CA1152769A - Fertilizer solutions containing soluble iron - Google Patents

Abstract

ABSTRACT
FERTILIZER SOLUTIONS CONTAINING SOLUBLE IRON
Fertilizer solutions suitable for foliar ap-plication or application to turf, for correction of iron deficiency, having a nitrogen to iron ratio of at least about 3:1 and citrate as the iron complexing agent. A
preferred form of solution is aqueous ferric ammonium citrate.

Description

~lS2769 DESCRIPTION
FERTILIzER SOLUTIONS CONTAININ~ SOLUBLE IRON
BACKGROUND OF THE INVENTION
This invention relates to plant nutrient solu-tions containing a readily and highly soluble iron complex and to the foliar application of such solutions.
Iron is a commonly re~uired trace metal for proper plant growth. Although iron salts are abundant in most soils, plants are often unable to utilize the iron, since the soil renders the iron salts water insoluble and unavail-able. The deficiencies of iron have been corrected somewhat by the application of foliar sprays, and especially foliar sprays containing iron as the sole trace metal nutrient or as one of several trace metal nutrients. Nevertheless, the limited solubility of most iron salts in commonly used plant nutrient solutions such as ammonium nitrate, ammonium sulfate, ammonium phosphate, urea and the like necessitates that the iron salts be separately applied, thereby increasing the expense of application. In addition, the limited solubility of the iron salts in aqueous sprays often limits the amount of metal that can be absorbed through ¦ 20 the cell walls and stomata so that the use of the soluble salts is often unsuitable.
Various iron chelates such as the chelate of ethylenediamine tetraethylamine (EDTA) have been used to obviate these problems. The chelates are complexes of the metals with certain chelating agents which have two or more cites in their molecules for bonding with the ,,,"," ,", ... ..
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" 1152769 metal and which are capable of forming a closed ring with the metal. In this form, the metals are stabilized and most of the solubility problems are obviated. These chelating agents, however, are relatively complex com-pounds which are too expensive for large scale agro-nomical use. In addition, many of the chelates are very stable compounds and the chelate structure hinders the utilization of the metal by the plant after its assimil-ation. Finally, iron complexes of organic ligands and iron salts when used in foliar sprays often cause objec-tionable spotting of foliage or crop.
U.S. Patents Nos. 3,679,377 and 3,753,67~
propose solutions to the above problem by utilizing iron in aqueous solution as the ammonium, alkali metal or alkaline earth metal salt of an ion comprising a complex of trivalent iron, sulfato and hydroxo ligands with a pH
of about 1 to about 3, and a sulfate to elemental iron ratio from about 0.25 to about 1.1. In U.S. Patent 3,753,675 a similar complex is described as prepared by admixing an iron source with an aqueous solution of ammonium nitrate having a pH of 1 to about 3 and expos-' ing the mixture to autooxidation conditions comprising a temperature and time sufficient to cause evolution of nitrogenous gases from the mixture and form an aqueous solution having a red coloration. Such fertilizer solu-tions have the drawbacks of being corrosive to common steel and probably phytotoxic if applied as foliar sprays to relieve an iron deficiency.
BRIEF DESCRIPTION OF THE INVENTION
3~ The present invention is based upon the dis-covery that iron complexed with citrate and provided in an aqueous solution wherein the weight ratio of nitrogen to iron is at least about 3 to 1 provides superior iron absorption into plants upon foliar application.
Accordingly, the present invention includes an improve-ment in an aqueous fertilizer solution containing ferric iron, an iron complexing agent, water-soluble nitrogen nutrient and water characterized by the weight ratio of ~L152769 water~soluble nitrogen nutrient (as N) to iron being at least about 3:1 and the iron complexing agent being citrate. A preferred means of introducing the iron into the solution is as ferric ammonium citrate.
The present invention also includes an improvement in a process for applying an iron-containing fertilizer solution to crops having an iron deficiency.
In the improvement, the fertilizer solution comprises ferric iron, citrate complexing agent, water-soluble nitrogen nutrient and water with a weight ratio of water-soluble nitrogen nutrient (as N) to iron of at least about 3:1.
DETAILED DESCRIPTION OF THE INVENTION
, The fertilizer solutions of the present inven-tion are designed to provide iron in a water soluble form that can easily be absorbed into a plant having an iron deficiency on foliar application. In these solu-tions, citrate is the complexing agent which preventsprecipitation of iron salts. Compared to more conven-tional complexing agents for iron, such as EDTA, citrate is relatively inexpensive and, furthermore, forms looser complexes. Accordingly, as shown in the examples that follow, the rate of iron absorption is increased compared to solutions of iron complexed with EDTA.
It is recognized that U.S. Pa~ent 3,798,020 to Parham, Jr. et al. describes fertilizer solutions wherein trace metals including iron are incorporated in increased amounts without precipitation by use of a synergistic combination of the micronutrient metal cation (e.g.
ferric), a water soluble polyphosphate and a watersoluble citric acid salt. In contrast thereto, the present invention employs iron in aqueous solutions high in nitrogen, with phosphate being neither required nor even preferred in significant amounts. Furthermore, in the present solutions, citrate alone is a sufficient complexing agent and polyphosphate is not required in a synergistic combination therewith. Nevertheless, the present invention does not exclude fertilizer solutions ilS~76~

which also contain polyphosphate provided that the added criteria of the present invention are met~
Nitrogen sources, which are a required part of the fertilizer solutions of the present invention in an amount at least 3 times the iron content, by weight, may be present in any water soluble nitrogen form.
Thus, for example, ammoniacal nitrogen, nitrate nitrogen, urea nitrogen or any combination of these may be present.
It is preferred, however, that nitrate nitrogen be present in at least about a 0.5:1 weight ratio of nitrate nitrogen (as N) to iron. Some preferred solu-tions of the present invention contain all three forms of water-soluble nitrogen as formed, for example, from mixtures of ammonium nitrate and urea. Aqueous solu-tions of ammonium nitrate and urea are commerciallyavailable and commonly used as fertilizers either alone or in combination with other major nutrients, in combination with various micronutrients or both.
The exact pH of the present solutions is not critical, but, in general, a pH of below about 8.0 is preferred to minimize precipitation of various iron hydroxides. Highly acidic pH's such as 1 to about 3, as required in U.S. Patents 3,679,377 and 3,753,675, are generally not preferred, with the preferred pH of the solution being between about 5~0 and about 7Ø
The present invention contemplates a combina-tion of ferric iron, citrate complexing agent, water-soluble nitrogen nutrient and water in the above pro-portions, optionally together with other materials that do not interfere with the above functions by precipitat-ing iron or otherwise. The preferred form of these materials is ferric ammonium citrate, a known material, prepared by any of a number of techniques including reacting an aqueous iron(III) solution such as ferric nitrate, sulfate or chloride or a solid iron salt such as ferric hydroxide or carbonate with citric acid in a molar amount about equal to the iron and then ammoniating with anhydrous ammonia or ammonium hydroxide -` ~15Z769 to the desired pH. It is preferred to start with ferric nitrate or hydroxide.
In utilizing the present solutions for foliar application, it is preferred to dissolve concentrated solution in water with or without a surfactant and apply as a spray. Application may occur at any time after leaves have developed sufficiently to intercept the spray. Repeated application may be required in cases of severe iron deficiencies or to perennial crops and turf.
EXAMPLES
In many of the following examples the follow-ing stock "Solution A" was used:
ferric ammonium citrate 22.6% by weight ammonium nitrate-urea mixture 45.0% by weight 15 water 32.4% by weight The ferric ammonium citrate used was a commer-cially available material, having a pH of about 6.5 and being generally brown in coloration. Typically, this material contained about 17.8% iron, about 7.5% nitrogen and about 60% citrate as citric acid. The ammonium nitrate-urea solution was a commercial ammonium nitrate-urea solution containing about 45.1% by weight ammoniumnitrate, 34.8~ by weight urea and 20.1% by weight water.
Analysis of the above solution indicated 16% total nitrogen including 5.1% ammoniacal nitrogen, 3.7%
nitrate nitrogen and 7.3% urea nitrogen (all by weight % as N). The product also had 4% iron by weiqht (as Fe). The solution had a specific gravity at 15.6C
(60F) of 1.280 compared to water at a like temperature.
The pH of the stock solution was 6.5. The solution was stable down to a temperature of -16.7C (2F) where crystallization occurred.
Example 1 Greenhouse application to corn, soybeans and ferns.
The above Solution A was applied to corn at a 5 to 6 leaf stage, soybeans at a stage of 2 tri-foliates and ferns at a height of 6 to 12 inc`nes (15-30 cm) at iron levels of 0, 0.11, 0.22 and 0.45 kg/ha ,, - 1152~69 (0, 0.1, 0.2 and 0.4 pounds per acre), all by weight of iron per area of greenhouse foliage. After 18 days, the leaves of the various plants were examined for apparent injury and, on a scale of 0 to 10, where 0 represents no injury, the corn and soybeans were judged uninjured, while the fern had levels of 0, 0.3, 1.5 and 3.0, respectively. Also on the 18th day, leaf samples were taken: the 8th and 9th leaves of the corn and the upper two trifolia~es of the soybeans. Iron levels in ppm were determined as indicated in Table 1 Table 1 Run Iron Application Tissue Analysis (Fe ppm) (kg/ha) corn soybeans A 0.00 101 153 B 0.11 112 145 C 0.22 130 135 D 0.45 157 138 Example 2 Field application to grain sorghum To a field of sorghum 2 ft. (0.6 m) in height, prior to heading, 40 blocks were selected and, on a random basis, subjected to one of ten treatments. The first group of blocks were untreated. The next three groups of blocks were treated with the above Solution A
at iron levels of 0.28, 0.56 and 1.12 kg/ha (0.25, 0.50 and 1.00 pounds per acre). The next three groups at blocks were treated with a lignin sulfonate chelate having 5% iron at iron levels of 0.28, 0.56 and 1.12 kg/ha (0.25, 0.50 and 1.00 pound per acre). The last three groups of blocks were treated with iron sulfate having 20% iron at iron levels of 0.28, 0.56 and 1.12 kg/ha (0.25, 0.50 and 1.00 lbs. per acre). After 10 days, leaf samples were taken as the second leaf from the top, taking 20 leaves from each Gf the 40 blocks.
The leaves were washed in 0.1 Normal hydrogen chloride solution, rinsed twice in distilled water and measured for iron (as ppm) by A&L Agricultural Laboratories, Memphis, Tennessee, a commercial tissue testing labor-lSZ76~

atory. In addition, the leaves were rated Eor color on a scale of 1 to 5 with 1 representing chlorosis and 5 representing good green color. The results are dis-played in the following Table 2.
Table 2 - Sorghum IronRate Tissue Run Source(Fe Kg/Ha)(Fe ppm) Color Rating A Control 0 73 1.0 B Solution A .28 105 2.5 C Solution A .56 98 4.3 D Solution A 1.12 84 4.8 E Chelate.28 84 2.0 F Chelate.56 89 2.3 G Chelate1.12 78 3.5 H Sulfate.28 85 1.8 I Sulfate.56 79 2.0 J Sulfate1.12 98 2.8 Example 3 - Peanuts In a similar fashion, using the same number of blocks and the same techniques for selecting blocks and the same iron analysis techniques, a comparison was run of the above stock solution against an iron-EDTA complex solution sold by Ciba-Geigy Corporation as Sequestrene~
330, which has about 10% iron by weight, and against an iron sulfate solution having about 20~ iron. Twenty-seven days after application, whole plant samples were taken, washed with 0.1 Normal hydrogen chloride solution and rinsed twice in distilled water. In addition to determining the iron level, a yield was measured 2 months after application in kg/ha (also indicated in pounds/acre) and the quality of the harvested peanuts was determined by New Mexico Department of Agriculture from grading each sample as sound mature kernels (SMK) and disclosed kernel (DK). The results are displayed in Table 3.

~lS2769 Table 3 Iron Yield*
Iron Rate (Fe Tissue(kg/ha and Quallty Sourcekg/ha) (Fe ppm)lbs/A) %SMK %DK
A Control 0 366498 (445) 6816 B Solution A 0.56 401 886 (791) 71 14 C Solution A 1.12 467 948 (846) 70 10 D Solution A 2.24 531 924 (825) 68 12 E EDTA 0.56 3111086 (970) 6914 Complex F EDTA 1.12 280972 (868) 6716 Complex 10 G EDTA 2.24 3481279 (1142) 66 20 Complex H Iron 0.56 404930 (830) 6918 Sulfate I Iron 1.12 473982 (877) 70 5 Sulfate 15 ~ Iron 2.24 483960 (857) 6918 Sulfate *All yields are significantly higher than the control at the 95% probability level.
Example 4 Application to onions and lettuce In a similar fashion, six plots of onions and six plots of lettuce were treated with one of six treat-ments with water at a solution rate of 188 L/ha (20 gal/
acre): A) control, B) Solution A 0.28 kg/ha (0.25 25 pound/acre) Fe, C) Solution A 0.56 kg/ha (0.50 pound/acre) Fe/ D) Solution A 1.12 kg/ha (1.00 pound/acre) Fe, E) Solution A 0.28 kg/ha (0.25 pound/acre) Fe + Tween 80 nonionic surfactant (Tween being a trademark of ICI Americas) 0.1~ by volume of spray solution, and F) Greenol (a trademark of Chevron Chemical for a solution containing iron sulfate with 6.13% Fe, 0.13% Cu, 0.10~ Zn and 3.65~ S) 0.56 kg/ha (0.50 pound/acre) Fe.
The onions were growing in a soil having 22 35 ppm iron and were treated at 25-30 cm (10-12 inch) height growth stage. Tissue samples (20 leaves) were taken 14 days after application at three locations within each plot.

115;2769 g The lettuce was growin~ in a soil having 24 ppm iron and was treated at a 13 cm (5 inch) diameter growth stage. Tissue samples (20 leaves) were taken 12 days after application from four replications.
The results are displayed in Tables 4 and 5.
Table 4 - Onions Fe Analysist Run Source (kg/ha) Solution (L/ha) (ppm Fe) A Control 0 0 59 B Solution A.28 188 103 C Solution A.56 188 161 D Solution A1.12 188 201 E Solution A*.28 188 191 F Sulfate .56 188 193 Solution**
tRun C, D, E, and F are significantly higher than the control at the 95% probability level.
Table 5 - Lettuce Run A Control 0 0 181 B Solution A.28 188 215 C Solution A.56 188 301 D Solution A1.12 188 313 E Solution A*.28 188 208 F Sulfate .56 188 248 Solution**
* Plus Tween-80 nonionic surfactant ** Greenol - 6.13% Fe, 0.13% Cu, 0.10% Zn, 3.64% S.
Example 5 Application to spinach Fifty-two random blocks of spinach were sub-jected to one of thirteen treatments (4 replications of each) at a volume of 188 L/ha (20 gal/acre) as follows:
A) control, B) Solution A 0.28 kg/ha (0.25 pounds/acre) Fe, C) Solution A 0.56 kg/ha (0.50 pound/acre) Fe, D) Solution A 1.12 kg/ha (1.00 pound/acre) Fe, E) Solution A 2.24 kg/ha (2.00 pounds/acre) Fe, F) Sequestrene 138 (a trademark of Ciba-Geigy for an iron-EDTA complex) 0.28 ~lS276~3 kg/ha (0.25 pounds/acre) Fe, G) Sequestrene 138 0.56 kg~ha (0.50 pounds/ acre) Fe, H) Sequestrene 138 1.12 kg/ha (1.0 pounds/acre) Fe, I) Sequestrene 138 2.24 kg ha (2.0 pounds/acre) Fe, J) ferrous sulfate 0.28 kg/ha (0.25 pound/acre) Fe, K) ferrous sulfate 0.56 kg/ha (0.50 pound/acre) Fe, L) ferrous sulfate 1.12 kg/ha (1.00 pound/acre) Fe and M) ferrous sulfate 2.24 kg/ha (2.00 pounds/acre) Fe. Treatment was at the 5-6 leaf stage. Samples of new growth were taken nine days later and analysed for iron (as ppm Fe) with the results displayed in Table 6.
Table 6 - Spinach Analysis*
Run Iron SourceFe (kg/ha) (ppm Fe) A Control 0 406 15 B Solution A .28 473 C Solution A .56 647 D Solution A 1.12 536 E Solution A 2.24 640 F Sequestrene 138 .28 410 20 G Sequestrene 138 .56 475 H Sequestrene 138 1.12 524 I Sequestrene 138 2.24 556 J Sulfate .28 485 K Sulfate .56 528 25 L Sulfate 1.12 539 M Sulfate 2.24 466 *Runs C and E are the only significantly high values above the control at the 95~ probability level.
Example 6 Application to so~beans Twenty random blocks of soybeans were sub~
jected to one of seven treatments at a volume of 188 L/ha (20 gal/acre) as follows: A) control, B) Solution A
0.17 kg/ha (0.15 pound/acre) Fe, C) Sequestrene 138 0.17 35 kg/na (0.15 pound/acre) Fe, D) Solution A 0.34 kg/ha (0.30 pound/acre) Fe, E) Sequestrine 138 0.34 kg/ha (0.30 pound/acre) Fe, F) Solution A 1.12 kg/ha (1.0 pound/acre) Fe and G) Sequestrene 138 1.21 kg/ha (1.0 pound/acre) Fe. Treatment was at the sixth trifoliate stage. Samples of new growth were taken ten days later and analyzed for iron (as ppm Fe), with the results for each block displayed in Table 7.
Table 7 - Soybeans Applied Iron Average Level Analyses (ppm Fe) Iron Run Iron Source (kg/ha) I II III Analysis*
A Control 0 125 132 128 128 10 B Solution A 0.17 202 211 220 211 C Sequestrene 0.17 191 177 186 185 D Solution A 0.34 217 216 223 218 E Sequestrene 0.34 213 131 206 183 F Solution A 1.12 346 207 286 280 15 G Sequestrene 1.12 202 165 198 188 *Run B, D, F and G are significantly higher than the control at the 95% probability level.
~xample 7 - Lemon, Orangè And Avacado Trees Fourteen fertilizer concentrates were pre-pared and diluted with water to give the following nutrient weight concentrations:
Run Ingredients %Fe %N %S
A Brown FAC + AN-U 416 0 B Brown FAC 42.4 0 25 C AC 02.4 0 F FAS + AN-U 416 4.5 G FAS 41 4.5 30 H AS 04 4.5 I FS 40 3.4 J FAC ~ U 416 0 L FS + AN-U 416 3.4 35 M Green FAC + AN-U 416 0 N AC + AN-U 016 0 ~15Z~7~9 FAC - ferric ammonium citrate AN-U - ammonium nitrate-urea mixture AC - ammonium citrate FC - ferric citrate FAS - ferric ammonium sulfate AS - ammonium sulfate FS - ferric sulfate U - urea Each was then diluted about 100:1 with water ~containing 0.1% Surfactant AL 1575 from ICI Americas) to make up a 495 L (130 gallons) solution, containing 0.23 kg (0.5 pound) of iron in the case of the concen-trates having 4~ iron. Tree branches of each of lemon trees, orange trees and avacado trees were dipped in each solution and in water and surfactant only (Run 0).
Leaf tissue (six replications) was taken from the lemon branches 60 days after treatment and from the orange branches 19 days after treatment. The average levels of iron in ppm is reported in Table 8. The avocado trees were observed to be damaged by all of treatments A-N
after 19 days. The treated branches were evaluated on a scale of 0 to 10 in three replications with the average results as reported in Table 8, with 0 representing no injury and 10 representing all leaves having dropped off.
In addition, the terminal leaf was dead in two of three cases in Run C, all three cases in Run D and one of three cases in each of Runs F, G and N.
Table 8 - Lemon and Orange Trees Injury i Analysis (ppm Iron) Level Treatment FeLemon* Orange*Avocado**
A Brown FAC + AN-U 4 218 30 1.0 B Brown FAC 4 198 28 4.0 C AC 0 166 17 10.0 D FC 4 211 34 10.0 E AN-U 0 167 19 5.3 F FAS + AN-U 4 219 73 9.3 G FAS 4 206 70 8.7 H AS 0 157 18 7.3 ., .. . .
.
.. ~ ' ' ~

~1:1S;276~

Injury Analysis (ppm Iron) Level Treatment FeLemon* Orange* Avocado**
I FS 4 226 84 4.3 J FAC + U 4 203 31 2.7 K u 0 159 16 6.7 L FS + AN-U 4 214 70 4.3 M Green FAC + AN-~ 4 184 29 1.0 N AC + AN-U 0 219 16 8.3 O Control 0 185 14 * A difference from the control of 39 ppm for lemon trees or 19 ppm for orange trees was determined signi-ficant at a 95% probability level.
** Leaf damage on scale of 0 to 10, average of three replications with a difference of 3.1 being significant at a 95% probability level.
Of the above treatments A, B, J and M con-tained iron together with a nitrogen source and citrate while D had only citrate and F, G and L had only the nitrogen source and I had neither. Iron levels were greater for oranges when sulfate was present (F, G, I and L) than when citrate was present (A, B, D, J and M). No significant differences in iron in the lemon tree leaves were observed between the various runs with different iron sources, although many of them were sig-nificantly better than the control. The leaf damage levels for avocado branches were lowest (below 5) for Runs A, B, I, J, L and M, high (5 to 8) for Runs E, H
and K and highest (above 8) for Run C, D, F, G and N.
All four runs with iron, nitroger, and citrate (A, B, J
and M) thus had among the lowest injury levels (1.0, 4.0, 2.7 and 1.0, respectively).
Example 8 - Celery The fourteen diluted solutions (A-N) of Example 7 and a control were applied to celery 36 cm (14 inches) in height at a rate of 1220 L/ha (130 gallons per acre) so that, when iron was present, it was applied at a rate of 0.56 kg/ha (0.5 pound per acre). The first ~15;~76~

rain was about 60 hours after treatment and no leaf injury was noted four days after treatment. Samples were taken (6 replications) 26 days after treatment and analyzed for iron. The crop was also harvested 26 days after treatment. The tissue analysis ln ppm iron and yields in metric tons (1000 kg) per hectare and British tons per acre are shown in Table 9.
Table 9 - Celery Yield* Fe(ppm) Metric British Analysis Tons/Hectare Tons/acre Fe(ppm) A Brown FAC + AN-U 63.0 28.1 160 B Brown FAC 63.0 28.1 149 C AC 59.4 26.5 149 D FC 60.1 26.8 135 E AN-U 62.5 27.9 138 F FAS + AN-U 56.5 25.2 141 G FAS 56.7 25.3 151 ~1 AS 55.9 25.4 146 I FS 59.0 26.3 160 J FAC + U 62.5 27.9 149 K U 59.4 26.5 130 L FS + AN-U 57.2 25.5 154 M Green FAC + AN-U 57.8 25.8 152 N AC + AN-U 59.2 26.4 148 O Control 59.4 26.5 147 *The yields and iron levels were not, general-ly, significantly better than the control.

Claims (10)

What is claimed is:

1. An aqueous fertilizer solution containing ferric iron, an iron complexing agent, water soluble nitrogen nutrient and water, characterized by the weight ratio of water-soluble nitrogen nutrient (as N) to iron being at least about 3:1 and the iron complexing agent being citrate.

2. The fertilizer solution of claim 1 wherein the water-soluble nitrogen nutrient includes nitrate at a weight ratio of nitrate (as N) to iron of at least about 0.5:1.

3. The aqueous fertilizer solution of claim 1 or 2 wherein the iron is present as ferric ammonium citrate.

4. The aqueous fertilizer solution of claim l or 2 wherein iron is between about 2 and about 8 weight percent of the aqueous fertilizer solution.

5. A process for applying an iron-containing fertilizer solution to crop plants having an iron defi-ciency, characterized by applying to the foliage of said plants a fertilizer solution comprising ferric iron, citrate as an iron complexing agent, water-solution nitrogen nutrient and water with a weight ratio of water-soluble nitrogen (as N) to iron of at least about 3:1, said solution being applied to said foliage in an amount sufficient to cure said deficiency at any time beginning with foliage development stage of growth.

6. The process of claim 5 wherein the water-soluble nitrogen nutrient includes nitrate at a weight ratio of nitrate (as N) to iron of at least about 0.5:1.

7. The process of claim 5 or 6 wherein the iron is present as ferric ammonium citrate.

8. The process of claim 5 or 6 wherein iron is between about 2 and 8 weight percent of the fertilizer solution.

9. The process of claim 5 or 6 wherein the crops are selected from the group consisting of grain sorghum, spinach, soybeans, onions, lettuce, peanuts, celery, orange, lemon and avocado.

10. The process of claim 5 or 6 wherein the iron-containing solution is applied to the leaves of crops.