Note: Descriptions are shown in the official language in which they were submitted.
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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
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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
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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
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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
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(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-
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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.
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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.
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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
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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
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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
D FC 40 0
E AN-U 016 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
K U 016 0
L FS + AN-U 416 3.4
35 M Green FAC + AN-U 416 0
N AC + AN-U 016 0
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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
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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
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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.
