Evaluation of biodegradable polymers as encapsulating agents for the development of a urea controlled-release fertilizer using biochar as support material

A Biohybrid Self-Dispersing Miniature Machine Using Wild Oat Fruit Awns for Reforestation and Precision Agriculture

Advances in bioinspired and biohybrid robotics are enabling the creation of multifunctional systems able to explore complex unstructured environments. Inspired by Avena fruits, a biohybrid miniaturized autonomous machine (HybriBot) composed of a biomimetic biodegradable capsule as cargo delivery system and natural humidity-driven sister awns as biological motors is reported. Microcomputed tomography, molding via two-photon polymerization and casting of natural awns into biodegradable materials is employed to fabricate multiple HybriBots capable of exploring various soil and navigating soil irregularities, such as holes and cracks. These machines replicate the dispersal movements and biomechanical performances of natural fruits, achieving comparable capsule drag forces up to ≈0.38 N and awns torque up to ≈100 mN mm-1. They are functionalized with fertilizer and are successfully utilized to germinate selected diaspores. HybriBots function as self-dispersed systems with applications in reforestation and precision agriculture.

Organo-monomers coated slow-release fertilizers: Current understanding and future prospects

The increasing urge to make an impactful contribution towards attaining nutritional security amidst the ever-rising demand for food, changing climate and maintaining environmental health and safety has become the main focal point for today's researchers globally. Slow-release fertilizers (SRFs) are a broad, dynamic, and advance category of fertilizers but despite its environmental benefits and scientifically proven results it often faces some critical challenges, primarily due to its high cost, often stemming from synthetic coatings, deteriorating soil health and with unrevealed potential environmental impacts. Organo-monomers have gained immense popularity due to their organic origin, biodegradable nature, biocompatibility, bio-sustainability and as a targeted delivery of nutrients in the plant system leading to increase in nutrient use efficiency (NUE). They can form strong bond with other monomers, fertilizers elements and improve the soil quality, carbon sequestration and holistically the environment. This review emphasizes on organo-monomers based SRFs, its synthesis, application and deliberate mechanism of nutrient release; boosting crop productivity and global economy. In conclusion, provided the significant challenges posed by the classical or synthetically coated fertilizers; the application of organo-monomers based SRFs demonstrates immense potential for achieving sustainable yield, to help build a global nutritionally secure population.

Climate adaptation through crop migration requires a nexus perspective for environmental sustainability in the North China Plain

Crop migration can moderate the impacts of global warming on crop production, but its feedback on the climate and environment remains unknown. Here we develop an integrated framework to capture the climate impacts and the feedback of adaptation behaviours with the land-water-energy-carbon nexus perspective and identify opportunities to achieve the synergies between climate adaptation and environmental sustainability. We apply the framework to assess wheat and maize migration in the North China Plain and show that adaptation through wheat migration could increase crop production by ~18.5% in the 2050s, but at the cost of disproportional increment in land use (~19.2%), water use (~20.2%), energy use (~19.5%) and carbon emissions (~19.9%). Irrigation and fertilization management are critical mitigation opportunities in the framework, through which wheat migration can be optimized to reduce the climatic and environmental impacts and avoid potential carbon leakage. Our work highlights the sustainable climate adaptation to mitigate negative environmental externalities.

Environmental applications and risks of engineered nanomaterials in removing petroleum oil in soil

Oil-contaminated soil posed serious threats to the ecosystems and human health. The unique and tunable properties of engineered nanomaterials (ENMs) enable new technologies for removing and repairing oil-contaminated soil. However, few studies systematically examined the linkage between the change of physicochemical properties and the removal efficiency and environmental functions (e.g., potential risk) of ENMs, which is vital for understanding the ENMs environmental sustainability and utilization as a safety product. Thus, this review briefly summarized the environmental applications of ENMs to removing petroleum oil from complex soil systems: Theoretical and practical fundamentals (e.g., excellent physicochemical properties, environmental stability, controlled release, and recycling technologies), and various ENMs (e.g., iron-based, carbon-based, and metal oxides nanomaterials) remediation case studies. Afterward, this review highlights the removing mechanism (e.g., adsorption, photocatalysis, oxidation/reduction, biodegradation) and the impact factor (e.g., nanomaterials species, natural organic matter, and soil matrix) of ENMs during the remediation process in soil ecosystems. Both positive and negative effects of ENMs on terrestrial organisms have been identified, which are mainly derived from their diverse physicochemical properties. In linking nanotechnology applications for repairing oil-contaminated soil back to the physical and chemical properties of ENMs, this critical review aims to raise the research attention on using ENMs as a fundamental guide or even tool to advance soil treatment technologies.

All-Natural Plant-Derived Polyurethane as a Substitute of a Petroleum-Based Polymer Coating Material

The development of efficient, biobased polyurethane controlled-release fertilizers from sustainable and eco-friendly biomaterials has received increased research attention, owing to concerns regarding global food security and environmental sustainability. Most previous studies focused on replacing petroleum-based polyols with biopolyols; however, the other main raw material, isocyanate, remained a petrochemical product. Herein, all-natural, plant-derived polyurethane-coated urea was successfully developed using castor oil and biobased isocyanate, and the performance of the coating shell before and after modification was compared. The results showed that the incorporation of a low dose of lauric acid copper into the coating material simultaneously enhanced the hydrophobicity and elasticity of the all-biobased polyurethane membrane, which prolonged the nitrogen release longevity from 3 to 112 days. In addition, the modified membrane showed excellent biodegradability in a soil environment. The novel all-biobased polyurethane coating material and modification technique provide insight for developing sustainable and eco-friendly controlled-release fertilizers.

Gel-Embedded Biochar and Hydroxyapatite Composite for the Improvement of Saline-Alkali Soil and Plant Growth Promotion

Soil amendments play a crucial role in modern agriculture, as they effectively enhance the planting environment. This study innovatively proposes the use of gel as a crosslinking agent to embed biochar and hydroxyapatite (HAP), thereby preparing a novel soil amendment. Furthermore, this study investigates the soil improvement effects of this amendment as well as its influence on plant growth. This study employed a hydrothermal method to combine corn stalk (CB) or sludge (SB) biochar with HAP at different ratios (0-20%). Subsequently, sodium alginate gel (SA) was utilized to encapsulate the biochar and minerals, successfully forming a ternary composite gel material (corn stalk biochar/sludge biochar-sodium alginate gel-hydroxyapatite: CB/SB-SA-HAP). Finally, the practical effectiveness of this amendment was verified through potted soil experiments. The results indicate that the CB/SB-SA-HAP composite materials exhibited a micrometre-scale spherical structure with well-developed micropores and possess the functional groups of CB/SB, SA, and HAP, along with unique mineral properties. Through pot experiments, it was verified that the composite material effectively enhances multiple soil properties. After 21 days of cultivation, the soil pH values stabilized within the neutral range (pH = 7 ± 0.3) across all treatment groups. Except for the CB0 (CB:HAP = 1:0) and CB2.0 (CB:HAP = 1:2) treatments, the remaining treatments significantly reduced the soil EC values by 3.27% to 47.92%. All treatments significantly increased the contents of alkali-hydrolysable nitrogen (AHN) (34.89~57.91%), available phosphorus (AP) (35.93~56.55%), and available potassium (AK) (36.41~56.80%) in the soil. In comparison, although the SB treatment was more effective in regulating the pH and electrical conductivity (EC) of saline-alkali soil than the CB treatment, it was less effective in promoting plant growth in the short term. Through correlation analysis and redundancy analysis, a significant positive correlation was found between soil pH and ryegrass germination rate and plant height, particularly with the most pronounced impact on soil pH observed in the CB1.0 and SB0 (SB:HAP = 1:0) treatments. This study underscores the potential of CB/SB-SA-HAP composite materials in soil improvement and plant growth promotion, providing valuable insights for soil remediation, enhancement, and plant cultivation advancements in the agricultural sector.

Nitrogen (N) "supplementation, slow release, and retention" strategy improves N use efficiency via the synergistic effect of biochar, nitrogen-fixing bacteria, and dicyandiamide

Irrational nitrogen (N) fertilizer management and application practices have led to a range of ecological and environmental problems that seriously threaten food security. In this study, an effective N fertilizer management strategy was established for improving N fertilizer utilization efficiency (NUE). Biochar, N2-fixing bacteria (Enterobacter cloacae), and a nitrification inhibitor (dicyandiamide, DCD) were simultaneously added to the soil during maize cultivation. The goal was to increase soil ammonium nitrogen content and NUE by regulating the relative abundance, enzyme activity, and functional gene expression of N conversion-related soil microbes. Biochar combined with E. cloacae and DCD significantly increased soil N content, and the NUE reached 46.69 %. The relative abundance of Burkholderia and Bradyrhizobium and the activity of nitrogenase increased significantly during biological N2 fixation. Further, the abundance of the nifH gene was significantly up-regulated. The relative abundance of Sphingomonas, Pseudomonas, Nitrospira, and Castellaniella and the activities of ammonia monooxygenase and nitrate reductase decreased significantly during nitrification and denitrification. Moreover, the abundance of the genes amoA and narG was significantly down-regulated. Correlation analyses showed that the increase in soil N2 fixation and the suppression of nitrification and denitrification reactions were the key contributors to the increase in soil N content and NUE. Biochar combined with E. cloacae and DCD synergistically enabled the supplementation, slow release, and retention of N, thus providing adequate N for maize growth. Thus, the combination of biochar, E. cloacae, and DCD is effective for mitigating the irrational application of N fertilizers and reducing N pollution.

Effect of a Prolonged-Release System of Urea on Nitrogen Losses and Microbial Population Changes in Two Types of Agricultural Soil

Urea is the nitrogen-containing fertilizer most used in agricultural fields; however, the nutrient given by the urea is lost into the environment. The aim of this research was to determine the effect of two soil textures by applying a prolonged-release system of urea (PRSU) on the N losses. This research shows an important decrease of the nitrate and ammonium losses from 24.91 to 87.94%. Also, the microbiological population increases after the application of the PRSU. It was concluded that both soil textures presented the same loss-reduction pattern, where the N from the nitrates and ammonium was reduced in the leachates, increasing the quality of the soil and the microbial population in both soil textures after the PRSU application.

Hyperspectral imaging for estimating leaf, flower, and fruit macronutrient concentrations and predicting strawberry yields

Managing the nutritional status of strawberry plants is critical for optimizing yield. This study evaluated the potential of hyperspectral imaging (400-1,000 nm) to estimate nitrogen (N), phosphorus (P), potassium (K), and calcium (Ca) concentrations in strawberry leaves, flowers, unripe fruit, and ripe fruit and to predict plant yield. Partial least squares regression (PLSR) models were developed to estimate nutrient concentrations. The determination coefficient of prediction (R2P) and ratio of performance to deviation (RPD) were used to evaluate prediction accuracy, which often proved to be greater for leaves, flowers, and unripe fruit than for ripe fruit. The prediction accuracies for N concentration were R2P = 0.64, 0.60, 0.81, and 0.30, and RPD = 1.64, 1.59, 2.64, and 1.31, for leaves, flowers, unripe fruit, and ripe fruit, respectively. Prediction accuracies for Ca concentrations were R2P = 0.70, 0.62, 0.61, and 0.03, and RPD = 1.77, 1.63, 1.60, and 1.15, for the same respective plant parts. Yield and fruit mass only had significant linear relationships with the Difference Vegetation Index (R2 = 0.256 and 0.266, respectively) among the eleven vegetation indices tested. Hyperspectral imaging showed potential for estimating nutrient status in strawberry crops. This technology will assist growers to make rapid nutrient-management decisions, allowing for optimal yield and quality.

Lignite Scaffolding as Slow-Release N-Fertilizer Extended the SN Retention and Inhibited N Losses in Alkaline Calcareous Soils

Conventional nitrogen (N) fertilizers particularly urea mineralized quickly in soil. Without sufficient plant uptake, this rapid mineralization favors the heavy N losses. Lignite is a naturally abundant and cost-effective adsorbent capable of extending multiple benefits as a soil amendment. Therefore, it was hypothesized that lignite as an N carrier for the synthesis of lignite-based slow-release N fertilizer (LSRNF) could offer an eco-friendly and affordable option to resolve the limitations of existing N fertilizer formulations. The LSRNF was developed by impregnating urea on deashed lignite and pelletized by a mixture of polyvinyl alcohol and starch as a binder. The results indicated that LSRNF significantly delayed the N mineralization and extended its release to >70 days. The surface morphology and physicochemical properties of LSRNF confirmed the sorption of urea on lignite. The study demonstrated that LSRNF also significantly decreased the NH₃-volatilization up to 44.55%, NO₃-leaching up to 57.01%, and N₂O-emission up to 52.18% compared to conventional urea. So, this study proved that lignite is a suitable material to formulate new slow-release fertilizers, suiting to alkaline calcareous soils favorably where N losses are further higher compared to non-calcareous soils.

Nitrogen retention potentials of magnesium oxide- and sepiolite-modified biochars and their impacts on bacterial distribution under nitrogen fertilization

Mitigating the loss and negative impacts of reactive N from fertilized soils remains a global environmental challenge. To optimize N retention by biochar, bamboo and pig manure biochars were modified as MgO- and sepiolite-biochar composites and characterized. Novel soil application of the modified biochars and their raw forms were comparatively evaluated for N-retention in a fertilized soil leached for 90 days in a column experiment. Changes in N-cycling-related enzyme and bacterial structure were also reported after 90 days. Results revealed low leaching losses of NH₄⁺, which reduced over time across all the treatments. However, while sole fertilizer (F) increased the initial and cumulative NO₃^- leached from the soil, the MgO-bamboo biochar (MgOBF) and sepiolite-bamboo biochar (SBF) treatments reduced leachate NO₃^- by 22.1 % and 10.5 % compared to raw bamboo biochar (BBF) treatment. However, 15.5 % more NO₃^- was leached from the MgO-pig manure biochar-treated soil (MgOPF) compared to its raw biochar treatment (PMBF) after 90 days. Dissolved organic N leached was reduced by 9.2 % and 0.5 % in MgOBF and SBF, as well as 15.4 % and 40.5 % in MgOPF and SPF compared to their respective raw forms. The total N of the biochars, adjustment of surface charges, cation exchange capacity, surface area, pore filling effects, and the formation of potential MgN precipitates on the modified-biochar surfaces regulated N leaching/retention. In addition, the modified biochar treatments reduced the hydrolysis of urea and stimulated some nitrate-reduction-related bacteria crucial for NO₃^- retention. Hence, unlike the raw biochar and MgOPF treatments, MgOBF, SBF, and SPF hold promise in mitigating inorganic-N losses from fertilized soils while improving the soil's chemical properties.

Eco-Friendly Starch Composite Supramolecular Alginate–Ca2+ Hydrogel as Controlled-Release P Fertilizer with Low Responsiveness to Multiple Environmental Stimuli

Environmentally friendly fertilizers (EFFs) have been developed to improve fertilizer efficiency and minimize adverse environmental impacts, but their release behavior under various environmental conditions has been less explored. Using phosphorus (P) in the form of phosphate as a model nutrient, we present a simple method for preparing EFFs based on incorporating the nutrient into polysaccharide supramolecular hydrogels using Cassava starch in the Ca2+-induced cross-link gelation of alginate. The optimal conditions for creating these starch-regulated phosphate hydrogel beads (s-PHBs) were determined, and their release characteristics were initially evaluated in deionized water and then under various environmental stimuli, including pH, temperature, ionic strength, and water hardness. We found that incorporating a starch composite in s-PHBs at pH = 5 resulted in a rough but rigid surface and improved their physical and thermal stability, compared with phosphate hydrogel beads without starch (PHBs), due to the dense hydrogen bonding-supramolecular networks. Additionally, the s-PHBs showed controlled phosphate-release kinetics, following a parabolic diffusion with reduced initial burst effects. Importantly, the developed s-PHBs exhibited a promising low responsiveness to environmental stimuli for phosphate release even under extreme conditions and when tested in rice field water samples, suggesting their potential as a universally effective option for large-scale agricultural activities and potential value for commercial production.

Biochar and activated carbon derived from oil palm kernel shell as a framework for the preparation of sustainable controlled release urea fertiliser

The oil palm kernel shell biochar (OPKS-B) and oil palm kernel shell activated carbon (OPKS-AC) were used as a framework to entrap urea using adsorption method. Batch adsorption studies were performed to gauge the influence of contact time on the adsorption of urea onto both OPKS-B and OPKS-AC. To evaluate the physicochemical traits of the studied materials, energy dispersive X-ray spectrometer (EDS), N2-sorption, X-ray diffraction (XRD), Fourier-transform infrared spectroscopy (FTIR), field emission scanning electron microscopy (FESEM), elemental analysis, differential thermal gravity (TG/DTG) and thermal gravity were applied. Result shows OPKS-AC has a better sorption capacity for urea compared to OPKS-B. The Langmuir isotherm model better justified the sorption isotherms of urea. For the adsorption process for both OPKS-B and OPKS-AC, the pseudo-second-order kinetic model was picked as it best fitted the experimental sorption outcome with the superior R2 values of > 65.1% and > 74.5%, respectively. The outcome of the experiments showcased that the maximum monolayer adsorption capacity of the OPKS-AC towards urea was 239.68 mg/g. OPKS-AC has showed promising attributes to be picked as an organic framework in the production of controlled release urea fertiliser for a greener and environmentally friendly agricultural practices.

Synthesis of Hydrogels and Their Progress in Environmental Remediation and Antimicrobial Application

As a kind of efficient adsorptive material, hydrogel has a wide application prospect within different fields, owing to its unique 3D network structures composed of polymers. In this paper, different synthetic strategies, crosslinking methods and their corresponding limitations and outstanding contributions of applications in the fields of removing environmental pollutants are reviewed to further provide a prospective view of their applications in water resources sustainability. Furthermore, the applications within the biomedical field, especially in wound dressing, are also reviewed in this paper, mainly due to their unique water retention ability, antibacterial ability, and good biocompatibility. Finally, the development direction of hydrogels in the fields of environmental remediation and biomedicine were summarized and prospected.

Encapsulation with Natural Polymers to Improve the Properties of Biostimulants in Agriculture

Encapsulation in agriculture today is practically focused on agrochemicals such as pesticides, herbicides, fungicides, or fertilizers to enhance the protective or nutritive aspects of the entrapped active ingredients. However, one of the most promising and environmentally friendly technologies, biostimulants, is hardly explored in this field. Encapsulation of biostimulants could indeed be an excellent means of counteracting the problems posed by their nature: they are easily biodegradable, and most of them run off through the soil, losing most of the compounds, thus becoming inaccessible to plants. In this respect, encapsulation seems to be a practical and profitable way to increase the stability and durability of biostimulants under field conditions. This review paper aims to provide researchers working on plant biostimulants with a quick overview of how to get started with encapsulation. Here we describe different techniques and offer protocols and suggestions for introduction to polymer science to improve the properties of biostimulants for future agricultural applications.

Environmentally friendly hydrogel: A review of classification, preparation and application in agriculture

Superabsorbent hydrogel (SH) is three-dimensional (3D) cross-linked hydrophilic polymer that can absorb and retain large quantities of water or other aqueous solutions. SH is made of water-affinity monomers and is widely used in biomedicine, wastewater treatment, hygiene and slow-release fertilizers (SRFs). This article focused on the preparation methods of SH, superabsorbent hydrogel composite and the application of SH in agriculture. By selecting various synthetic technologies and cross-linking agents, a series of chemical cross-linking or physical networks can be designed and tailored to meet specific applications. In view of the excellent characteristics of water absorption, biodegradability, water retention and slow-release capacity, SH occupies a dominant position in the SRFs market. In this work, the agricultural application of SH in double coated SRFs and nutrients carriers is also discussed. Some mechanisms related to the nutrient release were analyzed by mathematical models. In addition, some agronomic benefits of using superabsorbent hydrogels in improving water absorption, water holding capacity and increasing crop yields were also discussed. Although SH has certain shortcomings, from the perspective of long-term development, it will further show great potential in sustainable agriculture.

Enhancing N uptake and reducing N pollution via green, sustainable N fixation-release model

The overuse of N fertilizers has caused serious environmental problems (e.g., soil acidification, excessive N₂O in the air, and groundwater contamination) and poses a serious threat to human health. Improving N fertilizer utilization efficiency and plant uptake is an alternative for N fertilizers overuses. Enterobacter cloacae is an opportunistic pathogen, also used as plant growth-promoting rhizobacteria (PGPR), has been widely presented in the fields of bioremediation and bioprotection. Here we developed a new N fixation-release model by combining biochar with E. cloacae. The efficiency of the model was evaluated using a greenhouse pot experiment with maize (Zea mays L.) as the test crop. The results showed that biochar combined with E. cloacae significantly increased the N content. The application of biochar combined with E. cloacae increased total N in soil by 33% compared with that of N fertilizers application. The N-uptake and utilization efficiency (NUE) in plant was increased 17.03% and 14.18%, respectively. The activities of urease, dehydrogenase and fluorescein diacetate hydrolase (FDA) was improved, the catalase (CAT) activity decreased. Analysis of the microbial community diversity revealed the abundance of Proteobacteria, Actinobacteria, Firmicutes, and Gemmatimonadetes were significantly improved. The mechanism under the model is that E. cloacae acted as N-fixation by capturing N₂ from air. Biochar served as carrier, supporting better living environment for E. cloacae, also as adsorbent adsorbing N from fertilizer and from fixed N by E. cloacae, the adsorption in turn slower the N release. Altogether, the model promotes N utilization by plants, improves the soil environment, and reduces N pollution.

The preparation of slow-release fertilizers with biomass ash and water/waste acid solutions from desulfurization and denitrification of flue gas

In this study, a method of preparing fertilizers with the fly ash from biomass power plants and the waste acid solution from flue gas desulfurization and denitrification was disclosed. In addition, the study also explored the effects of added fine particles, unburned biochar, and other commercial fertilizers on soil water retention and slow-release effect of fertilizers. The analysis was done by comparing the aggregation degrees of crystalline salt and the variations of the chemical bonds. The experimental results showed that the added fine particles could effectively increase the water absorption of fertilizers, which helped to improve soil water retention. Meanwhile, the fine particles could strengthen the special adsorption of basic compounds containing N, P, and other nutrients by biochar and enhance the slow-release effect of fertilizers. Although adding part commercial fertilizers weakened the water absorption of fertilizers slightly, it had only a relatively small effect on the aggregation of water-soluble crystalline salt on the surfaces of fine particles and biochar. Furthermore, the microwave was applied to promote the absorption of N by unburned biochar, during which only small amounts of volatile were released and lost. The experiments had confirmed that microwave irradiation could promote the agglomeration of biochar on crystalline salt effectively, thus enhancing the slow-release effect of crystalline salt in fertilizers. Finally, pot experiments demonstrated that the self-prepared fertilizer improved plant growth by its better water absorption and slow-release properties during the whole growth period, which had promising application potential as the slow-release fertilizer in the plant growth field.

Development of biochar-impregnated alginate beads for the delivery of biocontrol agents for peanut aflatoxin

The competitive inhibition of aflatoxigenic fungi by non-aflatoxigenic Aspergillus flavus has proved to be an effective method to prevent and control peanut aflatoxin contamination, and most of the currently used inoculum carriers are grains. In this study, the reliability and efficiency of replacing grain kernels with novel chitosan-coated alginate-poly(N-isopropylacrylamide) (PNIPAAm) beads impregnated with biochar (CSACB) were evaluated. Characterisation of the beads was performed by SEM, thermogravimetry analysis (TGA), and swelling properties analyses. The optimised CSACB beads had good physical stability, shelf life, and entrapment efficiency. In addition, the water-holding capacity and porous structure were excellent, as the biochar provided a beneficial microenvironment for the attachment and microbial growth of the biocontrol fungus. The effect of reducing aflatoxin in peanuts was verified experimentally. Collectively, the novel CSACB beads are suitable carriers of non-aflatoxigenic A. flavus for the biocontrol of peanut aflatoxin.

Sustainable biochar: A facile strategy for soil and environmental restoration, energy generation, mitigation of global climate change and circular bioeconomy

The increasing agro-demands with the burgeoning population lead to the accumulation of lignocellulosic residues. The practice of burning agri-residues has consequences viz. Release of soot and smoke, nutrient depletion, loss of soil microbial diversity, air pollution and hazardous effects on human health. The utilization of agricultural waste as biomass to synthesize biochar and biofuels, is the pertinent approach for attaining sustainable development goals. Biochar contributes in the improvement of soil properties, carbon sequestration, reducing greenhouse gases (GHG) emission, removal of organic and heavy metal pollutants, production of biofuels, synthesis of useful chemicals and building cementitious materials. The biochar characteristics including surface area, porosity and functional groups vary with the type of biomass consumed in pyrolysis and the control of parameters during the process. The major adsorption mechanisms of biochar involve physical-adsorption, ion-exchange interactions, electrostatic attraction, surface complexation and precipitation. The recent trend of engineered biochar can enhance its surface properties, pH buffering capacity and presence of desired functional groups. This review focuses on the contribution of biochar in attaining sustainable development goals. Hence, it provides a thorough understanding of biochar's importance in enhancing soil productivity, bioremediation of environmental pollutants, carbon negative concretes, mitigation of climate change and generation of bioenergy that amplifies circular bioeconomy, and concomitantly facilitates the fulfilment of the United Nation Sustainable Development Goals. The application of biochar as seen is primarily targeting four important SDGs including clean water and sanitation (SGD6), affordable and clean energy (SDG7), responsible consumption and production (SDG12) and climate action (SDG13).

Biochar-based slow-release of fertilizers for sustainable agriculture: A mini review

Increasing global population and decreasing arable land pose tremendous pressures to agricultural production. The application of conventional chemical fertilizers improves agricultural production, but causes serious environmental problems and significant economic burdens. Biochar gains increasing interest as a soil amendment. Recently, more and more attentions have been paid to biochar-based slow-release of fertilizers (SRFs) due to the unique properties of biochar. This review summarizes recent advances in the development, synthesis, application, and tentative mechanism of biochar-based SRFs. The development mainly undergoes three stages: (i) soil amendment using biochar, (ii) interactions between nutrients and biochar, and (iii) biochar-based SRFs. Various methods are proposed to improve the fertilizer efficiency of biochar, majorly including in-situ pyrolysis, co-pyrolysis, impregnation, encapsulation, and granulation. Considering the distinct features of different methods, the integrated methods are promising for fabricating effective biochar-based SRFs. The in-depth understanding of the mechanism of nutrient loading and slow release is discussed based on current knowledge. Additionally, the perspectives and challenges of the potential application of biochar-based SRFs are described. Knowledge surveyed from this review indicates that applying biochar-based SRFs is a viable way of promoting sustainable agriculture.

Effect of Consecutive Application of Phosphorus-Enriched Biochar with Different Levels of P on Growth Performance of Maize for Two Successive Growing Seasons

Sustainable management of phosphorus (P) is one of the burning issues in agriculture because the reported P losses, when applied in the form of mineral fertilizer, give rise to another issue of water pollution as P is considered one of the limiting nutrients for eutrophication and so results in costly water treatments. In the present study, the enrichment of biochar with mineral P fertilizer was supposed to reduce such losses from the soil. Additionally, P can also be recycled through this technique at the same time as biochar is derived from biomass. Biochar was prepared using wheat straw followed by its enrichment with di-ammonium phosphate (DAP) at the ratio of 1:1 on a w/w basis. The first pot trial for spring maize (cv. Neelam) was conducted using phosphorus-enriched biochar (PEB) at 0% and 1% with different levels of recommended P (0%, 25%, 50%, and 100%). The treatments were arranged factorially under a complete randomized design (CRD) with three replications. After harvesting the spring maize, pots were kept undisturbed, and a second pot trial was conducted for autumn maize in the same pots to assess the residual impact of 1% PEB. In the second pot trial, only inorganic P was applied to respective treatments because the pots contained 1% PEB supplied to spring maize. The results revealed that the application of 1% PEB at P level 50% significantly increased all the recorded plant traits (growth, yield, and physiological and chemical parameters) and some selected properties of post-harvest soil (available P, organic matter, and EC) but not soil pH. In terms of yield, 1% PEB at 50% P significantly increased both the number of grains and 100-grain weight by around 30% and 21% in spring and autumn maize, respectively, as compared to 100% P without PEB. It is therefore recommended that P-enriched biochar should be used to reduce the inorganic P fertilizer inputs; however, its application under field conditions should be assessed in future research.

Mechanical Activation of Smectite-Based Nanocomposites for Creation of Smart Fertilizers

This research presents the mechanical creation of smart fertilizers from a mixture of smectite and urea in a 3:2 ratio by using the planetary milling technique. The smectite–urea composites show intercalation between urea and mineral, which increases steadily with increasing activation time. A shift of X-Ray Diffraction basal reflections, intensities of Fourier transform infrared spectroscopy (FTIR) peaks, and weight losses in thermogravimetric analysis (TG) document the systematic crystallo-chemical changes of the composites related to nitrogen interaction with activation. Observations of the nanocomposites by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) corroborate the inference. Nitrogen intercalates with smectite in the interlayer space and remains absorbed either within micro-aggregates or on the surface of activated smectites. Soil leaching tests reveal a slower rate of nitrogen than that of traditional urea fertilizers. Different forms of nitrogen within the composites cause their differential release rates to the soil. The formulated nanocomposite fertilizer enhances the quality and quantity of oat yield.

Biochar Phosphate Fertilizer Loaded with Urea Preserves Available Nitrogen Longer than Conventional Urea

Biochar, a carbon-rich material obtained by pyrolysis of organic wastes, is an attractive matrix for loading nutrients and producing enhanced efficiency fertilizers. In this study, poultry litter (PL) was enriched with phosphoric acid (H3PO4) and MgO to produce a biochar-based fertilizer (PLB), which was loaded with urea in a 4:5 ratio (PLB:urea, w/w) to generate a 15–15% N–P slow-release fertilizer (PLB–N) to be used in a single application to soil. A greenhouse experiment was carried out in which a common bean was cultivated followed by maize to evaluate the agronomic efficiency and the residual effect of fertilization with PLB–N in Ultisol. Six treatments were tested, including four doses of N (100, 150, 200, and 250 mg kg−1) via PLB–N in a single application, a control with triple superphosphate (TSP—applied once) and urea (split three times), and a control without N-P fertilization. The greatest effect of PLB–N was the residual effect of fertilization, in which maize showed a linear response to the N doses applied via PLB–N but showed no response to conventional TSP + urea fertilization. Biochar has the potential as a loading matrix to preserve N availability and increase residual effects and N-use efficiency by plants.

Combination of modified biochar and polyurea microcapsules to co-encapsulate a fumigant via interface polymerization for controlled release and enhanced bioactivity

BACKGROUND

Soil fumigants-the most effective agrochemicals for managing soil-borne diseases-have been used extensively. However, high volatility, moderate toxicity and insufficient effective duration considerably limit their application. In the present study, interface polymerization was used to combine modified biochar (BC) and polyurea microcapsules (MCs) to co-encapsulate allyl isothiocyanate (AITC), developing a model fumigant for controlled release (AITC@BC-MCs).

RESULTS

The physical characteristics of BC modified by sand-milling were significantly improved. In addition, chemical properties and morphological features of AITC@BC-MCs characterized by integrated methods revealed successful preparation of BC-MCs. Compared with monolayer MCs, BC-MCs could significantly delay AITC release owing to the composite obstruction effect. Moreover, modifying BC endowed the cargo molecules with a pH-responsive release property. Additionally, this composite showed a longer persistent duration by prolonging AITC degradation half-life, which was 3.2-3.5-fold greater than that of the AITC technical concentrate under different soil conditions. Finally, the control efficacy of the AITC@BC-MC against pathogens, including nematodes and fungi, as well as against weeds was significantly enhanced at the same dose, but the composite did not inhibit seed germination and growth after 10 days when fumigated soil was aerated.

CONCLUSION

Construction of a composite encapsulation system enhanced pesticide efficacy, reduced dose via controlled release and delayed fumigant degradation in soil, indicating the great potential of this strategy for developing an effective and environmentally friendly fumigant formulation. © 2021 Society of Chemical Industry.

Synthesis and Characterization of Slow-Release Fertilizer Hydrogel Based on Hydroxy Propyl Methyl Cellulose, Polyvinyl Alcohol, Glycerol and Blended Paper

In this study, biodegradable slow-release fertilizer (SRF) hydrogels were synthesized from hydroxyl propyl methyl cellulose (HPMC), polyvinyl alcohol (PVA), glycerol and urea (SRF1) and HPMC, PVA, glycerol, urea and blended paper (SRF2). The fertilizer hydrogels were characterized by SEM, XRD and FTIR. The swelling capacity of the hydrogels in both distilled and tap water as well as their water retention capacity in sandy soil were evaluated. The hydrogels had good swelling capacity with maximum swelling ratio of 17.2 g/g and 15.6 g/g for SRF1 and SRF2 in distilled, and 14.4 g/g and 15.2 g/g in tap water, respectively. The water retention capacity of the hydrogels in sandy soil exhibited higher water retention when compared with soil without the (SRFs). The soil with the hydrogels was found to have higher water retention than the soil without the hydrogels. The slow-release profile of the hydrogels was also evaluated. The result suggested that the prepared fertilizer hydrogels has a good controlled release capacity. The blended paper component in SRF2 was observed to aid effective release of urea, with about 87.01% release in soil at 44 days compared to the pure urea which was about 97% release within 4 days. The addition of blended paper as a second layer matrix was found to help improve the release properties of the fertilizer. The swelling kinetic of the hydrogel followed Schott's second order model. The release kinetics of urea in water was best described by Kormeye Peppas, suggesting urea release to be by diffusion via the pores and channels of the SRF, which can be controlled by changing the swelling of the SRF. However, the release mechanism in soil is best described by first order kinetic model, suggesting that the release rate in soil is depended on concentration and probably on diffusion rate via the pores and channels of the SRF.

Controlled release fertilizer: A review on developments, applications and potential in agriculture

Controlled release fertilizer (CRF) plays a crucial yet necessary part in the sustainable agriculture industry. An alarming rise in call for crop production directly influences the increasing need for synthetically derived fertilizers and pesticides production. The application of CRF has been a gamechanger as an environmentally sustainable pathway to increase crop yields by paving desired phase of plant growth via a direct or indirect mechanism. The mechanism of CRF does not only decreases nutrient dissipation due to volatilization and leaching, but also provides a precisely appropriate nutrient release design that is suitable in the physiological and biochemical aspect of the plant growth. However, CRF is not deployed on larger scale of commercial agriculture practices due to being expensive, has relatively low efficiency in releasing nutrients and its coatings are largely composed of petroleum-based synthetic polymers. Alternatively, there are many polymers derived from renewable and biodegradable sources that can be used as coating material for CRF in the form of bio-nanocomposites. Having said that, there is an apparent gap between the mechanism of the CRFs for promoting plant growth and the prominent role of the nanocomposites especially bio-nanocomposites as coating material for CRF synthesis, thus the importance of nanotechnology application in enhancing the effectiveness of CRF. Therefore, this review attempts to bridge the stated gap and summarizes the comprehensive developments, application mechanisms and future potential of CRF as a fertilizer for crop sustainability.

Synthesis of a slow-release fertilizer composite derived from waste straw that improves water retention and agricultural yield

To enhance waste straw utilization and improve fertilizer efficiency, a novel semi-interpenetrating polymer network fertilizer (CMCK-g-PAA/PDMUP) was prepared from straw cellulose and linear polymer by solution polymerization. Polydihydroxymethyl-urea potassium phosphate (PDMUP) was included to supply nitrogen, phosphorus, and potassium nutrients. Characterization of CMCK-g-PAA/PDMUP with FTIR, XPS, XRD, and SEM techniques provided evidence for semi-interpenetrating polymer networks (semi-IPNs) and component interactions. The prepared product exhibited excellent water absorbency (681.3 g/g) and enhanced the soil's water-retention capacity. Cumulative release of N, P, and K was 56.1%, 64.3%, and 74.1%, respectively, after 40 days-meeting a Committee of European Normalization (CEN) standard. Agricultural application of CMCK-g-PAA/PDMUP promoted wheat growth. Desirable water retention, slow-release properties, and wheat growth effects highlight the product's potential for improving agriculture.

Co-application of high temperature biochar with 3,4-dimethylpyrazole-phosphate treated ammonium sulphate improves nitrogen use efficiency in maize

This study aimed on the increasing nitrogen use efficiency (NUE) of maize via the use of high temperature produced biochar (700 °C). Maize was grown to maturity on two contrasting soils (acidic Cambisol and neutral Chernozem) in pots with a treatment of biochar co-applied with ammonium sulphate stabilised by a nitrification inhibitor (3,4-dimethylpyrazole-phosphate, DMPP) or un-stabilised. The combination of biochar with ammonium sulphate containing DMPP increased maize biomass yield up to 14%, N uptake up to 34% and NUE up to 13.7% compared to the sole application of ammonium sulphate containing DMPP. However, the combination of biochar with un-stabilised ammonium sulphate (without DMPP) had a soil-specific influence and increased maize biomass only by 3.8%, N uptake by 27% and NUE by 11% only in acidic Cambisol. Further, the biochar was able to increase the uptake of phosphorus (P) and potassium (K) in both stabilised and un-stabilised treatments of ammonium sulphate. Generally, this study demonstrated a superior effect from the combined application of biochar with ammonium sulphate containing DMPP, which improved NUE, uptake of P, K and increased maize biomass yield. Such a combination may lead to higher efficiency of fertilisation practices and reduce the amount of N fertiliser to be applied.

Synthesis, Characterization, and Encapsulation of Novel Plant Growth Regulators (PGRs) in Biopolymer Matrices

Novel plant growth regulators (PGRs) based on the derivatives of dehydroamino acids 2,3-dehydroaspartic acid dimethyl ester (PGR1), Z-isomer of the potassium salt of 2-amino-3-methoxycarbonylacrylic acid (PGR2) and 1-methyl-3-methylamino-maleimide (PGR3) have been synthesized and their growth-regulating properties investigated. Laboratory testing revealed their plant growth-regulating activity. PGR1 showing the most stimulating activity on all laboratory tested cultures were used in field experiments. Results showed that PGR1 is a highly effective environmentally friendly plant growth regulator with effects on different crops. Biopolymeric microcapsule formulations (chitosan/alginate microcapsule loaded with PGR) suitable for application in agriculture were prepared and characterized. Physicochemical properties and release profiles of PGRs from microcapsule formulations depend on the molecular interactions between microcapsule constituents including mainly electrostatic interactions and hydrogen bonds. The differences in the microcapsule formulations structure did not affect the mechanism of PGRs release which was identified as diffusion through microcapsules. The obtained results opened a perspective for the future use of microcapsule formulations as new promising agroformulations with a sustained and target release for plant growth regulation.

Biodegradable Polymer Coated Granular Urea Slows Down N Release Kinetics and Improves Spinach Productivity

Low nitrogen (N) utilization efficiency due to environmental N losses from fertilizers results in high-cost on-farm production. Urea coating with biodegradable polymers can prevent these losses by controlling the N release of fertilizers. We calculated N release kinetics of coated granular with various biodegradable polymeric materials and its impact on spinach yield and N uptake. Different formulations were used, (i) G-1: 10% starch + 5% polyvinyl alcohol (PVA) + 5% molasses; (ii) G-2: 10% starch + 5% PVA + 5% paraffin wax (PW); (iii) G-3: 5% gelatin + 10% gum arabic + 5% PW; (iv) G-4: 5% molasses + 5% gelatin + 10% gum arabic, to coat urea using a fluidized bed coater. The morphological and X-ray diffraction (XRD) analyses indicated that a uniform coating layer with no new phase formation occurred. In the G-2 treatment, maximum crushing strength (72.9 N) was achieved with a slowed-down N release rate and increased efficiency of 31%. This resulted in increased spinach dry foliage yield (47%), N uptake (60%) and apparent N recovery (ANR: 130%) from G-2 compared to uncoated urea (G-0). Therefore, coating granular urea with biodegradable polymers is a good choice to slower down the N release rate and enhances the crop yield and N utilization efficiency from urea.

Surface properties and suspension stability of low-temperature pyrolyzed biochar nanoparticles: Effects of solution chemistry and feedstock sources

Intensive application of biochar requires better understanding of their environmental behaviors such as stability, fate, and mobility. The release of bulk biochar into biochar nanoparticles (NPs) may bring risks because of their potential flowing into downstream water bodies with nutrients/containments attached. Low-temperature pyrolyzed biochars, namely fruit tree branch biochar of 350/450/550 °C (FB350, FB450 and FB550), corn straw biochar of 350 °C (CB350) and peanut straw biochar of 350 °C (PB350), were produced, and their NPs were extracted. The yield, elemental composition, mineral composition, surface functional groups and zeta potential of biochar NPs were characterized. Subsequently their suspension stability was evaluated in NaCl and CaCl₂ solutions by dynamic light scattering technique. The Hamaker constants and particle interaction energy of the biochar NPs were calculated by adopting Derjaguin-Landau-Verwey-Overbeek theory. For biochar NPs of same feedstock, the stability of FB350/450/550-NPs could be predicted well by their zeta potential values. The types of their surface functional groups were the same while their adsorption intensity differed. The scenarios for biochar NPs of different feedstock sources were different, that is, inconsistent variation was observed between their zeta potential and suspension stability, which were rooted in the variable type and quantity of surface functional groups. In conclusion, feedstock was the most significant factor that influenced the suspension stability of biochar NPs, followed by the pyrolysis temperature and solution chemistry, which were highly dependent on surface potential. The findings provide references for the environmental risk evaluation of biochar NPs and reasonable application of biochar in field.

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.

Slow-Release Urea Prills Developed Using Organic and Inorganic Blends in Fluidized Bed Coater and Their Effect on Spinach Productivity

The application of urea-based fertilizers in developing countries has gained significant momentum over time. urea usage is to meet demand and supply gap of food resources as world population is increasing at a fast pace. urea contains largest content of nitrogen (46%) among all the solid nitrogenous fertilizers. However, main drawback of urea is its higher dissolution rate. After soil application, most of urea nitrogen is lost through a leaching, runoff, nitrification-denitrification and ammonia volatilization. To tackle urea related environmental pollution, development of slow-release urea fertilizer is a need of the hour and this would also increase product use efficiency in terms of crop productivity and its N uptake. We studied the usage of polymeric materials in combination with inorganic substances like sulfur and plaster of Paris as effective and biodegradable coating substances for urea prills. For coating on urea prills, fluidized bed coater was used whereas paraffin wax and molasses were used as binding agents. The urea was coated with four different formulations, i.e., C-1: PVA 5% + plaster of Paris 10% + sulfur 5% + paraffin wax 2%, C-2: PVA 5% + starch 10% + sulfur 5% + paraffin wax 2%, C-3: gelatin 5% + plaster of Paris 10% + sulfur 5% + paraffin wax 2% and C-4: PVA 5% + starch 10% + sulfur 5% + paraffin wax 2.5% + molasses 2.5%. Each formulation along with uncoated urea prills (C-0) were evaluated for characterization and N release kinetics. All the formulations along with uncoated urea were applied to spinach crop in pot experiment. A control (No N: untreated) was also kept. Spinach biomass yield and N uptake were determined. The formulation C-1 yielded highest urea-N release efficiency and spinach N uptake of6.87% and 1.93 g N/pot, respectively. Themodified Schwarz and Sinclair formula gave the excellent representation of release of nutrient-N from coated urea prills. It is concluded that coating urea prills with organic and inorganic blends is better option to slow down N release kinetics and improve spinach productivity. Therefore, by using coated fertilizers, farmers can improve agro-environmental value of urea, worldwide.

Algal biomass from wastewater: soil phosphorus bioavailability and plants productivity

The cultivation of microalgae in wastewater allows to obtain a biomass concentrated in nutrients and organic material. This biomass added to phosphate fertilizers can promote a slow release of the nutrient and consequently a higher absorption of phosphorus (P). The objective of this study was to investigate P uptake by plants subjected to triple superphosphate (TSP) fertilization, added with microalgae biomass (MB) grown in wastewater. TSP was added with different MB proportions in order to verify if there would be a different behaviour in P release for millet (Pennisetum glaucum L.) plants. With the proportion that maximized P accumulation in plants, a second experiment was carried out to investigate whether MB exerts influence of P diffusion in the soil. Finally, a third trial was conducted in a greenhouse, where TSP and TSP + 12% MB were applied to the soil under different phosphorus doses in corn (Zea mays L.). The proportion of MB in TSP that maximized the increase of P content and concentration in plants was approximately 12% MB. From this proportion, a reduction in the values of the variables analysed in the plant with the increase of the proportion of MB in the biofertilizer was observed. Similar behaviour was observed when evaluating P diffusion in sandy and clay soils. Fertilizers TSP and TSP + 12% MB showed no difference in P diffusion in the soil, while the ratio of 30% MB clearly impaired P diffusion. In a greenhouse, the P content presented significant difference for the tests carried out with TSP and TSP + 12% MB fertilizer, in which the latter provided higher P recovery rate by plants. Therefore, MB added to TSP had a positive influence on plant development and its P recovery capacity when applied in a proportion of 12% MB to the fertilizer mass.

Biochar bound urea boosts plant growth and reduces nitrogen leaching

Over use of N fertilizers, most commonly as urea, had been seriously concerned as a major source of radiative N (Nr) for severe environment impacts through leaching, volatilization, and N₂O emission from fertilized croplands. It had been well known that biochar could enhance N retention and use efficiency by crops in amended croplands. In this study, a granular biochar-mineral urea composite (Bio-MUC) was obtained by blending urea with green waste biochar supplemented with clay minerals of bentonite and sepiolite. This Bio-MUC material was firstly characterized by microscopic analyses with FTIR, SEM-EDS and STEM, subsequently tested for N leaching in water in column experiment and for N supply for maize in pot culture, compared to conventional urea fertilizer (UF). Microscopic analyses indicated binding of urea N to particle surfaces of biochar and clay minerals in the Bio-MUC composite. In the leaching experiment over 30 days, cumulative N release as NH₄⁺-N and of dissolved organic carbon (DOC) was significantly smaller by >70% and by 8% from the Bio-MUC than from UF. In pot culture with maize growing for 50 days, total fresh shoot was enhanced by 14% but fresh root by 25% under Bio-MUC compared to UF. This study suggested that N in the Bio-MUC was shown slow releasing in water but maize growth promoting in soil, relative to conventional urea. Such effect could be related mainly to N retention by binding to biochar/mineral surfaces and partly by carbon bonds of urea to biochar in the Bio-MUC. Therefore, biochar from agro-wastes could be used for blending urea as combined organo/mineral urea to replace mineral urea so as to reduce N use and impacts on global Nr. Of course, how such biochar combined urea would impact N process in soil-plant systems deserve further field studies.

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.

Preparation and characterization of alginate-kelp biochar composite hydrogel bead for dye removal

The alginate-kelp biochar composite hydrogel bead (Alg-KBC) was successfully developed via physical crosslinking with Ca2+. The composite material was characterized by scanning electron microscopy (SEM), energy dispersive spectroscopy (EDS), Fourier transform infrared spectroscopy (FTIR), inductively coupled plasma optical emission spectrometry (ICP-OES), and elemental analyzer. The Alg-KBC showed high removal capacity for crystal violet (CV), from aqueous solution (33.8% more than that of the pristine alginate bead). The adsorption isotherm data were fitted to the nonlinear forms of the Langmuir, Freundlich, and Redlich-Peterson isotherm models. Also, the adsorption kinetics data were analyzed with the nonlinear forms of the pseudo-first-order, pseudo-second-order, and intra-particle diffusion models. Both chemisorption and physisorption with an indispensable role of external mass transfer and stagewise pore diffusion were essential in the adsorption process. Thus, by impregnating biochar powder in alginate, a bio-platform, a composite hydrogel bead which has higher affinity for cationic dye in aqueous medium and also eliminates the onerous task of separating biochar powder from the adsorbate solution, was obtained. Hence, the Alg-KBC can be considered for efficient dye removal in the wastewater treatment process.

Mechanochemical Preparation of Slow Release Fertilizer Based on Glauconite–Urea Complexes

We investigated the mechanochemical synthesis of complex slow release fertilizers (SRF) derived from glauconite. We studied the effectiveness of the mechanical intercalation of urea into glauconite using planetary and ring mills. The potassium-nitric complex SRFs were synthesized via a mechanochemical method mixing glauconite with urea in a 3:1 ratio. The obtained composites were analyzed using X-ray diffraction analysis, scanning electron microscopy, X-ray fluorescence analysis, and infrared spectroscopy. The results show that as duration of mechanochemical activation increases, the mineralogical, chemical, and structural characteristics of composites change. Essential modifications associated with a decrease in absorbed urea and the formation of microcrystallites were observed when the planetary milling time increased from 5 to 10 min and the ring milling from 15 to 30 min. Complete intercalation of urea into glauconite was achieved by 20 min grinding in a planetary mill or 60 min in a ring mill. Urea intercalation in glauconite occurs much faster when using a planetary mill compared to a ring mill.

A Biochar-Based Route for Environmentally Friendly Controlled Release of Nitrogen: Urea-Loaded Biochar and Bentonite Composite

Biochar-based fertilizers have attracted increased attention, because biochar can improve the soil fertility, promote plant growth and crop yield. However, biochar-based controlled release nitrogen fertilizers (BCRNFs) still face problems because of the high cost, inefficient production technology, instability of nitrides, and the challenge associated with the controlled release of nutrients. In this study, we hydrothermally synthesised novel BCRNFs using urea-loaded biochar, bentonite and polyvinyl alcohol for controlled release of nutrients. Scanning electron microscopy and gas adsorption were conducted to identify the urea-loading and storage of bentonite in the inner pores of the biochar particles. X-ray diffraction, Fourier transform infrared spectroscopic and X-ray photoelectron spectroscopic studies demonstrated that strengthening the interactions among biochar, urea, and bentonite, helps control the moisture diffusion and penetration of bentonite, thereby leading to nutrient retention. The BCRNF showed significantly improved nutrient release characteristic compared with that of a mixture of biochar and urea. This urea-bentonite composite loaded with urea provides control over the release of nutrients stored in the biochar. BCRNF, especially those produced hydrothermally, can have potential applications in sustainable food security and green agriculture.

A review on biochar modulated soil condition improvements and nutrient dynamics concerning crop yields: Pathways to climate change mitigation and global food security

The beneficial role of biochar on improvement of soil quality, C sequestration, and enhancing crop yield is widely reported. As such there is not much consolidated information available linking biochar modulated soil condition improvement and soil nutrient availability on crop yields. The present review paper addresses the above issues by compilation of world literature on biochar and a new dimension is introduced in this review by performing a meta-analysis of published data by using multivariate statistical analysis. Hence this review is a new in its kind and is useful to the broad spectrum of readers. Generally, alkalinity in biochar increases with increase in pyrolysis temperature and majority of the biochar is alkaline in nature except a few which are acidic. The N content in many biochar was reported to be more than 4% as well as less than 0.5%. Poultry litter biochar is a rich source of P (3.12%) and K (7.40%), while paper mill sludge biochar is higher in Ca content (31.1%) and swine solids biochar in Zn (49810 mg kg^-1), and Fe (74800 mg kg^-1) contents. The effect of biochar on enhancing soil pH was higher in Alfisol, Ferrosol and Acrisol. Soil application of biochar could on an average increase (78%), decrease (16%), or show no effect on crop yields under different soil types. Biochar produced at a lower pyrolysis temperature could deliver greater soil nutrient availabilities than that prepared at higher temperature. Principal component analysis (PCA) of available data shows an inverse relationship between [pyrolysis temperature and soil pH], and [biochar application rate and soil cation exchange capacity]. The PCA also suggests that the original soil properties and application rate strongly control crop yield stimulations via biochar amendments. Finally, biochar application shows net soil C gains while also serving for increased plant biomass production that strongly recommends biochar as a useful soil amendment. Therefore, the application of biochar to soils emerges as a 'win-win strategy' for sustainable waste management, climate change mitigation and food security.

Biobased Polyurethane, Epoxy Resin, and Polyolefin Wax Composite Coating for Controlled-Release Fertilizer

Reducing the use of petrochemical products in coated controlled-release fertilizers while regulating the release rate is a popular research topic in the field of controlled-release fertilizers. In this study, a novel biobased polyurethane (BPU), epoxy resin (ER), and polyolefin wax (PW) composite coating method for the controlled release of urea was successfully established. The method involved: (1) the use of PW as a modified inner coating, which improved fertilizer surface performance and reduced urea surface roughness; (2) the degradable BPU film was synthesized with liquefied starch (LS) as the outer coating material; and (3) epoxy resin is a protective layer, which improved the hydrophobicity of the coated urea for controlled release. The chemical structure, thermostability and microscopic morphology of composite-coated urea (CCU) were examined by Fourier transform infrared (FTIR) spectroscopy, thermogravimetric analysis (TGA), and scanning electron microscopy (SEM), respectively. A central composite design of response surface methodology was used to examine the effects of different film percentage, PW contents, and BPU/ER ratios on nutrient release behavior. The results showed that PW optimized the fluidity, thermal insulation properties, and microscopic surface of the particles and improved the uniformity of the heating of urea. When the same amount of ER was used, the CCU showed a 3-fold increase in the release period compared to that of the cross-linked interpenetrating coated urea. Polynomial mathematical models were established for CCU preparation and could be an effective tool for manufacturing CCUs with specific nutrient release characteristics that could meet the nutrient requirements of crops in different cropping systems. The new coating method introduced in this study could guide the development of a new generation of biobased controlled-release fertilizers.