Fabrication and Evaluation of Biodegradable Alginate Bead Controlled Release Fertilizer for the Controlled Release on Nitrogen

doi:10.21203/rs.3.rs-2226828/v1

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Fabrication and Evaluation of Biodegradable Alginate Bead Controlled Release Fertilizer for the Controlled Release on Nitrogen

https://doi.org/10.21203/rs.3.rs-2226828/v1

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Controlled-release fertilizers (CRFs) are a next-generation type of fertilizers, with several advantages over conventional fertilizer. However, using non-degradable and petroleum-based materials in the fabrication of CRFs possess considerable threat to agricultural soils and the environment. Therefore, this study aimed to develop a highly biodegradable, nontoxic, and biocompatible CRFs based on calcium alginate (CaAlg) beads. The results showed that the sphericity of the beads increased with decreasing CaCl₂ concentration and increasing gelation time. Additionally, there was a significant decrease in the viscosity of sodium alginate (NaAlg) suspension with increasing concentration of urea. Moreover, there was an increase in the urea loading (UL) efficiency and a decrease in the urea release rate of the beads with increasing concentration of CaCl₂. Furthermore, carrots grown in the control soil and soil containing urea were larger compared with those grown in soils containing CRF, indicating the controlled release of nitrogen by the CRF. Adding humic acid (HA), poly vinyl acid (PVA), and citric acid to the suspension increased the stability and improved the urea release profile of the CRF. Overall, the fabrication process is easy and could be applied for the mass production of CRFs.

controlled-release fertilizers

alginate

ionic crosslinking

nitrogen use efficiency

polyvinyl alcohol

urea

citric acid

humic acid

Nitrogen fertilizer is an essential nutrient for enhancing crop productivity, growth, and health [1–4]. Owing to the development of the Haber-Bosch process, there has been an increase in the production of nitrogen fertilizer [5, 6], leading to increased applications of fertilizers [7, 8]. However, a large proportion of applied fertilizers are lost through leaching, denitrification, and volatilization [9–11] owing to the high water solubility of urea, results in a low nitrogen use efficiency (NUE) of approximately 30–50% [4]. Therefore, more fertilizers are applied to meet crop nitrogen need, which further disrupts the ecosystem through soil degradation, eutrophication, and pollution [12–15].

Recently, controlled-release fertilizers (CRFs) [16], which functions based on similar principles to drug delivery systems have been developed to reduce fertilizer loss. Coated bead-type CRFs have a sustained release rate that is dependent on the coating thickness [17], thus providing a continuous supply of nitrogen-based nutrients to the soil. However, the materials used for the fabrication of coated beads are non-degradable petroleum-based polymers that accumulate in the soil after use, which can negatively soil structure [18, 19] and the environment. For instance, Nizzetto et al and Möller et al reported that approximately 63,000–430,000 and 44,000–300,000 tons of microplastics (MPs) accumulate yearly in farmlands in European and North American, respectively [20, 21], emphasizing the need to develop highly degradable and biocompatible CRFs for sustainable environment.

Recently, alginate has gained considerable attention as a promising eco-friendly coating material. Alginate is a polysaccharide in brown algae and is widely used as an encapsulating agent owing to its simple and unique process [22–24]. The “egg-box” structure formed by alginate can be utilized to produce biodegradable hydrogel beads in the presence of divalent cations [25–27]. However, beads absorb water and swell rapidly owing to their hydrophilic nature, indicating the need for further modification [25–27]. Zhang et al fabricated lignin-clay nanohybrid biocomposite-based CaAlg CRFs, which can increase the hydrophobicity of beads by combining modified quaternary ammonium lignin (QAL) with bentonite clay to form lignin-clay nanohybrid [28]. Additionally, Sathisaran et al. utilized chitosan-alginate and gelatin-alginate composite beads to control fertilizer release rate [29]. However, the application of these beads in controlled fertilizer release has been limited.

Therefore, the aim of this study was to develop a highly degradable, nontoxic, and biocompatible CRFs based on calcium alginate (CaAlg) beads. To achieve this, a modified CaAlg CRF system was fabricated by introducing poly vinyl alcohol (PVA) and citric acid (CA) as additional crosslinking chemicals, and humic acid (HA) as a physical barrier and chelating agent to increase nitrogen use efficiency. PVA and CA were chosen as additional materials for the CaAlg bead to introduce chemical crosslinking [30–33] to enhance the physical properties of the CRF coating and decrease fertilizer release rate. HA, an organic compound that can improve soil health [34] was incorporated into the system to function as a mesh-like material in the synthesized CRF and as a chelating agent [35, 36], owing to its various chemical groups. The effect of the CRF on carrot growth was examined [37, 38], and the release rate and profile of the CRF were evaluated by analyzing soil leachates. Additionally, the urea release behavior of CaAlg CRF in water medium was evaluated.

2.1. Materials

Sodium alginate (NaAlg) (Sigma-Aldrich), urea (Sigma-Aldrich, ReagentPlus, ≥ 99.5%), calcium chloride (CaCl₂) (Sigma-Aldrich, anhydrous, powder ≥ 97%), CA (Sigma-Aldrich, ACS reagent, ≥ 99.5%), PVA (Sigma-Aldrich, 13,000–23,000 g mol^-1, 87–89% hydrolyzed) and HA sodium salt (Sigma-Aldrich, technical grade) were used to fabricate CaAlg CRF. Deionized water (DI water) was used for solution preparation. 4-(dimethylamino) benzaldehyde (DMAB, 98%), methyl alcohol (CH₃OH), and hydrochloric acid (HCl, 37%) were used to analyze the concentration of urea. All the chemicals were used as received without further purification.

2.2. Preparation of CaAlg Bead by Extrusion Dripping

Exactly 60 ml of NaAlg suspension was transferred into 200 ml of CaCl₂ solution, using a syringe infusion pump (legato200, KD scientific) and 18 G needle (outer diameter 1.27 mm) at a rate of 1.0 ml/min to form CaAlg beads. After dripping, the mixture was left standing in a coagulation bath, without stirring, to induce ionic crosslinking. The distance between the needle tip and gelling solution surface was 25 cm. Thereafter, the beads were washed with DI water. Beads containing PVA and CA were prepared using the same procedures above, with some modification. PVA and CA was added in the NaAlg suspension, and the mixture was heated at 150 ℃ for 60 min after bead formation to induce chemical crosslinking. All beads were dried in a vacuum oven at 60 ℃ for 3 d and stored in a desiccator.

2.3. Optimization of CaAlg Beads for the Fabrication of ALG CRF

2.3.1. Fabrication and Characteristics of Non-urea Entrapped CaAlg Bead

The effect of different concentrations of NaAlg (1.0, 2.0, 3.0, 5.0, and 7.0 wt%) and CaCl₂ (1.0, 2.0, 3.0, 5.0, and 10.0 wt%) and gelation time (0, 30, and 60 min) on the formation of CaAlg beads were examined.

Optical image of the beads was taken with a digital camera (EOS 200D, Canon) for analysis. The degree of crosslinking was determined by the normalized weight of 10 beads. The diameters of the beads were determined using an optical microscope (BX51TF, Olympus), which was used to the sphericity of the beads. Normalized weight and sphericity were calculated according to the following equation [22].

$$\text{N}\text{o}\text{r}\text{m}\text{a}\text{l}\text{i}\text{z}\text{e}\text{d} \text{w}\text{e}\text{i}\text{g}\text{h}\text{t} \left(\frac{\text{g}}{\text{%}}\right)=\frac{\text{T}\text{h}\text{e} \text{w}\text{e}\text{i}\text{g}\text{h}\text{t} \text{o}\text{f} 10 \text{b}\text{e}\text{a}\text{d}\text{s} \left(\text{g}\right)}{\text{C}\text{o}\text{n}\text{c}\text{e}\text{n}\text{t}\text{r}\text{a}\text{t}\text{i}\text{o}\text{n} \text{o}\text{f} \text{e}\text{a}\text{c}\text{h} \text{s}\text{u}\text{s}\text{p}\text{e}\text{n}\text{s}\text{i}\text{o}\text{n} \left(\text{%}\right)}$$

$$\text{S}\text{p}\text{h}\text{e}\text{r}\text{i}\text{c}\text{i}\text{t}\text{y}=\frac{2{\text{d}}_{\text{m}\text{i}\text{n}}}{{\text{d}}_{\text{m}\text{i}\text{n}} + {\text{d}}_{\text{m}\text{a}\text{x}}}$$

Where d_min and d_max are the minimum and maximum diameters of the bead, respectively.

2.3.2. Fabrication and Characteristics of Urea Entrapped CaAlg Bead with Various Components

Exactly 100 g of NaAlg suspensions were prepared by mixing 5.0 g and 10.0 g of NaAlg powder in 95.0 g and 90.0 g of DI water, respectively, using a mechanical stirrer. Urea was dissolved in NaAlg suspensions at a weight ratio of 1:1. Thereafter, 5.0 wt% of HA, 3.0 wt% of PVA, and excess amounts of CA were added into the NaAlg and urea suspensions and stirred. In this procedure, HA, PVA, and CA were added according to the sample name, respectively. Urea entrapped CaAlg beads were fabricated using the same procedure described for the preparation of CaAlg beads via extrusion dripping method.

The viscosity of each NaAlg suspension was measured, using a digital rotational viscometer (DV1, Brookfield). The nitrogen contents of each bead were analyzed using an elemental analyzer (Unicube, Elementar Americas) after crushing the beads to powder and drying. Urea loading (UL) was calculated according to the equation below [38], using the nitrogen contents, which were obtained as the fraction of nitrogen.

$$\text{U}\text{L} \left(\text{%}\right)=\text{N} \text{f}\text{r}\text{a}\text{c}\text{t}\text{i}\text{o}\text{n} \times \frac{1 \text{m}\text{o}\text{l} \text{u}\text{r}\text{e}\text{a}}{28 \text{g} \text{N}} \times \frac{60.02 \text{g} \text{u}\text{r}\text{e}\text{a}}{1 \text{m}\text{o}\text{l} \text{u}\text{r}\text{e}\text{a}} \times 100 \left(\text{%}\right)$$

2.4.Carrot Cultivation Experiment

Carrots were planted in cube-shaped transparent plastic pots (30.0 × 30.0 × 30.0 cm3), with the lower layer filled with 3.0 kg of washed coarse sand (Gapjone, Republic of Korea) to enable drainage. The upper layer of the pot was filled with 3.5 kg mixture of topsoil (peat moss 80%, perlite 20%) and worm castings (Kebifarm, Republic of Korea) at 7:3. Three carrots were planted in each pot, and the environment was maintained at an average temperature of 15–20 ℃ under 12 h photoperiod per day.

Excess nitrogen was added in the form of urea (4 g of urea) to confirm the growth inhibitory effect of excess nitrogen. An equivalent dose of urea is applied to each pot in the form of CaAlg CRFs based the UL of the CRFs (Eq. 5, Table. 1). Water (2.5 l) was added to each pot every 7 d, and the leachates were collected and stored at -20 ℃ for chemical analysis.

$$\text{L}\text{i}\text{m}\text{i}\text{t}\text{e}\text{d} \text{a}\text{m}\text{o}\text{u}\text{n}\text{t}\text{s} \text{o}\text{f} \text{f}\text{e}\text{r}\text{t}\text{i}\text{l}\text{i}\text{z}\text{a}\text{t}\text{i}\text{o}\text{n} \text{i}\text{n} \text{c}\text{a}\text{r}\text{r}\text{o}\text{t} \text{c}\text{u}\text{l}\text{t}\text{i}\text{v}\text{a}\text{t}\text{i}\text{o}\text{n} \left(\text{g}\right) = \frac{15 \text{l}\text{b} \text{N}}{\text{a}\text{c}\text{r}\text{e}} \times \frac{453.59237 \text{g}}{\text{l}\text{b} } \times \frac{60.06 \text{g} \text{u}\text{r}\text{e}\text{a}}{28 \text{g} \text{N}} \times \frac{\text{a}\text{c}\text{r}\text{e}}{4046.9 {\text{m}}^{2}} \times \frac{{0.09 \text{m}}^{2}}{\text{p}\text{o}\text{t}}$$

$$= 0.3246 \text{g} \text{u}\text{r}\text{e}\text{a} {\text{p}\text{o}\text{t}}^{-1}$$

$$\text{T}\text{h}\text{e} \text{i}\text{n}\text{p}\text{u}\text{t} \text{a}\text{m}\text{o}\text{u}\text{n}\text{t} \text{o}\text{f} \text{C}\text{a}\text{A}\text{l}\text{g} \text{C}\text{R}\text{F} \left(\text{g}\right)=4 g Urea \times \frac{1g bead}{UL g urea}$$

Table 1

The amounts of CaAlg CRF in each carrot cultivation pot based on the urea content (g)
	Control	PC (PVA + CA)	HA	HPC (HA + PVA + CA)
5.0 wt% CaAlg CRF	5.66	6.83	7.01	7.33
10.0 wt% CaAlg CRF	6.19	7.19	7.44	11.89

After 90 days, the plants were harvested, divided into shoots and roots, and each sample was weighed. The number of shoots was counted, and the 20 longest shoots were selected to measure the average length of the shoots. The harvested carrots were vacuum-dried in an oven at 60 ℃ for 3 d, and dry weights were measured. Moisture was calculated using the equation below.

$$\text{M}\text{o}\text{i}\text{s}\text{t}\text{u}\text{r}\text{e} \left(\text{%}\right)= \frac{\text{F}\text{r}\text{e}\text{s}\text{h} \text{w}\text{e}\text{i}\text{g}\text{h}\text{t} \left(\text{g}\right)-\text{r}\text{e}\text{s}\text{h} \text{w}\text{e}\text{i}\text{g}\text{h}\text{t} \text{t}\text{h}}{\text{F}\text{r}\text{e}\text{s}\text{h} \text{w}\text{e}\text{i}\text{g}\text{h}\text{t} \left(\text{g}\right)} \times 100 \left(\text{%}\right)$$

2.5. Leachate Analysis

The leachates collected from the pots after watering were filtered, using a Whatman paper filter No. 42 that was previously washed with 2 N KCl solution to remove extractable combined nitrogen. The nitrogen content of the leachates was determined using the kjeldahl distillation method and a titration instrument (VAPODEST 50, Gerhardt). Soil nitrogen loss (g) was calculated using the formula below.

$$\text{S}\text{o}\text{i}\text{l} \text{n}\text{i}\text{t}\text{r}\text{o}\text{g}\text{e}\text{n} \text{l}\text{o}\text{s}\text{s} \left(\text{g}\right)= \text{m}\text{a}\text{s}\text{s} \text{o}\text{f} \text{l}\text{e}\text{a}\text{c}\text{h}\text{a}\text{t}\text{e} \left(\text{g}\right)\times \frac{\text{n}\text{i}\text{t}\text{r}\text{o}\text{g}\text{e}\text{n} \text{c}\text{o}\text{n}\text{t}\text{e}\text{n}\text{t}\text{s} \left(\text{%}\right)}{100}$$

2.6. Urea Release Behavior of CaAlg CRFs in Water Medium

The two types CaAlg CRF beads (5.0 g each) were packed in small tea bags and immersed in 100 g of distilled water (DW) for 24 h to compare the effect of different CaCl₂ concentrations, and 72 h for effect of PC added CRF beads. Thereafter, the bags were removed and 100 µl of the medium was collected for analysis. The bags were placed in vials containing 100 g of fresh DW and the process was repeated at specific times (3, 6, 12, 24, and 72 h). The amount of urea release in the aqueous medium was determined, using p-dimethylaminobenzaldehyde (D-MAB) colorimetry method [39]. The content of urea-N in each sample was determined at 440 nm, using UV-vis spectrophotometer (V-770, Jasco). Accumulative release rate graph was derived based on the result of calculated release rate (RR). The RR of each time period was calculated using the equation below.

$$\text{R}\text{e}\text{l}\text{e}\text{a}\text{s}\text{e} \text{r}\text{a}\text{t}\text{e} \left(\text{%}\right)=\frac{released amount of urea \left(g\right)}{5.0 g \times UL \left(\text{%}\right) /100\text{%}}\times 100\left(\text{%}\right)$$

3.1. Characteristics of Fabricated CaAlg Beads

In the present study, alginate beads were prepared by ionotropic gelation via Mⁿ⁺ ions [22–27]. The polyguluronate units in alginate molecules can form a chelated structure by coordinating metal ions into an “egg-box” morphology (Fig. 1) [22–27]. CaAlg beads can be fabricated by transferring NaAlg droplet into CaCl₂ solution, forming an emulsion reaction. This spherical pocket can hold substance and its capacity can vary with the concentration of NaAlg and CaCl₂. Therefore, the characteristics of basic CaAlg beads, including sphericity and diameter, were determined prior to incorporating urea. The results of the present study showed that the sphericity of the beads increased with increasing concentration of NaAlg and decreasing concentration of CaCl₂, peaking at 0.99 (Fig. 2). Generally, a perfect sphere has a sphericity of 1.00 [22]. Since CaCl₂ provides Ca²⁺ ions to the chelating system, it functions as the crosslinking point that determines the overall morphology of the bead. Therefore, an increase in CaCl₂ concentration can cause an increase in crosslinking density, resulting in stiff-structured beads. In contrast, an increase in the concentration of relatively flexible polyguluronate units (NaAlg) can promote the fabrication of highly spherical beads. Highly spherical beads tend to have lower surface areas compared with non-spherical beads, which can reduce contact with water, thus delaying the release rate of captured materials. Interestingly, the findings of the present study showed that the sphericity of beads increased from 0.78–0.92 with increasing NaAlg concentration (3.0–7.0 wt%) at high CaCl₂ concentration, which was attributed to high chelating capacity of NaAlg owing to its high viscosity. Further analysis of the effect of gelation time and the concentrations of NaAlg and CaCl₂ showed that the sphericity of the beads increased with decreasing CaCl₂ and increasing gelation time (Figs. 2b and d). In contrast, the sphericity of beads prepared using high concentrations of NaAlg and CaCl₂ remained unchanged with increasing time, indicating that the viscosity of the beads increases rapidly, reaching the maximum at high concentrations of both the chelating and the crosslinking units.

In the present study, the co-solvent used for both NaAlg and CaCl₂ was water, which has some several advantages, one of which is that the use water could facilitate the mass production of the beads. Additionally, since the fabrication procedure involves a swell-dry-swell process, which involves the gradual drying of water in the beads containing urea, the release rate of the fertilizer will be limited. Finally, the process adopted in this study is flexibly, and it is possible to add functional materials to further improve the release rate, stability, and mechanical strength of the beads. Functional material should be either water-soluble or dispersible in water to facilitate rapid fabrication.

The effect of urea addition on the viscosity of NaAlg suspension was examined (Fig. 3). Viscosity is an important determinant of the quality of beads when extrusion dripping method is used for fabrication [40, 41]. The results of the present study showed that there was a significant decrease in the viscosity of NaAlg suspension with increasing concentration of urea. Adding urea in the water medium increases the pH of the environment, with induces the ionization of COOH functional groups of NaAlg to form COO^- [42]. The negatively charged functional groups creates an electrostatic repulsion between ions, which increases the mobility of NaAlg and lowers its viscosity.

Furthermore, the effect of CaCl₂ concentration on the UL efficiency of CaAlg CRF beads was examined. The UL efficiency of the beads was calculated using equation number 4. There was a steady decrease in the UL efficiency of the beads with increasing concentration of CaCl₂ (Fig. 4). An increase in the concentration of crosslinking points (Ca²⁺ ions) could lead to highly dense structures, which can expel urea from the core. However, there was a significant decrease in urea release rate with increasing concentrations of CaCl₂ (3.0–10.0 wt%), corresponding to UL of 84.9 and 62.2%, respectively. These results indicated the UL and release rate of the beads exhibit an inverse relationship. Additionally, the effect of gelation time on UL and release rate was examined (Figure S1). Although the UL efficiency of the beads was not significantly affected by increasing gelation time at CaCl₂ concentration of 10.0 wt% (Fig. 4b), there was an increase in urea release rate with increasing gelation time (Fig. 5b). Additionally, the diameter of the dried beads decreased from 2.14–1.84 mm with increasing gelation time from 30–60 min (Figure S2). The non-significant difference in the UL of the beads with increasing gelation time could be related to the mobile capacity of the bead structure. The short gelation time of 30 min is insufficient for the formation of the egg-box structure, resulting in multiple defect points, which can negatively affect the structure and stability of the beads during the dry-reswell process. Moreover, the similar UL efficiency of the beads at 30 and 60 min gelation time indicates that the structure of the beads was highly stable. Additionally, the dry-reswell process can increase the stability of beads fabricated using 10.0 wt% of CaCl₂ and gelation time of 60 min by reducing excessive free space in the core of beads.

CaAlg beads are highly hydrophilic due to the basic structure of alginates, which swells rapidly when exposed to humid conditions, such as agricultural soils [43–45]. In the present study, three eco-friendly materials (PVA, HA, and CA) were used to modify the fabricated CaAlg CRFs to inhibit the rapid release of urea. Condensation reactions occur during the fabrication process, which produces esters between the –COOH groups and the –OH groups of PVA, HA, and CA, and these multifunctional molecules form crosslinks. Particularly, HA is an important absorbent of plant nutrients owing to its high specific surface and cation exchange capacity (CEC). The high CEC of HA is attributed to its negative charge, which can improve the NUE of CRF beads during decomposition [46, 47]. Optical images of CaAlg CRFs fabricated with the additives showed that there was no significant change in shape and size of beads, except for colors (Fig. 6a). The addition of PVA, HA, and CA enhanced the matrices of the beads, but decreased their UL efficiency (Fig. 6b), which could be attributed to competition between urea and the additive for limited free space in NaAlg chains.

Fertilizer is used in crop production to improve soil nutrient level to support optimal plant growth and yield. In the present study, we examined the growth inhibitory effect of excess nitrogen on carrot. Carrots require only a small amount of soil nitrogen for optimal growth. Kelley et al recommended less than 15 pounds of nitrogen fertilizer per acre for carrot cultivation [38]. In this study, the topsoil was mixed with vermicompost, thus providing some amount of soil nitrogen. Additionally, nitrogen was supplied in the form of urea and CaAlg CRFs to induce excessively high soil nitrogen levels. The soil were analyzed to measure controlled release effect. Compared with carrots grown in soils containing CRF, carrots grown in the control soil and in soil containing urea were larger (Figure. 7). In contrast, carrots grown in soil containing CRF were small, especially H and PC samples. However, carrots grown in soils supplied CRF containing 10.0 wt% of urea were larger than those in soils supplied CRF containing 5.0 wt% of urea.

Furthermore, the carrots were grown for 90 d and the wet and dry weights were measured to confirm the effect of nitrogen fertilizer. Nitrogen fertilizer did not significantly affect the stems of the plants, with only a slight increase in weight owing to the accumulation of moisture (Fig. 8a-c). In contrast, there was a decrease in the root weight of carrots grown in soils supplied nitrogen in the form of CRFs, which was attributed to a decrease in the weight of the carrot flesh. The controlled release effect of CRFs was determined by analyzing the nitrogen content of the soils after harvest. Compared with soils supplied CRF, control soils and soils supplied urea had significantly lower final nitrogen contents, which could be attributed to the leaching of organic nitrogen in the soil by watering during the cultivation period. In contrast, soils supplied CRF had higher final nitrogen content compared with initial content prior to cultivation and CRF addition. Regarding soils supplied CRF containing 5.0 wt% urea without additives (5C), the residual nitrogen level was similar to that of soils in the control group, indicated the rapid release and exhaustion of urea prior to cultivation. However, soils supplied CRF containing 10.0 wt% urea without additives (10C) had relatively higher amount of residual nitrogen, indicating that the bead had a better controlled release of urea. Interesting, the additives significantly suppressed the rapid release of urea from CRF. Furthermore, the addition of humic acid increased the residual nitrogen content of the soil, which was consistent with the nitrogen content of leachates collected weekly (Fig. 8 and S3). Generally, HA prevents the leaching of organic nitrogen by acting as a natural chelate. Regarding, There was considerable nitrogen loss during the cultivation period via leaching in soils supplied urea. However, soils supplied CRF containing 10.0 wt% of urea only lost approximately half the amount of nitrogen lost by soils supplied urea.

CaAlg beads containing urea were successfully fabricated and optimized via extrusion dripping method. The beads were formed through crosslink between the alginate chains by Ca²⁺ ions, and the higher the degree of crosslinking, the lower the release rate urea [48]. The finding of this study showed that the addition of urea in the absence of additives, including HA, PVA, and CA, increased the pH of the suspension, resulting in electrostatic repulsion and lower viscosity. However, the addition of HA, PVA, and CA reduced the release rate by strengthening the structure of the beads. Specifically, the addition of HA can improve the NUE after degradation of CRF beads. Additionally, carrots grown in soils supplied CRF were smaller in size owing to excess supply of nitrogen, indicating that CRF sustained continuous nitrogen release in the soil for the 90 d cultivation period. Overall, the fabricated CRF maintained continuous release of nitrogen; however, the additives improved the stability of the CRF, which could support plant growth during after the decomposition of the beads. The fabrication process applied in this study is easy and could be applied for the mass production of CRFs containing urea.

Author Contributions:

Conceptualization, J. M. Koo.; methodology, J. M. Koo and D. K. Hwang.; formal analysis and investigation, H. Y. Cho, T. V. Thanh, H. Kim and D. K Hwang.; writing—original draft preparation, D. K. Hwang and H. Y. Cho.; writing—review and editing, H. J. Kim, H. Jeon and J. M. Koo; visualization, H. Y. Cho.; supervision, J. Park, and J. M. Koo.; project administration, D. X. Oh.; All authors have read and agreed to the published version of the manuscript.

Funding:

This research received no external funding.

Data Availability Statement:

Not applicable

Acknowledgments:

This work was supported by the Technology Development Program (20008447, 20008628) funded by the Ministry of Trade, Industry & Energy (MOTIE, Republic of Korea), the Korea Research Institute of Chemical Technology (KRICT) core project (SS2242-10) and a project of “Ulsan City-KRICT technical cooperation project”, supported by KRICT and Ulsan Government.

Conflicts of Interest:

The authors declare no conflict of interest.

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No competing interests reported.

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Fabrication and Evaluation of Biodegradable Alginate Bead Controlled Release Fertilizer for the Controlled Release on Nitrogen

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Abstract

Figures

1. Introduction

2. Materials And Methods

2.1. Materials

2.2. Preparation of CaAlg Bead by Extrusion Dripping

2.3. Optimization of CaAlg Beads for the Fabrication of ALG CRF

2.3.1. Fabrication and Characteristics of Non-urea Entrapped CaAlg Bead

2.3.2. Fabrication and Characteristics of Urea Entrapped CaAlg Bead with Various Components

2.4.Carrot Cultivation Experiment

2.5. Leachate Analysis

2.6. Urea Release Behavior of CaAlg CRFs in Water Medium

3. Results And Discussion

3.1. Characteristics of Fabricated CaAlg Beads

4. Conclusions

Declarations

References

Additional Declarations

Supplementary Files

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