Background of the Invention
Fertilizers are added to the soil of crops or in some cases they can
be applied directly to crop foliage to supply elements needed for plant nutrition.
Seventeen elements are known to be essential to the health and growth of plants.
Typically, nitrogen, phosphorus, and potassium are provided in the greatest quantity.
With increasing knowledge of the role of each of the nutrients essential to plants,
there is a better understanding of the importance of providing a given nutrient
at the appropriate stage of phenology. To accomplish this, rapid changes in fertilizer
formulations and methods of application have been necessary.
Another factor changing fertilization formulations and methods is
due to pressure from federal, state and local regulatory agencies and citizen groups
to reduce the total amount of fertilizer in general, and of specific nutrients in
particular, being applied to the soil. Additionally, the loss of registration of
existing synthetic plant growth regulators and organic pesticides and the prohibitively
high costs involved in the successful registration of new ones, also plays a role
in the changing arena of crop fertilization.
The principal source of phosphorus for the fertilizer industry is
derived from the ores of phosphorus-containing minerals found in the Earth's crust,
termed phosphate rock. Elemental phosphorus does not exist in nature; plants utilize
phosphorus as the dihydrogen phosphate ion (H2PO4-).
While untreated phosphate rock has been used for fertilizer, it is most commonly
acidulated with dilute solutions of strong mineral acids to form phosphoric acid,
which is more readily absorbed by crops.
Until recently, phosphate and polyphosphate compounds were considered
the only forms in which phosphorus could be supplied to plants to meet the plant's
nutritional need for phosphorus. Indeed, the only phosphite compound cited for use
as a fertilizer in the Merck Index (M. Windhols, ed., 1983, 10th edition,
p.1678) is calcium phosphite (CaHPO3). No phosphite fertilizer formulations
are listed in The Farm Chemical Handbook (Meister Publishing Co., 1993, Willoughby,
OH 834 p.) or Western Fertilizer Handbook (The Interstate, Danville, IL 288
p.) Historically, calcium phosphite was formed as a putative contaminant in the
synthesis of calcium superphosphate fertilizers [McIntyre et al.,Agron. J.
42:543-549 (1950)] and in one case, was demonstrated to cause injury to corn
[Lucas et al., Agron. J. 71:1063-1065 (1979)]. Consequently, phosphite
was relegated for use only as a fungicide (Alliete®; U.S. Pat. No. 4,075,324)
and as a food preservative.
More recently, it has been shown that plants can obtain phosphorus
from phosphite [Lovatt, C. J., March 22, 1990, "Foliar phosphorus fertilization
of citrus by foliar application of phosphite" In: Citrus Research Advisory Committee
(eds) Summary of Citrus Research, University of California, Riverside, CA pp 25-26;
Anon., May, I990, "Foliar applications do double duty" In: L. Robison (ed) Citrograph
Vol. 75, No. 7, p 161; Lovatt, C. J., I990, "A definitive test to determine whether
phosphite fertilization can replace phosphate fertilization to supply P in the metabolism
of 'Hass' on 'Duke 7': - A preliminary report" California Avocado Society Yearbook
74:61-64; Lovatt, C. J., I992]. Formulations based on phosphorous acid and hypophosphorous
acid, as phosphite is; generally undergo oxidation to phosphate and thus lose the
benefits that could be derived from the use of phosphite fertilization applications.
The phosphate and polyphosphate fertilizers currently used have a
number of properties that compromise their desirability as fertilizers. Generally,
they tend to form precipitates during storage and shipping.
This limits the ability to formulate concentrated solutions of fertilizers.
Additionally, formulations must generally be maintained at a narrow pH range to
prevent precipitation, resulting in fertilizers that are limited to particular uses.
Another drawback of phosphate fertilizers is that they are not readily taken up
by the foliage of many plants and must instead be delivered to the soil for uptake
by plant roots. The mobility of phosphate fertilizers in the soil is limited leading
to rapid localized depletion of phosphorus in the rhizosphere and phosphorus deficiency
of the plant. Frequent reapplication of phosphate fertilizers is undesirable because
it leads to leaching of phosphate into the groundwater resulting in eutrophication
of lakes, ponds and streams.
Phosphate and polyphosphate fertilizers have also been shown to inhibit
the beneficial symbiosis between the roots of the plants and mycorrhizal fungi.
They tend to support the growth of algae and promote bacterial and fungal growth
in the rhizosphere, including the growth of pathogenic fungi and other soil-borne
Even though phosphorus, once in the plant, is very phloem mobile (i.e.
readily moving from old leaves to young tissues), phosphate is poorly absorbed through
the leaves of most plant species. This is unfortunate because successful foliar
phosphorus feeding would result in the application of less phosphate fertilizers
to the soil and reduce phosphorus pollution of the ground water.
Accordingly, there is a need for a phosphorus fertilizer that can
be utilized in irrigation systems and applied to foliage without the formation of
precipitates that reduce nutrient availability and uptake by the plant and plug
emitters and sprayers. There is also a need for new methods of fertilizer application
that allow nutrients in a readily available form to be supplied at the exact time
the plant needs them. This need includes the facility of a foliar product to be
sold in a single formulation for use as a concentrated material for airplane or
helicopter application or as a dilute solution for ground spray application and
yet able to be maintained at a suitable pH range optimal for leaf uptake despite
the need to be diluted prior to application.
Additionally, there is a demand for phosphorus fertilizers that have
the facility to be used as liquids or solids (granule or powder). There is also
a demand for fertilizers that do more than just supply nutrients. It is desired
that the fertilizers also have demonstrated plant growth regulator activity, increase
the plants' resistance to pests, promote plant health in general and root health
in particular, increase the production of allelopathic compounds, increase pre-
and post-harvest quality, improve stress tolerance, enhance beneficial symbioses,
and improve yield over existing traditional soil or foliar fertilizers.
Summary of the Invention
Given the above-mentioned deficiencies and demands of fertilizers
in general, and of phosphorus fertilizers in particular, it is an object of the
present invention to provide phosphorus to plants in a formulation that renders
phosphorus readily available to the plants under a number of application methods
such as through soil, foliar uptake, irrigation, and other methods.
It is also an object that the phosphorus fertilizer formulations be
conveniently formulated in concentrated solutions that are stable during storage
Another object of the present invention is to provide a phosphorus
fertilizer that is not as inhibitory to mycorrhizal fungi as traditional phosphate
It is a further object of the present invention to provide a phosphorus
fertilizer that does not support the growth of algae to the same degree that traditional
phosphate fertilizers do.
Additional objects and features of the invention will be apparent
to those skilled in the art from the following detailed description and appended
The above objects and features are accomplished by a concentrated
phosphorus fertilizer comprising a buffered composition comprising an organic acid
and salts thereof and a phosphorous-containing acid and salts thereof. The concentrated
phosphorus fertilizer can be diluted with water of pH ranging from about 6.5 to
about 8.5 at ratios of concentrate to water at about 1:40 to about 1:600 to result
in a fully solubilized fertilizer having a pH in a range acceptable for foliar uptake
In one embodiment, the phosphorous-containing acid is selected from
the group consisting of phosphorous acid, hypophosphorous acid, polyphosphorous
acid, and polyhypophosphorous acid and the organic acid is preferably selected from
the group consisting of dicarboxylic acids and tricarboxylic acids such as citrate.
In one embodiment, the concentrated phosphorus fertilizer is an essentially
clear liquid devoid of precipitate that can be diluted at a ratio of about 1:40
to about 1:600 with water having pH of about 6.5 to about 8.5, to result in a fertilizer
having a pH of about 5.0 to about 7.0, and more preferably from about 5.5 to about
6.5, to facilitate the uptake of phosphorus by a variety of plants.
A method of providing phosphorus to plants is also disclosed. The
method comprises diluting a concentrated phosphorus fertilizer comprising a buffered
composition comprising an organic acid and salts thereof and a phosphorous-containing
acid and salts thereof with water to form a substantially fully solubilized use-dilution
fertilizer having a pH in a range acceptable for foliar uptake of phosphorus, and
applying the fertilizer to the plant foliage.
Detailed Description of the Invention
The present invention provides phosphorus fertilizers essentially
devoid of phosphate. The fertilizer comprises a double or multiple buffer system
of organic acids and their salts with a phosphorous-containing acids and their salts.
The formulation stabilizes the phosphorous against oxidation to phosphate. Suitable
phosphorous-containing acids are phosphorous acid and polyphosphorous acid, based
generally on the formula H3PO3, and hypophosphorous acid and
polyhypophosphorous acid, based generally on the formula H3PO2.
Phosphite, the salt of phosphorous acid, has properties that are known to be beneficial
to crop production. It is taken up through the foliage of avocado and citrus, two
species which classically do not take up phosphate through their foliage. Phosphite
has fungicidal properties with regard to some species of pathogenic fungi:
Rhizoctonia solani, Botrytis cinerea, Piricularia oryzae, Plasmopora viticola,
Phytophthora cinnamomi, and Phytophthora parasitica. Recently, it has
been demonstrated that phosphite also serves as a source of metabolically active
phosphorus in plants. The properties of phosphite that make it desirable as a fertilizer
are enhanced when it is formulated according to the present invention as a double
or multiple buffer with phosphorous acid, hypophosphorous acid, polyphosphorous
acid and/or polyhypophosphorous acid and their respective salts and organic acids
and their salts per this invention.
Suitable organic acids have the formula R-COOH or R-COO-
where R is hydrogen or a carbon-containing molecule or group of molecules. Suitable
organic acids are those that maintain the phosphite ion in a substantially fully
solubilized form upon dilution with water at pH varying from about 6.5 to about
8.5 and that result in a use-dilution fertilizer having a foliage-acceptable pH
for phosphorus uptake. Preferred organic acids are dicarboxylic and tricarboxylic
By the term "substantially fully solubilized" it is meant that upon
dilution, the phosphite does not precipitate, or at least not appreciably, so as
to affect administration of the liquid product to the plant foliage, and thus is
in a form available to the plant. With present phosphite fertilizers, there is a
tendency for phosphite to precipitate if diluted with alkaline water, thereby rendering
the phosphite in a form that is unavailable to the plant for uptake.
By the term "foliage-acceptable pH for phosphorus uptake", it is meant a pH that
allows phosphorus to be absorbed by the plant without causing damage to the foliage.
A foliage-acceptable pH for phosphorus uptake usually ranges between about 5.0 to
about 7.0, and preferably between about 5.5 to about 6.5. Phosphorus is most readily
taken up by foliage at pH 6.0. Depending on the plant species, a pH below 5.0 can
cause damage to leaves and/or the flowers and/or fruit. At higher pH, between about
7.0 to about 7.5, there is reduced uptake of nutrients, although generally there
is no plant damage. A pH between about 7.5 and 8.0, depending on the plant species,
plant damage may result. A pH greater than 8.0, generally causes damage to the plant
in addition to reducing uptake of the nutrients. Accordingly, suitable organic acids
are those that help provide a "buffered composition" having the desired pH range.
This means that a "use-dilution fertilizer" having an acidic to neutral pH (pH 5.0
to 7.0) can be achieved upon high dilutions (up to about 1/600) of the concentrated
fertilizer with highly alkaline water (up to a pH of about 8.5).
Organic acids that meet this criteria include but not limited to intermediates
in the Kreb's Tricarboxylic Acid Cycle, amino acids such as glutamic acid and aspartic
acid, vitamin acids such as ascorbic acid and folic acid, and their respective salts.
Particularly preferred organic acids are dicarboxylic and tricarboxylic acids selected
from the group consisting of citrate, pyruvate, succinate, fumarate, malate, formate,
oxaloacetate, citrate, cis-aconitate, isocitrate, and α-ketoglutarate. Citrate
is a particularly preferred organic acid because of it is relatively inexpensive
and readily available.
These formulations allow the maintenance of continued solubility,
and thus availability for uptake by plants, of phosphorus, with or without other
nutrients, over a significantly wide range of concentrations and pHs. The increased
solubility of these formulation over that of phosphate or phosphite fertilizers
makes it possible to prepare fertilizers with a greater concentration of phosphorus
per unit volume than traditional phosphate or polyphosphate fertilizers or the simple
unbuffered salts of phosphorous acid recently being marketed as fertilizers for
foliar application which are available as super saturated solutions with only about
16% phosphite, and which are diluted approximately 1:100 to about 1:300. The resulting
pH of these fertilizers varies significantly depending upon the pH of the water
used, thus affecting the availability of the nutrients for foliar uptake. In contrast,
the highly concentrated fertilizers of the present invention, which can be diluted
with water at a ratio of about 1:600, allow for more cost effective shipping, handling,
and application. They result in greater uptake of phosphorus by the canopy of plants
than traditional phosphate or recent phosphite fertilizers not formulated in this
The formulations provided herein also make it possible to formulate
various combinations of other essential plant nutrients or other inorganic or organic
compounds as desired and maintain their solubility when used over a wide range of
concentrations and pHs, which is not possible for present phosphate or phosphite
fertilizers. For example, boron, manganese, calcium, iron and other elements can
be provided at relatively high concentrations in these formulations. Thus, these
phosphorus fertilizers also enhance the canopy uptake of other mineral nutrients
essential to plants. They can be used as a canopy application to improve pre- and
post-harvest crop quality.
Formulations can also prepared with copper. However, when high concentrations
of copper are used, the copper is not fully solubilized. In this situation, the
insoluble copper is desirable as it prevents rapid uptake of the copper and thus
minimizes the potential for copper toxicity. As the insoluble copper is rewetted
over night by dew, dissolution occurs so that additional copper is taken up. The
buffering capacity of the formulation maintains the pH at a foliage-acceptable pH
when the insoluble copper is rewetted so that conditions are optimal for uptake
and are benign to the plant tissues. While copper is an element essential to plants,
it is required in only small amounts. In relation to nitrogen, plants require, in
general, 10,000- to 75,000-fold less copper. Provided to the foliage of the plant
at the rate provided by this formulation, copper is a very effective fungicide,
in addition to being a plant nutrient and fertilizer.
In addition to the above-mentioned advantages, the formulations disclosed
have a direct benefit to the environment. Because the formulations allow successful
foliar feeding of phosphorus to a number of plants that do not effectively take
up phosphorus when supplied in phosphate or polyphosphate forms, and because these
formulations enhance the uptake of other nutrients, they are cost-effective and
can replace less efficient, traditional soil-feeding methods. This results in reducing
phosphate pollution of the groundwater and eutrophication of freshwater ponds, lakes
The phosphorus fertilizers disclosed herein can also be advantageously
applied through the soil or by irrigation systems as solid (granular) or liquid
formulations. These formulations can be used at pHs sufficiently low to clean irrigation
lines and alter the pH of the soil to solve alkalinity problems while supplying
essential nutrients to plants. Example 2, below discloses a suitable formulation
for irrigation application. With irrigation application, the fertilizer flowing
through the irrigation system will typically have a pH lower than about 2.5, usually
less than about pH 1.5. The low pH is designed to supply phosphorus while killing
bacteria and algae (slime) which plug irrigation lines, thus cleaning the lines.
The low pH also dissolves calcium carbonate deposits at and around the emitters,
and solubilizes the calcium carbonate so Ca2+ is available to the plant.
Once delivered to the soil near the plant, sufficient water is applied to achieve
a pH suitable for phosphorus uptake by the plant. The form in which the phosphorus
is supplied in these formulations is more mobile than phosphate fertilizers or than
the simple salts of phosphorous acid recently being sold as fertilizers, and thus
more available and more readily taken up by the roots of plants. An advantage of
these formulations is that the form in which phosphorus is supplied does not inhibit
the development of mycorrhizal fungi to the same degree that traditional phosphate
fertilizers do. The present compositions can also be formulated with certain nutrients
in addition to phosphorus that are readily absorbed through soil applications at
pH of about 5.5 to about 7.0. Such nutrients include nitrogen, calcium, magnesium,
potassium, molybdenum, boron, and sulfur.
Another advantage with the phosphorus fertilizers disclosed herein
is that they do not support the growth of green algae to the same degree that traditional
phosphate fertilizers do. This is of significant importance to agriculture, commercial
nurseries, the ornamental and cut flower industry, and the home and garden industry,
as it will prevent the growth of green algae which typically proliferate and plug
irrigation emitters, foul pots and benches, and provide a niche for the growth of
pathogenic bacteria and fungi. These formulations also endow the phosphorus fertilizer
with anti-viral, anti-bacterial and anti-fungal activity. This bacterialcidal activity
in a phosphorus fertilizer makes it possible to use this fertilizer to inhibit ice-nucleating
bacteria to thus protect plants from frost damage.
Methods of Preparation
The phosphorus fertilizers are prepared by first forming solutions
of the phosphorous and organic acids. Other desired nutrients can then be added
with constant stirring. The amount of phosphorous relative to organic acid is not
critical, as long as appropriate buffering and solubility are achieved. Generally
the amount of organic acid that is added will depend upon the form in which the
nutrient elements are added. For example, if calcium is to be added in the form
of calcium hydroxide (a base), then the acid form of the organic acid, for example
citric acid, would be used rather than its salt, citrate. In addition to the desired
nutrients, other additives, that are known in the fertilizer industry, can be added.
These include, for example, wetting-agents, surfactants, spreaders, stickers etc.,
and are described in The Farm Chemical Handbook, supra (incorporated
herein by reference). The fertilizer compositions can also be prepared as solid
formulations, identical to the liquid ones by simply leaving out all of the water.
The properties are the same as the liquid formulations but have the additional advantage
of weighing less for the same amount of nutrient.
Methods of Application
The fertilizer is applied according to crop-specific recommendations
which will depend upon the application method (foliar, soil, irrigation, etc.),
time of application, rate of application, and product formulation. Crops that will
benefit from the fertilizer include, but are not limited to, avocado, citrus, mango,
coffee, deciduous tree crops, grapes and other berry crops, soybean and other commercial
beans, corn, tomato, cucurbits and cucumis species, lettuce, potato, sugar beets,
peppers, sugarcane, hops, tobacco, pineapple, coconut palm and other commercial
and ornamental palms, hevea rubber, and ornamental plants.
In addition to the foliar, soil, and irrigation application methods
mentioned above, the present fertilizer may prove beneficial to certain crops through
other application methods. For example, trunk paints or other methodologies may
provide for a continuous low supply of fertilizers, such as, for example, "intravenous"
feeding as practiced in the boron nutrition of soybeans.
In order that the invention described herein may be more fully understood,
the following examples are set forth. All chemicals used were of analytical reagent
quality and approximately 100% by weight unless otherwise specified. All formulations
are expressed in terms of weight to volume. It should be understood that these examples
are for illustrative purposes only and are not to be construed as limiting the scope
of the invention in any manner.
A formulation was prepared of 1 gallon of 0-40-0 fertilizer with 3.86
lbs H3PO3, 1.34 lbs tripotassium citrate, 1.34 lbs of trisodium
citrate, and 4.0 lbs of 58% ammonium hydroxide. The components were dissolved in
water with constant stirring. This single formulation can be used at a rate of 2
quarts in as little as 20 gallons of water of pH 6.5 to 8.5 up to 300 gallons of
water of pH 6.5 to 8.5 and maintain a pH between 5.5 to 6.5 without the formation
of any precipitate.
A formulation was prepared of 1 gallon of 0-40-0 fertilizer with 3.86
lbs H3PO3 and 0.5 lbs citric acid. This formulation is stable
at pH 1.0 or less and is designed for application through the irrigation system.
It is stable against oxidation and precipitation when supplied through the irrigation
A formulation was prepared of 1 gallon of 0-30-0 fertilizer with 74.89%
elemental boron with 2.89 lbs H3PO3, 28.67 lbs borax (Na2B4O7•10
H2O), 17.16 lbs boric acid (H3BO3), 1.54 lbs H2SO4
and 2.67 lbs citric acid. A solution of the phosphorous and citric acid was first
prepared, then the other elements were added with constant stirring. This formulation
can be used at the rate of 2 quarts in as little as 20 gallons of water of pH between
6.5 to 8.5 up to 300 gallons of water of pH 6.5 to 8.5 and maintain a pH between
5.5 to 6.5 without the formation of any precipitate.
A formulation was prepared of 1 gallon of 0-30-0 fertilizer with 21.57%
Zn and 23.22% Mn with 2.89 lbs of H3PO3, 7.92 Ibs ZnSO4,
7.16 lbs Mn(H2PO2)2•H2O, 0.61 lbs
citric acid and 0.87 lbs 58% NH4OH. This formulation can be used at the
rate of two quarts in as little as 20 gallons of water of pH between 6.5 to 8.5
up to 300 gallons of water of pH between 6.5 to 8.5 and maintain a pH between 5.5
to 6.5 without the formation of any precipitate.
A formulation was prepared of 1 gallon of 0-30-0 fertilizer with 5.4%
Ca. It was packaged in a two-container system where 1 gallon of solution A contained
2.89 lbs H3PO3, 0.68 lbs Ca(OH)2, and 0.28 lbs
citric acid, and 1 gallon of solution B contained 0.16 lbs Ca(OH)2, 0.60
lbs KOH, 3.34 lbs 58% NH4OH, 0.28 lbs citric acid, and 0.67 lbs EDTA
(ethylenediaminetetraacetic acid). Two quarts of solution A can be added to as little
as 20 gallons of water of pH between 6.5 to 8.5 up to 300 gallons of water of pH
between 6.5 to 8.5 followed by the addition of two quarts of solution B. The final
solution is between pH 5.5 to 6.5 and without precipitation.
A formulation of 1 gallon of 0-30-0 fertilizer with 4.32% Ca can be
made without requiring EDTA. This formulation is also packaged in a two-container
system where 1 gallon of solution A contains 2.89 lbs H3PO3,
0.67 lbs Ca(OH)2 and 0.28 lbs of citric acid, while 1 gallon of solution
B contains 2.67 lbs of 58% NH4OH, 0.6 lbs KOH. Two quarts of solution
A can be added to as little as 20 gallons of water of pH between 6.5 to 8.5 up to
300 gallons of water of pH between 6.5 and 8.5 followed by the addition of two quarts
of solution B. The final pH of the solution is between 5.5 and 6.5 and without precipitation.
A formulation was prepared of 1 gallon of 0-30-30 fertilizer with
2.89 lbs H3PO3, 2.99 lbs KOH, and 0.84 lbs citric acid. Two
quarts can be added to as little as 20 gallons of water of pH between 6.5 to 8.5
and up to 300 gallons of water of pH between 6.5 and 8.5. The pH of the final solution
is between 5.5 and 6.5 without precipitation.
A formulation was prepared of 1 gallon of 0-30-0 fertilizer having
4.8% iron with 2.89 H3PO3, 1.75 Ibs iron-citrate, 0.74 lbs
KOH, 0.62 lbs NaOH, and 2.00 lbs of 58% NH4OH. Two quarts of the formulation
can be added to as little as 20 gallons of water pH 6.5 to 8.5 and up to 300 gallons
of water of pH 6.5 to 8.5. The pH of the final, solution is between 5.5 to 6.7 without
A formulation was prepared of 1 gallon of 0-30-0 fertilizer having
23.22% manganese with 2.89 H3PO3, 7.16 lbs. Mn(H2PO2)2,
and 0.133 lbs. sodium citrate. Two quarts of the formulation can be added to as
little as 20 gallons of water pH 6.5 to 8.5 and up to 300 gallons of water of pH
6.5 to 8.5. The pH of the final solution is between 5.5 to 6.5 without precipitation.
A formulation was prepared of 1 gallon of 0-30-0 fertilizer having
57% copper with 2.89 H3PO3, 7.3 lbs Cu(OH)2 (57%
Cu), and 1.34 lbs of 58% NH4OH. Two quarts can be added to as little
as 20 gallons of water of pH 6.5 to 8.5 up to 300 gallons of water of pH 6.5 to
8.5. The pH of the final solution is between 5.5 to 6.5. The copper is not fully
soluble, however this is desirable in that it prevents the rapid uptake of copper
when applied to plant foliage.