FIELD OF THE INVENTION

The present invention is directed to fertilizer compositions including urea and a water soluble alkenylphenyl sulfonate polymer which serves to inhibit the decomposition of urea by the action of urease enzyme. More particularly, the invention is concerned with such compositions, methods of fertilizing soils using the compositions, methods of preparing fertilizer compositions, and methods of inhibiting soil-borne urease through use of an alkenylphenyl sulfonate polymer, such as polystyrene sulfonate.

BACKGROUND

Urea is the most widely used form of nitrogenous fertilizer, and is formulated as dry granules, prills, or as fluids made up of urea alone or mixed with ammonium nitrate as UAN (a mixture containing urea, ammonium nitrate, and water). Urea is also present in animal manures. These forms of urea have a significant disadvantage in that they undergo rapid decomposition and generate ammonia gas when applied to soil. This is due to the presence of urease enzyme in soils, which reacts with urea to produce ammonium bicarbonate and ammonia. This general set of processes is known in the art as volatilization. Volatilization results in decreased efficiency of nitrogen fertilizer use, lower yields, plant symptoms of nitrogen deficiency, undesirable odors, and potentially harmful ammonia gas concentrations.

In response to these problems, considerable research has been done towards the development of urease enzyme inhibitors. For example, catechol, benzoquinone, and related compounds have been shown to be effective urease inhibitors; however, problems relating to cost, safety, convenience, and stability have limited the use of these types of inhibitors. A number of phosphoramide compounds have also long been known to act as effective urease inhibitors. One such compound, N-(n-butyl) thiophosphoric triamide (NBPT) has achieved substantial commercial use in products such as the Agrotain® family of inhibitors.

However, NBPT products require storage at temperatures that do not exceed 36-38° C., which can be problematical for some distributors and users. Moreover, these products may be subjected to temperature conditions during transport or storage, unbeknownst to the ultimate user; in such cases, the products may be substantially below label strengths in terms of active ingredients. Research has also shown that up to 40% of the NBPT content of commercial fertilizer products including NBPT may be lost after storage at 25° C. for three months and, after six months, over 99% of the NBPT content was lost.

Another very important problem related to NBPT urease inhibition is that while it is effective for inhibiting soil-borne urease, it also inhibits urease in plants causing urea to accumulate in plant tissues. This phenomenon is harmful to plants and can result severe tissue necrosis. NBPT can also negatively affect modes of urea uptake and assimilation by plant roots, corn in particular. As such, even when NBPT is successfully used for soil-borne urease inhibition, this may cause a significant decrease in plant yield. In some cases, NBPT inhibitors are not cost effective, in that the expense of purchasing and applying the inhibitors does not result in sufficiently increased yields to justify the usage.

A number of polymeric materials can serve as urease inhibitors. For example, as disclosed in US Patent Publication No. 2008/0173053, carboxylate polymers in partial salt form, and especially maleic-itaconic copolymer salts, may be employed as useful inhibitors. It is believed that these polymers interact with nickel atoms urease enzyme to generate an inhibitory response.

Background references include: U.S. Pat. Nos. 9,249,102, 8,980,893, 8,969,554, 8,951,636, 8,946,270, 8,864,867, 8,841,100, 8,642,636, 8,618,126, 8,575,067, 8,568,505, 8,461,176, 8,426,460, 8,361,184, 8,198,214, 8,197,572, 8,110,017, 5,489,370, and 5,405,509; and US Patent Publications Nos. 2016/0045841, 2015/0366186, 2015/0359221, 2015/0319945, 2015/0203457, 2015/0183785, 2015/0174255, 2015/0158776, 2015/0126/23, 2014/0349375, 2014/0315794, 2014/0179746, 2014/0142114, 2014/0076012, 2013/0111960, 2013/0108872, 2013/0102468, 2013/0065967, 2012/0220667, 2012/0198899, 2011/0269920, 2011/0269919, 2011/0245157, 2011/0226028, 2011/0152312, 2011/0136210, 2011/0105623, 2010/0144859, 2010/0125089, 2009/0229331, 2007/0066487, and 2006/0154824.

Focused searching has developed the following references: U.S. Pat. Nos. 8,241,387, 7,666,241, 7,494,525, 6,489,438, 5,190,797, 4,832,728, 4,789,391, 4,756,738, 4,752,317, 3,565,599, and 2,689,173; US Patent Publications No. 2002/0042346; Foreign Publication Nos. WO 1987006575, WO 1989003811, WO2015031521, WO2015179552; and non-patent literature references Ambrose et al., “Inhibition of Urease by Sulfur Compounds”JACS,1950, Vol. 72, pp 317-321; Lukowska et al., “Preparation of Sulfonated Polysulfone Membrane for Enzymes Immobilisation”Biocybernetics and Biomedical Engineering,2012, Vol. 32, pp 77-86; and Upadhyay, “Urease Inhibitors: A Review”Indian Journal of Biotechnology,2012, Vol. 11, pp 381-388.

PCT Publication WO 89/03811 describes sulfonated polymer coatings used for the preparation of controlled release fertilizer products, such as urea and ammonium sulfate fertilizers. One goal is to reduce nitrogen losses by controlling the release of nitrogen from the coated fertilizers. In order to obtain such controlled or slow-release fertilizer products, it is essential that the applied polymers be essentially water insoluble. As set forth on p. 12, II. 15-29 of the ‘811 reference, the controlled release coatings include a water insoluble sulfonated polymer dissolved in an organic solvent system. The polymers include a maximum of about 200 milliequivalents (meq.) of pendant sulfonate groups per 100 g of polymer. This translates to a maximum of 25 mole % of pendant sulfonate groups. Usable polymers in accordance with the ‘811 reference may also include substantial amounts of hydrocarbon (aliphatic and/or aromatic) repeat units, such as butyl, ethylene, propylene, isobutylene, and vinyl repeat units (p. 13, II. 1-20 and pp. 15-16).

There is accordingly a need in the art for improved urease inhibitors which are more effective, are less expensive, and do not have the problems associated with prior products of this type.

SUMMARY OF THE INVENTION

The present invention overcomes the problems outlined above and provides urease inhibitors which can be used in conjunction with nitrogen-containing fertilizers, e.g., urea fertilizers in order to significantly reduce fertilizer urea decomposition. The inhibitor compositions include one or more water soluble polymers having alkenylphenyl sulfonate repeat units in a quantity sufficient to inhibit the decomposition of urea by the action of soil-borne urease enzyme. It has been found that the inhibitors of the invention provide substantially greater urease inhibition at substantially smaller rates of use, as compared with prior art inhibitors, such as NBPT.

The inhibitor polymers may be in the form of homopolymers such as polystyrene sulfonate, or as copolymers including other sulfonated or non-sulfonated repeat units; the latter would advantageously be carboxylate or dicarboxylate repeat units. Moreover, the polymers may be used in free acid, partial salt, or complete salt forms. The amounts of inhibitor polymers used are very small, owing to the very high urease inhibition properties thereof.

The inhibitors may be directly applied to soil, or mixed with solid or liquid urea-containing fertilizers, and applied using conventional techniques. In either case, the inhibitors serve to substantially prevent decomposition of urea.

Polystyrene sulfonate polymers in the free acid or salt (typically sodium or calcium salt) form are highly suitable for use in the invention. Such polymers are commercially available from a number of sources, or can be synthesized using well-known methods.

The useful polymers of the invention have two properties: first, the polymers contain sufficient alkenylphenyl repeat units to provide enhanced inhibition of soil-borne enzyme-induced urea decomposition; and second, the polymers, whatever their repeat unit makeup apart from the necessary presence of alkenylphenyl repeat units, must be sufficiently water soluble.

In embodiments, the subject matter described herein is directed to fertilizer compositions comprising one or more water soluble polymers having alkenylphenyl sulfonate repeat units in a quantity sufficient to inhibit the decomposition of urea by the action of soil-borne urease enzyme.

In embodiments, the subject matter described herein is directed to methods of inhibiting urease activity in soil comprising contacting the soil with one or more water soluble polymers having alkenylphenyl sulfonate repeat units in a quantity sufficient to inhibit the decomposition of urea by the action of soil-borne urease enzyme. The polymers can be admixed with a fertilizer prior to use, such as contacting with the soil.

In embodiments, the subject matter described herein is directed to methods of preparing a nitrogen-containing fertilizer composition comprising one or more water soluble polymers having alkenylphenyl sulfonate repeat units in a quantity sufficient to inhibit the decomposition of urea by the action of soil-borne urease enzyme.

Still other embodiments are described herein.

