Foliar phosphate fertilizers

Details Foliar phosphate fertilizers Foliar phosphate fertilizers

1994-06-17

2002-08-20

Marcantoni, Paul (Department: 1755)

Chemistry: fertilizers

Processes and products

Inorganic material

C071S035000

Reexamination Certificate

active

06436165

ABSTRACT:

TECHNICAL FIELD
This invention relates to aqueous foliarly applicable phosphorus fertilizers and methods for production thereof.
BACKGROUND OF THE INVENTION
Foliar application of phosphorus fertilizers is known and has been used for many years in spite of certain difficulties such as for example: (1) leaf damage in the form of necrotic areas or burning of the leaves; (2) difficulties in achieving absorption of phosphorus bearing compounds through the waxy cuticle of the leaf; (3) poor translocation from the leaf to other parts of the plant through the narrow phloem vessels. The tendency to cause nutritional imbalances under some circumstances.
To avoid leaf burning or necrosis associated with prior art fertilizers, the agriculturist typically diluted the phosphorus containing fertilizers with substantial amounts of water. When these relatively dilute solutions are used at low application rates, such as 10 or 20 gallons per acre, very little nutritive value is associated with the fertilizer. For most annual crops such as cereal grains, the volumes of fertilizer to be applied are preferably less than 10 gallons per acre. This is particularly true when herbicides are to be applied at the same time.
Because under some circumstances inadequate nutritive value is obtained from the foliar application of phosphate fertilizer without damage to the plants from burning, it is more common to apply phosphate fertilizers to the soil. Many versions of phosphates have been applied to the soil (“The Role of Phosphorus in Agriculture”, F. E. Khasawneh, E. C. Sanple and E. J. Kamprath,
Eds. American Soc. of Agron
., Madison, Wis., 1980) but one of them is of special interest. That type is disclosed in Soviet Union patent 566,809 to Borisov which discloses phosphate esters for application to the soil and a method of making them. Also, a procedure for synthesizing an ethylene glycol phosphate was taught by P. Carre (Compt. Rend. 138: 374-37. Carre (Compt. Rend. 138: 374-375, 1904).
The use of a phosphate ester for soil fertilization is based on the belief that a low reactivity of the organic compound will avoid phosphorus fixation (plant unavailability) in the soil. Neither the patent to Borisov nor the publication of P. Carre disclose use of a phosphate ester as a foliar fertilizer and the methods they disclose for the synthesis of their phosphate ester are time-consuming and have low yields. The yields are sufficiently low and the time preparation sufficiently long as to render them uneconomical.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the invention to provide novel phosphorus-containing fertilizer and method of synthesizing it for foliar application.
In accordance with the above and further objects of the invention, crops are fertilized by spraying a liquid solution onto the leaves of the plants, which liquid solution contains at least one phosphate together with other ingredients such that the solution: (1) is sufficiently concentrated to be of substantial nutritive value to the plants when applied at an appropriate volume per acre, such as having a phosphate ester concentration above 0.5 molar; (2) is in liquid form with sufficient fluidity for spraying; (3) remains in liquid form without crystalizing for a sufficient time to be absorbed by the leaves and provides a sufficiently low osmotic pressure to avoid necrosis of the leaves when absorbed; (4) is able to translocate throughout the plant from the leaves with efficiency; (5) is able to penetrate into the leaves easily; (6) when appropriately formulated does not cause nutritional imbalances in the plant; and (7) is economical to use. For most applications, the fertilizer is applied at a rate of less than 10 gallons per acre but for some plants than can tolerate more phosphate or need more to obtain nutritional balance it may be higher such as for example 40 gallons per acre in two twenty gallon per acre spraying runs.
In its preferred form, the liquid solution: (1) is either hygroscopic or includes sufficient hygroscopic material or both so as to draw moisture from the air and maintain itself in liquid form; and (2) has improved capabilities for sticking to and remaining on the leaves of plants being fertilized, which can advantageously be provided by a water miscible or water emulsifiable adhering agent which helps to retain the phosphate ester compound and hygroscopic agent on the leaf during application and rainfall.
One category of such phosphorus containing fertilizers includes at least one phosphate ester compound. The phosphate ester compounds are formed by reacting a phosphoric acid and ethylene glycol with an esterification promoter such as a metal oxide or hydroxide in a sufficient amount for a sufficient time and under pressure and temperature conditions that enhance water removal without carbonization, resulting in a relatively high yield. The ethylene glycol phosphate esters may then be neutralized and boiled to convert the diesters and triesters to monoesters. The material provides an excess of ethylene glycol to increase its hygroscopic properties and is diluted to mobility suitable for foliar application.
The phosphate ester compounds are typically produced using alcohols consisting of or incorporating an alkane diol or triol having a carbon chain length of preferably 2 to 4, more preferably 2 to 3 and most preferably 2. The phosphate esters are present in the liquid fertilizers in amounts of one-half molar. The phosphate ester compounds are preferably present in the aqueous fertilizer solution in concentrations from 0.5 to 4 molar. More preferably, the concentrations range from 1 to 3 molar of the applied phosphate ester compound.
The preferred fertilizer mixtures or solutions remain in a sustained liquid state sufficiently long to avoid crystalization, such as from one to seven days. The sustained liquid state is preferably accomplished by a water-miscible hygroscopic agent. This may be accomplished through the hygroscopic activity of the ester and/or other hygroscopic agent which allows moisture to be taken from the atmosphere to maintain the fertilizer in an active liquid form on the foliage. The hygroscopic agent is preferably liquid and can be provided as an excess amount of a suitable non-phytotoxic alcohol such as the alkane diol or triol alcohol used in compounding the alcohol phosphate ester forming the active source of phosphorus in the fertilizer solution.
Preferably, the liquid hygroscopic agent or agents is: (1) present in amounts sufficient to maintain the applied fertilizer sprays in liquid form on the plant leaf for a sustained period after application, such as 1-7 days; (2) included in amounts sufficient to provide collective concentration thereof of approximately one molar or greater; and (3) is provided in collective concentrations of approximately 1 to 10 molar. The hygroscopic agent is advantageously the phosphate ester and/or alcohol forming one of the moieties of the phosphate ester.
Generally, the foliar fertilizer is intended to solve a dilemma that has been determined. That dilemma occurs because of two conflicting factors.
One factor is that foliar feeding of plants has been of limited use due to problems of penetration and translocation of the applied nutrients. Some fertilizer compounds penetrate the waxy cuticle of the leaves with difficulty. In many cases this is due to rapid crystallization of the fertilizer on the leaf surface impeding its subsequent movement through the cuticle. In the case of macronutrients like phosphorus, relatively large amounts of the nutrient need to be foliarly absorbed to be effective. However, it has not been possible previously to supply foliarly such large amounts of phosphorus because the application of phosphorus at high rates has caused “leaf burning” as described in “Foliar fertilization”, A. Alexander, Ed. Martinus Wijhoff Publishers, 1986, Dordrecht.
The other factor is that, when phosphorus is applied in compositions that do not crystallize (because of their hygroscopic properties in humid air) leaf burning is caused by osmotic effects

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