Dried particulate, hydrophilic gel as micronutrient delivery system

The inclusion of certain organic hydroxy acids, most notably citric acid, in the iron sulfate formulations of at least one prior art hydrophilic polymer delivery system followed by drying and crushing the product into particles has been found to significantly improve the efficiency and ease of application of iron source fertilizer materials for iron-sensitive plants growing on iron-deficient soils for periods exceeding one year. The dried particles most preferably may be selectively metered into soil in or near the seed row as a band application at or prior to planting or spot placed in the root zone of growing plants in soil. The dry band absorbs soil moisture to provide a unique environment which restricts contact of soluble iron fertilizers with the soil and provides for complexation of iron in the formulation with organic hydroxy acids also contained in the formulation, thereby minimizing the extent of chemical reactions with the soil that reduce the availability of the applied iron to plant roots. A unique characteristic of the invention is the maintenance of iron in water soluble plant available form in soil outside the particles or band. Thus, root penetration and proliferation into and around the band also is greater than in the soil matrix, resulting in greater uptake efficiency of applied iron. The ease of precise application to soil, coupled with significantly enhanced crop response and utilization of iron contained in the product, offer considerable advantage over existing iron source fertilizer materials.

INTRODUCTION 
Chlorosis of plants, which is attributed to iron deficiency, has been 
widely reported in the open literature for well over a century, yet 
presently there is no effective, economical method including direct soil 
application to correct such iron deficiencies in plants. Chlorosis is 
characterized by a yellowing of plant leaves due to substantially 
diminished amounts of chlorophyll, the formation of which chlorophyll 
requires adequate quantities of the micronutrient iron. Theoretically, 
such conditions could be quickly corrected by application of, either 
directly to the plant or indirectly to the soil at the plant situs, iron 
sources which are in a form readily available to such plant. Until the 
present time, however, numerous problems have been found to exist with 
many iron-containing compounds which tend to prevent their general use for 
successfully treating such iron deficiencies in plants. Examples of such 
problems encountered comprise the cost of the materials, the difficulty of 
delivery to a crop, the need and expense for multiple applications, and 
the lack of plant response under various soil conditions wherein iron 
chlorosis occurs. 
The materials most commonly utilized to date for effecting treatment, 
albeit, not totally successful, of iron deficiencies have been ferrous and 
ferric sulfates and certain organic iron-containing compounds known as 
synthetic chelates or natural organic complexes. (John Mortvedt, Iron 
Sources and Management Practices for Correcting Iron Chlorosis Problems, 
Journal of Plant Nutrition 9:961-974, 1986). While the inorganic ferrous 
and ferric sulfates are relatively inexpensive, plant response to them has 
been found to be generally inadequate if they are applied directly to 
calcareous soils, wherein most such iron deficiencies occur. For instance, 
it has been long known that subsequent to soil application, iron sulfates 
quickly react to form compounds such as, for example, ferric hydroxides, 
the iron values of which are unavailable to plants. While some other 
sources of iron, generally characterized as chelates, do not react with 
soil to form unavailable compounds, they are so expensive that their use 
is restricted to application on high-value crops or for other specialized 
situations. 
Until the present time, the most economical method used to correct iron 
chlorosis has been multiple and timely foliar applications of ferrous 
sulfate (FeSO.sub.4) to the growing plants. This has been practical only 
on moderately iron-deficient soils. Economically justifiable results with 
such periodic foliar application have been poor or are frequently not 
obtained on soils which are characterized as being very low in available 
iron. In addition, the timing of foliar spray applications has been found 
to be quite critical in order to obtain satisfactory correction of the 
chlorosis condition. It has also been observed by researchers and reported 
in the literature that the leaves of sprayed plants may be damaged by some 
foliar sprays containing certain compounds or by sprays containing 
relatively high salt concentrations of other compounds. In addition, it 
has been reported that such foliar application, unless continued 
periodically over a substantial period of time may not be particularly 
effective since new growth appearing after initial spraying may again be 
chlorotic. Accordingly, it may reasonably be concluded that foliar spray 
applications are not always a satisfactory and/or economical method for 
correcting iron deficiencies in plants. 
Until the present time, the second most economical method used to correct 
iron chlorosis has been a single soil application of a band of hydrated 
hydrophilic polymer (i.e., in the form of a fluid, thixotropic gel, such 
as commonly seen in certain gel toothpastes) which contains inorganic iron 
sulfate (Mortvedt, et. al. U.S. Pat. No. 5,221,313, Jun. 22, 1993). 
However, these products are relatively expensive, not conveniently applied 
to the soil, and require specialized application equipment, such as 
positive displacement pumps, which are not part of the normal inventory of 
farming equipment. 
However, it has now been discovered that many of the shortcomings for 
treating chlorosis with the invention of Mortvedt, supra, could be 
overcome by practice of an improvement over said invention. This 
improvement is an iron delivery system characterized by its ability to 
effectively isolate, and provide chemical protection by complexing with, 
for substantial periods of time, the iron sulfates contained and delivered 
therein from the deleterious effects of various soil constituents which 
normally give rise to rendering such iron sulfates unavailable to growing 
plants. In addition, this improvement is in such form that allows for soil 
situs placement with existing, widely used, and commercially available 
equipment and is less costly per unit of iron and simultaneously more 
effective in alleviating iron chlorosis in plants than said hydrophilic 
delivery systems of Mortvedt, supra. Accordingly, the instant invention is 
presented in a principal embodiment directed to overcoming the chlorosis 
problem and an alternative improved embodiment to hydrophilic polymer 
micronutrient delivery systems directed to delivery and focus for more 
effective uptake of iron which is known to be required by growing plants. 
BACKGROUND OF THE INVENTION 
1. Field of the Invention 
The present invention relates to the development of inexpensive materials 
and means to apply them, which materials are eminently suitable for the 
correction of iron deficiency-induced chlorosis in plants. More 
particularly, the present invention relates to the development of certain 
materials selected from the group of gel-forming hydrophilic polymers, 
comprising polyacrylamides, cellulose ethers, guar gums, 
propenoate-propenamide, or mixtures thereof, said polymer disposed in 
combination with citric acid, and the resulting combinations in further 
combination with certain iron source materials including, but not limited 
to iron sulfates. Still, more particularly, the instant invention relates 
to the discovery that certain organic acids, particularly citric acid, if 
added to the aforementioned already hydrated hydrophilic gel-forming 
polymers or fluid gels of Mortvedt, supra, will significantly increase the 
efficacy of the hydrated gels in correcting iron chlorosis of plants. 
Still, even more particularly, the instant invention relates to the 
discovery that certain formulations of the hydrated gels which are 
properly combined with predetermined proportions of citric acid, and from 
which is removed sufficient moisture to result in a friable material from 
which particulates are easily recovered can, upon subsequent wetting by 
water in the soil, react to re-form, in situ, such hydrated gel. The 
resulting re-formed gel complexes and otherwise protects selected iron 
compounds to provide an economical and readily available iron source 
imminently suitable for correcting iron deficiencies in plant life growing 
at such situs. On the other hand, it has been found that the same gel 
formulations, sans said citric acid, will not perform in such a desirable 
manner. Such new and improved product is herein designated as "dried 
iron-containing gel particles;" "dried gel particles;" or more simply 
"DGP." It has also now been determined that such DGP most preferably 
should be band applied in a continuous intact band at or prior to 
planting, or spot placed in the root zone of growing plants in soil to 
minimize the contact of these products with the soil so that chemical 
reactions which adversely affect the availability of iron in these 
products to plants are minimized. When applied in such fashion, the DGP 
will hydrate and coalesce to form a continuous, intact gel entity, either 
in the form of a gel band or other such isolated gel area, in essentially 
the same final form as the gel delivery system of Mortvedt, supra, but 
with considerably enhanced ease of application. Moreover and most 
significantly, the instant invention relates to the discovery that the 
addition of citric acid to such combinations of polyacrylamide polymers 
and iron-containing materials causes the formation of a compound or 
compounds, not previously observed to occur with other hydrophilic 
polymer/iron source materials, which will diffuse out of the hydrated band 
of DGP into the surrounding soil as evidenced by a diffuse orange-colored 
zone or "halo", radiating outward from the band into the soil. This zone, 
as evidenced by the orange coloration, likely contains iron in an 
oxidized, water-soluble form. Incomplete polymerization of acrylic acid 
during polyacrylamide synthesis results in free, water-soluble monomers of 
acrylic acid within the polymer structure. It is speculated that these 
monomers react with citric acid and iron to form a cyclic, water-soluble 
iron complex which diffuses from the gel band into the soil. The bonding 
strength of the complex for iron is sufficient to prevent soil reactions 
which result in precipitation of iron as compounds which are unavailable 
to plants. The acrylic acid alone will not form a sufficiently strong 
complex with iron to prevent these reactions (log K.degree.=4.2 for 
Fe(II)acrylate). Moreover, and still more significantly, observation of 
the soil matrix in which this orange-colored zone or halo occurs, clearly 
shows an unusual propensity of root and root hair growth in the region 
where DGP was applied, in preference to the surrounding soil matrix. Such 
root proliferation typically occurs in zones of enhanced fertility in 
soils, and in such instances where DGP has been applied such enhancement 
is likely due to a greater concentration of available iron in this zone 
than in the surrounding soil. This enhanced and concentrated region of 
root growth occurred to a much lesser extent in like polymer systems which 
contained iron, but not citric acid, and did not occur at all when iron 
and citric acid were omitted from otherwise similar formulations. 
Furthermore, it has now been discovered that oftentimes the DGP will absorb 
up to 100 times its own weight in water from contact with moist soil. This 
process results in swelling of the DGP such that veins or islands of 
micronutrient-enriched hydrogel are established along with concomitant 
displacement of the soil around the DGP which results in a zone more 
easily penetrated and expanded into by plant roots than is a normal soil 
matrix and which by virtue of copious amounts of water of hydration 
available to roots growing therein, as well as the abundant supply of 
micronutrients, provides a region where root growth is substantially 
enhanced. 
In addition, it has now been demonstrated in field testing that such DGP is 
in a form which may be easily, selectively, and precisely dispensed into 
soil as a sub-surface band of dry particles by means of a device known in 
the trade as a pesticide applicator box. This device is designed to 
contain only small amounts of pesticides, as compared to equipment used 
for application of major plant nutrients, or "macronutrients", such as 
nitrogen (N), phosphorus (P), and potassium (K), since such pesticides are 
normally applied to soil in small amounts (on the order of 1 to 5 pounds 
per acre, much as with applications of iron) and thus precise metering of 
the material is required. This precise metering consideration is most 
important because iron chlorosis resulting from iron deficiencies in soil 
has been found to occur in separate or isolated areas within any of a 
number of given fields, which areas range from less than one, up to 
several acres in dimension, which are oftentimes isolated one from another 
and which produce little, if any, gainful yield. Unfortunately, currently 
practiced commercial practices for planting such high pH, calcareous and 
iron-deficient fields, wherein macronutrients, which are required in large 
amounts by plants are routinely applied to such areas in a blanket 
application, do not provide a means which is practical to selectively 
dispense these micronutrients only in such isolated areas. However, in the 
practice of the instant invention, if the locations of these 
iron-deficient areas are known by previous experience, or are otherwise 
effectively mapped, the DGP can be selectively applied during application 
of the macronutrients by using a variable rate pesticide applicator box 
equipped with a banding attachment for subsurface banding of DGP only upon 
reaching such susceptible areas and not across the whole area of the 
field. Thus, gainful yields may be realized from areas where before little 
or none were possible and the added expense of the DGP is therefore more 
than offset by the increased economic return of such yields. 
2. Description of the Prior Art 
Iron is an essential element in plant nutrition and generally is classified 
as a micronutrient. It is known to be involved in the synthesis of 
chlorophyll which in turn is required for photosynthesis in plants. A 
deficiency of this micronutrient in growing plants, which can be greatly 
exaggerated in calcareous type soils, is oftentimes the cause of 
chlorosis, which is characterized by a yellowing of plant leaves and stems 
and which results in particularly poor growth. 
Currently available practices for alleviating such iron deficiencies in 
growing plants include the application of synthetic iron chelates to soil 
or the use of various soluble iron compounds as foliar sprays for direct 
application to the plants or the use of certain hydrophilic polymer 
delivery systems. Currently, the least expensive, in terms of up-front per 
unit cost, water-soluble iron compound in use is iron sulfate, either in 
its reduced state, e.g., (FeSO.sub.4) or in the ferric state, e.g. 
[Fe.sub.2 (SO.sub.4).sub.3 ]. However, neither form supra, of iron sulfate 
should be applied directly to soil lest either source quickly becomes 
combined with certain components in the soil to form water-insoluble 
compounds thereby rendering such iron unavailable to growing plants. 
The synthetic chelate, FeEDDHA [ferric chelate of ethylenediamine 
(di-(o-hydroxyphenyl acetate))], has long been considered by many skilled 
in the art to be the most effective iron fertilizer for soil application, 
especially in calcareous soils (Arthur Wallace, A Decade of Synthetic 
Chelating Agents in Inorganic Plant Nutrition, Edwards Brothers, Inc., Ann 
Arbor, Mich., 1962). However, the per unit cost of iron in FeEDDHA is 
quite high, which makes this iron chelate material much too expensive for 
application to relatively low-value field crops. Another currently 
available and somewhat less expensive iron chelate material, FeEDTA 
(monosodium ferric ethylenediamine tetraacetate), has proven to be 
effective for crops growing in near neutral soils but not in calcareous, 
high-pH soils wherein most iron deficiencies occur. Another recent 
discovery also somewhat less costly than chelates, are hydrophilic polymer 
delivery systems (Mortvedt, supra). However, application of the materials 
of Mortvedt, is difficult and requires specialized equipment and the 
polymer in the formulations is also relatively expensive. Nevertheless, 
the initial per unit cost of iron is significantly lower than in the 
chelates. Accordingly, it should be readily apparent that iron sulfate 
would be the most economical and eminently suitable iron source material 
for use on field crops if it only remained available to growing plants 
subsequent to its contact or juxtapositioning with the soil situs. 
Therefore, additives or conditions which can significantly improve the 
effectiveness of iron sulfate intended for the treatment of chlorosis 
could, in turn, result in an economically effective iron source for soil 
application. 
Currently, it is the practice in the trade for iron source material to be 
applied to soil separately or to be incorporated with other materials in 
the processing or blending of fertilizers or to be applied in a 
hydrophilic gel polymer matrix. The effectiveness of iron source materials 
in maintaining a supply of iron to growing plants depends upon the 
chemical nature of such iron source materials and/or the soil, as well as 
rate and/or frequency of their application. Economic considerations 
regarding the use of iron source materials are determined by costs and 
rate of their application as well as the ease of application relative to 
the returns attributable to increased yields of the crops to which they 
are applied. Presently, the most effective iron chelate, FeEDDHA, is so 
costly that its use is restricted to high-cash value crops such as, for 
example, apples, grapes, and peaches, or high-cash value ornamental crops 
such as, for example, rhododendrons, azaleas, and dwarf citrus, while 
other methods, i.e., fluid hydrophilic polymer delivery systems, are 
nonetheless still expensive in addition to being difficult to apply and 
are not as effective as FeEDDHA. The least costly, on a front-end per unit 
cost basis, iron source materials are ineffective when used in procedures 
designed to correct iron chlorosis in many lower value field crops, such 
as, for example, corn, grain sorghum and soybean, which nonetheless are 
planted in large acreage and constitute the major portion of modern 
production agriculture. 
From the aforesaid, it should now be abundantly clear that the prior art 
materials designed as, or intended to be, iron sources are too costly up 
front to be economical for use on most field crops or are difficult to 
apply and require specialized application equipment, or although available 
at relatively low unit cost, are still highly uneconomical to use since 
they are ineffective in maintaining a supply of available iron to crops 
growing on iron-deficient soils. 
SUMMARY OF THE INVENTION 
It has now been discovered that significant improvements have been made to 
the invention of Mortvedt, supra. These improvements include 1) the 
addition of citric acid (or other similar organic acids within the same 
chemical family, known as "hydroxy acids", such as lactic acid, malic 
acid, or tartaric acid, etc.) to the hydrophilic polymer delivery systems 
of Mortvedt, supra, to significantly and greatly increase the efficacy of 
said delivery system in alleviating iron deficiency-induced chlorosis in 
plants grown on calcareous, high pH soil; 2) formulating the polymer 
delivery materials of Mortvedt, supra, to include citric acid or other 
organic acid of the same chemical family, thereafter drying and crushing 
the resulting material to a relatively uniform particle size to 
significantly and greatly facilitate ease of packaging, handling and 
application to soil, whether in band or spot application, with significant 
increase in efficiency in alleviating iron chlorosis in plants; 
accordingly, the application of this material in relatively narrow 
continuous bands, on the order of about 1/4 to 3/4 inches in diameter, 
along or parallel to the seed row or spot placed in the root zone of 
living plants is normally the easiest and most convenient manner of 
distribution; and 3) cellulose ethers, plant-derived guar gums, and 
propenoate-propenamides, which are all different chemical classes of 
hydrophilic polymers, and which were previously shown by Mortvedt, supra, 
to be mediocre for use in hydrophilic polymer delivery systems, may now be 
used with as good and essentially equal effectiveness as the more costly 
polyacrylamide or polyacrylamide-polyacrylate polymers as carriers of iron 
in DGP formulations. 
It would appear that the principal mechanisms which are responsible for 
preserving, for a substantial period of time, these iron source materials 
in formulations of DGP in a form which ultimately is readily available to 
growing plants is one of isolation by chemical means of complexing with 
citric acid, and by physical means afforded by the hydrated gel matrix, of 
such iron source materials from the deleterious effects of or combinations 
with soil components, including aqueous media, at or near the application 
situs. In addition, it has now been discovered that the most preferred 
methods of application of such citric acid-containing DGP, namely, 
subsurface band application to soil at or prior to planting or spot 
application in the root zone of growing plants in soil, will result in the 
formation of a hydrated continuous gel band when exposed to moisture in 
the soil, thus isolating such materials from reacting with the soil to 
form compounds which are unavailable to plants. Furthermore, observation 
of citric acid-containing DGP in situ in soil revealed the formation of a 
diffusion zone of iron from the gel band into the surrounding soil, such 
iron being in forms protected from soil reactions, which thus 
substantially increased plant utilization of the iron contained in the 
formulations over the same products which do not contain citric acid. 
Results of greenhouse investigations indicated that these dried 
formulations of iron sources, citric acid, and hydrophilic polymer 
combinations are effective for use on a variety of iron-sensitive crops 
growing in iron-deficient soils. It has also been discovered that they may 
be band applied near the seed row at planting. In addition, it is proposed 
that they may be used as specialty fertilizers to other crops, providing 
they are spot placed in the root zone or what will be the root zone in the 
soil rather than on or juxtaposed the soil surface. These combinations may 
be especially beneficial for certain slower growing perennial crops such 
as fruit trees, grape vines, and shrubs because biodegradation of the 
mixture buried within soil occurs slowly over a long period of time. Iron 
in the formulations is thus protected from reactions with soil and 
maintained in a form available to these plants during periods of active 
growth and of active iron uptake as well as during slower growth periods 
when demand for iron is low. These combinations may also be especially 
beneficial to lower-cash value row crops such as grain sorghum, corn, and 
soybeans since the product is less costly to produce and use than 
alternative methods of iron fertilization and also provides for sustained 
iron availability for such field crops during an entire growing season, or 
longer. One DGP produced according to the practice of the instant 
invention recently has been field tested for corn growing on high pH, 
calcareous soil in Nebraska, where iron deficiencies typically occur. 
Photographic documentation of plant vigor and growth substantiated the 
effectiveness of the DGP as a superior iron source for the plants during 
early growth stages, throughout the season until crop maturity, and for a 
subsequent corn crop planted one year later. Further elaboration of this 
test is given within the Examples, infra. 
Investigations into the utilization of iron in the DGP revealed that band 
application established veins of the DGP in the immediate vicinity 
anticipated for plant root development. These bands of dry material 
subsequently were hydrated by moisture in the soil to form continuous, 
intact gel bands, in exactly the same physical form as the fluid gels of 
Mortvedt, supra. After sufficient time had elapsed for such development, 
cross sectioning of such veins and observing the soil matrix surrounding 
same clearly showed an unusual propensity of root and root hair growth in 
the product region in preference to the surrounding soil matrix. In 
addition, the development of an orange-colored zone or "halo" in the soil 
around the product was suggestive of iron transport in soluble form away 
from the gel band, thereby increasing the volume of iron-enriched soil 
available for root exploration with resultant significantly increased 
efficiency of iron uptake by the plant. This clearly established that the 
instant new and novel delivery system focuses plant root development in a 
fashion whereby contact with and uptake of iron in such veined regions is 
not only substantially enhanced but is, indeed, totally optimized. 
Another aspect of the instant invention relates to a method of enhancing 
the yield and/or growth of plants by distributing the composition of this 
invention in the "plant growth media" in which the plants are being grown 
within reach of the root system of the plants (hereinafter referred to as 
"root zone"). As used herein, the term "plant growth media" refers to 
various natural and artificial media which support plant growth, including 
but not limited to soil, potting mixtures of organic and inorganic matter, 
and artificial media such as vermiculite or polyurethane foam. 
Yet another aspect of the present invention relates to a method for 
inhibiting the degradation of certain water-soluble iron source 
micronutrient materials, principally iron sulfates, including ferric 
sulfate or ferrous sulfate or both, when said iron source micronutrients 
are applied to such plant growth media, which aspect comprises providing 
an effective isolation said water-soluble iron source micronutrients from 
said plant growth media such that same do not react with components 
therein in a fashion whereby the iron sulfates form water-insoluble or 
substantially water-insoluble compounds, which water-insoluble compounds 
are or become unavailable to plant growth sought to be treated with such 
iron source micronutrients. A principal embodiment of this invention, 
which provides such effective isolation is the homogeneous mixing and 
resultant chemical interaction between the polymer, citric acid and iron 
sources in the DGP from which arises complexation and protection of iron 
sulfates from soil reactions by citric acid, and physical isolation and 
containment of iron by the gel matrix from soil reactions which would 
otherwise render iron unavailable to plants. Practice of the instant 
invention ensures that iron sulfates so processed remain substantially 
water-soluble in the resulting formed mixture. 
As used herein, the term "effective isolation" refers to the protective 
mechanism of isolation and containment by a gel matrix and complexation of 
the iron sulfates, supra, in an intimate mixture formed with citric acid 
or other such organic acid and iron sulfate that encompasses an isolation 
or separation so effective that all or most of the so-treated iron 
sulfates remain substantially water-soluble for at least a period of about 
2 weeks and preferably a period ranging from at least about 4 to about 6 
weeks, more preferably at least about 120 days, and most preferably for a 
period of time ranging upwards to 1 year, or more. 
As used herein, the terms "dried iron-gel particles," "dried gel 
particles," or more simply, "DGP" refer to the product resulting from 
mixing of predetermined amounts of iron source, effective amounts of 
citric acid or other similar organic acid and a hydrophilic polymer into a 
fluid gel which is then dried and crushed into appropriately sized 
particles for ease of application. The effective amount of citric acid for 
use in the DGP formulations was calculated mathematically by use of a 
procedure known in the trade as "mole fraction calculations," which 
calculations determine the concentration of a ligand (citric acid) that 
will complex with a given concentration of metal (iron), or vice-versa, up 
to a maximum amount where equilibria between the two is reached and no 
further complexation will occur. As an example, given a 5 percent solution 
of iron sulfate, containing 1 percent iron, the effective concentration of 
citric acid was mathematically determined to be 10 percent. 
As used herein, the term "substantially water-soluble" encompasses 
materials which are initially water-soluble such as ferric sulfate or 
materials which have only degraded, by reaction with components in growth 
media to the point that the resulting reaction products in combination 
with the unreacted materials, in the aggregate, provide a material which 
is at least about 60 percent water-soluble. 
As used herein, the term "root zone" refers to that area in the plant 
growth media within the reach of the root system of a particular desired 
plant or crop and in the field normally comprises that portion of the soil 
matrix generally beneath the seed planting band and areas juxtaposed 
thereto, generally parallel with the band and protruding downwardly from a 
few inches to perhaps about a foot. In the practice of the invention there 
will oftentimes be provided veins or islands of iron-enriched DGP through 
such root zone in a fashion such that any plant roots entering therein 
will be provided with an environment enhanced both mechanically and 
nutritionally by virtue of the uniformity of consistency of said mixture 
which is considerably more easily penetrated and expanded into than is a 
normal soil matrix and which by virtue of the ease of wetting of the 
mixture for the roots growing therein, as well as the abundant supply of 
desirable iron within the mixture and in an iron rich diffusion zone 
immediately outside the mixture and extending perhaps 4 up to 7 
centimeters into the soil away from the mixture band, provides a 
micro-environment wherein root growth is substantially enhanced. 
As used herein, the term "enhanced root growth region" refers to such plant 
growth media discontinuities comprising iron-enriched DGP mixtures and the 
associated diffusion zone of the type herein contemplated and referenced. 
As used herein and applied to the resulting dried hydrogel, the term 
"friable" refers to a physical characteristic whereby the normally 
resilient or tacky hydrogel has sufficient water removed therefrom to 
convert it into a relatively hard, brittle friable material, whereby 
ordinary crushing means and methods including roller crushers or the like 
are easily comminuted. 
Still yet another aspect of the instant invention relates to the ease of 
application to soil. The physical properties (dry, granular, and 
free-flowing) of the DGP product render it eminently more suitable for 
state of the art variable rate technology in modern agricultural 
applicator equipment, which enables soil application rates to be made 
selectively, precisely, and accurately, and thus, economically, to 
predetermined areas, and only to those areas, if so desired, within a 
field. Thus, crop yields may be obtained in areas, such as, for example, 
high pH, calcareous regions within a field which previously had no history 
of gainful yields. 
OBJECTS OF THE INVENTION 
It is therefore a principal object of the present invention to provide a 
new and improved combination of materials which are eminently suitable for 
supplying iron to soil systems and/or to the situs of growing plants for 
substantial periods of time of at least about 28 days, preferably of at 
least about 60 days, and most preferably of at least about 120 days or 
longer, and in a form such that they can readily be absorbed by the roots 
of such growing plants. 
Another principal object of the present invention is to provide a new and 
improved method, as well as a new combination of materials eminently 
suitable for supplying iron to soil systems and/or to the situs of growing 
plants for substantial periods of time and in a form such that, although 
such materials most preferably may be band applied near the seed row in 
soil or spot placed directly in the root zone of growing plants, they will 
be readily available for absorption by the roots of such growing plants. 
Still another principal object of the present invention is to provide a new 
and improved method, as well as an improved combination of materials 
eminently suitable for soil applications and for supplying iron to soil 
systems and/or to the situs of growing plants in a form such that will be 
absorbed by the roots of such growing plants and wherein such materials 
comprise either separate components or admixtures of components including 
hydrophilic polymers of various chemical classes, certain organic acids, 
particularly citric acid, and iron source materials, said iron source 
materials including ferrous and ferric sulfate. 
A further principal object of the present invention is to provide a new and 
improved method, as well as a new combination of materials eminently 
suitable for supplying iron to soil systems and/or to the situs of growing 
plants to act as a most efficient delivery system for such iron, and for 
uptake by growing plants in a manner wherein upon contact and penetration 
of said DGP, the plant roots evidence an unusual propensity for further 
growth thereinto, and into a defined diffusion zone of a plant nutrient, 
whereby the uptake of iron values are more effectively utilized than if 
iron were homogeneously mixed in the surrounding soil matrix. 
Still a further principal object of the present invention in a principal 
embodiment thereof is to provide new procedures to effect the mixing of 
certain gel-forming polymers with aqueous citric acid-containing and 
aqueous iron-containing solutions to result in the formation of gels which 
can be dried and subsequently be broken into particles which can be more 
easily applied to soil situses than fluid gels to provide thereat 
sufficient available iron as may be required by growing plants. 
Still further and more general objects and advantages of the present 
invention will appear from the more detailed description set forth in the 
following disclosure and examples, it being understood, however, that this 
more detailed description is given by way of illustration and explanation 
only and not necessarily by way of limitation, since various changes 
therein may be made by those skilled in the art without departing from the 
true spirit and scope of the gist underlying the present invention. 
DESCRIPTION OF THE PREFERRED EMBODIMENTS 
The present invention is directed to methods of mixing, as well as the 
specific compositions utilized therein for applying to a designated soil 
situs, various combinations of hydrophilic polymer, citric acid, and 
selected water-soluble compounds of iron including, in the most preferred 
embodiments, ferrous sulfate, or ferric sulfate. Practice of the instant 
invention results in the formation of new compounds for improved 
fertilizers having incorporated therein water-soluble compounds of iron in 
forms wherein same are sufficiently isolated, both chemically and 
physically, at least temporarily, from contact with soil media but are 
juxtaposed such media such that the iron values therein remain available 
to maintain the prerequisite supply of iron in a form readily useful to 
plants growing at or near such situs. 
The combinations of hydrophilic polymer, citric acid, and iron sulfate were 
analyzed with a Nicolet 60SX Fourier transformed infrared spectroscopy 
(FTIR) system before hydration with deionized water, and after hydration 
and drying, to confirm the formation of new compounds. Each sample 
material was pelletized with KBr for analysis; the spectrum from a KBr 
pellet, used as a background blank, was subtracted from each initial 
sample spectrum. 
Referring now generally to Table I-a through Table V-b, there are shown by 
peak number (for convenience) the infrared spectral peak positions, 
intensities, and relative intensities for various individual composite 
mixtures of a hydrophilic polymer, citric acid, and iron sulfate. A table 
designated with the letter "a" shows the infrared absorption data for a 
given mixture before hydration and drying; the counterpart table 
designated with the letter "b" shows the data for the mixture after 
hydration and drying, i.e., the dried gel, or DGP. The peaks that were 
present in the spectra, and which are designated by peak number and peak 
position in Table I-a through Table V-b, represent the frequencies of 
vibrational bending and stretching that occurred within the molecules of 
the compounds due to the absorbance of light energy. Shifts in such 
vibrational frequencies in the region where light was absorbed (due to 
peak splitting, additions or deletions, or a change in the relative 
intensity of an existing peak) were indicative of changes in chemical 
bonding within the mixtures after hydration and drying. Such changes in 
bonding consistently occurred, regardless of the polymer type, and thus 
resulted in the formation of new compounds which were notably, if not 
entirely, different from those present in the original, unhydrated 
mixtures. For example, an unhydrated mixture containing a polyacrylamide 
polymer, iron sulfate, and citric acid was spectrally similar to an 
analogous mixture containing a polyacrylate due to the close similarities 
in the chain backbone structure. Although each mixture shared many of the 
same spectral traits after hydration and drying, each also exhibited such 
changes as to be not only different from each other, but also different in 
form from the original mixture. 
Referring now specifically to Table I-a and Table I-b, therein are shown 
the infrared data for a mixture of a polyacrylamide polymer, citric acid, 
and iron sulfate, said mixture either unhydrated or previously hydrated 
and then dried. Significant differences are noted between the absorption 
spectra for the unhydrated mixture (Table I-a) and for the hydrated and 
dried mixture (Table I-b). Twenty absorption peaks were identified in the 
unhydrated mixture versus 29 peaks in the dried gel. There were 10 
absorption peaks common to both spectra (peak matches). Splitting and/or 
addition of peaks occurred with the dried gel in the regions 2600-4000, 
1500-2000, and 650-1500 cm.sup.-1. Changes in the relative intensity and 
magnitude of peaks common to both spectra were also apparent. The major 
changes in the region 2600-4000 cm.sup.-1 were the splitting of peak 
number 1 (Table 1-a) into two peaks occurring at wavenumbers 3481 and 3400 
(peak numbers 1 and 2, Table 1-b) and the addition of peak numbers 3 and 5 
(Table 1-b). Peak number 6 (Table 1-b) did not occur in the unhydrated 
mixture. Three additional peaks occurred in the region 1500-2000 cm.sup.-1 
with the hydrated and dried gel mixture (peak numbers 9, 10, and 11, Table 
1-b). Eight additional peaks occurred in the region 650-1500 cm.sup.-1 
with the hydrated mixture (peak numbers 12, 14, 15, 16, 18, 19, 21, and 
25, Table 1-b). There was no discernible pattern to changes in magnitude 
and relative intensity of the seven peaks in this region common to both 
the unhydrated mixture and the hydrated and dried mixture. 
TABLE I-a 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Polyacrylamide Polymer, 
and Citric Acid) Before Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
1 3429 S-B 8 
2 3275 Sh 7 
3 3018 Sh 6 
*4 2625 W-B 3 
5 2565 Sh 3 
6 1981 VW-B 1 
*7 1726 S-Sp 9 
8 1628 M-Sp 4 
*9 1398 M-Sp 4 
10 1338 W-B 3 
*11 1221 MS-Sp 6 
12 1134 Sh 5 
*13 1115 M-Sp 5 
14 1088 Sh 4 
*15 987 VW-Sp 2 
*16 937 VW-Sp 2 
*17 897 VW-Sp 2 
*18 791 W-Sp 2 
*19 606 M-Sp 4 
20 507 Sh 4 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
TABLE I-b 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Polyacrylamide Polymer, 
and Citric Acid) After Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
1 3481 MS-Sp 4 
2 3400 MS-Sp 4 
3 3215 MS-B 4 
4 2937 Sh 3 
5 2700 Sh 2 
*6 2621 W-B 2 
7 2540 W-B 2 
*8 1730 S-Sp 5 
9 1659 Ms-Sp 4 
10 1610 S-Sp 4 
11 1566 Sh 4 
12 1419 Ms-Sp 4 
*13 1396 S-Sp 4 
14 1377 Sh 4 
15 1325 MS-Sp 3 
16 1286 Ms-Sp 3 
*17 1225 Ms-Sp 4 
18 1194 MS-Sp 4 
19 1142 S-Sp 4 
*20 1109 S-Sp 4 
21 1074 MS-Sp 4 
*22 978 Sh 3 
*23 937 W-Sp 2 
*24 891 M-Sp 3 
25 850 M-Sp 3 
*26 795 M-Sp 3 
*27 613 Ms-Sp 4 
28 580 Ms-Sp 4 
29 540 Sh 4 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
Referring now specifically to Table II-a and Table II-b, therein are shown 
the infrared data for a mixture of a guar gum polymer, citric acid, and 
iron sulfate, either unhydrated or previously hydrated and dried. 
Significant differences are noted between the absorption spectra for the 
unhydrated mixture (Table II-a) and for the hydrated and dried mixture 
(Table II-b). Thirty-six absorption peaks were identified in the 
unhydrated mixture versus 20 peaks in the dried gel. There were eight 
absorption peaks common to both spectra (peak matches). The major changes 
noted in the spectrum for the dried gel were the loss of four peaks in the 
region 2600-4000 cm.sup.-1, the loss of one peak in the region 1500-2000 
cm.sup.-1, and the loss of twelve peaks in the region 500-1500 cm.sup.-1. 
There were also minor changes in the intensity and magnitude of peaks 
common to both spectra. 
TABLE II-a 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Guar Gum Polymer, and 
Citric Acid) Before Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
1 3495 S-Sp 8 
2 3454 S-Sp 7 
3 3383 S-Sp 6 
4 3292 S-Sp 3 
*5 2943 Sh 3 
6 2640 W-B 1 
7 2563 VW-B 9 
*8 1998 VW-B 4 
9 1743 S-Sp 4 
10 1714 S-Sp 3 
*11 1626 W-Sp 6 
12 1416 W-Sp 5 
13 1392 M-Sp 5 
14 1360 W-Sp 4 
15 1340 W-Sp 2 
16 1321 W-Sp 2 
17 1308 W-Sp 2 
18 1292 W-Sp 2 
19 1240 M-Sp 4 
20 1217 MS-Sp 5 
21 1198 Ms-Sp 4 
22 1176 Ms-Sp 5 
23 1144 Ms-Sp 5 
24 1113 Ms-Sp 5 
*25 1082 Ms-Sp 4 
26 989 Sh 2 
*27 941 VW-Sp 2 
*28 904 VW-Sp 1 
*29 881 VW-Sp 1 
30 818 VW-Sp 2 
31 783 W-Sp 2 
32 685 Sh 2 
33 638 Sh 3 
*34 600 M-Sp 3 
35 546 W-Sp 3 
36 498 W-Sp 3 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
TABLE II-b 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Guar Gum Polymer, and 
Citric Acid) After Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
1 3388 S-B 8 
*2 2941 Sh 5 
3 2629 W-B 2 
*4 1992 VW-B 1 
5 1732 S-Sp 8 
*6 1633 W-Sp 2 
7 1400 M-Sp 4 
8 1194 S-Sp 7 
9 1138 Ms-Sp 6 
*10 1082 MS-Sp 6 
11 1018 Sh 4 
12 976 Sh 2 
*13 941 Sh 2 
*14 897 VW-Sp 2 
*15 874 VW-Sp 2 
16 812 W-Sp 3 
17 665 W-Sp 2 
18 623 W-Sp 3 
*18 602 W-Sp 3 
19 525 W-Sp 3 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
Referring now to Table III-a and Table III-b, therein are shown the 
infrared data for a mixture of a polyacrylate polymer, citric acid, and 
iron sulfate, either unhydrated or previously hydrated and dried. 
Significant differences are noted between the absorption spectra for the 
unhydrated mixture (Table III-a) and for the hydrated and dried mixture 
(Table III-b). Eighteen absorption peaks were identified in the unhydrated 
mixture versus 35 peaks in the dried gel. There were 12 absorption peaks 
common to both spectra (peak matches). Splitting and/or addition of peaks 
occurred with the dried gel in the regions 2600-4000, 1500-2000, and 
1000-1500 cm.sup.-1. The majority of splitting and/or additions occurred 
in the region 1000-1500 cm.sup.-1. The only clear increases in relative 
intensity of peaks common to both spectra occurred at peak numbers 9, 21, 
and 22 (Table III-b) with the hydrated and dried gel mixture. 
TABLE III-a 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Polyacrylate Polymer, 
and Citric Acid) Before Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
1 3429 S-B 8 
2 3250 Sh 7 
3 2953 Sh 5 
*4 2600 W-B 3 
*5 1986 VW-B 1 
*6 1728 S-Sp 8 
*7 1630 M-Sp 4 
8 1514 Sh 1 
*9 1400 W-Sp 4 
10 1350 Sh 3 
*11 1221 M-Sp 5 
*12 1144 M-Sp 4 
*13 1105 M-Sp 4 
*14 982 VW-Sp 2 
*15 937 VW-Sp 2 
*16 893 VW-Sp 2 
*17 793 VW-Sp 2 
18 609 W-Sp 4 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
TABLE III-b 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Polyacrylate Polymer, 
and Citric Acid) After Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
1 3479 MS-Sp 7 
2 3398 S-Sp 8 
3 3242 Sh 6 
4 2976 Sh 5 
*5 2619 W-Bp 3 
6 2542 Sh 3 
*7 1981 Vw-B 1 
*8 1728 S-Sp 9 
*9 1610 M-Sp 6 
10 1564 W-Sp 4 
11 1554 W-Sp 4 
12 1502 Sh 2 
13 1479 Sh 2 
14 1419 M-Sp 5 
*15 1396 M-Sp 5 
16 1375 Sh 4 
17 1325 W-Sp 4 
18 1286 M-Sp 4 
*19 1230 M-Sp 5 
20 1194 M-Sp 5 
*21 1144 M-Sp 6 
*22 1103 M-Sp 6 
23 1072 M-Sp 4 
*24 982 VW-Sp 2 
*25 939 VW-Sp 2 
*26 893 VW-Sp 2 
*27 876 Sh 2 
28 850 VW-Sp 2 
29 795 W-Sp 3 
30 700 Sh 3 
31 669 Sh 3 
32 617 W-Sp 4 
33 580 W-Sp 4 
34 563 Sh 4 
35 540 W-Sp 4 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
Referring now to Table IV-a and Table IV-b, therein are shown the infrared 
data for a mixture of a cellulose ether polymer, citric acid, and iron 
sulfate, either unhydrated or previously hydrated and dried. Slight, but 
significant differences are noted between the absorption spectra for the 
unhydrated mixture (Table IV-a) and for the hydrated and dried mixture 
(Table IV-b). Seventeen absorption peaks were identified in the unhydrated 
mixture and in the dried gel. There were 14 absorption peaks common to 
both spectra (peak matches). A clear increase in the relative 
intensity/resolution of peaks 7, 8, 10, 11, and 12, and a significant 
shift in wavenumber location of peaks 10 and 11 were the major 
distinguishing differences noted in the spectrum of the dried gel 
material. 
TABLE IV-a 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Cellulose Ether, Polymer, 
and Citric Acid) Before Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
*1 3417 S-B 6 
*2 2941 Sh 4 
*3 2627 W-B 2 
*4 2023 VW-B 1 
*5 1728 S-Sp 5 
*6 1632 W-Sp 2 
*7 1385 M-Sp 3 
*8 1358 Sh 2 
9 1327 Sh 2 
10 1225 M-Sp 3 
11 1113 M-Sp 3 
12 1061 M-Sp 3 
*13 937 VW-Sp 1 
*14 887 VW-Sp 1 
*15 791 VW-Sp 1 
*16 598 W-Sp 2 
17 503 Sh 2 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
TABLE IV-b 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Cellulose Ether, Polymer, 
and Citric Acid) After Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
*1 3423 S-B 7 
*2 2941 M-B 4 
*3 2621 VW-B 2 
*4 2010 VW-B 1 
*5 1728 S-Sp 7 
*6 1632 W-Sp 3 
*7 1390 W-Sp 3 
*8 1350 W-Sp 3 
9 1298 W-Sp 3 
10 1205 MS-Sp 6 
11 1126 MS-Sp 5 
12 1078 MS-Sp 5 
*13 945 Sh 2 
*14 883 VW-B 1 
*15 796 W-B 2 
*16 602 M-Sp 3 
17 523 Sh 3 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
Referring now to Table V-a and Table V-b, therein are shown the infrared 
data for a mixture of a propenoate-propenamide polymer, citric acid, and 
iron sulfate, either unhydrated or previously hydrated and dried. Slight, 
but significant differences are noted between the absorption spectra for 
the unhydrated mixture (Table V-a) and for the hydrated and dried mixture 
(Table V-b). Fifteen absorption peaks were identified in the unhydrated 
mixture versus 19 peaks in the dried gel. There were 12 absorption peaks 
common to both spectra (peak matches). An obvious increase in the relative 
intensity/resolution of peak numbers 8 and 19 of the dried gel 
(corresponding to peak numbers 7 and 16, respectively, of the unhydrated 
material) and the splitting of peak number 11 in Table V-a into two 
sharply resolved peaks (numbers 12 and 13) in Table V-b were the major 
differences noted in the spectrum of the dried gel material. 
TABLE V-a 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Propenoate-Propenamide 
Polymer, and Citric Acid) Before Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
*1 3450 S-B 7 
2 2935 Sh 4 
*3 2619 Sh 3 
*4 2087 Sh 2 
*5 1726 M-Sp 4 
6 1637 M-B 3 
*7 1400 VW-Sp 2 
*8 1385 VW-Sp 2 
*9 1344 Sh 2 
*10 1227 W-Sp 2 
1122 W-Sp 2 
*11 982 VW-Sp 1 
*12 937 Vw-Sp 1 
*13 887 Sh 1 
*14 791 Sh 1 
*15 619 W-Sp 2 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
TABLE V-b 
______________________________________ 
Infrared Absorption Bands Frequency (cm.sup.-1) for a Composite 
Mixture of DGP (Iron Sulfate, a Propenoate-Propenamide 
Polymer, and Citric Acid) After Hydration and Drying 
Peak Peak Peak Relative 
No. Position Intensity 
Intensity 
______________________________________ 
*1 3454 S-B 6 
2 3225 Sh 5 
*3 2949 Sh 3 
*4 2640 Sh 2 
*5 2077 Sh 1 
*6 1722 Ms-Sp 4 
7 1660 M-Sp 3 
*8 1398 W-Sp 2 
*9 1387 Sh 2 
*10 1331 Sh 1 
*11 1227 W-Sp 2 
12 1130 W-Sp 2 
13 1115 W-Sp 2 
*14 982 VW-Sp 0 
*15 937 VW-Sp 0 
*16 897 Sh 0 
17 850 Sh 0 
*18 793 Sh 1 
*19 619 W-Sp 2 
______________________________________ 
Sh = shoulder; B = broad; Sp = sharp; S = strong; MS = medium strong; M = 
medium; W = weak; VW = very weak. Relative intensities are on a scale of 
to 10. 
*Peaks that occurred in mixtures both before and after hydration are 
indicated with an asterisk. 
From the discussion of the infrared absorption data, supra, it should now 
be abundantly clear that changes occurred in the polymer-citric acid-iron 
sulfate mixtures after hydration and drying which resulted in the 
formation of compounds not present in the original mixture, and that these 
compounds represent new compositions of matter.

EXAMPLES 
In order that those skilled in the art may better understand how the 
present invention can be practiced, the following examples are given by 
way of illustration only and not necessarily by way of limitation, since 
numerous variations thereof will occur and will undoubtedly be made by 
those skilled in the art without substantially departing from the true and 
intended scope and spirit of the instant invention herein taught and 
disclosed. 
Greenhouse pot experiments were conducted to determine availability of iron 
from various commercially available iron sources and DGP, said DGP mixture 
being formulated with different chemical classes of polymers, with each 
iron source or DGP mixture being applied in a band (1/4 to 3/4 inch in 
diameter and 4 to 6 inches long at a depth of 2 inches below the soil 
surface and 1 inch away from the seed row to a calcareous iron-deficient 
soil at an application rate ranging between about 10 and about 40 pounds 
of iron per acre. For comparison purposes, each iron fertilizer, namely, 
iron (ferrous or ferric) sulfate and FeEDDHA was band applied by itself at 
the same soil depth and distance from the seed row. In addition, a 
polyacrylamide polymer formulation of DGP was field-tested to determine 
the effectiveness of the DGP for the iron nutrition of corn growing under 
actual field conditions. 
In the following three examples, unless otherwise indicated, all parts and 
percentage compositions are by weight. In the greenhouse studies, each pot 
was 6 inches in diameter and was charged with about 1 kilogram of Epping 
silt loam soil. The soil in all greenhouse pots was fertilized uniformly 
with all known plant nutrients except iron at rates known to provide 
optimum plant response, so that any crop responses could be attributed to 
iron contained in the various materials, including the DGP mixtures, or 
iron source materials or FeEDDHA or hydrophilic polymer-iron source 
materials applied as comparisons to the DGP mixture. See Konrad Mengel, 
and E. A. Kirkby, Principles of Plant Nutrition, International Potash 
Institute, Bern, Switzerland (1982), herein incorporated by reference 
thereto, for an example of the variety and concentrations of 
micronutrients used to satisfy such requirements. The test crop for the 
greenhouse experiments was grain sorghum (Sorghum bicolor L. Moench), 
cultivar RS-626, a variety known to be susceptible to iron chlorosis when 
grown on iron-deficient soils such as the Epping silt loam type herein 
used. Three replicates of each treatment were used in a completely 
randomized design. Deionized water was used during the entire growth 
period and forage was harvested after 6 weeks' growth. The soil in 
greenhouse pots was sliced longitudinally post-harvest to examine 
fertilizer band characteristics. In the field study, the DGP were tested 
as an iron source for corn (Zea mays L.) in a factorial design against 
other iron source materials using four replications plus an untreated 
check on high pH Cozad silt loam soil in the State of Nebraska. 
The resulting DGP mixtures, containing a proper diet of required iron, have 
now been found to act to more effectively deliver to the plants treated 
therewith the nutrient contained therein. It is believed that these 
products act to focus the beneficial effects of such therein contained 
iron due to the fact that proper placement thereof at the soil situs 
juxtaposed the plant root both provide a protective matrix for iron 
contained therein and effectively causes or enhances root development and 
growth to and throughout the regions of soil displaced by "islands" or 
"veins" of such mixtures while at the same time supplying a zone of iron 
outside the DGP band in such form that it is readily available and 
accessible to plants, and iron uptake, and thus plant growth, is 
considerably enhanced. 
Accordingly, a first series of tests, reported in Example I, below, was 
designed to test the response of grain sorghum to iron contained in the 
DGP mixtures, iron contained in hydrophilic polymer delivery systems, iron 
contained in FeEDDHA, and iron contained in iron sulfates. The application 
rates for iron were 18 and 24 mg of iron per kilogram of pot soil for all 
materials tested. The hydrophilic delivery systems were the same as those 
described in the preferred embodiments of Mortvedt, supra. 
A second series of tests, reported in Example II, below, was designed to 
test the response of grain sorghum to iron contained in the DGP mixtures 
formulated with different chemical classes of hydrophilic polymer, the 
response to iron contained in hydrophilic polymer delivery systems which 
contained either no citric acid or which contained reagent grade citric 
acid, and the response to FeEDDHA and iron sulfate. The application rate 
for all iron source materials tested was 18 mg of iron per kilogram of pot 
soil. 
A third series of tests, reported in Example III, below, was designed to 
test the response of corn growing in the field environment to iron 
contained in a DGP mixture formulated with a polyacrylamide polymer, or 
iron contained in iron sulfate, or iron contained in an iron 
sulfate/elemental sulfur/citrate/iron-lignosulfonate mixture, or iron 
contained in two foliar spray applications of 1.5 percent iron sulfate as 
FeSO.sub.4. In this example, the application rate of iron varied with each 
iron-source treatment. 
In all series of tests, projected results correlate with the hypothesis 
that such DGP product and application procedure will very effectively act 
to enhance plant growth and improve iron nutrition. In addition, results 
correlate with the hypothesis that such procedure will very effectively 
act to focus plant root growth in the specific regions and areas of iron 
placement. Finally, such procedure will thereby provide a new, improved, 
economical, and highly efficient, delivery system for iron to preselected 
plants or plant pots. 
Example I 
In the tests comprising this example, iron sulfate, in the reduced state, 
was band applied according to the procedures outlined above to a 
calcareous iron-deficient soil of the type Epping silt loam either alone 
or in combination with the DGP mixture containing a polyacrylamide 
polymer, or in combination with hydrophilic polymer gels of varying 
chemical structure, to wit, a polyacrylamide, or a polyacrylamide plus 
polyacrylate. The procedure used to prepare the gels comprising the 
polymer and iron sulfate combination was as described in the description 
of the preferred embodiments in Mortvedt, supra. The resulting materials 
were subsurface band applied to soil forming about 1/4 inch diameter bands 
onto the soil in the test pots. The synthetic chelate, FeEDDHA, also was 
similarly band applied alone to soil. All iron source materials were 
applied at two different rates, i.e., at 18 and at 24 mg of iron per 
kilogram of pot soil. It should be noted that in the test comprising this 
Example I, described in detail infra, typical 6-inch (150-millimeter) 
diameter greenhouse pots were used, with each 6-inch pot containing, on 
the average, 1 kilogram of iron-deficient soil. Also, typical to iron 
response tests, the potted crop was sorghum since it has long been used as 
a standard for such types of testing with 6 plants being maintained in 
each pot. See, for example, Aubra Mathers, Effect of ferrous sulfate and 
sulfuric acid on grain sorghum yields, Agron. J. 62:555-556 (1970). 
Typically, after six weeks' of growth in the greenhouse environment the 
above-ground plant forage was harvested, dried, and weighed to determine 
response to testing materials relative to sorghum grown in pots as 
standards. Post-harvest examination of the bands was made by slicing the 
soil longitudinally along the fertilizer band. Visual observations for 
treatment effects, as judged by the degree of chlorosis in plants, 
indicated that there were no differences in effectiveness between the DGP 
and FeEDDHA. However, sorghum forage yields and uptake of iron were 
highest with the DGP mixture, see Table VI, infra; the synthetic chelate 
FeEDDHA which was previously known to be the most effective iron 
fertilizer, ranked second below the DGP in yields and iron uptake. The 
hydrophilic polymer delivery system of Mortvedt, supra, ranked third. Crop 
response was lower still with FeSO.sub.4 band applied alone. Post-harvest 
examination of soil showed well-hydrated, or gelled, bands of DGP into 
which roots had freely penetrated and proliferated. In addition, plant 
roots tended to be concentrated in the DGP band, and in an orange-colored 
diffusion zone around the DGP band, rather than evenly distributed 
throughout the plant growth media, i.e., an enhanced root growth region. 
TABLE VI 
__________________________________________________________________________ 
Source/ 
Source/ 
Fe band applied to soil (mg/pot) 
Test 
Wt. % Wt. % of 
0 18 
24 
0 18 24 0 18 24 
No. 
of Fe Polymer.sup.1 
Chlorosis.sup.2 
Yield, g/pot 
Fe uptake, mg/pot 
__________________________________________________________________________ 
1 DGP.sup.3 
A -- 
A A -- 
47.2 
48.3 
-- 3.22 
3.45 
(1.0) (10) 
2 Hydro- A -- 
B B -- 
32.0 
34.0 
-- 2.53 
2.54 
gel.sup.4 
(4.5) 
(0.12) 
3 Hydro- B -- 
B B -- 
27.0 
28.1 
-- 2.02 
2.29 
gel (4.5) 
(0.12) 
4 FeEDDHA 
-- -- 
A A -- 
42.7 
49.1 
-- 2.83 
2.39 
(100) (0) 
5 FeSO.sub.4 
-- -- 
D D -- 
17.2 
17.7 
-- 0.73 
0.78 
(100) (0) 
6 Control 
-- D -- 
-- 
3.8 
-- -- 0.27 
-- -- 
(0) (0) 
__________________________________________________________________________ 
.sup.1 Apolyacrylamide; Bcommercial polyacrylamide and polyacrylate 
mixture (50% w/w). 
.sup.2 Chlorosis rating scale: A = none; B = slight; C = moderate; D = 
severe. 
.sup.3 DGP dried gel particles consist of 7% polymer, 10% citric acid, 5 
FeSO.sub.4 to give an iron concentration of 1.0%). 
.sup.4 Hydrogel fluid gel formulated to Mortvedt, supra. 
Example II 
In the tests comprising this example, the DGP, formulated with (Test No. 1, 
Table VI, supra) or without citric acid, and a polyacrylamide polymer, and 
four other different chemical classes of polymer 
(polyacrylamide/polyacrylate, cellulose ether, guar gum, and 
propenoate-propenamide) which contained citric acid, were compared against 
hydrophilic polymer delivery systems of Mortvedt, supra, which either 
contained or did not contain (Table VII, infra, Test No. 3 and 4) citric 
acid, for effectiveness as iron sources for grain sorghum. The same 
fertilizing, planting, and cropping procedures used in Example I, above, 
were followed in these tests. Both FeSO.sub.4 and FeEDDHA were each band 
applied alone to soil and all iron sources were applied at a rate of 18 mg 
of iron per pot. As in Example I, supra, in this and subsequent examples, 
the reference to band application is understood to mean the procedure set 
forth in the introductory portion of this section. Crop response to the 
iron sources was greatest with the DGP formulated with a polyacrylamide 
polymer plus citric acid. The FeEDDHA treatment ranked second, and the 
hydrophilic delivery system of Mortvedt, supra, consisting of 
polyacrylamide and iron sulfate to which citric acid was added (Test No. 
3) ranked third. Crop response was poorest with FeSO.sub.4 alone. Although 
the DGP containing the propenoate-propenamide polymer (Test No. 9, infra) 
did not produce as satisfactory results as the other DGP, and it ranked 
below FeEDDHA and Test No. 3 in effectiveness, it nonetheless prevented 
iron chlorosis in the plants and is still less costly than the chelate. 
The same qualities of root penetration and proliferation as shown in 
Example I, supra, were again evident with all the DGP, although only the 
DGP containing the polyacrylamide and the cellulose ether manifested the 
orange-colored diffusion zone, supra. The ranking of the products in this 
test according to yields and iron uptake of plants is presented in Table 
VII, infra, wherein there is clearly demonstrated the superior attributes 
of the instant invention in this example and, further wherein is clearly 
shown that citric acid is an essential component of such systems, without 
which plant vigor and iron nutrition is much reduced. 
TABLE VII 
______________________________________ 
Cit- Fe band applied 
ric to soil (18 mg/pot) 
Source/ Source/ acid Chloro- Fe 
Test Wt. % Wt. % of Wt. sis Yield, 
uptake, 
No. of Fe Polymer.sup.1 
% rating.sup.2 
g/pot mg/pot 
______________________________________ 
1 DGP.sup.3 A 10.0 A 41.1 2.27 
(1.0) (7) 
2 DGP A -- D 13.2 0.37 
(1.0) (7) 
3 Hydro- A 5.0 A 35.0 1.83 
gel.sup.4 (4.5) 
(0.12) 
4 Hydro- A -- B 30.2 1.29 
gel (4.5) 
(0.12) 
5 Hydro- B 5.0 B+ 28.1 1.59 
gel (4.5) 
(0.12 
6 Hydro- B -- C 20.7 1.01 
gel (4.5) 
(0.12 
7 DGP C 10.0 A 33.0 2.06 
(1.0) (7) 
8 DGP D 10.0 A 32.9 2.11 
(1.0) (7) 
9 DGP E 10.0 A 27.1 1.60 
(1.0) (10) 
10 FeEDDHA -- -- A 39.1 1.83 
(100) (0) 
11 FeSO.sub.4 -- -- D 11.4 0.45 
(100) (0) 
12 Control -- -- D 6.2 0.46 
(0) (0) 
______________________________________ 
.sup.1 Apolyacrylamide; Bcommercial polyacrylamide and polyacrylate 
mixture (50% w/w); Ccellulose ether; Dguar gum; Epropenoate-propenamide. 
.sup.2 Chlorosis rating scale: A = none; B = slight; C = moderate; D = 
severe. 
.sup.3 DGP dried gel particles consist of 7% polymer, 10% citric acid, 5 
FeSO.sub.4 (to give an iron concentration of 1.0%). 
.sup.4 Hydrogel fluid gel formulated to Mortvedt, supra. The citric acid 
concentration of 5% was the maximum that could be absorbed in these gels. 
On a dry weight basis, the concentrations of iron, polymer, and citric 
acid are 9.63%, 90.4%, and 25%, respectively. 
Example III 
A third series of tests, reported below, was designed to test the response 
of corn to a polyacrylamide plus citric acid formulation of DGP in a field 
environment. The experiment was a factorial design using two corn 
varieties (tolerant and non-tolerant to high soil pH, designated as P3362 
and P3398, respectively, in Table VIII, below) and five iron treatments 
applied in the seed furrow, plus an untreated check. Four replications of 
each treatment and of the untreated check were used. The experiment was 
established in Nebraska on three areas of Cozad silt loam soil that ranged 
in pH from slightly above neutral (pH 7.7) to calcareous (pH 8.6). Plot 
size was four individual rows 15 feet long with 30 inch spacing between 
rows. Iron source treatments consisted of DGP applied at 5 and 10 pounds 
of iron per acre (designated as DGP1 and DGP2 in Table VIII, below), iron 
sulfate applied at 50 pounds per acre (designated as FeSO.sub.4 in Table 
VIII), an iron sulfate/elemental sulfur/citrate/iron-lignosulfonate 
mixture (designated as FeMIX in Table VIII) applied at 90 pounds per acre, 
or two foliar spray applications of 1.5 percent iron sulfate as FeSO.sub.4 
(designated as FOLIAR in Table VIII). Measures of treatment effectiveness 
were plant height, the chlorophyll content of leaves (since iron is 
essential for chlorophyll formation), and yields of corn grain reported as 
bushels per acre. An increase in plant height and in the leaf chlorophyll 
content are at least strong indicators of increased plant vigor, while an 
increase in yield is the final definitive measure of product 
effectiveness. The effectiveness of the DGP as an iron source in 
calcareous soil (site 1) is clearly shown in Table VIII, where plant 
height and leaf chlorophyll content (both measured 80 days after 
planting), and final grain yields are significantly greater with the DGP 
applications than with the other iron source treatments. Moreover, the DGP 
treatments resulted significant improvement in the three measured 
parameters for the crop variety which has been developed to be less 
susceptible to iron deficiency, which was an even stronger indication of 
the efficacy of the DGP materials. In addition, photographic 
documentation, commencing at an early stage of plant growth and 
development (14 days) and continuing until plant senesence and harvest of 
grain (120 days) clearly showed the dramatic differences in the plant 
height and green color of plants treated with DGP and further 
substantiated the actual measurements shown in Table VIII. As pointed out 
in the description of the prior art, supra, iron deficiency occurs most 
frequently in calcareous, high pH soils, and chlorosis occurs most usually 
in plants grown therein, but usually with decreasing occurrence and 
severity as soils tend towards a neutral pH. Correction of chlorosis is 
also the most difficult in such soils, and in general, tends to be more 
easily corrected as soils tend toward a neutral pH if, indeed, the problem 
occurs at all. The vigor and yields of the plants grown on Site 2 and Site 
3 support this contention, while the increase in plant vigor and yields on 
Site 1 demonstrate the efficacy of the DGP product. 
The exact location of the original test plots was mapped at the end of the 
growing season. A corn crop was then planted one year later in the plots 
to test for residual effects of the DGP treatments. No additional DGP or 
other iron source was applied at planting. Photographic documentation 
clearly showed a response to the original DGP application, as evidenced by 
a marked increase in plant vigor (plant height, growth rate, and absence 
of chlorosis) over plants growing in other areas of the test plots. This 
response was evident throughout the entire growing season. The plants 
growing in plots which had received other treatments listed in Table VIII, 
supra, the previous year were stunted and chlorotic. This clearly 
indicates the long-term efficacy of the DGP, and supports the economic 
viability of the DGP since yearly applications may be unnecessary. 
TABLE VIII 
__________________________________________________________________________ 
Iron Plant Height 
Chlorophyll Meter 
Yield, bu/A 
Test Treat- 
Site.sup.3 
Site Site 
No. Variety.sup.1 
ment.sup.2 
1 2 3 1 2 3 1 2 3 
__________________________________________________________________________ 
1 P3362 
Check 
14.8 
21.8 
28.3 
12.3 
52.1 
53.4 
44 174 
181 
2 FOLIAR 
17.0 
22.8 
26.5 
25.1 
53.1 
55.5 
80 180 
195 
3 FeSO.sub.4 
19.5 
23.3 
29.5 
32.9 
54.5 
55.9 
98 181 
199 
4 FEMIX 
20.3 
25.0 
28.3 
27.1 
53.3 
54.1 
102 
185 
186 
5 DGP1 22.8 
24.5 
28.3 
46.8 
51.5 
54.8 
133 
176 
198 
6 DGP2 22.3 
24.8 
29.3 
47.9 
55.5 
56.0 
131 
182 
188 
7 P3398 
Check 
6.3 
20.8 
25.0 
4.4 
49.1 
51.1 
1 164 
179 
8 FOLIAR 
8.0 
22.0 
24.3 
14.5 
47.3 
51.9 
6 174 
176 
9 FeSO.sub.4 
17.5 
23.0 
24.8 
12.3 
49.4 
50.5 
26 170 
182 
10 FEMIX 
19.5 
22.0 
27.0 
20.9 
51.4 
52.5 
44 178 
182 
11 DGP1 23.8 
24.8 
26.2 
45.7 
52.2 
53.6 
102 
173 
183 
12 DGP2 24.3 
24.0 
26.0 
51.3 
51.6 
52.8 
110 
178 
184 
__________________________________________________________________________ 
.sup.1 Variety P3362 is a Pioneer, high pHiron deficiency tolerant 
variety; Variety P3398 is a Pioneer, high pHiron deficiency susceptible 
variety. 
.sup.2 Checkno applied iron; FOLIARtwo foliar spray applications of 1.5% 
iron sulfate; FeSO4iron sulfate applied at 50 lb/A; FEMIXiron 
sulfate/elemental sulfur/citrate/ironliqnosulfonate mixture applied at 90 
lb/A; DGPdried gel particles contain 7.0% polyacrylamide, 10.0% citric 
acid, and 5.0% FeSO.sub.4 (to give an iron concentration of 1.0%). DGP1 
applied at 5 lb Fe/A; DGP2 applied at 10 lb Fe/A. 
.sup.3 Site 1: Calcareous pH 8.6; Site 2: Slightly calcareous pH 8.2: 
Site 3: Near neutral pH 7.7. 
INVENTION AMETERS 
After sifting and winnowing through the data herein presented, as well as 
other results and operations of our new, novel, and improved technique, 
including methods and means for the effecting thereof, the operating 
variables, including the acceptable and preferred conditions for carrying 
out our invention are summarized below: 
______________________________________ 
Most 
Operating Preferred Preferred 
Variables Limits.sup.1 
Limits.sup.1 
Limits.sup.1 
______________________________________ 
Polymer.sup.2 1-15% 5-15% 7% 
(14-60) (30-38) (32) 
Iron Sulfate 1-15% 3-10% 5% 
(14-30) (20-25) (23) 
Citric Acid 5-20% 5-15% 10% 
(0.7-50) (38-50) (45) 
Water .ltoreq.93% 
.ltoreq.87% 
78% 
Film Thickness of 
1/8"-1/2" 1/4"-1/2" 1/4" 
Undried Hydrogel 
Drying Temperature 
90-120 100-110 105 
(.degree.C.) 
Time of Effective 
4-20 10-16 10 
Drying (h) 
______________________________________ 
.sup.1 Concentrations of polymer, iron sulfate, and citric acid, on a 
weight basis, in formulations on a per kilogram basis after mixing with 
deionized water, but before drying. Approximate concentrations after 
drying shown in parenthesis. Final concentrations of ingredients on a dry 
weight basis may total less than 100% due to water loss during drying. Th 
solvation capacity of a given polymer often limits the amounts of soluble 
salts (i.e., sulfates and/or citrates) contained in the final, dried 
product. 
.sup.2 Crosslinked polyacrylamide, polyacrylate, guar gum, cellulose 
ether, or propenoatepropenamide, preferably from about 1 to about 5% 
crosslinking, and most preferably from about 1 to about 3% crosslinking 
(above about 10% crosslinking could result in a plastic or solid material 
before drying, with insufficient absorption of iron and citric acid), or 
natural guar polymer with no crosslinking. 
While we have shown and described particular embodiments of our invention, 
modifications and variations thereof will occur to those skilled in the 
art. We wish it to be understood therefore that the appended claims are 
intended to cover such modifications and variations which are within the 
true scope and spirit of our invention.