Review on materials & methods to produce controlled release coated urea fertilizer

Preliminary Study on Sustainable NPK Slow-Release Fertilizers Based on Byproducts and Leftovers: A Design-of-Experiment Approach

In this study, an organic nitrogen-based coating was developed based on black soldier fly (BSF) prepupae reared on poultry dejections and deposited on ceramic lightweight aggregates (LWAs), containing phosphorous (P) and potassium (K) from agroresidues, leading to a complete nitrogen, phosphorus, and potassium (NPK) fertilizer. To obtain a resistant coating with good adhesion to LWAs, different plasticizing agents were tested (e.g., glycerol, cellulose, and polyethylene glycol). The coating formulation was optimized through a design-of-experiment (DoE) approach to correlate the effect of each mixture component on the coating's performance. BSF biomass was characterized through chemical and thermal routes, as well as the final coated LWAs, confirming their general agreement to fertilizer's requirements. Release tests in static conditions highlighted the barrier action of the coating, preventing uncontrolled release of potassium and phosphorus contained in the LWAs as well as the release of nitrogen after 21 days (near to 20%). Germination and growth tests indicated a valuable increase of the growth index, whereas the germination process is limited by the coating barrier effect. This work proposes a new product in the field of slow-release fertilizers designed by rational methodologies and innovative materials based on waste valorization, fully in agreement with a circular economy perspective.

Ranking Potential Renewable Energy Systems to Power On-Farm Fertilizer Production

Farmers across the world have long used chemical fertilizers to achieve higher production outputs. One of the basic inputs for the production of nitrogen fertilizer is fossil fuel, which is not only finite but also has tangible impacts on the environment. This study aims to determine the most suitable renewable energy resource (RER) for the production of fertilizer in Iranian farmlands. The resources considered in this study were photovoltaic energy, biomass energy, wind energy, and solar thermal energy. This assessment was carried out in terms of six general criteria derived from a PESTEL (Political, Economic, Socio-cultural, Technological, Environmental and Legal) analysis, and thus 20 sub-criteria were obtained with the help of experts. The criteria were weighted using the Fuzzy AHP (Analytic Hierarchy Process) method. Because of the use of criteria with crisp, fuzzy, and interval-type values, the ranking was performed using the extended TODIM (an acronym in Portuguese of interactive and multi-criteria decision-making) method. A sensitivity analysis was performed to determine the effects of the sub-criteria on the results. The results showed that the technological criterion is the most important measure for this assessment, and that photovoltaic energy and wind energy are the top two options for powering chemical fertilizer production in Iranian farmlands.

Enhanced Agronomic Efficiency Using a New Controlled-Released, Polymeric-Coated Nitrogen Fertilizer in Rice

Fertilizer-use efficiency is one of the most critical concerns in rice cultivation to reduce N losses, increase yields, and improve crop management. The effects of a new polymeric-coated controlled-release fertilizer (CRF) were compared to those of other slow-release and traditional fertilizers in a microscale experiment, which was carried out in cuvettes under partly controlled ambient conditions, and a large-scale field experiment. To evaluate the fertilizer’s efficiency, nitrogen and water-use efficiency were calculated using the measurement of different photosynthetic and crop yield parameters. Improved responses regarding some of the analyzed physiological and growth parameters were observed for those plants fertilized with the new CRF. In the microscale experiment, significantly increased yields (ca. 35%) were produced in the plants treated with CRF as compared to traditional fertilizer. These results were in accordance with ca. 24% significant increased levels of N in leaves of CRF-treated plants, besides increased P, Fe, Mn, and cytokinin contents. At the field scale, similar yields were obtained with the slow-release or traditional fertilizers and CRF at a 20% reduced N dose. The new controlled-release fertilizer is a urea-based fertilizer coated with lignosulfonates, which is cheaply produced from the waste of pulp and wood industries, containing humic acids as biostimulants. In conclusion, CRF is recommended to facilitate rice crop management and to reduce contamination, as it can be formulated with lower N doses and because it is ecological manufacturing.

Starch and castor oil mutually modified, cross-linked polyurethane for improving the controlled release of urea

Due to the poor controlled release ability, bio-based materials are difficult for large scale application on controlled release fertilizers (CRFs). Starch-based polyol (SP) and castor oil (CO) were mutually modified, and a cross-linked polymer film was formed on the surface of urea by in-situ reaction, which improved the slow release ability of the bio-based material. The results showed that increasing the CO ratio reduced porosity of coating and prolonged the nitrogen (N) release period, while the SP changed the high-temperature wrinkle characteristics and regulated the early N release rate. The mutual modification achieved an ultra-long release period of bio-based CRUs for 7 months. The degradation rate during nine months of bio-based coatings (5.05 %) was significantly higher than that of petroleum-based (3.74 %), and the coating was non-toxic to rice seeds. Mutual modification provided a safe and effective solution for the preparation of bio-based CRFs with long-term controlled release capability.

Research Progress in Lignin-Based Slow/Controlled Release Fertilizer

As a skeleton component of plants, lignin is an organic macromolecule polymer that can be regenerated and naturally degraded. Annually, plant growth produces about 150 billion tons of lignin. In industrial processes such as paper and biomass-refining industry, large amounts of lignin are formed as by-products. Most of technical lignins are directly combusted to obtain heat, which not only is a waste of organic matter but also leads to environmental pollution and other issues. Interestingly, lignin can be used as slow-release carriers and coating materials for fertilizers due to its excellent slow release properties as well as chelating and other functionalities. Preparation of lignin-based slow/controlled release fertilizers can be achieved by sustainable chemical (ammoxidation, Mannich reaction, and other chemical modifications), coating (without or with chemical modification), and chelation modifications. This Review systematically summarizes the methods, mechanisms, and application of the above methods for preparing lignin-based slow/controlled release fertilizers. Although the evaluation standards and methods of lignin-based slow/controlled release fertilizers are not perfect, it is believed that more and more scholars will pay more attention to them to accelerate the development and application of lignin-based slow/controlled release fertilizers, so as to improve their relevant standards. In short, there is an urgent need to improve the preparation process of lignin-based slow/controlled release fertilizers and application as lignin-based slow/controlled release fertilizers to production practice as soon as possible.

Development of fertilizers for enhanced nitrogen use efficiency - Trends and perspectives

Despite nitrogen (N) being the most important crop nutrient, its use as fertilizer is associated with high losses. Such losses pollute the environment and increase greenhouse gas production and other environmental events associated with high ammonia volatilization and nitrous oxide emission. They also cause soil nitrate leaching and run-off that pollute surface and underground waters, with human health implications. The net outcomes for the plant are reduced N uptake and crop productivity that, together, increase the costs associated with fertilization of agricultural lands and dampen farmers' confidence in the efficacy and profitability of fertilizers. To address these problems, enhanced efficiency fertilizers (EEFs) are continuously being developed to regulate the release of N from fertilizers, allowing for improved uptake and utilization by plants, thereby lowering losses and increasing crop productivity per unit of fertilizer. The EEFs are classified based on whether they are inorganic- bio- or organic-coated; their mode of action on different N forms, including urease activity and nitrification inhibition; and the technologies involved in their development, such as targeted compositing of multiple nutrients and nanotechnology. This review is a critical revisit of the materials and processes utilized to coat or formulate enhanced efficiency N-fertilizers for reducing N losses, including their shortcomings, advances made to address such shortcomings, and effects on mitigating N losses and/or enhancing plant uptake. We provide perspectives that could assist in further improving promising and potentially effective and affordable coating or formulation systems for scalable improvements that allow for reducing the rate of N-fertilizer input in crop production. It is especially critical to develop multi-nutrient fertilizers that provide balanced nutrition to plants and humans, while improving N use efficiency and mitigating N-fertilizer effects on human and environmental health.

Preparation of biochar as a coating material for biochar-coated urea

Biochar was used as a coating material for slow release urea. However, influence of biochar performance on preparing biochar-coated urea (BCU) and nitrogen release characteristics is rarely reported. In this study, total of 24 biochars were prepared and characterized from six biomass residues (rice straw, chicken manure, vinasse, Phyllostachys pubescens, Arundo donax and sugarcane bagasse) at four pyrolysis temperatures (400-700 °C). Grey correlation analysis (GCA) was used to select biochar as a coating material for BCU based on biochar performance indicators. The feasibility (BCU formability) for preparing BCU and characteristics of nitrogen release in BCU based on hydrostatic dissolution test and soil column leaching experiment were evaluated. Biochar prepared at low pyrolysis temperature was not suitable as a coating material for BCU due to low specific surface area. Biochars derived from pyrolysis of Phyllostachys pubescens (B_P6), vinasse (B_V6) and rice straw (B_R6) at 600 °C were selected as coating materials for BCU based on grey correlation analysis (GCA). The adhesion of biochar to urea surface was related to biomass type that preparing biochar. B_V6 was recommended for use as coating material for BCU because the feasibility of the biochars followed the order B_R6 > B_V6 > B_P6, and the practicality of the biochars followed the order B_P6 > B_V6 > B_R6. The findings suggest that biochar with a high specific surface area, hydrophilic oxygen-containing functional groups and low pH is a suitable material for BCU.

Alternative uses for tannery wastes: a review of environmental, sustainability, and science

Abstract

The manufacture of leather covers a wide productive chain and beyond contributes to the economic flow. The various stages of leather processing result in high volumes of solid waste. In Brazil, a daily generation of 375 tons of solid waste is estimated, and landfills are still the most used route to its destination. In this review, emphasis will be given to researches that have sought alternatives for the use of solid waste from the tannery industry. Among the main applications of solid tannery wastes, the following stand out production of adsorbent materials, biodiesel, biogas, biopolymers, applications in agriculture and other applications involving extraction/recovery of compounds of industrial/commercial interest, isolation of microorganisms and production of enzymes and applications in the animal diet. In each alternative of waste application, the technologies used, the opportunities, and the challenges faced are mentioned. We hope that this review can provide valuable information to promote the broad understanding of the possibilities that tannery solid wastes has for the development of biodegradable and agricultural products, wastewater treatment, extraction of compounds of industrial and commercial interest, among others.

Graphical abstract

Copolymerized Natural Fibre from the Mesocarp of Orbignya phalerata (Babassu Fruit) as an Irrigating-Fertilizer for Growing Cactus Pears

Cactus pears face challenges due to global climate change, which is leading to in-depth research to monitor and increase their water activity. The objective of this study was to evaluate the use of the natural test hydrogel (TH) from Orbignya phalerata fibre as nutrients and water for growing cactus pear genotypes (“Baiana” and “Doce” [Nopalea cochenillifera], ‘Gigante’ [Opuntia fícus-indica], and “Mexican Elephant Ear” [Opuntia stricta]) compared to the use of commercial hydrogel (CH), which is based on polymers composed of polyacrylamide, and a treatment without the use of hydrogel (WH). A completely randomized design was used, in a factorial scheme (4 × 3), with four genotypes of cactus pear and three forms of hydration, with five replications. The number and area of cladode was greatest (p < 0.01) in plants with CH and TH irrigation-fertilization in the ‘Doce’ cactus genotype. The dry biomass of the cladode and root in the ‘Gigante’ cactus genotype was greatest (p < 0.01) in the treatments with CH and TH irrigation-fertilisation. The ‘Baiana’, ‘Doce’, and ‘Gigante’ cactus genotypes exhibited more (p < 0.01) dry matter content with the TH irrigation-fertilisation. The highest (p < 0.01) neutral detergent fibre content was observed in the ‘Baiana’ and ‘Doce’ cactus genotypes when irrigation occurred with WH treatment, and the highest acid detergent fibre content in the ‘Gigante’ genotype. The copolymerized natural fibre from the mesocarp of Orbignya phalerata (babassu fruit) induced a better growth and chemical composition of cactus pear genotypes than the hydrogel based on polymers composed of polyacrylamide.

Impact of controlled-release urea on rice yield, nitrogen use efficiency and soil fertility in a single rice cropping system

Overuse of nitrogen (N) fertilizer has led to low N use efficiency (NUE) and high N loss in single rice cropping systems in southeast China. Application of controlled-release urea (CRU) is considered as an effective N fertilizer practice for improving crop yields and NUE. Here, field experiments were conducted during 2015–2017 to assess the effects of two CRUs (resin-coated urea (RCU) and polyurethane-coated urea (PCU)) on rice yields, NUE and soil fertility at two sites (Lincheng town (LC) and Xintang town (XT)). Four treatments were established at each site: (1) control with no N application (CK), (2) split application of conventional urea (U, 270 kg N ha⁻¹), (3) single basal application of RCU (RCU, 216 kg N ha⁻¹), and (4) single basal application of PCU (PCU, 216 kg N ha⁻¹). The N application rate in the CRU treatment compared to the U treatment was reduced by 20%. However, the results showed that, compared to split application of urea, single basal application of CRU led to similar rice grain yields and aboveground biomass at both sites. No significant difference in the N uptake by rice plant was observed between the U and CRU treatments at either site. There were no significant differences in the N apparent recovery efficiency (NARE) among the U, RCU and PCU treatments, with the exception of that in XT in 2015. Compared to application of U, application of CRU increased the N agronomic efficiency (NAE) and N partial factor productivity (NPFP) by 17.4–52.6% and 23.4–29.8% at the LC site, and 15.0–84.1% and 23.2–33.4% at the XT site, respectively, during 2015–2017. Yield component analysis revealed that greater rice grain yield in response to N fertilizer was attributed mainly to the number of panicles per m², which increased in the fertilized treatments compared to the CK treatment. The application of CRU did not affect the soil fertility after rice harvest in 2016. Overall, these results suggest that single basal application of CRU constitutes a promising alternative N management practice for reducing N application rates, time- and labor-consuming in rice production in southeast China.

Self-Assembly of Hydrophobic and Self-Healing Bionanocomposite-Coated Controlled-Release Fertilizers

Self-healing materials have received increased attention because of their automatic detecting and repairing damage function. In this paper, a novel self-assembly and self-healing bionanocomposite was developed as a coating material for controlled release fertilizers. This nanotechnology-enabled coating is environmentally friendly and highly efficient and possesses a tunable nutrient-releasing characteristic. In the synthesis process, bio-based polyurethane coated urea (BPCU) was prepared by the reaction of bio-polyols with isocyanate. The BPCU was then modified by the layer-by-layer technology to prepare self-assembling modified BPCU (SBPCU). Last, hollow nano-silica (HNS) particles loaded with the sodium alginate (SA) were used to modify SBPCU to fabricate of self-assembling and self-healing BPCU (SSBPCU). The results show that the self-assembled materials were synthesized through electrostatic adsorption. The self-healing was observed through scanning electron microscopy and 3D-X-ray computed tomography, revealing the mechanism was that the repair agent released from HNS reacted with the curing agent to block the pore channels and cracks of the coating. As a result, the SSBPCU exhibited the highest hydrophobicity and surface roughness and thus the slowest release rate. For the first time, this work has designed a novel strategy to solve the bottleneck problem that restricts the development of a controlled-release fertilizer.

Effects of Mixed Controlled Release Nitrogen Fertilizer with Rice Straw Biochar on Rice Yield and Nitrogen Balance in Northeast China

A 3-year fixed site experiment was carried out on a Planosol in Northeast China to study the effects of biochar and controlled-release nitrogen fertilizer on rice yield, nitrogen-use efficiency, residual nitrogen, and nitrogen balance in soil-crop system. Five treatments were established: control (CK), bare urea (BU), controlled-release urea (CRU), 50% BU + 50% CRU (MBC), and 50% BU + 50% CRU + biochar (MBCB) treatments. The results showed that, compared with the BU treatment, the yield, N-use efficiency (NUE) and N agronomic efficiency (NAE) of the CRU treatment increased by 12.2%, 33.9% and 4.3 kg kg⁻¹, respectively; while the soil residual N and N surplus at harvest decreased by 11.6% and 10.7%, respectively. Compared with the MBC treatment, the yield, NUE and NAE of the MBCB treatment increased by 10.2%, 16.5% and 4.0 kg kg⁻¹, respectively; while the soil residual N and N surplus at harvest decreased by 10.8% and 12.3%, respectively. Therefore, mixed application of bare urea, controlled-release urea and biochar was effective for obtaining high rice yield, and high fertilization efficiency as well as for sustainable agricultural development in Northeast China.

Sustainable coating material based on chitosan-clay composite and paraffin wax for slow-release DAP fertilizer

The coating of fertilizers by polymers is one of the most efficient tools for their slow and control release into soil. This strategy avoids excessive use of the fertilizers and increases their availability to the crops needs. In the present paper, hydro-soluble diammonium phosphates (DAP) fertilizer was double coated following the dip-coating process by chitosan-clay composites as inner coating and paraffin wax as an outer coating. The chitosan composite preparation and characterization were deeply investigated. The montmorillonite (MMT) clay incorporation as filler improves the water barrier diffusion, mechanical properties, and thermal stability of the composite. The combination of the swelling behavior of the chitosan-clay composite (inner coating) and the hydrophobic property of paraffin wax (outer coating) was confirmed by the water holding capacity evaluation and the phosphorus release essays in water and soil. Indeed, the phosphorus dissolution from the coated DAP granules was significantly delayed compared to the uncoated DAP. Moreover, the biodegradation study of composite material in soil and the biochemical oxygen demand (BOD) tests revealed that the coating system proposed could be considered as a carbon source for microorganisms after the fertilization process, which confirms its sustainability.

The eternal battle to combat global warming: (thio)urea as a CO2 wet scrubbing agent

(Thio)Urea scaffolds are best known for their importance as intermediates in organic synthesis. In this work, a mechanistic study of the reaction between urea (U), (2-hydroxyethyl)urea (U-EtOH) and thiourea (tU)/NaH in DMSO with CO2 was carried out. While both U/tU reacted with CO2via a 1 : 2 mechanism through the formation of the keto (thio)carbamide-carboxylate adducts (k-U/tU-CO2- Na+), U-EtOH gave mixed CO2-adducts composed of organic carbonate and carbamide-carboxylate moieties (Na+-CO2-U-Et-OCO2- Na+). Moreover, we recorded for the first time, a new type of bond, namely sodium carbamimidothiocarbonate (e-tU-SCO2- Na+), upon bubbling CO2 in the DMSO solution of tU due to the persistence of the enol form (e-tU) and the better nucleophilicity of sulfur over nitrogen focal points. The reaction mechanisms were proven by 1D and 2D nuclear magnetic resonance (NMR) and ex situ attenuated total reflectance-Fourier transform infrared (ATR-FTIR) spectroscopies. The stability of these bonds was studied following the changes in 1H-NMR as a function of temperature, which indicated the reversibility of these reactions. Furthermore, the proposed mechanisms were explored theoretically via density functional theory (DFT) calculations by analyzing the energetics of the anticipated products.

A Theoretical Multifractal Model for Assessing Urea Release from Chitosan Based Formulations

This paper reports the calibration of a theoretical multifractal model based on empirical data on the urea release from a series of soil conditioner systems. To do this, a series of formulations was prepared by in situ hydrogelation of chitosan with salicylaldehyde in the presence of different urea amounts. The formulations were morphologically characterized by scanning electron microscopy and polarized light microscopy. The in vitro urea release was investigated in an environmentally simulated medium. The release data were fitted on five different mathematical models, Korsmeyer–Peppas, Zero order, First order, Higuchi and Hixson–Crowell, which allowed the establishment of a mechanism of urea release. Furthermore, a multifractal model, used for the fertilizer release for the first time, was calibrated using these empirical data. The resulting fit was in good agreement with the experimental data, validating the multifractal theoretical model.

Synthesis and characterization of dopamine-modified Ca-alginate/poly(N-isopropylacrylamide) microspheres for water retention and multi-responsive controlled release of agrochemicals

The multi-responsive controlled-release system could enhance crop yield while improving utilization efficiency of agrochemicals, and minimize environmental pollution caused by agrochemicals overuse. This work reports a novel Ca-alginate/Poly(N-isopropylacrylamide)@polydopamine (Ca-alginate/PNIPAm@PDA) microsphere to control the agrochemicals release. Microsphere with a semi-interpenetrating network, which contained pH-sensitive Ca-alginate, temperature-sensitive poly(N-isopropylacrylamide) (PNIPAm), and sunlight-sensitive polydopamine (PDA), was characterized by thermogravimetric analysis, zeta potential, Fourier transform infrared spectroscopy, and scanning electron microscopy to prove the successful synthesis. Moreover, the comprehensive performances, including photothermal conversion, water absorbency, water retention, and controlled-release agrochemicals behaviors, were systematically investigated. The results indicated that the composite microsphere was a prosperous water and agrochemicals manager to effectively retain water and control the release of agrochemicals by external stimulation. Consequently, the Ca-alginate/PNIPAm@PDA microsphere with outstanding water-retention and controlled-release capacities is economical and eco-friendly and thus is promising for utilization as water and agrochemicals controlled-release carrier material in agriculture applications.

Applying and Optimizing Water-Soluble, Slow-Release Nitrogen Fertilizers for Water-Saving Agriculture

A novel, eco-friendly, water-soluble, slow-release nitrogen fertilizer was developed to enhance water solubility and nitrogen use efficiency. A test was performed to determine the interactive effects of process parameters using a central composite design and response surface methodology. The quadratic polynomial mode for slow-release nitrogen was determined and yielded differences (p < 0.01). The soluble, slow-release nitrogen fertilizers were analyzed using nuclear magnetic resonance, and the release characteristics of soil nitrogen from the fertilizer at 25 °C were also determined. The effects of the fertilizer on plant growth were determined using rape (Brassica campestris L.) outdoors. Conversion rates from the fertilizer to inorganic nitrogen were 30.0, 52.2, and 60.0% at 7, 24, and 40 days, respectively. This soluble, slow-release nitrogen fertilizer resulted in increased yields and nitrogen use efficiencies in rape plants compared with a standard urea fertilizer. The yields of rape plants treated with a mixture of the fertilizer and urea (BBW100%) were significantly higher than all of the other treatments. When the nitrogen application rate was reduced by 20%, the resulting "SSNF80%" and "BBW80%" treatments produced nearly the same yields as "UREA100%". Nitrogen use efficiencies for treatments with the study fertilizer ("SSNF") and the mixture bulk blend fertilizer ("BBW") were significantly higher than that with urea ("UREA") treatment by 37-52 and 42-43%, respectively. Hence, the fertilizer showed great potential for improving the production of rape and possibly other crops.

Biodegradable Urea-Formaldehyde/PBS and Its Ternary Nanocomposite Prepared by a Novel and Scalable Reactive Extrusion Process for Slow-Release Applications in Agriculture

Novel binary composite urea-formaldehyde/poly(butylene succinate) (UF/PBS) and its ternary nanocomposite UF/PBS/potassium dihydrogen phosphate (MKP) were prepared by a simple and scalable reactive extrusion approach using methylolurea (MU), PBS, and MKP as the raw materials. The results show that MUs react by melt polycondensation to form UFs with different polymerization degrees at the high temperature in the extruder, giving the two polymer components molecular segment-scale mixing in composites. Meanwhile, MKPs dissolved in the water generated by the melt polycondensation are perfectly confined to the nanometer scale during their precipitation process in ternary composites due to the hydrogen bonding interactions between them and UF and the "cage effect" of UF and PBS macromolecule chains. Both composites have excellent processability, mechanical properties, and slow-release performances. Compared with UF prepared by direct synthesis or reactive extrusion, N release speeds of the two composites are much lower in the early incubation stage but much higher in the subsequent stages; ternary composites can also impart MKP with excellent slow-release properties. This study can provide a good feasibility for large-scale applications of UF-based or PBS-based composites and nanocomposites used as slow-release fertilizers or other products in agriculture or horticulture.

Inorganic matter modified water-based copolymer prepared by chitosan-starch-CMC-Na-PVAL as an environment-friendly coating material

Inorganic matter modifications were used to improve the hydrophobic properties and slow-release effects of water-based copolymer films. Water-based copolymers were prepared by aqueous polymerization of polyvinyl alcohol, starch, chitosan, and sodium carboxymethyl cellulose, and then, zeolite powder, volcanic ash or biochar were added to prepare the inorganic matter modified water-based copolymer films. The results showed that the inorganic matter modified water-based copolymer films had enhanced thermal stability, reductions in O-H and water vapour permeability, and increased crystallinity and roughness. Compared with water-based copolymer films, the water absorption capacities of the zeolite powder modified water-based copolymer films, volcanic ash modified water-based copolymer films, and biochar modified water-based copolymer films were reduced by 42.8 %, 50.0 % and 39.0 %, and their ammonium permeability was reduced by 53.0 %, 12.1 % and 1.1 %, respectively. Inorganic matter modified water-based copolymer films have properties that make them suitable for use in preparing slow-release coating materials.

Controlled release micronutrient fertilizers for precision agriculture - A review

The rapid growth of the global population and the resulting need to ensure sufficient food safety in highly productive agricultural practices. Intensive cultivation of plants contributes to the impoverishment of soils and thus forces farmers to apply intensive fertilization with microelements. Precise fertilization techniques are the future of agriculture, in which nutrients are supplied in controlled way with minimized losses to the environment, caused by leaching to groundwater. Kinetics of nutrients release should be thus adjusted to plant requirements and kinetics of uptake by the plant. The paper presents current achievements in the field of fertilizers with controlled release of microelements, which, apart from the main fertilizer components, are also very significant for proper plant growth. Fertilizers are divided into four basic groups, which include low-solubility fertilizers, fertilizers with external coating, bio-based and nano-fertilizers. Despite structural differences, all groups show properties of controlled microelement release. The paper presents new fertilization technologies with consideration of their influence on the environment.

Nitrogen Pollution Impact and Remediation through Low Cost Starch Based Biodegradable polymers

The world does not have too much time to ensure that the fast-growing population has enough land, food, water and energy. The rising food demand has brought a positive surge in fertilizers’ demand and agriculture-based economy. The world is using 170 million tons of fertilizer every year for food, fuel, fiber, and feed. The nitrogenous fertilizers are being used to meet 48% of the total food demand of the world. High fertilizer inputs augment the reactive nitrogen levels in soil, air, and water. The unassimilated reactive nitrogen changes into a pollutant and harms the natural resources. The use of controlled-release fertilizers for slowing down the nutrients’ leaching has recently been practiced by farmers. However, to date, monitoring of the complete discharge time and discharge rate of controlled released fertilizers is not completely understood by the researchers. In this work, corn starch was thermally processed into a week gel-like coating material by reacting with urea and borate. The granular urea was coated with native and processed starch in a fluidized bed reactor having bottom-up fluid delivery system. The processed starch exhibited better thermal and mechanical stability as compared to the native starch. Unlike the pure starch, the storage modulus of the processed starch dominated the loss modulus. The release time of urea, coated with processed starch, remained remarkably larger than the uncoated urea.

New Eco-Friendly Polymeric-Coated Urea Fertilizers Enhanced Crop Yield in Wheat

Presently, there is a growing interest in developing new controlled-release fertilizers based on ecological raw materials. The present study aims to compare the efficacy of two new ureic-based controlled-release fertilizers formulated with water-soluble polymeric coatings enriched with humic acids or seaweed extracts. To this end, an experimental approach was designed under controlled greenhouse conditions by carrying out its subsequent field scaling. Different physiological parameters and crop yield were measured by comparing the new fertilizers with another non polymeric-coated fertilizer, ammonium nitrate, and an untreated ‘Control’. As a result, on the microscale the fertilizer enriched with humic acids favored a better global response in the photosynthetic parameters and nutritional status of wheat plants. A significant 1.2-fold increase in grain weight yield and grain number was obtained with the humic acid polymeric fertilizer versus that enriched with seaweed extracts; and also, in average, higher in respect to the uncoated one. At the field level, similar results were confirmed by lowering N doses by 20% when applying the humic acid polymeric-coated produce compared to ammonium nitrate. Our results showed that the new humic acid polymeric fertilizer facilitated crop management and reduced the environmental impact generated by N losses, which are usually produced by traditional fertilizers.

Potential of Oil Palm Empty Fruit Bunch Resources in Nanocellulose Hydrogel Production for Versatile Applications: A Review

Oil palm empty fruit bunch (OPEFB) is considered the cheapest natural fiber with good properties and exists abundantly in Malaysia. It has great potential as an alternative main raw material to substitute woody plants. On the other hand, the well-known polymeric hydrogel has gathered a lot of interest due to its three-dimensional (3D) cross-linked network with high porosity. However, some issues regarding its performance like poor interfacial connectivity and mechanical strength have been raised, hence nanocellulose has been introduced. In this review, the plantation of oil palm in Malaysia is discussed to show the potential of OPEFB as a nanocellulose material in hydrogel production. Nanocellulose can be categorized into three nano-structured celluloses, which differ in the processing method. The most popular nanocellulose hydrogel processing methods are included in this review. The 3D printing method is taking the lead in current hydrogel production due to its high complexity and the need for hygiene products. Some of the latest advanced applications are discussed to show the high commercialization potential of nanocellulose hydrogel products. The authors also considered the challenges and future direction of nanocellulose hydrogel. OPEFB has met the requirements of the marketplace and product value chains as nanocellulose raw materials in hydrogel applications.

Bioactive carbon improves nitrogen fertiliser efficiency and ecological sustainability

Agriculture’s most pressing challenge is raising global food production while minimising environmental degradation. Nutrient deficiencies, principally nitrogen (N), limit production requiring future increases in fertiliser use and risk to proximal non-agricultural ecosystems. We investigated combining humate with urea, globally the most widely used N-suppling fertiliser, in a four-year field study. Humate increased pasture yield by 9.8% more than urea and significantly altered soil microbial diversity and function. Humate increased N retention suggesting microbial sequestration may lower N leaching and volatilisation losses. Humic microbial bio-stimulation could feasibly increase fertiliser efficiency and development of ecologically sustainable agriculture.

Production and Characterization of Controlled Release Urea Using Biopolymer and Geopolymer as Coating Materials

Synthetic polymers-based controlled release urea (CRU) leaves non-biodegradable coating shells when applied in soil. Several alternative green materials are used to produce CRU, but most of these studies have issues pertaining to nitrogen release longevity, process viability, and the ease of application of the finished product. In this study, we utilized tapioca starch, modified by polyvinyl alcohol and citric acid, as coating material to produce controlled release coated urea granules in a rotary fluidized bed equipment. Response surface methodology is employed for studying the interactive effect of process parameters on urea release characteristics. Statistical analysis indicates that the fluidizing air temperature and spray rate are the most influential among all five process parameters studied. The optimum values of fluidizing air temperature (80 °C), spray rate (0.13 mL/s), atomizing pressure (3.98 bar), process time (110 min), and spray temperature (70 °C) were evaluated by multi-objective optimization while using genetic algorithms in MATLAB^®. Urea coated by modified-starch was double coated by a geopolymer to enhance the controlled release characteristics that produced promising results with respect to the longevity of nitrogen release from the final product. This study provides leads for the design of a fluidized bed for the scaled-up production of CRU.

Biochar for delivery of agri-inputs: Current status and future perspectives

Biochar, a carbonaceous porous material produced from the pyrolysis of agricultural residues and solid wastes has been widely used as a soil amendment. Recent publications on biochar are primarily focussed with its application in climatic aspects, contaminant immobilization, soil amendment strategies, nutrient recovery, engineered material production and waste-water treatment. Numerous studies have reported the positive attribute of biochar's nutrient value that helps in improving plant growth and fertilizer use efficiency. The renewability, low-cost, high porosity, high surface area and customizable surface chemistry of biochar offers ample prospect in several engineering applications, some of which needs significant attention. This review aims at systematically assessing the uses of biochar as a potential carrier material for delivery of agrochemicals and microbes. The key parameters of biochar that are crucial to assess the potential of any material to be used for delivery purposes are discussed. The parameters such as the physicochemical properties of biochar, the mechanistic aspects of adsorption and release of agrochemicals and microbes from biochar, comparative assessment of biochar over other carrier materials, long-term effects of biochar and the economic and environmental benefits of biochar are discussed in detail. At the end, a brief perspective has also been laid out to discuss how nano-interventions could further be helpful to tailor biochar properties useful for delivery applications.

Combined effects of nitrification inhibitor and zeolite on greenhouse gas fluxes and corn growth

Field and incubation experiments were conducted to determine the emission rate of greenhouse gases, nitrogen change, populations of AOB, NOB, and fungi as well as growth of corn in response to amendment of urea granulated with and without nitrification inhibitors and zeolite. The application of urea with neem, urea with zeolite, urea with zeolite + neem, urea with zeolite + dicyandiamide, and urea with dicyandiamide (UD) decreased the N₂O emissions by 16.3%, 59.6%, 66.8%, 81.9%, 16.3%, and 86.7%, respectively. Meanwhile, patterns of CH₄ fluxes were mostly determined by small emissions. Increase in corn height, weight of cobs, biomass, and chlorophyll leaf contents were not significantly different between urea alone and urea with NIs and zeolite. In the incubation experiment, the highest concentration of NH₄⁺ and N₂O production was detected during the first week and it remained high up to the second week of incubation in the combination of urea with NIs and zeolite treatments, although there was no significant difference compared with urea. During NH₄⁺ decrease, the concentration of NO₃^- started to accumulate from the second to the third weeks. Production of CO₂ showed no significant differences among treatments. The static production of CO₂ could also explain that NIs and zeolite additions did not change AOB, NOB, and fungi activities after the fourth week of incubation.

Optimizing nitrogen management to achieve high yield, high nitrogen efficiency and low nitrogen emission in winter wheat

Achieving both high yield and high nitrogen (N) use efficiency (NUE) simultaneously is a current research hotspot in crop production. To investigate approaches for achieving high yield and NUE, field experiments using N fertilizer rates of 0, 120, 180, 240, 300 and 360 kg N ha^-1 were conducted to study relationships between yield, N uptake and N efficiency during three wheat growing seasons from 2013 to 2016 in three experimental sites (Shangshui, Kaifeng and Wenxian) in the Huang-Huai Plain. Yield, biomass and N concentrations of plants and soil were determined. The results indicated that increased N application would affect soil N residue and increase N₂O emission, suitable N application rate (N240-N268) contributed to maintaining soil fertility and reducing N₂O emission for achieving high yield, high NUE and low N₂O emission. High plant N accumulation (PNA) during jointing to anthesis had the best correlation coefficient with yield and NUE compared to other growth stages, which contributed to achieving high yield and NUE simultaneously. The dry matter produced by a unit of N was defined as N productivity, such as plant N net phase productivity (PNPn) and leaf N productivity (LNP). High PNPn during jointing to anthesis was significantly related to both yield and NUE. The LNP indicator (i.e. photosynthetic N use efficiency, PNUE) in the flag showed significant correlation with both yield and NUE after booting under high PNA levels. These results suggest that PNPn and PNUE could combine high yield and high NUE under high PNA conditions. Besides, to match soil N supply to plant N demand, optimum soil nitrate N accumulation and alkali-hydrolysable N (AHN) content ranges were determined. This study provides a theoretical basis to achieve high yield, high NUE and low N₂O emission for N management in wheat field production.

Cellulose based materials for controlled release formulations of agrochemicals: A review of modifications and applications

Controlled release formulations (CRFs) of agrochemicals have been attracted considerable attention due to their friendliness to environment. The commercial supporting materials for CRFs of agrochemicals are non-degradable, leading to secondary pollution issue. Cellulose, as the most abundant natural materials in the world, is regarded as one of the most ideal substitutes for non-degradable supporting materials thanks to its good biocompatibility and biodegradability. As raw cellulose materials suffer several problems, such as poor mechanical strength, fast release rate, etc., chemical modifications are commonly performed to improve their properties. In this review, modification methods of cellulose materials for CRFs of agrochemicals were introduced. The relationships between release rate and cellulose based materials were discussed in detail. The applications of cellulose materials for CRFs of agrochemicals were also expounded.

Leaching of Organic Toxic Compounds from PVC Water Pipes in Medina Al-Munawarah, Kingdom of Saudi Arabia

It is well established that the use of synthetic material in water pipes significantly affects the quality of domestic water, especially trace organics that are leached through with the flow of water. In the present study, the migration of volatile organic compounds (VOCs) from water pipes manufactured of polyvinyl chloride (PVC) has been investigated using static laboratory conditions and in residential areas. The contact of deionized water with various PVC pipes for three successive test periods of 24, 48, and 72 h duration has been made. Twenty water samples were collected from houses within Medina Al-Munawarah residential area and were analyzed by using solid phase extraction, followed by high resolution gas chromatography with flame ionized detector (GC-FID). The presence of carbon tetrachloride (CTC), toluene, chloroform, styrene, o-xylene, bromoform (BF), dibromomethane (DBM), cis-1,3-dichloropropane (Cis-1,3-DCP), and trans-1,3-dichloropropane (Trans-1,3-DCP) was initially confirmed. The most frequent contaminants found were DBM, CTC, and toluene that were monitored in 55%, 50%, and 45% of samples, respectively. The levels of CTC, Cis-1,3-DCP, and Trans-1,3-DCP were found to exceed the World Health Organization (WHO) limits in 50%, 20%, and 20% of samples, respectively. The migration test indicated that nine of the targeted contaminants occur in a double distilled water sample incubated in pipe in laboratory level experiment. This implies that these components are more likely to migrate from PVC pipe in home plumbing systems network.

Estimating Nitrogen from Structural Crop Traits at Field Scale—A Novel Approach Versus Spectral Vegetation Indices

A sufficient nitrogen (N) supply is mandatory for healthy crop growth, but negative consequences of N losses into the environment are known. Hence, deeply understanding and monitoring crop growth for an optimized N management is advisable. In this context, remote sensing facilitates the capturing of crop traits. While several studies on estimating biomass from spectral and structural data can be found, N is so far only estimated from spectral features. It is well known that N is negatively related to dry biomass, which, in turn, can be estimated from crop height. Based on this indirect link, the present study aims at estimating N concentration at field scale in a two-step model: first, using crop height to estimate biomass, and second, using the modeled biomass to estimate N concentration. For comparison, N concentration was estimated from spectral data. The data was captured on a spring barley field experiment in two growing seasons. Crop surface height was measured with a terrestrial laser scanner, seven vegetation indices were calculated from field spectrometer measurements, and dry biomass and N concentration were destructively sampled. In the validation, better results were obtained with the models based on structural data (R2 < 0.85) than on spectral data (R2 < 0.70). A brief look at the N concentration of different plant organs showed stronger dependencies on structural data (R2: 0.40–0.81) than on spectral data (R2: 0.18–0.68). Overall, this first study shows the potential of crop-specific across‑season two-step models based on structural data for estimating crop N concentration at field scale. The validity of the models for in-season estimations requires further research.

Dimethylolurea as a Novel Slow-Release Nitrogen Source for Nitrogen Leaching Mitigation and Crop Production

Rapid hydrolysis of urea results in further fertilization frequency and excessive nitrogen (N) input. A modified urea, dimethylolurea (DMU), was synthesized in this study. The structure of the sample was characterized by Fourier transform infrared and nuclear magnetic resonance analysis, manifesting the formation of DMU. N release investigation confirmed that DMU enabling provided a gradual N supply. The N leaching experiment indicated that increasing the applied DMU significantly reduced the NH₄⁺-N, NO₃^--N, and total N leaching, compared with urea application alone. The application effect on maize and wheat was evaluated. The results revealed that singly applied DMU with 100% or 80% N input, irrespective of the amount, promoted crop yield and agronomic characteristic and N use efficiency (NUE) of maize and wheat, beyond urea with two split applications at the recommended rate. Thus, the potential availability of DMU was proven; this could be widely used in agricultural fields as a slow-release fertilizer.

Designing chitosan based eco-friendly multifunctional soil conditioner systems with urea controlled release and water retention

The paper reports new soil conditioner systems obtained by in situ hydrogelation of chitosan with salicylaldehyde in the presence of urea fertilizer, designed to address both fertilization and water retention of the soil. The new systems were structural, supramolecular and morphological characterized by FTIR spectroscopy, XRD diffraction, POM and SEM microscopy. The rate of urea release has been investigated by NMR analysis and the release mechanism has been assessed by fitting five mathematical models. The formulations showed high water absorbency of 68 g/g, and they induced water holding capacity in soil up to 154% and an increment of the nitrogen content in soil to almost double, leading to a growth of plants with almost 70% higher compared to the reference soil. All these data revealed the new systems as new multifunctional soil conditioner ecoproducts capable to address both fertilizing and water retention issues, with high potential of application for sustainable agriculture.