Controlled Release Fertilizers for Climate-Smart Agriculture PDF

Environmental Science and Pollution Research (2022) 29:53967–53995 https://doi.org/10.1007/s11356-022-20890-y REVIEW ARTICLE Controlled release fertilizers (CRFs) for climate‑smart agriculture practices: a comprehensive review on release mechanism, materials, methods of preparation, and effect...

Environmental Science https://doi.org/10.1007/s11356-022-20890-y REVIEW ARTICLE Controlled release fertilizers (CRFs) for climate‑smart practices: a comprehensive review on release mechanism, methods of preparation, and effect on environmental Hiral Jariwala1 · Rafael M. Santos1 · John D. Lauzon2 Received: 30 November 2021 / Accepted: 12 May 2022 © The Author(s), under exclusive licence to Springer-Verlag Abstract Fertilizers play an essential role in increasing crop for plant requirements. The excessive use of conventional ent loss through volatilization in the atmosphere, environmental issues and improve the longevity of The application of CRFs can reduce the loss of nutrients, simultaneously to achieve the goals of climate-smart are (1) CRFs can prevent direct exposure of fertilizer oxide emissions; (2) CRFs are less affected by the soil compared to conventional fertilizers; and (3) reduce GHG emissions, lead to optimum pH for plant give good insights into the ongoing development and Keywords Controlled release fertilizer · Fertilizer agriculture · Agrochemicals Introduction Background The world population growth rate is 1.05% and is expected to reach 9 billion people by the end of 2050. Food demand will increase with the increasing population and require 60% more food than existing food demand worldwide (FAO 2009; Purnomo and Saputra 2021). Fertilizers are an essential source of nutrients for plants to meet the global food demand. Macronutrients required for plants are often in limited supply in the soil, including Oxygen, Carbon, Responsible Editor: Philippe Garrigues * Yi Wai Chiang [email protected] ing nitrate into groundwater, ammonia volatilization, and nitrous oxide emissions. To overcome conventional fertilizer issues, the application of slow release or CRFs application is recommended (Azeem et al. 2014). CRFs proved a safer, economical, and efficient way to provide 13 Vol.:(0123456789) Environmental Science and Pollution Research (2022) 29:53967–53995 2020). CRFs can increase nitrogen use efficiency (NUE) and increase crop yield (Shoji et al. 2007). With the application of CRFs, reduction in GHGs emissions, increase in yield, and mitigation of environmental impacts were observed in various research studies. CRFs can be an actual driver to promote CSA and address GHGs emissions from the agri- cultural system. Controlled release fertilizers reduces/ Controlled release fertilizers (CRFs), also called coated or encapsulated fertilizers, can be defined as “a granular ferti- lizer coated with polymer/resin/coating materials which can delay the nutrient release from fertilizer core and extends its availability significantly longer than traditionally avail- able nutrient fertilizer” (Trenkel 2010). There is a difference between slow-release fertilizers (SRFs) and controlled- release fertilizers. In SRFs, the nutrient release pattern is slower than water-soluble fertilizer, but the release pattern and duration are less predictable than CRFs. In CRFs, the nutrient release pattern, rate, and duration can be predicted within certain limits and known in controlled environmental conditions (Oertli and Lunt 1962; Rajan et al. 2021). CRFs are designed to meet nutrient demand for crops based the growth cycle (Liu et al. 2017). CRFs are manufactured with fertilizer as a core material and resin/polymer coating/coat- ing materials to protect the core and release the core nutri- ent material in a controlled manner (Purnomo and Saputra 2021). The longevity of CRFs can be achieved based on the materials used for their manufacturing. The expected release of ≥ 80% of nutrients was observed between 28 and 46 days for polymer-coated urea (PCU) and polymer-coated sulfur- coated urea (PCSCU) compared to uncoated urea, which 53969 collected by using the Web of Science (WOS) search tool. Figure 2 shows the increasing number of publications from 2001–2010 to 2011–2020 by 468%. This data shows us the interest and opportunities of CRF research in current research academia. Figure 3 shows the information on the number of publications by country from 1960 to 2020, which was collected from WOS search tool by using keywords: “controlled release fertilizer” OR “coated fertilizer” OR “coated urea” OR “enhanced efficiency fertilizer.” The top five counties in terms of publications in descending order are the United States of America (USA), China, India, Aus- tralia, and Brazil. The purpose of representing this data is to identify the countries active in controlled release fertilizer- based research. The developed countries are generating more research articles regarding CRFs studies, which may build sustainable food production in the respective country. Here, Fig. 2 shows the publication from 1960 to 2020, and the total number of articles in 2021 is 1209. Method for preparing this review This review article provides extensive information on the development of controlled-release fertilizer. The scientific lit- erature review was carried out and organized in the following two steps: for the syn- i. The research articles were retrieved using Web of Sci- ence and Google Scholar. All articles were searched based on their keywords and title. The keywords used for the literature review are “controlled release ferti- lizer,” “enhanced efficiency fertilizer,” “coated ferti- lizer,” and “coated urea.” These keywords are often used in most articles, and the number of publications can be tracked easily from this data. While review- ing the collected articles, few cited references were found insightful and informative to support this review article. Those articles were also added to this review article. ii. Most relevant articles were screened by abstracts and titles. The articles were screened and categorized for the presented sections in this review paper. Few arti- cles were cited more than once to show the relevance a2+ to different topics. A total of 110 articles were selected from 1960 to 2021, and more articles were cited to support their applicability to particular research. Review paper outline This review article is divided into four broad categories of CRF release mechanism, materials, methods of preparation, and impact of CRFs on environment, soil, and plant. The CRFs release mechanism section discussed how CRF is released in the soil. The CRFs materials section of this paper discusses the 13 Science and Pollution Research (2022) 29:53967–53995 53971 cause the failure of fertilizer. The pressure gradient should be balanced across the coating, which may avoid rupture of the coating (Shaviv et al. 2003). In the decay phase, diffusion of fertilizer happens, and the internal core starts dissolving continuously with a flux of water into the granule (Shaviv 2000; Shaviv et al. 2003). The complete diffusion of ferti- lizer granules will leave the microcapsule of the granule, which is made from polymers. Not all polymers are biode- gradable in the environment, and non-biodegradable poly- mers stay in the soil. This microcapsule can cause micro- plastic pollution (Katsumi et al. 2021), which is explained in “Impact of microplastics in agricultural soil” section. The release mechanism is explained by the schematic diagram in Fig. 4. The release of nutrients follows a sigmoidal pat- tern for nutrients that match the plant requirement and is described in Fig. 5. There are four types of mode of release mechanisms: (1) Diffusion, (2) Swelling, (3) Osmosis, (4) Biochemical reaction, and (5) Erosion/degradation (Siegel and Rathbone 2012). The diffusion model is defined as the uniform distri- bution of nutrient release from fertilizer granule. Diffusion of nutrients in the soil is governed by fertilizer solubility, membrane conductance, coated fertilizer density distribu- tion (mass of applied coated fertilizer per unit volume of soil), soil moisture content, and nutrients uptake by plants (Friedman and Mualem 1994). Swelling is defined as the uptake of water by coating, which increases the volume of coating. Swelling mechanism is mainly observed in ferti- lizer formulations made using hydrogel (hydrophilic poly- mer with a three-dimensional crosslinked structure that can hold a large quantity of water). Fertilizer made from hydrogels helps to reduce the usage of irrigation water and improve fertilizer retention in soil. The swelling of granules depends on soil solution, ionic strength, particle size, and pH conditions (Li et al. 2016). Osmosis is defined as a flow of water from high concentration to low con- centration through a semipermeable membrane. In CRF, a semipermeable membrane is a coating, and soil–water concentration will be higher than fertilizer granule. With the osmosis principle, water will flow through the coating into fertilizer granule and start dissolving core nutrients. Because of water intrusion inside the granule, the coat- ing layer will not stretch much and water inside the gran- ule will begin dissolving the nutrients. Here, water flows through a semipermeable coating membrane to displace fertilizer nutrients inside via membrane pores into the soil (Siegel and Rathbone 2012). Presence of microorganisms and chemical species in soil account for the release of nutrients from fertilizer granules. Biochemical interaction can also cause loss of nutrients in soil or atmosphere (Sha- viv and Mikkelsen 1993). The environmental factors can degrade the coating layer and cause erosion of nutrients in the soil (Siegel and Rathbone 2012). 13 Environmental Science and Pollution Research (2022) 29:53967–53995 applied nitrogen in the form of urea (NH2CONH2), with a nitrogen content of 46%, is a widely used nitrogen fertilizer throughout the world (Nadarajan and Sukumaran 2021). The plant uptakes nitrogen in the form of ammonium (NH+4 ) and nitrate (NO−3 ) (von Wirén et al. 2001). The uptake of nitrogen in the form of and NO−3 depends on the type of crop plants, e.g., cereals are prone to uptake and respond to NO−3 faster than NH+4 cations. But some other crops, e.g., potatoes and grass, are prone to uptake and respond NH+4 and NO−3 equally (Finch et al. 2014). Urea transformation in soil takes place according to the following reactions (Trenkel 2010; Coyne 2015; Francis et al. 2015; Kissel et al. 2015; Norton 2015): Urea reaction in soil NH2 CONH2 + 2H2 O → (NH4 )2 CO3 (process driven by urease enzyme) (1) NH4 2 CO3 + 2H+ → 2NH+4 + CO2 ↑ +H2 O(Ammonification) ( ) (2) NH+4 + → NH3(g) ↑ + H (pH > 7.0∕ureaseenzyme) (3) in three-stage (Lag, for the figure are Nitrification 2NH+4 + O2 → 2NO−2 + 2H2 O + 4H+ (Nitrosomonasmicroorganism) (4) 2NO−2 + O2 → 2NO−3 (Nitrobactermicroorganism) (5) Denitrification 2NO−3 → N2 ↑ +N2 O ↑ (Anaerobicconditions∕Denitrif iers) (6) 53973 duration. Oertli and Lunt reported that with increasing from 10 to 20 °C, the release rate nearly doubled (Oertli and Lunt 1962). The nutrient release pattern can be linear or sigmoidal with changing the temperature. The sigmoi- dal pattern begins with the lag phase, and later it achieves a constant release and decay phase. With a linear release pattern, CRFs lack a lag phase and start with a constant release and decay phase (Trenkel 2010). When fertilizer is applied to bare soil surfaces, direct exposure of fer- tilizer to high surface temperature affects the outermost layer of fertilizer granules and diminishes the longevity of the polymer. The diminished layer will start developing cracks on the surface and diffuse urea from the granule to the outer environment. The quick release of nutrients from granules will also affect the nutrient release rate (Ransom et al. 2020). Engelsjord et al. studied the release of NPK slow and controlled release fertilizers (sulfur-coated urea (SCU), urea–formaldehyde (UF), coated calcium nitrate (CCN), sulfur coated-NPK and compound-NPK) using micro-lysimeters in a growth chamber for 6 weeks. The experiment was done at 4, 12, and 21 °C temperatures to study the release pattern of fertilizers. N fertilizers release rates were not significantly affected at 4 °C and 12 °C, but 4) → NO(+ 2) →N2 O considerably higher at 21 °C. Less than 10% of N applied was released at 4 °C and 12 °C for UF, SCU, and CCN and release increased to 15–20% at 21 °C for UF and SCU, and 50% for CCN. The release rate of P and K fertilizer was not affected by temperature (Engelsjord et al. 1996). Fertilizer application on bare soil is exposed to fluctuating surface temperature, which can reduce the longevity of fertilizer products. For optimizing release time and avoid- ing temperature effects, fertilizer needs to be incorporated into the soil (Ransom et al. 2020). Clark and Zheng use container-grown shrubs to check CRFs rate in a temperate climate. They found that CRFs can be used as a manage- ment tool for regulating plant growth, nutrient disorders, and production time in a temperate climate (Clark and Zheng 2015). as tem- Soil moisture from Soil moisture is a limiting parameter for nutrient release because of water infiltration into CRF granules (Carson and Ozores-Hampton 2013). Soil moisture regulates oxy- gen diffusion in soil with aerobic conditions for microbes at soil moisture levels of 50–70% of water holding capac- ity (WHC) (Linn and Doran 1984). Maximum urea hydrolysis occurred at 50% WHC. WHC increased with soil moisture; less soil moisture can reduce urease activity and diffusion of urea in soil. Increased soil moisture can increase mineralization and conversion of ammonium to nitrate (Agehara and Warncke 2005). Ransom et al. studied the effects of soil moisture on controlled release fertilizer 13 Environmental Science and Pollution Research (2022) 29:53967–53995 conversion of applied nitrogen fertilizer nutrients in soil by nitrification and denitrification pro- from (Bernhard 2010; Trenkel 2010; Aczel 2019) between anions, which could decrease the swelling capacity. At high pH (> 8), the presence of cations (Na+, K+, Ca2+) prevents repulsion between anions. Presence of COO− (car- boxylic group) in the coating can control the effect of pH on fertilizer swelling (Araújo et al. 2017). Biological activity water in Biological activity in agricultural soil by soil microorgan- isms and enzymes is also responsible for the degradation of fertilizer coating. CRFs coating is made from either natural or synthetic polymer. These polymers may have fast, com- plete, partial, slow, and very slow biodegradability in soil. The common CRFs coatings used in publications are polyure- thane (PU), polydopamine, chitosan, polycaprolactone (PCL), ethylcellulose (EC), starch/PVA/PLA, polyethylene/paraffin, and soy protein isolate (Majeed et al. 2015). Polymer-coated CRFs were tested under conditions when granules were in contact with soil microorganisms (Ge et al. 2002; Jaworska 2012; Jia et al. 2013). Jia et al. studied the biodegradabil- ity of polydopamine (Pdop)-coated fertilizer in sterilized and unsterilized soil. Unsterilized soil has shown high nitrogen release compared to sterilized soil in the same environmen- tal conditions. Moreover, degradation of Pdop in unsteri- lized soil was faster than in sterilized soil (Jia et al. 2013). 53975 Coating materials for CRFs The coating materials for CRFs have been classified comprehen- sively according to various literature. Multiple authors have clas- sified coating materials based on their chemical characteristics. Shaviv has classified fertilizer based on fertilizers coated with non-organic coatings, polymer coating of sulfur coated fertilizer, and fertilizers coated with organic polymers (Shaviv 2000). Sem- peho et al. classified coated fertilizer based on polymer solution, modified clay, and other components (Sempeho et al. 2014). Chen et al. classified coating material based on environmentally friendly materials derived from natural materials (Chen et al. 2018). Azeem et al. classified CRFs’ coating materials based on organic compounds, water-soluble fertilizers, and inorganic low solubility compounds (Azeem et al. 2014). Lawrencia et al. categorized coating materials in inorganic materials, organic materials, polymer, and natural polymers (Lawrencia et al. 2021). Different studies have been done using various types of coating materials, which include inorganic materials (gypsum, sulfur, minerals), organic materials (biochar, sewage sludge, agricul- tural residues), polymers (synthetic and naturally occurring), and miscellaneous materials (advanced engineering materials, e.g., graphene, nanomaterials). This review study categorized coating materials into four groups: (1) inorganic materials, (2) organic materials, (3) polymers, and (4) miscellaneous materials. al. 2015). Inorganic materials Inorganic materials are widely used in the coating of fertilizer granules because of their availability, cost, and ease of application to agriculture. Inorganic materials which are widely used in the coating of fertilizers are sulfur, gypsum, and minerals (Azeem et al. 2014; Naz and Sulaiman 2016; Lawrencia et al. 2021). The first coated fertilizer was made using molten sulfur by Tennessee Valley Authority (TVA) in 1968, which was later modified by adding a sealing coat of wax and conditioner (Sharma 1979). Sulfur is a low-cost plant-available macronutri- loam > silt > clay ent and is prepared in three stages: preheating the urea granules for preparing the surface, spraying molten sulfur, and coating of petroleum-based sealant (Jarrell et al. 1979). The sulfur coating is not enough to withstand the longevity of fertilizer, and cracks developed on the coating may cause a sudden release of nutrients. The outer coating of polymer can prevent the instant release and increase the longevity of sulfur-coated urea in soil (Ransom et al. 2020). Various sulfur-coated urea has been made by using the outer layer of a polymer such as wax (Ransom et al. 2020), gum acacia (Shivay et al. 2016a), and polyethylene (Salman 2002). Shivay et al. studied different compositions of (1–5%) sulfur- coated urea for wheat crop, and yield increased by 11.21% with 5% sulfur-coated urea compared to uncoated urea. Moreover, sulfur uptake is also increased, and the overall nitrogen uptake efficiency of the crop increased by 60% (Shivay et al. 2016a). 13 Environmental Science and Pollution Research (2022) 29:53967–53995 residues in soil. The decomposition of residues or biochar can increase soil organic matter, provide nutrients to crops, and improve soil structure (Santana-Méridas et al. 2012; Guo 2020; Fu et al. 2021). Cen et al. developed a bio-asphalt-based controlled release nitrogen fertilizer (BCRNF) by hydrothermal lique- faction of corn stover powder to bio-asphalt and made four formulations BCRNF180, BCRNF200, BCRNF230, and BCRNF240 by temperatures 180, 200, 230, and 240 °C. The nitrogen release experiment was carried out by put- ting BCRNF granules in the water. The results showed BCRNF230 has a slower rate of N release compared to other formulations because of the specific porosity structure on the particles. The porous structure is highly affected by bio-asphalt melting temperature, and BCRNF230 has the smallest pore structure. The high hydrophobicity, decreasing pore size, and increasing pore numbers resist water access to nutrients insider the fertilizer and result in a lower N release rate and longer release time (Cen et al. 2020). Xie et al. formulated a wheat straw (WS)-based CRF. The outer surface of urea was coated with WS and poly(acrylic acid-2-acryloylamino-2-methyl-1-propanesulfonic acid-N-hy- droxymethyl acrylamide). The slow-release behavior of CRF was tested, and three treatments were applied using uncoated, core (treatment of uncoated urea with poly(dimethylourea phos- phate) and carboxymethyl cellulose powder but without WS coating), and CRF (WS and polymer coating). The uncoated urea, core, and CRF released 98%, 46.3%, and 10.8% in 24 h respectively. Moreover, the water holding capacity of untreated and CRF added soil was 33.1% and 46.8% respectively. Adding CRF could reduce irrigation cycles (Xie et al. 2012). Biochar contains high carbon content produced under anaerobic conditions by thermochemical treatment of organic materials such as animal manure, agriculture waste, sludge, food waste, and animal manure. To produce biochar, thermochemical treatments such as pyrolysis, gasification, and hydrothermal carbonization are utilized (Banitalebi et al. 2019). The benefits of using biochar are improvement in the water holding capacity of soil (Lateef et al. 2019), immobili- zation of heavy metals in soil (Chen et al. 2018), and ability to sequester carbon (Dominguez et al. 2020). Dong et al. formulated a slow-release fertilizer using rice straw biochar by slow pyrolysis of rice straw. The slow-release fertilizer was made using biochar, humic acid, and bentonite with a starch solution sprayed to coat the compound fertilizer. The formulation made with 25% biochar, 4% bentonite and humic acid with cornstarch adhesive showed slow-release property of fertilizer. The release rate was 12.8% by 24 h and 20.1% by day 28. Moreover, agronomic efficiency was tested using a field study for rice crop. There were no significant differences in grain yield and aerial biomass compared to compound fertilizer (Dong et al. 2019). 53977 Authors soils, increase yield, (Jarrell et al. 1979; Salman 2002; Shivay et al. 2016a; sulfur coating requires addi- Perveen et al. 2021) for longevity provide readily avail- (Handreck 1986; Eghbali Babadi et al. 2015; Shivay et al. to plants, additional sealant 2016b; Rahman et al. 2018) release characteristics of soil, improve physi- (Dixon 1998; Noh et al. 2015; Kottegoda et al. 2017; Liu of soil, reduce fertilizer et al. 2019b; Ahmad et al. 2021) can increase the price of required to accommo- water, supply nutrients to (Xie et al. 2012; Cen et al. 2020) cycle, low production cost holding capacity, provide (Banitalebi et al. 2019; Lateef et al. 2019; Dominguez et al. to bind fertilizer nutrients 2020; Sim et al. 2021) water-resistant, (Tomaszewska and Jarosiewicz 2002;Zebarth; DeBruin on environmental param- et al. 2021) synthesized from natural (Costa et al. 2013; Olad et al. 2018; Lubkowski et al. 2019; Suprabawati et al. 2020) low-cost, biodegradable, (Wang et al. 2012; Zhang and Yang 2020; Gumelar et al. coating application, and 2020; Chen et al. 2020; Shen et al. 2020) to crosslink with monomers of coating, improve water metal ions, effective delivery (Geim and Novoselov 2007; Allen et al. 2009; Zhang et al. cost of fertilizer and pro- 2014; Kabiri et al. 2017; Li et al. 2019) assess for field applications reduce loss of nutrients, (Wang et al. 2016; Chhowalla 2017; Mikkelsen 2018) uptake of micronutri- the fertilizer. Polymer-coated controlled release fertilizer (PCRF) has many advantages over conventional fertilizer, including better nutrient use efficiency, less water pollu- tion, and decrease the loss of nutrients. The polymer film on CRFs can be semipermeable, permeable, water-soluble or impermeable, with pores that can control water penetra- tion and dissolution rate (Remya et al. 2021). There are three types of polymers widely used in fertilizer coatings: (1) syn- thetic polymers, (2) semi-synthetic polymers, and (3) natural polymers (Fu et al. 2018). of using Synthetic polymers Synthetic polymers are defined as polymers made artifi- cially in a lab and are often called man-made polymers. Generally, synthetic polymers are derived from petroleum oil-based products with specific temperatures and pressure 13 Environmental Science and Pollution Research (2022) 29:53967–53995 strength than uncoated fertilizer. They reported that tem- perature directly affects the release of nutrients and increases the release with increasing temperature (Tomaszewska and Jarosiewicz 2002). The second study by Tomaszewska and Jarosiewicz has added a polymer layer of N,N-dimeth- ylformamide and studied release properties. They found that adding a second layer does not change the property of polysulfone and decreases the release of nutrients by 25% (Tomaszewska and Jarosiewicz 2006). Polyvinyl alcohol (PVA) is a synthetic-biodegrad- able, water-soluble polymer, and self-crosslinked by [CH2CH(OH)]n. PVA is widely used in agrochemicals, dye manufacturing, disinfectants, and water treatment chemicals (Havstad 2020). Han et al. prepared starch/PVA (10–50%) blend coating film by crosslinking. With increasing the PVA content, experimental parameters such as water per- meability, water absorbency, and ammonium permeability of the coating film are improved. The increment in PVA content will not decrease the release of nutrients (Han et al. 2009). Ozen et al. developed ammonium sulfate loaded fertilizer coated with two different PVA (high and low molecular weight) types and used glutaraldehyde (GA) as a crosslinking agent. They found that adding glutaralde- hyde for crosslinking worsened the release pattern due to its intermolecular crosslinking instead of an intramolecular. Using a high molecular weight (HMV) polymer, release time increased, and water absorption decreased. They conclude that crosslinking agent is not required for the HMV PVA polymer for fertilizer coating (Özen et al. 2018). Wang et al. developed poly tannic acid (PTA)-coated fertilizer and com- pared it with a second coating as a PVA. Release behavior of three treatments was compared, and results showed that in 30 min, urea, urea + PTA, and urea + PTA + PVA nitrogen release were 100%, 32%, and 27%, respectively. The addi- tional barrier as a PVA works better, and pot experiment data showed that using PVA, fertilizer can stay longer in soil, and that increased the plant height and dry weight of cotton plant (Wang et al. 2020). Polylactic acid (PLA) is a biodegradable synthetic and aliphatic polymer. PLA is widely used in packaging materi- als due to its decomposition characteristics (Hagen 2012). PLA is a low molecular weight (LMW) polymer and is natu- rally degraded in soil and decomposes into natural products or gas which are not harmful to the environment and crops (Qi et al. 2017). PLA is widely accepted for making CRFs due to its biodegradability and longevity in soil. Kaavessina et al. prepared a PLA-coated urea using lactic acid, which was polymerized through direct polycondensation. They conducted a static release experiment to study the release behavior of urea in water and found that PLA can decrease permeability which can increase the release period. Moreo- ver, the impact on pH study showed that urea coated PLA granules increased water pH during the first few hours when 53979 slow release fertilizer (Suprabawati et al. 2020). Ethylcel- lulose (EC) is a cellulose-derived polymer widely used to coat drugs and tablets. Cost et al. made a double-coated urea fertilizer. The outer core was made using immersion of EC, and the inner core was produced by spraying poly- hydroxybutyrate (PHB). Using EC coating, the urea release rate was reported 10–15 times slower than the uncoated urea (Costa et al. 2013). Lubkowski et al. developed EC-coated NPK fertilizer using 10% wt solution of EC by immersion method. The release experiment was conducted for phospho- rus and reported that phosphorus release was less than 15% within 24 h and less than 75% in 28 days. EC-coated ferti- lizer fulfills the requirements for higher longevity and better mechanical properties. The main barrier to commercializing this product is the high price of EC (Lubkowski et al. 2019). Natural polymers Natural polymers are defined as polymers directly derived from materials widely available in nature or extracted from plants or animal-based materials (Shrivastava 2018). Natu- ral polymers used in CRFs preparation are starch, cellulose, lignin, alginate, natural rubber, and chitosan because of their low cost, biodegradability, and eco-friendly source (Chen et al. 2018). 1. Starch Starch is a homo-polysaccharide and widely used coat- ing material due to its low cost, biodegradability, and ease of availability worldwide. Commercially available starches are potato, rice, wheat, cassava, and maize (Bello Perez and Agama-Acevedo 2017). Ibrahim et al. used corn starch and borate to make coated urea using a fluidized bed spray reac- tor at 80 °C followed by drying at 60 °C. The surface mor- phology study showed that the uncoated urea surface was highly porous, rough, and rigid, whereas coated urea surface was highly dense, smooth, uniform, and hard. Moreover, the mechanical strength of uncoated and coated urea was 20 and 30 N, respectively. The additional layer of starch can provide higher strength to fertilizer. The dissolution study in water exhibits that uncoated urea dissolves in 60 s, whereas coated with starch takes 300 s for complete dissolution (Ibrahim et al. 2020). Jyothi et al. made cassava starch-based CRF and studied water retention and slow-release properties. The grafting (“chemical grafting involves the formation of bonds between the substrate surface atoms and organic layer mol- ecules.” (Paoprasert et al. 2012)) with a higher percentage (> 30%) of acrylonitrile showed lower retention capacity than 28% of grafting, and overall water retention capacity was in the range of 74.2–426.6%. The release behavior was studied in soil using uncoated and coated urea. The results of the seven-day incubation study showed that the uncoated 13 Environmental Science and Pollution Research (2022) 29:53967–53995 materials such as black liquor and acetylated with acetic acid to block hydrophilic groups present in black liquor. The coated urea was made using a fluidized bed reactor, and lignin solution was sprayed through the nozzle. By using modified lignin, acetylated and sulfite lignin was made using 5, 10, and 15% of the coating. A nitrogen release test was conducted in water, and the result showed that 5% w/w of coating released 88 and 97% nitrogen, whereas 15% w/w of coating released 43 and 72% nitrogen from acetylated kraft and sulfite lignin. They conclude that higher coating thickness results in a slower release of nitrogen from modi- fied lignin coated urea. Moreover, lignin-modified coated urea and sulfur-coated urea (SCU) release were compared in soil, and the result showed that in 7 days, SCU released all nitrogen. In contrast, acetylated kraft lignin has released 70% of nitrogen. The main reason behind prolonged release time was the temperature-independent property of lignin, whereas sulfur is highly temperature-sensitive (Behin and Sadeghi 2016). Mulder et al. developed lignin film-based CRFs using 10% and 25% w/w lignin and 6.25% w/w plasticizer as a crosslinking agent. Dispersion of lignin was applied using pan coater, and 70 °C temperature was maintained for crosslinking with lignin. Lignin is highly sensitive when it contacts water, and crosslinking with hydrophobic material/ plasticizer can reduce water sensitivity. The nitrogen release test was conducted, and the release pattern was compared with uncoated urea. Uncoated urea released 80% of nitrogen, whereas lignin coated fertilizer crosslinked with plasticizer released 58% of the nitrogen in 25 min (Mulder et al. 2011). Lignin is a good, cost-effective material for coating, and it can be used with a combination of hydrophobic materials to increase the longevity of CRF. 4. Chitosan Chitosan is a biodegradable polymer and polysaccharide- based raw material derived from seafood shells (mainly from shrimp, crab, krill and, lobsters). It is widely used in pharmacy, agriculture, textile, paper industries, and medi- cine (Morin-Crini et al. 2019). Chitosan is a good coating material for CRFs due to its biodegradability, biocompat- ibility, and antimicrobial properties (Michalik and Wandzik 2020). Wu and Liu developed a chitosan-based NPK ferti- lizer using chitosan powder as an inner coating (12.3%wt) and polyacrylic acid co-acrylamide superabsorbent polymer as an outer coating (34.9%wt). The slow release behavior of CRF was tested in soil. The author reported that 75% of nutrients were released on the 30th day, which followed the standards of slow-release fertilizer by the Committee of European Normalization (CEN). Chitosan coating has good water retention capacity, and the author reported that during 30 days of the experiment, soil without CRF lost all water, where soil with CRF had a 7.8% water retention ratio after 53981 on how alginate formulation can make higher longevity for CRF. The findings of using polymer materials for fertilizer coating are listed in Table 1. Miscellaneous materials Various fertilizer formulations have been made using advanced engineering materials, which include graphene (Kabiri et al. 2017) and other nanomaterials (copper, zinc, iron, silicon, magnesium) (Wang et al. 2016; Mikkelsen 2018). These advanced engineering materials are widely used in research, but are still under the research and devel- opment phase. Graphene is a widely used advanced engineering mate- rial because of its high surface area, unique 2-D structure, remarkable electrical, thermal, optical, and thermal prop- erties, which are used in biomedical, biological sensing, supercapacitors, plant biology, and drug delivery (Geim and Novoselov 2007; Allen et al. 2009). Graphene is used as a micronutrient carrier because of its high adsorption capacity of metal ions, high specific surface area (~ 2620 m2/g), and presence of oxygen functional groups which can interact with inorganic metal ions (Zhao et al. 2011). Due to its high adsorption capacity of metal ions and effective delivery of molecules, it is recommended to use as a carrier for micro- nutrients. Micronutrient fertilizers available in the market have a fast release, low nutrient use efficiency, and increased crop production cost. Graphene oxide (GO)-based fertilizer demonstrated a large holding capacity for micronutrients, and this application can be used for making slow-release fertilizer (Kabiri et al. 2017). Zhang et al. developed slow- release fertilizer using potassium nitrate pellets encapsu- lated in GO film. The release properties of GO-coated and uncoated pellets were tested and found that thermal treat- ment to GO-coated fertilizer, graphene film resists water penetration in pellets. The complete release of nutrients for GO-coated fertilizer took 8 h compared to uncoated pellets which reached equilibrium in 1 h (Zhang et al. 2014). Li et al. prepared chitosan (CS)-based GO film-coated ferti- lizer using potassium nitrate beads. The slow-release prop- erties were tested for coated and uncoated fertilizer beads. Uncoated beads were completely dissolved in 10 min, and CS-GO film-coated fertilizer took 7 days for complete equilibrium. The crosslinking between GO and CS could enhance the mechanical strength and porosity of CS-GO films (Li et al. 2019). Nanomaterials are used in agriculture, such as nanoscale fertilizer (contains plant nutrients), nanoscale additives (contains micronutrients with traditional fertilizer), and nanoscale coating (fertilizer coated with nanomaterials) (Mikkelsen 2018). Dimpka et al. developed a zink-coated urea fertilizer using ZnO-nanoparticles (ZnO-NP) and bulk ZnO powder. Both fertilizers were tested under drought 13 Environmental Science and Pollution Research (2022) 29:53967–53995 keep the bed in fluidized condition (Teunou and Poncelet 2002). During the fluidization process, the temperature is a limiting factor that can impact on quality of coated ferti- lizer. High and low temperatures are unsuitable for particle growth during the coating process and control urea dissolu- tion (da Rosa and dos Santos Rocha 2010). Azeem et al. studied release characteristics and coating uniformity using starch-based biopolymer in a rotary fluidized-bed reactor and reported fluidized gas temperature and coating time are the most critical parameters during the process. They have reported optimum values for gas temperature and coating time are 80.38 °C and 150 min (Azeem et al. 2018). Most of the previous studies have been done at a temperature range of 50–80 °C, reaction time varies from 10 min to 2 h (depending on coating material and fluidization tempera- ture), and pressure 0.2–0.4 MPa (da Rosa and dos Santos Rocha 2010; Cong et al. 2010; Tao et al. 2011; Azeem et al. 2018; Wang et al. 2020). The benefits, limitations, and coat- ing efficiency of the FBD process are mentioned in Table 2. Rotary pan The coating process using a rotary pan involves a spray- ing nozzle and rotating pan on an inclined axis. In various studies, a rotating pan has been used due to its flexibility, versatility of the equipment, ability to handle a wide range of particle sizes, and large throughputs (Babadi et al. 2019). The inclined axis provides a longer retention time in the pan. During the coating process, granules move in a spiral path due to gravity force, and granules grow with the coating surface and eventually reach the top level of the bed surface. The coating liquid or melted slurry (sulfur) is sprayed with the help of a nozzle spraying system, and fine particles are dispersed on the granules surface (Scherer et al. 2000). Most of the previous studies of CRFs using rotary pan have men- tioned pan rotating speed 12–16 rpm and pan inclination of 37.5°–45° (Babadi et al. 2019, 2021; Dubey and Mailapalli 2019). The benefits, limitations, and coating efficiency of the rotary pan process are mentioned in Table 2. Rotary drum Rotary drum type granulator is widely used in the fertilizer manufacturing industry because of its large production capacity and less process time. The rotating drum is inclined at 5–10° for adequate product movement toward the end and connected with a rotating shaft. The coating liquid is fed by a pump from the adjacent part of the drum and sprayed uni- formly with a spraying nozzle. Fixed or movable scrappers inside the drum can remove or reduce caking or big lumps inside the drum (Scherer et al. 2000). In previous studies, the inclination angle was set at 4° (Hanafi et al. 2000) and 30° (Lu et al. 2020), retention time taken 30 min (Hanafi et al. 53983 be improved (Chen et al. 2013). Interfacial crosslinking can be done by four different methods: (1) radical polymeriza- tion, (2) chemical reaction of complementary groups, (3) ionic interactions, (4) crystallization (Ullah et al. 2015). For example, in a study by Chen et al., crosslinking agent suber- oyl chloride was used to crosslink chitosan for the improve- ment of chitosan membrane (Chen et al. 2013). The benefits and limitations of the interfacial crosslinking process are mentioned in Table 2. Impact of CRFs on environment, soil, and plant The inefficiency of fertilizer cause air pollution, water pol- lution, and impact on soil physicochemical characteristics. CRFs play an important role in reducing nitrous oxide emis- sions from agricultural soil and improving soil quality by optimal pH, improving water retention capacity and increase soil organic matter (Chen et al. 2018). coated with Impact on nitrogen (N2O) emissions from soil Agricultural activities are responsible for 27% of global N2O emissions. The primary source of N2O emissions is nitro- gen fertilizer applied to agricultural soil and responsible for 16% of global N2O emissions annually (Fowler et al. 2015). The Intergovernmental Panel on Climate Change (IPCC) has mentioned the potential effects of greenhouse gas (GHG) emissions and their value in C O2 equivalents. The global warming potential of N2O emission is 298 times more potent than CO2 as a factor in global warming. Total 6% of N2O emissions are accountable for global annual GHG emissions as CO2 equivalent (Myhre et al. 2013). IPCC has defined a method to calculate the emissions factor (EF) for N 2O as kg N2O-N/kg N fertilizer input. EF depends on local climate patterns and varies by fertilizer type. In wet climate, the EF value for inorganic and organic N input value is set at 1.6% and 0.6%. In dry climate, the EF value for inorganic and organic N input value is set at 0.6% (Hergoualc’h et al. 2006). Excessive application of traditional nitrogen fertiliz- ers (inorganic fertilizers or manure) and low nitrogen use efficiency in croplands have caused various environmental problems such as eutrophication, nitrogen emissions, and nitrate leaching in groundwater (Beauchamp 1997; Chai et al. 2019). There are mainly three factors that can cause nitrous oxide emissions from agricultural soil: (1) environ- mental factors: which include soil characteristics (pH, salin- ity, temperature, texture, microbial population, soil available C, and N concentration); (2) management factors: which include fertilizer application, irrigation, tillage system; and (3) measurement factors: which include a length of measure- ment period and type of measurement (Wang et al. 2021). 13 53984 Limitations Coating efficiency (%) transfer rates (Roy et al. 2014) Long residence time, expensive equipment, chances of solvent 44–74% (da Rosa and dos loss and well mixing of granules (Tao et al. explosion (Teunou and Poncelet 2002) Santos Rocha 2010) distribution in reactor (Azeem et al. 2018) cost (Lawrencia et al. 2021) ease of adding materials, easy to operate and Poor control of humidity results in improper coating (Lawrencia 46% (Babadi et al. 2021) et al. 2021) 35% (Babadi et al. 2019) continuous and easy to scale up to large produc- Require a large quantity of coating materials, low repeatability, 26% (Ibrahim et al. 2014) leading to rough coating (Er et al. 2009) stability for uniform dispersion, excellent method Affected by the presence of strong acids and inhibit the polyaddi- – particles where polymer particles are tion reaction rate of the in-situ polymerization (Liao et al. 2021) (Arzac et al. 2014) It required low elastomer viscosity (Papageorgiou et al. 2015) Macromolecular chain may attach to carbon nanofillers and not allow them to form an interconnecting network which can cause lower electrical conductivity (Tang et al. 2019)

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