BACKGROUND OF THE INVENTION

Field of the Invention

The present invention is directed to compositions and methods for controlling enzyme-induced urea decomposition attendant to the application of solid or liquid urea-containing fertilizers to soils. More particularly, it is concerned with selected triarylmethane compounds found to be highly effective urease inhibitors, either alone or in combination with tetrapolymer synergists. The compositions of the invention have good storage stability, long-lived activity in soil, and avoid the toxicity issues common with present-day urease inhibitors used in agriculture.

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. 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. For example, an article by J. H. Quastel, entitled, “CXLIX. The Action of Polyhydric Phenols on Urease; the Influence of Thiol Compounds” (Biochem J. 1933:27(4):1116-1122), described experiments confirming that these compounds were effective urase inhibitors at concentrations of about 1 ppm by weight in solution. See also, “CC. The Action of Dyestuffs on Enzymes. III. Urease” (Biochem J. 1932:26(5):1685-1696). However, for reasons of cost, safety, convenience, stability, and ease of use, these compounds are not currently used for urease inhibition on a commercial scale. Moreover, subsequent research has determined that the urease-control effects of these small molecules is essentially short term, on the order of 3-14 days.

A number of phosphoramide compounds are 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 in 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. Hendrickson teaches (J. Prod. Agric., 5:131-137 (1992)) that on average, when used with UAN, NBPT gives about 1.6 bushels/acre average improvement in yield (Hendrickson FIG. 3), with about 40% of trials resulting in yield losses (this being result of 87 trials and 487 comparisons).

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.

Other references include: 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, ll. 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, ll. 1-20 and pp. 15-16).

Despite these research efforts, there still remains a significant need in the art for improved methods and compositions for controlling enzyme-induced urea decomposition.

SUMMARY OF THE INVENTION

The present invention overcomes the problems outlined above and provides methods and compositions which are highly effective in the control of enzyme-induced urea decomposition. Generally speaking, the compositions include triarylmethane compounds having a central carbon atom bonded with three individual six-membered aryl groups having specific substituents bonded at various positions around the aryl groups. Particular examples include catechol-like compounds (e.g., catechol violet and related compounds), and compounds where at least one of the aryl groups includes at least one amine, with optional alkylation of the amine(s), such as polymethylated pararosanilines. Some of the compounds are dye materials having the added advantage of serving as pH-dependent colorants for the compositions.

Additionally, certain tetrapolymers, when used with the triarylmethane compounds, provide a synergistic improvement in urease inhibition. Such tetrapolymers are polyanionic in character, and also include aliphatic sulfonate groups bonded to the polymer backbone, at a level of at least about 1 mol percent. Advantageously, the polymeric synergists include maleic, itaconic, and sulfonate repeat units

