AU747244B2 - A soil supplement containing plant available silicon - Google Patents

Description

WO 01/58831 PCT/AU01/00108 1 A SOIL SUPPLEIMENT CONTAINING PLANT AVAILABLE SILICON FIELD OF THE INVENTION The present invention is directed to a soil supplement, typically in granular form, and which contains plant available silicon The invention is s also directed to least one method for producing such a soil supplement.

BACKGROUND ART The use of silicon as a soil supplement to assist in the growth of plants is known. Certain plants such as sugar cane and rice require silicon soil supplements. While many soils contain silicon, the silicon is either in a lo form of silicon dioxide which is highly stable and cannot be absorbed by plants or its total content has been leached from the soil by heavy rainfall or it has been removed from the soil by the plant when it is harvested. It is necessary for the silicon to be in a plant available form. While natural silicates have broken down over time, the amount of plant available silicon which is naturally available in certain soils is now very low.

A known soil supplement which is being used on sugar cane is an artificial calcium silicate. This material is spread at a rate of between tonnes per hectare which is a very high application rate. With this material, a lesser application rate does not result in appreciable amounts of plant available silicon being provided.

Plants also benefit from cations such as calcium and magnesium as well as potassium. An advantage of the known artificial calcium silicate product was that it provided calcium to the soil.

As well as providing silicon to the soil in a plant available manner, there is also a great advantage in being able to provide silicon which is reasonably soluble to allow it to be taken up more readily by plants. If this can be achieved, less material needs to be spread over a certain area of soil.

This can result in enormous savings to the farmer.

Japanese patent application 07069764 describes a method to produce a silicate fertiliser. However, it is found that a silicate fertiliser provides less plant available silicon. Japanese patent application 07101792 similarly describes a liquid silicate fertiliser where a sodium or potassium silicate is mixed with gluconic acid. Again, a silicate fertiliser does not provide WO 01/58831 PCT/AU01/00108 2 silicon in a format which is easily absorbed by a plant. Japanese patent application 11314986 describes a fertiliser made from a metal silicate which is reacted with an acid and is then subjected to a washing and drying steps to produce the fertiliser. The fertiliser is stated as having about 90% silicon dioxide content which is a form difficult to be absorbed by plants. The fertiliser is added to water to give a 5 ppm concentration within 24 hours.

This fertiliser thus has a very low solubility in water which makes it difficult to be absorbed by plants.

OBJECT OF THE INVENTION The present invention is directed to a soil supplement which can provide silicon in a plant available format and which can provide a much higher level of dissolved silicon. The present invention is also directed to a method by which a soil supplement can be manufactured.

In one form, the invention resides in a soil supplement containing, as a component thereof, silicon in the form of amorphous silica.

In another form, the invention resides in a soil supplement containing, as a component thereof, silicon in the form of mono silicic acid.

Suitably, the soil supplement contains a mixture of amorphous silica and mono silicic acid.

In another form, the invention resides in a soil supplement comprising amorphous silica, mono silicic acid, magnesium sulphate and calcium sulphate.

The soil supplement may be formed by reacting a metal silicate material with an acidic solution. Preferably, the reaction is carded out in a substantially solid moist state by which is meant that the liquid components are kept to a minimum and that the reaction is not carried out in an aqueous medium.

In another form, the invention resides in a modified soil supplement formed by reacting a metal silicate material with an acidic solution to form a soil supplement, and reacting the soil supplement with an alkali material and water to form the modified soil supplement. It is believed that this modified or processed soil supplement contains amorphous silica and mono silicic acid. It is believed that the addition of the alkali step increases WO 01/58831 PCT/AU01/00108 3 the amount of available amorphous silica and mono silicic acid which is supplied to a soil, the mono silicic acid being a form of silicon which is available for uptake by plants.

The alkali material may be selected from the group consisting of: potassium bicarbonate; potassium carbonate; sodium carbonate; calcium hydroxide; potassium hydroxide; sodium hydroxide; magnesium hydroxide; calcium carbonate; magnesium carbonate; and calcium carbonate. A convenient source of calcium carbonate is limestone. A convenient source of magnesium carbonate is magnesite. A convenient source of calcium carbonate and magnesium carbonate is dolomite.

The yield of mono silicic acid is found to be particularly high (which is desirable) when the alkali material is a mixture of potassium bicarbonate and calcium carbonate suitably in substantially equal proportions.

Typically, the soil supplement is reacted with the alkali material and a minimum of water such that the pH of the modified or processed soil supplement is in the order of 6-8 to provide a more pH neutral substance.

It is believed that the soil supplement provides plant available silicon to the soil by reacting with. water and the soil to yield mono silicic acid.

One or more other products may also be yielded from the reaction with the soil, the soil supplement and water.

The soil supplement and the modified or processed soil supplement can be in the form of a soil conditioner or fertiliser. Typically, the supplement is granulated or pellitised. A typical granule size range can be between 1 mm-10 mm.

The metal silicate material preferably comprises magnesium silicate and/or calcium silicate. When reacted to form the soil supplement, the cations (magnesium and calcium) are also considered useful as a plant supplement. The metal silicate may be selected from basic rocks, ultra basic rocks, ultra mafic rocks, rocks (wollastonite rich), zeolite rich rocks, artificial slags produced as by products in steel production, artificial slags produced as by products in superphosphate production, ash products from sugar mills, ash products from coal burning facilities, and artificial silicates produced from plasterboard manufacture.

WO 01/58831 PCT/AU01/00108 4 Suitably, the metal silicate is in the form of a crushed solid material such as crushed rock. To facilitate reaction with the acid, it is preferred that the metal silicate has a high surface area and therefore has been finely crushed for instance ranging in size from 3mm to fines preferably less than 0.25mm.

It has been found that particularly high yields of mono silicic acid are yielded when the silicate material comprises wollastonite (Ca[SiO3]), olivine Fe) 2 SiO 4 or serpentine Mg 3 [Si 2 0 5

](OH)

4 Rocks containing wollastonite include calc silcates (metamorphosed limey sediments and volcanics) and rocks containing olivine or serpentine include partially or completely serpentinised dunite, peridotite, harzburgite, wehrlite, Iherzolite, gabbro or basalt.

In one form of the invention, the soil supplement is formed by reacting the metal silicate with an acid. It appears that a better product is obtained if the reaction is carried out in a dry to moist solid state. It is therefore preferred that the liquid components of the reaction are kept to a minimum such that the reaction is not carried out in an aqueous solution or slurry but is instead carried out in a substantially solid state A preferred acid is sulphuric acid which is preferably in the form of a concentrated sulphuric acid. A concentration of sulphuric acid of between 50%-100% by weight can be used. It is considered that other acids may be used instead of or with sulphuric acid, these including nitric acid.

Sulphuric acid is preferred as it results in the creation of cation sulphate such as magnesium and/or calcium sulphate which are useful to plants.

The mixing ratio of the metal silicate material to the acid is preferably such that the solid metal silicate material is in the larger amount to ensure that the reaction is carried out in a substantially solid or dry state.

Mixing ratios may be between 2:1 to 10:1 of metal silicate material to the acid.

It is considered that a solid state reaction results in an acidolysis process, as opposed to a hydrolysis process which would occur if the reaction was carried out in a substantially aqueous manner.

The metal silicate material can be preheated such that most or WO 01/58831 PCT/AU01/00108 substantially all the water of crystallisation is removed from the material prior to reacting with the acid. If the metal silicate is a rock containing olivine and/or serpentine, the rock may be preheated to a temperature of between 350°C-750°C. If required, the rock may be cooled prior to being reacted with the acid. The rock may be crushed either prior to or after the heating step.

While not wishing to be bound by theory, it appears that the soil supplement makes the silica much more available for uptake by plants due to the silica being in an amorphous state. When the amorphous silica is contacted with water, it may convert to mono silicic acid which can be taken up by the plants. The soil supplement may contain a percentage of mono silicic acid as well as amorphous silica depending on the amount of moisture in the soil supplement or processed soil supplement after it has been granulated or pellitised.

It is found that the soil supplement provides good improvements to plant growth if the supplement is added to the soil on or before planting.

Therefore, in another form, the invention resides in a method of improving the growth rate of plants; the method comprising adding a soil supplement to the soil at or before planting, the soil supplement comprising amorphous silica. It can be applied after planting but with less effect to the plant. Suitably, the method can comprise a soil supplement as described above, that is containing other components such as calcium and magnesium sulphate.

BEST MODE In order to achieve a better understanding of the nature of the present invention, several embodiments of the invention are given below.

Example 1 (Magnesium Silicate) A metal silicate is the form of dunite rock mainly magnesium silicate) which has been crushed to a particle size of minus 0.25 mm, and the acidic solution is a sulphuric acid solution (98% by weight sulphuric acid). A sample of dunite is well mixed and reacted in an exothermic reaction with 1Og of sulphuric acid and 1 Og of water until reacted. The low amount of water and the use of concentrated acid results in a solid state reaction, as opposed to an aqueous solution or slurry. The product can be used as a soil WO 01/58831 PCT/AUO1/00108 6 supplement and contains amorphous silica and magnesium sulphate. The products of this reaction typically have a pH of The soil supplement can be further modified or processed as follows: The products are mixed with Og of water and 5g of an alkali material consisting of crushed limestone, until reacted. The low amount of added water, and the use of a solid alkali (limestone) results in a substantially "dry" or solid state reaction. The result is a mixture of amorphous silica, mono silicic acid, magnesium sulphate and silicate and calcium sulphate, which after granulating or pelletising can be applied directly to soils. The pH of the 1o pellet is typically The modified soil supplement has a remarkably improved solubility of silicon in water, making the silicon very plant available. As an example, lg of the granules in 1000ml of 0.01M calcium chloride solution were mixed in a bottle roller at 4rpm, for 24hrs and centrifuged. An analysis (described below) gives 12,000-16,000mg silicon/kg, 28,000-31,000mg magnesium/kg and 15,000-18,000mg calcium/kg. The amount of soluble silica was very much higher than with conventional soil supplements where the amount of soluble silica is about 1/3 as much.

Example 2 (Calcium Silicate) The metal silicate in this example is a rock with wollastonite which has been crushed to a particle size of minus 0.25mm, and the acidic solution is a sulphuric acid solution (98% by weight sulphuric acid).

A 50g sample of the is well mixed and reacted in an exothermic reaction with of the sulphuric acid solution and 10g of water until reacted in a solid state solution. The products of this reaction typically have a pH of 4.5, and can be used as a soil supplement.

The products can be further processed to a modified or processed soil supplement by mixing with 2.5g of water and 2.5g of an alkali material consisting of limestone, until reacted in a solid state solution. The result is a mixture of amorphous silica, mono silicic acid, and calcium sulphate and silicate, which after granulating or pelletising can be applied directly to soils.

The pH of the pellet is typically WO 01/58831 PCT/AU01/00108 7 On dissolving 1g of these granules in 1000ml of 0.01M calcium chloride solution in a bottle roller at 4rpm, for 24hrs and centrifuged before analysis (described below) gives 16,000-20,000mg silicon/kg, 100-150mg magnesium/kg and 61,000-64,000mg calcium/kg.

Example 3 (Mixture of Magnesium Silicate and Calcium Silicate) The metal silicate in this example is a 50/50 mixture of dunite and rock with 50% wollastonite both of which have been crushed to a particle size of minus 0.25mm, and the acidic solution is a sulphuric acid solution (98% by weight sulphuric acid). A 50g sample of this mixture is well mixed and reacted in an exothermic reaction with 10g of the sulphuric acid solution and 10g of water until reacted in a solid state solution. The products of this reaction typically have a pH of 4.5, and can be used as a soil supplement.

The products can be further processed to a modified or processed soil supplement by mixing 2.5g of water and 2.5g of an alkali material consisting of limestone, until reacted in a solid state solution. The result is a mixture of amorphous silica, mono silicic acid, and magnesium and calcium sulphates and silicates, which after granulating or pelletising can be applied directly to soils. The pH of the pellet is typically On dissolving 1g of these granules in 1000ml of 0.01M calcium chloride solution in a bottle roller at 4rpm, for 24hrs and centrifuged before analysis (described below) gives 22,000-26,000mg silicon/kg, 15,000- 18,000mg magnesium/kg and 35,000-38,000mg calcium/kg.

Example 4 The metal silicate in this example is a dunite rock which has been crushed to a particle size of minus 0.5 mm, and the acidic solution is a sulphuric acid solution. (98% by weight sulphuric acid). This dunite typically contains 65% olivine and 35% serpentine. A typical chemical analysis of olivine includes: MgO- 40% to SSiO2 39% to 42%; Fe 2 6% to 9%; CaO 0.3% and and WO 01/58831 PCT/AU01/00108 8 other oxides 0.3% to 3%.

A 50g sample of dunite is well mixed and reacted in an exothermic reaction with 10g of the sulphuric acid solution. The products of this reaction can be applied to soils, where it can react with the soil and water to form mono silicic acid.

Example The metal silicate in this example is a dunite rock which has been preheated to a temperature of 600°C for 15 minutes and then crushed to a particle size of minus 0.25mm. The acidic solution is sulphuric acid solution (98% by weight sulphuric acid). The dunite can be completely or partially serpentinised and may have up to 10% free moisture (H 2 0) added to it after it has been crushed to minus 0.25mm. A 50g sample of dunite is mixed and reacted in an exothermic reaction with 8g of the sulphuric acid.

The products of this reaction typically have a pH of 3-4. The products are then mixed with 4g of alkali material consisting of about 2g of calcium carbonate and about 2g of potassium bicarbonate, and about 4g of water, until reacted. The resultant solid material comprises a mixture of amorphous silica, mono silicic acid, magnesium silicate, magnesium, calcium and potassium sulphates, and magnesium, calcium and potassium carbonates, and can be applied directly to soils after it has been granulated. The pH of the material is typically 7-8.

Method of Silicon Analysis Si was analysed using a modified approach to the blue silicomolybdate acid procedure (Weaver et al., 1968, 'Determination of silica in citrate-bicarbonate-dithionite extracts in soils', Soil Science Society of America Proceedings, 32:497-501) this is a colourmetric method where the samples are read on a spectrophotometer after colour development.

Method of Magnesium and Calcium Analyses The magnesium and calcium cations were analysed on an atomic absorption spectrometer.

Growth Response Rates The processed soil supplement of Example 1 was applied to the soil at the time of planting of sugar cane and with the planting fertiliser (of WO 01/58831 PCT/AU01/00108 9 conventional type). The supplement was added at rates of between 50-100 kg per hectare.

A growth response became clearly evident from emergence, and at 60 days after planting the growth response was estimated to be 70% greater than with the planting mix without silicon. There appeared to be no significant difference between the 50-100kg Si product/ha rates. At days after planting a growth response was still evident, with plants in treated silicon areas being 45cms higher, and at 120 days after planting being higher than sugar cane plants without added silicon. After 120 days after planting, the cane sticks which were grown in the soil treated with additional silicon were filling out with sugar at a greater rate than the untreated cane. There was an observed increased stooling, estimated to be more cane sticks. Sugar yields are expected to be significantly different over the untreated cane.

A person skilled in the art will understand that there are many other rocks which contain wollastonite, olivine and/or serpentine. Rocks with lower percentage of olivine, such as partially or completely serpentinised peridotites, harzburgites, wehrlites, Iherzolites or basalts may be substituted for dunite in the above examples.

It will be appreciated by persons skilled in the art that numerous variations and/or modifications may be made to the present invention without departing from the spirit or scope of the invention as broadly described. The above examples are therefore to be considered in all respects illustrative and not restrictive.

Claims (20)

1. A method of producing an amorphous silica-based soil supplement or growth aid comprising the steps of crushing a natural rock containing metal silicate and reacting the crushed rock in an acidolysis reaction, with a relatively concentrated acid in a substantially solid state, wherein the reaction is carried out in a dry or moist state without excess moisture.

2. A method of producing an amorphous silica-based soil supplement or growth aid as claimed in claim 1, further comprising the step of reacting with an alkali to form a processed soil supplement.

3. A method of producing an amorphous silica-based soil supplement or growth aid as claimed in claim 1 or 2, further comprising the step of adding water to produce silicic acid.

4. The method of claim 1, wherein the metal silicate is selected from the group :0,0 :comprising magnesium silicate and calcium silicate or mixtures thereof.

5. The method of Claim 4, wherein the natural rock containing metal silicate is selected from the group comprising mafic and ultramafic rock containing olivine and/or serpentine, wollastonite (calc-silicate) rich rock, zeolite-rich rock or mixture thereof crushed to 3mm or finer.

6. The method of claim 4, wherein the acid is sulphuric acid.

7. The method of claim 2, wherein the alkali is limestone crushed to 3mm or finer.

8. The method of claim 1 comprising reacting crushed dunite with sulphuric acid in a substantially solid state to form a product, and further reacting the product with :crushed limestone in a substantially solid state to form the soil supplement.

9. The method of claim 1 comprising reacting crushed rock with 20-70% wollastonite with sulphuric acid in a substantially solid state to form a product, and further reacting the product with crushed limestone in a substantially solid state to form the soil supplement. The method of claim 1 comprising reacting a mixture of dunite and crushed rock with 20-70% wollastonite with sulphuric acid in a substantially solid state to form a product, and further reacting the product with crushed limestone in a substantially solid state to form the soil supplement. 11

11. An amorphous silica-based soil supplement or growth aid when produced by the method in claim 1.

12. An amorphous silica-based soil supplement or growth aid when produced by the method in claim 2.

13. An amorphous silica-based soil supplement or growth aid when produced by the method in claim 3.

14.An amorphous silica-based soil supplement or growth aid when produced by combining materials as claimed in claim 11 and claim 12. amorphous silica-based soil supplement or growth aid when produced by combining materials as claimed in claim 11 and claim 13.

16.An amorphous silica-based soil supplement or growth aid when produced by combining materials as claimed in claim 12 and claim 13.

17.An amorphous silica-based soil supplement or growth aid when produced by combining materials as claimed in claims 11-13.

18. The amorphous silica-based soil supplement or growth aid as claimed in any one of claims 11-17, additionally comprising monosilicic acid.

19.The amorphous silica-based soil supplement or growth aid of claim 18, additionally comprising magnesium sulphate. amorphous silica-based soil supplement or growth aid of claim 19, additionally comprising calcium sulphate.

21. The amorphous silica-based soil supplement or growth aid as claimed in any one of claims 11-17, wherein the amorphous silica has a solubility in 1 litre of aqueous solution of at least 10,000 mg silicon/kg of product.

22.A method for promoting plant growth, the method comprising adding a soil supplement containing the amorphous silica-based soil supplement or growth aid as claimed in any one of claims 11-21, to the soil at or prior to planting.

23. The method of claim 22, wherein the supplement is added at rates of minimum to a maximum of 1000kg/hectare. 0 0 .00. 0 0: 0 0.00 4 ,0 0 .0 6 00 0 00 0 0 0 *000 0 0000 0 0000 0 0000