SWELLABLE FERTILIZER GRANULES CONTAINING ELEMENTAL SULFUR WITH INCREASED OXIDATION RATES

Abstract

Fertilizer granules containing elemental sulfur and a hydrogel which expands or swells in the soil to more readily disperse the elemental sulfur surface throughout the soil, which increases the elemental sulfur surface area available for oxidation, and ultimately uptake of sulfur by the plant. The elemental sulfur and hydrogel can be added to a fertilizer composition as either an exterior coating or co-granulated with the base fertilizer composition.

Claims

1. A swellable sulfur-containing granule comprising: a base fertilizer composition; a source of elemental sulfur; and a hydrogel, wherein the granule is configured to swell upon introduction to a soil environment to disperse the source of elemental sulfur within the soil environment.

2. The granule of claim 1, wherein a rate of oxidation of the elemental sulfur of the granule is greater than a rate of oxidation of elemental sulfur contained with a granule without hydrogel.

3. The granule of claim 1, wherein the hydrogel is selected from the group consisting of bentonite or other water-absorbent clays, psyllium husk, corn starch, carrageenan gum, rice starch, sodium polyacrylate, glucose, calcium alginate, inulin, chitosan, carboxymethycellulose, fumed silica, guar gum, Xanthan gum, bean gum, gum arabic, and combinations thereof.

4. The granule of claim 3, wherein the hydrogel comprises a gum.

5. The granule of claim 1, wherein the hydrogel is present in an amount of from about 0.1 weight percent to about 20 weight percent of the granule.

6. The granule of claim 5, wherein the hydrogel is present in an amount of from about 1 weight percent to about 10 weight percent of the granule.

7. The granule of claim 6, wherein the hydrogel is present in an amount of about 5 weight percent of the granule.

8. The granule of claim 1, wherein the elemental sulfur is present in an amount of from about 0.1 weight percent to about 20 weight percent of the granule.

9. The granule of claim 8, wherein the elemental sulfur is present in an amount of from about 1 weight percent to about 10 weight percent of the granule.

10. The granule of claim 9, wherein the elemental sulfur is present in an amount of about 5 weight percent of the granule.

11. The granule of claim 1, wherein the hydrogel material and elemental sulfur is applied as a coating to an outer surface of a granule formed from the base fertilizer composition.

12. The granule of claim 11, wherein the dispersion coating further comprises sodium bentonite in an amount of about 1 to about 10 weight percent of the granule.

13. The granule of claim 1, wherein the hydrogel material and elemental sulfur are co-granulated with the base fertilizer composition to form the granule.

14. The granule of claim 1, wherein the base fertilizer composition is selected from the group consisting of MAP, DAP, triple super phosphate, urea, MOP, or combinations thereof.

15. The granule of claim 15, wherein the base fertilizer composition comprises MAP.

16. The granule of claim 1, wherein the base fertilizer composition comprises a primary nutrient, and one or more sources of micronutrients and/or secondary nutrients selected from the group consisting of boron (B), zinc (Zn), manganese (Mn), molybdenum (Mo), nickel (Ni), copper (Cu), iron (Fe), and/or chlorine (Cl), an additional source of sulfur (S) in its elemental form, sulfur in its oxidized sulfate form (SO4), magnesium (Mg), and/or calcium (Ca), and combinations thereof.

Description

BRIEF DESCRIPTION

[0016] FIG. 1 depicts a sulfur-containing fertilizer granule according to the prior art.

[0017] FIG. 2 depicts an expandable sulfur-containing fertilizer granule according to an embodiment in which the hydrogel and ES are coated on the granule.

[0018] FIG. 3 depicts an expandable sulfur-containing fertilizer granule according to another embodiment in which the hydrogel an ES are cogranulated with the granule.

[0019] FIGS. 4A-4E depict dissolution in water of single granules with various formulations according to embodiments.

[0020] FIG. 5 depicts the dispersion in moist soil of sulfur-expandable fertilizer granules with various formulations according to the embodiments.

[0021] FIG. 6 depicts column oxidation of elemental sulfur in fertilizer according to the embodiments.

[0022] While the invention is amenable to various modifications and alternative forms, specifics thereof have been shown by way of example in the drawings and will be described in detail. It should be understood, however, that the intention is not to limit the invention to the particular embodiments described. On the contrary, the intention is to cover all modifications, equivalents, and alternatives falling within the spirit and scope of the invention.

DETAILED DESCRIPTION

[0023] Embodiments of the invention are directed to fertilizer granules containing elemental sulfur which expand in the soil to increase the elemental sulfur surface area exposed to soil, thereby increasing the availability of the elemental sulfur for oxidation, and ultimately uptake by the plant. The fertilizer granules contain an expandable material, such as a hydrogel, which draws in moisture and swells when exposed to moist soil, pushing the elemental sulfur particles or platelets away from the granule residue and out into the soil, thereby increasing their available surface area exposed to microorganisms. By the incorporation of materials, and particularly hydrogels, oxidation rates can be tuned or tailored for different crops to speed up oxidation in climates where oxidation of elemental sulfur is too slow to meet early sulfur requirements of the crops.

[0024] In a first embodiment, and referring to FIG. 2, an expandable sulfur containing granule 100 includes particles or platelets of elemental sulfur 102 dispersed within or blended with a hydrogel material 104 to form a coating material. The coating material can optionally contain a clay material, such as sodium bentonite, to further aid in absorbing or imbibing water. The coating material is then applied, such as, but not limited to, in the form of a dry powder coating, with or without a liquid binder, to an outer surface of a base fertilizer granule 106 in one or more layers. The hydrogel material is soluble or biodegradable when applied to the soil such that, upon introduction to the soil, the hydrogel disperses away from the granule, leaving individual particles or platelets of elemental sulfur in the soil available for oxidation.

[0025] In this embodiment, base fertilizer granule 106 can comprise any of a variety of suitable NPK fertilizers, including, for example, a nitrogen based fertilizer (e.g. urea), a potassium based fertilizer (e.g. potash or muriate of potash (MOP)), or a phosphate based fertilizer (e.g. MAP, DAP, and/or TSP), or combinations thereof. The base fertilizer granule 106 can optionally contain one or more sources of micronutrients and/or secondary nutrients, such as, but not limited to, micronutrients including boron (B), zinc (Zn), manganese (Mn), molybdenum (Mo), nickel (Ni), copper (Cu), iron (Fe), and/or chlorine (Cl), and/or secondary nutrients including an additional source of sulfur (S) in its elemental form, sulfur in its oxidized sulfate form (SO.sub.4), magnesium (Mg), and/or calcium (Ca), or any of a variety of combinations thereof at various concentrations.

[0026] Hydrogel material 104 can comprise any of a variety of liquid or dry hydrogel materials which expand with force and which have the potential to expand within the confines of the soil, and can include, for example, gelatinous materials, gums, and/or polysaccharides. Hydrogel materials 104 can comprise, for example, a material that provides one or more of the polymeric network described in Table 1 below:

TABLE-US-00001 TABLE 1 Hydrogel materials Material Description Sodium bentonite Clay, [(Si Al).sub.4(AlFeMg).sub.2O.sub.10(OH).sub.2].sub.2•Na•H.sub.2O Corn starch Carbohydrate, C.sub.27H.sub.48O.sub.20 Calcium alginate Edible gelling agent, (C.sub.12H.sub.14CaO.sub.12).sub.n Rice starch Polysaccharide, (C.sub.6H.sub.10O.sub.5).sub.n Inulin Fructose polymers from plants Sodium polyacrylate Sodium salt of poly acrylic acid, [—CH.sub.2—CH(CO.sub.2Na)—]n Carrageenan gum Polysaccharides ex red seaweed (1,3-α-1,4-β galactans) Psyllium husk Edible fibrous husk from Pantago Ovata plant Gum Arabic Glycoproteins and polysaccharides from Acacia Chitosan Linear polysaccharide from NaOH on shrimp shells Xanthan gum Bacterial polysaccharide, (C.sub.35H.sub.49O.sub.29).sub.n Carboxymethyl cellulose Sodium salt of cellulose with (—CH.sub.2—COOH)groups (CMC) Guar gum Galactose and mannose polysaccharides ex Guar beans Barley husk Hemicellulose with (~4% wt) glucuronic acid Carob -locust bean gum Galactose and mannose polysaccharides ex carob seeds

[0027] In embodiments, elemental sulfur particles 102 are present to obtain total elemental sulfur in an amount of from about 0.1 weight percent to about 20 weight percent, more specifically from about 1 weight percent to about 10 weight percent, and more particularly no more than about 5-6 weight percent. Hydrogel material 104 is present in an amount of from about 0.1 weight percent to about 20 weight percent, more specifically from about 1 weight percent to about 10 weight percent, and more particularly no more than about 5-6 weight percent.

[0028] In an alternative embodiment, and referring to FIG. 3, an expandable sulfur containing granule 200 contains co-granulated elemental sulfur particles or platelets 202 and hydrogel material 204. More specifically, individual particles or platelets of elemental sulfur 202 are blended with a hydrogel material 204, and optionally sodium bentonite, which are then co-granulated with an underlying base fertilizer composition to form the granules 200.

[0029] In this embodiment, the base fertilizer composition can comprise any of a variety of suitable NPK fertilizers, including, for example, a nitrogen based fertilizer (e.g. urea), a potassium based fertilizer (e.g. potash or MOP), or a phosphate based fertilizer (MAP, DAP, and/or TSP), or combinations thereof. The base fertilizer granule can optionally contain or be co-granulated with one or more sources of micronutrients micronutrients, such as boron (B), zinc (Zn), manganese (Mn), molybdenum (Mo), nickel (Ni), copper (Cu), iron (Fe), and/or chlorine (Cl), and/or secondary nutrients including an additional source of sulfur (S) in its elemental form, sulfur in its oxidized sulfate form (SO.sub.4), magnesium (Mg), and/or calcium (Ca), or any of a variety of combinations thereof at various concentrations.

[0030] Hydrogel material 204 can comprise any of a variety of hydrogel materials which expand with force, and have the potential to expand within the confines of the soil, including those described in Table 1 above.

[0031] In embodiments, elemental sulfur particles 202 are present to obtain total elemental sulfur in an amount of from about 0.1 weight percent to about 20 weight percent, more specifically from about 1 weight percent to about 10 weight percent, and more particularly no more than about 5-6 weight percent. Hydrogel material 204 is present in an amount of from about 0.1 weight percent to about 20 weight percent, more specifically from about 1 weight percent to about 10 weight percent, and more particularly no more than about 5-6 weight percent.

Examples and Testing

[0032] Both coated and co-granulated MAP granules were formed and evaluated for their dispersion in both water and soil.

[0033] Preparation

[0034] The coated granules were prepared by the following method: MAP granules having a particle size in a range of about 2.36-3.35 mm were pipetted with water and rolled for about 20 seconds. Elemental sulfur particles having a particle size in a range of about 20-65 μm blended with a hydrogel material having a particle size of about 0.15 μm and sodium bentonite were added to the wetted MAP such that the elemental sulfur, hydrogel material, and sodium bentonite were each present in an amount of about 5 weight percent of the composition.

[0035] The co-granulated granules were prepared by milling MAP to sizes below 250 μm. Elemental sulfur particles having a particle size in a range of about 20-65 μm blended with a hydrogel material having a particle size of about 0.15 μm and sodium bentonite were added to the MAP and homogenized, such that the elemental sulfur, hydrogel material, and sodium bentonite were each present in an amount of about 5 weight percent of the composition. Water was added via a nebulizer to the powder to build granules. Undersized granules (i.e. <1 mm) were recycled to the granulation circuit until granules having a particle size in a range of about 1-2.8 mm were produced.

[0036] Another series of coated and co-granulated granules were made in the same way but without any addition of sodium bentonite.

Testing—Dispersion in Water

[0037] Dispersion in water of the granules was tested by imaging, at various intervals, a single granule's dissolution in tap water over 60 or 120 seconds in Petri dishes. The following granules were tested, as control samples depicted in FIG. 4A-C namely Microessentials® with zinc (MESZ), which had 5% elemental sulfur incorporated, MAP, and MAP with 5% elemental sulfur coated on its surface. These control samples contained no hydrogel and/or bentonite coating or co-granulation. All showed very little dispersion in water over 60 or 120 seconds.

[0038] FIG. 4D shows a coating dispersion comparison between the MAP coated with 5% ES without hydrogel or bentonite (control) compared with MAP coated with 5% ES plus 5% hydrogel and 5% bentonite in the coating. The hydrogels tested included rice starch, corn starch, bentonite, to now include 10%, carrageenan, psyllium husk, and polyacrylate. The dispersion is much more pronounced with these hydrogel coatings as seen in the images.

[0039] FIG. 4E shows differences in the dispersion in water of MAP granules with hydrogel, in this case carrageenan/bentonite, either in the coating or granulated uniformly throughout the granule, the wider dispersion for the co-granulated granule being clearly evidenced in these images.

[0040] FIG. 5 shows stereomicroscope images using a Nikon SMZ25 with CCD camera of MAP with 5% ES and 5% hydrogel (no bentonite) both coated or co-granulated and incubated in moist soil for 16 and 220 hours. These show granule swelling in soil and reinforce the need for a hydrogel with swelling force.

Testing—Column Oxidation

[0041] The oxidation of elemental sulfur in soil for the various compositions, both coated and cogranulated with elemental sulfur and hydrogel (but without any addition of bentonite), was measured over 72 days using a column oxidation technique. To do this, 50 g of a sandy soil (pH(water) 8.5, 0.7% OC) was placed in a vertical column with 240 mg of fertilizer (for a total elemental sulfur weight percent of about 12 mg) mixed through the soil.

[0042] Each column was leached immediately with de-mineralized water to remove sulfur in the form of sulfate. The columns were then incubated at 25° C. The columns were leached weekly and the leachate was analyzed for sulfate content to measure the amount of elemental sulfur converted to sulfate over the course of the week. Each treatment was carried out with four replicates. The results are shown in FIG. 6. Table 2 gives the amount of ES oxidized recovered in the leachate at the end of the experiment:

TABLE-US-00002 TABLE 2 % ES oxidized for coated and uncoated MAP 5% ES with hydrogels in a soil column study after 72 days. Different letters indicate significant (P ≤ 0.05) differences within the column. Hydrogel Coated Co-granules % ES oxidized/72 d Xanthan gum 74.8 a 61.0 bc Guar gum 66.2 ab 78.8 A Carrageenan 52.9 bc 67.3 ab Gum arabic 51.2 c 67.3 ab CMC 47.9 c 52.6 cd Chitosan 41.2 c n/a Bean gum 37.4 c n/a Control 42.5 c 44.2 D

[0043] The results of both the water dispersion and column oxidation tests showed that although most of the hydrogel materials promoted dispersion of the granules in water, only some of these hydrogels, particularly xanthan gum, guar gum, and carrageenan, promoted the oxidation of elemental sulfur in soil, possibly because the force from the hydrogel itself must be greater than the counteracting force from the soil on the granule in order to promote dispersion of the sulfur particles within the soil.

[0044] The invention may be embodied in other specific forms without departing from the essential attributes thereof; therefore, the illustrated embodiments should be considered in all respects as illustrative and not restrictive.