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Article Contents

1 introduction, 2 research framework and data preparation, 3 knowledge-mapping model, 4 conclusions, conflicts of interest.

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The impact of agricultural chemical inputs on environment: global evidence from informetrics analysis and visualization

Lu Zhang and Chengxi Yan contribute equally to this work.

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Lu Zhang, Chengxi Yan, Qing Guo, Junbiao Zhang, Jorge Ruiz-Menjivar, The impact of agricultural chemical inputs on environment: global evidence from informetrics analysis and visualization, International Journal of Low-Carbon Technologies , Volume 13, Issue 4, December 2018, Pages 338–352, https://doi.org/10.1093/ijlct/cty039

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This paper identifies and analyzes salient research frontiers, research hotspots and high-frequency terms using aggregated and multiple-source literature records related to the topic of ‘effects of agricultural chemical inputs on the environment.’ We employ a set of Informetrics Theory methods (i.e. document co-citation analysis, document clustering and co-words analysis via co-occurrence network of subject terms) for our analysis. Our findings suggest that in the past 30 years, research about this topic can be divided into three stages, namely the early stage (1990–99), the middle stage (2000–07) and the late stage (2008–16). Research directions for the three identified stages deal primarily with (a) the effects of pesticides and veterinary drugs on the environment, (b) the influence of fertilizer application on the environment and food safety and (c) the technologies and strategies to monitor and control the impact of agricultural chemical inputs on the environment. Particularly, we find that research in the topic of interest primarily focusses on agricultural scenarios of food crop production and fish farming. In terms of agricultural chemical inputs, major attention is given to pesticides and fertilizers. With respect to the impact of agricultural inputs, pollutant formation and transferring process, nitrogen and phosphorous cycles, impact assessment indicators, as well as pollution prevention and reduction strategies are the most researched areas, and soil and water constitute the main researched environmental media. Finally, institutions and organization based in North America, East Asia and Europe are main research contributors on this topic.

Agricultural inputs broadly refer to the materials used or added in the process of agricultural production and include biological inputs, chemical inputs, and agricultural facilities and equipment. In particular, agricultural chemical inputs denote the different types of chemical applications in agricultural production, such as pesticides (including natural and biological pesticides), chemical fertilizers, veterinary drugs and feed additives, among others.

Agricultural management practices—for example, an increased use of agricultural chemicals or fertilizers—are often evaluated based on their benefits for economic efficiencies in production (e.g. reduction in total production costs and increased production yield) while less attention is generally given to their potential environmental effects [ 1 ]. For example, pesticide and fertilizer application plays a vital role in increasing agricultural production and ensuring the supply of agricultural products. Pesticide spraying can significantly reduce or offset the economic costs from plant diseases, insect pests, and weeds on agricultural production and fertilizer application can provide a variety of nutrients required for the growth of crops and for an increased yield in production. However, many countries have reported alarming residues of agricultural chemicals in soil, water, air, agricultural products, and even in human blood and adipose tissue [ 2 , 3 ].

Research suggests that the massive use of inorganic fertilizers world-wide is associated with the accumulation of contaminants, e.g. arsenic (As), cadmium (Cd), fluorine (F), lead (Pb) and mercury (Hg) in agricultural soils [ 1 ]. In the USA, according to a survey of 51 major river basins and aquifer systems by the US Geological Survey, pesticides were detected 97% of the time in samples from stream water in agricultural areas [ 4 ]. In Japan, pesticides were frequently detected in the air of residential environments and childcare facilities following the application of pesticides—this is consistent with the findings that outside pesticide applications are major contributors to indoor air pollution in agricultural communities [ 5 ].

In most developing countries, the pollution caused by agricultural chemicals is even more serious [ 6 , 7 ]. The usage volume of fertilizers and pesticides in China has been the recorded as the highest in the world. Specifically, its chemical fertilizer usage volume has reached more than 59 million tons and pesticide more than 1.8 million tons [ 8 ]. Alarmingly, the total utilization rate of fertilizers and pesticides is only ~35% [ 9 ], and thus, any fertilizer and pesticide losses are likely to contaminate soil, surface water and groundwater. In China, estimates indicate that contaminated arable land area is ~150 million acres, accounting for 8.3% of the total arable land in the nation [ 10 ]. In addition, nearly half of the groundwater resources have been inordinately polluted by agricultural chemicals, which seriously threaten the safety of drinking water in China, especially in rural areas. [ 11 ] reports that consequences of an increased use of agricultural chemicals transcend the environment. Farmers in developing countries are experiencing, either short-term or long-term, health effects from exposures to agricultural chemicals, including severe symptoms (e.g. headaches, skin rashes, eye irritations) and some chronic effects (e.g. cancer, endocrine disruption, birth defects).

Policy makers recognize that the excessive and unsystematic application of agrichemical inputs, pesticides and fertilizers in particular, is an obstacle to the development of sustainable agriculture, and poses a threat to the environment and humans alike. Several countries have enacted policies to regulate the usage volume and types of agricultural chemicals [ 12 , 13 ]. For instance, in the USA, the 1972 Federal Environmental Pesticide Control Act (FEPCA) and subsequent amendments acknowledge the negative effects of pesticide applications on both the environment and human health, regulate the use of pesticides and enforce compliance against banned pesticide products. The 2003, European Union Regulation EC No. 2003/2003 establishes that electrical conductivity fertilizers should meet a specific criteria in terms of nutrient content, safety and absence of adverse effects to the environment [ 14 ]. In 2015, the Chinese Ministry of Agriculture introduced the ‘Action to Achieve Zero Growth in the Application of fertilizer’ and ‘Action Plan for Zero Growth in the Application of Pesticide’, which both set specific goals, strategies, plans and relevant safeguard measures for controlling the usage of agricultural chemicals by year 2020 [ 15 ].

Scholars in the fields of agriculture, chemistry, environmental science, ecology, medicine and economics have also been highly concerned about the threat of excessively using agricultural chemicals to the environment and human health. In the last two decades, researchers have mainly focused on the following four areas regarding the increased use of agrichemicals and their impact. First, prior literature has explored the pollution derived from using pesticides and chemical fertilizers for the natural environment (i.e. soil microbial community response, agricultural water pollution, agricultural greenhouse gas emissions, agricultural fertilizer loss) [ 16 – 18 ]. Secondly, researchers have investigated the effects of using pesticides and fertilizers on agricultural production (i.e. soil fertility, farmland diseases, farmland weeds and farmland pests) [ 16 , 18 , 19 ]. Thirdly, other research has focused on the impact of using pesticides and fertilizers for society (i.e. social economy, food security and human health) [ 20 – 22 ]. Finally, extant literature has explored the interactions among chemical inputs, crop yield and the ecological environment [ 23 , 24 ].

Previous literature review studies documenting the impact of agricultural chemicals on the environment have normally employed qualitative methods (e.g. manual investigation and literature classification) rather than quantitative methods (e.g. Informetrics analysis and visualization), and have used limited sources of data (e.g. key documents and reports) to perform the reviews. In addition, the research scale for most review studies has been narrow, focusing on a specific type of agricultural chemical input (e.g. pesticides or fertilizers) and analyzing its impact on a single environmental element (e.g. soil, water or air). To our knowledge, only a few scholars have reviewed the impact of agricultural chemicals on water, soil and human health conjunctively [ 1 , 25 , 26 ].

The present study addresses these limitations and utilizes a robust quantitative approach (i.e. information metrology) to exploit the data richness from aggregated and multiple-source records to perform the review. We aim to systematically and objectively present the research evolution of the literature conducted on the macro-environmental effects induced by excessive use chemical inputs (i.e. fertilizers and pesticides) in agriculture (i.e. fertilizers and pesticides) and to provide further insight into future research directions or intersections that may of interest for researchers and policy makers.

2.1 Research framework

The field of Informetrics deals with the quantitative analysis of information, aiming to reveal patterns and associations of information objects, their production, structure and dissemination [ 27 ]. Citation analysis is a core method in Informetrics. With feature statistics, citation analysis can effectively find common domains of knowledge for analyzed records. Based on citation analysis, generalized Informetrics—a combination of statistical description, mathematical model and machine learning—has become a cross-discipline approach for scientific knowledge evaluation, and includes popular methods, such as ‘co-word network,’ ‘clustering Analysis’ and ‘mapping knowledge domain.’

Co-word network is a relational network based on the co-occurrence of keywords or subject terms in the literature; this method belongs to the catalog of ‘Content Analysis Method’. Cluster analysis comes from the notion of automatic categorization for similar abstract objects based on the theory of machine learning, and aims to cluster analogous members and divide unrelated objects. Mapping knowledge domain enables to reveal relevant research frontiers and frameworks, and intuitively demonstrates the development process of a discipline or knowledge using graphical representations and tools.

2.2 Data retrieval and preprocessing

First, we ascertain scientific subject terms through the platform ‘LCSH’ (Library of Congress Subject Headings) from which candidate words are examined using query entries via the function ‘LC Linked Data Service’. Second, we conduct the preprocessing stage (i.e. data cleaning, knowledge representation, formation of co-word matrix) using 16 459 articles retrieved from the core data set of web of science (WOS). The result of the latter phase is the development and creation of a knowledge-mapping model with focus on the main theme of ‘agricultural chemical inputs and environmental impact.’

Query reformulation is a critical phase of searching and collecting target articles [ 28 ]. In this paper, the preliminary query formulation is formed according to the integration of candidate words, including ‘agricultural chemicals’, ‘farm chemicals’, ‘pesticides’, ‘fertilizers’, ‘fertilizers’, ‘manures’ and ‘environment’. Through associated retrieval by the ‘LC Linked Data Service’ tool, ‘agricultural chemicals’, ‘pesticides’, ‘fertilizers’ and ‘manures’ are identified as conception topics. ‘Agricultural chemicals’ is the extension of the concept terms ‘pesticides’ and ‘fertilizers’ (i.e. broader term relationship). ‘Manures’, by contrast, is a narrower term for ‘pesticides’ (i.e. narrower term relationship). ‘Fertilizers’ and ‘farm chemicals’ should not be taken as independent subject terms as they are lexical variants of ‘fertilizers’ and ‘agricultural chemicals.’ Therefore, for this study the independent subject terms are as follows: ‘agricultural chemicals’, ‘pesticides’, ‘fertilizers’ and ‘environment’.

After identifying the subject terms, we scanned selected databases (i.e. SCI-E, SSCI, A&HCI, CPCI-S and CPCI-SSH) in WOS. Specifically, the query reformulation of term collocation is ‘(TOPIC: (agricultural chemical) AND TOPIC: (environment)) OR (TOPIC: (pesticides) AND TOPIC: (environment)) OR (TOPIC: (fertilizers) AND TOPIC: (environment))’. The time span used for this query is from 1990 to 2016 (last updated on 21 October 2016).

The data preprocessing phase aims to unify inconsistent formats and units of data from different systems or platforms [ 29 ]. This paper adopts three methods (i.e. data cleaning, knowledge representation and automation formation of co-word matrix) to conduct the data preprocessing. For data cleaning and in anticipation that WOS records may be subject to noise or missing data, we conduct an artificial exclusion and consistency check by removing unrecognizable keywords with high frequency, such as ‘u 238’ or ‘34’. Then, for knowledge representation, we use citation network analysis via CitesSpace and formed 6 079 nodes and 5 217 edges. Finally, based on the revised pagerank index, we employ the Gelphi platform to form a co-work matrix, which is an efficient method for analyzing and exploring potential rules and interplay amid various literature records.

Constructing a knowledge-mapping model for the topic ‘the impact of agricultural chemicals on environment’ can provide further guidance on the research directions, hot topics and research frontiers, as well as on the distributions and discipline evolution. Figure 1 shows the knowledge-mapping model established in this paper. The part A of Figure 1 shows a green highlighted area in the middle of the network called ‘giant component’ and represents the tightest and most stable part of the overall knowledge network about ‘the impact of agricultural chemicals on environment’. This paper analyzes different aspects of the ‘giant component’ network. Special attention is paid to mining and interpreting the distinctive nodes in order to further understand the knowledge baseline and research frontiers for the topic of interest. Using clustering and visualization analysis with the construction of a co-word matrix, this study offers a summary of the main and timely areas of interest or concern, as well as major objects and research methods used in the research of this topic. The following section provides the results for a set of Informetrics Theory-based analyses: document co-citation analysis, document citation-clustering and co-words analysis via co-occurrence network of subject terms.

Global and macro-scope view based on citation analysis.

3.1 Co-citation analysis

Citation analysis explores the citation relationship and co-occurrence patterns of original papers and their references. It aims to reveal the knowledge connection, knowledge structure and knowledge rules of the target scientific area. A time-dimensional visualized intellectual landscape is constructed and provided in Part B of Figure 1 . In the past 30 years, researches on the environmental impacts from agricultural chemical inputs could be divided into three stages, namely early stage from 1990 to1999 (B1), middle stage from 2000 to 2007 (B2) and late stage from 2008 to 2016 (B3). Using the results from citation analysis, we identify two proliferous authors, Yi-fan Li and Dana W. Kolpin, for the research topic of interest (i.e. the impact of agricultural chemical inputs on the environment). These two authors were selected based on the number of authored and published journal articles and their consistent contribution to the aforementioned research topic in the last three decades. For illustration purposes, we use their research to exemplify the evolution of the lines of inquiry and investigation in the discipline over the three identified stages.

As shown, in the early stage, researches mainly focused on the application of agricultural chemicals, pollutants emissions and the degree of concentration in the environment. The measurement of pollution in the environment is the salient line of inquiry in this early stage. For example, a distinguished scholar in research related to the topic of interest is Yi-Fan Li, a scientist in the Atmospheric Quality Institute, Dalian Maritime University and Harbin Institute of Technology in Canada. For decades, he has dedicated his career to study the effects of persistent organic pollutants (POPs) on the ecological environment. In the first stage, articles authored or co-authored by Li focus on the pollution degree of POPs, the usage rate of hexachlorocyclohexane and their impact on the environment [ 30 – 32 ]. Another salient author in the early stage in Dana W. Kolpin, head of the US Geological Survey’s Emerging Contaminants Project, who has dedicated decades to the investigation of how pharmaceuticals and other contaminants move through the environment. In the first stage, his researches mainly focused on assessing the levels of selected pesticides and their metabolites in groundwater or streams in the USA [ 33 – 38 ].

Articles published within the period of the middle stage focused on to the analysis of influence mechanisms, including pollutant generation mechanism, source analysis, transmission channel and source sink relationship. During this stage, Li and colleagues studied the gridded emission inventories of hexachlorocyclohexane and the aspects that stimulate the transport of hexachlorocyclohexane. His research concentrated in exploring the sources and transport mechanism of POPs in the environment [ 39 – 42 ]. Similarly, Kolpin, in the second stage, mainly focused on the environmental occurrence, transport and the ultimate fate of many synthetic organic chemicals after their intended use. He paid special attention to the organic wastewater contaminants in the groundwater and streams in the USA. Specifically, he monitored the concentrations, analyzed the source and transport paths, mined the impact on the environment and put forward relevant control strategies [ 43 – 47 ].

In the late stage, researchers mainly studied the specific types of pollutants (e.g. pharmaceuticals, polycyclic aromatic hydrocarbons (PAHs)), discussed their impacts on the environmental media (e.g. air, soil or water), as well as compared changes under different conditions (e.g. spatial and temporal variations, varying types of crops and agricultural inputs). Publications during this stage normally focused on a specific geographical area (e.g. Dalian in China or Iowa in the USA), or an agricultural production environment (e.g. basins containing livestock farming operations or a high corn and soybean producing region). Articles by Li, in the third stage, mainly researched sources and distributions of Dechlorane plus or PAHs in specific parts of China and their implications for human exposure. His studies further explored the sources, characteristics and potential human health risks of POPs in water, soil and the atmosphere within a certain geographical area [ 48 – 53 ]. Kolpin, in the late stage, primarily investigated the occurrence of chemical contaminants in water plants (e.g. sewage treatment plants) or bodies of water (e.g. wastewater-impacted streams, agricultural basins). In his recent studies, he analyzed the chemicals contaminants’ spatial and temporal variations and exposures to fish (e.g. smallmouth bass), livestock and human health [ 54 – 64 ].

Our findings suggest that the three stages identified (i.e. B1, B2 and B3) for the topic of interest reflect the evolution and sequential advancement of knowledge in the field. The B1 stage mirrors the foundational knowledge research conducted about the presence of pollutants in the environmental media. As observed, the B1 stage informs the B2 phase by providing scientific data and evidence about agricultural chemical inputs and chemical contaminants in the environment. The B3 stage is the current research frontier, which explores the occurrence and potential risks of chemical pollutants in specific contexts. For instance, in the latter stage, publications mainly revolve around the response mechanisms of environmental systems to chemical pollutants and on the potential risk for human health and ecological health induced by chemical pollutants. The transition from the initial stage (B1) to the current research frontier (B3) reflect the gradual progression in research for this topic: assessment of the situation, evaluation of overall impact, and analysis of transdisciplinary and context-specific impact.

3.2 Citation-clustering analysis

Top five highest-frequency articles in the first two clusters and top dive pivot nodes in Cluster A3.

To assess the research focus of environmental impacts induced by agricultural chemical inputs, this paper conducts cluster optimization with the relevant literature review. The results show that researches about this topic primarily consists of three clusters, namely A1 (the upper part in Figure 2 ), A2 (the middle part in Figure 2 ) and A3 (the lower part in Figure 2 ).

Network of high-cited frequency clusters.

Research studies within the A1 cluster largely focus on the effects of pesticides and veterinary drugs on the environment. The A1 cluster can be further divided in two Subclusters A1_1 and A1_2 where the former concentrates in the study of chemical residues in various environmental media after their application and their impact on human health in countries or regions [ 42 , 65 – 67 ], while the latter deals with research on veterinary drug residues in various environmental media as well as the pollutants monitoring techniques and methods (i.e. passive sampling techniques) are studied [ 44 , 70 , 71 , 84 , 85 ]. Particularly, the distinctive light green region on the left side of A1 represents key research on the impact of pesticide exposure on wildlife and human conducted at end of 1990s [ 72 , 73 , 86 ]. It is worth noting that articles in cluster A1 have been frequently cited since year 2000, and may be conceived as the initial stage of research on agricultural chemicals and their impact on the environmental.

Furthermore, the A2 cluster contains publications with emphasis on the effects of chemical fertilizer applications for the environment, especially on farmland. Specifically, the research in the A2 cluster addresses the topic of soil problems due to the improper application of chemical fertilizer. For example, articles within this cluster study the loss of soil elements due to the non-proportional application of chemical fertilizer and soil acidification due to the excessive use of chemical fertilizers [ 52 , 74 , 76 , 77 ]. This cluster also embodies investigations on ways to promote sustainable management practices for cultivated land without compromising the global food demands and security [ 75 , 87 , 88 ].

Finally, the A3 cluster distinctively connects A1–A2, serving as an ‘information bridge’. Research within cluster A3, represented nodes situated in the middle of the network, includes novel methods and technologies for monitoring and controlling the environmental impact of agricultural chemicals inputs [ 79 , 80 , 89 , 90 ]. Specifically, these methods include techniques to determine pollutant sources (e.g. stable isotope analysis), to measure the toxicity of pollutants, and to evaluate the negative effects of pesticides on environment, as well as methods to control the spread of pollutants and to reduce the negative effects of agricultural chemicals [ 79 , 83 ]. As shown in Figure 3 , three areas are circled out in A3, which represent five significant records. For instance, studies within Cluster A3 explore specific techniques to monitor chemical pollutants in the environment and lays the foundation for pollutant measurement, sources and characteristic analysis and environmental impact assessment. Interestingly, research stem from this line of inquiry connects previous research on pesticide contamination and monitoring captured by Clusters A1 and A2 [ 85 , 89 , 91 – 97 ]. Finally, A3 cluster research dealing with techniques to control chemical pollutants in the environment connects previous research on the environmental impact of the application of chemical fertilizer (Cluster A1) and studies on strategic practices for reducing environmental impact of fertilizer pollutants while ensuring food security and promoting the sustainable development of agricultural industry (Cluster A2) [ 87 , 98 – 100 ].

pivot nodes in the knowledge area ‘A3’.

3.3 Co-occurrence network of subject terms analysis

Top five subject terms in seven categories.

The carrier category in Table 2 represents the carrier of chemical pollutants, namely the subject that exerts influence on the environment. The most frequent terms in this category are pesticide and fertilizer. Other high-frequency terms include organochlorine pesticides and nitrogen fertilizer. Our findings reveal that based on the evaluated records, pesticide and fertilizer in agricultural chemicals are the main source of pollutants research in the literature.

The category of environmental object represents objects affected by agricultural chemical inputs. In the context of our study, the most frequent terms (objects) are soil, water and air. Other high-frequency words include groundwater, wastewater, surface water and sewage sludge. Our results indicate that water, soil and air are the most researched environmental media when it comes to pollution derived from pesticides and fertilizers. Specifically, our findings suggest that researchers have focused on monitoring the concentration and diffusion of agricultural chemicals in soil, water and atmosphere. In addition, climate change is a frequent term in this category, with emphasis on the impact mechanism of agricultural chemicals on the atmospheric environment.

The process category include research dealing with the process of agricultural chemicals exerting impacts on the environment. The most frequency terms include pollute, leach, irrigation, runoff and eutrophication. It indicates that studies about the phenomenon of water eutrophication caused by the loss of nitrogen and phosphorus in the process of rainfall or irrigation has been of great concern and merited the attention of researchers.

The cycle category represents the biogeochemical cycle, that is, the transfer process of the chemical elements needed by a living organism between the organism and the environment. Nitrogen and phosphorus have the highest frequency among chemical elements, and it indicates that studies mainly focus on effects of excessively using agricultural chemicals on the process of nitrogen and phosphorus cycles. Meanwhile, the degradation of nitrogen, phosphorus and other chemical pollutants in the environment, especially biodegrade, appear to be another salient topic.

The method category represents research methods and management strategies, including research methods for exploring the environmental impact of agricultural chemical inputs, as well as management strategies for reducing the environmental hazards induced by agricultural chemicals. Model and risk assessment are the top two frequency terms. Other high-frequency terms include bioremediation, integrated pest management, monitor and passive sample. This indicates that assessing the environmental risk and controlling the usage of agricultural chemicals based on various models have deemed relevant and timely issues in the literature. For example, researchers have collected samples based on various means (such as passive air samplers) and used various risk indicators to assess the environmental impact of agricultural chemicals. In addition, studies have extensively explored measures and strategies (e.g. bioremediation and integrated pest management) to reduce and mitigate environmental hazards caused by agricultural chemical inputs.

The agricultural object category includes the high-frequency words, such as wheat, fish, maize, rice, plant and crop. Overall, this category reflects the major research emphasis on the crops and fisheries. Interestingly, the word ‘China’ is also the key word in this category, indicating that with high consumption and low efficiency of agricultural chemicals inputs, China has become one of the main researched geographical region in terms of environmental problems.

Indicator category includes the different factors used when assessing the environmental impact induced by agricultural chemicals. The most frequent terms include heavy metal, nitrate, POP, organophosphate, pesticide residue and endocrine disruptor. Our results indicate that chemical pollutants including metal nitrate, pesticide and residue heavy have been widely investigated as major determinants of pollution. Importantly, we find that the extant literature has predominantly examined the effect and risk of pollutants for bodies of water, soil organism, air, fishes, bees and human health.

Finally, to better understand the key nodes and their relationships among the categories, we conduct a visualized analysis in the Gephi platform based on the co-occurrence relationship, PageRank value and the seven identified categories (see Figure 4 ). Based on the PageRank value, we identified the top three categories. ‘Carrier’, ‘agricultural object’ and ‘indicator’ are the top three categories, which indicate that scholars have largely paid attention to analyze the transport process of chemical pollutants and assessing their impact on the environment, especially under agricultural production scenarios. The difference in thickness for the graphed lines denote the strength of links or connections. As shown in Figure 4 , agriculture and environment, pollute and environment, pesticide and environment, and nitrate and leach have a strong semantic relation.

Co-occurrence network of filtered subject terms.

3.4 Academic cooperation and knowledge sharing among countries and institutions

The mutually beneficial cooperation among different research institutes and countries plays a key role in promoting the development of science and technology. Citation number analysis and co-authorship analysis are important methods for evaluating the cooperation and research level of different institutes and countries. In the present paper, we first summarize the global development trends based on citation statistics of different countries. Then, we employ co-authorship metrics to analyze the scientific knowledge communication and organization distribution in the collaboration network. Ultimately, we present an overall knowledge-sharing network among different countries and institutions.

From a time sequence perspective, the relevant and selected 16 459 articles on ‘the environmental impact of agricultural chemical inputs’ demonstrate an exponential growth (see Figure 5 ). This indicates that based on direction, the current research is in the middle and preliminary stage of a rapid forecasted development, and the volume of scientific knowledge is expected to grow dramatically with optimistic future predictions. Our findings suggest that prior to 2006, Asian and South American countries, such as China, India and Brazil, lagged far behind in terms of technological advancement when compared to developed countries such as the USA, Canada, Australia and some European countries (e.g. UK, France, Germany and Holland), the same trend is observed for the number of publication amounts generated and growth rates. In recent years, the gap has narrowed down significantly, which can be attributed to the strengthening and investment in science and technology (especially the advancement of environmental science and ecological science) in Asian and South American countries. It is noticeable that, in China, the number of articles grew significantly from 54 to 267 during 2006–15 period. Then in 2015, the number of publications (267 articles) produced by China surpassed the number of publications generated in USA (239 articles). Interestingly, the citation growth rate has gradually decreased in developed countries, such as the UK and Holland, but has steadily increased in developing countries, such as India and Brazil. This result reveal the cooperation among countries in the newly advanced economic development (i.e. Brazil, Russia, India, China and South Africa) in order to advance and promote the technology and innovation in the agricultural sector.

Rapid increase of scientific papers on the world-wide scale.

Moreover, results from co-authorship network analysis suggest that institutions and organizations based in North America, East Asia and Europe are the major research contributors; this trend is visualized via Google Earth View (see part A of Figure 6 ). Each area has established close cooperation relations. Leading countries, such as the USA and Canada in North America, and France and Germany in Europe have dominating effects upon scientific development and collaboration. Data statistics and visualization can help to discover rules and distributions of academic collaborations within this topic. As shown in part B of Figure 6 , the co-author communities are identified in the large linked network. Greater density indexes are marked by deeper colors in the thermodynamic diagram. Some hubs are most prominent, such as the Chinese Academy of Sciences ‘Chinese AcadSci,’ the Public Scientific and Technical Research Establishment in France ‘CNRS,’ the United States Department of Agriculture—Agricultural Research Service ‘USDA ARS,’ the Canadian Natural Resources ‘Nat Resource Canada,’ and the University of Paris Diderot, Paris 7 ‘University Paris 07.’ Darker color vertices have relatively higher diameter and can be observed as a side-by side comparison demonstrated in above four-part visualized images. As seen, CNRS ranks first with 17 units and is followed by Chinese Academy of Sciences with 15 units.

Visualization of Academic collaboration network.

Detailed information of scientific research organizations-based co-authorship weights.

Using informetrics theory-based methods (i.e. document co-citation analysis, document clustering and co-words analysis via co-occurrence network of subject terms), this study distinguishes and further explores research frontiers, research hotspots and high-frequency terms using aggregated and multiple-source literature records related to the topic of ‘effects of agricultural chemical inputs on the environment.’

From a macro-level view, citation network analysis shows that the impact of agricultural chemicals on the environment can be divided into three periods. In the early stage (1990–99), studies mainly focus on the application of agricultural chemicals, pollutant emissions and their concentration in various environmental media. During the middle stage (2000–07), studies mainly focus on the production mechanism, source apportionment, transmission channel and source/sink relationship of pollutants. In the late stage (2008–16), studies mainly focus on discussing the influence of specific pollutants on various environmental medias and comparing the changes under different conditions.

Citation-clustering analysis, a meso-level method, shows that the main research directions include the effects of pesticides and veterinary drugs on the environment (A1), the influence of fertilizer application on environmental and food safety (A2), and the technologies and strategies for monitoring and controlling the impact of agricultural chemicals on environment (A3). The A3 cluster contains special pivot nodes in the knowledge network, connecting A1 and A2, providing research in A1 and A2 with technical supports for revealing the impacts.

From a micro-level perspective, results from co-occurrence network of subject terms analysis, show that pesticides and chemical fertilizer are the main types of agricultural chemicals. As for pollutant types, POPs, heavy metals, nitrates and pesticide residue in environmental media appear to be of major interest and concern. Moreover, agricultural chemical inputs and their environmental impact derived from the production of wheat, maize and rice seem to be main focal point. For environmental objects impacted by agricultural chemicals, particular attention in the literature has been paid to soil, air and water, studying the potential risks of environmental pollution to fishes, bees and human health. Major concern is given to the process of environmental pollution caused by agricultural chemicals. For example, the impact process of excessively using agricultural chemicals on nitrogen and phosphorus cycles, as well as water eutrophication and other problems caused by this process, has raised widespread concern. Close attention has been paid to methods to control these negative effects. For example, these is research about methods to biodegrade nitrogen, phosphorus and other chemical pollutants in environmental media, to achieve the sustainable development of agriculture.

Citation analysis suggests that the volume of scientific knowledge and contributions, as measured by number of publications related to the topic, has grown dramatically with an optimistic future forecast. The gap of publication numbers between developing and developed countries is gradually narrowing down. The co-authorship analysis shows that authors based in North America (USA and Canada), East Asian (China, South Korea and Japan) and Europe (France and Germany) are the major research contributors for the topic of interest. National academic research organizations (e.g. Chinese Academy of Sciences), equipped with comprehensive and interdisciplinary expertise and social influence, have adopted leading research roles as compared to universities and other educational research institutes. In particular, the Chinese Academy of Sciences (China), National Institute of Agricultural Research (France), French National Center for Scientific Research (France), US Department of Agri/culture (the USA) and Cornell University (the USA) constitute the main hubs for research concerning the impact of agricultural chemicals on the environmental media.

Though the results of this study provide a useful summary of last three decades of research conducted in the topic of the effects of agricultural inputs on the environment, this research is not exempt from limitations. For example, the salient agricultural inputs used for the analysis (i.e. pesticides and fertilizers) have distinctive uses in agricultural activities and their effects on the environment may greatly vary by input. In addition, pesticides can further be divided based on their function (e.g. fumigants, insecticides, biopesticides, herbicides, etc.) and the impact of these on the environment may differ. The same is true for agricultural fertilizers which are often classified based on their efficiency, origin and phase. Finally, future literature review research may benefit from a narrower focus for targeting records that concern a single environmental media.

This work was supported by the Natural Sciences Foundation of China (41501213 and 71333006); the Fundamental Research Funds for Central Universities (2662017PY045); the Key Project for Studies of Philosophy and Social Sciences by Ministry of Education (15JZD014); the Major Program of National Social Science Foundation of China (15ZDC038); the project of philosophy and social sciences of Guangdong Province (GDXK201721); the project of Guangdong Institute for International Strategies (17ZDA19) and the University of Florida International Center’s Global Fellowship Award.

The authors declare no conflict of interest.

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Fertilizers: challenges and solutions

At the start of the 20th century, German chemists Fritz Haber and Carl Bosch developed a method for taking nitrogen from the air and melding it with hydrogen. It would prove to be one of the great scientific advances of the century.

Combined, the two elements made liquid ammonia, a key ingredient in synthetic fertilizers, which would drive an unprecedented agricultural expansion and help feed a fast-growing world.

But there has been a downside. During the last 100 years, the amount of man-made nitrogen compounds in water, soil and the air has doubled – an increase driven in large part by the widespread use of synthetic fertilizers.

Nitrogen is essential for life on Earth but in excess, it is a dangerous pollutant and is poisoning water bodies, plants, animals and humans, while driving climate change through emissions of the potent greenhouse gas, nitrous oxide. Though little known to the general public, experts call the flood of excess nitrogen one of the most severe pollution threats facing humanity today.

At the beginning of the 19th century, there were almost no man-made nitrogen compounds in the environment. But in the years after the Haber-Bosch breakthrough, their levels began to skyrocket, driven by the massive uptake of synthetic fertilizers and other human activities like the manufacturing of munitions and the burning of fossil fuels, both of which create chemically reactive forms of nitrogen.

Nutrient run-off from farms laced with synthetic fertilizer has adversely affected land ecosystems, according to the United Nations-backed Intergovernmental Science-Policy Platform on Biodiversity and Ecosystem Services (IPBES). But freshwater and marine habitats have been hit hardest, with recurrent algal blooms such as in Lake Erie, and “dead zones” bereft of aquatic life as in the Gulf of Mexico, it says.

Human health is also at risk. Agricultural ammonia emissions can combine with pollution from vehicle exhausts to create dangerous particulates in the air and exacerbate respiratory diseases, including COVID-19. One study has estimated that air pollution may increase mortality associated with COVID-19 by 15 per cent.

To stem the tide of nitrogen pollution, a growing number of governments, companies and international bodies, including the United Nations Environment Programme (UNEP), have been working with scientists to better understand the risks associated with human use of nitrogen, and to raise awareness.

To that end, almost exactly a year ago United Nations Member States endorsed the Colombo Declaration on Sustainable Nitrogen Management , which sets an ambition to halve nitrogen waste from all sources by 2030.

UNEP also recently established the global “Halve Nitrogen Waste” campaign, highlighting the fact that improving nitrogen use efficiency not only supports climate, nature and health goals but also saves US$100 billion globally annually (an estimate based on half the value of global synthetic fertilizer sales).

“The sustainable use of nitrogen offers a triple win – for the economy, for human health, and for the environment.”

Globally, synthetic fertilizers are behind the bulk of global food production and they’re especially important in developing countries. That, experts say, will make a transition away from them challenging. However, initiatives to stake out a more sustainable way of growing food, are plentiful.

A recent study from the Soil Association, a United Kingdom-based charity and advocate of organic farming, calls for much greater attention to nitrous oxide emissions in global greenhouse gas accounting; more integrated efforts to tackle nitrogen excess as a climate, nature and health issue; and incentives for better nitrogen management at farm level.

But organic farming methods are not the only example of sustainable nutrient management: agroecological approaches , including conservation, low-input, and minimum tillage agriculture, are all recognized as “nature-positive” and regenerative practices.

From farm to fork, 80 per cent of nitrogen is wasted and lost to the environment , according to a study by the Centre for Ecology & Hydrology in the United Kingdom. More efficient use of animal manure and greater use, in rotations, of nitrogen-fixing crops – such as legumes which convert nitrogen from the air into a form that is biologically useful – will be crucial to replace synthetic nitrogen as part of the process of rebuilding soil fertility.

What are nitrogen-fixing plants?

Nitrogen-fixing plants have partner bacteria in their roots able to grab dinitrogen (N 2 ) out of the atmosphere. They convert the N 2 into ammonia (NH 3 ), which the plant can use to make protein, amino acids and DNA. Only a few plants can achieve this amazing trick, like the pea family (legumes) and the floating fern Azolla. Where the availability of manure is limited, these plants become very important in farming systems aiming to avoid synthetic nitrogen fertilizers.

There is consensus that everyone should be using manure and urine better, says Mark Sutton, a lead author of the study. “Simple actions include putting a lid on the manure tank, which stops ammonia being lost to air. If you can smell your manure, it means you are wasting it to the atmosphere,” he says.

“Financial incentives and political buy-in will be necessary to overcome the many obstacles in the way of nitrogen-light farming methods,” says Susan Gardner, head of the UNEP Ecosystems Division. “But the bottom line remains: we need to dramatically reduce the quantity of reactive nitrogen being released into the environment from all sources, especially from synthetic fertilizers which represent one of the biggest nitrogen flows.”

“The sustainable use of nitrogen offers a triple win – for the economy, for human health, and for the environment,” she adds.

The International Nitrogen Management System (INMS) is a global science-support system for international nitrogen policy development established as a joint activity of UNEP and the International Nitrogen Initiative. It is supported with funding through the Global Environment Facility and around 80 project partners through the “Towards INMS” project (2016-2022). INMS provides a cross-cutting contribution to multiple programmes and intergovernmental conventions relevant for the nitrogen challenge.

For more information, please contact Mahesh Pradhan: [email protected]

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Further Resources

• Colombo Declaration calls for tackling global nitrogen challenge
• Why nitrogen management is key for climate change mitigation
• Bittersweet nature of nitrogen calls for better management practices
• Reactive Nitrogen

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• Introduction

Essential plant nutrients

Determining nutrient needs, the economics of fertilizers, synthetic fertilizers, farm manure, green manuring, methods of application.

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fertilizer , natural or artificial substance containing the chemical elements that improve growth and productiveness of plants. Fertilizers enhance the natural fertility of the soil or replace chemical elements taken from the soil by previous crops.

Soil fertility is the quality of a soil that enables it to provide compounds in adequate amounts and proper balance to promote growth of plants when other factors (such as light, moisture, temperature, and soil structure) are favourable. Where fertility of the soil is not good, natural or manufactured materials may be added to supply the needed plant nutrients. These are called fertilizers, although the term is generally applied to largely inorganic materials other than lime or gypsum .

In total, plants need at least 16 elements, of which the most important are carbon , hydrogen , oxygen , nitrogen , phosphorus , sulfur , potassium , calcium , and magnesium . Plants obtain carbon from the atmosphere and hydrogen and oxygen from water; other nutrients are taken up from the soil. Although plants contain sodium , iodine , and cobalt , these are apparently not essential. This is also true of silicon and aluminum .

Overall chemical analyses indicate that the total supply of nutrients in soils is usually high in comparison with the requirements of crop plants. Much of this potential supply, however, is bound tightly in forms that are not released to crops fast enough to give satisfactory growth. Because of this, the farmer is interested in measuring the available nutrient supply as contrasted to the total nutrient supply. When the available supply of a given nutrient becomes depleted , its absence becomes a limiting factor in plant growth. Excessive quantities of some nutrients may cause a decrease in yield, however.

Determination of a crop’s nutrient needs is an essential aspect of fertilizer technology . The appearance of a growing crop may indicate a need for fertilizer, though in some plants the need for more or different nutrients may not be easily observable. If such a problem exists, its nature must be diagnosed, the degree of deficiency must be determined, and the amount and kind of fertilizer needed for a given yield must be found. There is no substitute for detailed examination of plants and soil conditions in the field, followed by simple fertilizer tests, quick tests of plant tissues, and analysis of soils and plants.

Sometimes plants show symptoms of poor nutrition. Chlorosis (general yellow or pale green colour), for example, indicates lack of sulfur and nitrogen. Iron deficiency produces white or pale yellow tissue. Symptoms can be misinterpreted, however. Plant disease can produce appearances resembling mineral deficiency, as can various organisms. Drought or improper cultivation or fertilizer application each may create deficiency symptoms.

After field diagnosis , the conclusions may be confirmed by experiments in a greenhouse or by making strip tests in the field. In strip tests, the fertilizer elements suspected of being deficient are added, singly or in combination, and the resulting plant growth observed. Next it is necessary to determine the extent of the deficiency.

An experiment in the field can be conducted by adding nutrients to the crop at various rates. The resulting response of yield in relation to amounts of nutrients supplied will indicate the supplying power of the unfertilized soil in terms of bushels or tons of produce. If the increase in yield is large, this practice will show that the soil has too little of a given nutrient. Such field experiments may not be practical, because they can cost too much in time and money. Soil-testing laboratories are available in most areas; they conduct chemical soil tests to estimate the availability of nutrients. Commercial soil-testing kits give results that may be very inaccurate, depending on techniques and interpretation. Actually, the most accurate system consists of laboratory analysis of the nutrient content of plant parts, such as the leaf. The results, when correlated with yield response to fertilizer application in field experiments, can give the best estimate of deficiency. Further development of remote sensing techniques, such as infrared photography, are under study and may ultimately become the most valuable technique for such estimates.

The practical goal is to determine how much nutrient material to add. Since the farmer wants to know how much profit to expect when buying fertilizer, the tests are interpreted as an estimation of increased crop production that will result from nutrient additions. The cost of nutrients must be balanced against the value of the crop or even against alternative procedures, such as investing the money in something else with a greater potential return. The law of diminishing returns is well exemplified in fertilizer technology. Past a certain point, equal inputs of chemicals produce less and less yield increase. The goal of the farmer is to use fertilizer in such a way that the most profitable application rate is employed. Ideal fertilizer application also minimizes excess and ill-timed application, which is not only wasteful for the farmer but also harmful to nearby waterways. Unfortunately, water pollution from fertilizer runoff , which has a sphere of impact that extends far beyond the farmer and the fields, is a negative externality that is not accounted for in the costs and prices of the unregulated market.

Fertilizers can aid in making profitable changes in farming . Operators can reduce costs per unit of production and increase the margin of return over total cost by increasing rates of application of fertilizer on principal cash and feed crops. They are then in a position to invest in soil conservation and other improvements that are needed when shifting acreage from surplus crops to other uses.

Modern chemical fertilizers include one or more of the three elements that are most important in plant nutrition: nitrogen , phosphorus , and potassium . Of secondary importance are the elements sulfur, magnesium, and calcium.

Most nitrogen fertilizers are obtained from synthetic ammonia ; this chemical compound (NH 3 ) is used either as a gas or in a water solution, or it is converted into salts such as ammonium sulfate, ammonium nitrate , and ammonium phosphate, but packinghouse wastes, treated garbage, sewage, and manure are also common sources of it. Because its nitrogen content is high and is readily converted to ammonia in the soil, urea is one of the most concentrated nitrogenous fertilizers. An inexpensive compound, it is incorporated in mixed fertilizers as well as being applied alone to the soil or sprayed on foliage . With  formaldehyde  it gives methylene-urea fertilizers, which release nitrogen slowly, continuously, and uniformly, a full year’s supply being applied at one time.

Phosphorus fertilizers include calcium phosphate derived from phosphate rock or bones. The more soluble superphosphate and triple superphosphate preparations are obtained by the treatment of calcium phosphate with sulfuric and phosphoric acid , respectively. Potassium fertilizers, namely potassium chloride and potassium sulfate, are mined from potash deposits. Of commercially produced potassium compounds, almost 95 percent of them are used in agriculture as fertilizer.

Mixed fertilizers contain more than one of the three major nutrients—nitrogen, phosphorus, and potassium. Fertilizer grade is a conventional expression that indicates the percentage of plant nutrients in a fertilizer; thus, a 10–20–10 grade contains 10 percent nitrogen, 20 percent phosphoric oxide, and 10 percent potash. Mixed fertilizers can be formulated in hundreds of ways.

Organic fertilizers and practices

The use of manure and compost as fertilizers is probably almost as old as agriculture. Many traditional farming systems still rely on these sustainable fertilizers, and their use is vital to the productivity of certified organic farms , in which synthetic fertilizers are not permitted.

Among sources of organic matter and plant nutrients, farm manure has been of major importance. Manure is understood to mean the refuse from stables and barnyards, including both excreta and straw or other bedding material. Large amounts of manure are produced by livestock ; such manure has value in maintaining and improving soil because of the plant nutrients, humus , and organic substances contained in it.

Due to the potential for harbouring human pathogens, the USDA National Organic Standards mandate that raw manure must be applied no later than 90 or 120 days before harvest, depending on whether the harvested part of the crop is in contact with the ground. Composted manure that has been turned five times in 15 days and reached temperatures between 55 and 77.2 °C (131 and 171 °F) has no restrictions on application times. As manure must be managed carefully in order to derive the most benefit from it, some farmers may be unwilling to expend the necessary time and effort. Manure must be carefully stored to minimize loss of nutrients, particularly nitrogen. It must be applied to the right kind of crop at the proper time. Also, additional fertilizer may be needed, such as phosphoric oxide, in order to gain full value of the nitrogen and potash that are contained in manure.

Manure is fertilizer graded as approximately 0.5–0.25–0.5 (percentages of nitrogen, phosphoric oxide, and potash), with at least two-thirds of the nitrogen in slow-acting forms. Given that these nutrients are mostly in an unmineralized form that cannot be taken up by plants, soil microbes are needed to break down organic matter and transform nutrients into a bioavailable “mineralized” state. In comparison, synthetic fertilizers are already in mineralized form and can be taken up by plants directly. On properly tilled soils, the returns from synthetic fertilizer usually will be greater than from an equivalent amount of manure. However, manure provides many indirect benefits. It supplies humus, which improves the soil’s physical character by increasing its capacity to absorb and store water, by enhancement of aeration, and by favouring the activities of lower organisms. Manure incorporated into the topsoil will help prevent erosion from heavy rain and slow down evaporation of water from the surface. In effect, the value of manure as a mulching material may be greater than is its value as a source of essential plant nutrients.

In reasonably humid areas the practice of green manuring can improve yield and soil qualities. A green manure crop is grown and plowed under for its beneficial effects, although during its growth it may be grazed. These green manure crops are usually annuals , either grasses or legumes , whose roots bear nodule bacteria capable of fixing atmospheric nitrogen. Among the advantages of green manure crops are the addition of nitrogen to the soil, an increase in general fertility, a reduction of erosion , an improvement of physical condition, and a reduction of nutrient loss from leaching. Disadvantages include the chance of not obtaining satisfactory growth; the possibility that the cost of growing the manure crop may exceed the cost of applying commercial nitrogen; possible increases in disease , insect pests, and nematodes (parasitic worms); and possible exhaustion of soil moisture by the crop.

Green manure crops are usually planted in the fall and turned under in the spring before the summer crop is sown. Their value as a source of nitrogen, particularly that of the legumes, is unquestioned for certain crops such as potatoes , cotton , and corn (maize); for other crops, such as peanuts (groundnuts; themselves legumes), the practice is questionable.

Compost is used in agriculture and gardening primarily as a soil amendment rather than as fertilizer, because it has a low content of plant nutrients. It may be incorporated into the soil or mulched on the surface. Heavy rates of application are common.

Compost is basically a mass of rotted organic matter made from waste plant residues. Addition of nitrogen during decomposition is usually advisable. The result is a crumbly material that when added to soil does not compete with the crop for nitrogen. When properly prepared, it is free of obnoxious odours. Composts commonly contain about 2 percent nitrogen, 0.5 to 1 percent phosphorus, and about 2 percent potassium. The nitrogen of compost becomes available slowly and never approaches that available from inorganic sources. This slow release of nitrogen reduces leaching and extends availability over the whole growing season . Composts are essentially fertilizers with low nutrient content, which explains why large amounts are applied. The maximum benefits of composts on soil structure (better aggregation, pore spacing, and water storage) and on crop yield usually occur after several years of use.

In practical farming, the use of composted plant residues must be compared with the use of fresh residues. More beneficial soil effects usually accrue with less labour by simply turning under fresh residues; also, since one-half the organic matter is lost in composting, fresh residues applied at the same rate will cover twice the area that composted residues would cover. In areas where commercial fertilizers are expensive, labour is cheap, and implements are simple, however, composting meets the need and is a logical practice.

Sewage sludge, the solid material remaining from the treatment of sewage, is not permitted in certified organic farming, though it is used in other, nonorganic settings. After suitable processing, it is sold as fertilizer and as a soil amendment for use on lawns, in parks, and on golf courses. Use of human biosolids in agriculture is controversial, as there are concerns that even treated sewage may harbour harmful bacteria, viruses, pharmaceutical residues, and heavy metals.

Liming to reduce soil acidity is practiced extensively in humid areas where rainfall leaches calcium and magnesium from the soil, thus creating an acid condition. Calcium and magnesium are major plant nutrients supplied by liming materials. Ground limestone is widely used for this purpose; its active agent, calcium carbonate , reacts with the soil to reduce its acidity. The calcium is then available for plant use. The typical limestones, especially dolomitic, contain magnesium carbonate as well, thus also supplying magnesium to the plant.

Marl and chalk are soft impure forms of limestone and are sometimes used as liming materials, as are oyster shells. Calcium sulfate ( gypsum ) and calcium chloride, however, are unsuitable for liming, for, although their calcium is readily soluble , they leave behind a residue that is harmful. Organic standards by the European Union and the U.S. Food and Drug Administration restrict certain liming agents; burnt lime and hydrated lime are not permitted for certified organic farms in the U.S., for example.

Lime is applied by mixing it uniformly with the surface layer of the soil. It may be applied at any time of the year on land plowed for spring crops or winter grain or on permanent pasture. After application, plowing, disking, or harrowing will mix it with the soil. Such tillage is usually necessary, because calcium migrates slowly downward in most soils. Lime is usually applied by trucks specially equipped and owned by custom operators.

Fertilizers may be added to soil in solid, liquid, or gaseous forms, the choice depending on many factors. Generally, the farmer tries to obtain satisfactory yield at minimum cost in money and labour.

Manure can be applied as a liquid or a solid. When accumulated as a liquid from livestock areas, it may be stored in tanks until needed and then pumped into a distributing machine or into a sprinkler irrigation system. The method reduces labour, but the noxious odours are objectionable. The solid-manure spreader, which can also be used for compost, conveys the material to the field, shreds it, and spreads it uniformly over the land. The process can be carried out during convenient times, including winter, but rarely when the crop is growing.

Application of granulated or pelleted solid fertilizer has been aided by improved equipment design. Such devices, depending on design, can deposit fertilizer at the time of planting, side-dress a growing crop, or broadcast the material. Solid-fertilizer distributors have a wide hopper with holes in the bottom; distribution is effected by various means, such as rollers, agitators, or endless chains traversing the hopper bottom. Broadcast distributors have a tub-shaped hopper from which the material falls onto revolving disks that distribute it in a broad swath. Fertilizer attachments are available for most tractor-mounted planters and cultivators and for grain drills and some types of plows. They deposit fertilizer with the seed when planted, without damage to the seed, yet the nutrient is readily available during early growth. Placement of the fertilizer varies according to the types of crops; some crops require banding above the seed, while others are more successful when the fertilizer band is below the seed.

The use of liquid and ammonia fertilizers is growing, particularly of anhydrous ammonia, which is handled as a liquid under pressure but changes to gas when released to atmospheric pressure . Anhydrous ammonia, however, is highly corrosive, inflammable, and rather dangerous if not handled properly; thus, application equipment is specialized. Typically, the applicator is a chisel-shaped blade with a pipe mounted on its rear side to conduct the ammonia 13 to 15 cm (5 to 6 inches) below the soil surface. Pipes are fed from a pressure tank mounted above. Mixed liquid fertilizers containing nitrogen, phosphorus, and potassium may be applied directly to the soil surface or as a foliar spray by field sprayers where close-growing crops are raised. Large areas can be covered rapidly by use of aircraft, which can distribute both liquid and dry fertilizer.

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Chemical fertilizers: advantages and disadvantages

In the world of intensive agriculture, chemical fertilizers are frequently used. These fertilizers are made artificially from soil-essential macronutrients like nitrogen, phosphorous, and potassium, making them robust and powerful. They may contain ammonium sulfate, urea, potash and ammonia, among other substances, depending on their structure and the crops and soils for which they are intended. These fertilizers can be applied and spread in a variety of methods, either mechanically or by hand.  What are the advantages and disadvantages of chemical fertilizers in addition to all of these essential aspects?

Advantages of chemical fertilizers

The versatility of chemical fertilizers is undeniable: they possess properties that match the high expectations and needs of intensive agriculture.  The following are some of the advantages offered by this type of product:

► Higher production per hectare

Chemical fertilizers improve the spaces and surfaces available for agricultural work.  Because of their high contribution of macronutrients, these can encourage higher yields per hectare sowed and help plants develop to their full potential.  These fertilizers, in addition to boosting nutrient absorption from the soil, increase the depth of the roots by up to one meter: as a result, the plants are considerably stronger and can be fully supplied by the under-ground waters.

►  Soil adjustment

Different soil elements, such as very low or high acidity levels, can be adjusted through the application or usage of fertilizers that complement other chemicals and procedures, such as liming. In addition to other natural and environmentally friendly products, the moderate and conscious use of these products helps agricultural soils preserve their quality and fertility for fresh production cycles.

►  Reaction to critical cultivation scenarios

When severe crop problems arise and plants do not appear to be developing properly, chemical fertilizers might provide an immediate answer. Through foliar treatments, N-P-K fertilizers – which include nitrogen, phosphorous, and potassium – can boost the health and expectations of plants in advanced stages of cultivation. This practice consists of diluting the fertilizer in water to propagate it directly in the area of the plant.

► adaptability to specific needs These fertilizers have distinct chemical features as well as accurate indices of various nutrients, substances, and values. As a result, you can find items tailored to your demands on the market, with precise values and features to fulfill your needs in specific scenarios or stages of the cycles.

Disadvantages of chemical fertilizers

The previous paragraph highlighted chemical fertilizers' enormous potential. However, keep in mind that intensive use of chemical solutions for fertilization might have serious effects.

As a result, it is required to identify equilibrium points and supplement them with fertilizers and organic chemicals, as well as to regularly analyze soils and plants to guarantee that the various values are optimal and to detect negative reactions in real time.

The following are some of the consequences and downsides of the unintentional and excessive usage of chemical fertilizers:

► Soil degradation - Excessive use of fertilizers can significantly raise acidity levels, create macronutrient saturation, or change it to the point where the soil loses sensitivity and absorbency to various nutrients.

► Groundwater contamination - Applying excessive doses of fertilizer may leak into the area below the root zone and reach the groundwater.

► Salt burns - These burns indicate excessive use of chemical fertilizers. Fertilizers with a high saline index and chemicals like sodium nitrate are the ones that get the most attention or follow-up to avoid salt burns.

► Excessive growth - Because of the excessive and uncontrolled application of chemical fertilizers, the proportions and growth of the plants may exceed typical criteria. When this point is reached, the harvest and survival of the plants are jeopardized, rather than improving productivity.

Chemical fertilizers are valuable allies in intensive agriculture, but they can also have an impact on production cycles, soils, and surfaces if they are not managed and applied effectively.

Combining them with organic fertilizers, regularly observing, and, in general, aiming for rationality are critical parts of increasing productivity in a safe and sustainable manner.

The best way to avoid these disadvantages is by high efficiency fertilizers applied according to the 4R nutrient stewardship (Right fertilizer source, Right rate, Right time, Right placement). Haifa fertigation and controlled release fertilizers are excellent for application according to the principles of 4R , to minimize damage to the environment, while taking into account the economic needs of the farmers.

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Chemical Fertilizers, Formulation, and Their Influence on Soil Health

• First Online: 08 December 2020

Cite this chapter

• Shazia Iqbal 5 ,
• Umair Riaz 6 ,
• Ghulam Murtaza 5 ,
• Moazzam Jamil 7 ,
• Maqshoof Ahmed 7 ,
• Azhar Hussain 7 &
• Zafar Abbas 8  

1549 Accesses

7 Citations

The world population continues to increase at an alarming rate. To meet the increasing demand for food, intensive cultivation using more cropland areas and increased use of fertilizers had been practiced. According to the FAO, chemical fertilizers are the solitarily most important contributor to the rise in the world’s agricultural production. Fertilizers comprising of nitrogen, phosphorus, and potassium are regarded as the drivers of modern agriculture. Their worldwide use had been increased since the inception of the so-called green revolution. Chemical fertilizers recently provided 192 million tons as input to the agricultural soils in which 109 million tons was nitrogen, 45 million tons was phosphorus (expressed as P 2 O 5 ), and 38 million tons was potassium (expressed as K 2 O). Fertilizer use increased by about 30% per hectare from 2002 to 2017, which was about 95 tons per hectare. By nutrient, the increase was about 24% for nitrogen, 25% for P 2 O 5 , and 53% for K 2 O. Low fertilizer use efficiencies in most of the soils are another factor adding in more use of chemical fertilizers. Intensive land use with continuous and injudicious use of higher doses of inorganic fertilizers significantly influences soil health and crop growth. Soil health is collectively defined by physical (texture, bulk density, infiltration rate, hydraulic conductivity, porosity, etc.), chemical (essential nutrients, cation exchange capacity, electrical conductivity, etc.), and biological (microbial community including bacteria, fungi, algae, archaea, protozoa, earthworm, etc.) properties. Chemical fertilizers affect soil properties both positively and negatively. Keeping in view these points, an understanding of chemical fertilizer formulations and their effect on soil health is necessary to overcome low fertilizer use efficiencies and more fertilizer use.

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Department of Environment & Water Management, Sri Pratap College, Cluster University, Srinagar, Jammu and Kashmir, India

Mohammad Aneesul Mehmood

Division of Environmental Sciences, Sher-e-Kashmir University of Agricultural Sciences and Technology of Kashmir-Srinagar, Srinagar, Jammu and Kashmir, India

Rouf Ahmad Bhat

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Iqbal, S. et al. (2021). Chemical Fertilizers, Formulation, and Their Influence on Soil Health. In: Hakeem, K.R., Dar, G.H., Mehmood, M.A., Bhat, R.A. (eds) Microbiota and Biofertilizers. Springer, Cham. https://doi.org/10.1007/978-3-030-48771-3_1

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Here's the scoop on chemical and organic fertilizers

CORVALLIS, Ore. – Fertilizers are especially important when growing vegetables and small fruits. There are a lot of choices, which can make it hard to decipher what’s best for your approach to gardening.

Organic fertilizers such as manures, compost or bone meal are derived directly from plant or animal sources, said Chip Bubl, Oregon State University Extension Service horticulturist. Other organic fertilizers are rock minerals that are finely ground like limestone and rock phosphate.

Organic fertilizers usually contain plant or animal nutrients in lower concentrations, depending on the raw material, but may have a much wider range of nutrients.

Fertilizers such as ammonium sulfate or ammonium phosphate are often called conventional or synthetic fertilizers because they go through a manufacturing process. That said, finished conventional fertilizers start with naturally occurring mineral deposits and/or nitrogen in the atmosphere.

Conventional fertilizers usually contain only a few nutrients – generally nitrogen, phosphorus, potassium, sulfur and sometimes micronutrients, either singly or in combination. These nutrients are in a form generally more available to plants. Some nutrients, such as nitrate, are quickly available for uptake by plant roots, Bubl said. If you need only a certain element such as nitrogen and want it to be quickly available to your plants, an inorganic fertilizer such as ammonium sulfate might be in order. However, since they are lost from the soil quickly, you may have to fertilize plants several times during the growing season unless you use a specially formulated, slow-release type.

Many of these nutrients have to be converted into inorganic forms by soil bacteria and fungi before plants can use them, so they typically are more slowly released, especially during cold weather when soil microbes are not as active. This is especially critical with nitrogen in the early part of the growing season.

Advantages of organic fertilizers

But organic fertilizers have advantages. They don’t make a crust on the soil as inorganic fertilizers sometimes do. They improve water movement into the soil and, in time, add structure to the soil. Organics feed beneficial microbes, making the soil easier to work. But they may cost significantly more than conventional fertilizers, because they are less concentrated, supplying fewer nutrients pound for pound.

Since many conventional/synthetic fertilizers are concentrated and very soluble, it’s easier to apply too much and damage your plants, especially when watering with fertilizer added to the water.

Fresh, non-composted manure can damage your plants as well, because some manure contains harmful amounts of salts. Manures can also be a source of weed seeds and, if fairly fresh, human pathogens. Organic standards require fresh manure be worked into the ground 120 days before harvesting a crop that directly touches the soil (beets, onions, lettuce, radishes, etc.). There is only a 90-day pre-harvest interval for crops where the edible portion won’t touch the soil like pole beans and sweet corn.

One of the most puzzling things for a gardener to determine is how much fertilizer, especially nitrogen, to apply, Bubl said. For a 1,000 square feet vegetable garden, the usual recommendation is 3 pounds of “actual” nitrogen per 1,000 square feet every year.

So, what is this “actual” nitrogen? The first number on a fertilizer bag is what percent of the bag is “actual” nitrogen. For a fertilizer with an N-P-K ratio of 12-11-2, this means 12 percent is nitrogen, 11 percent is phosphorus and 2 percent is potassium. In simple terms, this means each 100 pounds of the fertilizer would contain 12 pounds of nitrogen, 11 pounds phosphorus and two pounds potassium. To know how much fertilizer you need, divide 3/.12, which equals 25 pounds that would need to be applied to get 3 pounds of nitrogen per 1,000 square feet.

Blood meal (12.5-1.5-0.6) releases nutrients over a period of two to six weeks. Chicken feather meal, which releases nitrogen a little faster, is also about 12% nitrogen.

A common conventional fertilizer like 16-16-16 would be used at the rate of 3/.16 = 19 pounds per 1,000 square feet.

To boost the nitrogen content of your soil, apply non-organic nitrogen-rich urea (42-46% nitrogen or N) or organic materials like feather meal (12% N), blood meal (12.5% N) or dried blood (12% N).

If you add a lot of organic matter that is not well-composted (strawy manure, freshly tilled in cover crops, etc.) to your garden, you will need to “feed” the composting organisms with nitrogen until the composting process is complete. Otherwise, those tiny composting microorganisms instead of your vegetables will get the nitrogen in the soil. This can lead to poor-colored and stunted vegetable plants.

Organic amendments highest in phosphorus include rock phosphate (20%-33% phosphorus or P), bone meal (15-27 percent P) and colloidal phosphate (17%-25% P). Organic materials high in potassium are kelp (4%0-13% potassium or K), wood ash (3%-7% K), granite meal (3%-6% K) and greensand (5% K).

To make soil less acidic, gardeners use materials rich in calcium, including clamshells, oyster shells, wood ashes, agricultural lime, dolomite lime and gypsum.

Many garden centers and feed stores carry both inorganic and organic fertilizers and amendments for gardens. For more information, see the OSU Extension publication " Fertilizing Your Garden: Vegetables, Fruits and Ornamentals. "

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Article Versions Notes

Song, H.; Chang, Z.; Hu, X.; Li, Y.; Duan, C.; Yang, L.; Wang, H.; Li, T. Combined Application of Chemical and Organic Fertilizers Promoted Soil Carbon Sequestration and Bacterial Community Diversity in Dryland Wheat Fields. Land 2024 , 13 , 1296. https://doi.org/10.3390/land13081296

Song H, Chang Z, Hu X, Li Y, Duan C, Yang L, Wang H, Li T. Combined Application of Chemical and Organic Fertilizers Promoted Soil Carbon Sequestration and Bacterial Community Diversity in Dryland Wheat Fields. Land . 2024; 13(8):1296. https://doi.org/10.3390/land13081296

Song, Hongmei, Zixuan Chang, Xuan Hu, Yan Li, Chengjiao Duan, Lifan Yang, Haoying Wang, and Tingliang Li. 2024. "Combined Application of Chemical and Organic Fertilizers Promoted Soil Carbon Sequestration and Bacterial Community Diversity in Dryland Wheat Fields" Land 13, no. 8: 1296. https://doi.org/10.3390/land13081296

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Agriculture in India

Essay on biofertilizers | organic farming.

Here is an essay on ‘Biofertilizers’ for class 9, 10, 11 and 12. Find paragraphs, long and short essays on ‘Biofertilizers’ especially written for school and college students.

Essay on Biofertilizers  

Essay Contents:

• Essay on the Development of Biofertilizer Industry

Essay # 1. Meaning of Biofertilizer:

Biofertilizer is a large population of a specific or a group of beneficial microorganisms for enhancing the productivity of soil either by fixing atmospheric nitrogen or by solubilising soil phosphorus or by stimulating plant growth through synthesis of growth promoting substances.

Bio-fertilizers based on renewable energy sources are cost effective supplement to chemical fertilizers, eco-friendly and can help to economize on the high investment needed for chemical fertilizer use as far as nitrogen and phosphorus are concerned.

Biofertilizer is a 100% natural and organic fertilizer that helps to provide and keep in the soil all the nutrients and microorganisms required for the benefit of the plants.

Biofertilizers do not come under the purview of the definition of the term fertilizers, as they do not contain substantial quantity of plant nutrients as other fertilizers like urea, diammonium phosphate, muriate of potash etc. contain. The term biofertilizer is a misnomer but is in wider use. They should be termed as inoculants, after the name of the microorganisms they contain, viz., Rhizobium inoculant, Azospirillum inoculant or blue green algae inoculant.

Bioinoculants or biofertilizers are different from chemical fertilizers. Biofertilizers on application remain in soils, multiply and keep benefiting the growing crops. They do not get depleted as in the case of fertilizers and, therefore, if the optimum soil conditions prevail, population of added microorganisms builds up and frequent application of biofertilizers can be avoided.

There are millions of microscopic organisms near the plants that not only provide nutrients to the plants but also help to keep the water and retain the nutrients in the soil, for its easy availability to the plants.

Biofertilizer can be defined as a substance which contains living microorganisms which, when applied to seed, plant surfaces, or soil, colonize the rhizosphere or the interior of the plant and promotes growth by increasing the supply or availability of primary nutrients to the host plant. This definition is based on the logic that the term biofertilizer is a contraction of the term biological fertilizer.

As biology is the study of living organisms, biofertilizer should contain living organisms which increase the nutrient status of host plant through their on-going existence in association with the plant. This definition separates biofertilizers from organic fertilizer (fertilizer containing organic compounds which directly, or by their decay, increase soil fertility).

Likewise, the term biofertilizer should not be used interchangeably with the terms, green manure, intercrop, or organic supplemented chemical fertilizer. Oken and Landera Gonzalez (1994) argue that rhizosphere organisms which improve utilization of soil nutrient but do not replace soil nutrients (like chemical fertilizers) should not be called biofertilizers.

Some plant growth promoting rhizobacteria (PGPR), that represent a wide variety of soil bacteria when grown in association with a host plant, result in stimulation of growth of their host. However, not all PGPR can be considered as biofertilizers. Bacteria that promote plant growth by control of deleterious organisms are biopesticides, but not biofertilizers.

Interestingly some PGPR appear to promote growth by acting as both biofertilizer and biopesticide. For example, strains of Burkholderia cepacia have been shown to have biocontrol characteristics to Fusarium spp., but also can stimulate growth of maize under iron- poor conditions via siderophore production.

The biofertilizer has a relative high nutrient concentration, and even so, it can be used directly over soil before planting. Once diluted, it constitutes a high quality foliar fertilizer, and in this form, it is known as diluted biofertilizer. Diluted biofertilizer also has all the needed conditions to be used as a complete nutrient solution in organic hydroponics. The advantages of using the biofertilizer are enormous. Not only it is very economical, but also for the high agricultural yields which it produces.

Most fertilizers add nitrogen to the soil. This can be done via chemical fertilizers, or through a process called biological nitrogen fixation (BNF). On a worldwide basis it is estimated that about 175 million tons of nitrogen per year is added to soil through biological nitrogen fixation (BNF).

The term bio means living; so bio-fertilizers refer to living, microbial inoculants that are added to the soil. These bio­fertilizers are products consisting of selected and beneficial microorganisms, which are known to improve plant growth through supply of plant nutrients.

The soil microorganisms commonly used in biofertilizers are- Phosphate Solubilizing microbes, Mycorrhizae, Azospirillum, Azotobacter, Rhizobium, blue green algae, and Azolla.

Biofertilizers are ready to use live formulates of such beneficial microorganisms which on application to seed, root or soil, mobilize the availability of nutrients by their biological activity in particular, and help build up the micro-flora and in turn the soil health in general.

Essay # 2. Need for Biofertilizers:

Biofertilizers have definite advantage over chemical fertilizers. Chemical fertilizers supply nitrogen whereas biofertilizers provide, in addition to nitrogen certain growth promoting substances like hormones, vitamins, amino acids, etc. Crops have to be provided with chemical fertilizers repeatedly to replenish the loss of nitrogen utilized for crop growth.

On the other hand biofertilizers supply the nitrogen continuously throughout the entire period of crop growth in the field under favourable conditions. Continuous use of chemical fertilizers adversely affects the soil structure whereas biofertilizers when applied to soil improve the soil structure. The deleterious effects of chemical fertilizers are that they are toxic at higher doses. Biofertilizers, however, have no toxic effects.

It may be borne in mind that biofertilizers are no substitute for chemical fertilizers. At present, the use of chemical fertilizers is far below the recommended level. Therefore, the aim and object of spread of biofertilizer technology as an Industry, is to build up efficiency in use of chemical fertilizers, supplemented by low cost inoculants to the extent possible. Biofertilizers are used for integrated farming-systems mainly in the agricultural sector or areas with little or no access to chemical fertilizer.

Essay # 3. Types of Biofertilizers:

Organisms used for biological fertility management, are either free living or having symbiotic association with plants. They directly or indirectly contribute nutrition to crop plants.

Based on the type of microorganisms, the biofertilizers can also be classified as follows:

1. Bacterial biofertilizers e.g., Rhizobium, Azospirillum, Azotobacter, Acetobacter Phosphobacteria.

2. Fungal bio fertilizers: e.g., Mycorrhiza.

3. Algal bio fertilizers: e.g., blue green algae (BGA) and Azolla- Anabaena association.

4. Actinomycetes biofertilizers: e.g., Frankia.

Biofertilizers are mostly cultured and multiplied in the laboratory. However, blue green algae and Azolla can be mass-multiplied in the field.

Essay # 4. PGPR (Plant Growth Promoting Rhizobacteria) as Biofertilizers :

Numerous species of soil bacteria which flourish in the rhizosphere of plants, but which may be grown in or around plant tissues, stimulate growth by a plethora of mechanisms. These bacteria are collectively known as PGPR. Research on PGPR has been increasing at an ever increasing rate since the term was first used by Kloepper and Co­workers. Not all PGPR are biofertilizers. Many PGPR stimulate the growth of plants by helping to control pathogenic organisms.

For PGPR to have a beneficial effect on plant growth via an enhancement of the nutrient status of their host, their needs to be an intimate relationship between the two, that can be categorized into two levels- (1) Rhizospheric, (2) Endophytic.

In rhizospheric relationships, PGPR many colonize the rhizosphere, the surface of the root, or even superficial intercellular spaces (although this later situation may often involve dead cell layers). In many rhizospheric relationships, the PGPR will actually attach to the surface of plants. How, ever, the means of attachment is much less known.

Azospirillum spp. is one group of PGPR where mechanism involved in attachment, have been well characterized. Colonization of root surfaces by PGPR is not uniform. For example, Kluyvera ascorbata colonizes the upper two-thirds of the surface of canola roots, but no bacteria were detected around tips.

In endophytic relationship, PGPR actually reside within apoplastic spaces inside the host plant. The best characterized symbioses involving colonization of hosts by endophytes are the legume-rhizobia symbiosis. Likewise the infection process and development of N 2 -fixing specialized structures in the non-legume symbiosis of Parasporia rhizobia, Alnus- Frankia, Azolla-Anabaena, Gunnera-Nostoc and Cycads-Cyanobacteria have also been well characterized.

Some PGPR and endophytic species are known to have cellulose and pectinase activities. Some endophytic PGPR may utilize other organisms as, vectors to gain access to apoplastic spaces in their host. For example both the pink sugarcane mealybug Saccharicoccus sacchari and arbuscular mycorrhizae have been implicated in the infection of host plants by the endohytic diazotroph, Gluconoacetobacter diazotrophicus (formerly Acetobacter diazotrophicus).

The means by which PGPR enhance the nutrient status of host plants can be categorized into five areas:

1. Biological N 2 fixation

2. Increasing the availability of nutrients in the rhizosphere

3. Inducing increases in the root surface area.

4. Enhancing other beneficial symbiosis of the host.

5. Combination of modes of action.

A list of PGPR, for which evidence exists that their promotion of plant growth is based on their ability to fix N 2 in situ are provided in Table 11.2.

Many PGPR increases the availability of nutrients for the plant in rhizosphere. It involves solubilization of unavailable forms of nutrients and/or siderophore production which helps facilitate the transport of certain nutrients (notably ferric iron). Examples of recently studied associations include Azotobacter chroococcum and wheat, Bacillus circulans and Cladosporium herbarum and wheat, Enterobacter agglomerans and tomato, Pseudomonas chlororaphis and P. putida and soybean, Rhizobium leguminosarum bv. Phaseoli and maize.

Despite wide ranges in the solubility’s and availabilities of soil nutrient species, PGPR that affect root morphology, and more specifically, increases root surface area, can have huge influence on nutrient uptake potentials. Bacterial mediated increases in root weight are commonly reported responses to PGPR inoculations. Most importantly increases in root length and root surface area are sometimes reported.

Inoculation of maize with Azospirillum brasitense resulted in a proliferation of root hours which could have dramatic effect on increasing root surface area. Due to which there is an increase in the volume of soil explored. For e.g., treatment of clipped soybean roots with A. brasilense Sp7 caused a 63% increase in root dry weight, but more than or 6-fold increase in specific root length (root length per unit root dry weight), and more than a 10-fold increase in total root length.

Many actual and putative biofertilizing PGPR produce phyto hormones that are believed to be related to their ability to stimulate plant growth. Indole 3-acetic acid is a phyto- hormone which known to be involved in root initiation, cell division, and cell enlargement. This hormone is very commonly produced by PGPR. Table 11.3 lists recent papers where the production of this hormone has been implicated in the growth promotion by biofertilizing PGPR.

Evidence of GA (Gibberellic acid) production, that are phytohormones associated with modifying plant morphology by the extension of plant tissues, by PGPR, is rare. However Guiterrez-Manero et al, (2001) provide evidence that four different forms of GA are produced by Bacillus pumilus and Bacillus licheniformis.

Inoculation of alder (Alnus glutinosa) with these PGPR, could effectively reverse a chemically induced inhibition of stem growth. The recent discoveries of the involvement of cytokinins, ACC deaminase and possibly GA producing PGPR, opens the possibility that even more plant growth regulating substances may be involved in the promotion of plant growth by some PGPR.

There are evidences in some systems that PGPR may be directly affecting root respiration which in turn leads to increase in the root growth.

Some biofertilizing PGPR sometimes enhance plant growth indirectly by stimulating the relationship between the host plant and beneficial rhizospheric fungi such as arbuscular mycorrhizae (AM) although AM by themselves are well known to enhance the uptake of various soil nutrients (especially phosphorus).

Ratti et al (2001) found that the combination of arbuscular mycorrhizal fungus Glomus aggregatum and the PGPR Bacillus polymyxa and Azospirillum brasilense maximized biomass and P content of the aromatic grass palmarosa (Cymbopogon martini) when grown with an insoluble source of inorganic phosphate. Toro et al (1997) found that both Enterobacter spp. and Bacillus subtilis promoted the establishment of the AM, Glomus itraradices, and increased plant biomass and tissue N and P contents.

Thus there is a huge potential for the use of PGPR as biofertilizing agents for a wide variety of crop plants in a wide range of climatic and edaphic conditions. There has been little extensive commercialization of biofertilizing PGPR. An exception to this is Azospirillum inoculant which is available for a variety of crops in Europe and Africa.

No doubt, the lack of consistent responses in different host cultivars and different field sites, are reasons limiting to the more widespread commercialization of biofertilizing PGPR. A better understanding of rhizosphere ecology, the influence of rhizosphere organisms on each other, must increase before we can be assured that biofertilizing PGPR in inoculants will successfully colonize host rhizosphere and consistently promote the growth of the host plant.

Essay # 5. Phosphate Solubilizing Biofertilizers :

Phosphorus is an important nutrient for plants. There are several microorganisms which can solubilize the cheaper sources of phosphorus, such as rock phosphate. Bacteria like Pseudomonas striata, and Bacillus megaterium are also important phosphorus solubilizing soil microorganisms. Many fungi like Aspergillus and Penicillium are potential solubilizers of bound phosphates. They solubilise the bound phosphorus and make it available to the plant, resulting in improved growth and yield of crops.

Soil phosphates are rendered available to plants by soil microorganisms through secretion of organic acids. Therefore, phosphate dissolving soil microorganisms play some part in correcting phosphorus deficiency in plantation soils. They may also release soluble inorganic phosphate into soil through decomposition of phosphate rich organic compounds. These microbial inoculants can substitute almost 20 to 25% of the phosphorus requirement of plants.

Phosphate solubilizing microbes can also be inoculated to coffee husk along with rock phosphate while preparing compost, to enrich the compost with available phosphorus.

Phosphorus is second most important plant nutrient responsible for various essential metabolic processes in plant growth and development. In nature phosphorus is found in soil, manure, plants and microorganisms in organic and inorganic form in various combinations, but the availability of phosphorus to the plants is critical. The plant absorbs phosphorus from the soil solutions mainly in the form of H 2 PO 4 – (orthophosphate) ionic form and smaller amount in the form of secondary orthophosphate ions (HPO 4 -2 ).

The concentration of soluble phosphorus in soil solution is 0.1 ppm out of which only an infinitesimal part is available to plants at any time. This is because of the fact that soluble orthophosphate rapidly reacts in soil to form insoluble phosphorus through precipitation and adsorption, this process called “Phosphate fixation”.

A large number of microorganisms belonging to diverse families and genera and of heterotrophic to autotrophic in nature are known to have the capacity of phosphate solubilzation. Out of which Pseudomonas striata, Bacillus polymyxa, Aspergillus awamorii, A. niger and Penicillium digitatum have been found to be most promising and are used as mother culture in the production of phosphate solubilizing biofertilizers. These formulations are popularly known as PSM, Phosphotika, Microphos etc.

When carrier based phosphetic biofertilizers are applied to the crops as seed, seedling root, or soil treatment, the microorganism present in the inoculant multiply along the developing roots and develop a thick population in the soil adjacent to roots.

Here these microorganisms develop a sort of temporary associative symbiotic type of relationship, in which they derive their food from roots in the form of root exudates and provide mineral nutrients which normally could not be solubilzed by the roots including phosphorus.

Essay # 6. Mycorrhizae:

Mycorrhizae are a group of fungi that include a number of types based on the different structures formed inside or outside the root. These are specific fungi that match with a number of favourable parameters of the host plant on which it grows. This includes soil type, the presence of particular chemicals in the soil types, and other conditions.

These fungi grow on the roots of these plants. In fact, seedlings that have mycorrhizal fungi growing on their roots survive better after transplantation and grow faster. The fungal symbiont gets shelter and food from the plant which, in turn, acquires an array of benefits such as better uptake of phosphorus, salinity and drought tolerance, maintenance of water balance, and overall increase in plant growth and development.

While selecting fungi, the right fungi have to be matched with the plant. There are specific fungi for vegetables, fodder crops, flowers, trees, etc.

Mycorrhizal fungi can increase the yield of a plot of land by 30%- 40%. It can absorb phosphorus from the soil and pass it on to the plant.

Mycorrhizal plants show higher tolerance to high soil temperatures, various soil- and root-borne pathogens, and heavy metal toxicity.

Essay # 7. Role of Biofertilizers :

Biofertilizers are inputs containing microorganisms, which are capable of mobilizing nutritive elements from non-usable form to usable form through biological processes. They are less expensive, eco-friendly and sustainable. The beneficial microbes in the soil, which are of greater significance to horticultural crops are, biological nitrogen fixers, phosphate solubilizers and mycorrhizal fungi which are the phosphate scavengers.

Nitrogen is one of the chief and important constituents of protein and nucleic acid molecules that play the basic role in cell metabolism, growth, reproduction and transmission of heritable characters. Therefore, without a constant supply of this unavoidable element, life cannot go on.

Biological nitrogen fixation (BNF) is the reduction of atmospheric nitrogen to ammonia by microorganisms in the soil. It involves highly specialized and intricately evolved interactions between soil microorganisms and higher plants for harnessing the atmospheric nitrogen. It is a fascinating biological phenomenon studied extensively to provide low-cost nitrogen and improve crop productivity.

The nitrogen fixing organisms associated with horticultural crops are the Rhizobium species, living in symbiotic relationship with the leguminous plants and free living fixers belonging to the Azotobacter family and the Azospirilla living in association with the root system of crop plants.

Some soil microorganisms play an important role in improving soil fertility and crop productivity due to their capability to fix atmospheric nitrogen, solubilize insoluble phosphate and decompose farm wastes resulting in the release of plant nutrient. The extent of benefit from these microorganisms depends upon their number and efficiency, which however, is governed by a large number of soil and environmental factors.

When the number and activity of specific microorganism called microbial inoculant or biofertilizer is used to hasten biological activity to improve availability of plant nutrient. One of the essential plant nutrients on which successful agriculture depends to a great extent is nitrogen. High crop requirements, susceptibility to gaseous and leaching losses have made nitrogen the most in demand fertilizer material followed by phosphorus.

Although air has about 80% of nitrogen, plants cannot make use of atmospheric N. The discovery of bacteria which had the ability to reduce non-usable (atmospheric nitrogen) into usable form (ammoniacal) had been a major breakthrough in the field of agricultural research.

Of late, increasing attention is being paid to harmness the potential benefits from these renewable sources of plant nutrients because of the following reasons:

1. Depleting soil fertility due to widening gap between nutrient removal and supplies.

2. Depleting feedstock/fossil fuels and increasing cost of fertilizers.

3. Growing concern about environmental hazards.

4. Increasing threat to sustainable agriculture.

A number of products are now available that are generally referred to as soil and plant additives, of non-traditional nature.

These products include:

1. Microbial fertilizers and soil inoculants contain unique and beneficial strains of soil microorganisms.

2. Microbial activators that supposedly contain special chemical formulations for increasing the numbers and activity of beneficial microorganisms in soil.

3. Soil conditions that claim to create favourable soil physical and chemical conditions which result in increased growth and yield of crops.

4. Vermicompost helps in improving soil health and fertility.

Nitrogen fixing organisms can be provided to the farmers in the name of microbial inoculants otherwise termed as biofertilizers.

The biofertilizers containing biological nitrogen fixing organisms are of utmost important in agriculture in view of the following advantage:

1. They help in the establishment and growth of crop plants and trees.

2. They enhance biomass production and grain yields by 10-20%.

3. They are useful in sustainable agriculture.

4. They are suitable in organic farming.

5. They play an important role in agroforestry/silvipastoral systems.

After the advent of the acetylene test for assessing nitrogen fixing potential, rapid progress has been made in identifying nitrogen fixing organisms. Out of a large number of microorganisms possessing the property of nitrogen fixation, only a few such as Rhizobium, Azotobacter, Azospirillum, BGA, Azolla, etc. have been commercially exploited. The reaction in biological nitrogen fixation is essential the same as in production of chemical fertilizers (Haber-Bosch process) i.e., the catalytic reduction of dinitrogen (N 2 ) to ammonia (NH 3 ).

In India, Rhizobium biofertilizers specific for different legumes and blue green algae are the most popular among farmers, Azospirillum and Azotobacter are at an intermediate stage of acceptance while phosphate solubilizing microorganisms (PSM), VAM, Azolla, cellulose decomposing organisms etc. are at preliminary stage.

Essay # 8. Economic and Environmental Benefits of Biofertlizer:

The production of fertilizers depends on nonrenewable energy sources and is energy intensive. The energy requirements for production of one kg fertilizer nitrogen are 11.2, phosphorus 1.1 and potash 1.0 KWH respectively. The requirement of petroleum based energy source in the production of biofertilizer is almost negligible. Organisms like Rhizobium, Azospirillum etc. assimilate 20-40 mg nitrogen g-1 of carbon.

The biofertilizer production cost is very low so is the selling price. It has been estimated that one kg of fertilizer nitrogen costs more than rupees six while biofertilizer nitrogen costs only twenty paise through Rhizobium and fifty paise through Blue green algae (BGA).

On nutrient basis, one tonne of Rhizobium biofertilizer is equivalent to 100 tonnes of fertilizer nitrogen (considering 50 kg N fixed ha-1 by application of 500 g Rhizobium biofertilizer) and one tonne of soil base BGA is equivalent to two tonnes of fertilizer nitrogen (considering 20 kg of N fixed ha -1 ) by application of 10 kg BGA.

Biofertilizers are cost effective as well as environment friendly. They have a favourable influence on soil health. Biofertilizers are compatible with chemical fertilizers and agrochemicals like pesticides and herbicides without demanding extra or special care in their handling. They are safe to crops and users both.

The use of biofertilizer in various cropping systems may save 20-40 kg ha -1 of fertilizer nitrogen and 10-20 kg ha -1 phosphoric acid per cropping season. The success in the transfer of nif operon from nitrogen fixing bacterium Klebsiella pneumonia into non-nitrogen fixing bacterium Escherichia coli has shown promising possibilities like achieving nodule formation in non-modulating plants, industrial preparation of nitrogenase enzymes and their use in nitrogen fixation by-passing the use of non-renewable energy sources.

Biofertilizers are available for almost all crops and for three nutrients – nitrogen, phosphorus and zinc and, therefore, the biofertilizer consumption is expected to increase many folds in coming years.

Essay # 9. Development of Biofertilizer Industry :

The prominent role of legumes in soil fertility was first noted by J. B. Boussingault (1834), a French farmer, substantiated by Hellreigel (1886) in Germany by identifying root nodule as advantageous growth and Biejerinck (1888), a Dutch Scientist, who discovered that nodule is formed by bacteria, now called Rhizobia. Beginning of legume inoculation was made by Nobbe and Hiltner (1895) in Germany by using extracts of crushed root nodules under trade name Nitrogin.

The early method of an application of inoculum involved top dressing of new fields with large quantity of soils transported from places where the legume grew well. This cumbersome soil transfer method was probably the reason for the birth of the present day inoculant production industry. Instead of the bulk transfer of soil which involves spreading of soil borne pathogens, weed seeds, ineffective rhizobia etc. The present method, supplies Rhizobium biofertilizers in small packets commercially.

The first inoculants were pure cultures of Rhizobium growing on solid medium and these were marketed in 8-10 ounces glass bottles. Since then, the methods of producing inoculants commercially have undergone a significant evolution to meet the demands of present day utilization of biological nitrogen fixation technology in agriculture. Rhizobium biofertilizers are commercially produced in both developed where fertilizer N is affordable and developing countries.

The earliest documented evidence of the production of biofertilizers from isolated Rhizobium strains exist in India. India is the largest producer and consumer of biofertilizers in the world, Madhya Pradesh, Tamil Nadu and Gujarat being the major producing states.

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NoumanAhmad 2 / 8   Sep 16, 2014   #5 The first thing I would mention is that the beginning was very abrupt. You did not developed your point and just started straight off. The content quality was very low, maybe because you had not much information. One more thing is that you should focus on your organization of essay. You can also give some references to support your point. That would make your essay more clear and understandable.

OP nasir1112 1 / 1   Sep 16, 2014   #6 thank you very much for your time and consideration. I have decide to participate in Ielts exam after one month in general module, can you tell me what is my level now?

NoumanAhmad 2 / 8   Sep 16, 2014   #7 The thing is that I have never taken any IELTS. Sorry. But on the basis of what I have heard from my friends about IELTS, I guess that your level will be medium.

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Journal of Materials Chemistry A

Manipulating protons and oxygen vacancies in nickelate oxides via thermochemical dehydration †.

* Corresponding authors

a Zhejiang University, Hangzhou 310027, China

b School of Engineering, Westlake University, Hangzhou 310030, China E-mail: [email protected]

c Key Laboratory for Quantum Materials of Zhejiang Province, School of Science, Westlake University, Hangzhou 310030, China

d Shanghai Synchrotron Radiation Facility, Shanghai Advanced Research Institute, Chinese Academy of Sciences, Shanghai 201204, China

e Research Center for Industries of the Future, Westlake University, Hangzhou 310030, Zhejiang, China

Tuning ionic defects, i.e. , protons and oxygen vacancies, in perovskite nickelates can lead to the discovery of new physical properties that cannot be achieved through alternative strategies. However, the existing chemical method used for tuning ionic defects, such as topotactical chemical treatment using metal hydrides, often degrades the crystal quality due to the harsh chemical environment used. To tackle this challenge, we developed a thermochemical dehydration method to induce phase transition from protonated H x NdNiO 3 (H-NNO) to oxygen-deficient NdNiO 3− δ (NNO- δ ) at a low temperature of 300 °C. We systematically investigated the change in physical properties during the dehydration process, including the crystal structure, electrical conductivity and Ni valence state. Importantly, through fine-tuning of the dehydration reaction, we further designed a gradient of oxygen vacancy concentration into a single thin film to establish a quantitative correlation between the oxygen vacancy concentration and the lattice constant, Ni valence state, oxygen content, transport property, and optical properties of NNO- δ . Our work offers a new pathway for converting protonic defects to oxygen vacancies and understanding the effect of ionic defects on physical properties in nickelate perovskite oxides.

• This article is part of the themed collection: Journal of Materials Chemistry A HOT Papers

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Manipulating protons and oxygen vacancies in nickelate oxides via thermochemical dehydration

H. Chen, Z. Xu, L. Wei, M. Dong, Y. Hu, Y. Lu, N. Zhang, J. Wu and Q. Lu, J. Mater. Chem. A , 2024, Advance Article , DOI: 10.1039/D4TA03609C

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