Urea Release Research Articles

Novel Controlled Release Microspheric Soil Conditioner Based on the Temperature and pH Dual-Stimuli Response.

A novel type of temperature and pH dual-stimuli-responsive microspheric soil conditioner was prepared for the controlled release of urea. First, poly(N-isopropylacrylamide-co-methacrylic acid) [P(NIPAM-co-MAA)] was synthesized, and the microspheric soil conditioner was prepared on the basis of chitosan-coated P(NIPAM-co-MAA) via the emulsion cross-linking method. The structure and morphology of the microsphere were characterized by Fourier transform infrared spectroscopy, hydrogen nuclear magnetic resonance, polarization optical microscopy, and scanning electron microscopy. The microsphere showed controlled release behavior in different temperature and pH conditions, indicating good stimuli responsiveness. The plant experiment revealed that the microsphere can effectively promote plant growth in acidified soil and high-temperature conditions, and the pH value of acidified soil could be improved. In addition, the microsphere possessed good biodegradation property in the soil. Therefore, the multi-responsive microspheric soil conditioner owns a great potential value to amend soil conditions and promote plant growth in agriculture applications.

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

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

Characterization; formulation and application of Natural Nano zeolitic materials from Kenya as Smart Delivery Systems for fertilizers and pesticides

This study aimed at using natural zeolitic materials sampled form different places and characterized as nano porous smart delivery systems for storage and controlled release of fertilizer and pesticide molecules. XRD characterization of sample ZT-GA-01 showed that it was zeolite A artificial, abbreviated as Linde Type A (LTA), sample EL-GA-06 was Phillipsite natural zeolites. IR Spectroscopy for ZT-GA-01 and EB-GA-02 showed similar peaks between 3420 – 3480 cm-1, 2350 – 2360 cm-1 and 1630 – 1660 cm-1 indicating H-O-H stretching and bending, while 440 – 670 cm-1 representing Si-O-Si bending for internal tetrahedral. Besides comparable EDX characterized silica to alumina composition of sample EB-GA-02 and the artificial zeolite A applied as the standard, determined as 37.4 % to 18.8 % and 43.6 % to 56.4 % respectfully. Physical properties of samples ZT-GA-01 and EB-GA-02 in terms of BET surface area, BJH pore volume and pore sizes were obtained as; 0.6716 m2/g, 0.002333 cm3/g, 151.519 Å and 0.7099 m2/g, 0.006767 cm3/g, 389.846 Å respectively. Urea loaded samples EB-GA-02 indicated a 39.844 % reduction in pore sizes after successful loading of urea fertilizer into the nano-spaces, while pesticide loading indicated a reduction in pore volumes and pore sizes by 19.15 % and 32.74 % respectively. The simulated release shoed about 82.8 % of stacked urea fertilizer discharged in water and 74.2 % loaded urea released in soil, while 34.4 % and 40.1 % lambda cyhalothrin pesticide amounts were released by pesticide loaded zeolitic sample EB-GA-02 in water and soil respectively. Application of zeolitic sample EB-GA-02 as smart delivery systems demonstrated a sustained slow release of both urea and Lambda cyhalothrin pesticide on tomato and spinach growing and monitoring experiments for the 60 days’ period. In conclusion, our study showed that there exist zeolites and zeolitic materials in some selected parts in Kenya. As well, identified zeolitic sample EB-GA-02 can be used to successfully store agrochemical molecules and significantly delay their release in soil hence applied as nanozeolitic smart delivery systems.

Swelling capacity of sugarcane bagasse-g-poly(acrylamide)/attapulgite superabsorbent composites and their application as slow release fertilizer

In this work, sugarcane bagasse (SCB)-g-poly(acrylamide)/attapulgite superabsorbent composites (SBCs) were prepared by graft copolymerization of acrylamide (AM) onto SCBin presence of attapulgite (ATP) using N,N′-methylene-bis-acrylamide (MBA) as crosslinker and potassium persulfate (KPS) as initiator in aqueous solution. The composite structures were characterized by Fourier Transform Infrared spectroscopy (FT-IR), Thermal Gravimetric Analysis (TGA), X-ray powder diffraction (XRD) and Scanning Electron Microscopy (SEM). The effect of the initiator, crosslinker amounts and attapulgite/hydrogel weight ratio (0.0–14.4 wt%) on the swelling capacity was investigated. The results indicated that highest swelling capacity in distilled water was 920 g/g, obtained with the composite containing 1.3 wt% KPS, 0.08 wt% MBA, 79.9 wt% AM, 5.3 wt% ATP and 13.3 wt% SCB. Different SCBs were loaded with urea and its release was evaluated over time, showing that the urea release rate decreased by increasing ATP amount up to14.4 wt%. Therefore, the SCB-g-poly(AM)/ATP composites could have promising applications also as controlled urea release fertilizer.

Synthesis and Characterization of Controlled-Release Urea Fertilizer from Superabsorbent Hydrogels

It is very important to develop controlled-release fertilizers to ensure efficiency and environmental protection. This study aims to make a superabsorbent hydrogel-based controlled-release urea fertilizer. Superabsorbent hydrogels were prepared from the cellulose of corn cobs cross-linking with epichlorohydrin, and then an amount of urea as a fertilizer was stored inside the hydrogels (GEL-A). The GEL-A functionalization with carboxy-methyl was also carried out in this study to improve the hydrophilicity of hydrogels (GEL-B). GEL-A and GEL-B were immersed in water at a certain pH and temperature range and the urea concentration released from the hydrogels was monitored by a spectrophotometer. The results showed that the urea released by GEL-A and GEL-B was not much different. Respectively, the urea efficiency of GEL-A and GEL-Bwas around 5.29% and 5.56% for 180 min. The urea released from both hydrogels was not significantly affected by changes in the temperature of the solution. Urea release was influenced by pH, and the rate of urea release of GEL-B was faster than GEL-A, so pH control was needed in the application of this slow-release fertilizer.

Agronomic evaluation of controlled release of micro urea encapsulated in rosin maleic anhydride adduct

Plant derived bio-based materials are environmental-friendly and provide a cheap and an attractive source for synthesis of controlled release urea fertilizers which have positive impact on plants’ health. In this work, application of rosin-maleic anhydride adduct encapsulated controlled release micro urea fertilizer (RA-mCRUF) was investigated for the optimization of its controlled urea release properties and evaluation of growth promoting effect on maize (Zea mays) plant under three different soil texture classes. Through response surface methodology, the independent response variables, were optimized for controlled release response of urea. Study found optimized coating repeats, 5.00 cycles; drying time, 11.71 h; and particle size, 41.82 µm; at urea release response of 331.62 mg L−1 in distilled water. Optical microscopy images further demonstrated a more compact and homogeneous surface of RA-mCRUF without any coating defects. Besides, RA-mCRUF predicted a better growth performance of maize plant in clay loam soil. Moreover, RA-mCRUF treated maize plant showed 9.0–24.5 mg g−1 increase in chlorophyll contents and 7.44–12.75 g rise in plant dry biomass. This work successfully produced a new type of RA-mCRUF which has applied role in soil nutrients conservation and addressing effectively food security through crops protection.

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 (BP6), vinasse (BV6) and rice straw (BR6) 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. BV6 was recommended for use as coating material for BCU because the feasibility of the biochars followed the order BR6 > BV6 > BP6, and the practicality of the biochars followed the order BP6 > BV6 > BR6. 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.

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

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

Starch-g-poly(acrylic acid-co-acrylamide) composites reinforced with natural char nanoparticles toward environmentally benign slow-release urea fertilizers

Loss control of nutrients and water has been considered as a global challenge of agriculture because it faced with concurrent management of these two necessities of crop production. Herein, a bio-based slow-release fertilizer (SRF) has been developed using reinforcement of starch-g-poly(acrylic acid-co-acrylamide) superabsorbent polymer with natural char nanoparticles (NCNPs). Incorporation of urea in the matrix of nano-biocomposite resulted in the efficient SRF formulation with remarkable water absorbency (215.1 g/g). Variables including starch, monomers, cross-linker, and nano-filler dosages were optimized using screening the urea release behavior of samples in various pHs (3–10) and salt solutions (NaCl, CaCl2, and FeCl3). NCNPs acted as physical cross-linker as well as nano-filler and formed H-bondings between the oxygenated groups of the polymer and nanoparticles. Urea release measurements in water indicated a well slow-release property of SRF formulations, 70 % of nitrogen released during 21 days. The release time was prolonged with increasing the amount of NCNPs because the favorable interfacial polymer-filler interactions resulted in slower nitrogen diffusion and consequently, slower release rate at neutral and basic pHs. The water-retention of soils containing two different SRFs (with and without nano-filler) showed that NCNPs could double the water-retention compared with the neat polymer. While nitrate leaching rate in the soil for pure urea was measured to be 591.8 mg/L, the starch-g-poly(acrylic acid-co-acrylamide)/NCNPs/Urea decreased the leaching loss of N up to 49.5 mg/L. The soil burial degradation test indicated that the presence of NCNPs in the network of polymer could facilitate the degradation process of the SRF samples.

Fabrication of double crosslinked chitosan/gelatin membranes with Na+ and pH dual-responsive controlled permeability

A double crosslinked membrane based on chitosan/gelatin with controlled release properties was synthesized in aqueous system using potassium pyroantimonate and genipin as the ionic crosslinker and covalent crosslinker, respectively. The membranes were characterized using FT-IR, UV–vis spectra, and SEM. In addition, the thermal stability, contact angle, mechanical and controlled release properties were measured. Double-crosslinking significantly improved the hydrophobicity, thermal stability, and tensile strength of the membrane. The permeabilities of various plant nutrients, including urea and plant growth regulators (PGRs), were evaluated. Under the optimized conditions, the lowest flux (J) of urea was 2.89 mg/ (cm2·h). Urea and PGR release were sustained for up to 3 and 10 days, respectively. The release of agrochemicals in this study followed the Weibull model, demonstrating the Na+-responsive and pH-responsive permeability of the films. This dual-responsive film has potential applications in salinized barrier soil, water treatment, separations, and other membrane applications.

Spout Fluidized Bed Assisted Preparation of Poly(tannic acid)-Coated Urea Fertilizer.

Slow-release fertilizers (SRFs) have been widely used to reduce environment pollution derived from excessive nutrients. Coated fertilizers have been designed and prepared using various materials. However, development of new green coating materials and simple process is still a huge challenge. In this study, tannic acid (TA), a natural polyphenol, was used to prepare poly(tannic acid) (PTA)-coated fertilizers with urea prills as the core, and the technology of the coating process in a spout fluidized bed was developed. PTA coating could be formed rapidly by the fast oxidation of TA by an oxidation solution containing CuSO4 and H2O2. The coated urea release behavior was systematically studied in water and soil. In both water and soil, the release rate of nitrogen from coated urea is much slower than that from raw urea. Raw urea was completely dissolved within 30 min, while 27% of urea was released from coated urea. The pot experiments indicated that coated urea has a positive effect on the plant growth as well. Our results provide an effective method to prepare environment-friendly SRFs, indicating a promising application in sustainable agriculture.

Correlation Between Gel Strength of Starch-Based Hydrogel and Slow Release Behavior of Its Embedded Urea

Starch-based hydrogels have attracted increasingly attention for application in controlled release fertilizers. However, there is currently a lack of knowledge on ways to characterize this system. In this work, we employed a hot-compression vulcanizer to in-situ synthesize monolithic urea-embedded grafted starch hydrogels with a slab geometry, which facilitates the subsequent measurement of gel strength and urea release kinetics. The results revealed that the greater the gel strength induced by a decreased urea load, an increased graft content, and an increased cross-linking density of starch-based hydrogels, the less the initial burst release of embedded urea. The unavoidable burst release could be ascribed to the heterogeneous network structure of starch-based hydrogels. The network of the hydrogels also afforded an zero-order, or at least time-independent, release kinetics of urea at intermediate stable stage, regardless of their microstructural parameters. Our results could provide a guideline to the design of hydrogel-based fertilizer delivery systems.

Pseudo-zwitterionic microvesicles for sustained urea release

Zwitterionic microvesicles formed by catanionic system, based on sodium dodecyl sulfate and hexadecyltrimethyl ammonium bromide, have been investigated for sustained urea release using UV?visible absorption spectroscopy. The change in variables such as temperature, sonication time and initial urea concentration was related to urea entrapment efficiency and release from microvesicles. Korsmeyer?Peppas model was applied to highlight release mechanism and kinetics. Both diffusion and erosion were responsible for urea release and rate constant varied with change in conditions. The quantification of association between urea and catanionic vesicles in terms of binding constant (Kbin) and binding free energy showed that urea binding was thermodynamically favored. Our results indicate that biocompatible pseudo-zwitterionic vesicles have enormous potential to act as sustained release system for nitrogenous fertilizers such as urea.

Biodegradable oil-based polymeric coatings on urea fertilizer: N release kinetic transformations of urea in soil

Polymer coatings are used to control the rate of release of plant available nutrients from fertilizers as well as to reduce nutrient losses such as ammonia (NH3) volatilization. Although the literature presents several examples of materials used to coat urea, little is known about nitrogen (N) release properties such as the mechanism involved and phenomena (e.g., pore opening) in the polymer coating. Thus, this study investigated urea release from polyurethane (PU) derived from two renewable raw materials (castor oil and soybean oil), to explain how the oil structure and coating microstructure influence release and urea-N dynamics in soil. The results demonstrated that the profile of urea release and the urea-N mineralization in the soil could be controlled by altering the thickness of the coating on the urea granules. Coating by eco-friendly polymer was efficient in controlling urea release in soil to reduce volatilization of ammonia and increase the availability of N in the soil.

Analysis of NH3-N Slow Release systems for fiber digestibility of low-quality forage: in vitro approach

ABSTRACT: Urea is a common non-protein supplement used in ruminant feed; however, excessive consumption may lead to poisoning by NH3. Although the slow release of urea into the rumen has shown to be an essential aspect for ruminant feed, to date only a few studies have addressed this matter. In this study we examined the influence of five different NH3-N slow release systems based on clay-urea nanocomposites on the fiber digestibility of low-quality forage (sugarcane straw) in vitro. Physical properties of nanocomposites were evaluated and their effects on digestibility were tested in vitro using pristine urea as a positive control (level of 1 % of DM of sugarcane straw sample) and sugarcane (with no additives) as a negative control. Ammonia release and digestibility were evaluated at 12, 24, 36, 48, 72 and 96-h. Generally, all nanocomposites increased (p < 0.05) digestibility of fiber over control under all the conditions stipulated, but the samples with hydrogel content were more expressive. We concluded that an ideal release rate and optimum environment for microbial synthesis are necessary to maximize the digestion of sugarcane.

Development and characterization of allicin using palm stearin as a binder on urea granules

The potency of allicin as a urease inhibitor has been discovered and the demand for using a biodegradable material as a coating is increasing. The loss of nitrogen can be reduced, and the efficiency of the fertilizer can be increased by utilizing a coating. The objective of this study was to determine the compatibility of allicin and urea with palm stearin as an adhesive agent in the coating process. Four treatments were used in this study; urea as the control, urea coated with palm stearin (UPS), urea coated with allicin and palm stearin (UPSA) and urea coated with NBPT (UNBPT). The treatments were analyzed for thickness, chemical structure, total N content, dissolution rate in water and hardness. Results from FT-IR and SEM images demonstrated that palm stearin was compatible with allicin and urea with smoother coated layer. The efficiency of coated urea with allicin and plam stearin was enhanced by reducing 70% of urea release in 24 hours as compared to the urea. The crushing strength was significantly improved by using palm stearin as the binder. Coating urea with palm stearin and allicin appears to increase the efficiency of urea.

Environmentally Friendly Fertilizers Based on Starch Superabsorbents.

Superabsorbents starches (SASs) were synthesized and characterized starting from native corn starch, bitter cassava and sweet cassava by graft copolymerization with itaconic acid. Additionally, their swelling behavior was studied both in water and in buffer solutions with different pHs and saline solutions. Their applicability was tested as environmentally friendly fertilizers in the absorption and release of urea, potassium nitrate and ammonium nitrate at different concentrations of fertilizers. The values of swelling at the equilibrium (H∞) in water and different media of the graft copolymers demonstrated their superabsorbent capacity, polyelectrolyte behavior, and smart response to environmental stimuli. The percentage of fertilizer absorbed and released from the SASs was a function of the initial concentration of the fertilizer in the medium. The loading and release of SASs were depended on the initial concentration of the fertilizer in the medium as well as the nature, structure, and morphology of the starch used.

Effects of fertilizer types and water quality on carbon dioxide emissions from soil in wheat-maize rotations

The use of fertilizers as addition inputs in agricultural systems can increase the yield of wheat and maize, while also stimulating the emission of carbon dioxide from soil that the main man-made greenhouse gas. Our objectives focused on the impact of different types of synthetic fertilizers and water quality. The purposes were to determine the feasibility of using wasted water for irrigation and to relate CO2 fluxes to the yield of maize and wheat, as well as to select the best fertilizer type with low CO2 emission and high yield. The experiment consisted of a double factors test focusing on four forms of fertilizer (urea, amine and slow release fertilizer) and the quality of water (reclaimed water and underground water). The results showed that the reclaimed water was not significant on the CO2 discharge rate, the maize-wheat yield or the soil properties in 2014 or 2015; however, the CO2 emission increased slightly in 2015. Focusing on fertilizer treatments, the reclaimed water & amine fertilizer treatment (CAF) that had higher cumulative CO2 emissions was 32.75 t·ha−1 in 2014 and 33.86 t·ha−1 in 2015. According to the ratio CO2/Y, the slow released fertilizer that reduces CO2 emissions and keeps the yield high is the preferred choice.

Urea Uptake and Release by Novel Macrogels from Dimethylacrylamide

ABSTRACTA novel macrogels poly(N,N-Dimethylacrylamide) (p(DMAAm)) and its derivatives were synthesized from DMAAm for use in urea uptake and release. p(DMAAm) surface was modified by NaOH and HCl to obtain p(DMAAm)/NaOH and p(DMAAm)/HCl, which are negatively and positively charged, respectively. The dynamic swelling behaviors, water retention and pH sensitivities of the macrogels were studied. It was found that all macrogels exhibited the equilibrium swelling ratio (SR) in the range 1068–1451%. Swelling kinetics showed that the macrogels possessed Fickian diffusion behavior while the diffusion coefficient of the macrogels varied from 1.41.10–5 to 2.53.10–5 cm2/min. Furthermore, urea uptake capacity and controlled release properties of the macrogels were studied. The maximum urea uptake capacity at pH 6 for p(DMAAm), p(DMAAm)/HCl, p(DMAAm)/NaOH macrogels were obtained to be 76.7 mg/g, 88.2 mg/g, 110.5 mg/g, respectively. It was concluded that the Langmuir isotherm fits quite well the experimental data. To describe the urea release kinetics, experimental data recorded at different pH solutions were computed through common release models. At pH 8, the p(DMAAm)/NaOH showed the highest release among the three prepared macrogel. Consequently, the results demonstrated that synthesized novel macrogels had high swelling rate and ability of absorbing and releasing of urea at different medium conditions.

From hollow lignin microsphere preparation to simultaneous preparation of urea encapsulation for controlled release using industrial kraft lignin via slow and exhaustive acetone-water evaporation

AbstractLignin nano/microparticles have recently attracted growing interest for various value-additive applications of lignin, especially encapsulation. In this study, in order to establish a highly efficient and highly productive preparation process to effectively utilize technical lignin, a brand-new, slow and exhaustive solution evaporation process following a simple, self-assembly principle was developed using industrial softwood kraft lignin (SKL) from a starting acetone-water (80/20, v/v) solution to recover 100% of the lignin as homogeneous and well-shaped microspheres. The prepared microspheres had a typical average diameter of 0.81 ± 0.15 μm and were hollow with very thin shells (of nanoscale thickness). Based on this developed technique, encapsulation of urea by these lignin microspheres was directly achieved using the same process as hollow lignin microspheres with urea attached to the outside and entrapped inside of the wall. Two distinct urea release rates were observed for the urea-encapsulated microspheres: a fast release of the urea outside the shell wall and a slow (controlled) release of the urea inside the shell wall. The encapsulation efficiency was as high as 46% of the trapped urea as encapsulated inside the lignin microspheres. The slow and exhaustive solution evaporation procedure reported here is a simple and straightforward method for the valorization of industrial kraft lignin as hollow microspheres with controllable, homogeneous and desired morphologies, and especially for the direct preparation of lignin-based encapsulating fertilizers for controlled release.