides used on residential lawns or on farms have on nearby water bodies like rivers, streams—or even the ocean for those of us who live near the shore?With the advent of the so-called Green Revolution in the second half of the 20th century—when farmers began to use technological advances to boost yields—synthetic fertilizers, pesticides and herbicides became commonplace around the world not only on farms, but in backyard gardens and on front lawns as well.These chemicals, many of which were developed in the lab and are petroleum-based, have allowed farmers and gardeners of every stripe to exercise greater control over the plants they want to grow by enriching the immediate environment and warding off pests.But such benefits haven’t come without environmental costs—namely the wholesale pollution of most of our streams, rivers, ponds, lakes and even coastal areas, as these synthetic chemicals run-off into the nearby waterways.Another recent study from Indiana found that a variety of corn genetically engineered to produce the insecticide Bt is having toxic effects on non-target aquatic insects, including caddis flies, a major food source for fish and frogs. .
States have difference regulations and statutes that address fertilizer use and production to protect human health and the environment.Fertilizer producers take great care in the safe use and storage of anhydrous ammonia and have implemented safety measures to help prevent or mitigate an incident. .
 For most modern agricultural practices, fertilization focuses on three main macro nutrients: Nitrogen (N), Phosphorus (P), and Potassium (K) with occasional addition of supplements like rock dust for micronutrients.Farmers apply these fertilizers in a variety of ways: through dry or pelletized or liquid application processes, using large agricultural equipment or hand-tool methods.Historically fertilization came from natural or organic sources: compost, animal manure, human manure, harvested minerals, crop rotations and byproducts of human-nature industries (i.e. fish processing waste, or bloodmeal from animal slaughter).However, starting in the 19th century, after innovations in plant nutrition, an agricultural industry developed around synthetically created fertilizers.This transition was important in transforming the global food system, allowing for larger-scale industrial agriculture with large crop yields.The use of fertilizer has also led to a number of direct environmental consequences: agricultural runoff which leads to downstream effects like ocean dead zones and waterway contamination, soil microbiome degradation, and accumulation of toxins in ecosystems.Founded in 1812, Mirat , producer of manures and fertilizers, is claimed to be the oldest industrial business in Salamanca (Spain).Egyptians, Romans, Babylonians, and early Germans are all recorded as using minerals or manure to enhance the productivity of their farms. The science of plant nutrition started well before the work of German chemist Justus von Liebig although his name is most mentioned.Nicolas Théodore de Saussure and scientific colleagues at the time were quick to disprove the simplications of Justus von Liebig.There was a complex scientific understanding of plant nutrition, where the role of humus and organo-mineral interactions were central, and which was in line with more recent discoveries from 1990 onwards. Prominent scientists on whom Justus von Liebig drew were Carl Ludwig Sprenger and Hermann Hellriegel.A factory based on the process was built in Rjukan and Notodden in Norway, combined with the building of large hydroelectric power facilities.The Haber process produces ammonia (NH 3 ) from methane (CH 4 ) gas and molecular nitrogen (N 2 ). After World War II, Nitrogen production plants that had ramped up for war-time bomb manufacturing were pivoted towards agriculture uses.The development of synthetic nitrogen fertilizer has significantly supported global population growth — it has been estimated that almost half the people on the Earth are currently fed as a result of synthetic nitrogen fertilizer use.The second mode by which some fertilizers act is to enhance the effectiveness of the soil by modifying its water retention and aeration.three main macronutrients: Nitrogen (N): leaf growth Phosphorus (P): Development of roots, flowers, seeds, fruit; Potassium (K): Strong stem growth, movement of water in plants, promotion of flowering and fruiting;.micronutrients: copper (Cu), iron (Fe), manganese (Mn), molybdenum (Mo), zinc (Zn), boron (B).Only some bacteria and their host plants (notably legumes) can fix atmospheric nitrogen (N 2 ) by converting it to ammonia.Phosphate is required for the production of DNA and ATP, the main energy carrier in cells, as well as certain lipids.Ammonia-oxidizing bacteria (AOB), such as species of Nitrosomonas, oxidize ammonia to nitrite, a process termed nitrification. Nitrite-oxidizing bacteria, especially Nitrobacter, oxidize nitrite to nitrate, which is extremely mobile and is a major cause of eutrophication.Urea is another popular source of nitrogen, having the advantage that it is solid and non-explosive, unlike ammonia and ammonium nitrate, respectively.A few percent of the nitrogen fertilizer market (4% in 2007) has been met by calcium ammonium nitrate (Ca(NO 3 ) 2 • NH 4 • 10H 2 O)."Single superphosphate" (SSP) consists of 14–18% P 2 O 5 , again in the form of Ca(H 2 PO 4 ) 2 , but also phosphogypsum (CaSO 4 • 2H 2 O).NPK ratings consist of three numbers separated by dashes (e.g., 10-10-10 or 16-4-8) describing the chemical content of fertilizers.Iron presents special problems because it converts to insoluble (bio-unavailable) compounds at moderate soil pH and phosphate concentrations.(Mt pa) China 18.7 3.0 India 11.9 N/A U.S.
9.1 4.7 France 2.5 1.3 Germany 2.0 1.2 Brazil 1.7 0.7 Canada 1.6 0.9 Turkey 1.5 0.3 UK 1.3 0.9 Mexico 1.3 0.3 Spain 1.2 0.5 Argentina 0.4 0.1. In this energy-intensive process, natural gas (CH 4 ) usually supplies the hydrogen, and the nitrogen (N 2 ) is derived from the air.Deposits of sodium nitrate (NaNO 3 ) (Chilean saltpeter) are also found in the Atacama desert in Chile and was one of the original (1830) nitrogen-rich fertilizers used.These minerals are converted into water-soluble phosphate salts by treatment with sulfuric (H 2 SO 4 ) or phosphoric acids (H 3 PO 4 ). In the nitrophosphate process or Odda process (invented in 1927), phosphate rock with up to a 20% phosphorus (P) content is dissolved with nitric acid (HNO 3 ) to produce a mixture of phosphoric acid (H 3 PO 4 ) and calcium nitrate (Ca(NO 3 ) 2 ).Potash is soluble in water, so the main effort in producing this nutrient from the ore involves some purification steps; e.g., to remove sodium chloride (NaCl) (common salt).Organic fertilizers can also describe commercially available and frequently packaged products that strive to follow the expectations and restrictions adopted by “organic agriculture” and ”environmentally friendly" gardening – related systems of food and plant production that significantly limit or strictly avoid the use of synthetic fertilizers and pesticides.It is an immature form of coal and improves the soil by aeration and absorbing water but confers no nutritional value to the plants.Organic fertilizers such as composts and manures may be distributed locally without going into industry production, making actual consumption more difficult to quantify.The most widely used solid inorganic fertilizers are urea, diammonium phosphate and potassium chloride.For fertilizer use, granules are preferred over prills because of their narrower particle size distribution, which is an advantage for mechanical application.During summer, urea is often spread just before or during rain to minimize losses from volatilization (a process wherein nitrogen is lost to the atmosphere as ammonia gas).Drilling must not occur on contact with or close to seed, due to the risk of germination damage.In grain and cotton crops, urea is often applied at the time of the last cultivation before planting.Nitrification inhibitors (also known as nitrogen stabilizers) suppress the conversion of ammonia into nitrate, an anion that is more prone to leaching. Urease inhibitors are used to slow the hydrolytic conversion of urea into ammonia, which is prone to evaporation as well as nitrification. Agricultural and chemical minerals are very important in industrial use of fertilizers, which is valued at approximately $200 billion. Potash is produced in Canada, Russia and Belarus, together making up over half of the world production. Conservative estimates report 30 to 50% of crop yields are attributed to natural or synthetic commercial fertilizers.Data on the fertilizer consumption per hectare arable land in 2012 are published by The World Bank. The diagram below shows fertilizer consumption by the European Union (EU) countries as kilograms per hectare (pounds per acre).This figure equates to 151 kg of fertilizers consumed per ha arable land on average by the EU countries.The large growing consumption of fertilizers can affect soil, surface water, and groundwater due to dispersion of mineral use.This waste takes the form of impure, useless, radioactive solid called phosphogypsum.The main contributor to eutrophication is phosphate, which is normally a limiting nutrient; high concentrations promote the growth of cyanobacteria and algae, the demise of which consumes oxygen.The nitrogen-rich compounds found in fertilizer runoff are the primary cause of serious oxygen depletion in many parts of oceans, especially in coastal zones, lakes and rivers.The resulting lack of dissolved oxygen greatly reduces the ability of these areas to sustain oceanic fauna. As of 2006, the application of nitrogen fertilizer is being increasingly controlled in northwestern Europe and the United States. If eutrophication can be reversed, it may take decades before the accumulated nitrates in groundwater can be broken down by natural processes. High application rates of nitrogen-containing fertilizers combined with the high water solubility of nitrate leads to increased runoff into surface water as well as leaching into groundwater, thereby causing groundwater pollution. The excessive use of nitrogen-containing fertilizers (be they synthetic or natural) is particularly damaging, as much of the nitrogen that is not taken up by plants is transformed into nitrate which is easily leached.Nitrate levels above 10 mg/L (10 ppm) in groundwater can cause 'blue baby syndrome' (acquired methemoglobinemia). The phosphate rock used in their manufacture can contain as much as 188 mg/kg cadmium (examples are deposits on Nauru and the Christmas islands). Where high annual rates of phosphorus fertilizer are used, this can result in uranium-238 concentrations in soils and drainage waters that are several times greater than are normally present. However, the impact of these increases on the risk to human health from radinuclide contamination of foods is very small (less than 0.05 mSv/y).Steel industry wastes, recycled into fertilizers for their high levels of zinc (essential to plant growth), wastes can include the following toxic metals: lead arsenic, cadmium, chromium, and nickel.These highly water-soluble fertilizers are used in the plant nursery business and are available in larger packages at significantly less cost than retail quantities.Some inexpensive retail granular garden fertilizers are made with high purity ingredients.Attention has been addressed to the decreasing concentrations of elements such as iron, zinc, copper and magnesium in many foods over the last 50–60 years. Although improved crop yields resulting from NPK fertilizers are known to dilute the concentrations of other nutrients in plants, much of the measured decline can be attributed to the use of progressively higher-yielding crop varieties that produce foods with lower mineral concentrations than their less-productive ancestors.Fertilizers are, in fact, more likely to solve trace mineral deficiency problems than cause them: In Western Australia deficiencies of zinc, copper, manganese, iron and molybdenum were identified as limiting the growth of broad-acre crops and pastures in the 1940s and 1950s. Soils in Western Australia are very old, highly weathered and deficient in many of the major nutrients and trace elements.High levels of fertilizer may cause the breakdown of the symbiotic relationships between plant roots and mycorrhizal fungi.The greenhouse gases carbon dioxide, methane and nitrous oxide are produced during the manufacture of nitrogen fertilizer.[needs update] Nitrogen fertilizer can be converted by soil bacteria to nitrous oxide, a greenhouse gas. Nitrous oxide emissions by humans, most of which are from fertilizer, between 2007 and 2016 have been estimated at 7 million tonnes per year, which is incompatible with limiting global warming to below 2C.It has a global warming potential 296 times larger than an equal mass of carbon dioxide and it also contributes to stratospheric ozone depletion.These emissions contribute to global climate change as methane is a potent greenhouse gas. .
Fifteen-Year Application of Manure and Chemical ...
High-throughput quantitative PCR and sequencing technologies were employed to assess the effects of long-term manure or chemical fertilizer application on the distribution of ARGs and microbial communities.In addition, manure application increased the abundance of mobile genetic elements (MGEs), which were significantly and positively correlated with most types of ARGs, indicating that horizontal gene transfer via MGEs may play an important role in the spread of ARGs.Furthermore, the application of manure and chemical fertilizers significantly affected microbial community structure, and variation partitioning analysis showed that microbial community shifts represented the major driver shaping the antibiotic resistome.Taken together, our results provide insight into the long-term effects of manure and chemical fertilization on the dissemination of ARGs in intensive agricultural ecosystems.The increasing dissemination and propagation of antibiotic resistance genes (ARGs) in various environments has aroused great concern worldwide (Zhu et al., 2013; Fahrenfeld et al., 2014) and might threaten antibiotic effectiveness and public health in the 21st century (Berendonk et al., 2015).China is the largest consumer of antibiotics in the world, with a total usage of approximately 162 kt in 2013, and half of the total antibiotics consumed in China were used to treat animal diseases and promote animal growth (Zhang et al., 2015).The overuse of antibiotics in modern livestock husbandry has been proven to be a potential key driver of the expansion of environmental ARG reservoirs (Boxall et al., 2003; Brandt et al., 2009).Indeed, prior studies have demonstrated that manure is an important reservoir of antibiotic-resistant bacteria (ARB), ARGs and mobile genetic elements (MGEs) (Heuer et al., 2011; Su et al., 2014; Udikovic-Kolic et al., 2014; Chen Q. et al., 2016).Importantly, horizontal gene transfer (HGT) by MGEs can promote the ready dissemination of ARGs among microbial communities (Xie et al., 2018a).Furthermore, previous studies assumed that environmental ARGs could be transferred into the food chain through HGT mechanisms, creating great risks to human health (Berendonk et al., 2015; Wang et al., 2015).The excessive use of chemical fertilizers in this region has caused serious negative environmental effects, such as soil acidification, ammonia volatilization, and nitrate contamination in groundwater (Chen et al., 2018; Wang et al., 2018).Applying organic manure to replace some amount of conventional chemical fertilizer has been proven to be an effective approach on the NCP with respect to crop yield and soil carbon and nitrogen stocks (Gai et al., 2018).Moreover, ARGs were observed to be stable in the microbial community of a soil that regularly received manure application (Heuer and Smalla, 2007).In addition, chemical fertilizer application can induce significant changes in soil properties and microbial communities (Wang et al., 2018; Xie et al., 2018b).Therefore, the importance of investigating and controlling ARGs and microbial communities in agricultural soils cannot be understated.However, only a few studies to date have systematically assessed the distribution and transport of ARGs in soil under long-term manure and chemical fertilizer application.In the present study, high-throughput quantitative PCR technology combined with high-throughput sequencing technology was employed to explore the influence of the application of chemical fertilizer and pig manure on the resistome profile, MGEs, and microbial communities of soil.This study contributes to a better understanding of the dissemination and persistence of soil ARGs caused by manure application and chemical fertilization.The long-term field experiment was set up in 2001 at the Luancheng Ecological Station, Hebei Province, China (37°53’N, 114°41’E) with a winter wheat-summer maize rotation.Detailed information about the experimental design and the fertilization scheme is shown in Supplementary Figures S1, S2, respectively.Fresh manure was applied as a base fertilizer to the agricultural soil in the M and MN treatments before wheat sowing every year (early October).Sampling occurred in the winter, when the wheat plants were small and had basically stopped growing.Briefly, soil organic matter (OM) was determined using the K 2 Cr 2 O 7 oxidation method.Soil available phosphorus (AP) was extracted with 0.5 M NaHCO 3 and determined using the molybdenum blue method.Available potassium (AK) was extracted with 1 M ammonium acetate and measured using flame photometry (ZEENIT®700P, Analytik Jena AG, Germany).The quality and quantity of the extracted DNA were examined using a Nanodrop spectrophotometer (NanoDropTM One, Thermo Fisher Scientific, United States).The relative abundance of each ARG/MGE was calculated using a formula from a previous study (Chen Q.
et al., 2016): relative gene abundance = 10 ( ( 31 - C t ( t a r g e t ) ) / ( 10 / 3 ) ) 10 ( ( 31 - C t ( 16 s ) ) / ( 10 / 3 ) ) , where Ct (target) and Ct ( 16 S) referred to the threshold cycles of the ARGs/MGEs and the 16S rRNA gene, respectively.Fold changes were calculated to illustrate the enrichment of soil ARGs under the application of manure or chemical fertilizers according to a previous study (Wang et al., 2014b).Genes were regarded as statistically enriched compared with the CK treatment if the range calculated by two standard deviation of the mean fold change was entirely >1.To depict bacterial communities, the 341F/785R primer pair was used to amplify the V3-V4 region of the 16S rRNA gene (Yasir et al., 2015).The clean data generated were analyzed using Quantitative Insights Into Microbial Ecology (QIIME) software.Operational taxonomic units (OTUs) were determined at the 97% similarity level using the UCLUST program (Edgar, 2010).The sequencing data were deposited in the European Nucleotide Archive database under accession number PRJEB29291.In this study, the long-term application of chemical fertilizers (N, NP, and NPK) significantly reduced soil pH (P < 0.05), while the increases in the soil OM, TC, TN, and AP were not significant (except that of AP in the NP and NPK treatments).Compared to the chemical fertilizer treatments, the application of manure fertilizer significantly decreased the pH and the C/N ratio and increased the concentrations of OM, TC, TN, AK, and AP (P < 0.05) (Supplementary Table S1).The total relative abundance of ARGs was 1.31 (±0.21) copies/16S rRNA gene copies in the PM (Supplementary Table S3).The 114 ARGs detected in soil samples potentially encoded resistance to major types of antibiotics, including multidrug antibiotics (18%), MLSB (18%), aminoglycoside (16%), beta_lactamase (17%), tetracycline (15%), FCA (fluoroquinolone, quinolone, florfenicol, chloramphenicol and amphenicol) (3%), vancomycin (6%), and sulfonamides (4%) (Supplementary Figure S3A), covering three major resistance mechanisms: antibiotic deactivation (39%), efflux pump (31%) and cellular protection (27%) (Supplementary Figure S3B).Compared with the CK and chemical-fertilized treatments, manure application significantly increased the ARG abundance, with total relative abundances of ARGs in the M and MN of 0.13 (2.6 times) and 0.23 (4.6 times) copies/16S rRNA gene copies, respectively (Figure 2B).FCA, fluoroquinolone, quinolone, florfenicol, chloramphenicol, and amphenicol; MLSB, macrolide-lincosamide-streptogramin B; MGEs, mobile genetic elements.(A) Venn diagram illustrating the ARGs shared by the CK, N, NP, and NPK treatments.(C) Venn diagram illustrating the ARGs shared by the CK, M, and MN treatments and PM.(D) The relative abundance of ARGs shared among the CK, M, and MN treatments and PM.The PCoA based on Bray-Curtis distance showed that the ARG distributions in the CK treatment and fertilized soil samples were separated (Supplementary Figure S4B).In addition, the changes in soil properties caused by fertilization might contribute to the structural variances in ARGs.RDA showed that the selected soil properties explained a total of 47.9% of the structural variance in ARGs.Among them, the pH and the C/N ratio were negatively correlated with the abundance of ARGs in soil, whereas other soil properties, such as TC, OM, TN, AK, and AP, were positively correlated with ARG abundance (P < 0.05) (Supplementary Figure S6).The total enrichment of ARGs in fertilized soils displayed marked differences, ranging from 482.1-fold (NP) to 3574.9-fold (MN) compared with the CK treatment (Figure 4).Genes encoding resistance to aminoglycoside, multidrug and tetracycline were the three most dominant types of ARGs in the fertilized treatments.The distribution of each ARG subtype in fertilized soils determined using Circos software (http://circos.ca/).Numbers on the outer ring represent the percentages of ARG subtypes in each fertilization treatment.Additionally, the total relative abundance of MGEs was significantly correlated with the total relative abundances of aminoglycoside (r = 0.89, P < 0.001), beta_lactamase (r = 0.59, P < 0.05), FCA (r = 0.64, P < 0.01), MLSB (r = 0.79, P < 0.001), sulfonamide (r = 0.92, P < 0.001), tetracycline (r = 0.93, P < 0.001), and vancomycin (r = 0.56, P < 0.05) resistance genes, based on Pearson’s correlation analysis (Figure 5B).Differences in the composition of microbial communities among the CK, manure-fertilized and chemical-fertilized treatments were also clearly identified (Supplementary Figure S11).The soil properties, i.e., TC, TN, OM, AK, AP, pH, and C/N ratio, were important factors in the separation of the microbial communities, explaining a total of 35.9% of the structural variance in the microbial community (Supplementary Figure S12).Network analysis was performed to illustrate the correlations between ARG subtypes and bacterial taxa (at the family level).The resulting network was composed of 52 nodes and 196 edges, including 28 unique ARG subtypes, 1 intI1 gene, and 23 families (Figure 6).These 23 bacterial taxa were affiliated with the phyla Bacteroidetes, Actinobacteria, Proteobacteria, Planctomycetes, and Firmicutes and had strong correlations with various ARGs (Spearman’s r2 > 0.36, P < 0.01).In addition, other families, such as Nocardioidaceae, Sphingomonadaceae, and Pirellulaceae, also had significant correlations with diverse ARGs (P < 0.01) (Figure 6).Edges are dependent on the coefficient values, and node size is weighted based on the relative abundance of ARGs/bacterial taxa.Redundancy analysis was employed to evaluate the relationships among the microbial community, soil properties, and ARGs (Figure 7A).Three phyla (Actinobacteria, Planctomycetes, and Gemmatimonadetes) exhibited significant correlations with ARGs in soil (P < 0.05).In addition, VPA was applied to explore the effects of the microbial community, MGEs, and soil properties on the distribution of ARGs (Figure 7B) and illustrated that the microbial community, MGEs and soil properties contributed to 27.6, 7.1, and 9.9% of the ARG variation, respectively.(A) Redundancy analysis (RDA) revealing correlations among ARGs, main phyla taxa (>1% in any sample) and soil properties.After 15 years of continuous manure amendment, the diversity and abundance of ARGs were significantly increased in manure-fertilized soil (Figure 2), and the antibiotic deactivation and efflux pump mechanisms were the two most dominant resistance mechanisms (Supplementary Figure S3).The PCoA also showed that manure application influenced the ARG composition (Supplementary Figure S4).Previous studies have shown that manure application correlates with the emergence and proliferation of ARGs in indigenous microbiota (Su et al., 2014; Chen Q. et al., 2016).This may have been caused by the introduction of new types of ARGs and ARB from animal manure (Heuer et al., 2011; Chen et al., 2017; Pu et al., 2018) or by selection pressure forced by antibiotics, heavy metals and disinfectants in the manure-fertilized soils (Knapp et al., 2010; Su et al., 2014; Udikovic-Kolic et al., 2014; Xie et al., 2018a).Moreover, as indicated by the network analysis, genes that encoded resistance to different types of antibiotics were placed in the same module (Supplementary Figure S8); they might change and transfer together under the selection pressure imposed by manure application because these ARGs may be located on the same DNA fragment or in the same host bacterium (Qian et al., 2018).The variation in the ARG profile between chemical fertilization treatments and the CK treatment was likely caused by alterations in the soil properties and the microbial community composition, including ARB already in the soil (Forsberg et al., 2014; Xie et al., 2018b).The existence of ARGs in unfertilized soil has traditionally been explained by the presence of antibiotic producers that harbor genes to protect themselves from these secondary metabolites (Heuer et al., 2011).Previous studies have also shown that antibiotic resistance is an ancient phenomenon, as confirmed by the detection of ARGs in permafrost sediments (D’Costa et al., 2011), pristine forests (Zhu et al., 2013; Wang et al., 2014a), and the Tibetan environment (Chen B. et al., 2016).Only manure amendment dramatically increased the relative abundance of MGEs in soil, while chemical fertilizer did not (Figure 5), indicating that MGEs originating from manure-derived bacteria could be established well in manured soils (Heuer et al., 2011).HGT of ARGs via MGEs, such as integrons, transposons, interactive conjugative elements and plasmids, from manure to soil microbes is a potential pathway for the spread and propagation of ARGs (Stokes and Gillings, 2011) since some of the bacteria from manure might not be well adapted to soil and may only survive from weeks to months in the environment (Heuer et al., 2011).A previous study demonstrated that ARGs could undergo “mobilization” when they appeared on MGEs (Stokes and Gillings, 2011).The Soil Microbial Community Is the Main Driver Shaping ARG Profiles.In this study, the five most abundant phyla in soils, Proteobacteria, Actinobacteria, Bacteroidetes, Planctomycetes and Firmicutes, were assumed to be possible bacterial hosts for ARGs, as revealed by the network analysis (Figure 6).These bacterial phyla have been recognized as important hosts for ARGs that encode resistance to multiple antibiotics in metagenomics analysis (Forsberg et al., 2014).A previous study demonstrated that manure application could induce a significant selective advantage for ARGs affiliated with the Micromonosporaceae family (Xiong et al., 2018).Another study showed that the genera Bacillus and Mycobacterium were possible bacterial pathogen hosts of ARGs that were enriched in a tetracycline-added soil treatment (Xia et al., 2019).Therefore, since these ARB could readily grow there, their eventual antibiotic exposure would be much more likely to contribute to the selection pressure for resistance during environmental dissemination.A pronounced difference in the diversity and structure of the microbial community was found between the manure-fertilized soils and the CK and chemical-fertilized treatments (Supplementary Figure S10).Multiple factors could result in this phenomenon, such as plant species, root growth, exudate production, and soil properties (Chaparro et al., 2014; Wang et al., 2015).Importantly, the variation in the microbial community played the main role in causing the shifts in the antibiotic resistome, rather than soil properties or MGEs (Figure 7B), since to the extent of the manure application, all soil microbes would have been exposed to selection for the resistance and mobilization of ARGs (Su et al., 2015; Chen Q. et al., 2016; Han et al., 2018).Previous studies have demonstrated that microbial community structure is closely related to the ARGs harbored in different environments (Forsberg et al., 2014; Johnson et al., 2016; Xie et al., 2018b).In addition, soil has been deemed an important reservoir of ARGs due to its complex microbial community and diverse antibiotic-producing microbes (Su et al., 2014), and the establishment of ARGs in the soil microbial community can be promoted by the periodic addition of manure (Heuer and Smalla, 2007).In summary, this study demonstrated that long-term manure application markedly enhanced the abundance and diversity of ARGs that encode resistance to a variety of antibiotics, such as aminoglycoside and tetracycline.FW, WH, and SC collected the soil samples and performed the laboratory measurements and data analysis.The authors declare that the research was conducted in the absence of any commercial or financial relationships that could be construed as a potential conflict of interest.We would like to thank Prof.
Yongguan Zhu, Prof. Jianqiang Su, Prof. Xiaofang Li, Prof.
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fertilizer, natural or artificial substance containing the chemical elements that improve growth and productiveness of plants.Modern chemical fertilizers include one or more of the three elements that are most important in plant nutrition: nitrogen, phosphorus, and potassium.On modern farms a variety of machines are used to apply synthetic fertilizer in solid, gaseous, or liquid form.Broadcast distributors have a tub-shaped hopper from which the material falls onto revolving disks that distribute it in a broad swath. .