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Article

Multilayer Silk Sericin-Based Coating for Controlled Release of Water and Nutrients in Soil: Development, Characterization, and Performance Evaluation in Agricultural Production Model

by
Natalia Jaramillo-Quiceno
1,*,
Dora M. Carmona
2,
Mabel Torres-Taborda
3,
Gustavo Adolfo Hincapié-Llanos
3 and
Catalina Álvarez-López
1,3
1
Grupo de Investigación Sobre Nuevos Materiales, Universidad Pontificia Bolivariana, Medellín 050031, Colombia
2
Grupo de Investigaciones Ambientales, Universidad Pontificia Bolivariana, Medellín 050031, Colombia
3
Grupo de Investigaciones Agroindustriales, Universidad Pontificia Bolivariana, Medellín 050031, Colombia
*
Author to whom correspondence should be addressed.
Horticulturae 2024, 10(3), 273; https://doi.org/10.3390/horticulturae10030273
Submission received: 23 January 2024 / Revised: 26 February 2024 / Accepted: 6 March 2024 / Published: 11 March 2024
(This article belongs to the Section Plant Nutrition)
Browse Figures
Versions Notes

Abstract

:
The use of fertilizers coated with insoluble organic compounds is a promising approach for enhancing fertilizer efficiency and crop yield. Silk sericin (SS) is a protein with a high potential for the development of materials oriented toward fertilizer coating and soil amendment because of its biodegradability and the fact that it represents an important source of nitrogen for plants. Thus, this study proposes the design and evaluation of a novel SS-based multilayer coating for fertilizer granules. A pan-coating process was applied to form two distinct layers on the granules: an inner layer made of silk sericin/polyvinyl alcohol, SS/PVA (50/50 w/w), which has low solubility and porosity, and an outer hydrogel layer of SS/PVA with carboxymethyl cellulose CMC (SS/CMC/PVA 45/25/30 w/w/w). Scanning electron microscopy (SEM) was employed for the morphological characterization of the coated fertilizer (CF), examining both the cross-section and surface, while SEM with energy-dispersive X-ray spectroscopy (SEM/EDS) was used to analyze the chemical composition of the surface. The ability of the coating to reduce the nutrient-release rate was studied using water- and soil-release tests. Furthermore, its performance was evaluated in in vivo assays using jalapeño bell pepper (Capsicum annum) plants. The results revealed that the structure and composition of the multilayer coating significantly influenced its ability to delay nutrient release in both water and soil. Moreover, the inclusion of SS in the coating potentially contributed to the increased nitrogen content in the soil, thereby improving plant growth rates.

1. Introduction

It is estimated that the world population will reach 10 billion inhabitants by 2050 [1]. This trend implies that the demand for food will continue to grow, and to meet this demand, it is necessary to increase water and fertilizer efficiency in crops worldwide [2]. In particular, nitrogen fertilizer efficiency is only 40% in most crops, whereas only 16% of globally extracted phosphorus is utilized for human consumption [3,4]. This represents a significant economic and environmental challenge in the future.
There are different approaches to improve the efficiency of fertilizers and, consequently, increase crop yields and minimize the loss of nutrients due to phenomena such as volatilization and leaching. The most studied are (1) the formation of low-solubility matrices, in which nutrients are dispersed, (2) the coating of fertilizers with insoluble organic materials [5,6], and (3) biofertilizers [7,8,9,10]. Matrices and coated fertilizers are technologies oriented toward the encapsulation of chemical fertilizers, and biofertilizers are substances that can contain plant-growth-promoting bacteria or other living organisms that colonize the rhizosphere, adding nutrients to soil by nitrogen fixation, mineral solubilization, phosphate and potassium absorption, etc. [8].
Regarding matrices, they can be made of rubber or gel-forming polymers, also known as hydrogels [2,11]. They have a high water absorption capacity and allow the release of nutrients by diffusion, contraction, or hydrolysis. The coatings are applied to fertilizer granules of urea or blends of nitrogen, phosphorous, and potassium (NPK) and act as membranes that limit their interaction with the water present in the soil, and therefore, prevent their rapid dissolution [2]. Nutrient release is mainly due to diffusion or membrane degradation [12,13,14]. Given the simplicity of the manufacturing process, most developments in the field of controlled-release fertilizers have been of the matrix type. However, coated fertilizers have generated considerable interest because they can have a longer shelf life than matrix fertilizers [5,6,15]. By optimizing nutrient utilization in the long term, coatings could contribute to sustainable agricultural practices, which are crucial for mitigating the environmental effects of climate change and urbanization [2,16].
Sulfur was the first material used to develop a coating to reduce the dissolution rate of fertilizer granules, specifically urea [2,17]. Since its introduction to the market in the 1960s, this type of coated fertilizer has been widely used because of its low cost, ease of production, and the advantages of its composition. Sulfur can act as an agent to prevent soil alkalinization and can also be used by plants as a nutrient [18]. However, sulfur-coated urea exhibits irregular release rates, which are associated with the presence of surface defects (cracks) and easy oxidation by microorganisms [19,20]. Hybrid coatings have been developed to improve the quality of fertilizers. These incorporate an additional coating based on a synthetic polymer, which allows a less irregular release of nutrients [21].
In the late 1990s, fertilizers coated with only polymeric materials began to emerge. In these new materials, release is not significantly affected by soil properties (pH, texture, microbial activity, salinity, etc.); however, the barrier properties exhibited by the selected polymeric coating play an important role [22]. Thus, polymeric coatings improve the design of controlled-release fertilizers, adjusting their performance precisely according to the requirements of different types of crops.
Different synthetic polymers derived from petroleum have been used to coat fertilizer granules, such as polysulfone, polystyrene, polyethylene, polypropylene, polyvinyl chloride, and acrylonitrile butadiene styrene [15]. However, these types of materials have low degradation and, in some cases, their dissolution requires the use of organic solvents, such as dichloromethane, chloroform, or N,N-dimethylformamide, which are considered potentially polluting and toxic to the soil [23]. For this reason, around 2004, the use of natural polymers for the manufacture of coated fertilizers (polysaccharides, proteins, etc.) began to be discussed [24].
Natural polymers, also called biopolymers, are alternatives for the development of biomaterials owing to their hydrophilic properties, biodegradability, abundance, and low cost [24]. These polymers can be used to form coatings of different types: hydrophobic films, hydrogels, and multilayer systems [15]. The hydrophobic film exhibits low or no water absorption, thus delaying the release of the fertilizer. On the other hand, hydrogel-type coatings have a porous structure that facilitates the passage of water, and the release rate can be modulated through the application of crosslinking processes. It has been found that hydrogels, in addition to making the use of nutrients more efficient in crops, improve soil moisture retention [25]. For this reason, some authors have recommended using multilayer systems, in which an inner layer of hydrophobic film is combined with one or more hydrogel layers, allowing the controlled release of water and nutrients into the soil [15,26,27].
Different biopolymers have the potential to be developed into hydrogels. However, some of these can affect food security, as in the case of starch [28]. Therefore, much of the research in this area has been focused on the exploration of natural polymers with low nutritional potential, such as alginate, chitosan, cellulose (and its derivatives), and some proteins, including sericin [29,30,31,32]. Sericin and carboxymethyl cellulose (CMC) are biopolymers composed mainly of polar amino acids with carboxyl and hydroxyl groups, respectively [33]. These functional groups favor the water absorption capacity [34] and facilitate crosslinking and blending with other polymers to increase the structural stability of the processed materials [35,36]. This is accomplished by the formation of covalent and non-covalent bonds during crosslinking, resulting in materials with a three-dimensional structure that promotes water absorption and limits the solubilization of their hydrophilic fractions.
This study proposes for the first time the use of SS-based materials for the coating of fertilizer granules. This is a novel proposal, considering that this protein has been mostly exploited in the biomedical, cosmetic, and food industries. Its use in the development of technologies in the agricultural sector is minimal [37]. In this study, the coating of fertilizer granules in a multilayer system was evaluated. The system was composed of an inner layer of SS/PVA (50/50 w/w) and an outer layer of SS/CMC/PVA (45/25/30 w/w). Both materials have been previously studied. The internal layer was selected because of its low solubility and porosity, while the external layer exhibited high water absorption and retention, which allowed it to behave as a hydrogel. After adjusting the coating methodology using a coating pan, morphological characterization of the cross-section and surface of the coated fertilizer (CF), as well as the chemical composition of its surface, was performed. The behavior of the CF was studied using both water- and soil-release assays, and its performance was evaluated in vivo using jalapeño bell pepper plants (Capsicum annum).

2. Materials and Methods

2.1. Materials

Defective cocoons (non-reworkable, double, spotted, and perforated cocoons) of the Colombian hybrid Bombyx mori L. were obtained from the Corporación para el Desarrollo de la Sericultura del Cauca CORSEDA (Popayán, Colombia). The cocoons were air-dried and cut to eliminate pupae and other impurities. Polyvinyl alcohol (PVA, MW: 146.000–186.000, 99% hydrolyzed, Sigma Aldrich, St. Louis, MO, USA) and food-grade sodium carboxymethyl cellulose (CMC, high viscosity: 3500–4500 cP, degree of substitution: 0.7–0.9, Antioqueña de Químicos S.A.S, Medellín, Colombia) were used to prepare the mixtures.
The soil used in this study originated from the municipality of Sopetrán, Colombia (6 30.0083 N, 75 44.0152 W). To collect soil samples, the existing vegetation cover, including branches, roots, and other plant residues, was cleared, and the samples were procured at depths ranging from 0 to 20 cm. An assessment of the soil texture using the Bouyoucos method revealed that the obtained soil sample exhibited characteristics consistent with a sandy loam type. The composition analysis indicated that the relative proportions of sand, silt, and clay were 76%, 14%, and 10%, respectively.
The coating assays were developed using a granular NPK complex fertilizer (F) from the NUTRIMON brand, containing 10.3% w/w ammonia nitrogen (NH4–N), 4.7% w/w nitric nitrogen (NO3–N), 15% w/w assimilable phosphorus (P2O5), and 15% w/w water-soluble potassium (K2O).

2.2. Extraction and Concentration of SS Solution

The sericin was extracted using high-temperature, high-pressure degumming (HTHP). The cocoons were cut into small pieces (approximately 5 mm) and immersed in distilled water in a bath ratio of 1:30 (g cocoons: mL water). An AV autoclave (Phoenix Ltd., Araraquara, Brazil) was used at 120 °C for 30 min.
The obtained solution was filtered to remove fibroin fibers. A dilute aqueous solution of sericin (~0.5% w/v) was obtained and concentrated using the freeze-thaw thaw method, as described below: The diluted solution was stored overnight in a closed container at room temperature to obtain a gel. The hydrogel was frozen at 80 °C for 24 h and then thawed at 35 °C for 1 h. The precipitated sericin was then filtered and autoclaved at 120 °C for 15 min. The solution obtained was adjusted to 2% (w/v) by dilution in distilled water. The concentration of the sericin solutions was confirmed by the Biuret method using a calibration curve obtained with a commercial sericin standard.

2.3. Preparation of SS/PVA Blend

Polyvinyl alcohol (PVA) was dissolved in distilled water (50 mL) at 85 °C and continuously stirred for 2 h. The resulting PVA solution with a concentration of 2% w/v was prepared, followed by the addition of the SS solution (50 mL) at a concentration of 2% w/v to achieve a final mixing volume of 100 mL. Subsequently, the combined solution underwent a shaking process for 2 h to ensure thorough homogenization.

2.4. Preparation of SS/CMC/PVA Mixtures

PVA was dissolved in distilled water (93 mL) at 85 °C with constant stirring for 2 h. The obtained PVA solution (0.68% w/v) was cooled to room temperature, and the CMC powder (0.53 g) was then incorporated, resulting in a concentration of CMC in the PVA/CMC solution of 0.5% w/v. The double mixture was mechanically stirred for 1 h at room temperature. Subsequently, 47 mL of concentrated SS solution (2% w/v) was added to reach a final mixing volume of 140 mL. The resulting SS/CMC/PVA solution (1.5% w/v) was shaken for 2 h for homogenization.

2.5. Coating of NPK Fertilizer Granules

The coating of fertilizer granules was carried out in an adapted Panner coating pan, using a rotation speed of 46 rpm, continuous air flow at 70 °C, and a batch size of 50 g. Each mixture (SS/PVA and SS/CMC/PVA) was maintained at 45 °C using a heating plate, and a drip was added at a rate of 3 drops/min, maintaining a drying time of 1 min between drips (Figure 1). The conditions described above were selected based on preliminary tests.
The fertilizer coating was performed in two stages. In the first stage, different volumes of the SS/PVA mixture (50/50) (35, 40, 45, and 50 mL) were evaluated to determine the condition that would allow the formation of a homogeneous SS/PVA layer on the fertilizer granules (layer 1). In the second stage, the formation of SS/CMC/PVA coating (layer 2) on layer 1 was evaluated. The volume selected for layer 1 (SS/PVA) was also used for layer 2. The fertilizer granules coated with both layers were then heat-treated at 90 °C for 4 h to improve their stability in humid environments (water and soil). The resulting controlled-release system, referred to as heat-treated, multilayer-coated F, was identified as the CF.

2.6. Morphological Characterization of the Coated Fertilizer

Morphological characterization of the uncoated and coated granules under different conditions was performed. Surface and cross-sectional images of the granules were obtained using a scanning electron microscope (FE-SEM) (Thermo Fisher Scientific, model Apreo 2 S LoVac, Waltham, MA, USA) operated at an accelerating voltage of 15 kV. In addition, the chemical composition of the RF surface was evaluated using SEM with energy-dispersive X-ray spectroscopy (SEM/EDS).

2.7. Nutrient Release in an Aqueous Medium

For nutrient-release tests in water, the methodology proposed by Scaffaro, et al. [38] and Olad, et al. [39] was used in this study. This methodology proposes the use of electrical conductivity as an indirect measure of the fertilizer content (ions) in aqueous media. As illustrated in Figure 2, fertilizer granules (F or CF) with a weight between 40 and 50 mg and diameter in the range of 50–60 mm were used to set up the water-release test.
Each granule was placed inside a non-woven bag and immersed in a Falcon tube containing 50 mL of deionized water. This assembly was performed separately for each immersion time (5, 10, 15, 30, 60, and 120 min and 24 h). The temperature and relative humidity were set at 22 °C and 38%, respectively, using an environmental chamber. After each immersion, the non-woven bag containing the fertilizer granule was removed from the tube, and the electrical conductivity of the resulting water was measured using a HANNA conductivity meter (model HI 993310).

2.8. Nutrient Release in Soil

Soil nutrient release was evaluated using dynamic leaching tests at the laboratory scale [40]. These tests involved the application of periodic irrigation to soil columns to evaluate the leaching of nutrients from the soil matrix [41]. Figure 3 shows the design of the leaching column. The assembly consisted of a PVC column, 6 cm in diameter and 30 cm in height, with a filtering mesh adapted at its base. The control column consisted of two layers of different materials. The first layer contained 2 cm of filtering material (sand and stones), and the second layer was composed of 17 cm of sandy loam soil (control soil). This column was named CS. Two more columns were tested to evaluate the effects of F and CF, in which 2 g of fertilizer was placed 4 cm below the surface, as shown in Figure 3. These columns were named CS + F and CS + CF, respectively.
To prepare the CS column, 200 mL of water was added to the filter material and control soil. In the cases of CS + F and CS + CF, the filter material and 13 cm of the control soil were saturated. The objective was to reach a saturation condition and ensure an initial moisture content that simulated the interaction between the fertilizer and the soil solution, avoiding high dissolution of the fertilizers in the initial saturation stage. After 24 h, when the soil in the column reached field capacity moisture (32%), fertilizer (F or CF) was added, and finally, 4 cm of CS was added, which was also saturated 24 h before.
Irrigation with 100 mL of deionized water per column was performed on days 7, 14, 21, 21, 28, 28, 35, 35, 35, 42, 49, and 56 to obtain the leachates. Under these conditions, a low average rainfall of approximately 45 mm was simulated. This precipitation was estimated from the historical data (1991–2021) of the average monthly precipitation in Medellín recorded between July and August, which was 190 mm [42].
A day after irrigation, the volume of the leachate samples was recorded and filtered using Whatman No. 2 paper. A multiparameter photometer was used to determine the nutrient content of the leachate (HANNA Instruments, model No. HI 83325-01, Woonsocket, RI, USA). The amount of ammonia nitrogen ( N H 3 − N ) was determined using Nessler’s method, adapted from the standard ASTM D1426 [43]. Nitrate, expressed as nitrate nitrogen ( N O 3 − − N ) , was quantified using the cadmium-reduction method [44]. Phosphate ( P O 4 3 − − P ) was determined by the ascorbic acid method [45], and potassium (K) by the tetraphenylborate turbidimetric method [46].

2.9. Performance in an Agricultural Model

2.9.1. Description of the Agricultural Production Model

The model was evaluated using jalapeño bell pepper (Capsicum annum) plants with an average height of 15 cm, which were transplanted into P14 pots (14 cm diameter × 12 cm height) containing 950 g of CS. Three treatments were evaluated: CS (control), CS + F, and CS + CF. For each treatment, three pots were set up, each containing two plants (Figure 4). According to the recommendation for similar commercial products (complex fertilizer in granules), the fertilizer dosage used for the CS + F and CS + CF treatments was 9 g per pot), which was incorporated into a superficial layer of soil surrounding the plant (crown method).
The plants were irrigated manually every 3 days. A volume of 100 mL was used, as defined by the preliminary evaporation testsThe pots were maintained in a controlled greenhouse environment for two months.

2.9.2. Growth Monitoring of Jalapeño Bell Pepper Plants

Plant growth was monitored weekly using a photographic follow-up. At the end of the two-month period, the plants were removed from the pots for subsequent morphological and gravimetric analyses, as well as for the determination of leaf color [47,48,49].
For color determination, the leaves obtained from each plant were analyzed using a sphere spectrophotometer (X rite Series SP60). The CIELAB chromatic model was used, which is based on three parameters: color brightness (L*, taking values from 0 (white) to 100 (black)), red–green chromaticity (a*, positive values indicate red and negative values indicate green), and yellow–blue chromaticity (b*, positive values indicate yellow and negative values indicate blue) [50].
The morphological parameters evaluated were the stem height, root length, and total leaf area. Gravimetric parameters, such as total dry biomass (stems, leaves, fruits, and roots), shoots (stems–leaves–fruits)/roots, and leaf/stem dry weight ratios, were also evaluated [48].

3. Results and Discussion

3.1. Characterization of Coated Fertilizer Granules

Figure 5 shows the SEM images obtained for the surface of the uncoated fertilizer granules (F) and for the fertilizer coated with the first layer of SS/PVA at different solution volumes (35, 40, 45, and 50 mL). The surface of the uncoated NPK granule exhibited a porous morphology resulting from the agglomeration of the different components (salts) that constitute it, such as nitrates (nitric N), monoammonium phosphate (ammonium P and N), and potassium chloride (KCl) [51].
When using 35 mL of the coating solution, fragments of polymeric material were observed surrounding the surface fertilizer particles, which appeared to have some erosion due to their interaction with the aqueous fraction of the SS/PVA solution. As the volume of SS/PVA increased, a more homogeneous coverage of the fertilizer granule was observed, which was more noticeable in the 50 mL SS/PVA condition. However, under the latter conditions, the SS/PVA layer exhibited a porous morphology. This could be due to the aqueous nature of the SS/PVA solution, which not only impregnated the surface of the fertilizer granule but also could have penetrated the granule, and then, when its aqueous phase evaporated, part of the observed porosity was generated. Considering that a volume of 50 mL generated sufficient mass to homogeneously cover the NPK granules, it was decided to use this volume for both layer 1 (SS/PVA) and layer 2 (SS/CMC/PVA).
Figure 6 shows photographs of the uncoated NPK granules and multilayer coating (SS/PVA layer + SS/CMC/PVA layer). The multilayer coating generated a slight color change in the fertilizer granule, without significantly affecting its size.
Figure 7 shows the SEM images obtained for the surface (A and B) and cross-section (C and D) of the multilayer-coated granules. A complete coating is observed, characterized by the presence of rounded plates, which are associated with the formation of a mixture between the hydrogel (external layer) and the salts present in the fertilizer. Circular porosities were observed on these plates, which were found to be very similar to those found in the SS/PVA layer, suggesting that part of the hydrogel solution also permeated the interior of the granule. This idea could be confirmed by observing the cross-section of the CF, in which the coating layer, with a thickness between 80 and 100 µm, appears to be over a region where a less uniform impregnation of the fertilizer with the polymeric mixture is observed.
In addition to morphological analysis, an area of the CF surface was selected and mapped to determine its elemental composition using EDS. The mapping results are shown in Figure 8. Figure 8A,B show the presence of elements that are not typical of the composition of the polymeric coating, such as phosphorus and potassium; this is confirmed by quantitative analysis (Figure 8C). These results suggest that, during the coating process, a fraction of the fertilizer is dissolved and subsequently deposited together with the hydrogel on the layer that covers the granule, supporting the hypothesis of the formation of planar and rounded structures on the CF surface.

3.2. Nutrient-Release Test in an Aqueous Medium

Figure 9 shows the electrical conductivity results obtained at different times during the immersion test of the F and CF in an aqueous medium. According to Scaffaro et al. [38], conductivity can be associated with the concentration of electrolytes in a solution, including ammonium ions (NH4+), nitrate (NO3−), phosphorus (PO43−), and potassium (K+). Thus, changes in the electrical conductivity are indirectly associated with fertilizer release.
The conductivity values for F reached a maximum between 1200 and 1400 µS/cm after 15 min. No significant changes were observed in the remaining tests. The CF reached 1200 µS/cm after 1 h of testing. For both conditions, it was observed that complete release of the fertilizer occurred in the first 2 h. After this period and up to 24 h, no significant differences in conductivity values were observed. Similar studies on coating NPK granules with polymeric blends have shown that they can delay the complete release of the fertilizer for 30 days or longer [15]. However, many of these studies incorporated polymers of acrylamide (PAMs), polyacrylic acid (PAA), or copolymers of PAMs and PAA, which may reduce the biodegradability of the coating and make it potentially toxic to the soil [52,53].
The results of the water-release test indicated that the multilayer coating did not significantly retard the release of NPK from the granules. This is a consequence of the morphological and structural properties of the coating materials. The SS/PVA and SS/CMC/PVA mixtures both have a three-dimensional porous structure with high water affinity, which makes it difficult for the coatings to significantly decrease the permeability of water to and from the interior of the granules [15,26,27]. In addition, the existence of pores on the CF surface (evidenced in the SEM images), as well as the formation of defects in the polymeric matrix due to the phosphorus and potassium fractions, favor greater dissolution of the fertilizer. Considering that the application of the CF will be in soil and not in aqueous media, it is possible that this nutrient-release system will present a differentiated performance when it is incorporated in soil or other solid substrates [38], even more so if controlled irrigation strategies are implemented in these substrates.

3.3. Nutrient Release in Soil

Figure 10 shows the total amount of NPK and inorganic nitrogen (ammoniacal and nitric) found in the leachates produced weekly in the soil columns as well as their cumulative values. A significant amount of NPK was leached in week 2 from the soil with the F. However, leaching from the soil with the CF was lower and more controlled during the six weeks (see Figure 10A). Much of the fertilizer leached under both conditions was associated with inorganic nitrogen forms (ammoniacal and nitric), as shown in Figure 10B. In particular, at week 5, the CS + CF sample exhibited a higher release of inorganic nitrogen than the SC + F sample. It could be suggested that, from this week onward, the multilayer coating tended to release this nutrient more easily. However, it is also possible that these forms of nitrogen are associated with protein degradation in soil [54].
After studying the cumulative amounts of leached nutrients (Figure 10C,D), it was established that the coating was able to reduce the amount of NPK and inorganic nitrogen leached from week 1. It was found that, at week 6, the cumulative leaching of both NPK and inorganic nitrogen in the CS + CF columns (17.4% w/w and 40.8% w/w) was slightly lower (p < 0.05) than that found in the SC + F condition (21.3% w/w and 45.4% w/w).
Considering that a rainfall regime close to the average for the city of Medellin was simulated during the leaching trials, the results suggest that the coated fertilizer performs well in conditions in which there is no controlled irrigation of the crop. Therefore, it was concluded that the CF can be used both in crops with controlled irrigation and in those that are exposed to rain (outdoors). In both cases, fertilizer leaching would be reduced, and a greater availability of nutrients for the plants would be ensured.

3.4. Performance in an Agricultural Production Model

Figure 11 shows the photographs obtained for the jalapeño plants in each treatment at 2 months (CS, CS + F, CS + CF). Plants grown in CS + F and CS + CF had larger and greener leaves than those grown in control soil. The size of the leaves of the plants treated with fertilizer was much larger than that of the plants grown in CS. In general, the plant height showed high dispersion within each treatment.
The leaf color results are presented in Table 1. In contrast to the leaves produced by plants in the CS group, those obtained in the CS + F and CS + CF groups showed a significant decrease in brightness (L*), green coloration (a*), and yellow coloration (b*). This result indicates that leaves grown in the F or CF group were darker green than those grown on CS plants. Plants grown with the F and CF exhibited no significant differences between the values of their CIEL*a *b *coordinates.
The morphological parameters (Figure 12) showed no significant differences in stem length between the three treatments and the CS. However, the root lengths for the F and CF treatments were much lower than those for the CS. This result is consistent with the greater amount of nutrients available in the CS with the F and CF. According to the functional balance theory proposed by Brower, higher nutrient availability results in lower root growth [55,56]. No significant differences in either morphological parameter were observed between the CS + F and CS + CF.
The average leaf area of plants in the CS + F (2.54 × 104 mm2) and CS + CF (3.18 × 104 mm2) groups showed significant differences with respect to that found in those cultivated in the CS (1.12 × 104 mm2). No significant differences were observed between the F and CF conditions. However, the slight difference in leaf area in CS + CF may indicate the action of the hydrogel as a nutrient (nitrogen source) and that it favors a greater production of chlorophyll, which contributes to the growth of plant tissue, mainly leaves.
No significant differences were observed among the total dry biomasses of the three treatments (Figure 13). The leaf–stem relationships showed statistically significant differences between the samples. These results are related to the increase observed in leaf area, where it is evident that the coated fertilizer exhibited the best performance. The root–shoot relationships (stem, leaves, and fruits) also showed differences between the treatments evaluated. The data suggest that the CF promotes the availability of nutrients necessary for the plant to develop its leaves and perform its functions more efficiently.
According to the functional balance theory proposed by Brower [55,56], low levels of CO2 and light in the aerial environment of plants favor shoot biomass, whereas root biomass increases in response to low levels of water and nutrients in the soil. Because the incorporation of the F or CF in the soil increases the availability of nitrogen in the form of ammonia and nitrate, this ratio is expected to be low for plants grown under these conditions. In particular, the root–shoot ratio for CS + CF was lower than that for SC + F. This result proves the capacity of the coating to increase not only the soil moisture but also the nitrogen availability. An increase in this element is obtained when the SS present in the coating degrades, thereby increasing the presence of nitrates [54].

4. Conclusions

In this study, a methodology for coating fertilizer granules (NPK) using a multilayer system composed of SS/PVA (layer 1) and SS/CMC/PVA (layer 2) was successfully implemented. According to the morphological and elemental analyses performed on the final coating, pores were present on the surface, as well as some traces of phosphorus and potassium. Additionally, a study of the cross-section showed that, during the coating process, both polymeric mixtures impregnated the interior of the granules. This could have contributed to phenomena such as dissolution of the fertilizer and its subsequent incorporation into the coating mixture.
The water-release study suggested that the multilayer coating did not significantly retard the release of fertilizers in aqueous media. This was associated with the porous structure of the coating as well as its affinity for water. However, in soil-release trials, the amount of NPK leached in the soil with coated fertilizer was lower and more controlled than that observed in the soil with uncoated fertilizer. In the first two weeks, the coating significantly reduced the leaching of inorganic nitrogen (ammonia and nitric acid).
The performance of the CF in an agricultural production model allowed us to conclude that the presence of SS in the coating contributed to increased nitrogen availability to plants, resulting in higher leaf area and lower root growth with respect to shoot growth in plants grown in CS + F.
Overall, the findings of this study demonstrate the potential of SS in the development of materials for agricultural purposes. The proposed coating methodology represents an advance in the use of this protein in the design of controlled-release fertilizers. However, it is necessary to continue researching the formulation of SS-based mixtures that will make the coating process more efficient, limit the dissolution of the fertilizer, and facilitate nutrient-release systems with specific performance. In this way, it is intended that, in the long-term future, SS-based coated fertilizers could become a viable and attractive alternative for improving nutrient efficiency, reducing environmental impact, and protecting soil health as an important part of sustainable agricultural systems.

Author Contributions

Conceptualization, N.J.-Q. and C.Á.-L.; Data curation: N.J.-Q.; Formal analysis; N.J.-Q., C.Á.-L., D.M.C. and M.T.-T.; Funding acquisition: C.Á.-L., G.A.H.-L. and M.T.-T.; Investigation, N.J.-Q. and C.Á.-L.; Methodology: N.J.-Q., C.Á.-L., D.M.C., G.A.H.-L. and M.T.-T.; Project administration, G.A.H.-L. and M.T.-T.; Resources, G.A.H.-L. and D.M.C.; Supervision, C.Á.-L. and D.M.C.; Visualization, N.J.-Q.; Writing—original draft: N.J.-Q.; Writing—review and editing, N.J.-Q., C.Á.-L., D.M.C., G.A.H.-L. and M.T.-T. All authors have read and agreed to the published version of the manuscript.

Funding

This is a product of the Research Program “Technologies in Urban Farming”, called Minciencias 852, 2019 (Grant Number: 127-2021). It was funded with resources from the “Patrimonio Autónomo Fondo Nacional de Financiamiento para la Ciencia, la Tecnología y La Innovación Francisco José de Caldas” (Francisco José de Caldas National Fund for Science, Technology, and Innovation), Ministerio de Ciencia, Tecnología e Innovación (Minciencias), Colombia. This work also received financial support from Minciencias through Ph.D. degree Grant 785 of 2017.

Data Availability Statement

The data presented in this study are available upon request from the corresponding author.

Conflicts of Interest

The authors declare no conflicts of interest.

References

  1. United Nations, Department of Economic and Social Affairs. World Population Prospects 2019—Highlights (ST/ESA/SER.A/423); United Nations: New York, NY, USA, 2019. [Google Scholar]
  2. Mansouri, H.; Ait Said, H.; Noukrati, H.; Oukarroum, A.; Ben Youcef, H.; Perreault, F. Advances in Controlled Release Fertilizers: Cost-Effective Coating Techniques and Smart Stimuli-Responsive Hydrogels. Adv. Sustain. Syst. 2023, 7, 2300149. [Google Scholar] [CrossRef]
  3. Govindasamy, P.; Muthusamy, S.K.; Bagavathiannan, M.; Mowrer, J.; Jagannadham, P.T.K.; Maity, A.; Halli, H.M.; Sujayananad, G.K.; Vadivel, R.; Das, T.K.; et al. Nitrogen Use Efficiency—A Key to Enhance Crop Productivity under a Changing Climate. Front. Plant Sci. 2023, 14, 1–19. [Google Scholar] [CrossRef] [PubMed]
  4. Umar, W.; Ayub, M.A.; Rehman, M.Z.; Ahmad, H.R.; Farooqi, Z.U.R.; Shahzad, A.; Rehman, U.; Mustafa, A.; Nadeem, M. Nitrogen and Phosphorus Use Efficiency in Agroecosystems. In Resources Use Efficiency in Agriculture; Springer: Singapore, 2020; pp. 213–257. [Google Scholar]
  5. Calabria, L.; Vieceli, N.; Bianchi, O.; de Oliveira, B.R.V.; Filho, I.D.N.; Schmidt, V. Soy Protein Isolate/Poly(Lactic Acid) Injection-Molded Biodegradable Blends for Slow Release of Fertilizers. Ind. Crops Prod. 2012, 36, 41–46. [Google Scholar] [CrossRef]
  6. Pang, L.; Gao, Z.; Feng, H.; Wang, S.; Wang, Q. Cellulose Based Materials for Controlled Release Formulations of Agrochemicals: A Review of Modifications and Applications. J. Control. Release 2019, 316, 105–115. [Google Scholar] [CrossRef]
  7. Solomon, W.; Janda, T.; Molnár, Z. Unveiling the Significance of Rhizosphere: Implications for Plant Growth, Stress Response, and Sustainable Agriculture. Plant Physiol. Biochem. 2024, 206, 108290. [Google Scholar] [CrossRef]
  8. Kisvarga, S.; Hamar-Farkas, D.; Ördögh, M.; Horotán, K.; Neményi, A.; Kovács, D.; Orlóci, L. The Role of the Plant–Soil Relationship in Agricultural Production—With Particular Regard to PGPB Application and Phytoremediation. Microorganisms 2023, 11, 1616. [Google Scholar] [CrossRef]
  9. Chieb, M.; Gachomo, E.W. The Role of Plant Growth Promoting Rhizobacteria in Plant Drought Stress Responses. BMC Plant Biol. 2023, 23, 407. [Google Scholar] [CrossRef] [PubMed]
  10. Xiong, J.; Peng, S.; Liu, Y.; Yin, H.; Zhou, L.; Zhou, Z.; Tan, G.; Gu, Y.; Zhang, H.; Huang, J.; et al. Soil Properties, Rhizosphere Bacterial Community, and Plant Performance Respond Differently to Fumigation and Bioagent Treatment in Continuous Cropping Fields. Front. Microbiol. 2022, 13, 923405. [Google Scholar] [CrossRef]
  11. Helaly, F.M.; Nashar, D.E.E. Slow Release Rubber Formulations Containing ZnSO4. Polym. Test. 2002, 21, 867–875. [Google Scholar] [CrossRef]
  12. Ganetri, I.; Essamlali, Y.; Amadine, O.; Danoun, K.; Aboulhrouz, S.; Zahouily, M. Controlling Factors of Slow or Controlled-Release Fertilizers. In Controlled Release Fertilizers for Sustainable Agriculture; Elsevier: New York, NY, USA, 2021; pp. 111–129. [Google Scholar]
  13. Shaviv, A.; Raban, S.; Zaidel, E. Modeling Controlled Nutrient Release from a Population of Polymer Coated Fertilizers: Statistically Based Model for Diffusion Release. Environ. Sci. Technol. 2003, 37, 2257–2261. [Google Scholar] [CrossRef]
  14. Jahns, T.; Kaltwasser, H. Mechanism of Microbial Degradation of Slow-Release Fertilizers. J. Polym. Environ. 2000, 8, 11–16. [Google Scholar] [CrossRef]
  15. Ramli, R. Slow Release Fertilizer Hydrogels: A Review. Polym. Chem. 2019, 10, 6073–6090. [Google Scholar] [CrossRef]
  16. Iqbal, A.M. Nano-Fertilizers for Sustainable Crop Production under Changing Climate: A Global Perspective. In Sustainable Crop Production; IntechOpen: London, UK, 2020. [Google Scholar]
  17. Yan, X.; Jin, J.; He, P.; Liang, M. Recent Advances on the Technologies to Increase Fertilizer Use Efficiency. Agric. Sci. China 2008, 7, 469–479. [Google Scholar] [CrossRef]
  18. Rindt, D.W.; Blouin, G.M.; Getsinger, J.G. Sulfur Coating on Nitrogen Fertilizer to Reduce Dissolution Rate. J. Agric. Food Chem. 1968, 16, 773–778. [Google Scholar] [CrossRef]
  19. Azeem, B.; KuShaari, K.; Man, Z.B.; Basit, A.; Thanh, T.H. Review on Materials & Methods to Produce Controlled Release Coated Urea Fertilizer. J. Control. Release 2014, 181, 11–21. [Google Scholar] [CrossRef]
  20. Beig, B.; Niazi, M.B.K.; Jahan, Z.; Kakar, S.J.; Shah, G.A.; Shahid, M.; Zia, M.; Haq, M.U.; Rashid, M.I. Biodegradable Polymer Coated Granular Urea Slows Down N Release Kinetics and Improves Spinach Productivity. Polymers 2020, 12, 2623. [Google Scholar] [CrossRef]
  21. Fertahi, S.; Ilsouk, M.; Zeroual, Y.; Oukarroum, A.; Barakat, A. Recent Trends in Organic Coating Based on Biopolymers and Biomass for Controlled and Slow Release Fertilizers. J. Control. Release 2021, 330, 341–361. [Google Scholar] [CrossRef]
  22. Trenkel, M.E. Slow-and Controlled-Release and Stabilized Fertilizers: An Option for Enhancing Nutrient Use Efficiency in Agriculture; International Fertilizer Industry Association (IFA): Paris, France, 2010. [Google Scholar]
  23. Akhter, M.; Shah, G.A.; Niazi, M.B.K.; Mir, S.; Jahan, Z.; Rashid, M.I. Novel Water-soluble Polymer Coatings Control NPK Release Rate, Improve Soil Quality and Maize Productivity. J. Appl. Polym. Sci. 2021, 138, 51239. [Google Scholar] [CrossRef]
  24. Guilherme, M.; Aouada, F.A.; Fajardo, A.R.; Martins, A.F.; Paulino, A.T.; Davi, M.F.T.; Rubira, A.F.; Muniz, E.C. Superabsorbent Hydrogels Based on Polysaccharides for Application in Agriculture as Soil Conditioner and Nutrient Carrier: A Review. Eur. Polym. J. 2015, 72, 365–385. [Google Scholar] [CrossRef]
  25. Ghobashy, M. The Application of Natural Polymer-Based Hydrogels for Agriculture. In Hydrogels Based on Natural Polymers; Chen, Y., Ed.; Elsevier Inc.: Amsterdam, The Netherlands, 2020; pp. 329–356. ISBN 9780128164211. [Google Scholar]
  26. Qiao, D.; Liu, H.; Yu, L.; Bao, X.; Simon, G.P.; Petinakis, E.; Chen, L. Preparation and Characterization of Slow-Release Fertilizer Encapsulated by Starch-Based Superabsorbent Polymer. Carbohydr. Polym. 2016, 147, 146–154. [Google Scholar] [CrossRef]
  27. Noppakundilograt, S.; Pheatcharat, N.; Kiatkamjornwong, S. Multilayer-Coated NPK Compound Fertilizer Hydrogel with Controlled Nutrient Release and Water Absorbency. J. Appl. Polym. Sci. 2015, 132, 1–11. [Google Scholar] [CrossRef]
  28. Luo, M.T.; Li, H.L.; Huang, C.; Zhang, H.R.; Xiong, L.; Chen, X.F.; Chen, X. De Cellulose-Based Absorbent Production from Bacterial Cellulose and Acrylic Acid: Synthesis and Performance. Polymers 2018, 10, 702. [Google Scholar] [CrossRef]
  29. Feng, D.; Bai, B.; Wang, H.; Suo, Y. Novel Fabrication of Biodegradable Superabsorbent Microspheres with Diffusion Barrier through Thermo-Chemical Modification and Their Potential Agriculture Applications for Water Holding and Sustained Release of Fertilizer. J. Agric. Food Chem. 2017, 65, 5896–5907. [Google Scholar] [CrossRef]
  30. Skrzypczak, D.; Witek-Krowiak, A.; Dawiec-Liśniewska, A.; Podstawczyk, D.; Mikula, K.; Chojnacka, K. Immobilization of Biosorbent in Hydrogel as a New Environmentally Friendly Fertilizer for Micronutrients Delivery. J. Clean. Prod. 2019, 241, 118387. [Google Scholar] [CrossRef]
  31. Kong, W.; Li, Q.; Li, X.; Su, Y.; Yue, Q.; Gao, B. A Biodegradable Biomass-Based Polymeric Composite for Slow Release and Water Retention. J. Environ. Manag. 2019, 230, 190–198. [Google Scholar] [CrossRef]
  32. Pushpamalar, J.; Langford, S.J.; Ahmad, M.B.; Lim, Y.Y.; Hashim, K. Eco-Friendly Smart Hydrogels for Soil Conditioning and Sustain Release Fertilizer. Int. J. Environ. Sci. Technol. 2017, 15, 2059–2074. [Google Scholar] [CrossRef]
  33. Zhang, Y.-Q. Applications of Natural Silk Protein Sericin in Biomaterials. Biotechnol. Adv. 2002, 20, 91–100. [Google Scholar] [CrossRef] [PubMed]
  34. Gupta, D.; Agrawal, A.; Chaudhary, H.; Gulrajani, M.; Gupta, C. Cleaner Process for Extraction of Sericin Using Infrared. J. Clean. Prod. 2013, 52, 488–494. [Google Scholar] [CrossRef]
  35. Dash, B.C.; Mandal, B.B.; Kundu, S.C. Silk Gland Sericin Protein Membranes: Fabrication and Characterization for Potential Biotechnological Applications. J. Biotechnol. 2009, 144, 321–329. [Google Scholar] [CrossRef] [PubMed]
  36. da Silva, T.L.; da Silva, A.C.; Vieira, M.G.A.; Gimenes, M.L.; da Silva, M.G.C. Biosorption Study of Copper and Zinc by Particles Produced from Silk Sericin—Alginate Blend: Evaluation of Blend Proportion and Thermal Cross-Linking Process in Particles Production. J. Clean. Prod. 2016, 137, 1470–1478. [Google Scholar] [CrossRef]
  37. Sonjan, S.; Ross, G.M.; Mahasaranon, S.; Sinkangam, B.; Intanon, S.; Ross, S. Biodegradable Hydrophilic Film of Crosslinked PVA/Silk Sericin for Seed Coating: The Effect of Crosslinker Loading and Polymer Concentration. J. Polym. Environ. 2021, 29, 323–334. [Google Scholar] [CrossRef]
  38. Scaffaro, R.; Citarrella, M.C.; Gulino, E.F. Opuntia Ficus Indica Based Green Composites for NPK Fertilizer Controlled Release Produced by Compression Molding and Fused Deposition Modeling. Compos. Part. A Appl. Sci. Manuf. 2022, 159, 107030. [Google Scholar] [CrossRef]
  39. Olad, A.; Zebhi, H.; Salari, D.; Mirmohseni, A.; Reyhani Tabar, A. Slow-Release NPK Fertilizer Encapsulated by Carboxymethyl Cellulose-Based Nanocomposite with the Function of Water Retention in Soil. Mater. Sci. Eng. C 2018, 90, 333–340. [Google Scholar] [CrossRef]
  40. Duan, Q.; Jiang, S.; Chen, F.; Li, Z.; Ma, L.; Song, Y.; Yu, X.; Chen, Y.; Liu, H.; Yu, L. Fabrication, Evaluation Methodologies and Models of Slow-Release Fertilizers: A Review. Ind. Crops Prod. 2023, 192, 116075. [Google Scholar] [CrossRef]
  41. Garcés, C.D.M. Recuperación de Suelos Acidificados y Contaminados Por Minería Metálica: Ensayos En Columnas. Ph.D. Thesis, Universidad Politécnica de Cartagena, Cartagena, Spain, 2012. [Google Scholar]
  42. Climate-Data.org. Clima Medellín (Colombia). Available online: https://es.climate-data.org/america-del-sur/colombia/antioquia/medellin-4088/ (accessed on 1 May 2023).
  43. ASTM D1426-08; Standard Test Methods for Ammonia Nitrogen in Water. ASTM International: West Conshohocken, PA, USA, 2008.
  44. Standard Methods Committee of the American Public Health Association; American Water Works Association; Water Environment Federation 4500-NO2 Nitrogen (Nitrite). Standard Methods for the Examination of Water and Wastewater; Standard Methods for the Examination of Water and Wastewater, Baird, R.B., Eaton, A.D., Franson, M.A.H., Eds.; American Public Health Association: Washington, DC, USA, 2017; ISBN 978-0-87553-299-8. [Google Scholar]
  45. Standard Methods Committee of the American Public Health Association; American Water Works Association; Water Environment Federation 4500-P Phosphorus. Standard Methods for the Examination of Water and Wastewater; Baird, R.B., Eaton, A.D., Franson, M.A.H., Eds.; American Public Health Association: Washington, DC, USA, 2017; ISBN 978-0-87553-299-8. [Google Scholar]
  46. Ståhlberg, S. A Simple Turbidimetric Method for Determination of Exchangeable Soil Potassium. Commun. Soil. Sci. Plant Anal. 1979, 10, 1345–1353. [Google Scholar] [CrossRef]
  47. Zhao, H.; Song, J.; Zhao, G.; Xiang, Y.; Liu, Y. Novel Semi-IPN Nanocomposites with Functions of Both Nutrient Slow-Release and Water Retention. 2. Effects on Soil Fertility and Tomato Quality. J. Agric. Food Chem. 2019, 67, 7598–7608. [Google Scholar] [CrossRef] [PubMed]
  48. Versino, F.; Urriza, M.; García, M.A. Cassava-Based Biocomposites as Fertilizer Controlled-Release Systems for Plant Growth Improvement. Ind. Crops Prod. 2020, 144, 112062. [Google Scholar] [CrossRef]
  49. Sarmah, D.; Karak, N. Biodegradable Superabsorbent Hydrogel for Water Holding in Soil and Controlled-Release Fertilizer. J. Appl. Polym. Sci. 2020, 137, 48495. [Google Scholar] [CrossRef]
  50. Li, Y.; Sun, Y.; Jiang, J.; Liu, J. Spectroscopic Determination of Leaf Chlorophyll Content and Color for Genetic Selection on Sassafras Tzumu. Plant Methods 2019, 15, 73. [Google Scholar] [CrossRef] [PubMed]
  51. Monómeros Colombo Venezolana S.A. Nutrimon 15-15-15. 2009. Available online: https://croper-production.s3.amazonaws.com/product_provider_files/files/000/009/029/original/Fertilizante-Triple-15-Nutrimon.pdf (accessed on 7 May 2022).
  52. Demitri, C.; Scalera, F.; Madaghiele, M.; Sannino, A.; Maffezzoli, A. Potential of Cellulose-Based Superabsorbent Hydrogels as Water Reservoir in Agriculture. Int. J. Polym. Sci. 2013, 2013, 435073. [Google Scholar] [CrossRef]
  53. Azeredo, H.; Waldron, K. Crosslinking in Polysaccharide and Protein Films and Coatings for Food Contact—A Review. Trends Food Sci. Technol. 2016, 52, 109–122. [Google Scholar] [CrossRef]
  54. Murase, A.; Yonebayashi, K. Nitrogen Mineralization of Silk Waste Applied to Soil under Aerobic Conditions. Soil. Sci. Plant Nutr. 2001, 47, 233–240. [Google Scholar] [CrossRef]
  55. Brouwer, R. Functional Equilibrium: Sense or Nonsense? Neth. J. Agric. Sci. 1983, 31, 335–348. [Google Scholar] [CrossRef]
  56. Brouwer, R. Nutritive Influences on the Distribution of Dry Matter in the Plant. Neth. J. Agric. Sci. 1962, 10, 399–408. [Google Scholar] [CrossRef]
Horticulturae 10 00273 g001
Figure 1. Coating of granules using a drum coater.
Figure 1. Coating of granules using a drum coater.
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Figure 2. Details of the experimental design used in the nutrient-release test.
Figure 2. Details of the experimental design used in the nutrient-release test.
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Figure 3. Design of leaching columns for sandy loam soil (CS), soil with commercial fertilizer (CS + F), and soil with a controlled-release system (CS + CF).
Figure 3. Design of leaching columns for sandy loam soil (CS), soil with commercial fertilizer (CS + F), and soil with a controlled-release system (CS + CF).
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Figure 4. Setup used in the experiment with jalapeño plants.
Figure 4. Setup used in the experiment with jalapeño plants.
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Figure 5. Surface of uncoated granules (A) and granules coated with different volumes of SS/PVA mixture: (B) 35 mL, (C) 40 mL, (D) 45 mL, and (E) 50 mL.
Figure 5. Surface of uncoated granules (A) and granules coated with different volumes of SS/PVA mixture: (B) 35 mL, (C) 40 mL, (D) 45 mL, and (E) 50 mL.
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Figure 6. Visual appearance of uncoated fertilizer granules (A) and fertilizer granules coated with two layers (B).
Figure 6. Visual appearance of uncoated fertilizer granules (A) and fertilizer granules coated with two layers (B).
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Figure 7. Surface of granules coated with the multilayer system at 500X (A) and 1000X (B) and their cross-section at 500X (C) and 1000X (D).
Figure 7. Surface of granules coated with the multilayer system at 500X (A) and 1000X (B) and their cross-section at 500X (C) and 1000X (D).
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Figure 8. EDS mapping of coated granule surface (A), details of elements (B), and quantitative analysis (C).
Figure 8. EDS mapping of coated granule surface (A), details of elements (B), and quantitative analysis (C).
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Figure 9. Conductivity of the aqueous medium as a function of immersion time (h) of F and CF. Error bars indicate the standard deviation ( n = 5 ) .
Figure 9. Conductivity of the aqueous medium as a function of immersion time (h) of F and CF. Error bars indicate the standard deviation ( n = 5 ) .
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Horticulturae 10 00273 g010
Figure 10. The amount in milligram of NPK (A,C) and inorganic nitrogen (B,D) leached and accumulated per week. Error bars indicate standard deviation n = 3 .
Figure 10. The amount in milligram of NPK (A,C) and inorganic nitrogen (B,D) leached and accumulated per week. Error bars indicate standard deviation n = 3 .
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Figure 11. Photographs of plants grown in control soil (CS), soil with fertilizer (CS + F), and soil with coated fertilizer (CS + CF) at the end of the test (2 months).
Figure 11. Photographs of plants grown in control soil (CS), soil with fertilizer (CS + F), and soil with coated fertilizer (CS + CF) at the end of the test (2 months).
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Figure 12. Average stem and root length (A) and average leaf area (B) of plants. Error bars indicate the standard deviation (n = 4). Different letters indicate statistically significant differences between treatments (p < 0.05).
Figure 12. Average stem and root length (A) and average leaf area (B) of plants. Error bars indicate the standard deviation (n = 4). Different letters indicate statistically significant differences between treatments (p < 0.05).
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Figure 13. Box plots for (A) the total dry biomass (g), (B) the leaf-to-stem ratio (g/g), and (C) the root–shoot ratio (g/g) of plants subjected to the different treatments (n = 4). Different letters indicate statistically significant differences between treatments (p < 0.05).
Figure 13. Box plots for (A) the total dry biomass (g), (B) the leaf-to-stem ratio (g/g), and (C) the root–shoot ratio (g/g) of plants subjected to the different treatments (n = 4). Different letters indicate statistically significant differences between treatments (p < 0.05).
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Table 1. Leaf color of plants subjected to different treatments.
Table 1. Leaf color of plants subjected to different treatments.
TreatmentCIELAB Color AttributesAverage Color RGB
L*a*b*
CS46.12 ± 2.93 a−11.39 ± 1.10 a28.49 ± 4.28 aHorticulturae 10 00273 i001
CS + F34.99 ± 2.19 c−7.47 ± 0.92 b13.13 ± 2.89 b,cHorticulturae 10 00273 i002
CS + CF34.72 ± 1.69 c−7.33 ± 1.45 b12.43 ± 2.91 cHorticulturae 10 00273 i003
Mean values and standard deviations (±) are presented. Different letters indicate statistically significant differences between treatments (p < 0.05).
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MDPI and ACS Style

Jaramillo-Quiceno, N.; Carmona, D.M.; Torres-Taborda, M.; Hincapié-Llanos, G.A.; Álvarez-López, C. Multilayer Silk Sericin-Based Coating for Controlled Release of Water and Nutrients in Soil: Development, Characterization, and Performance Evaluation in Agricultural Production Model. Horticulturae 2024, 10, 273. https://doi.org/10.3390/horticulturae10030273

AMA Style

Jaramillo-Quiceno N, Carmona DM, Torres-Taborda M, Hincapié-Llanos GA, Álvarez-López C. Multilayer Silk Sericin-Based Coating for Controlled Release of Water and Nutrients in Soil: Development, Characterization, and Performance Evaluation in Agricultural Production Model. Horticulturae. 2024; 10(3):273. https://doi.org/10.3390/horticulturae10030273

Chicago/Turabian Style

Jaramillo-Quiceno, Natalia, Dora M. Carmona, Mabel Torres-Taborda, Gustavo Adolfo Hincapié-Llanos, and Catalina Álvarez-López. 2024. "Multilayer Silk Sericin-Based Coating for Controlled Release of Water and Nutrients in Soil: Development, Characterization, and Performance Evaluation in Agricultural Production Model" Horticulturae 10, no. 3: 273. https://doi.org/10.3390/horticulturae10030273

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