Impact of Modifications from Potassium Hydroxide on Porous Semi-IPN Hydrogel Properties and Its Application in Cultivation

This study synthesized and modified a semi-interpenetrating polymer network hydrogel from polyacrylamide, N,N'-dimethylacrylamide, and maleic acid in a potassium hydroxide solution. The chemical composition, interior morphology, thermal properties, mechanical characteristics, and swelling behaviors of the initial hydrogel (SH) and modified hydrogel (SB) in water, salt solutions, and buffer solutions were investigated. Hydrogels were used as phosphate fertilizer (PF) carriers and applied in farming techniques by evaluating their impact on soil properties and the growth of mustard greens. Fourier-transform infrared spectra confirmed the chemical composition of SH, SB, and PF-adsorbed hydrogels. Scanning electron microscopy images revealed that modification increased the largest pore size from 817 to 1513 µm for SH and SB hydrogels, respectively. After modification, the hydrogels had positive changes in the swelling ratio, swelling kinetics, thermal properties, mechanical and rheological properties, PF absorption, and PF release. The modification also increased the maximum amount of PF loaded into the hydrogel from 710.8 mg/g to 770.9 mg/g, while the maximum % release of PF slightly increased from 84.42% to 85.80%. In addition, to evaluate the PF release mechanism and the factors that influence this process, four kinetic models were applied to confirm the best-fit model, which included zero-order, first-order, Higuchi, and Korsmeyer-Peppas. In addition, after six cycles of absorption and release in the soil, the hydrogels retained their original shapes, causing no alkalinization or acidification. At the same time, the moisture content was higher as SB was used. Finally, modifying the hydrogel increased the mustard greens' lifespan from 20 to 32 days. These results showed the potential applications of modified semi-IPN hydrogel materials in cultivation.

Assessment of energy cane bagasse-derived cellulosic microfiber hydrogels on the growth of potted chili peppers

Energy cane (Saccharum spp.) bagasse, a type of biomass waste, is often underutilized, burned, or left to dispose of itself. This research aimed to evaluate the potential of converting this bagasse into high-value cellulosic microfiber hydrogels (CMH) for water conservation and potted chili (Capsicum annuum) plant growth. CMH offers a biodegradable alternative to synthetic polyacrylamide (PA) hydrogels and provides the dual benefit of improved water use efficiency and reduced environmental impact due to their ability to naturally break down in the soil. In this study, CMH and PA hydrogels were compared for water retention value (WRV), and reswelling kinetics (RK), as well as their effects on plant height, leaf count, root-to-shoot ratios (R:S ratio), and soil moisture retention. Two versions of CMH, CMH65 and CMH60, were prepared with varying cellulose-chitosan ratios: 65:35 and 60:40, respectively. The hydrogels were tested at four concentrations (0, 0.5, 1.0, and 2.0% w/w) by being mixed in Promix® soil. Observations were recorded over a 16-day period without additional water. Also, the WRV of hydrogels at 240 min and RK (10-180 min) were compared over three swelling-deswelling cycles. The PA hydrogel exhibited higher WRV (exceeding 450%) compared to CMH (45%). However, PA led to reduced plant height, leaf count, and R:S ratio when compared to higher concentrations of CMH65 and CMH60. In general, CMH60 (0.5% and 2%) exhibited superior plant growth. All hydrogels exhibited a significant decrease (p < 0.05) in WRV across successive cycles. Notably, during cycle 2, both CMH65 and CMH60 peaked in WRV at 10 and 20 min, respectively, compared to cycle 1. This study demonstrates the potential of bagasse-derived hydrogels as a value-added product for water conservation and crop growth.

The water-retaining functional slow-release fertilizer modified by carboxymethyl chitosan

To solve the problem of shortage of agricultural water resources and low utilization rate of fertilizer, a slow-release fertilizer based on chitosan modified water retention function was developed. Solution polymerization and semi-interpenetrating network technology were used to load urea aldehyde into carboxymethyl chitosan superabsorbent resin network. This technology realizes the simultaneous slow release of nutrients and water by using modified chitosan, which has important implications for the application of chitosan in agriculture to regulate the soil water and fertilizer conditions. The optimal preparation conditions were: MBA 0.07 %, KPS 0.8 %, AM to AA mass ratio of 0.3:1, CMC content of 10 %, AA neutralization degree 85 %, UF 20 %, AA+AM mass sum of 10 g, reaction temperature 70 °C and reaction time 2 h. The maximum water absorption rate of the optimized NC reached 172.3 g/g. The cumulative release of nitrogen in 30 days was 83.67 %. The application of NC in sandy soil promoted seed germination and growth. The comprehensive results indicate that NC has broad application prospects in arid areas based on its excellent water retention and nutrient release performance.

Novel nano-fertilizers derived from drinking water industry waste for sustained release of macronutrients: performance, kinetics and sorption mechanisms

Nanotechnology has emerged as a promising approach for the controlled release of nutrients, particularly phosphorus and potassium. These essential plant nutrients are often applied in excess, leading to environmental pollution and loss of efficiency in crop production. Innovative economic and highly efficient fertilizers are urgently needed to achieve the targeted crop production worldwide in the presence of limited land and water resources. Therefore, in this study, novel, eco-friendly, cost-effective and enhanced efficiency nano-enabled fertilizers, NEF (nWTF1and nWTF2) were synthesized by impregnation of nanostructured water treatment residuals (nWTR) with (KH2PO4 + MgO) at 1:1 and 3:1 (w/w) ratios respectively using a planetary ball mill. The nWTR, nWTF1 and nWTF2 were extensively characterized. The water retention behavior and the sustained release of nutrients from the fabricated nano-enabled fertilizers (nWTF1 and nWTF2) in distilled water and sandy soil were investigated and monitored over time. The water retention capacity of the soil treated with nWTF2 after 26 days was 9.3 times higher than that of soil treated with conventional fertilizer. In addition, the nWTF2 exhibited lower release rates of P, K and Mg nutrients for longer release periods in comparison with the conventional fertilizers. This is a significant advantage over traditional fertilizers, which release nutrients quickly and can lead to leaching and nutrient loss. The main interaction mechanisms of PO4-K-Mg ions with nWTR surface were suggested. The results of the kinetics study revealed that power function was the best suitable model to describe the kinetics of P, K and Mg release data from NEF in water and soil. The produced NEF were applied to Zea maize plants and compared to commercial chemical fertilizer control plants. The obtained results revealed that the nano-enabled fertilizers (nWTF1 and nWTF2) significantly promoted growth, and P content compared with the commercial chemical fertilizer treated plants. The present work demonstrated the power of nano enabled fertilizers as efficient and sustained release nano-fertilizers for sustainable agriculture and pollution free environment.

Eco-friendly nano-enabled fertilizers derived from date industry waste for sustainable and controlled-release of P, K and Mg nutrients: sorption mechanisms, controlled-release performance and kinetics

Development of nano-enabled fertilizers from green waste is one of the effective options to enhance global agricultural productions and minimize environmental pollution. In this study, novel, eco-friendly and cost-effective nano- enabled fertilizers (NEF) were synthesized using the planetary ball milling procedure. The NEF (nDPF1and nDPF2) were prepared by impregnation of nanostructured date palm pits (nDPP) with (KH2PO4 + MgO) at 1:1 and 3:1 (w/w) ratios respectively. The nDPP, nDPF1 and nDPF2 were extensively characterized. The produced nano-fertilizers enhanced soil water retention capacity with nDPF2 being the most effective. The water retention capacity of nDPF2 treated soil was 5.6 times higher than that of soil treated with conventional fertilizers. In addition, the nDPF2 exhibited superior sustained lower release rates of P, K and Mg nutrients for longer release periods in comparison with the conventional fertilizers. For instance, P cumulative release percentages from conventional fertilizers, nDPF1 and nDPF2 in soil reached 22.41%, 10.82 and 8.9% respectively within 384 h. Findings from FTIR and XPS analyses suggested that hydrogen bonding and ligand exchange were the main interaction mechanisms of PO4-K-Mg ions with nDPP surface. The released kinetics data of the NEF revealed that power function was the best suitable model to describe the kinetics of P, K and Mg release data from NEF in water and soil. Pot study ascertained that the nano-enabled fertilizers (nDPF1 and nDPF2) significantly promoted biomass production and nutrient uptake of maize plants as compared to commercial fertilizer treated plants. The present work demonstrated the potential of NEF to increase nutrients uptake efficiency, mitigate moisture retention problem in arid soils and reduce nutrients loss through leaching and safeguard the environment.

Cellulosic wastepaper modified starch/ itaconic acid/ acrylic acid-based biodegradable hydrogel as a sustain release of NPK fertilizer vehicle for agricultural applications

In this work, wastepaper powder was used as a modifying agent for a biodegradable hydrogel composite of starch, itaconic acid, and acrylic acid. After the addition of an optimum amount of the modifying agent, the swelling ability of the hydrogel was enhanced from 503 g/g to 647 g/g. Further, the hydrogel was also used for sustained release of NPK fertilizer and subsequent effect of the fertilizer loaded hydrogel in okra seed germination was also studied. The NPK loaded-hydrogel showed good sustained-release behavior and 98 % of N, 81 % of P and 95 % of K release were observed after 20th day of incubation. Moreover, the release study was explained by using different kinetic models. In seed germination study, a higher and faster germination rate for okra seeds was observed in case of NPK loaded hydrogel compared to the control system, which was attributed to the synergistic effect of essential macronutrients (N, P, and K) and water that were inside the hydrogel. Most importantly, the hydrogel was found to be biodegradable by using soil burial method and further confirmed by FTIR and SEM analyses. Thus, this work provides an efficient way for utilization of wastepaper in the production of a biodegradable hydrogel for agricultural applications.

Release Kinetics of Potassium, Calcium, and Iron Cations from Carboxymethyl Cellulose Hydrogels at Different pH Values

In an in-depth study of the mechanism of cation release from carboxymethyl cellulose hydrogels synthesized through Schiff base reaction, we analyze the differences in the release kinetics of potassium, calcium, and iron cations with Peleg model at pH values of pH 3.5 and pH 8.5 using ICP-OES (inductively coupled plasma optical emission spectroscopy) technique.

Progress in the Preparation of Stimulus-Responsive Cellulose Hydrogels and Their Application in Slow-Release Fertilizers

Agriculture is facing challenges such as water scarcity, low fertilizer utilization, food security and environmental sustainability. Therefore, the development of slow-release fertilizer (SRF) with controlled water retention and release is particularly important. Slow-release fertilizer hydrogel (SRFH) has a three-dimensional (3D) network structure combined with fertilizer processing, displaying excellent hydrophilicity, biocompatibility and controllability. Cellulose has abundant hydroxyl groups as well as outstanding biodegradability and special mechanical properties, which make it a potential candidate material for the fabrication of hydrogels. This work would analyze and discuss various methods for preparing stimulus-responsive cellulose hydrogels and their combinations with different fertilizers. Moreover, the application and release mechanism of stimulus-responsive cellulose hydrogels in SRF have been summarized as well. Finally, we would explore the potential issues of stimulus-responsive cellulose hydrogels serving as an SRF, propose reasonable solutions and give an outlook of the future research directions.

Significance of biopolymer-based hydrogels and their applications in agriculture: a review in perspective of synthesis and their degree of swelling for water holding

Hydrogels are three-dimensional polymer networks that are hydrophilic and capable of retaining a large amount of water. Hydrogels also can act as vehicles for the controlled delivery of active compounds. Bio-polymers are polymers that are derived from natural sources. Hydrogels prepared from biopolymers are considered non-toxic, biocompatible, biodegradable, and cost-effective. Therefore, bio-polymeric hydrogels are being extensively synthesized and used all over the world. Hydrogels based on biopolymers finds important applications in the agricultural field where they are used as soil conditioning agents as they can increase the water retention ability of soil and can act as a carrier of nutrients and other agrochemicals. Hydrogels are also used for the controlled delivery of fertilizer to plants. In this review, bio-polymeric hydrogels based on starch, chitosan, guar gum, gelatin, lignin, and alginate polymer have been discussed in terms of their synthesis method, swelling behavior, and possible agricultural application. The urgency to address water scarcity and the need for sustainable water management in agriculture necessitate the exploration and implementation of innovative solutions. By understanding the synthesis techniques and factors influencing the swelling behavior of these hydrogels, we can unlock their full potential in fostering sustainable agriculture and mitigating the challenges posed by an ever-changing environment.

Layered Double Hydroxides for Regulating Phosphate in Water to Achieve Long-Term Nutritional Management

Hunger and undernourishment are increasing global challenges as the world's population continuously grows. Consequently, boosting productivity must be implemented to reach the global population's food demand and avoid deforestation. The current promising agricultural practice without herbicides and pesticides is fertilizer management, particularly that of phosphorus fertilizers. Layered double hydroxides (LDHs) have recently emerged as favorable materials in phosphate removal, with practical application possibilities in nanofertilizers. This review discusses the fundamental aspects of phosphate removal/recycling mechanisms and highlights the current endeavors on the development of phosphate-selective sorbents using LDH-based materials. Specific emphasis is provided on the progress in designing LDHs as the slow release of phosphate fertilizers reveals their relevance in making agro-practices more ecologically sound. Relevant pioneering efforts have been briefly reviewed, along with a discussion of perspectives on the potential of LDHs as green nanomaterials to improve food productivity with low eco-impacts.

Improvement of tomato yield and quality using slow release NPK fertilizers prepared by carnauba wax emulsion, starch-based latex and hydrogel nanocomposite combination

The modern agriculture is working on introducing new generation of fertilizers that apt to slow down the nutrients release to be more in synchrony with plant's need throughout growth season, enhance fertilizer performance, and decrease nutrient losses into the environment. The aim of this research was to develop an advanced NPK slow-release fertilizer (SRF) and investigate its effect on yield, nutritional and morphological responses of tomato plant (Lycopersicon esculentum Mill.) as a model crop. To this goal, three water-based bio-polymeric formulations including starch-g-poly (acrylic acid-co-acrylamide) nanocomposite hydrogel, starch-g-poly(styrene-co-butylacrylate) latex, and carnauba wax emulsion were synthesized and used for production of NPK-SRF samples. Different samples of coated fertilizers (urea, potassium sulfate, and superphosphate granules) were prepared using different ratios of latex and wax emulsion, and for phosphorus and potash (R-treatment). Moreover, some of coated fertilizers (15 and 30 wt.%) was replaced with nanocomposite hydrogel containing fertilizers, named D and H treatments, respectively. The effect of SRF samples were compared with commercial fertilizers (NPK treatment) and a commercial SRF (T treatment), on the growth of tomato in the greenhouse, at two different levels (100 and 60). The efficiency of all the synthesized formulations were higher than NPK and T treatments, and among them, H100 significantly improved the morphological and physiological characteristics of tomato. For instance, amount of residual elements (nitrogen, phosphorus and potassium) as well as micro elements of calcium, iron and zinc in tomato cultivation bed and accordingly the uptake of these elements in the roots, aerial parts and fruits were increased in the R, H, and D treatments. The highest yield (1671.54 g), highest agricultural agronomy efficiency of fertilizer, and the highest dry matter percentage (9.52%) were obtained in H100. The highest amount of lycopene, antioxidant capacity and vitamin C was also observed in H100. Nitrate accumulation in tomato fruit in the synthesized SRF samples were decreased significantly compared to NPK100, and the lowest amount was observed in H100, which was 55.24% less than NPK100. Accordingly, it is suggested that combination of natural-based nanocomposite hydrogels along with coating latexes and wax emulsions can be a successful method to synthesize efficient NPK-SRF formulations for improvement of crop growth and quality.

Characterization of a New Silk Sericin-Based Hydrogel for Water Retention in Soil

Hydrogel-type absorbent materials are currently a technological alternative for improving water retention in the soil and reducing nutrient loss by leaching and evaporation. This study aimed to evaluate the application of a new hydrogel based on silk sericin (SS) as a water retention material in soil. The morphology of the hydrogel was characterized using Scanning Electron Microscopy (SEM), and its impact on moisture retention in sandy loam soil (SLS) under different levels of matric pressure (MP) was evaluated. Additionally, water content data were collected over time for both SLS and SLS with hydrogel (SLS + H), and the data were used to fit predictive models. The results indicate that the hydrogel had a porous morphology that promoted water retention and soil release. Under a MP of 0.3 bar, the use of the hydrogel increased water retention by 44.70% with respect to that of SLS. The predictive models developed were adequately adjusted to the behavior of the moisture data over time and evidenced the incidence of the absorbent material on the dynamics of the moisture content in the soil. Therefore, these models could be useful for facilitating subsequent simulations or for designing automatic soil moisture control systems oriented to smart farming.

Cellulose-based slow-release nitrogen fertilizers: Synthesis, properties, and effects on pakchoi growth

The application of most slow-release fertilizers is limited by complex preparation processes and short slow-release periods. In this study, carbon spheres (CSs) were prepared by a hydrothermal method using cellulose as the raw material. Using CSs as the fertilizer carrier, three new carbon-based slow-release nitrogen fertilizers were prepared using direct mixing (SRF-M), water-soluble immersion adsorption (SRFS), and co-pyrolysis (SRFP) methods, respectively. Examination of the CSs revealed regular and ordered surface morphology, enrichment of functional groups on the surfaces, and good thermal stability. Elemental analysis showed that SRF-M was rich in nitrogen (total nitrogen content of 19.66 %). Soil-leaching tests showed that the total cumulative nitrogen release of SRF-M and SRF-S was 55.78 % and 62.98 %, respectively, which greatly slowed down the release of nitrogen. Pot experiment results revealed that SRF-M significantly promoted the growth of pakchoi and improved crop quality. Thus, SRF-M was more effective in practical applications than the other two slow-release fertilizers. Mechanistic studies showed that CN, -COOR, pyridine-N and pyrrolic-N participated in nitrogen release. This study thus provides a simple, effective, and economical method for the preparation of slow-release fertilizers, providing new directions for further research and the develop of new slow-release fertilizers.

In situ forming dialdehyde xanthan gum-gelatin Schiff-base hydrogels as potent controlled release fertilizers

Controlled release fertilizer (CRF) hydrogels have blossomed into promising materials in agriculture owing to the sustained release of the fertilizer and also as soil conditioner. Apart from the traditional CRF hydrogels; Schiff-base hydrogels have garnered significant thrust that release nitrogen slowly in addition to reducing the environmental pollution. Herein, we have fabricated Schiff-base CRF hydrogels composed of dialdehyde xanthan gum (DAXG) and gelatin. The formation of the hydrogels was accomplished via the simplistic in situ crosslinking reaction between the aldehyde groups of DAXG and the amino groups of gelatin. The hydrogels acquired a compact network upon increasing the DAXG content in the matrix. The phytotoxic assay on different plants indicated the hydrogels to be nontoxic. The hydrogels demonstrated good water-retention behaviour in soil, along with reusability even after 5 cycles. A controlled release profile for urea was evident from the hydrogels wherein macromolecular relaxation played a crucial role in the release mechanism. Growth assays on Abelmoschus esculentus (Okra) plant presented an intuitive evaluation on the growth and water-holding capacity of the CRF hydrogel. The present work demonstrated a facile preparation of CRF hydrogels to enhance the utilization of urea and retain soil humidity as fertilizer carriers.

Preparation and properties of Sanxan gel based fertilizer for water retention and slow-release

The advent of gel fertilizers has benefited agriculture and the environment. This study utilized sanxan, a novel polysaccharide, as a carrier and loaded it with urea to create sanxan gel fertilizer (SGF), thus creating a new, effective gel fertilizer. Water retention and sustained release ability of SGF were evaluated, and crop experiments were carried out. The results showed that, SGF that content 2.0 % solution of sanxan and loaded 20 g g^-1 of urea were prepared by heating-cooling method. The water-retention ratio of SGF was attained at 56.4 g g^-1 for 10 h. The urea releases of SGF in water have a more significant persistence than pure urea. In addition, wheat growth was promoted by SGF, compared with pure urea, the biomass of wheat shoot and root increased 27.4 % and 62.2 % during 20 days, respectively. Consequently, SGF has the ability to retain water and slowly release nutrition, which was an ideal carrier for managing water and urea. The SGF developed in this study provides data support and theoretical basis for the application of sanxan gel in agriculture and the environment.

Polyacrylamide Hydrogel Enriched with Amber for In Vitro Plant Rooting

In this work, a new material for in vitro plant rooting based on highly dispersed polyacrylamide hydrogel (PAAG) enriched with amber powder was synthesized and investigated. PAAG was synthesized by homophase radical polymerization with ground amber addition. Fourier transform infrared spectroscopy (FTIR) and rheological studies were used to characterize the materials. They showed that the synthesized hydrogels have physicochemical and rheological parameters similar to those of the standard agar media. The acute toxicity of PAAG-amber was estimated based on the influence of washing water on the viability of plant seeds (pea and chickpea) and Daphnia magna. It proved its biosafety after four washes. The impact on plant rooting was studied using the propagation of Cannabis sativa on synthesized PAAG-amber and compared with agar. The developed substrate stimulated the rooting of the plants to more than 98% in comparison to standard agar medium (95%). Additionally, the use of PAAG-amber hydrogel markedly enhanced metric indicators of seedlings: root length increased by 28%, stem length-by 26.7%, root weight-by 167%, stem weight-by 67%, root and stem length-by 27%, root and stem weight-by 50%. This means that the developed hydrogel significantly accelerates reproduction and allows obtaining a larger amount of plant material within a shorter period of time than the standard agar substrate.

Development of a novel silk sericin-based hydrogel film by mixture design

Sericin has been used in functional and potentially biodegradable materials for cosmetics, biomedical, agricultural, and food applications. It is a natural polymer with applications in absorbent materials, such as hydrogels, because of its hydrophilic character. However, sericin by itself is brittle, and in contact with water has low structural stability, being necessary its blending with other polymers or the application of crosslinking processes. In this work, hydrogel films were prepared from different mixtures containing sericin (SS), carboxymethylcellulose (CMC), and polyvinyl alcohol (PVA), using a simple and environmentally friendly method consisting of a gelling process followed by solvent casting. A mixture design was applied to assess the incidence of each component and its interaction with the output variables of interest. Two response variables were evaluated in each formulation: water absorption capacity (WA) and gel fraction (GF). It was also possible to model the output variables based on the proportions of the sample components. In addition, a set of formulations were used to produce hydrogels with high water absorption rates while maintaining their structural stability. The optimal hydrogel formulation (HF) was structurally and thermally characterized by FTIR and TGA, respectively. Hydrogel morphology was also studied by scanning electron microscopy (SEM). The results of this study constitute an important contribution to the design of novel processing routes to extend the use of silk sericin in the development of new materials.

Temperature-responsive hydrogel prepared from carboxymethyl cellulose-stabilized N-vinylcaprolactam with potential for fertilizer delivery

The growth of plants is highly dependent on sufficient water and suitable fertilizer nutrients, but the soil often loses moisture and the fertilizers are low efficiency. To address this issue, the temperature-responsive hydrogels were developed using the N-vinylcaprolactam (NVCL) dispersed in water through the emulsification of carboxymethyl cellulose (CMC) and acrylamide (AM), and urea was loaded into the hydrogel as a fertilizer. The amount of CMC and monomer have an effect on the structure, mechanical properties, swelling ability, and temperature sensitivity of the hydrogel. Therefore, the maximum swelling ratio of the hydrogel can reach 2056 % with the increasing hydrophilic groups, and the hydrogel exhibits a deswelling behavior as the temperature rises to higher than LCST due to the temperature responsiveness. Moreover, the fertilizer can rapidly release when the temperature is higher than LSCT, and exhibits similar release behavior in water and soil. Thus, the temperature-responsive hydrogel shows a great potential application for the controlled release of water and fertilizer in agriculture and forestry.

Controlled release of harmful pesticide dichlorvos through synthesized biodegradable aloe vera–acrylic acid-based hydrogel and its utilization in soil water management

The present work deals with the synthesis of biodegradable hydrogel of a natural polysaccharide aloe vera and vinyl monomer acrylic acid. In this synthesis, ammonium persulfate–glutaraldehyde was used as initiator-cross-linker system, acrylic acid as monomer and aloe vera as backbone. Grafting was confirmed by different techniques like SEM, FT-IR, XRD and EDS. Maximum percentage swelling of synthesized hydrogel was found to be 756%. Biodegradation behavior of synthesized hydrogel [Av-cl-poly(AA)] was studied by soil burial, composting and vermicomposting methods. Maximum biodegradation was found to be 90%, 94% and 93% in case of soil burial, composting and vermicomposting methods, respectively. Biodegradation of Av-cl-poly(AA) was confirmed by FT-IR and SEM techniques. Water retention capacity was prolonged from 11 to 20 days using synthesized Av-cl-poly(AA). Water content of clay soil and sandy loam soil was increased to an extent of 6.1% and 5.79%, respectively. Synthesized Av-cl-poly(AA) has been found to be effective in sustained release of harmful pesticide dichlorvos. The results showed that maximum release of dichlorvos was found to be 1024.34 ppm after 44 h.

The strategic applications of natural polymer nanocomposites in food packaging and agriculture: Chances, challenges, and consumers' perception

Natural polymer-based nanocomposites have received significant attention in both scientific and industrial research in recent years. They can help to eliminate the consequences of application of petroleum-derived polymeric materials and related environmental concerns. Such nanocomposites consist of natural biopolymers (e.g., chitosan, starch, cellulose, alginate and many more) derived from plants, microbes and animals that are abundantly available in nature, biodegradable and thus eco-friendly, and can be used for developing nanocomposites for agriculture and food industry applications. Biopolymer-based nanocomposites can act as slow-release nanocarriers for delivering agrochemicals (fertilizers/nutrients) or pesticides to crop plants to increase yields. Similarly, biopolymer-based nanofilms or hydrogels may be used as direct product coating to extend product shelf life or improve seed germination or protection from pathogens and pests. Biopolymers have huge potential in food-packaging. However, their packaging properties, such as mechanical strength or gas, water or microbial barriers can be remarkably improved when combined with nanofillers such as nanoparticles. This article provides an overview of the strategic applications of natural polymer nanocomposites in food and agriculture as nanocarriers of active compounds, polymer-based hydrogels, nanocoatings and nanofilms. However, the risk, challenges, chances, and consumers' perceptions of nanotechnology applications in agriculture and food production and packaging have been also discussed.

Agricultural Applications of Superabsorbent Polymer Hydrogels

This review presents data from the past five years on the use of polymeric superabsorbent hydrogels in agriculture as water and nutrient storage and retention materials, as well as additives that improve soil properties. The use of synthetic and natural polymeric hydrogels for these purposes is considered. Although natural polymers, such as various polysaccharides, have undoubted advantages related to their biocompatibility, biodegradability, and low cost, they are inferior to synthetic polymers in terms of water absorption and water retention properties. In this regard, the most promising are semi-synthetic polymeric superabsorbents based on natural polymers modified with additives or grafted chains of synthetic polymers, which can combine the advantages of natural and synthetic polymeric hydrogels without their disadvantages. Such semi-synthetic polymers are of great interest for agricultural applications, especially in dry regions, also because they can be used to create systems for the slow release of nutrients into the soil, which are necessary to increase crop yields using environmentally friendly technologies.

Mineral-hydrogel composites for mitigating harmful algal bloom and supplying phosphorous for photo-biorefineries

Harmful algal blooms (HAB) are a major environmental concern in eutrophic aquatic systems. To mitigate HABs and recover the phosphorus that drives algal growth, this study developed hydrogel composites seeded with calcium phosphate and wollastonite particles, which first adsorb phosphate (P) and then precipitate it as calcium phosphate. Using a fast-growing cyanobacterium, Synechococcus elongatus 2973, as a model microalga, we found that the mineral-hydrogel composites reduced dissolved P in BG11 media from 5.1 mg/L to 0.31 mg/L, initially reducing the biomass growth rate by up to 73 % and ultimately reducing the total biomass concentration by 75 %. When applied to municipal wastewater and agricultural run-off, the composites removed 96 % and 91 % of the dissolved P, respectively. Moreover, when the recovered P-enriched composites were reused as a slow-release bio-compatible fertilizer in a photobioreactor, they effectively supported algal growth without blocking light and interfering with photosynthesis. The P-enriched composites could tune the P concentration in the culture medium and significantly promote algal lipid accumulation. This study demonstrates the mineral-hydrogel composites' potential to treat point sources of P pollution and subsequently facilitate photoautotrophic biofuel production as a nutrient, effectively recycling the captured P.

Multicomponent biodegradable hydrogels based on natural biopolymers as environmentally coating membrane for slow-release fertilizers: Effect of crosslinker type

This work aims to explore the suitable crosslinker type for synthesizing multicomponent biodegradable hydrogels of cassava starch (CSt) grafted with acrylic acid (AA) semi-interpenetrated by natural rubber (NR)/polyvinyl alcohol (PVA) blend (CSt-g-PAA/NR/PVA, CSB semi-IPN hydrogel) as coating membranes for slow-release urea fertilizers. Three crosslinker types (ethylene glycol dimethacrylate (EGDMA), glutaraldehyde (GA) and N,N'- methylene-bis-acrylamide (MBA)) were employed to investigate their influences on the properties of CSB semi-IPN hydrogels. The results revealed that the different crosslinkers clearly exhibited different water-retention capacity, biodegradation, slow release and plant growth performance of the CSB semi-IPN hydrogels. The CSB-G2 hydrogel (crosslinked with GA at 2 wt%) remained higher water-retention at 30 days (20.2 %), greater rate of degradation (1.37 %/day) and better biosafety (OD600 = 2.26) compared to CSB-M2 and CSB-E2 hydrogels. After urea pellets were coated by CSB hydrogels and wax layers (UCSBw formulation), the urea release rates from the UCSBw-M2, UCSBw-E2 and UCSBw-G2 formulations in 30 days were 67.7 %, 68.7 % and 78.3 %, respectively, corresponding well with swelling ratio and pore size. Besides, the UCSBw-G2 formulation yielded the greater plant growth performance (height, leaf length and product weight) than other two formulations and commercial fertilizer. In conclusion, GA is the suitable crosslinker for synthesizing the CSB-g-PAA/NR/PVA hydrogels with high water-retention, excellent biodegradation, less negative impact on environments, acceptable slow-release rate, good biosafety and reasonable price for slow-release fertilizers.

Controlled release fertilizers (CRFs) for climate-smart agriculture practices: a comprehensive review on release mechanism, materials, methods of preparation, and effect on environmental parameters

Fertilizers play an essential role in increasing crop yield, maintaining soil fertility, and provide a steady supply of nutrients for plant requirements. The excessive use of conventional fertilizers can cause environmental problems associated with nutrient loss through volatilization in the atmosphere, leaching to groundwater, surface run-off, and denitrification. To mitigate environmental issues and improve the longevity of fertilizer in soil, controlled release fertilizers (CRFs) have been developed. The application of CRFs can reduce the loss of nutrients, provide higher nutrient use efficiency, and improve soil health simultaneously to achieve the goals of climate-smart agricultural (CSA) practices. The major findings of this review paper are (1) CRFs can prevent direct exposure of fertilizer granule to soil and prevent loss of nutrients such as nitrate and nitrous oxide emissions; (2) CRFs are less affected by the change in environmental parameters, and that can increase longevity in soil compared to conventional fertilizers; and (3) CRFs can maintain required soil nitrogen levels, increase water retention, reduce GHG emissions, lead to optimum pH for plant growth, and increase soil organic matter content. This paper could give good insights into the ongoing development and future perspectives of CRFs for CSA practices.

Silicon as a Smart Fertilizer for Sustainability and Crop Improvement

Silicon (Si), despite being abundant in nature, is still not considered a necessary element for plants. Si supplementation in plants has been extensively studied over the last two decades, and the role of Si in alleviating biotic and abiotic stress has been well documented. Owing to the noncorrosive nature and sustainability of elemental Si, Si fertilization in agricultural practices has gained more attention. In this review, we provide an overview of different smart fertilizer types, application of Si fertilizers in agriculture, availability of Si fertilizers, and experiments conducted in greenhouses, growth chambers, and open fields. We also discuss the prospects of promoting Si as a smart fertilizer among farmers and the research community for sustainable agriculture and yield improvement. Literature review and empirical studies have suggested that the application of Si-based fertilizers is expected to increase in the future. With the potential of nanotechnology, new nanoSi (NSi) fertilizer applications may further increase the use and efficiency of Si fertilizers. However, the general awareness and scientific investigation of NSi need to be thoughtfully considered. Thus, we believe this review can provide insight for further research into Si fertilizers as well as promote Si as a smart fertilizer for sustainability and crop improvement.

Fertilizers and Fertilization Strategies Mitigating Soil Factors Constraining Efficiency of Nitrogen in Plant Production

Fertilizer Use Efficiency (FUE) is a measure of the potential of an applied fertilizer to increase its impact on the uptake and utilization of nitrogen (N) present in the soil/plant system. The productivity of N depends on the supply of those nutrients in a well-defined stage of yield formation that are decisive for its uptake and utilization. Traditionally, plant nutritional status is evaluated by using chemical methods. However, nowadays, to correct fertilizer doses, the absorption and reflection of solar radiation is used. Fertilization efficiency can be increased not only by adjusting the fertilizer dose to the plant's requirements, but also by removing all of the soil factors that constrain nutrient uptake and their transport from soil to root surface. Among them, soil compaction and pH are relatively easy to correct. The goal of new the formulas of N fertilizers is to increase the availability of N by synchronization of its release with the plant demand. The aim of non-nitrogenous fertilizers is to increase the availability of nutrients that control the effectiveness of N present in the soil/plant system. A wide range of actions is required to reduce the amount of N which can pollute ecosystems adjacent to fields.

Chelating Agents in Assisting Phytoremediation of Uranium-Contaminated Soils: A Review

Massive stockpiles of uranium (U) mine tailings have resulted in soil contamination with U. Plants for soil remediation have low extraction efficiency of U. Chelating agents can mobilize U in soils and, hence, enhance phytoextraction of U from the soil. However, the rapid mobilization rate of soil U by chelating agents in a short period than plant uptake rate could increase the risk of groundwater contamination with soluble U leaching down the soil profile. This review summarizes recent progresses in synthesis and application of chelating agents for assisting phytoremediation of U-contaminated soils. In detail, the interactions between chelating agents and U ions are initially elucidated. Subsequently, the mechanisms of phytoextraction and effectiveness of different chelating agents for phytoremediation of U-contaminated soils are given. Moreover, the potential risks associated with chelating agents are discussed. Finally, the synthesis and application of slow-release chelating agents for slowing down metal mobilization in soils are presented. The application of slow-release chelating agents for enhancing phytoextraction of soil U is still scarce. Hence, we propose the preparation of slow-release biodegradable chelating agents, which can control the release speed of chelating agent into the soil in order to match the mobilization rate of soil U with plant uptake rate, while diminishing the risk of residual chelating agent leaching to groundwater.

pH-Responsive Eco-Friendly Chitosan–Chlorella Hydrogel Beads for Water Retention and Controlled Release of Humic Acid

For improving the mechanical strength of controlled release fertilizer (CRF) hydrogels, a novel material of Chlorella was employed as a bio-based filler to prepare chitosan–chlorella hydrogel beads with physical crosslink method. Here, the synthesis mechanism was investigated, and the chitosan–chlorella hydrogel beads exhibited enhanced mechanical stability under centrifugation and sonication than pure chitosan hydrogel beads. Chlorella brought more abundant functional groups to original chitosan hydrogel, hence, chitosan–chlorella hydrogel beads represented greater sensitivity and controllable response to external factors including pH, salt solution, temperature. In distilled water, the hydrogel beads with 40 wt% Chlorella reached the largest water absorption ratio of 42.92 g/g. Moreover, the mechanism and kinetics process of swelling behavior of the chitosan–chlorella hydrogel beads were evaluated, and the loading and releasing of humic acid by the hydrogel beads as a carrier material were pH-dependent and adjustable, which exhibit the potential of chitosan–chlorella hydrogel beads in the field of controlled release carrier biomaterials.

Emerging Fabrication Strategies of Hydrogels and Its Applications

Recently, hydrogels have been investigated for the controlled release of bioactive molecules, such as for living cell encapsulation and matrices. Due to their remote controllability and quick response, hydrogels are widely used for various applications, including drug delivery. The rate and extent to which the drugs reach their targets are highly dependent on the carriers used in drug delivery systems; therefore the demand for biodegradable and intelligent carriers is progressively increasing. The biodegradable nature of hydrogel has created much interest for its use in drug delivery systems. The first part of this review focuses on emerging fabrication strategies of hydrogel, including physical and chemical cross-linking, as well as radiation cross-linking. The second part describes the applications of hydrogels in various fields, including drug delivery systems. In the end, an overview of the application of hydrogels prepared from several natural polymers in drug delivery is presented.

Materials diversity of hydrogel: Synthesis, polymerization process and soil conditioning properties in agricultural field

BACKGROUND

The cumulative influence of global warming, climate abrupt changes, growing population, topsoil erosion is becoming a threatening alarm for facing food challenges and upcoming global water issues. It ultimately affects the production of food in a water-stressed environment and slows down the production with more consumption of fertilizers by plants. The superabsorbent hydrogels (SAHs) have extensive applications in the agricultural field and proved very beneficial for plant growth and soil health. These polymeric materials are remarkably distinct from hygroscopic materials owing to their multidimensional network structure. It retains a lot of water in its 3D network and releases it slowly along with nutrients to plant in stressed environment.

AIM OF REVIEW

A soil conditioner boosts up the topology, compactness, and mechanical properties (swelling, water retention, and slow nutrient release) of soil. The superabsorbent hydrogel plays an astonishing role in preventing the loss of nutrients during the heavy flow of rainwater from the upper surface of soil because these SAHs absorb water and get swollen to keep water for longer time. The SAHs facilitate the growth of plants with limited use of water and fertilizers. Beyond, it improves the soil health and makes it fertile in horticulture and drought areas.

KEY SCIENTIFIC CONCEPT OF REVIEW

The SAHs can be synthesized through grafting and cross-linking polymerization to introduce value-added features and extended network structure. The structure of superabsorbent hydrogel entirely based on cross-linking that prompts its use in the agricultural field as a soil conditioner. The properties of a SAHs vary due to its nature of constituents, polymerization process (grafting or cross-linking), and other parameters. The use of SAHs in agricultural field comparatively enhances the swelling rate up to 60-80%, maximum water retaining, and slowly nutrient release to plants for a longer time.

Regenerated Cellulose Products for Agricultural and Their Potential: A Review

Cellulose is one of the most abundant natural polymers with excellent biocompatibility, non-toxicity, flexibility, and renewable source. Regenerated cellulose (RC) products result from the dissolution-regeneration process risen from solvent and anti-solvent reagents, respectively. The regeneration process changes the cellulose chain conformation from cellulose I to cellulose II, leads the structure to have more amorphous regions with improved crystallinity, and inclines towards extensive modification on the RC products such as hydrogel, aerogel, cryogel, xerogel, fibers, membrane, and thin film. Recently, RC products are accentuated to be used in the agriculture field to develop future sustainable agriculture as alternatives to conventional agriculture systems. However, different solvent types and production techniques have great influences on the end properties of RC products. Besides, the fabrication of RC products from solely RC lacks excellent mechanical characteristics. Thus, the flexibility of RC has allowed it to be homogenously blended with other materials to enhance the final products' properties. This review will summarize the properties and preparation of potential RC-based products that reflect its application to replace soil the plantation medium, govern the release of the fertilizer, provide protection on crops and act as biosensors.

Synthesis of a Dual-Functional Nanofertilizer by Embedding ZnO and CuO Nanoparticles on an Alginate-Based Hydrogel

Recent scientific breakthroughs in the field of agriculture have led to the abundant usage of nanoparticles in agrochemicals to maintain proper nutrient uptake in plants. Since less attention has been given to the supply of vital micronutrients to crop plants, the objective of this study was to develop a nanofertilizer capable of releasing micronutrients while nourishing its surrounding soil. As the initial nanonutrients, Zn and Cu were used in their metal oxide forms, which promote seed germination. Alginic acid was used as the agent responsible for soil conditioning. To form the fertilizing complex, nanoparticles were reacted with sodium alginate, which resulted in a hydrogel where alginate chains were cross-linked with Zn(II) and Cu(II) and excess metal oxide nanoparticles were distributed on the hydrogel. Spectroscopic characterization of the nanofertilizer confirmed that alginate chains were cross-linked by Zn(II) and Cu(II), while morphological analysis by scanning electron microscopy (SEM) showed that ZnO and CuO nanoparticles were embedded on the alginate matrix. The release behavior of cations in soil and water environments, experimented using the tea bag method, revealed that the cationic release was slowly increasing with time. Micronutrient uptake by plants was studied by conducting leaf analyses in tomato plants for 30 consecutive days. To experiment the release behavior of micronutrients in the presence of compost, the nanofertilizer was added with predetermined amounts of compost to tomato plants. Flame atomic absorption spectroscopy (FAAS) results indicated that in the fertilizer-applied plants, Cu concentrations showed a steady increase with time while Zn concentrations remained undetected.

Renewable Mixed Hydrogels Based on Polysaccharide and Protein for Release of Agrochemicals and Soil Conditioning

The study deals with the combination of biopolymers to develop hydrogels intended for agriculture application. The aim is to propose a renewable and eco-compatible solution to enhance agrochemicals and water efficiency and contribute to maintaining soil fertility. We developed a set of hydrogels based on casein and chitosan for water retention and release of agrochemicals, in particular nitrogen fertilizer urea. The weight ratio of biopolymers, from 0.5 to 2, was investigated to understand the influence of their content on the morphology, swelling, swelling-drying cycles, and water retention in soil. The average content of urea in the hydrogels was 30% of the total weight, and up to 80% was released in the soil in 50 days. The biodegradation of the hydrogels in soil has been investigated by the burial method and monitoring the release of CO2. Results demonstrated that by increasing the content of chitosan, the biodegradation time is prolonged up to 20% in 90 days. The obtained results support the ultimate purpose of the work that the combination of two biopolymers at proper weight ratio could be a valid alternative of the marketed hydrogels with the final goal to promote soil fertility and water retention and prolong biodegradation.

Current and future perspectives on the use of nanofertilizers for sustainable agriculture: the case of phosphorus nanofertilizer

Over the last century, the demand for food resources has been continuously increasing with the rapid population growth. Therefore, it is critically important to adopt sustainable farming practices that can enhance crop production without the excessive use of fertilizers. In this regard, there is a growing interest in the use of nanomaterials for improving plant nutrition as an alternative to traditional chemical or mineral fertilizers. Using this technology, the efficiency of micro- and macro-nutrients in plants can increase. Various nanomaterials have been successfully applied in agricultural production, compared to conventional fertilizers. Among the major plant nutrients, phosphorus (P) is the least accessible since most farmlands are frequently P deficient. Hence, P use efficiency should be maximized to conserve the resource base and maintain agricultural productivity. This review summarizes the current research and the future possibilities of nanotechnology in the biofortification of plant nutrition, with a focus on P fertilizers. In addition, it covers the challenges, environmental impacts, and toxic effects that have been explored in the area of nanotechnology to improve crop production. The potential uses and benefits of nanoparticle-based fertilizers in precision and sustainable agriculture are also discussed.

Phosphates-Containing Interpenetrating Polymer Networks (IPNs) Acting as Slow Release Fertilizer Hydrogels (SRFHs) Suitable for Agricultural Applications

Novel, phosphorus-containing slow release fertilizer hydrogels (SRFHs) composed of interpenetrating polymer networks (IPNs) with very good swelling and mechanical properties have been obtained and characterized. It was found that introducing organophosphorus polymer based on a commercially available monomer, 2-methacryloyloxyethyl phosphate (MEP), as the IPN’s first component network results in much better swelling properties than for a terpolymer with acrylic acid (AAc), 2-methacryloyloxyethyl phosphate (MEP) and bis[2-(methacryloyloxy)ethyl] phosphate (BMEP) when the same weight ratios of monomers are employed. The procedure described in this paper enables the introduction of much larger amounts of phosphorus into polymer structures without significant loss of water regain ability, which is crucial in the application of such materials in the agricultural field.

A Mini-Review on Chitosan-Based Hydrogels with Potential for Sustainable Agricultural Applications

Agriculture is an important sector of the economy, but this industry consumes significant amounts of water, which is a precious and limited natural resource. Irrigation techniques and efforts to mitigate water usage influence the growth, survival, and yield of crops. However, superabsorbent polymers in combination with fertilizers can be employed to obtain sustained release of nutrients and improved water retention capacity of the soil. Despite significant recent progress in this area involving synthetic polyacrylate hydrogels, there are no industrially applicable solutions exhibiting similar performance using natural biopolymers or synthetic polymers enriched with natural components. This review focuses on biodegradable chitosan-based hydrogels (both natural and semi-synthetic), and discusses their potential agricultural and horticultural applications. The methods for synthesizing hydrogels via physical or chemical crosslinking, and the resulting functional properties of recently reported hydrogels, such as water retention and release of active ingredients, are presented herein.

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.