Hydrogel containing an extract of at least one agarophytic red alga, in particular an agar hydrogel, method for the preparation thereof and use thereof as a water-retaining fertilizer

Abstract

To provide a product suitable for use in agriculture for food and biological purposes, which is applied to the base of a plant, thereby reducing the frequency of watering the plant while increasing resistance to water stress that can also limit the need for watering the plant.SOLUTION: Hydrogel based on at least one gelling agent, in particular agar-agar, containing a product obtained from the extraction, with an alkaline aqueous solution, of at least one agarophytic red alga originating from the family Gelidiaceae. Said hydrogel is advantageously in the form of pieces or blocks, such as spheres or cubes.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to an aqueous gel containing an extract of at least one red agarophyte alga, a method for its preparation, and its use as a water-retaining fertilizer.

[0002] Water stress has become a major and prevalent problem, exacerbated by persistent climate projections that predict more intense water stress in the future. To reduce the impact and consequences of water stress, crops require water and repeated waterings. However, water is lost with each watering either by evaporation or by infiltration into the water table.

[0003] Water that is no longer available is lost and therefore not absorbed by cultivated plants. It is estimated that at least 40% of water is lost during watering. This loss is increased in dry regions and during the summer.

[0004] Gels capable of capturing water available to roots are commercially available. However, it should be pointed out that these well-known hydrogels are generally not approved for use in food and agriculture. In fact, synthetic water-retaining polymers often contain carcinogenic monomers. Summary of the Invention [Problem to be solved by the invention]

[0005] The object of the present invention is to provide a product suitable for use in agriculture, for food and biological purposes, to be applied to the base of the plant, thereby making it possible to water the plant less frequently while increasing its tolerance to water stress, which can also limit the watering needs of the plant. [Means for solving the problem]

[0006] To this end, the inventors have succeeded in developing a water-retaining fertilizer formulation in the form of a gel that can capture water during its preparation and during the watering of plants to which it is applied. This gel contains water, at least one gelling agent, and a liquid fertilizer derived from agarophyte red algae. The advantage is that both the water and the liquid fertilizer are accessible to the cultivated plants, thus increasing their tolerance to water stress. As shown below, water consumption is very low, which significantly reduces the number of times crops need to be watered.

[0007] Furthermore, thanks to the judicious selection of gelling agents, the product is composed mainly of organic matter, which does not have any harmful effects in agriculture. When these organic materials decompose, they do not cause any harmful effects. This makes the product safe for use in agriculture, especially food agriculture. DETAILED DESCRIPTION OF THE INVENTION

[0008] A first object of the present invention is therefore a hydrogel based on at least one gelling agent, containing, as a fertilizer, a product obtained from the extraction with an alkaline aqueous solution of at least one agarophyte red algae from the Gelidiaceae family.

[0009] In particular, the at least one agarophyte red alga of the Agaricaceae family can be selected from Gelidiella acerosa, Gelidium amansii, Gelidium cartilagineum, Gelidium liatulum, Gelidium pacificum, Gelidium lingulatam, Gelidium sesquipedale, Gelidium corneum and Gelidium pristoides.

[0010] According to certain embodiments, the fertilized extraction product is an aqueous phase obtained by extracting the at least one red algae with an alkaline aqueous solution, followed by filtration to recover the aqueous phase, which may then be concentrated, dehydrated or freeze-dried, and then redissolved in water.

[0011] In particular, the extraction is carried out at a high temperature of 40 to 98°C, preferably 60 to 80°C, for 30 minutes to 8 hours, and the red algae are extracted at a temperature of 10 to 20 m 3 It was used at a rate of 600 to 900 kg in an alkaline aqueous solution.

[0012] In particular, an alkaline aqueous solution containing 0.1-20% by weight, preferably 1-5% by weight, of sodium hydroxide or potassium hydroxide was used for extraction.

[0013] The alkaline aqueous phase obtained after filtration can be neutralized with an acid, in particular nitric acid, sulfuric acid or phosphoric acid.

[0014] The gelling agent is advantageously agar, in particular agar derived from agarophyte red algae such as those of the Gelidiaceae and Gracilariaceae families, gelatin, Alginates, such as sodium alginate, in the presence of trivalent or divalent ions (such as calcium ions); Carrageenan in the presence of calcium or potassium ions, in particular carrageenan derived from red algae, such as kappa carrageenan; pectin in the presence of calcium or barium ions, in particular pectin derived from fruit peels; You can choose from:

[0015] The algae from the Gelidaceae family that are used to produce the agar may be those already mentioned above, and the algae from the Gracilaria family may be selected from, for example, Gracilaria verrucosa and Gracilaria gracilis.

[0016] The hydrogel according to the invention may contain 0.05 to 100 g, in particular 0.1 to 20 g, of at least one gelling agent per 0.1 to 500 g, preferably per 1 to 100 g, of dry extract, in particular of the fertilized extraction product, and per 1000 mL of water.

[0017] The hydrogels according to the invention may be in the form of small pieces or blocks, such as spheres or cubes, or in the form of a flowable jelly or viscous mass. Mass or block forms, such as spheres or cubes, are particularly interesting for transport and for the controlled, periodic release of contained water over time.

[0018] Another object of the invention is a process for the preparation of a hydrogel as defined above, characterized in that the extraction product as defined above is mixed with a gelling agent in an aqueous medium, the mixture being heated to a temperature above the solubilization temperature of the gelling agent and being made to solidify, or to form a jelly or viscous mass that can flow, when cooled, the water being at least partly derived from the extraction product.

[0019] The heated mixture can be poured into a mold and cooled to give a solid shaped mass that can be cut into pieces or blocks such as spheres or cubes, or the heated mixture can be poured into a mold to directly give pieces or blocks such as spheres or cubes.

[0020] According to a particular embodiment, the gelling agent used is powdered agar, and the mixture is heated to 50 to 120°C, preferably 80 to 120°C, for 10 to 20 minutes to solubilize the agar, and the mixture is gelled by cooling the heated mixture.

[0021] Gelation then occurs via hydrogen bonding at 34-38°C for agar derived from algae in the Agaraceae family, and 40-53°C for agar derived from algae in the Gracilaria family. Once stabilized and in the form of a solid block, agar loses its consistency only at 80°C.

[0022] Another object of the present invention is the agricultural use of a hydrogel as defined above, or a hydrogel prepared by the method as defined above, as an agent capable of retaining water available to the roots of plants while providing a fertilizing effect.

[0023] Finally, an object of the present invention is a method for fertilizing cultivated plants under conditions of retention of water used for watering cultivated plants, with the aim of reducing or even preventing water loss due to evaporation or infiltration into the water table, characterized in that a hydrogel as defined above, or a hydrogel prepared by the method as defined above, is placed on the soil around the plants or in the soil around the roots of the plants.

[0024] The plants are in particular chosen from market plants (tomatoes, melons, lettuce, spinach, beans, etc.), fruit trees (banana trees, avocado trees, pear trees, apple trees, nectarine trees, etc.), ornamental plants, horticultural plants (rose bushes, grassland plants and field crops, etc.).

[0025] The hydrogel according to the invention is advantageously applied at a frequency of 1 to 5 repetitions throughout the harvest period, in particular at 1 g to 10 kg hydrogel per plant, more in particular at 10 g to 500 g hydrogel per plant. [Example]

[0026] The following examples illustrate the present invention without, however, limiting its scope.

[0027] Example 1: Preparation of fertilized extracts by alkaline treatment of Gelidium sesquipedale 800 kg of red algae Gelidium sesquipedale was placed in a 20 m 3 It was placed in water.

[0028] NaOH was added at a mass concentration of 3% at room temperature, and the mixture was stirred for 2 hours to carry out an alkali treatment.

[0029] Then, it is filtered through a 0.1 micron filter and the 3 The liquid portion was collected in an amount of 100 ml.

[0030] This liquid product has a basic pH.

[0031] This was neutralized to pH 7 with nitric acid.

[0032] Examples 2-10: Preparation of water-retentive fertilized gel spheres The following mixtures were prepared: [Table 1]

[0033] Each mixture was heated to boiling point (approximately 98°C) for 15 minutes and then poured into a mold. The mixture gelled when the temperature dropped below 35°C. The formulations were allowed to stand for 3 hours.

[0034] Hydrogel spheres were obtained and subjected to the tests described in Examples 11 and 12 below.

[0035] Example 11 Lettuce was planted in 1 kg pots at one plant per pot, with eight pots per cultivation condition.

[0036] 40 g of hydrogel spheres from Examples 2-6 were placed on top of the soil in each pot. Eight pots were used in this example.

[0037] 40 g / pot of hydrogel spheres from Examples 2-6 were placed in the pots by burying them 1 cm deep near the roots. For the examples, eight pots were used.

[0038] Eight control pots were prepared for each of Examples 2 and 3, 4 and 5, and 6. These did not contain hydrogel spheres.

[0039] Control pots were watered daily for 40 days with 50 mL of water per pot.

[0040] All other pots were watered equally with 50 mL of water per pot, but only on one out of every two days during the same 40-day period. The leaf mass (in grams) of the lettuce grown over these 40 days is reported in Table 1 below. [Table 2]

[0041] The yield increase is defined as the ratio (mass ex - mass c) / mass c*100.

[0042] For each of Examples 2-6, increased yields were observed despite a 50% reduction in water supply. [Brief explanation of the drawings]

[0043] [Figure 1] Figure 1 shows the control and lettuce plants from Example 2 with the roots removed from the soil after treatment. [Figure 2] FIG. 2 shows the control and lettuce plants from Example 3 with the roots removed from the soil after treatment. [Figure 3] FIG. 3 shows the water loss in grams after watering and settling of buried spheres in Examples 2 and 3. [Figure 4] FIG. 4 shows the water loss in grams after watering and settling the spheres in Example 4. [Figure 5] FIG. 5 shows the average weight in grams of the buried spheres in Example 6 after watering and settling.

[0044] From these figures, it can be seen that both the surface (above the soil) and buried hydrogel spheres in Examples 2 and 3 are penetrated by the lettuce roots, but the buried hydrogel spheres are penetrated to a greater extent by the roots. The fertilizer extract and water are more available to the plants when buried than when surface.

[0045] Parallel monitoring of gel sphere mass was performed on hydrogel spheres that had been watered and then allowed to settle. The procedure was as follows: the spheres were placed on a filter, and the water leaking out due to syneresis was filtered, collected in a graduated beaker, and measured. In parallel, the mass of the spheres was measured. The results are shown in Figures 3, 4, and 5.

[0046] An increase in weight was observed during watering, indicating that the spheres absorbed some of the water used for watering and then gradually released it. It is possible to capture and store water from several watering sessions and keep this water available to the plants for an extended period of time.

[0047] Example 12 Proceeding as in Example 11, except that 8 g of spheres were applied instead of 40 g of spheres and hydrogel spheres according to Examples 2 and 3 were used. The control was watered daily for 21 days, the other pots were watered only once during these 21 days. The results are reported in Table 2 below. [Table 3]

[0048] A yield increase comparable to that observed in Example 11 was observed with a smaller amount of hydrogel spheres, i.e., 8 g instead of 40 g. Also, despite higher water stress, i.e., only one watering in 21 days, the yield of lettuce using hydrogel spheres was improved compared to the control, which was watered daily for 21 days.

Claims

1. 1. A hydrogel based on at least one gelling agent, which contains, as a fertilizer, a product obtained from the extraction with an alkaline aqueous solution of at least one agarophyte red algae of the Gelidiaceae family.

2. 2. The hydrogel of claim 1, wherein the at least one agarophyte red alga of the Gelidaceae family is selected from Gelidiella acerosa, Gelidium amansii, Gelidium cartilagineum, Gelidium liatulum, Gelidium pacificum, Gelidium lingulatam, Gelidium sesquipedale, Gelidium corneum, and Gelidium pristoides.

3. 3. The hydrogel according to claim 1, wherein the fertilized extraction product is an aqueous phase obtained by extracting the at least one red algae with an alkaline aqueous solution or by subsequent filtration to recover the aqueous phase, which can then be concentrated, dehydrated or freeze-dried, and then redissolved in water.

4. The extraction is carried out at a high temperature of 40 to 98°C, preferably 60 to 80°C, for 30 minutes to 8 hours, and the red algae are extracted at a temperature of 10 to 20 m ３ 4. The hydrogel according to claim 3, wherein the hydrogel is used in an amount of 600 to 900 kg in an alkaline aqueous solution of 1000 kJ / g.

5. 5. Hydrogel according to any one of claims 3 and 4, characterized in that an alkaline aqueous solution of sodium hydroxide or potassium hydroxide in a concentration of 0.1 to 20% by weight, preferably 1 to 5% by weight, is used for extraction.

6. 6. Hydrogel according to any one of claims 3 to 5, characterized in that the alkaline aqueous phase obtained after filtration has been neutralized with an acid, in particular with nitric acid, sulfuric acid or phosphoric acid.

7. The gelling agent is agar, in particular agar derived from agarophyte red algae such as those of the Gelidaceae and Gracilariaceae families, gelatin, Alginates, such as sodium alginate, in the presence of trivalent or divalent ions (such as calcium ions); Carrageenan in the presence of calcium or potassium ions, in particular carrageenan derived from red algae, such as kappa carrageenan; pectin in the presence of calcium or barium ions, in particular pectin derived from fruit peels; 7. The hydrogel according to claim 1, wherein the hydrogel is selected from the group consisting of:

8. 8. Hydrogel according to any one of claims 1 to 7, characterized in that it contains 0.05 to 100 g, in particular 0.1 to 20 g, of at least one gelling agent per 0.1 to 500 g, preferably per 1 to 100 g, of dry extract of the fertilized extraction product and per 1000 ml of water.

9. 9. A hydrogel according to any one of claims 1 to 8, characterized in that it is in the form of small pieces or blocks such as spheres or cubes, or in the form of a flowable jelly or viscous mass, in particular in the form of small pieces or blocks such as spheres or cubes.

10. 10. A method for producing a hydrogel according to any one of claims 1 to 9, comprising:

10. A method according to any one of claims 1 to 9, wherein the extraction product is mixed with the gelling agent in an aqueous medium, the mixture being heated to a temperature above the solubilization temperature of the gelling agent and, upon cooling, being caused to solidify or form a flowable jelly or viscous mass, and the water is at least partially derived from the extraction product.

11. 11. The method according to claim 10, characterized in that the heated mixture is poured into a mould to obtain a block which can be cut into pieces or blocks such as spheres or cubes, or the heated mixture is poured into a mould to directly obtain the pieces or blocks such as spheres or cubes.

12. 12. The method according to claim 10, wherein the gelling agent used is powdered agar, the mixture is heated to 50-120°C, preferably 80-120°C, for 10-20 minutes to solubilize the agar, and the mixture is gelled by cooling the mixture thus heated.

13. 13. Agricultural use of a hydrogel according to any one of claims 1 to 9, or a hydrogel prepared by the method according to any one of claims 10 to 12, as an agent capable of retaining water available to plant roots while providing a fertilizing effect.

14. 13. A method for fertilizing cultivated plants under conditions of retention of water used for watering cultivated plants, with the aim of reducing or even preventing the loss of water due to evaporation or seepage to the water table, characterized in that a hydrogel according to any one of claims 1 to 9 or a hydrogel prepared by the method according to any one of claims 10 and 12 is placed on the soil around the plants or in the soil around the roots of the plants.

15. 15. The method according to claim 14, characterized in that the plants are selected from market plants (tomatoes, melons, lettuce, spinach, beans, etc.), fruit trees (banana trees, avocado trees, pear trees, apple trees, nectarine trees, etc.), ornamental plants, horticultural plants (rose bushes, grassland plants and field crops, etc.).

16. 16. The method according to any one of claims 14 and 15, characterized in that the hydrogel is applied with a repetition frequency of 1 to 5 times throughout the harvest period, in particular at 1 g to 10 kg hydrogel per plant, more in particular at 10 g to 500 g hydrogel per plant.

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