Fertilizer based on alginate and double layered hydroxides intercalated with borate and production process.

Abstract

This invention relates to an organic-inorganic hybrid fertilizer, obtained from the combination of sodium alginate (as) and layered double hydroxides (LDHs) intercalated with borate anions, referred to as HDL-as-b, and its production process. LDHs, also known as anionic clays, are characterized by acting as host matrices for ions in their interlamellar spaces, thus neutralizing the positive charges of their lamellae. As-based polymers are natural and low-cost, formed by a group of anionic polysaccharides extracted from brown algae. The production of granulated fertilizers from the mixture of as and LDHs allows the formation of stable granulated hybrid materials for application in soils. Therefore, the purpose of producing hdl-as-b is its use as fertilizer to supply boron (b) to plants.The material produced falls within the technical area of ​​soils and plant nutrition (soil fertility), and can be used by producers as a slower-release fertilizer of boron, as an alternative to conventional soluble sources (boric acid - H3BO3).

Description

1 / 19 Descriptive report Fertilizer based on alginate and double layered hydroxides intercalated with borate and production process. TECHNICAL FIELD OF THE INVENTION [1] The present invention consists of organic-inorganic hybrid fertilizers, obtained from the combination of sodium alginate (SA) and layered double hydroxides (LDHs) intercalated with borate anions, referred to as HDL-SA-B, and its production process. LDHs, also known as anionic clays, are characterized by acting as host matrices for ions in their interlamellar spaces, in order to neutralize the positive charges of their lamellae. SA-based polymers are natural and low-cost, formed by a group of anionic polysaccharides extracted from brown algae. The production of granulated fertilizers from the mixture of SA and HDHs allows the formation of stable granulated hybrid materials for application in soils. Therefore, the purpose of producing HDL-SA-B is its use as fertilizers to supply boron (B) to plants.The material produced falls within the technical area of ​​Soils and Plant Nutrition (Soil Fertility), and can be used by producers as an alternative fertilizer to conventional soluble sources (boric acid H3BO3). STATE OF THE ART [2] The application of fertilizers for plant nutrition depends on the levels of nutrients present in the fertilizer. In addition, the Petition 870200133673, dated 10 / 23 / 2020, p. 10 / 33 The 2 / 19 recommendation is based on the processes of nutrient loss through volatilization, leaching, and adsorption, depending on which fertilizer is being applied and what losses it is subject to. Specifically for borate fertilizers, losses are due to leaching, and these losses intensify in soils with higher sand content and low organic matter content, as well as in locations with high rainfall. Therefore, producing borate fertilizers with lower solubility than conventional sources (boric acid - H3BO3) is an important way to minimize B losses in the soil through leaching and increase B accumulation in the surface layers of the soil, thus increasing the efficiency of the borate fertilizer and B absorption by plants. [3] Boron (B) is an important micronutrient used for plant growth and development. Some of the B added to the soil as fertilizer remains soluble and can be leached into the soil profile. B that is not initially in solution can also be desorbed and leached. The removal of added B from the soil depends on the amount of percolated water and the soil texture. Sandy soils, poor in organic matter, tend to have low B availability. This is especially important in very rainy areas, where B can be leached. However, clayey soils tend to retain added B for longer periods, which also occurs in soils with more organic matter and a higher cation exchange capacity. Increasing the efficiency of plant absorption of this nutrient is essential to increase agricultural productivity.One alternative for sustainably providing boron is storing it in two-dimensional inorganic host matrices. In this sense, the intercalation of borate ions into layered double hydroxides is a good example. Petition 870200133673, dated 10 / 23 / 2020, page 11 / 33 3 / 19 (HDLs) emerges as an interesting option for evaluating new ways of making B available to plants (Castro, GF; Ferreira, JA; Zotarelli, L, Mattiello, EM; Novais, RF; Tronto, J. Layered double hydroxides intercalated with borate: effect of fertilization on boron leaching and successive sunflower cultivations. New Journal of Chemistry. p. 1- 8. 2019). It is worth noting that in all the studies consulted, the application of nutrients by HDLs was carried out in powder form. The hydroxyl groups released from HDLs have an alkaline buffer, which retains the layered structure and decreases the rate of nutrient release from the HDL structure. However, the use of powdered HDLs can increase the fertilizer's exposure to soil acidity and decrease the fertilizer's buffering capacity, increasing its solubilization. Thus, the use of powdered material will directly influence the dissolution rate, absorption of atmospheric moisture, and nutrient use efficiency of fertilizers.Furthermore, the use of powdered fertilizers hinders precise applications under field conditions. Biodegradable natural polymers, such as alginate, have been suggested as a matrix for synthesizing granular fertilizers. Alginate is a low-cost polymer that can be prepared from a group of anionic polysaccharides extracted from brown algae. This natural polymer is composed of residues of βD-mannuronic acid and α-L-guluronic acid in varying proportions of 1-4 linkages. Alginate has been reported as a matrix for the formation of microspheres to be used in the sustained release of nutrients. In a solution containing Ca2+ or other polyvalent cations, there is a strong interaction between the cations and the carboxylate groups of the residual base of the guluronic acid of alginate. The cations are trapped in a continuous, stable, and thermo-irreversible three-dimensional network, whose configuration is like an egg carton (G. Petition 870200133673, dated 10 / 23 / 2020, page 12 / 33 4 / 19 T. Grant, ER Morris, DA Rees, PJC Smith and D. Thom, FEBS Letters, 1973, 32, 195-198; M. Malinconico, B. Immirzi, G. Santagata and E. Schettini, An overview on innovative biodegradable materials for agricultural applications, 2008). The synthesis of alginate microspheres containing HDLs, as an organic-inorganic hybrid nanomaterial, is still incipient and has not been reported in the literature. In theory, this synthesis of microspheres could provide physical protection for the HDL, decreasing the contact surface between the HDL and the soil, which could modify the chemical characteristics of the HDL, such as reactivity, dissolution, and nutrient release. [4] The fertilizer proposed in this invention meets the qualities presented by conventional B sources used by producers (H3BO3), without their problems of high solubilization. Usually, the application of conventional B sources is often carried out by the foliar method, due to the difficulty in obtaining highly efficient granulated products. In this sense, the HDL-AS-B product obtained has a granulated form and is easy to apply to soils. In addition, the borate fertilizer (HDL-AS-B) efficiently reduces the dissolution and release of B in water, as well as the leaching of B in the soil, which increases its accumulation in the surface layers of the soil and also the efficiency and accumulation of B by plants. Thus, the use of HDL-AS-B as a borate fertilizer is an interesting, viable and potentially useful alternative for supplying B to plants. DESCRIPTION OF THE FIGURES [5] Figure 1: Images of alginate microspheres containing layered double hydroxide intercalated with borate (HDL-AS-B). The average diameter of HDL-AS-B is 3.40 mm. Petition 870200133673, dated 10 / 23 / 2020, page 13 / 33 5 / 19 [6] Figure 2: Scanning electron microscopy (SEM) images at different magnifications for alginate microspheres containing layered double hydroxide intercalated with borate (LDH-AS-B). [7] Figure 3: Cumulative release of B from H3BO3, HDL-AS-B and Ulexite in water buffer solution at pH 6.5 and 7.5. [8] Figure 4: Cumulative leaching of boron from H3BO3, HDL-AS-B and Ulexite in soil with pH 6.5 and pH 7.5. DETAILED DESCRIPTION OF THE INVENTION Preparation of Layered Double Hydroxide with Borate Intercalated Between Lamellae [9] In this method, 200-300 mL of a solution containing: 0.5-1.5 mol kL-1 of Mg(NOs)2-6-H2O and 0.5-1.5 mol L-1 of Al(NO3)3·9·H2O was added dropwise, at a rate of approximately 1-2 drops per second, under vigorous stirring, to 500-700 mL of a solution containing 0.75-1.25 mol kL-1 of H3BO3. All solutions were prepared with previously distilled and deionized water, and the synthesis was carried out under a N2 atmosphere to eliminate interference from atmospheric carbon dioxide. During the synthesis, a 1.0-2.0 mol L-1 NaOH solution was added to maintain the pH between 8.0 and 10.0. After synthesis, the solid was washed using a reduced-pressure filtration system with approximately 3 to 5 L of decarbonated water, and subsequently, the material was dried under reduced pressure in the presence of silica gel. This material was named HDLB. Preparation of alginate microspheres containing layered double hydroxide with borate intercalated between lamellae using the complex coacervation method. Petition 870200133673, dated 10 / 23 / 2020, page 14 / 33 6 / 19

[10] In the synthesis method of alginate microspheres containing HDL-B, a solution containing 0.5 - 1 g of sodium alginate and 25 - 50 mL of distilled and deionized water was prepared. This was left under constant stirring for about 1-2 h at room temperature (25 - 30 °C) to ensure complete solubilization of the sodium alginate. After complete solubilization, 2.5 - 5.0 g of HDL-B was added and stirred again for another 20 - 40 min. Then, the resulting suspension was transferred to a burette and dripped at a rate of approximately 1-2 drops per second into a solution containing 5 - 10% Ca(NOa)2 (m / v), also prepared with distilled and deionized water. Subsequently, it was filtered and then dried under reduced pressure in a desiccator in the presence of silica gel (Figure 1). The material obtained was named HDL-AS-B. Fertilizer characterization

[11] HDL-AS-B was characterized by scanning electron microscopy (SEM). Total B concentrations in HDL-B and HDL-ASB were evaluated by optical emission spectrometer, model Optima 8300. Samples were solubilized in a 45 mol L-1 HNO3 solution using a 1:60 fertilizer:solution ratio (w / v).

[12] SEM images of HDL-AS-B showed microspheres with diameters ranging from 2500 to 3000 μm (Figure 2). Cracks are present in the HDL-AS-B microspheres, indicating an interaction between the alginate and HDL-B powder. A coating and distribution of HDL-B powder in the alginate matrix can be visualized (indicated by the arrows - Figure 2). SEM images of the microspheres indicate a physical protection of HDL-B by an alginate polymer network. This physical protection may produce a barrier to reduce the rate of water diffusion into the microspheres and decrease the release of B to Petition 870200133673, dated 10 / 23 / 2020, page 15 / 33 7 / 19 outside the microspheres, indicating good slow-release properties.

[13] The total concentration of B in HDL-B was 50.60 g kg⁻¹ of B per HDL, corresponding to 5.06% of B. Previous research reported values ​​of 14.00, 37.90, 25.50 and 45.23 g kg⁻¹ of B for MgAl-CO₃-LDH, MgAl-NO₃-LDH, calcined MgAl-LDH and uncalcined MgAl-LDH, respectively (OP Ferreira, SG De Moraes, N. Durán, L. Cornejo and OL Alves, Chemosphere, 2006, 62, 80-88; L. Kentjono, J. Liu, W. Chang and C. Irawan, Desalination, 2010, 262, 280-283; ED Isaacs-Paez, R. Leyva-Ramos, A. Jacobo-Azuara, JM Martinez-Rosales and JV Flores-Cano, Chemical Engineering Journal, 2014, 245, 248-257). The total B determined for HDL-B indicated greater incorporation of B, which is an important consideration when micronutrient studies are conducted, due to the small amounts required by plants. HDL-ASB presented 4.20% B, indicating that the formation of microspheres did not significantly decrease the total concentration of B in the powdered fertilizer (5.06% B). DEMONSTRATION EXPERIMENT Boron release test in water using HDL-AS-B

[14] The B release test was performed and adapted from the “in vitro” release method. A 2 x 6 x 3 factorial design was established with two water buffer solutions (pH values ​​of 6.5 and 7.5), six collection times (0, 1, 2, 4, 6, and 12 hours), and three B sources (HDL-AS-B, H3BO3, and Ulexite). The experiment was conducted in a randomized block design with four replicates. H3BO3 (17.5% B) and Ulexite (10% B) were chosen because they are commercial sources of B with high and low solubility, respectively. The pH value of Petition 870200133673, dated 10 / 23 / 2020, page 16 / 33 8 / 19 buffer solution was adjusted using 0.14-0.24 mol L-1 HNO3 or 0.1-0.2 mol L-1 NaOH. Using a 250 mL Erlenmeyer flask, 45 mg L-1 of the total B from sources B and 100 mL of water buffer solution (pH 6.5 and 7.5) were added. At pre-established times (0, 1, 2, 4, 6, and 12 hours), the solution was gently agitated to homogenize it, and 5 mL aliquots were withdrawn. Immediately afterward, 5 mL of buffer solutions (pH 6.5 and 7.5) were added to maintain a constant volume. The internal temperature of the incubator was maintained at 25-35°C. The analyses of B concentration were performed according to the method described by López et al (FJ López, E. Giménez and F. Hernández, Fresenius Journal of Analytical Chemistry, 1993, 346, 984-987). Leaching of boron in soil columns

[15] A soil sample from a 0-20 cm depth layer of a Yellow Dystrophic Red Latosol, a sandy latosol, was collected in the Três Marias region, Minas Gerais, Brazil. The soil samples were homogenized, sieved (<2 mm) and air-dried. The soil presented the following physicochemical properties: clay 270 g kg-1; silt 14 g kg-1; fine sand 470 g kg-1; coarse sand 240 g kg-1; bulk density 1.34 g cm-3; total porosity 0.49 m3 m-3; pH (H2O) 4.36; B 0.1 mg dm-3; cation exchange capacity 3.99 cmolc dm-3 and total organic carbon 1%. Limestone was applied to the soil to achieve pH values ​​of 6.5 and 7.5. For this purpose, CaCO3 and MgCO3 were used in a Ca:Mg ratio of 4:1. After 30 days of incubation with soil moisture at field capacity, the soil samples were air-dried and sieved (<2 mm). Leaching test B was performed, in which syringes (columns) with a diameter of 3 cm and a height of 12 cm were... Petition 870200133673, dated 10 / 23 / 2020, p. 17 / 33 Syringes 9 / 19 were filled with 60 cm³ of soil. Glass wool was used at the bottom of the syringe to prevent soil loss. To accommodate the soil sample in the columns, water was added in an amount corresponding to the volume of soil pores (30 mL) and drained from the bottom using a syringe system. After drainage, a rate of 20 mg dm⁻³ of B was incorporated into the top 0.5 cm of soil in the center of the column. A 2 x 7 x 3 factorial design was established with two soil pHs (6.5 and 7.5), seven incubation times (1, 5, 10, 15, 20, 25, and 30 days before leaching), and three B sources (HDL-AS-B, H₃BO₃, and Ulexite) and a control treatment without B application. The experiment was conducted in a randomized block design with four replications. At 1, 5, 10, 15, 20, 25, and 30 days of incubation, water corresponding to the pore volume (30 mL) was applied, and the leachate was collected. During the leaching test, the soil columns were maintained at 25 °C.The analyses of B concentrations in the leachate were performed according to the method described by López et al (FJ López, E. Giménez and F. Hernández, Fresenius Journal of Analytical Chemistry, 1993, 346, 984-987). Greenhouse experiment with plants

[16] A sequential cultivation using B-sensitive plants (sunflower and cotton) was carried out to evaluate the efficiency and residual effect of B sources. The soil was the same as that used in the leaching test, which was a B-deficient soil (0.1 mg dm-3 of B). Basal fertilization was added to all treatments, providing a total dose per dm3 of soil of 200 mg of P, 150 mg of K, 60 mg of S and 100 mg of N. The sources used were KH2PO4, NH4H2PO4 and (NH4)2SO4. At the same time, treatments with boron fertilizers were applied at a rate of 2 mg dm-3 of B. The soil and fertilizers were homogenized and the plastic pots were Petition 870200133673, dated 10 / 23 / 2020, p. 18 / 3310 / 19 pots filled with 2 dm³ of soil. A 2 x (3 + 1) factorial design was established with two soil pHs (6.5 and 7.5), three B sources (HDLAS-B, H3BO3 and Ulexite) and a control without B application. The experimental design was a randomized block design with four replications. Eight sunflower seeds (Helianthus annuus - hybrid ALTIS 99) were sown per pot. After seven days, the seedlings were thinned to the four most uniform in each pot. Other liquid basal nutrients were added twice, in 20 mL of solution per pot, resulting in a total dose of basal nutrients per dm3 in soil of 100 mg of N as urea, 1.32 mg of copper (Cu) as CuSO4 5H2O, 1.55 mg of iron (Fe) as FeSO4 7H2O, 3.66 mg of manganese (Mn) as MnSO4 H2O, 0.15 mg of molybdenum (Mo) as (NH4)6Mo7O24 and 4.0 mg of Zn as ZnSO4 7H2O.Ten days after emergence, plants grown in treatments with a soil pH of 7.5 showed visual symptoms of cationic micronutrient deficiency (Cu, Fe, Mn, and Zn). Therefore, the treatments with a soil pH of 7.5 received an extra application of cationic micronutrients (1.32 mg dm⁻³ of Cu, 1.55 mg dm⁻³ of Fe, 3.66 mg dm⁻³ of Mn, and 4.0 mg dm⁻³ of Zn). The pots were watered daily with distilled water to 80% of the soil's field capacity. After 30 days of cultivation, the sunflower plants were harvested by cutting the stems at the soil surface. The plant biomass was dried at 65°C for 96 hours and weighed to obtain the dry matter (DM). 50 g soil samples from each experimental unit were collected after the first cultivation to determine B availability. Limestone application rates of 1.0 and 2.0 tons ha-1 were applied before the second cultivation to maintain soil pH values ​​at 6.5 and 7.5, respectively. The limestone used was the same as that described in the B leaching test.The soil was moistened to 80% of its capacity. Petition 870200133673, dated 10 / 23 / 2020, p. 19 / 33 On November 19th, sunflower seeds were sown in the field and incubated for 30 days in plastic bags at 25°C. Forty-five days after sunflower harvest, eight cotton seeds (hybrid Gossypium vitifolia - TMG 47 B2RF) were sown per pot. Five days after plant emergence, each pot was thinned to two plants. No boron (B) fertilization was applied, requiring the plants to utilize residual B in the soil. Other nutrients were applied at the same rate and from the same sources as in the first cultivation. The pots were irrigated with distilled water to maintain 80% of the soil's field capacity. Fifty days after sowing, the plants were harvested, and the plant biomass was dried at 65°C for 96 hours and weighed. This sequential cultivation produced results at 30 and 125 days after B application.The plant biomass was crushed, and the concentration of boron (B) in the plant tissue was analyzed according to the method described by Embrapa (Embrapa, Methods of analysis of plant tissues used at Embrapa Solos, Embrapa Solos, Rio de Janeiro, 1st edn., 2000). Additionally, a greenhouse experiment was conducted on soils subjected to leaching. The study was established with three boron sources (HDL-AS-B, H3BO3, and Ulexite) and a control treatment without boron application. The experimental design was a randomized block design with four replications, using pots with a soil capacity of 2.0 dm³. A 5 mm layer of glass wool was placed at the bottom of the pots to prevent soil loss during the leaching event. Each pot was filled with sandy soil (clay 2 g kg-1; silt 6.4 g kg-1; sand 91.6 g kg-1; bulk density of soil 1.49 g cm-3; pH (H2O) = 6.3; B 0.16 mg dm-3; cation exchange capacity 3.1 cmolc dm-3 and soil organic carbon 5 g kg-1).A total rate of 2 mg dm-3 of B from each source (HDL-AS-B, H3BO3, and Ulexite) was applied, and subsequently the sources were homogenized in the soil. After the... Petition 870200133673, dated 10 / 23 / 2020, page 20 / 33 In the 12 / 19 fertilizer applications, a volume of distilled water corresponding to 20 mm of precipitation was applied to the topsoil and drained. The leachate was collected and the concentration of boron (B) in the leachate was determined. After leaching, the residual effect of the B sources was evaluated in successive sunflower and cotton crops without B replacement. The data were subjected to an analysis of variance. Differences between treatment means were evaluated using Tukey's test, with the smallest difference considered significant at p < 0.05. The R program was used for statistical analysis. Results of the Boron Release Test Experiment using HDL-ASB

[17] In the first collection time, the total B released at pH 6.5 by H3BO3, Ulexite, and HDL-AS-B was equivalent to 4.0, 0.7, and 0.6%, respectively, of the total B applied (Figure 3A). At pH 7.5, in the first collection time, the total B released was 2.8, 0.9, and 0.7% for H3BO3, Ulexite, and HDL-AS-B, respectively (Figure 3B). There was no effect of pH value on B release for the H3BO3 and Ulexite sources (Figure 3). However, the pattern of B release by HDL-AS-B was lower at pH 7.5. After 12 hours of HDL-AS-B application, 91% and 84% of the B at pH 6.5 and 7.5 were released, respectively. Increasing the pH in the buffer solution contributes to the stability of the HDL structure, allowing for a slower release of intercalated anions and even cations that make up the layered structure. The HDL-AS-B showed a much lower cumulative release of B than all other B sources used in this study (Figures 3A and 3B).Thus, the results presented by HDL-AS-B in our study are attributed to the protection of borate anions found in them. Petition 870200133673, dated 10 / 23 / 2020, page 21 / 33 13 / 19 interlamellar spaces of HDLs and also for the physical protection of HDL by the alginate polymer. Results of the Boron Leaching Experiment in Soil Columns

[18] As expected, the leachate had more B when H3BO3 was applied. For the first leaching event, approximately 37% and 19% of the total B applied as H3BO3 was leached into the soil at pH 6.5 and 7.5, respectively (Figures 4A and 4B). There was an effect of soil pH on B release (Figure 4). The percentage of B leached from H3BO3, HDL-AS-B, and Ulexite was lower for soil pH 7.5. After 20 days of H3BO3 application to soil at pH 6.5, 100% of the B was recovered in the leachate (Figure 4A). For Ulexite and HDL-AS-B, after 30 days of application to soil at pH 6.5, 90% and 74% of B were recovered, respectively (Figure 4A). In soil with pH 7.5, 100% of B from H3BO3 was leached after 30 days of source application, respectively (Figure 4B). At 30 days after source application in soil with pH 7.5, 74% and 59% of B from Ulexite and HDL-AS-B were leached, respectively (Figure 4B).These results suggest a greater formation of borate anions in alkaline soil pH, resulting in a greater affinity with the solid phase of the soil, decreasing boron leaching. The slow-release boron profile of HDL-AS-B resulted in a significant reduction in leached boron compared to all boron sources for both soil pHs. The low leaching potential of HDL-AS-B is an important property of the fertilizer to increase the residence time of boron in the root zone, consequently increasing the probability of boron absorption by plants. Slow-release sources can prolong boron availability and reduce leaching losses in the soil, thus allowing the use of lower rates or a decrease in the frequency of fertilizer applications. In regions with soils... Petition 870200133673, dated 10 / 23 / 2020, page 22 / 33 14 / 19 sandy soils, such as the one used in this study, combined with high rainfall and low organic matter content, the results indicate the advantage of HDL-AS-B as a novel fertilizer to supply B to plants. Results of the experiment in a greenhouse with plants

[19] There was no significant effect of B sources on the total shoot dry matter of sunflower and cotton (Table 1). There was a significant effect of B fertilizer treatments on the B content in the shoots of sunflower and cotton (Table 1). Application of B as H3BO3, HDL-AS-B, and Ulexite resulted in a higher B content in sunflower and cotton compared to the control treatment without B addition and in total B uptake in the soil at pH 6.5. There was an effect of soil pH on the total dry matter of sunflower and on the B content (Table 1). Total dry matter and B content from B sources were lower at soil pH 7.5 than at 6.5. This effect can be attributed to the decreased availability of cationic micronutrients in the soil, such as Cu, Fe, Mn, and Zn. After 10 days of emergence, plants grown in treatments with soil pH 7.5 showed visual symptoms of a deficiency of Cu, Fe, Mn, and Zn.The total boron (B) content of plants fed with HDL-AS-B at soil pH 7.5 was significantly higher than that of plants fed with other sources and may be attributed to a slower release of nutrients by HDLs at alkaline pH. The increase in soil pH may contribute to the formation of microsites with higher pH values, which also increase the structural stability of HDLs in the soil. The increased stability of HDLs may lead to a gradual release of nutrients from HDLs and increase nutrient uptake by plants in subsequent crops. The availability of B in the soil after the first crop without micronutrient replenishment was not significant among H3BO3. Petition 870200133673, dated 10 / 23 / 2020, page 23 / 33 15 / 19 The availability of boron (B) in soil pH 6.5 was significantly higher than in the control treatment. Available B at soil pH 6.5 was 1.51, 1.79, 1.48, and 0.09 mg dm⁻³ for H₃BO₃, HDL-AS-B, Ulexite, and the control treatment, respectively. For soil pH 7.5, available B was 1.70, 1.83, 1.70, and 0.16 for H₃BO₃, HDL-AS-B, Ulexite, and the control treatment, respectively. The results of B availability in the soil suggest that HDL-AS-B has a solubilization similar to the other sources in greenhouse experiments where soil moisture is maintained daily at field capacity. In annual crops, which require immediate availability of nutrients in the soil, these results confirm that the B release profile of HDL-AS-B did not affect B accumulation by plants.The release of nutrients from slow-release sources should be slow enough to minimize leaching losses and toxicity in plants, but fast enough to deliver nutrients when plants need them.

[20] In the greenhouse experiment with leached soil, there was an effect of B sources on the total B leached before sunflower cultivation. The concentration of B in the leachate when applying H3BO3 was 3.01 mg L-1 of B. Meanwhile, the concentration of B in the leachate was 0.7, 0.6 and 0.4 mg L-1 of B for HDL-AS-B, Ulexite and control treatment, respectively, and were significantly lower compared to H3BO3. The residual concentration of B in the soil after the first sunflower cultivation was 1.57, 0.82, 0.73, and 0.66 mg dm-3 of B for the HDL-AS-B, control, Ulexite, and H3BO3 treatments, respectively. Residual boron (BO) in the soil was significantly higher for HDL-AS-B compared to the other B sources, and there were no significant differences between the control, ulexite, and H3BO3 treatments. There were no differences in dry matter accumulation. Petition 870200133673, dated 10 / 23 / 2020, page 24 / 33 16 / 19 of cotton as a function of B sources in the second crop (Table 2). However, the total absorbed B in the aerial part and total (sum of root and aerial part) of the plants were significantly higher for HDL-AS-B compared to H3BO3, Ulexite, and the control treatment. A similar response was observed for the total absorption of B by the sum of sunflower and cotton crops (Table 2).

[21] The slow release of B from HDL-AS-B, compared with all sources applied in water release and soil B leaching tests, suggests a potential increase in B accumulation in the root zone and in the efficiency of B use by HDL-AS-B. At the same time, HDL-AS-B showed B release in the soil and uptake by plants similar to other sources in the greenhouse study. Thus, the results of our study corroborate the proposed assumptions for obtaining the ideal slow-release fertilizer. It is worth noting that Ulexite is the commercial borate fertilizer with slow-release B standards, recommended for soils prone to leaching. The results of the B release and leaching tests showed lower B release and leaching from HDL-AS-B compared to Ulexite. At the same time, HDL-AS-B supplied B to plants with the same efficiency as Ulexite in soil with pH 6.5 and with superior efficiency in soil with pH 7.5.Thus, the results showed that HDL-AS-B would be the most recommended fertilizer for areas with high leaching, where slow-release sources are needed.

[22] Table 1: Dry matter and boron content in the aerial part of plants as a function of the boron sources applied in the first (sunflower) and second (cotton) crops, and in the total summed for the two crops. Petition 870200133673, dated 10 / 23 / 2020, page 25 / 33 17 / 19 First crop (sunflower) Dry matter (g pot1) Boron content (mg pot'1) Source Soil pH 6.5 Soil pH 7.5 | Soil pH 6.5 | Soil pH 7.5 H3BO3 10.68aA 3.18aB 2.79aA 0.78aB HDL-AS-B 10.62aA 3.03aB | 3.37aA | 0.84aB Ulexite 10.40aA 2.46aB 3.48aA 0.55aB Control 10.83aA 2.27aB | 1.46aB | 0.56aB Second crop (cotton) Dry matter (g pot'1) | Boron content (mg pot'1) Source Soil pH 6.5 Soil pH 7.5 Soil pH 6.5 Soil pH 7.5 H3BO3 11.60aB 12.68aA | 2.49bA | 2.12bcB HDL-AS-B 12.27aB 12.36aA 2.97aA 3.03aA Ulexite 12.22aB 12.77aA | 2.65abA | 2.32bB Control 11.91aB 13.38aA 1.37cA 1.33dA | Total | | Dry matter (g pot'1) Boron content (mg pot'1) Source Soil pH 6.5 Soil pH 7.5 | Soil pH 6.5 | Soil pH 7.5 H3BO3 22.28aA 15.86aB 5.28bA 2.90bB HDL-AS-B 22.89aA 15.39aB | 6.34aA | 3.87aB Ulexite 22.62aA 15.23aB 6.13abA 2.87bcB Control 22.74aA 15.65aB | 2.83cA | 1.89cB Lowercase letters compare the effect of boron sources at each soil pH. Uppercase letters compare the effect of soil pH on each boron source. Identical letters do not differ statistically by Tukey's test at 5%.

[23] Table 2: Dry matter and boron content in the aerial part of plants as a function of the boron sources applied in the first (sunflower) and second (cotton) crops, and in the total summed for the two crops. First cultivation (sunflower) Dry matter (g pot'l) Boron content (mg pot'l) Source PA Root Total PA Root Total H3BO3 15.66a 4.25a 19.91a 2.09a 0.31a 2.40a HDL-AS-B 15.89a 5.03a 20.92a 3.14a 0.51a 3.65a Ulexite 17.66a 3.99a 21.65a 2.58a 0.34a 2.92a Control 17.78a 4.25a 22.03a 2.17a 0.26a 2.43a Second crop (cotton) Petition 870200133673, dated 10 / 23 / 2020, page 26 / 33 18 / 19 Dry matter (g pot1) Boron content (mg pot'1) Source PA Root Total PA Root Total H3BO3 49.66a | 6.00a | 55.66a 1.01bc 0.20ab | 1.21bc | HDL-AS-B 53.20a 5.89a 59.09a 1.74a 0.31a 2.05a Ulexite 48.24a | 6.15a | 54.39a 1.14b 0.26ab | 1.40b | Control 47.24a 5.45a 52.69a 0.71c 0.09b 0.80c Total (sunflower and cotton combined) I Dry matter (g pot'1) Boron content (mg pot'1) Source PA | Root | Total PA Root | Total | H3BO3 65.32a 10.25a 75.57a 3.10bc 0.51ab 3.61c HDL-AS-B 69.09a | 10.92a | 80.01a 4.88a 0.82a | 5.70a | Ulexite 65.90a 10.14a 76.04a 3.72b 0.60ab 4.32b Control 65.02a | 9.70a | 74.72a 2.88c 0.35b | 3.23c | PA = aerial part. Values ​​followed by the same lowercase letter within the columns and within each crop indicate that the average dry matter and B absorption by the plant are not significantly different (p <0.05) according to Tukey's test between B sources. CONCLUSION

[24] B release and leaching were much lower for HDLAS-B compared to H3BO3 and ulexite. HDL-AS-B was similarly solubilized in the soil compared to the other B sources in greenhouse experiments. In annual crops, which require immediate availability of nutrients in the soil, these results confirm that the B release profile of HDL-AS-B did not affect B accumulation by plants.

[25] The lower release and leaching of B by HDL-AS-B improves the accumulation of B in the root zone, consequently increasing fertilizer efficiency and B uptake by the plant. In sandy soils with low organic matter combined with high rainfall, the results validated the use of HDL-AS-B as a new slow-release B fertilizer with micronutrient release adjusted according to plant requirements.

[26] Under plant growing conditions where the pots were subjected to leaching, the use of HDL-AS-B resulted in greater absorption of B in the aerial part and total (sum of aerial part and roots) in cotton (second crop) and for the total sum of the crops of Petition 870200133673, dated 10 / 23 / 2020, page 27 / 33 19 / 19 sunflower and cotton. The use of HDL-AS-B increases the residence time of B in the surface layers of the soil and the absorption of B by plants compared to the sources H3BO3 and Ulexite. In conclusion, the application of HDL-AS-B under controlled conditions was the most promising source of B to be used in soils subject to B leaching and with poor retention of this nutrient. Petition 870200133673, dated 10 / 23 / 2020, pages 28 / 33

Claims

1 / 2 Claims 1. Fertilizer characterized by comprising alginate microspheres with a diameter between 2500 and 3000 µm, containing 4.20% boron in the form of a layered double hydroxide with borate intercalated between the lamellae.

2. Production process of the fertilizer defined in claim 1, characterized by comprising the steps: a) preparation of 200-300 mL of a solution containing 0.5-1.5 mol-L-1 of Mg(NO3)2-6-H2O and 0.5-1.5 mol-L-1 of Al(NO3)3-9-H2O; b) dropwise addition of the solution prepared in step a, at a rate of 1-2 drops per second, under vigorous stirring, to 500-700 mL of a solution containing 0.75-1.25 mol-L-1 of H3BO3 under a N2 atmosphere; c) addition of a 1.0-2.0 mol-L-1 NaOH solution to the synthesis to maintain the pH between 8.0 and 10.0; d) obtaining the layered double hydroxide solid with borate intercalated between the layers; e) washing the solid obtained in step d; f) drying the solid obtained in the reduced pressure step in the presence of silica gel; g) preparation of a solution containing 0.5-1 g of sodium alginate and 25-50 mL of distilled and deionized water; h) addition of 2.5-5.0 g of layered double hydroxide with borate intercalated between lamellae to the solution from step g;i) Transfer of the suspension obtained in step h to a burette; j) Drip-feeding at a rate of 1-2 drops per second into a solution containing 5-10% Ca(NO3)2 (m / v); k) Filtration of the alginate microspheres containing layered double hydroxide with borate intercalated between lamellae; l) Drying under reduced pressure in a silica gel desiccator.

3. Process, according to claim 2, step aeb, characterized in that solutions of Mg(NO3)2-6-H2O, 0.5-1.5 mol-L-1 of Petition 870260058051, dated 15 / 06 / 2026, page 10 / 11 2 / 2 Al(Nθ3)3·9·H2θ and 0.75-1.25 mol L-1 of H3BO3 are prepared with distilled and deionized water.

4. Process, according to claim 2, step e, characterized in that the washing of the double lamellar hydroxide with borate intercalated between lamellae is carried out in a reduced pressure filtration system with 3 to 5 L of decarbonated water.

5. Process according to claim 2, step g, characterized in that the preparation of the sodium alginate solution is carried out under constant stirring for 1-2 hours at a temperature between 25-30 °C.

6. Process, according to claim 2, step h, characterized by the addition of 2.5 - 5.0 g of layered double hydroxide with borate intercalated between lamellae to the solution of step g, with stirring for 20-40 minutes.

7. Process, according to claim 2, step j, characterized in that the Ca(NO3)2 (m / v) solution is prepared with distilled and deionized water. Petition 870260058051, dated 06 / 15 / 2026, page 11 / 11

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