AU2006225072B2 - Sequestering agent for micronutrient fertilisers - Google Patents

Description

WO 2006/096912 PCT/AU2006/000334 1 SEQUESTERING AGENT FOR MICRONUTRIENT FERTILISERS FIELD OF THE INVENTION The present invention relates to a composition and method for improving the bioavailability of micronutrients to plants. 5 DESCRIPTION OF THE PRIOR ART Agriculture is a multi-million dollar industry. In order to improve plant growth good fertile soils are required and, in the absence of these, fertilisers are often used in order to facilitate the growth of agricultural crops. Essential nutrients for plant growth include metal ions, such as Cu, Zn, Mn, etc. 10 which are crucial to various metabolic pathways of plants such as photosynthesis and so forth. Traditional farming methods have resulted in general deficiency of such metal ions in soil and indeed in some areas these metal ions are almost completely absent and this can result in diminished yields and poor plant growth of crops grown in such areas. It is well known that the 15 addition of surplus metal ions to either the soil or plant foliage can help to significantly alleviate such growth deficiencies in agricultural crops. One of the more common ways of delivering the appropriate metal micronutrient has been to form a chelated complex of the metal ion with a synthetic chelate as this maintains the metal ion in a soluble form for ease of application and reduces 20 metal adsorption and fixation in soil. However, the use of the synthetic chelates, although widely used, has some significant drawbacks such as high cost associated with production and, more recently, concerns over the fact that they are synthetic and may persist in the environment for extended periods of time. Accumulation in soil and waterways 25 due to the recalcitrant nature of synthetic chelates may lead to some negative impact on the environment.

WO 2006/096912 PCT/AU2006/000334 2 Examples of synthetic chelates include EDTA, EDDHA, DTPA and NTA. Moreover, EDTA is such an efficient complexor of metal ions that it can compete with the plants for the metal ion, thus resulting in inefficiencies in delivery of the metal ion to the plant. 5 In addition to the use of synthetic chelates, it has also been known to use organic acids, such as citrate, as the chelating agent, however, this is found not to be generally acceptable due to inferior stability constants at pH's greater than 7 and the rapid biodegradation of citrate in the soil. Moreover, the use of acids as chelating agents also has a drawback in relation to the corrosive nature of 10 such compounds and the damaging effect that this can have on machinery if inadvertently mixed in high concentrations. In each of the above cases, the use of synthetic chelates or organic acids have become the standard accepted way of providing micronutrients to plants on the thought that such agents were the best possible and most efficient compounds 15 available. Clearly, with society's changing views on agriculture and in particular a more accepted view of organic agriculture wherein synthetic agricultural compounds are not accepted due to their potential damaging effects along the food chain, there is then a need to develop more acceptable chelating agents for the delivery of micronutrients to plants. 20 OBJECT OF THE INVENTION It is an object of the present invention to provide new metal chelating compounds that are capable of delivering micronutrients to plant crops. It is a further object of the present invention to provide a method of providing micronutrients to plants that is significantly more environmentally friendly than 25 those currently in use. A further problem with the use of EDTA is its inability to biodegrade in the environment. EDTA can be found in many natural waterways and is often found WO 2006/096912 PCT/AU2006/000334 3 in high concentrations in waste water effluents. Because of its lack of ability to biodegrade, EDTA has been banned in some parts of Europe and indeed other countries may soon follow suit. A further problem with the use of NTA is that it has carcinogenic properties. 5 Because of its toxicity and inability to biodegrade, NTA has been banned in the United States of America and indeed other countries may soon follow suit. It is an object of the present invention to overcome, or at least substantially ameliorate, the disadvantages and shortcomings of the prior art. Other objects and advantages of the present invention will become apparent 10 from the following description, taking in connection with the accompanying drawings, wherein, by way of illustration and example, an embodiment of the present invention is disclosed. SUMMARY OF THE INVENTION The summary of the invention is as follows: 15 What we have found then is that by employing a compound being a.surfactant having the general formula (1) and in particular a surfactant of the general formula (111), being the biosurfactant rhamnolipid, in which the single carboxylate group has the capability of sequestering micronutrient ions such as copper, zinc, manganese, iron etc. This then results in the formation of what is 20 hereinafter referred to as a "lipid soluble" complex wherein the term "lipid soluble" refers to the ability of the chelated or complexed metal to permeate through the plant membranes or cuticle to provide the metal ion to the plant. This then is in contrast to the action of EDTA and other conventionally used chelating agents, which are not generally absorbed by plant roots and indeed 25 are known to compete against the plant roots for the micronutrients present in the rhizosphere, being the zone that surrounds the roots of the plants.

WO 2006/096912 PCT/AU2006/000334 4 Moreover, when a rhamnolipid or other biologically produced sequestering agent are used, the biodegredation of the sequestering agent is dramatically greater than that of the synthetic chelating agents therefore resulting in less pollution and greater acceptance in the wider community. Additionally, they 5 may also obtain organic registration, thus permitting the use of such agents in organic farms and the like. Conventional synthetic chelating agents cannot be used on organic farms due to the fact that they are synthetically manufactured. It has also now been discovered that the use of sequestering agents produced from Bacillus bacteria, such as surfactin, also have the ability to sequester or 10 complex with micronutrients such as those previously mentioned and have an increased level of biodegradability compared to that of synthetic complexing agents. In addition, it has been discovered that these biosurfactants, having both hydrophobic and hydrophilic groups, are also able to provide transportation of 15 the micronutrients through the foliage. The hydrophobic leaf cuticle is the main barrier for fertiliser uptake when micronutrients are applied directly to the plant foliage. We have found that rhamnolipid - metal complexes can be absorbed into hydrophobic zones thus transporting micronutrients from an aqueous phase into a lipophilic phase. 20 According to the present invention, although this should not be seen as limiting the invention in any way, there is provided a method of sequestering micronutrients when used to provide the micronutrients to a plant, which comprises applying to an area of the plant or soil/substrate surrounding the plant an effective amount of a plant fertiliser composition comprising a 25 surfactant capable of forming coordinate bonds with the micronutrients, transporting the micronutrients across a membrane of the plant and releasing the micronutrients for use by the plant. In preference, the surfactant has the general formula (I): WO 2006/096912 PCT/AU2006/000334 5 R2 0 R1) A O-1 R3 wherein R 1 is a hydrophilic group, and R2 is a hydrophobic group and R 3 is selected from the group consisting of hydrophilic and hydrophobic groups. In preference, R 3 is a hydrophilic group. 5 In preference, R 1 = (C 3

-C

6 ) cyclic alkyls or (C 1

-C

10 ) alkyls, each of which may be interrupted by one heteroatom selected from the group consisting of 0, S and N; R 2 = H, (C 1

-C

10 ) saturated, mono or polyunsaturated alkyl or (C 3

-C

6 ) cyclic alkyls, and R 3 = H, (C 1

-C

10 ) saturated, mono or polyunsaturated alkyls, (C 3

-C

6 ) cyclic alkyls, or Na, Ca or K. 10 In preference the surfactant is a biosurfactant produced from the group of bacteria consisting of Bacillus or Pseudomonas bacteria. In preference, when the Bacillus group is selected the biosurfactant is surfactin. In preference, R 1 has the structure (11): HO0 0 HO

OR

4 (II) 15 wherein R 4 = H, (C 1

-C

10 ) saturated, mono or polyunsaturated alkyl or unsubstituted a-L-rhamnopyranosyl. In preference, the molecular weight of the biosurfactant is between 450 and 700 atomic mass units. In preference, the composition is in a form selected from the group consisting of 20 liquids, suspensions, dispersions, emulsions, powders, and pellets.

.WO 2006/096912 PCT/AU2006/000334 6 In preference, the composition further includes a pesticide and/or insecticide. In preference, the composition is applied to the foliage of the plant, soil or other substrate, seeds, fruits shoots, flowers or nuts. In a further aspect of the invention there is provided a method of increasing the 5 bioavailability of nutrients to plant roots or foliage, comprising applying an effective amount of a plant fertilizer composition comprising one or more rhamnolipids with the general formula (Ill)

R

2 0 HO 0 0zR3 HO

OR

1 (III) wherein R 1 = H, unsubstituted a-L-rhamnopyranosyl, R 2 = H, (C 1

-C

10 ) saturated, 10 mono or polyunsaturated alkyl, R 3 = H, (C-C1o) saturated, mono or polyunsaturated alkyl, -CHR 4

-CH

2

CO

2

R

6 , where R 4 = -(CH 2

)-CH

3 , wherein x = 4-10 and RE = H, Na, Ca, K. In preference, R 1 is a hydrophilic group, and R 2 is a hydrophobic group and R 3 is selected from the group consisting of hydrophilic and hydrophobic groups. 15 In preference, R 3 is a hydrophilic group. In yet a further aspect of the invention there is described a plant fertiliser composition including a surfactant capable of forming coordinate bonds with soil micronutrients and transporting the coordinated micronutrients across a membrane of the plant and releasing the micronutrients for use by the plant, 20 when used to increase the rate of micronutrient uptake by the plant. In preference, the surfactant has the general formula (1): WO 2006/096912 PCT/AU2006/000334 7 R2 0 R1 )O R3 wherein R 1 is a hydrophilic group, R 2 is a hydrophobic group and R 3 is selected from the group consisting of hydrophilic and hydrophobic groups. In preference, R 3 is a hydrophilic group. 5 In preference the surfactant is a biosurfactant produced from the group of bacteria consisting of Bacillus or Pseudomonas bacteria. In preference, when the Bacillus group is selected the biosurfactant is surfactin. In preference, R 1 = (C3-C6) cyclic alkyl or (Cl-C 1 o) alkyl, each of which may be interrupted by one heteroatoms selected from the group consisting of 0, S and 10 N; R 2 = H, (Cr-C 10 ) saturated, mono or polyunsaturated alkyl, and R 3 = H, (C C10) saturated, mono or polyunsaturated alkyl, Na, Ca or K. In preference R 1 has the structure (i1): HO 0 HO

OR

4 (11) wherein R 4 = H, (C-C1o) saturated, mono or polyunsaturated alkyl or 15 unsubstituted a-L-rhamnopyranosyl. In preference, the molecular weight of the biosurfactant is between 450 and 700 atomic mass units. In preference, the composition is in a form selected from the group consisting of liquids, suspensions, dispersions, emulsions, powders, and pellets. 20 In preference, the composition includes a pesticide and/or insecticide.

WO 2006/096912 PCT/AU2006/000334 8 In preference, the composition is applied to the foliage of the plant, soil or other substrate, seeds, fruits shoots, flowers or nuts. . In preference, the composition is applied as a seed coat or pre-treatment to the seed prior to planting. 5 In preference, the composition is applied in combination with the micronutrients, either alone or in combination, Mn, Zn, Cu, Fe, Ni. In preference, the composition is applied either alone or in combination with the macronutrients N, P, K, S, Ca, Mg. As will be appreciated by those skilled in this particular field, the invention will 10 have many other uses in other related industries such as horticulture and aquaculture, wherever there is a need to supply micronutrients BRIEF DESCRIPTION OF THE DRAWINGS By way of example, an employment of the invention is described more fully the renown for with reference to the accompanying drawings, in which: 15 FIG 1 is a graph of octanol-water partition coefficients of metal ion with varying rhamnolipid concentrations. FIG 2 is a graph of Total Zn absorbed by canola roots and translocated into shoots (t 1 S.E) FIG 3 is a graph of plant foliar dry matter response to applied Zn. 20 DETAILED DESCRIPTION OF THE INVENTION Having now generally described the invention, a further understanding can be obtained by reference to certain specific examples that are provided herein for purposes of illustration only and are not intended to be limiting.

WO 2006/096912 PCT/AU2006/000334 9 n-Octanol/Water Partition Coefficients of Zn- Rhamnolipid complexes n-Octanol/water partition coefficients (Kow) are commonly used to determine whether molecules can partition into hydrophobic (lipid-soluble) phases. Polar molecules, ie metals, generally partition in the water phase. Neutral, lipid 5 soluble organic molecules may partition within the octanol phase according to their Kow. Most conventional chelate complexes (ie ZnEDTA2-) partition within the water phase. The partition coefficient has been defined as: Kow = C CW 10 where Co and Cw referred to the concentration of Zn in the n-octanol and water phase respectively (Chiou et al. 1977). The aim of this experiment was to determine whether Zn-Rhamnolipid complexes would partition within the n-octanol phase. Kow's were measured with varying Rhamnolipid concentrations. 15 Methods Kow's were determined using the shake-flask method. 20ml of 1 mM ZnSO 4 .7H 2 0 solution was mixed with Rhamnolipid biosurfactant in 50ml polyethylene tubes. Final Rhamnolipid concentrations were (mM) 0, 0.1, 0.24, 0.5, 1, 1.5, 2, 2.5. Two millilitres of n-Octanol was added to the solutions before 20 they were shaken end-over-end for 24 hours. Following shaking, 3ml of solution was removed from the water phase and digested in concentrated HNO 3 before analysis for total Zn by ICP-OES. The partition coefficient was calculated according to the equation above. Results WO 2006/096912 PCT/AU2006/000334 10 Unlike the Rhamnolipid, EDTA complexes with Zn, Mn and Cu did not partition within the n-octanol phase, as shown in Figure 1. Clearly then the use of Rhamnolipid dramatically facilitates the transfer of the metal ion from the aqueous phase into the octanol phase. 5 The use of Rhamnolipid to sequester Zn on alkaline and calcareous soils The purpose is to determine whether Rhamnolipids would increase the availability of Zn fertiliser to Canola grown on alkaline and calcareous soils. The performance of this ligand was benchmarked against EDTA, the most commonly used chelating agent on alkaline and calcareous soils in Australia. 10 Materials and Methods A pot experiment was designed to test the availability of Zn to Canola when applied to calcareous and alkaline soils either as ZnSO 4 .7H 2 0 or sequestered with, Rhamnolipids or EDTA. Soil samples were collected from field sites known to be Zn responsive at 15 Streaky Bay, South Australia and Birchip, Victoria (Table 1). Topsoils from each location were collected, oven dried and passed through a 2mm sieve. The experimental fertilisers were mixed with 20g of soil, which was banded between 100g of the unfertilised bulk soil. Total nutrient application equated to (pg/g soil) P 60, N 27, applied as TGMAP, and Zn 0.2 as ZnSO 4 .7H 2 0. Chelate rates were 20 based on the concentrations required to complex between 75 and 100% of the Zn in the fertiliser solution. Rates varied depending on the equilibrium constant (logK) and the stoichiometry of the Zn-ligand complexes. GEOCHEM was used to predict the degree of chelation in the EDTA and Rhamnolipid fertiliser solutions. Chelate application rates were ( LM/g soil) Rhamnolipid 1.25 (75% of 25 Zn complexed), EDTA 0.37 (100% Zn complexed), Experimental controls were chelate free (ZnSO 4 only) and chelate and Zn free. Each treatment was replicated four times.

WO 2006/096912 PCT/AU2006/000334 11 Two pre-germinated Canola seeds (variety Pinnacle) were transferred to each pot. The pots were watered to Og = 0.5 with deionised water every second day and evaporation was reduced with polyethylene beads, which were spread over the exposed surface of each pot. The plants were grown for 21 days in a 5 controlled environment growth chamber (10 h dark at 150C, 14 h light at 200C, 41% humidity) before the shoots were harvested, rinsed, dried, weighed and then digested in concentrated HNO 3 . Plant digests were analysed for 6 5 Zn by gamma spectroscopy and for total nutrient contents by ICP-OES. Analysis of Data 10 Data for shoot dry weight, shoot nutrient concentrations and Zn fertiliser uptake were analysed by analysis of variance (ANOVA). Significance between means was determined using the Least Significant Difference (LSD) test. Results Table 1. Properties of the soils used for the experimentsa. Site Soil description and Carbonate pH (H 2 0) % Clay Classification (%) Streaky Bay Calcareous grey sandy 39 8.7 ±.02 25 loam Birchip Sodosol light clay 2.8 8.8 ± 0.01 40 15 aoven dry soil. EDTA was ineffective on both the calcareous grey sandy loam from streaky bay and the Sodosol from Birchip, Victoria (Figure 2) (LSD=1.72). This result was not unexpected, as the efficacy of EDTA is known to decrease with increasing pH (Norvell 1972). Rhamnolipid significantly increased total Zn uptake by 20 canola on both soils (p<0.01).

WO 2006/096912 PCT/AU2006/000334 12 The published logK for ZnEDTA is 16.5 whereas the published logK for Zn rhamnolipid is only 5.9 (Martell and Smith 1974; Ochoa-Loza et al. 2001). Canola dry matter response to foliar applied Zn Foliar sprays are commonly used to apply micronutrient fertilisers to growing 5 crops. The leaf cuticle, a hydrophobic waxy layer, represents the major barrier for nutrient absorption by leaves. Previous scientific reviews have shown that lipophilic molecules should, in theory, diffuse across cuticles more readily than charged solutes (Schonherr and Riederer 1989). However, to date, the foliar application of lipophilic fertilisers has not been widely tested. In a previous 10 experiment Zn-Rhamnolipid complexes were found to readily partition within the hydrophobic n-octanol phase, suggesting that these complexes possess lipophilic qualities. The aim of this experiment was to determine whether Canola shoots would absorb neutral Zn-Rhamnolipid complexes more readily than ZnSO 4 or 15 ZnEDTA. Dry matter response in Zn deficient Canola was used as a measure of fertiliser effectiveness because it considers metabolically available Zn, rather than total Zn uptake. Methods Pre-germinated Canola seedlings (var. Pinnacle) were grown in Zn free nutrient 20 solution, in a controlled environment growth chamber (10 h dark at 150C, 14 h light at 20'C, 41% humidity) for three weeks. After 13 days, whole shoots were immersed in ZnSO 4 .7H 2 0 solutions for five seconds. The solutions contained (_M Zn) 10, 100, 1000, and were either complexed with EDTA and Rhamnolipid, or ligand free. EDTA rates were ( 1 iM) 3.75, 37.5 or 375 and 25 Rhamnolipid rates were (mM) 1, 1.1 or 1.9. Rhamnolipid rates were high enough to ensure a Zn Kow of at least 50 at the highest Zn application rate. Rhamnolipid free solutions contained 0.1% v/v Spreadwet 1000 wetting agent to enhance Zn uptake by reducing the surface tension of the solutions. Wetting WO 2006/096912 PCT/AU2006/000334 13 agent was not required in the Rhamnolipid solutions because of the surfactant properties of the ligand. Following shoot immersion, roots were rinsed twice in Zn-free hydroponic solutions to ensure that Zn applied to the surface of shoots did not contaminate 5 the root systems. After the three-week growth period, plant roots and shoots were harvested, dried and weighed for dry matter production. Results As shown in figure 3, Rhamnolipid significantly increased dry matter response 10 to Zn (P<0.05, LSD = 0.1496), which suggests that the Rhamnolipid may have increased Zn absorption through the plant foliage, compared with ZnSO 4 or ZnEDTA. Visual observations indicated that plants supplied with Zn Rhamnolipid had a larger leaf area and less chlorosis than those supplied with ZnEDTA or ZnSO 4 . 15 Although the invention has been hearing shown and described in one is conceived to be the most practical and preferred embodiment, it is recognized that departures can be made within the scope of the invention, which is not to be limited to the details described herein and that modifications may be made that do not depart from the scope of the invention so as to embrace any and all 20 equivalent compositions and methods. References Chiou C T, Freed V H, Schmedding D W and Kohnert R L 1977 Partition coefficient and bioaccumulation of selected organic chemicals. Environ. Sci. Technol. 11, 475-478. 25 Martell A E and Smith R M 1974 Critical Stability Constants Volume 1: Amino Acids. Plenum Press, Inc., New York.

WO 2006/096912 PCT/AU2006/000334 14 Norvell W A 1972 Equilibria of metal chelates in soil solution. In Micronutrients in agriculture, Eds J J Mortvedt, P M Giordano and W L Lindsay. pp 115-138. Soil Science Society of America, Inc., Madison. Ochoa-Loza F J, Artiola J F and Maier R M 2001 Stability constants for the 5 complexation of various metals with a rhamnolipid biosurfactant. J. Environ. Qual. 30, 479-485. Kaschl A, Romheld V and Chen Y 2002 Cadmium binding by fractions of dissolved organic matter and humic substances from municipal solid waste compost. J. Environ. Qual. 31, 1885-1892. Schonherr J and Riederer M 1989 Foliar penetration and accumulation of 10 organic chemicals in plant cuticles. Reviews of environmental contamination and toxicology 108, 1-70. Stevenson F J 1994 Stability constants of metal complexes with humic substances. In Humus Chemistry: Genesis, Composition, Reactions. pp 405 428. John Wiley & Sons, Inc., New York.

Claims (15)

1. 2. The method of claim 1, wherein the surfactant is a biosurfactant 20 produced from the group of bacteria consisting of Bacillus or Pseudomonas bacteria.
2. 3. The method of claim 2, wherein the Bacillus group is selected the biosurfactant is surfactin.
3. 4. The method of claim 1, wherein R 1 has the structure HO 0 HO 25 OR 4 (ii) neceiveu o mvjarcu £Iu I 16 wherein R4 = H, (C-C 1 o) saturated, mono or polyunsaturated alkyl or unsubstituted ct-L-rhamnopyranosyl, 5, The method of claim 4, wherein the molecular weight of the biosurfactant is between 450 and 700 atomic mass units. 5 6. The method of claim 5, wherein the composition is in a form selected from the group consisting of liquids, suspensions, dispersions, emulsions, powders, granules, prills, and pellets.
4. 7. The method of claim 6, wherein the composition further includes a pesticide and/or insecticide. 10 8. The method of claim 7, wherein the method further includes the addition of micronutrients and I or macronutrients.
5. 9. The method of claim 8, wherein the composition applied to foliage of the plant, soil or other substrate, irrigation water, seeds, fruit shoots, flowers or nuts, 15 10. A plant fertilizer including one or more rhamnolipids with the general formula (Ill): R 2 0 HO 0 R3 HO OR 1 (1ll) wherein R 1 = H, unsubstituted a-L-rhamnopyranosyl, R 2 = H, (C-C10) saturated, mono or polyunsaturated alkyl, R$ = H, (C-CO) saturated, 20 mono or polyunsaturated alkyl, -CHR 4 -CH 2 CO 2 R 6 , where R 4 = -(CH2)r CH 3 , wherein x = 4-10 and R 6 = H, Na, Ca, K.
6. 11. The plant fertilizer of claim 10, wherein R, is a hydrophilic group, and R 2 is a hydrophobic group and R 3 is selected from the group consisting of hydrophilic and hydrophobic groups. Keceee 5 iviarcn 4uu / 17
7. 12. A plant fertiliser composition including a surfactant capable of forming coordinate bonds with soil micronutrients and transporting the coordinated micronutrients across a membrane of the plant and releasing the micronutrients for use by the plant, when used to increase 5 the rate of micronutrient uptake by the plant wherein the surfactant has the general formula (1): R 2 0 wherein R 1 = (C 3 -C 6 ) cyclic alkyl or (C 1 -C 0 ) alkyl, each of which may be interrupted by one heteroatom selected from the group consisting of 0, 10 S and N; R2 - H, (C-C 1 ) saturated, mono or polyunsaturated alkyl, and R3 = H, (C-C 10 ) saturated, mono or polyunsaturated alkyl, Na, Ca, Mg, orK, or wherein the surfactant is a biosurfactant produced from the group of bacteria consisting of Bacillus or Pseudomonas bacteria. 15
8. 13. The composition of claim 12, further characterised in that when the Bacillus group is selected the biosurfactant is surfactin.
9. 14. The composition of claim 13, wherein R 1 has the structure (II): HO 0 HO OR 4 (II) 20 wherein R 4 = H, (C-C 10 ) saturated, mono or polyunsaturated alkyl or unsubstituted a-L-rhamnopyranosyl.
10. 15. The composition of claim 14, wherein the molecular weight of the biosurfactant is between 450 and 700 atomic mass units. KeceiveU a iviaren SuU 18
11. 16. The composition of claim 15, wherein the composition is in a form selected from the group consisting of liquids, suspensions, dispersions, emulsions, powders, granules, pills, and pellets.
12. 17. The composition of claim 16, further including a pesticide and/or 5 insecticide.
13. 18. The composition of claim 17, further including at least one micronutrient and . or a macronutrient.
14. 19. The composition of claim 18, wherein the micronutrient is selected from the group consisting of Mn, Zn, Cu, Fe and Ni. 10 20. The composition of claim 19 wherein the macronutrient is selected from the group consisting of N, P, K, S, Ca and Mg,
15. 21. The composition of claim 20, when applied to the foliage of the plant, soil or other substrate, irrigation water, seeds, fruits shoots, flowers or nuts.