Chemistry: fertilizers – Processes and products – Organic material-containing
Reexamination Certificate
2002-08-07
2004-12-14
Sayala, C. (Department: 1761)
Chemistry: fertilizers
Processes and products
Organic material-containing
C071S064020
Reexamination Certificate
active
06830603
ABSTRACT:
BACKGROUND OF THE INVENTION
(1) Field of the Invention
The present invention relates to volatility-inhibited fertilizers comprised of granular urea coated with a coating including a binding agent having a boron anion and a hydrogen bonding group to adhere said binding agent to the granular urea, and optionally with additional plant nutrients, and to process for their preparation.
(2) Description of the Prior Art
Urea is widely employed as a non-burning nitrogen source for agricultural and forest fertilization. The granular form is commonly used for forest fertilization whereas granular and liquid forms may be used for agricultural fertilization. When applied to the soil, the granular form of urea dissolves by absorbing water and entering the soil solution. The water may come from rain or irrigation, atmospheric moisture and from water in the soil (soil moisture).
Once in the soil solution, urea is subject to hydrolysis by the enzyme urease. The hydrolysis reaction may ultimately produce ammonia as indicated in equation 1.
H
2
NCONH
2
+H
2
O→2NH
3
+CO
2
(1)
The actual hydrolysis process proceeds through intermediates of ammonium carbamate and ammonium carbonate (see reviews by Terman “Volatilization Losses of Nitrogen as Ammonia From Surface Applied Fertilizers, Organic Amendments, and Crop Residues”—Adv. Agronomy 31:189-223, 1979 and Freney et. al.—“Volatilization of Ammonia” in
Gaseous Loss of Nitrogen from Plant Soil
-
Systems
Freney and Simpson editors, Martinus and Nijhoff, 1983). The volatilization problem with fertilizers has been the subject of much study and when urea is the fertilizer nitrogen source applied the governing factors are the ability of a given soil to release ammonia and the activity of the enzyme urease.
The loss of ammonia nitrogen from urea nitrogen is governed by the relationship between the ammonia/ammonium ion equilibrium and a number of soil variables. The soil variables include: temperature, soil pH, soil chemistry (cation exchange capacity and organic matter), and soil moisture. Increases in temperature favor ammonia release by increasing the base dissociation constant of ammonia and reducing the solubility of ammonia in the soil solution. An alkaline soil pH favors ammonia release by increasing the equilibrium percent of ammonia present in the soil solution. Soils with a high cation exchange capacity are better able to absorb ammonium ions reducing volatilization losses. Organic matter can absorb ammonia reducing losses as bacteria convert the ammonia to organic nitrogen. Applying urea or ammonia forming compounds to damp soils which are drying out due to wind or sunlight can increase ammonia losses.
The activity of the enzyme urease in a given soil is affected by temperature, soil pH, and the amount of enzyme present and dilution of the urea as it dissolves. Increases in temperature favor urea hydrolysis by increasing the activity of the enzyme urease. An alkaline soil pH also increases the activity of the enzyme urease. Organic matter is a significant source of the enzyme urease, which increases ammonia losses from urea. Urea applied under low moisture conditions takes longer to dissolve before hydrolysis can begin. Rainfall washes urea into the soil and dilutes the compound, which helps to reduce volatility losses.
Several methods have been used to reduce nitrogen losses from surface applied granular urea. Acidic coatings have been used to control the ammonia/ammonium ion equilibrium in the area where the particle dissolves. Urease inhibitors have been developed to reduce the activity of the enzyme urease, thus reducing volatile nitrogen losses. Finally, expensive, slow release urea compositions can be formed which extend the time needed to release the urea nitrogen.
As illustrative of acidic coatings, Young (U.S. Pat. No. 4,073,633; Feb. 14, 1978) teaches the use of an acid generating substance to keep the soil pH at 7 or less in the area where granular urea is applied. The acid generating substances include acids (inorganic and organic); salts such as ferric sulfate that are acidic in water; and compounds such as sulfur which are metabolized by soil microorganisms to acid compounds or form acidic oxidation products with oxygen. The products needed to exploit the invention can be made by coating urea granules or forming agglomerates of urea and the acid generating substances (e.g. the agglomerate indicated of urea, gypsum and an acid generating compound). The invention, also, indicates that clays such as kieselguhr in the range of 5% to 20% can be used to prevent sticking of coated products.
Whitehurst et. al. (U.S. Pat. No. 6,030,659; Feb. 29, 2000) teaches the formation of phosphate coatings on the surface of a urea granule by first reacting urea with an acid then allowing the acid surface to react with an insoluble phosphate mineral. The reaction with the insoluble phosphate mineral causes the formation of a soluble phosphate salt on the urea surface. The salts formed on the urea surface are typically acidic and help to reduce the volatile nitrogen losses.
Products having acidic coating materials are potentially corrosive to some metals used in fertilizer application equipment when damp. In addition, some micronutrients such as boron are unusable in aqueous acids due to low solubility—e.g. boric acid forms a suspension in phosphoric acid which is difficult to use to form coated products. In addition to the difficulty of handling the boric acid suspension, coated products produced with the suspensions can be sticky with poor flow characteristics.
A number of compounds are known to inhibit urease. Examples are the benzoquinones (Anderson GB 1,142,245; Feb. 5, 1969); dithiocarbamates (Tomlinson GB 1,094,802—Dec. 13, 1967 and Hyson U.S. Pat. No. 3,073,694—Jan. 15, 1963); urea derivatives such as methylurea or thiourea (Sor et. al. U.S. Pat. No. 3,232,740; Feb. 1, 1966); phosphoric triamides (Kolc et. al. U.S. Pat. No. 4,530,714; Jul. 23, 1985); and organic bromine compounds and organic nitrates (Norden et. al. (U.S. Pat. No. 4,576,625; Mar. 18, 1986). Many of these compounds are expensive to use and some can be highly toxic.
In addition to the compounds identified above, metal ions and boron containing salts have been studied as urease inhibitors. Tabatabi (Soil Biology and Biochemistry 9:9-13, 1977) reported on the inhibition of soil urease by various metal ions and other compounds. All soils except one displayed less than 30% inhibition due to sodium tetraborate when used at a rate of 5 mole per gram soil. The exception was the Waller soil which had the lowest pH and lowest urease activity of the soils used in study.
Sor (U.S. Pat. No. 3,388,989; Jun. 18, 1968) discloses the formation of granules containing urea, a urease inhibitor and a hydrocarbon binder. The urease inhibitors revealed include soluble metal salts (Ag, Co, Cu, Hg, Mn, Mo, Pb), soluble borate salts, soluble metal fluorides and formaldehyde. The hydrocarbon binder includes waxes and asphalt. The urea, urease inhibitor and the heat softened hydrocarbon binder are mixed to form a granule. Sor indicates that it is desirable to heat all the ingredients when preparing the fertilizer mixture.
Sor et. al. (U.S. Pat. No. 3,565,599; Feb. 23, 1971) teaches the use of a urease inhibitor such as an alkali metal borate (sodium tetraborate) or boric acid in combination with a hydrophobic substance to reduce the nitrogen loss from urea fertilizers when applied to the soil. The boron source and the hydrophobic substance are preferentially distributed in the urea melt prior to prilling. The hydrophobic substances can include: waxes, vegetable oils, oleyl ether, polyethylene glycol, N-tallow trimethylene diamine, calcium petroleum sulfonate, naphthalene spray oils, octadecylamine and dimethylpolysioxane. The patent, also, claims a coating of octadecyl amine and sodium tetraborate coated unto urea.
Geissler (U.S. Pat. No. 3,523,018; Aug. 4, 1970) discloses the formation of urea granules containing urease inhibitors. The granules are formed by incorporating the inhibitor int
Whitehurst Brooks M.
Whitehurst Garnett B.
,MacCord Mason PLLC
Sayala C.
Whitehurst Associates Inc.
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