Utilization of wheat straw for the preparation of coated controlled-release fertilizer with the function of water retention

Sustainable SMART fertilizers in agriculture systems: A review on fundamentals to in-field applications

Agriculture will face the issue of ensuring food security for a growing global population without compromising environmental security as demand for the world's food systems increases in the next decades. To provide enough food and reduce the harmful effects of chemical fertilization and improper disposal or reusing of agricultural wastes on the environment, will be required to apply current technologies in agroecosystems. Combining biotechnology and nanotechnology has the potential to transform agricultural practices and offer answers to both immediate and long-term issues. This review study seeks to identify, categorize, and characterize the so-called smart fertilizers as the future frontier of sustainable agriculture. The conventional fertilizer and smart fertilizers in general are covered in the first section of this review. Another key barrier preventing the widespread use of smart fertilizers in agriculture is the high cost of materials. Nevertheless, smart fertilizers are widely represented on the world market and are actively used in farms that have already switched to sustainable technologies. The advantages and disadvantages of various raw materials used to create smart fertilizers, with a focus on inorganic and organic materials, synthetic and natural polymers, along with their physical and chemical preparation processes, are contrasted in the following sections. The rate and the mechanism of release are covered. The purpose of this study is to provide a deep understanding of the advancements in smart fertilizers during the last ten years. Trends are also recognized and studied to provide insight for upcoming agricultural research projects.

Preparation of Novel Biodegradable Polymer Slow-Release Fertilizers to Improve Nutrient Release Performance and Soil Phosphorus Availability

Inspired by the gradual collapse of carbon chain and the gradual release of organic elements into the external environment during the degradation of biodegradable polymers, a novel biodegradable polymer slow-release fertilizer containing nutrient nitrogen and phosphorus (PSNP) was prepared in this study. PSNP contains phosphate fragment and urea formaldehyde (UF) fragment, which are prepared by solution condensation reaction. Under the optimal process, the nitrogen (N) and P₂O₅ contents of PSNP were 22% and 20%, respectively. The expected molecular structure of PSNP was confirmed by SEM, FTIR, XRD, and TG. PSNP can release N and phosphorus (P) nutrients slowly under the action of microorganisms, and the cumulative release rates of N and P in 1 month were only 34.23% and 36.91%, respectively. More importantly, through soil incubation experiment and leaching experiment, it was found that UF fragments released in the degradation process of PSNP can strongly complex soil high-valence metal ions, thus inhibiting the phosphorus nutrient released by degradation to be fixed in the soil and ultimately effectively increasing the soil available P content. Compared with ammonium dihydrogen phosphate (ADP), a small molecule phosphate fertilizer that is easily soluble, the available P content of PSNP in the 20-30 cm soil layer is almost twice that of ADP. Our study provides a simple copolymerization method to prepare PSNP with excellent slow-release N and P nutrients, which can promote the development of sustainable agriculture.

Maleic acid as an important monomer in synthesis of stimuli-responsive poly(acrylic acid-co-acrylamide-co-maleic acid) superabsorbent polymer

Poly(acrylic acid-co-acrylamide-co-maleic acid) (p(AA-co-AM-co-MA)) superabsorbent polymer was synthesized from acrylic acid (AA), acrylamide (AM), and maleic acid (MA) via free radical copolymerization. Results showed the presence of maleic acid in structure of superabsorbent has the key and superior role in creating a smart superabsorbent. The structure, morphology, and strength of the superabsorbent were characterized using FT-IR, TGA, SEM, and rheology analysis. The effect of different factors was investigated to determine the ability of water absorbency of the superabsorbent. According to optimized conditions, the water absorbency capacity of the superabsorbent in distilled water (DW) was 1348 g/g and in a solution containing 1.0 wt.% NaCl (SCS) was 106 g/g. The water retention ability of the superabsorbent was also investigated. The kinetic swelling of superabsorbent was identified by Fickian diffusion and Schott's pseudo-second-order model. Furthermore, the reusability of superabsorbent was studied in distilled water and saline solution. The ability of superabsorbent was investigated in simulated urea and glucose solutions, and very good results were obtained. The response ability of the superabsorbent was confirmed by swelling and shrinking behavior against changes of temperature, pH, and ionic strength.

Environment-friendly bio-based controlled-release phosphate fertilizer with waste kitchen oil as coating material: Preparation, characterization, and mechanisms

Recently, Bio-based polyurethane controlled-release fertilizers (BPCF) have been developed rapidly owing to their environmental friendliness, renewability, and low cost. However, the unsatisfying controlled release prohibits their large-scale direct application in agricultural production. Here, we prepared bio-based controlled-release phosphate (P) fertilizers using harmful waste kitchen oils (WKO) as coating materials. The membrane shell surface was modified with multi-walled carbon nanotubes (CNT), and superhydrophobic controlled-release phosphorus fertilizers (SCRF) were obtained. After CNT modification, the controlled release period of SCRF was greatly improved. Phosphorus released period of SCRF reached over 67 d while that of BPCF was merely ∼49 d. Additionally, the surface energy, cracks, roughness, microstructure, cross-linking degree, etc., of the membrane shells were measured. The results showed that CNT greatly improved the hydrophobic properties of the membrane shells. The findings indicated the application of modified WKO with great agricultural value in preparing environment-friendly BPCFs.

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.

Fe-Based Metal-Organic Frameworks for the Controlled Release of Fertilizer Nutrients

Due to the controlled-delivery function of metal-organic frameworks (MOFs) for gases, drugs, and pesticides, iron-based MOFs (Fe-MOFs) were explored in the laboratory as a novel fertilizer, which showed potential for use in the fertilizer industry; the challenge in the industrial scale application of Fe-MOFs in practical crop production was mainly the impact of scaling-up to energy and heat transfer, as well as the reaction yield. In this study, Fe-MOFs were hydrothermally synthesized both in the laboratory scale and in the pilot scale, their structure and components were characterized using various spectroscopic techniques, and then their nutrient release and degradation behaviors were investigated. The results showed that Fe-MOFs were successfully synthesized in both scales with similar yields around 27%, and the Fe-MOFs showed a similar structure with the molecular formula of C₂H₁₅Fe₂N₂O₁₈P₃. The nutrients N, P, and Fe were present in the Fe-MOFs with the average contents of 6.03, 14.48, and 14.69%, respectively. Importantly, the nutrient release rate and pattern of Fe-MOFs well matched with the crop growth, which greatly promoted the rice yield. Therefore, the environmentally friendly compounds of Fe-MOFs could be industrially produced and used as an innovative fertilizer with unique features of varied nutrients and controlled release.

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.

Slow Release and Water Retention Performance of Poly(Acrylic Acid-Co-Acrylamide)/Fulvic Acid/Oil Shale Semicoke Superabsorbent Composites

In order to achieve the low cost and multifunction of superabsorbent composites, poly(acrylic acid-co-acrylamide)/fulvic acid/oil shale semicoke (PAMFS) were prepared by free radical copolymerization of fulvic acid (FA), oil shale semicoke (OSSC), acrylic acid (AA) and acrylamide (AM). The characterization results revealed that FA and OSSC were involved in the construction of a three-dimensional (3D) polymeric network via hydrogen bonding and covalent bonding. The water absorbency of PAMFS in distilled water and 0.9 wt% NaCl solution were 724 and 98 g/g, respectively. The FA slow release of PAMFS in distilled water and soil was achieved due to the interaction between FA and the functional groups of polymer matrix by hydrogen bonds and covalent bonds. Furthermore, the potted experiment indicated that the addition of PAMFS to soil can significantly promote plant growth compared with the pure soil, regardless of water stress. Therefore, this superabsorbent composite showed an excellent water absorption and salt resistance performance, as well as nice slow release performance. It has a broad application prospect.

A Bio-Based Hydrogel Derived from Moldy Steamed Bread as Urea-Formaldehyde Loading for Slow-Release and Water-Retention Fertilizers

In this work, a novel slow-release and water-retention nitrogen (N) fertilizer (SRWRNF) was prepared using moldy steamed bread-based starch-g-poly(acrylic acid-co-acrylic amide) (SBS-g-P(AA/AM)) as the skeleton and urea-formaldehyde oligomers (UF) incorporated as the slow-release N source by semi-interpenetrating methods. Various analysis technologies including scanning electron microscopy, Fourier transform infrared spectroscopy, X-ray diffraction, thermogravimetric analysis, and differential scanning calorimetry were used to characterize the structure and properties of SRWRNFs. Swelling measurements indicated that the maximum water absorbency of SBS-g-P(AA/AM)-UF samples was 104.2 g/g in distilled water. The water-retention study showed that the SBS-g-P(AA/AM)-UF improved the maximum soil water content by 15.3-17.6% while improving soil water-retention capacity. N release experiments confirmed that SBS-g-P(AA/AM)-UF enabling offered a gradual N supply in soil. In comparison to conventional urea and UF fertilizers, the maize yield of SBS-g-P(AA/AM)-UF was increased by 20.3 and 9.7%, respectively. This study implies that the SRWRNFs provide a promising feasibility for large-scale applications in agriculture.

Biodegradable phase change materials with high latent heat: Preparation and application on Lentinus edodes storage

In order to develop biodegradable phase change materials (PCMs) with high latent heat for cold chain logistics, superabsorbent resin (SAR) was prepared based on starch graft copolymerization. FTIR and DSC demonstrated that acrylic acid was successfully grafted onto starches and optimum latent heat of PCM was 330.4 J/g with 10% (w/w) starch. The water retention of PCM with 10% (w/w) starch was 0.49 after heating at 50 °C for 200 h, which was 4.9 folds higher than that of non-starch PCM. Biodegradation rate of PCM was 60.12% within 75-day burial, which was 6 folds higher than that of non-starch PCM. Moreover, significant reduction in browning index, odor, decay, relative conductivity and malondialdehyde (MDA) content was observed in Lentinus edodes treated by biodegradable PCM. These results indicated that the application of biodegradable PCM could extend the shelf life of fresh L. edodes stored at 25 °C.

Activated-carbon-filled agarose hydrogel as a natural medium for seed germination and seedling growth

An activated-carbon-filled agarose (Agar-AC) hydrogel containing various concentrations of activated carbon (AC) was successfully fabricated through a simple solvent cast technique. Compared to pure agarose hydrogels, Agar-AC hydrogels exhibited excellent mechanical properties, good thermal stability and a highly developed pore structure. The Agar-AC hydrogels also showed a certain degree of improvement in water retention performance, while their swelling ratio decreased with the addition of AC. The incorporation of AC did not influence the crystallinity of the agarose hydrogel, and no chemical modification occurred according to XRD and FTIR. In rapeseed seed germination experiments, the growth indexes of rapeseed, including the germination percentage, root length, stem length, fresh weight and dry weight, were enhanced by the incorporation of a suitable amount of AC. These results indicated that AC has great potential to enhance the properties of agarose hydrogels and improve seed germination and plant growth, which implies that Agar-AC hydrogels can be used as natural materials for agricultural applications.

Controlled Release Fertilizers: A Review on Coating Materials and Mechanism of Release

Rising world population is expected to increase the demand for nitrogen fertilizers to improve crop yield and ensure food security. With existing challenges on low nutrient use efficiency (NUE) of urea and its environmental concerns, controlled release fertilizers (CRFs) have become a potential solution by formulating them to synchronize nutrient release according to the requirement of plants. However, the most significant challenge that persists is the "tailing" effect, which reduces the economic benefits in terms of maximum fertilizer utilization. High materials cost is also a significant obstacle restraining the widespread application of CRF in agriculture. The first part of this review covers issues related to the application of conventional fertilizer and CRFs in general. In the subsequent sections, different raw materials utilized to form CRFs, focusing on inorganic and organic materials and synthetic and natural polymers alongside their physical and chemical preparation methods, are compared. Important factors affecting rate of release, mechanism of release and mathematical modelling approaches to predict nutrient release are also discussed. This review aims to provide a better overview of the developments regarding CRFs in the past ten years, and trends are identified and analyzed to provide an insight for future works in the field of agriculture.

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.

Novel Semi-IPN Nanocomposites with Functions of both Nutrient Slow-Release and Water Retention. 1. Microscopic Structure, Water Absorbency, and Degradation Performance

Few studies have been conducted on the use of general nanotechnology-based principles for providing nutrients to crops. Water and fertilizer are the most important inputs in determining crop yield and profit. In this paper, super-absorbent polymers SAP_WS (grafting wheat straw (WS) to poly(acrylic-co-acrylamide), which is WS-g-P(AA-co-AM)) and SAP_HEC (HEC (hydroxyethyl cellulose)-g-P(AA-co-AM)) and their semi-interpenetrating polymer network (semi-IPN) nanocomposites SI-PSRF/SAP_WS and SI-PSRF/SAP_HEC (formed by chemical bonding of SAP_WS or SAP_HEC with PSRF (NPK-containing polymeric slow-release fertilizer)) were prepared. Due to the differences between activity and number of functional groups in WS and HEC, the water absorption properties and degradation performances of SAP_WS and SAP_HEC and their chemically bonded function nanocomposites SI-PSRF/SAP_WS and SI-PSRF/SAP_HEC are different. The maximum water absorption ratios of SAP_WS, SAP_HEC, SI-PSRF/SAP_WS, and SI-PSRF/SAP_HEC can reach 200.00 g/g, 240.00 g/g, 119.91g/g, and 127.43 g/g, respectively. Effects of the structures of these four materials on their degradation performances were studied via a tomato pot experiment. The changes in microstructures of these materials during the degradation processes were characterized by TEM, SEM, FTIR, XRD, XPS, and other techniques. Results show that the degradation rate of the chemically bonded functional nanocomposites with a semi-IPN structure SI-PSRF/SAP system is higher than that of SAP+PSRF (the simple physically mixed system of PSRF and SAP). Due to the differences among the activities and quantities of functional groups in WS and HEC, the water absorption properties of SI-PSRF/SAP_WS and SI-PSRF/SAP_HEC are different, and there are different degradation rates for these two functional nanocomposites.

Effect of Hot-Pressing Temperature on Characteristics of Straw-Based Binderless Fiberboards with Pulping Effluent

This study aimed to improve straw-based fiberboard properties without resins by adding pulping effluent as well as to investigate the difference among boards under variable hot-pressing temperatures. The characterization of fiberboards produced from wheat straw under pressing temperatures ranging from 160 to 200 °C was first described. The surface appearance, surface chemistry, thermal transitions, and mechanical performance of the boards were evaluated to investigate the effect of varying hot-pressing temperature. The results indicated that the surface color of boards became darker when the temperature was above 190 °C. Additionally, Fourier transform infrared (FT-IR) measurements showed that more low-molecular constituents and hydrogen bonds were produced under higher pressing temperatures. Furthermore, the physical and mechanical property data were analyzed statistically using one-way analysis of variance (ANOVA) and Tukey's tests (α = 0.05). The results demonstrated that straw-based fiberboards with effluent under 190 °C exhibited superior strength and water resistance capacities, and showed great potential in commercial decorating and packaging applications.

Bio-based Large Tablet Controlled-Release Urea: Synthesis, Characterization, and Controlled-Released Mechanisms

To improve nitrogen (N) use efficiency and minimize environmental pollution caused by fertilizer overuse, novel bio-based large tablet controlled-release urea (LTCRU) was prepared using bio-based coating materials to coat large tablet urea (LTU) derived from urea prills (U). Nano fumed silica (NFS) was added to the bio-based coating materials to improve the slow-release properties. The surface area of the LTU and U was measured by three-dimensional scanning. In comparison to U, LTU had a smaller surface area/weight ratio, which can reduce the coating materials. Scanning electron microscopy analysis showed that the addition of NFS in bio-based coating materials reduced the porosity of the coating shells of LTCRUs and, thus, enhanced the N release longevity of the controlled-released fertilizer. Dependent upon the pores on the coating shells of LTCRU, two N release patterns were revealed. Because of the good release characteristics, the novel LTCRU shows great potential to support sustainable agricultural production.

Preparation and Properties of a Novel Semi-IPN Slow-Release Fertilizer with the Function of Water Retention

A new semi-interpenetrating polymer network (semi-IPN) slow-release fertilizer (SISRF) with water absorbency, based on the kaolin-g-poly(acrylic acid-co-acrylic amide) (kaolin-g-P(AA-co-AM)) network and linear urea-formaldehyde oligomers (UF), was prepared by solution polymerization. Nutrients phosphorus and potassium were supplied by adding dipotassium hydrogen phosphate during the preparation process. The structure and properties of SISRF were characterized by various characterization methods. SISRF showed excellent water absorbency of 68 g g^-1 in tap water. The slow-release behavior of nutrients and water-retention capacity of SISRF were also measured. Meanwhile, the swelling kinetics was well described by a pseudo-second-order kinetics model. Results suggested the formation of SISRF with simultaneously good slow-release and water-retention capacity, which was expected to apply in modern agriculture and horticulture.

Cellulose Anionic Hydrogels Based on Cellulose Nanofibers As Natural Stimulants for Seed Germination and Seedling Growth

Cellulose anionic hydrogels were successfully prepared by dissolving TEMPO-oxidized cellulose nanofibers in NaOH/urea aqueous solution and being cross-linked with epichlorohydrin. The hydrogels exhibited microporous structure and high hydrophilicity, which contribute to the excellent water absorption property. The growth indexes, including the germination rate, root length, shoot length, fresh weight, and dry weight of the seedlings, were investigated. The results showed that cellulose anionic hydrogels with suitable carboxylate contents as plant growth regulators could be beneficial for seed germination and growth. Moreover, they presented preferable antifungal activity during the breeding and growth of the sesame seed breeding. Thus, the cellulose anionic hydrogels with suitable carboxylate contents could be applied as soilless culture mediums for plant growth. This research provided a simple and effective method for the fabrication of cellulose anionic hydrogel and evaluated its application in agriculture.

Biomimetic Superhydrophobic Biobased Polyurethane-Coated Fertilizer with Atmosphere "Outerwear"

The development of efficient biobased controlled-release fertilizers has captured much research attention because of the environmental concerns and food scarcity problems. In this work, a biomimetic superhydrophobic biobased polyurethane-coated fertilizer (SBPF) was successfully fabricated by increasing surface roughness and reducing surface energy of polyurethane (PU) coating. The green PU coating was synthesized from low-cost, biodegradable, and renewable cottonseed oil. The nutrient release longevity of SBPF revealed 2-fold enhancement compared with the normal biobased PU-coated fertilizer (BPF). The significant improvement of nutrient release characteristics can be attributed to the atmosphere "outerwear" which ensured the nonwetting contact of water with superhydrophobic surfaces in gas state instead of in liquid state. The new concept introduced in this study can inform the development of the next generation of biobased controlled release fertilizers.

Bio-based Interpenetrating Network Polymer Composites from Locust Sawdust as Coating Material for Environmentally Friendly Controlled-Release Urea Fertilizers

A novel polymer-coated nitrogen (N) fertilizer was developed using bio-based polyurethane (PU) derived from liquefied locust sawdust as the coating material. The bio-based PU was successfully coated on the surface of the urea fertilizer prills to form polymer-coated urea (PCU) fertilizer for controlled N release. Epoxy resin (EP) was also used to further modify the bio-based PU to synthesize the interpenetrating network (IPN), enhancing the slow-release properties of the PCU. The N release characteristics of the EP-modified PCU (EMPCU) in water were determine at 25 °C and compared to that of PCU and EP-coated urea (ECU). The results showed that the EP modification reduced the N release rate and increased the longevity of the fertilizer coated with bio-based PU. A corn growth study was conducted to further evaluate the filed application of the EMPCU. In comparison to commercial PCU and conventional urea fertilizer, EMPCU was more effective and increased the yield and total dry matter accumulation of the corn. Findings from this work indicated that bio-based PU derived from sawdust can be used as coating materials for PCU, particularly after EP modification. The resulting EMPCU was more environmentally friendly and cost-effective than conventional urea fertilizers coated by EP.

Preparation and characterization of slow-release fertilizer encapsulated by starch-based superabsorbent polymer

To enhance the effectiveness of fertilizers, a novel double-coated slow-release fertilizer was developed using ethyl cellulose (EC) as inner coating and starch-based superabsorbent polymer (starch-SAP) as outer coating. For starch-SAPs synthesized by a twin-roll mixer using starches from three botanical origins, a reduced grid size and an increased fractal gel size on nano-scale (i.e., increased stretch of 3D network) contributed to increasing the water absorbing capacity with a reduced absorbing rate and thus improving the slow-release property of fertilizer. The fertilizer particles coated with starch-SAP displayed well slow-release behaviors. In soil, compared to urea particles without and with EC coating, the particles further coated with starch-SAP showed reduced nitrogen release rate, and in particular, those with potato starch-SAP coating exhibited a steady release behavior for a period longer than 96h. Therefore, this work has demonstrated the potential of this new slow-release fertilizer system for improving the effectiveness of fertilizers.

Microwave-assisted one-step synthesis and characterization of a slow release nitrogen fertilizer with inorganic and organic composites

Microwave-assisted one-step synthesis of a novel high-performance slow release nitrogen fertilizer with inorganic and organic composites.

Ultraviolet-induced polymerization of superabsorbent composites based on sodium humate and its urea release behavior

This study was carried out to develop a superabsorbent composite for agriculture application, which is based on acrylic acid and sodium humate and prepared by ultraviolet-induced polymerization in the presence of crosslinker and composite initiator.

Synthesis of adipic acid dihydrazide-decorated coco peat powder-based superabsorbent for controlled release of soil nutrients

We firstly employ adipic acid dihydrazide as an outstanding decoration substrate for the pretreatment of CP, and then synthesis a novel superabsorbent through grafting AA onto MA modified CP@ADH surface.

Optimizing the interaction between poly(vinyl alcohol) and sandy soil for enhanced water retention performance

PVA 1795 and 1797 was effective in improving the growth of plants in sandy soil, may be a good alterative of PAM.

Synthesis, characterization, and swelling behaviors of salt-sensitive maize bran-poly(acrylic acid) superabsorbent hydrogel

A novel composite hydrogel was prepared via UV irradiation copolymerization of acrylic acid and maize bran (MB) in the presence of composite initiator (2,2-dimethoxy-2-phenylacetophenone and ammonium persulfate) and cross-linker (N,N'-methylenebis(acrylamide)). Under the optimized conditions, maize bran-poly(acrylic acid) was obtained (2507 g g(-1) in distilled water and 658 g g(-1) in 0.9 wt % NaCl solution). Effects of granularity, salt concentration, and various cations and anions on water absorbency were investigated. It was found that swelling was extremely sensitive to the ionic strength and cation and anion type. Swelling kinetics and water diffusion mechanism in distilled water were also discussed. Moreover, the product showed excellent water retention capability under the condition of high temperature or high pressure. The salt sensitivity, good water absorbency, and excellent water retention capability of the hydrogels give this intelligentized polymer wide potential applications.

Recovery of ammonium onto wheat straw to be reused as a slow-release fertilizer

With the aim of improving fertilizer use efficiency and minimizing the negative impact of nitrogen pollution, a new multifunctional slow-release fertilizer was prepared by recovery of ammonium from aqueous solutions onto a superabsorbent composite. An eco-friendly superabsorbent composite based on wheat straw (WS) was synthesized and used as the carrier to control the release of nutrients. The adsorption studies with NH₄⁺ indicated that the superabsorbent composite showed good affinity for NH₄⁺, with an adsorption capacity of 7.15 mmol g⁻¹ when 20 wt % of WS was incorporated and that the adsorption system can reach equilibrium within 40 min. Afterward, the feasibility of reusing the composite as a multifunctional slow-release nitrogen fertilizer was investigated. The results showed that the product with good water-retention and slow-release capacities could regulate soil acidity and was economical and eco-friendly for application in agriculture and horticulture.

Potential of Cellulose-Based Superabsorbent Hydrogels as Water Reservoir in Agriculture

The present work deals with the development of a biodegradable superabsorbent hydrogel, based on cellulose derivatives, for the optimization of water resources in agriculture, horticulture and, more in general, for instilling a wiser and savvier approach to water consumption. The sorption capability of the proposed hydrogel was firstly assessed, with specific regard to two variables that might play a key role in the soil environment, that is, ionic strength and pH. Moreover, a preliminary evaluation of the hydrogel potential as water reservoir in agriculture was performed by using the hydrogel in experimental greenhouses, for the cultivation of tomatoes. The soil-water retention curve, in the presence of different hydrogel amounts, was also analysed. The preliminary results showed that the material allowed an efficient storage and sustained release of water to the soil and the plant roots. Although further investigations should be performed to completely characterize the interaction between the hydrogel and the soil, such findings suggest that the envisaged use of the hydrogel on a large scale might have a revolutionary impact on the optimization of water resources management in agriculture.