A biopolymer composition for generating a superabsorbent hydrogel for use in agriculture

Abstract

The present invention relates to a biopolymer composition for generating a superabsorbent hydrogel comprising at least a) a matrix formed by a mixture of polysaccharides; b) a hydrolysable tannin-derived physical cross-linking agent, and c) a chemical crosslinker of natural origin. This biopolymer composition is presented in dry powder form, which forms the superabsorbent hydrogel when applied to soil and in contact with water, the hydrogel having a water absorption capacity above 100 g / g. Moreover, in addition to water, said hydrogel can also store substances dissolved in water, such as salts, fertilisers or agrochemical products. As a result, it is suitable for releasing water and other agronomically useful substances.

Description

A BIOPOLYMERIC COMPOSITION FOR THE GENERATION OF A SUPERABSORBENT HYDROGEL FOR USE IN AGRICULTURE TECHNICAL SECTOR The technology is focused on the efficient use of water in agriculture, concentrating on the use of compositions that allow for greater moisture retention in the soil, better aeration, reduced water consumption, efficient use of fertilizers, and reduced soil degradation. STATE OF THE ART Water is a fundamental resource in agriculture. Plant growth and crop quality are closely linked to water quantity and use efficiency.[l] However, due to increased droughts, desertification, climate change, and the growing demand for food, this limited resource is becoming increasingly scarce. Recommendations for mitigating water risks include water treatment, reuse, and recycling, as well as green infrastructure, and improving water use efficiency in the agricultural sector. Globally, more than 70% of freshwater is used in agriculture, and it is estimated that a 50% increase in agricultural production will be required by 2050. Currently, the use of hydrogels in agriculture is of growing interest, as it allows for better efficiency in the use of water and nutrients in crops. Hydrogels are hydrophilic polymers that absorb water without dissolving. When water absorption exceeds 10 times their weight or more, they are called superabsorbent polymers [2]. In simple terms, during the During periods of rain or irrigation, hydrogels absorb and retain a large amount of water, acting as an additional water reservoir. As the soil dries out during a drought, the water absorbed in the SAP is released into the soil, providing water to the plant roots. The hydrogel also retains drainage water and thus reduces the frequency of irrigation, saving water, which is particularly important during droughts [3]. Among the main advantages of using hydrogels in agriculture are greater soil moisture retention, improved aeration, reduced water consumption, efficient use of fertilizers, reduced soil degradation, and reduced unnecessary environmental pollution linked to fertilizer losses through leaching, improved soil structure, and increased crop production, thus promoting the development of agriculture [4-7]. Most commercially available superabsorbents for agricultural applications involve the use of synthetic polymers such as poly(acrylic acid), poly(acrylamide), and poly(potassium acrylate). The main reason for using synthetic polymers is the high absorption capacity they achieve (100 and 500 g / g) [8]. Furthermore, synthetic hydrogels are notable for their high durability, greater mechanical strength, and lower cost [9]. While synthetic polymers are efficient at conserving soil moisture, they have low degradability and are considered potential soil contaminants, which limits their future use in agriculture.

[0010] The introduction of compounds with ion-exchange properties at high concentrations (e.g., poly(sodium acrylate)) produces soil salinization, which can reduce soil microbial activity and organic mineralization

[11] . The situation is more concerning for superabsorbents based on poly(acrylamide), which is considered non-toxic in its polymeric form; however, the presence of the residual monomer (acrylamide) and other toxic intermediates in the finished product can generate harmful effects on people and the environment

[0012] . Acrylamide is considered a neurotoxin for the human beings and its effects on human health are serious

[0013] , for example, acrylamide has been shown to be neurotoxic, genotoxic, carcinogenic, etc.[13-16]. In order to provide biodegradability to the polymer chain while maintaining high water absorption capacities, the synthesis of hydrogels composed of synthetic and natural components has been proposed

[0018] . Some recently addressed strategies include the synthesis of hydrogels based on mixtures of poly(acrylamide) and alginate or chitosan (absorption capacities 370 g / L). -1 )

[0019] , copolymers based on mixtures of lignin and poly(vinyl alcohol) (absorption capacities greater than 500 gg -1 )

[0020] , starch graft copolymers with acrylonitrile (absorption capacity 250 g'g 1 ), and starch-acrylamide graft copolymers (absorption capacity of 550 gg _1)

[0021] . Although the use of synthetic-natural multicomponent hydrogels turns out to be a more ecological alternative to synthetic polymers, with high water absorption capacities, good controlled release properties of fertilizers and good mechanical properties[4], the synthetic oligomer chains remain in the soil after the degradation that occurs mainly in the natural polymer chains. Along these same lines of ideas, the synthesis of hydrogels from natural sources has been proposed as an environmentally friendly alternative. In particular, polysaccharides have been reported in the synthesis of natural hydrogels with great potential for application in agriculture due to their biodegradability, low cost, non-toxicity, abundance, and renewability. Among the reported polysaccharides are pectin, starch, alginate, chitin, cellulose, and their derivatives [22, 23]. So far, similar technologies have attempted to address this problem, such as: EP2535359A1: Presents a biodegradable hydrogel polymer for the agricultural sector comprising an ionic polymer that is carboxymethyl cellulose (CMC) and citric acid. US11363813: Environmentally friendly hydrogel for modifying the rheological conditions of agricultural compositions. The main component is a lactose derivative. US2003232895: They present a reinforced hydrogel, where one of the possible components used to reinforce the hydrogel is CMC, and a form of use as a pharmaceutical composition that also incorporates tannic acid is described. US2011059162: It features a composition comprising a chitosan matrix with tannins, where this composition can be used as a nanoparticle, a hydrogel, a biogel, or the outer part of a liposome. US20220296720: Composition comprising chitosan, tannins and an active agent, wherein this composition can be used as a hydrogel for medical use. US20080132632: This product features an absorbent aerogel for domestic use, which primarily comprises clays. The description mentions an embodiment that also contains CMC and citric acid among its components. Despite the technologies described, there is still a need to find new bio-based superabsorbent alternatives that, in addition to being sustainable, promote sustainable crops, are price-competitive, have high absorption capacities, and good mechanical properties that give stability to the hydrogel in its swollen state. References [1] Misiewicz, A. Glogowski, K. Lejcus, D. Marczak, The Characteristics of Swelling Pressure for Superabsorbent Polymer and Soil Mixtures, Materials, 13 (2020) 5071. [2] MJ. Zohuriaan-Mehr, K. Kabiri, Superabsorbent polymer materials: A review, Iranian Polymer Journal (English Edition), 17 (2008) 451-477. [3] A. Saha, S. Sekharan, U. Manna, Superabsorbent hydrogel (SAH) as a soil amendment for drought management: A review, Soil and Tillage Research, 204 (2020). [4] R. Michalik, I. Wandzik, A mini-review on chitosan-based hydrogels with potential for sustainable agricultural applications, Polymers, 12 (2020) 2425. [5] B. Azeem, K. KuShaari, Z.B. Man, A. Basit, T.H. Thanh, Review on materials & methods to produce controlled release coated urea fertilizer, Journal of controlled release, 181 (2014) 11-21. [6] F. Ai, X. Yin, R. Hu, H. Ma, W. Liu, Research into the super-absorbent polymers on agricultural water, Agricultural Water Management, (2020) 106513. [7] Y. Yang, J. Wu, S. Zhao, C. Gao, X. Pan, D.W.S. Tang, M. van der Ploeg, Effects of long-term super absorbent polymer and organic manure on soil structure and organic carbon distribution in different soil layers, Soil and Tillage Research, 206 (2021) 104781. [8] A. Saha, B. Rattan, S. Sekharan, U. Manna, Quantifying the interactive effect of water absorbing polymer (WAP)-soil texture on plant available water content and irrigation frequency, Geoderma, 368 (2020) 114310. [9] S. Behera, P.A. Mahanwar, Superabsorbent polymers in agriculture and other applications: a review, Polymer-Plastics Technology and Materials, 59 (2020) 341-356.

[0010] B. Tomadoni, C. Casalongué, V.A. Alvarez, Biopolymer-based hydrogels for agriculture applications: Swelling behavior and slow release of agrochemicals, Polymers for Agri-food applications, Springer2019, pp. 99-125.

[0011] K. Singh, Microbial and Enzyme Activities of Saline and Sodic Soils, Land Degradation & Development, 27 (2016) 706-718.

[0012] X. Dai, F. Luo, J. Yi, Q. He, B. Dong, Biodegradation of polyacrylamide by anaerobic digestion under mesophilic condition and its performance in actual dewatered sludge system, Bioresource Technology, 153 (2014) 55-61.

[0013] K.L. Dearfield, C.O. Abernathy, M.S. Ottley, J.H. Brantner, P.F. Hayes, Acrylamide: its metabolism, developmental and reproductive effects, genotoxicity, and carcinogenicity, Mutation Research / Reviews in Genetic Toxicology, 195 (1988) 45-77.

[0014] J.H. Exon, A Review of the Toxicology of Acrylamide, Journal of Toxicology and Environmental Health, Part B, 9 (2006) 397-412.

[0015] R.M. LoPachin, The changing view of acrylamide neurotoxicity, NeuroToxicology, 25 (2004) 617-630.

[0016] V. Matoso, P. Bargi-Souza, F. Ivanski, M.A. Romano, R.M. Romano, Acrylamide: A review about its toxic effects in the light of Developmental Origin of Health and Disease (DOHaD) concept, Food Chemistry, 283 (2019) 422-430.

[0017] A. Nyyssólá, J. Ahlgren, Microbial degradation of polyacrylamide and the deamination product polyacrylate, International Biodeterioration & Biodegradation, 139 (2019) 24-33.

[0018] M. Klein, E. Poverenov, Natural biopolymer-based hydrogels for use in food and agriculture, Journal of the Science of Food and Agriculture, 100 (2020) 2337-2347.

[0019] A.M. Elbarbary, H.A. Abd El-Rehim, N.M. El-Sawy, E.-S.A. Hegazy, E.-S.A. Solimán, Radiation induced crosslinking of polyacrylamide incorporated low molecular weights natural polymers for possible use in the agricultural applications, Carbohydrate polymers, 176 (2017) 19-28.

[0020] L. Wu, S. Huang, J. Zheng, Z. Qiu, X. Lin, Y. Qin, Synthesis and characterization of biomass lignin-based PVA super-absorbent hydrogel, International journal of biological macromolecules, 140 (2019) 538-545.

[0021] X. Bao, L. Yu, S. Shen, G.P. Simon, H. Liu, L. Chen, How rheological behaviors of concentrated starch affect graft copolymerization of acrylamide and resultant hydrogel, Carbohydrate polymers, 219 (2019) 395-404.

[0022] B. Song, H. Liang, R. Sun, P. Peng, Y. Jiang, D. She, Hydrogel synthesis based on lignin / sodium alginate and application in agriculture, International journal of biological macromolecules, 144 (2020) 219-230.

[0023] E. Motamedi, B. Motesharezedeh, A. Shirinfekr, S.M. Samar, Synthesis and swelling behavior of environmentally friendly starch-based superabsorbent hydrogels reinforced with natural char nano / micro particles, Journal of Environmental Chemical Engineering, 8 (2020) 103583.

[0024] K. Wilpiszewska, AK Antosik, T. Spychaj, Novel hydrophilic carboxymethyl starch / montmorillonite nanocomposite films, Carbohydrate Polymers, 128 (2015) 82-89. BRIEF DESCRIPTION OF THE FIGURES Figure 1: Image of the superabsorbent. Figure 2: Absorption capacity at equilibrium for different types of water. Figure 3: Decay tests of the superabsorbent. Initial (left) and final (right) state samples. Figure 4: Ecotoxicity tests on Raphanus sativus, OEDC standard 208. Figure 5: Soil water tension curves. Figure 6: Morphometric study of Solatium lycopersicum DESCRIPTION OF THE INVENTION A biopolymer composition is presented for the generation of a superabsorbent hydrogel that improves water retention capacity in the soil. This composition features a mixture of biopolymer-based components that, through physical and chemical crosslinking, provide elasticity and structural stability to the superabsorbent. The composition has the capacity to absorb and retain water in the soil, enabling efficient use of this resource, which is essential for the development of sustainable agriculture. The first object of protection is a biopolymeric composition for the generation of a superabsorbent hydrogel, comprising at least: a) A matrix of a biodegradable polymer, comprising a mixture of polysaccharides, preferably carboxymethyl cellulose (CMC) and hydroxyethylcellulose (HEC) in a 3:1 ratio, maintaining a total polymer concentration of 1.0 to 5.0% w / v with respect to water, These provide hydrophilicity and biodegradability to the superabsorbent hydrogel; b) A hydrolyzable physical crosslinking agent derived from tannins, preferably tannic acid (TA), which will provide flexibility to the polymer matrix, and is present in a percentage between 0.25–3.0% w / w with respect to the polysaccharide mixture; and c) A chemical crosslinking agent of natural origin that reacts with the hydroxyl groups of the biopolymer, such as citric acid (CA), which will provide structural stability to the hydrogel. The percentage of addition of this crosslinking agent is between 0.5% and 5.0% w / w with respect to the polysaccharide mixture. This biopolymeric composition is presented as a dry powder, which, when applied to soil and in contact with water, forms a superabsorbent hydrogel. This hydrogel has a water absorption capacity exceeding 100 g / g. Furthermore, it can store not only water but also water-soluble substances such as salts, fertilizers, or agrochemicals. This hydrogel is suitable for the continuous release of water and other substances used in agriculture. The second object of protection is the process of obtaining this biopolymeric composition, which comprises at least the following stages: a) adding CMC to water while mechanically stirring at 80-120 rpm for 20-60 minutes at room temperature; b) adding HEC in a CMC / HEC ratio of 3:1, maintaining a total polymer concentration of 1.0 to 5.0% w / v with respect to water; c) mixing while stirring for 2-8 hours at room temperature until a homogeneous translucent mixture of the biopolymers is obtained; d) Add the CA in percentages between 0.5 - 5.0% w / w and tannic acid TA between 0.25 - 3.0% w / w, both with respect to the polymer, incorporating them by mechanical stirring at a speed of 80-120 rpm for 2 hours at room temperature; e) crosslinking and dehydration of the mixture obtained by heating at a temperature between 30-60 °C for 12 hours. The resulting solid is crushed to obtain solid particles with a crystalline appearance. The choice of CMC and HEC biopolymers is based on their outstanding ability to absorb and diffuse water within the copolymer matrix, utilizing both osmotic and electrostatic pressure phenomena, as well as their biodegradability. The selected crosslinkers are biodegradable, pose no ecological risks, can be obtained from natural sources, are economically accessible, and provide mechanical stability to the network (citric acid) and flexibility to accommodate water molecules (tannic acid). The proportions of both crosslinkers, both chemical and physical, as well as the amount of polysaccharides used in the superabsorbent synthesis, correspond to the concentrations that allow for maximum water absorption capacity in the hydrogel. The CMC used is a cellulose derivative containing carboxymethyl groups generated by the reaction of cellulose with chloroacetate in alkali. This reaction produces substitutions at the C2, C3, or C6 positions of the glucose units. These structural characteristics give the polymer high sensitivity to changes in pH and ionic strength. Furthermore, as a consequence of the Gibbs-Donnan effect, this polyelectrolyte promotes osmotic pressure, forcing water into the hydrogel and thus improving its swelling capacity. CMC is water-soluble at any temperature, highly hygroscopic, rapidly hydrating, and biodegradable. Furthermore, HEC is a biopolymer with a high number of hydroxyl groups, which gives it diffusibility, high swelling capacity, and crosslinking ability. These properties favor intermolecular crosslinking over intramolecular crosslinking when present in mixtures with other polysaccharides. In addition, it is renewable, low-cost, and has been shown to act as a soil conditioner, modifying microbial activity, increasing organic carbon content and average soil weight, and consequently promoting indirect plant growth. Crosslinking is key in the synthesis of hydrogels. As mentioned, natural polymers lack good mechanical properties and gel strength, and in this sense, crosslinking provides structural stability (preventing polymer dissolution) and provides volume to accommodate water molecules. However, a high degree of crosslinking leads to a decrease in absorption capacity because there are more points of contact between the polymer chains that resist network expansion. The present biopolymer composition has two crosslinking agents: tannic acid (TA) as a physical crosslinker and citric acid (CA) as a chemical crosslinker. Tannic acid (TA) is a biodegradable, natural plant polyphenol (non-flavonoid) that can form multiple hydrogen bonds with polyols and consequently provides tenacity and elasticity to the network for its expansion with the solvent.Citric acid (CA) can be considered a covalent crosslinking agent for various carbohydrate polymers that can be degraded without releasing toxic byproducts. Unlike other chemical crosslinkers (carbodiimide, glutaraldehyde, epichlorohydrin, etc.), CA has received considerable attention due to its low cost, availability, and, most importantly, its non-toxicity. CA provides structural stability to the biopolymer network through the covalent bonds it forms. All the compounds that make up the biopolymeric composition for obtaining the hydrogel have demonstrated their biodegradable properties. It is important to note that the presence of cross-linking in the polymer decreases the rate of biodegradation and thus extends the useful life of the hydrogel in the soil. The balance between these previously mentioned components allows us to obtain a superabsorbent polymeric hydrogel with highly competitive water absorption properties compared to commercial products. Furthermore, this product is based on 100% naturally derived compounds and is 100% biodegradable, making it an outstanding option in terms of environmental sustainability, high water absorption capacity, and seed germination promotion. APPLICATION EXAMPLES Example 1: Preparation of the superabsorbent. To manufacture the superabsorbent, CMC is initially added to water and mechanically stirred at 100 rpm for 30 minutes at room temperature. Subsequently, HEC is added at a CMC / HEC ratio of 3:1, maintaining a total polymer concentration of 1.0 to 5.0% w / v relative to water. The mixture is stirred for 4 hours at room temperature until a homogeneous, translucent mixture of biopolymers is obtained. Then, CA is added at percentages between 0.5 and 5.0% w / v, and tannic acid (TA) at percentages between 0.25 and 3.0% w / v, both relative to the polymer. This mixture is incorporated by mechanical stirring at 100 rpm for 2 hours at room temperature. Finally, the resulting mixture is dehydrated and cross-linked for 12 hours at a temperature between 30 and 60 °C. The resulting solid was crushed, giving rise to solid particles with a crystalline appearance (Fig. 1). Example 2: Evaluation of the Water Absorption Capacity of the HydrogelWater absorption capacity is influenced by several factors, primarily the degree of crosslinking, which depends on the concentration of the crosslinking agents TA and CA. Water absorption capacity was evaluated using swelling (Sw) tests. Sw was determined by the difference in hydrogel weight between the swollen sample after 24 h of hydration in water and the finally dried sample, according to the following general procedure. To ensure homogeneous hydration, samples were stirred in a multidimensional orbital shaker (Heidolph, Unimax 1010 DT) for 24 h at room temperature. After this time, the hydrogel was filtered through an 80 µm nylon mesh (Merck) to remove excess water and immediately weighed to obtain the swollen weight (ws). Subsequently, the hydrated samples were completely dried to obtain the dry weight (WD). All samples were analyzed in triplicate.Finally, Sw was calculated using the following equation:. After manufacturing the superabsorbent with the following formulation: biopolymer 5% w / w, AC 0.5% w / w AT 0.25% w / w, a Sw of 180 g / g was achieved. Evaluation of water types: The superabsorbent was immersed in different types of water to evaluate its performance. These types were: deionized water (type I), drinking water, and underground well water (see Fig. 2). No significant differences were observed in the water absorption capacity (Sw) of the superabsorbent with respect to the water type, demonstrating that the material can perform optimally under laboratory, domestic, and rural conditions. Example 3: Evaluation of superabsorbent disintegration in soils. Biodegradability was determined by evaluating the degree of disintegration of the materials tested according to ISO 20200:2015, simulating an intensive aerobic composting process. The solid matrix within the reactors consisted of a synthetic solid residue inoculated with mature compost from a municipal or industrial composting facility. Fragments of the tested materials were placed within the previously prepared solid matrix. The degree of disintegration was determined after a composting cycle of at least 45 calendar days, which could be extended to 90 days. For this procedure, a sample of the hydrogel reported in this invention was placed in one reactor, along with a positive blank (cellulose), a negative blank (polypropylene), and a reactor containing synthetic compost without a sample. The wet synthetic residue content in each reactor was 1500 g.The thermophilic incubation period, or the time during which the reactors remained inside a forced-air oven at 58 ± 1°C, was 45 calendar days. The composted material was then sieved using 10 mm, 4.75 mm, and 2 mm mesh screens to recover undecomposed residue. The reduction in mass and volume of the test sample is considered disintegrated material and is used to calculate the degree of disintegration. For each sample, the decrease in total volatile solids content between the initial synthetic residue and the compost obtained at the end of the test must be equal to or greater than 30%. In the case of the polymer reported in this invention, the value was approximately 90%, so the sample complies with the standard. Finally, a 100% disintegration rate is reported for the hydrogel reported in this invention after 15 days of study, indicating that it is a biodegradable superabsorbent (Fig. 3). Example 4: Determination of the ecotoxicity of the superabsorbent The ecotoxicological effects of the superabsorbent on the growth of higher plants were determined in accordance with OEDC 208 and Annex E of the UNE-EN 13432:2001 standard, which addresses ecotoxicity. For this purpose, pots containing 50% reference substrate and 50% compost by weight were used. Fourteen Sparkler radish seeds were sown in each pot and incubated at 20°C ±2°C in darkness for 5 to 7 days. Afterward, the plants were exposed to light of at least 3000 lux for at least 12 hours per day. The test ended after 11 ± 1 days. At the end of the trial, the total fresh and dry weight of the above-ground plant material was determined for each pot separately. The germination rate was also measured. The toxicity of any potential residues from the test item is assessed by comparing the germination and plant performance results of the test compost with the blank compost. The results shown in this trial indicated that the compost mixture under study did not negatively affect plant growth and extent compared to the control sample; all plants exhibited favorable seedling growth (Fig. 4), demonstrating that the superabsorbent is not ecotoxic. Finally, it should be noted that no signs of chlorosis or necrosis were observed. Example 5: Evaluation of the water retention of the superabsorbent in different soil types Tests were conducted using two soil types: sandy and sandy loam, with varying superabsorbent concentrations of 0.3, 0.5, 0.8, and 1.0% w / w relative to the amount of soil. The total mass of soil per test was one kilogram. The effect of adding hydrogel on the water retention capacity of soils was studied by obtaining the moisture retention curve. The specific pressures used in the experiment were 10, 33, 300, 500, and 1500 kPa. The points of 33 kPa, known as field capacity (FC), and 1500 kPa, designated as the permanent wilting point (PWP), are generally used to determine the capacity for accumulating water available to plants. The calculation of available water is performed using the following formula: Useful Water (UW) = CC — PMP The term "available water" refers to the amount of water in soil that is readily available and accessible to plants. When superabsorbents are incorporated into the soil, they have the capacity to retain and gradually release water according to the plants' needs. In this way, and based on the ability of certain materials to retain water in the soil and make it available to plants, it is possible to increase available soil water, which benefits agriculture and other fields where water availability is crucial. A notable improvement in moisture retention capacity was observed in sandy and sandy loam soils after the application of the superabsorbent. This is reflected in a marked difference in the moisture retention curves (see Figures 5A-5D). As the superabsorbent concentrations varied, each soil sample experienced a significant increase in volumetric water content. Thus, the sandy and sandy loam soils responded effectively to the incorporation of the superabsorbent. Regarding the water available to plants, there is a significant improvement in the moisture retention curve and the amount of usable water (see Figures 5E and 5F). Example 6: Morphometric response test of Solatium lycopersicum to the application of the superabsorbent. Fifty-cell plastic trays measuring 50 x 46 x 30 mm (0.073 L / cell) were used. The following gradient of superabsorbent concentrations per cell was established: 0.0 g (control); 0.17 g; 0.27 g; 0.37 g; 0.47 g for 10 replicates. The doses were applied and incorporated into the soil by mixing at a depth of approximately 2 cm, until homogeneity was achieved between the soil and the superabsorbent. Two seeds were sown in each cell and watered until moist. The trays were covered with a transparent plastic lid and placed in a growth chamber at a temperature of 20 ± 2°C, relative humidity of 60 ± 5%, and a light intensity of 50 pmol nr 2 s' 1and a 16 / 8 h (light / dark) photoperiod. After 15 days, the seedlings were thinned, leaving one plant per cell. Irrigation was carried out every 4 days for the control group, which is the standard frequency established for this seedling production model, and every 8 days for the treatments with the superabsorbent. During the first 4 weeks, 5 mL of water were applied per cell per irrigation, and this was subsequently increased to 10 mL until the end of the experiment. The experiment was evaluated 10 weeks after its establishment, based on the response of the following morphometric variables: plant length, number of true leaves, and main root length. In general, plant growth responded favorably to the superabsorbent, regardless of the variations between the different concentrations. It is normal for the control group to show a relatively better response, as these are the ideal growing conditions. In the control group, irrigation was carried out every 4 days, while in the treatments it was every 8 days. That is, the irrigation interval was doubled in the treatments. This increased irrigation frequency forced the plants to absorb the water released by the superabsorbent. In this case, the study was based on a stage corresponding to the initial growth of the tomato crop, where the plants can reach about 20 cm in height with approximately 15 to 20 true leaves. The morphometric results, defined by their length (Fig. 6A), number of true leaves (Fig. 6B), and root length (Fig. 6C), demonstrated that the superabsorbent perfectly guaranteed the development of these morphological variables, just as the control with half the irrigation dose did.

Claims

CLAIMS 1. A biopolymeric composition for generating a superabsorbent hydrogel, CHARACTERIZED in that it comprises at least: a. A biodegradable matrix comprising a mixture of polysaccharides, preferably carboxymethyl cellulose (CMC) and hydroxyethyl cellulose (HEC) in a 3:1 ratio, maintaining a total polysaccharide concentration of 1.0 to 5.0% m / v with respect to water; b. A hydrolyzable tannin-derived physical crosslinking agent, preferably tannic acid (TA), in a concentration between 0.25 - 3.0% m / m with respect to the polysaccharide mixture; and c. A chemical crosslinker of natural origin, preferably citric acid (CA), in a concentration between 0.5% and 5.0% m / m with respect to the polysaccharide mixture.

2. Biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 1, CHARACTERIZED in that the mixture of polysaccharides, preferably carboxymethyl cellulose (CMC) and hydroxyethylcellulose (HEC), provide hydrophilicity and biodegradability to the superabsorbent hydrogel.

3. Biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 1, CHARACTERIZED in that the physical crosslinking agent derived from hydrolyzable tannins provides flexibility to the polymeric matrix.

4. Biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 1, CHARACTERIZED in that the chemical crosslinker, preferably citric acid (CA), provides structural stability to the hydrogel.

5. Biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 1, CHARACTERIZED in that it is presented in the form of dry powder.

6. A process for obtaining a biopolymeric composition, CHARACTERIZED in that it comprises at least the following steps: i. adding CMC in water by mechanically stirring at 80 - 120 rpm for 20 - 60 minutes at room temperature; i. add HEC in a CMC / HEC ratio of 3:1, maintaining a total polymer concentration of 1.0 to 5.0% m / v with respect to water; iii. mix under stirring for 2 - 8 h at room temperature until a translucent homogeneous mixture of the biopolymers is obtained; iv. add the CA in percentages between 0.5 - 5.0% m / m and tannic acid TA between 0.25 - 3.0% m / m both with respect to the polymer, incorporate them by mechanical stirring with a stirring speed of 80 -120 rpm for 2 hours at room temperature; and v. crosslinking and dehydration of the mixture obtained by heating at a temperature between 30 - 60 ° C for 12 hours, followed by grinding until solid particles of crystalline appearance are obtained.

7. A process for obtaining a biopolymeric composition for generating a superabsorbent hydrogel, according to claim 6, CHARACTERIZED in that the crosslinking provides structural stability and provides volume to accommodate water molecules and elasticity to the network for its expansion with the solvent.

8. Use of the biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 1, CHARACTERIZED in that it can be applied to soils, and in contact with water, it forms the superabsorbent hydrogel.

9. Use of the biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 8, CHARACTERIZED in that it serves to improve the water retention capacity of the soil, essential for the development of sustainable agriculture.

10. Use of the biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 8, CHARACTERIZED in that it serves to form a hydrogel that is suitable for the release of water and other substances for agronomic use.

11. Use of the biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 8, CHARACTERIZED in that it allows crosslinking in the polymer that decreases the rate of biodegradation, extending the useful life of the hydrogel in the soil.

12. Use of the biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 8, CHARACTERIZED in that it allows crosslinking that provides structural stability, provides volume to accommodate water molecules and elasticity to the network for its expansion with the solvent.

13. Use of the biopolymeric composition for the generation of a superabsorbent hydrogel, according to claim 8, CHARACTERIZED in that it serves to generate a 100% natural origin and 100% biodegradable product, with a high water absorption capacity and promotion of seed germination.

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