Fertilizer comprising bioavailable Si and method for production thereof

Abstract

The present invention relates to a humic substance based Si-fertilizer product having storage-stable, bio-available Si, which is produced by forming a mixture of, 45-95% by weight of a humic acid-containing raw material, 5-50% by weight of amorphous silica, and 0.5-10 % by weight of an alkali, all amounts based on the total weight of the dry components, incubated in an aqueous medium, and optionally dried and granulated, wherein the bio-available silicon is in the form of water-soluble chelates of monosilicic acid-humate compounds. The invention also relates to a method of producing humic substance based Si-fertilizer, a method for increasing the uptake of silicon in plants and use of the humic substance based Si-fertilizer.

Claims

1. A humic substance based Si-fertilizer product comprising storage-stable bio-available Si, produced by forming an aqueous suspension of a mixture of 45-95% by weight of a humic acid-containing raw material, 5-50% by weight of amorphous silica, and 0.5-10% by weight of an alkali, wherein the amounts are based on the total weight of the dry components, the aqueous suspension is incubated for a time and a temperature where humic acid and amorphous silica dissolve forming humates and monosilicic acid, thereby forming an incubated suspension, in which the bio-available silicon is in the form of water-soluble chelates of monosilicic acid-humate compounds, formed by complexing reactions between the monosilicic acid and the humates.

2. The Si-fertilizer product according to claim 1, wherein the incubated suspension is dried until a residual moisture of less than 15% by weight.

3. The Si-fertilizer product according to claim 1, wherein the product includes a matrix comprising undissolved residues of the humic acid-containing raw material and undissolved residues of the amorphous silica.

4. The Si-fertilizer product according to claim 1, wherein the humic acid-containing raw material is selected from the group consisting of coal, brown coal, peat, humic soil, and a mixture of thereof.

5. The Si-fertilizer product according to claim 4, wherein the humic acid-containing raw material is brown coal.

6. The Si-fertilizer product according to claim 1, wherein the amorphous silica is selected from the group consisting of microsilica, diatomaceous earth, rice husk ash, zeolites, and a mixture thereof.

7. The Si-fertilizer product according to claim 6, wherein the amorphous silica is microsilica.

8. The Si-fertilizer product according to claim 1, wherein the alkali is selected from the group consisting of an alkali metal hydroxide, an alkaline earth metal hydroxide and a mixture thereof.

9. The Si-fertilizer product according to claim 1, wherein the dried product is de-agglomerated and/or granulated.

10. A method for the production of a humic substance based Si-fertilizer containing storage-stable, bio-available Si, comprising the following steps (amounts based on the total weight of the dry components), mixing 45-95% by weight of a humic acid-containing raw material, 5-50% by weight of an amorphous silica, and 0.5-10% by weight of an alkali, in an aqueous medium forming an aqueous suspension, incubating the suspension for a time and a temperature, and optionally drying the incubated suspension, wherein the amounts are based on the total weight of the dry components.

11. The method according to claim 10, wherein the incubated suspension is dried until a residual moisture content of less than 15% by weight.

12. The method according to claim 10, wherein the aqueous suspension is incubated at a temperature between 20-70° C. for a period of at least 1 hour.

13. The method according to claim 10, wherein the incubated mixture is dried by heating to a product temperature between 15 and 95° C.

14. The method according to claim 10, wherein the humic acid-containing raw material is selected from the group consisting of coal, brown coal, peat, humic soil, and a mixture of thereof.

15. The method according to claim 14, wherein the humic acid-containing raw material is brown coal.

16. The method according to claim 10, wherein the humic acid-containing raw material is added in an amount of 60-90% by weight, or 75-85% by weight, based on the total weight of dry components.

17. The method according to claim 10, wherein the amorphous silica is selected from the group consisting of microsilica, diatomaceous earth, rice husk ash, zeolites, and a mixture thereof.

18. The method according to claim 17, wherein the amorphous silica is microsilica.

19. The method according to claim 10, wherein the amorphous silica is added in an amount of 10-30% by weight, or 15-25% by weight, based on the total amount of dry components.

20. The method according to claim 10, wherein the alkali is selected from the group consisting of an alkali metal hydroxide, an alkaline earth metal hydroxide and a mixture thereof.

21. The method according to claim 10, wherein the amount of water is 25-70% by weight, based on the total weight of the suspension.

22. The method according to claim 10, wherein the initial pH in the aqueous suspension, before incubation, is 9.5 or higher.

23. The method according to claim 11, wherein the dried product is de-agglomerated, and/or granulated.

24. A method for increasing the uptake of silicon in cultivated plants, comprising adding the humic substance based Si-fertilizer according to claim 1 to the soil before seeding or planting and/or during the growth of the plants.

25. The method according to claim 24, where the humic substance based Si-fertilizer is added in an amount of 50-1000 kg/ha.

Description

DETAILED DESCRIPTION OF THE INVENTION

(1) According to the present invention a storage-stable humic substance based fertilizer containing bio-available Si is produced. The fertilizer is produced by forming a mixture of (based on the total weight of the dry components), 45-95% by weight of a humic acid-containing raw material, 5-50% by weight amorphous silica, and 0.5-10% by weight of an alkali, which mixture is incubated in an aqueous medium, possibly dried and de-agglomerated. The bio-available silicon in the thus produced product is in the form of water-soluble chelates of monosilicic acid-humate compounds.

(2) In the present context the term “incubating” may also be interpreted as leaching and/or maturing. Incubating is denoting the process step wherein the alkaline aqueous suspension is left for a time and at a temperature wherein the raw materials are leached in the alkaline solution. Further, the complexing reactions between dissolved monosilicic acid and humic acid takes place during the incubation.

(3) The humic acid-containing raw material may be any humic substances. The preferred humic acid-containing raw materials advantageously have a high content of humic acid. Examples of such humic substances having a high content of humic acid are different types of coal, such as e.g. brown coal (lignite, leonardite), peat and humic soil. The amount of humic acid-containing raw material is defined to be from 45-95% by weight, based on the total content of the dry materials. In an embodiment, the amount of humic acid-containing raw material may be between 60-90% by weight, e.g. 75-85% by weight. The amount of humic acid-containing raw material added in the mixture may rely on e.g. the content of humic acid in the raw material. The humic acid-containing raw material should be grounded to a fine powder, particle of mm size, e.g. 0.1-3 mm, to increase the reaction kinetics.

(4) The amorphous silica suitable for the method of production of the humic substance based Si-fertilizer, according to the present invention, may be a low cost silica selected from the group; microsilica, diatomaceous earth, rice husk ash, perlite and zeolites, or a combination of these. Amorphous silica is preferred silica source because it has a much higher solubility compared to crystalline silica, which is already present in the soil. A high specific surface area increases the dissolution rate of silica (provided it is available to the alkaline solution) to the desirable monosilicic acid. An amorphous silica especially suitable for the present invention has a specific surface area about 5-50 m.sup.2/g (BET), and a particle size in the nano or micron area, e.g. 0.01-50 μm, preferably less than 5 μm. The morphology and particle size distribution of the amorphous silica should be uniform, as this favors uniform dissolution of the particles in the alkali aqueous suspension. Microsilica is advantageous as it is available with uniform morphology and particle size distribution within a narrow range, as well as a suitable high specific surface area. The term “microsilica” used in the specification and claims of this application refers to particulate, amorphous SiO.sub.2 obtained from a process in which silica (quartz) is reduced to SiO-gas and the reduction product is oxidized in the vapor phase to form amorphous silica. Microsilica may contain at least 70% by weight silica (SiO.sub.2), and preferably >95% by weight SiO.sub.2, and has a specific gravity of 2.1-2.3 g/cm.sup.3 and a specific surface area of 5-50 m.sup.2/g (BET), typically 20 m.sup.2/g. The primary particles are substantially spherical and may have an average size of about 0.15 μm, as calculated by volume. Microsilica is preferably obtained as a co-product in the production of silicon alloys in electric reduction furnaces, but may also be (co)-produced in other processes.

(5) The amount of amorphous silica added to the mixture is 5-50% by weight. In an embodiment, the amount of amorphous silica is between 10-30% by weight, e.g. 15-25% by weight.

(6) The term “alkali”, as used herein, denotes soluble bases which contain and release hydroxide ions (OH.sup.−) in aqueous solutions to form an alkaline solution which has pH more than 7. The alkali should be a strong base such as alkali metal hydroxide, such as NaOH and KOH, an alkaline earth metal hydroxide, such as Ca(OH).sub.2, or a mixture thereof. The alkali may be added to the mixture as a solid material. The alkali neutralizes the humic acid in the humic acid containing raw material, thus bringing them to a water-soluble form as humates. The alkali also dissolves a significant amount of the amorphous silica. The primary reaction product is monosilicic acid, Si(OH).sub.4. The amount of alkali added to the mixture is between 0.5-10% by weight. Normally the amount of alkali added is less than the stoichiometric amount necessary to dissolve all silica and to convert all humic acid. However, the amount of alkali provides sufficient bio-available Si and humates for germination and initial growth period. The surplus amorphous silica will act as a slow release source, thus providing sufficient fertilizing in the later growth periods. The initial pH in the suspension should be at least 9.5, and may be even as high as 13.

(7) The method for the production of the humic substance based fertilizer according to the present invention, comprises mixing 45-95% by weight of a humic acid-containing raw material, 5-50% by weight of an amorphous silica, and 0.5-10% by weight of an alkali, (said amounts are based on the total weight of the dry components) in an aqueous medium forming an aqueous suspension, incubating the suspension at a temperature between 20-70° C. for a period of at least 1 hour and optionally drying the incubated mixture. The dried product should have a residual moisture content between 5-15% by weight.

(8) The humic acid-containing raw material, the amorphous silica and the alkali used in the method for the production of a humic substance based Si-fertilizer, containing storage-stable bio-available Si, should be the same as specified above.

(9) The amount of water should be more than the necessary (stoichiometric) amount for the reactions, the maturation during incubation and the chelate formations. The aqueous suspension should preferably have a water content such that the suspension is stirable and preferably also flowable, to be transportable e.g. by pumping. Thus, the amount of water may be 25-70% by weight, based on the total weight of the suspension. After incubation, the suspension may be used as an aqueous form of the invented Si-fertilizer product. However, for a dried version of the product, the dispersion should not contain too much water, as this will increase the energy demand for removing water in the drying step. Thus, for a dried product the water content is normally not more than about 50% by weight, based on the total weight of suspension. The water content is typically from 25-40% by weight, based on the total weight of the suspension.

(10) Any suitable mixer may be used for preparing the aqueous suspension, e.g. a dispersion mixer. Typically, the humic acid containing raw material and the amorphous silica source are mixed before addition of water and the alkali. This mixing sequence is however not mandatory as any mixing sequence may be used. The thus obtained mixture should be thoroughly mixed into a homogenous suspension, thereby forming an alkaline suspension of dissolved and undissolved constituents. The suspension is left for incubation for a time and a temperature, where the humic acid and the amorphous silica are dissolved, under the formation of humates and monosilicic acid. Without being bound by the theory it is believed that, as monosilicic acid is formed, the monosilicic acid is chelated by a complexing reaction with the water-soluble humates. Monosilicic acid chemically bound as chelates with humates are prevented from polymerization into polysilicic acid. Thus, the silicon is bound as monosilicic acid and remains in a bio-available form.

(11) The incubation temperature is preferable between 20 to 70° C. The incubation time should be from 1 hour to several days. Incubation time at normal temperatures, i.e. ambient temperatures, is typically from 2 to 7 days. An incubation time between 3-5 days at normal temperatures will typically be sufficient for leaching and complexing reactions. During the incubation the pH of the aqueous suspension will decrease from more than 9.5, or even higher, towards a neutral pH of about 6.5-7. Experiments show that similar effects, as for prolonged incubation time at ambient temperatures, may be obtained by a combination of an elevated temperature and agitation. In this case the incubation time may be reduced to a few hours, e.g. incubating at 50-60° C. for about 24 hours. In general, elevating incubation temperatures will reduce the incubation time. Agitation and/or stirring of the suspension during incubation may also promote homogenization and solubilization of monosilicic acid and humic acids, and thus reduce the incubation time. An optimized combination of agitation, temperature and alkaline may reduce incubation time to just about an hour. After incubation the suspension will typically have a pH of about 6.5-7.

(12) To make a dry product the incubated suspension is typically dried by heating to a product temperature between 15 and 95° C., to obtain a product having a residual moisture content of less than 15% by weight. The drying step may be performed in open air, or by use of any conventional drying equipment, possibly including heating means, to reduce the water content. When drying in open air, the drying time is depending on the air humidity and temperature. A residual moisture content in the product of about 10% are in most cases suitable, however it should be noted that the water content may deviate from this specific amount. The product should not be completely dried, as such drying may transform the monosilicic acid bound as chelates to silica, which is a bio-unavailable form of Si. Thus, the residual moisture should not be less than about 5% by weight. The dried product may be crushed and sieved as required, and/or granulated, to produce a product that is easy to handle and use.

(13) The use of the humic substance based Si-fertilizer, according to the present invention, results in a high uptake of Si in cultivated plants. The humic substance based Si-fertilizer, according to the present invention, is used for increasing crops yield, to enhance growth of plants, and prevent diseases in plants. The humic substance based Si-fertilizer, according to the present invention, is also used for protecting plants against biotic and abiotic stresses, and reducing the content of mobile heavy metals in soil and total content of heavy metals in the cultivated plants.

(14) The present invention will be illustrated by the following examples. The examples should not be regarded as limiting for the present invention as these are meant to illustrate different embodiments of the invention and the effect of the usage of the invention.

EXAMPLES

Example 1. Preparation of Dry Humic Substance Based Si-Fertilizer Product

(15) Brown coal (BC) and microsilica (MS) was weighted out in a weight ratio 5:1, in total 60 kg. The BC and MS was dry blended for 4 minutes. About 30 liters of water was added to the mixture of BC and MS, and the blending was continued. 0.6 kg KOH powder was added (1% by weight of dry mix), and the mixture was blended another 4 minutes.

(16) The wet mixture (total weight about 90.6 kg) was retained in the mixer for 3 days at ambient temperature (20-25° C.) and blended 3-4 times every day, 4 minutes each time (incubation process). After 3 days incubation process, the mix was dried in open air for 2 days to about 10% water content. The dried cake was put back into the mixer for de-agglomeration.

Example 2. Test of Plant Growth Under Different Treatments

(17) Table 1 shows the biomass of barley and peas grown under tested product application (without NPK fertilization and without contamination).

(18) The different products tested was brown coal (BC), microsilica, a product prepared according to Example 1, but without incubation, and a Si-fertilizer, according to the present invention, prepared according to the method in Example 1. In the test including precipitated silica (SiO.sub.2) (PS), a product was prepared by the same method as the product according to the present invention, as described in Example 1, replacing MS with precipitated silica.

(19) The amount of treatment added to the crop was 300 kg/ha.

(20) TABLE-US-00001 TABLE 1 The biomass of barley and peas grown under tested product application Leaves Stem Roots Leaves Stem Roots Treatments Average for 10 plants, g % BARLEY Control 0.95 0.08 0.85 100.0 100.0 100.0 Brown coal (BC) 0.96 0.08 0.86 101.1 100.0 101.2 Microsilica (MS) 1.04 0.09 0.98 109.5 112.5 115.3 BC + MS + KOH 1.03 0.12 0.98 108.0 150.0 115.3 (without incubation) BC + MS + KOH 1.26 0.13 1.24 132.5 162.5 146.4 (with incubation) Precipitated 0.97 0.08 0.84 102.1 100.0 98.8 silica (PS) BC + PS + KOH 1.01 0.09 0.88 106.3 112.5 103.5 (with incubation) PEAS Control 1.52 1.18 2.36 100.0 100.0 100.0 BC 1.51 1.20 2.39 99.3 101.3 101.3 MS 1.59 1.54 2.76 104.6 130.5 116.9 BC + MS + KOH 1.84 1.72 4.27 121.1 145.8 180.9 (without incubation) BC + MS + KOH 2.18 1.88 6.74 143.4 159.3 285.6 (with incubation) PS 1.53 1.19 2.38 100.7 100.8 100.8 BC + PS + KOH 1.84 1.23 2.84 121.1 104.2 120.3 (with incubation) LSD.sub.05 0.04 0.05 0.05

(21) The test results presented in Table 1, show a significant higher yield with the application of the Si-fertilizer according to the present invention.

Example 3. Uptake of Si in Plants Fertilized with the Inventive Si-Fertilizer

(22) Table 2 shows the uptake of Si, both monosilicic acid and polysilicic acid, in roots and leaves, in plants fertilized with the Si-fertilizer prepared in Example 1, or microsilica. The amount of treatment added to the crop was equivalent to 300 kg/ha.

(23) TABLE-US-00002 TABLE 2 Uptake of Si, both monosilicic acid and polysilicic acid, in crops. Amount of monosilicic acid in Amount of polysilicic acid in roots and leaves of barley roots and leaves of barley mg Si/kg dry weight mg Si/kg dry weight BARLEY BARLEY Apoplast Symplast Apoplast Symplast Roots Leaves Roots Leaves Roots Leaves Roots Leaves Control 21.4 35.2 275 285 240 396 322 453 MS 43.4 69.5 497 520 433 538 520 558 BC + MS + KOH 54.5 79.7 598 628 489 622 720 845 (with incubation) Amount of monosilicic acid in Amount of polysilicic acid in roots and leaves of peas roots and leaves of peas mg Si/kg dry weight mg Si/kg dry weight PEAS PEAS Apoplast Symplast Apoplast Symplast Roots Leaves Roots Leaves Roots Leaves Roots Leaves Control 20.1 29.3 150.8 182.3 82.4 145.6 415.8 283.5 MS 28.3 33.4 190.2 193.2 92.4 234.5 458.9 314.5 BC + MS + KOH 38.4 39.2 239.4 205.3 99.4 284.4 502.3 335.4 (with incubation)

(24) In the above tests the amount of treatment product added to the crop was equivalent to 300 kg/ha. This means that the product according to the present invention containing brown coal (BC), microsilica (MS) and KOH, only a total of 60 kg/ha of MS is added. This is 5 times lower amount compared to when MS is added on its own. In spite of this lower amount of MS added to the crop, there is still a significant increase in crop yield and uptake of Si in the plants.

Example 4. Si in Rice Plants Treated with the Inventive Si-Fertilizer Vs. Different Products

(25) Si in rice plants treated with different products has been extracted using different methods. Table 3 shows treatment with the Si-fertilizer, according to present invention, results in the highest uptake of Si in the rice plants, and this result is independent of the method used to extract the Si.

(26) TABLE-US-00003 TABLE 3 Si in rice, extracted by using various methods. Extractions Water, 0.1 n 0.1M 0.5M monosilicic acid HCl CaCl.sub.2 Acetic acid Treatment Si mg/kg Control 5.22 172.5 8.63 14.3 Microsilica 5.68 190.2 11.4 16.73 BC + MS + KOH 7.38 211.7 14.06 18.89 (incubated) Brown coal 5.03 174.9 9.32 15.96 Ground Slag 5.86 172.6 12.06 14.83

(27) Having described preferred embodiments of the invention it will be apparent to those skilled in the art that other embodiments incorporating the concepts may be used. These and other examples of the invention illustrated above are intended by way of example only and the actual scope of the invention is to be determined from the following claims.