GB2407577A - Water-soluble chelating polymer - Google Patents

Abstract

A composition comprises solubilised polyvalent cations and a chelating water-soluble polymer, wherein the polymer contains acidic functional groups other than aspartic acid residues. Preferably, at least some of the acidic groups are derived from maleic acid which may be copolymerised with sulphonated styrene or acrylic acid. Typically, the polyvalent cation is iron. A method for fertilising crops is also disclosed, wherein at least one nutritional polyvalent metal ion which is dissolved with a chelating water-soluble polymer having acid groups is applied to plant organs. The plant organs may be roots growing in calcareous soil.

Description

AGENTS FOR SOLUBILISING METAL IONS

FIELD OF THE INVENTION

The present invention relates generally to the sequestration of metal ions, more specifically the invention deals with the administration of chelated metallic nutrients to plants. The metallic nutrients under consideration are such that may form complexes with some organic molecules.

BACKGROUND OF THE INVENTION

As of today, the practice of supplying the various poly-valent metals to plants requires specific attention because of the complications associated with the distribution and acceptance of such metals by the plants, in the root zone or via the foliage. Iron is distinguished among other nutritive polyvalent cations (zinc, manganese, copper, calcium and magnesium) in the diminished availability to plants at high pH environment or calcareous soils. This is a result of the very low solubility product of trivalent iron with hydroxide ions. Thus only a small amount of trivalent iron remains available in the presence of hydroxide.

ho To overcome the impediments inflicted by high pH and or high alkalinity to crop production, several types of soil applied fertilizers were introduced, that exploit the tendency of ferric ions and other metallic ions to bind to organic molecules having a specific distribution of functional groups thus extending the time before precipitation with hydroxyl ions takes place. A chelate of the art is a combination of an organic molecule (typically referred to as the chelating agent) having several functional groups that bind to a metal cation, yet keep it water soluble.

Some of the chelating agents used in agriculture and industry are synthetic such as the chelating molecules based on the ethylene diamine core, and some are natural such as citric acid. Some modified natural products are also known in the art as complexing agents such as lignosulphonates.

lo A chelate comprises a ligand, typically an organic molecule containing at least two functional groups, and a metallic poly - valent cation. A very common ligand use in agriculture is EDTA, often for delivering nutritional metal ions of iron, manganese, copper and zinc. The ligands of choice in agriculture for delivering iron in high - pH soils are EDDHA and EDDHMA. Four properties characterize a proper ligand for iron intended for application to crops through the soil in high pH soils. First, a high affinity of the ligand to the Fe+3 ion, second, a high ratio between the affinity of the ligand to Fe+3 and the affinity to Fe+2, and third, a high ratio between the affinity of the ligand to Fe+3 and the affinity to Ca+2, all at the relevant pH range. The fourth property is the overall ho solubility in aqueous environment when bound to the metal. The need for a comparatively low affinity to Ca+2 stems from the fact that in many cases the high pH in the soil is associated with a high concentration of calcium carbonate.

The high calcium concentration in the soil may compete with the bonds on the chelate to eventually displace the iron ion in the chelate. If an iron chelate is to be applied in soils in which the pH is high without the presence of calcium, this requisite may not be relevant.

Ion exchange fertilizers have been used to load chelated metals for establishing a controlled release formulation (US 4396412), such ion exchangers are polymers which contain water soluble components such as polyacrylamide. The use of water soluble polymers was demonstrated as disclosed in US 5814582 in which polymers having carboxyl groups enhanced plant productivity. In US 5221313 gel forming organic polymers, typically polyacrylamides were disclosed as a provider of iron to plants in combination lo with cheap iron source.

Water soluble polyaspartic acid was disclosed in US 5,593,947 as an enhancer of plant nutrients. This was used alone or in combination with other organic polymers.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

In accordance with the present invention, organic polymers are used to solubilise metal ions in water. With respect to iron, which is more susceptible s to precipitation in high pH levels than other commonly occurring cations, the use of some organic polymers was found to be surprisingly effective. The compositions of the present invention can be easily introduced to the agricultural practice, but they can nevertheless be exploited in other fields of the industry in which sequestration of metals is required. The embodiments of the to present invention include certain polymer and certain polymer metal ion combinations, that provide beneficial results, as will be further described in the examples, infra. All the polymers contain acidic residues (functional groups).

First, a description of the solution used in the experiments is provided.

Solution A. To a 10 mis (millilitres) solution of poly(acrylic acid) co polymerised with maleic acid (50% in water of poly(acrylic acid-co-maleic acid) by Sigma Aldrich, hereinafter referred to as PACM, 5 ml water and 1. 0 gram of ferric nitrate nonahydrate were added. To the solution 3.2 grams KOH were added so while stirring, causing a gel to form. After a few hours of further stirring, the gel dissipated forming a clear reddish transparent solution. The solution, having a volume of about 22 mis (millilitres), is stable for at least two months, contains about 0.63 % iron.

Solution B 5.8 grams of poly(styrenesulfonic acid) copolymerised with maleic acid (poly(styrenesulfonic-co-maleic acid) sodium salt (by Sigma Aldrich) was mixed in 15 mis of water with 0.5 ferric nitrate nonahydrate, forming a gel s instantly. While stirring, 2.5 mis of acetic acid were added to the solution, and after a few hours of stirring the gel dissipated completely and a clear reddish transparent solution formed.

Solution C 0.4 grams of copper powder was mixed with 15 ml water, to which lo suspension 3.0 mis of PACM were added, forming a gel. After complete dissolution of the copper, 2 grams of KOH were added and the solution mixed until clear. The solution was stable for at least two months in room temperature.

Solution D To 14 mis of PACM 1.6 grams of MnCO3 (by Sigma Aldrich) were added. The mixture was stirred for two days until all the carbonate disappeared visually, forming a white slurry. 4.5 grams of KOH were gradually introduced while stirring, forming a clear transparent brown solution.

to Solution E To 0.8 grams of ferric nitrate nonahydrate (by Sigma Aldrich), 13 mis of polymethacrylate (sodium salt, 30% in water, by Sigma Aldrich), were introduced and 5 mis of water were added. To the gel formed, 6 mis of acetic acid were added. The mixture was stirred until the gel dissipated. Then 2.5 grams of KOH were added gradually, over hours, raising the pH to about 8. The solution is stable fro at least two months.

Solution F Five mis of sodium salt of polyaspartate (40% in water by Sigma Aldrich) was mixed with 30 ml water containing 0.1 gram ferric nitrate nonahydrate. After about 1 hour of stirring the gel completely dissipated forming a clear reddish solution of a pH between 8 and 9.

Solution G' Three grams of FeEDDHMA (commercial) was mixed with 40 ml of to water. To the deeply coloured purple solution formed, 0.2 grams of K2CO3 were added and the solution mixed.

Solution G2 One gram of FeEDDHMA (commercial) was mixed with 40 ml of water. To the deeply coloured purple solution formed, 0.2 grams of K2CO3 were added and the solution mixed.

Solution H Half a gram of ferric nitrate nonahydrate were mixed with 1.3 of citric acid, and a 10 ml of water, until a clear and homogeneous yellow transparent solution formed.

Solution I Half a gram of ferric nitrate nonahydrate were mixed with 1.5 EDTA (by Sigma Aldrich) in 10 mis of water. Adding 1.7 grams of K2CO3 caused the mixture to dissolve, forming a red clear transparent solution with a pH of about 9.5 Precipitation experiments Experiment 1.

To of solution F. 0.3 grams of K2CO3 was added. After a few minutes of stirring, a thick brown precipitate formed, settling at the bottom when stirring was stopped. The remaining solution became clear and non tinted.

Experiment 2.

To two mis of solution Go, 1 gram CaO (Sigma Aldrich) was added to the solution while stirring, and additional 20 mis of water added. After a few lo hours a brown precipitate formed and the deep purple colour of the solution turned red. After a day, when the stirring was stopped, a hazy reddish tinted supernatant appeared as the rich brown precipitate settled.

Experiment 3.

To 2 mis of solution G2, 1 gram of 1 K2CO3, was added and the solution mixed until clear. Following, 1 gram CaO (Sigma Aldrich) was added to the solution while stirring, and more 20 mis of water added. After 1 hour all the deep purple colour was eliminated and a suspension of brown colour developed. After a day, a slightly tinted hazy supernatant appeared as the brown precipitate settled.

ho Experiment 4.

To 2 mis of solution A, 40 mis of water were added, which formed a slightly acidic reddish brown solution. To the solution 1 gram of K2CO3 was added while stirring, raising the pH to above 9. After half an hour 20 more mis of water were added and 1 gram of CaO (by Sigma Aldrich) was added as well.

After 2 hours, the stirring was stopped, and a whitish precipitate formed, leaving a reddish - brown hazy supernatant, which cleared after 2 days without losing the colour. Constant stirring during the next four days did not make the supernatant lose the colour, but the precipitate turned light brown.

Experiment 5.

s To 5 mis of solution A, 40 mis of water were added, which formed a slightly acidic reddish brown solution. To the solution 1 gram of K2CO3 was added while stirring. After half an hour 20 more mis of water were added and 1 gram of CaO (by Sigma Aldrich) was added as well. After 2 hours, the stirring was stopped, and a whitish precipitate formed, leaving a reddish - brown hazy lo supernatant, which cleared after 2 days without losing the colour. Constant stirring during the next four days did not make the supernatant lose the colour.

Over a week, the precipitate turned light brown.

Experiment 6.

To 2 mis of solution H. 1 gram of K2CO3 was added, and 40 mis of water, forming a clear, yellow tinted stable solution. After a few hours, 1 gram of CaO was added while stirring, and 20 more mis of water were added. Quickly, a brown precipitate formed and after settling, the supernatant appearing was clear, transparent and non - tinted.

Experiment 7.

To 2 mis of solution 1, 1 gram of K2CO3 was added, and 40 mis of water, forming a clear, reddish yellow tinted stable solution. After a few hours, 1 gram of CaO was added while stirring, and 20 more mis of water were added.

Almost immediately, a brown precipitate formed and after settling, the supernatant appearing was clear and non - tinted.

Experiment 8.

To 2 mis of solution 1, 40 mis of water were added, forming a clear, reddish yellow tinted stable solution. After a few hours, 1 gram of CaO was added while stirring, and 20 more mis of water were added. Almost immediately, a brown precipitate formed and after settling, the supernatant appearing was clear and non - tinted.

Experiment 9.

To 2 mis of solution B. 40 mis of water were added, which formed a slightly acidic reddish brown solution. To the solution 1 gram of K2CO3 was lo added while stirring, raising the pH to above 9. After half an hour 20 more mis of water were added and 1 gram of CaO (by Sigma Aldrich) was added as well.

After 2 hours, the stirring was stopped, and a whitish precipitate formed, leaving a yellowish - brown hazy supernatant, which cleared after 2 days without losing the colour.

Is Experiment 10.

To 5 mis of solution B. 40 mis of water were added, which formed a slightly acidic reddish brown solution. To the solution 1 gram of K2CO3 was added while stirring. After half an hour 20 more mis of water were added and 1 gram of CaO (by Sigma Aldrich) was added as well. After 2 hours, the stirring ho was stopped, and a whitish precipitate formed, leaving a reddish - brown hazy supernatant, which cleared after 2 days without losing the colour.

Experiment 1 1.

To 2 mis of solution E, 40 mis of water were added, which formed a slightly brown - yellowish solution. To the solution 0.3 grams of K2CO3 were as added while stirring, raising the pH to about 8. The solution remained clear with no precipitate during the next few days. The addition of 0.3 grams CaO while stirring caused an almost immediate clearing of the colour with a brownish sticky precipitate forming.

s Drying experiments Experiment 12.

Two mis of solution E were placed in a drying beaker on a hot plate at 85 C after a few hours a paste formed which was completely solublisable in lo water.

Experiment 1 3.

Two mis of solution C were placed in a drying beaker on a hot plate at 150 C after half an hour a green brittle solid formed which was completely solubilisable in water.

Experiment 14.

Two mis solution of solution A were placed in a drying beaker on a hot plate at 150 C. After half an hour a brown brittle solid formed which was completely solubilisable in water.

to Implications of the chemical solubility experiments As observed, the maleic acid copolymers were effective sequestrants of ferric ion in basic solutions, which is indicative of the chelate formed by the trivalent iron ions bound to the polymer molecules. The superiority of such polymers as sequestrants of ferric ion in the environment of lime as compared to citric acid and EDTA based chelates, and their comparability to EDDHMA in 1 1 the high pH high lime environment is suggestive of a fertilising potential of iron and other metallic micronutrients in general. This potential may be exploited for applying poly-valent metals to plant organs, in high pH soils in particular, in combination with the chelating polymers of the invention. s

Agronomic experiments Solitary cherry tomato plants were grown in 10 cm pots filled with calcareous root medium, irrigated twice daily. The temperature was a warm summer temperature facilitating fast growth. The root medium was obtained lo from a chalk pit, and consisted of substantially minced chalk with no soil. Such a root medium has good water retention and aeration properties but is strongly buffered with carbonate and contains substantially no clay. The plants were fertilised with nitrogen and potassium. After about a week the plants developed a prominent chlorosis starting at the growth tips and spreading as the leaves increased in size. After about another weak some of the plants became almost completely yellow.

To each of 10 plants, 2 mis of solution A dissolved in about 20 mis of water was applied to the soil, after which irrigation was resumed a usual. To two other plants 1.5 mis of the same solution was supplied in the same manner. To to yet three other plants a 2 mis of solution B were supplied each, also in the same manner.

The results with respect to chlorosis became evident after a few days during which all the plants began to re-green. The response to 2 mis of solution A was unexpectedly fast, inciting substantial response within 2 days or even within a day and a half. Subsequent visible progressive greening in these cases was visible within hours.

Utility of the solutions of the invention s Fertigation is a modern agricultural practice in which irrigation and fertilization are combined, being performed by the same systems. Fertigation is unique also in confining the root activity to a limited volume of soil or root medium. Fertilizers in fertigation are supplied solubilised through the irrigation system. The chelating polymers and metal ion solutions of the invention are lo therefore readily adopted by fertigation. The exceptional chelating capabilities of the solutions A and B are promising with respect to crops growing in high pH and calcareous soils. However, the solutions of the invention can be employed in any fertilization scheme, which applies fertilisers to any absorptive organ of the plant, including foliar application, much the same as other chelates are used fro foliar application of nutrients. Some polymers, i.e. PACM and the co polymer of maleic acid and styrene (an aromatic functional group) were very efficient with respect of iron ion sequestration in the high pH, high calcium environment, however, polyaspartic acid was a poor sequestrant of such iron in high pH conditions.

Claims (11)

1. A composition including solubilised poly-valent cations, further comprising at least: s. a chelating water soluble polymer, wherein said polymer contains acidic functional groups with the exception of aspartic acid residues.

2. A composition as in claim 1 and wherein at least some of said to acidic functional groups are derived from maleic acid.

3. A composition as in claim 1 and wherein said poly - valent ions are nutritional elements.

4. A composition as in claim 2 and wherein said maleic acid is copolymerised with sulphonated styrene.

5. A composition as in claim 2 and wherein said maleic acid is copolymerised with acrylic acid.

6. A composition as in claim 1 and wherein said polyvalent cation is iron.

7. A method for fertilising crops comprising applying to the absorptive plant organs at least one nutritional poly - valent metal ion dissolved together with a chelating water soluble polymer solution, wherein said polymer contains acidic s functional groups.

8. A method as in claim 7 wherein said a plant organs are roots.

9. A method as in claim 7 and wherein said roots are growing in lo calcareous soil.

10. A method as in claim 7 and wherein at least some of said acidic functional groups are derivatives of maleic acid.

11. A method as in claim 7 and wherein at least some of said acidic functional groups are derivatives of styrene.