Soil Urease Inhibitors Research Articles

Recent Efforts in the Discovery of Urease Inhibitor Identifications.

Urease is an attractive drug target for designing anti-infective agents against pathogens such as Helicobacter pylori, Proteus mirabilis, and Ureaplasma urealyticum. In the past century, hundreds of medicinal chemists focused their efforts on explorations of urease inhibitors. Despite the FDA's approval of acetohydroxamic acid as a urease inhibitor for the treatment of struvite nephrolithiasis and the widespread use of N-(n-butyl)thiophosphoric triamide as a soil urease inhibitor as nitrogen fertilizer synergists in agriculture, urease inhibitors with high potency and safety are urgently needed. Exploration of novel urease inhibitors has therefore become a hot research topic recently. Herein, inhibitors identified worldwide from 2016 to 2021 have been reviewed. They structurally belong to more than 20 classes of compounds such as urea/thioure analogues, hydroxamic acids, sulfonamides, metal complexes, and triazoles. Some inhibitors showed excellent potency with IC50 values lower than 10 nM, having 10000-fold higher potency than the positive control thiourea.

Soil urease inhibition by various plant extracts.

Urea is the most popular and widely used nitrogenous fertilizer. High soil urease activity rapidly hydrolyses applied urea to ammonia which contributes to soil nitrogen (N) losses and reduces N use efficiency of crop plants. The ammonia losses can be minimized by the inhibition of soil urease activity which has been explored using various potential chemical inhibitors. However, the soil urease activity inhibition potential of plant extracts is rarely explored to date. In the present study, extracts of 35 plant materials were taken and evaluated against jack bean urease. Eleven extracts, showing >50% jack bean urease inhibition, were selected and further investigated in 13 soils collected from various districts of Punjab, Pakistan. Interestingly, except Capsicum annum, Melia azedarach, Citrus reticulata and Quercus infectoria, the plant extracts showed urease inhibition activities in soils, the extent of which was lower as compared to that observed in jack bean urease though. Maximum urea hydrolysis inhibition (70%) was noted with Vachellia nilotica which was 40% more than that of hydroquinone (50%) followed by that of Eucalyptus camaldulensis (24%). The extracts of V. nilotica and E. camaldulensis were coated on urea and applied to soil in the next step. At 21st day, 239% and 116% more urea-N was recovered from soil treated with V. nilotica and E. camaldulensis extracts coated urea, respectively, as compared to uncoated urea. Conclusively, these results indicated that the coating of V. nilotica and E. camaldulensis extracts on urea prills prolonged urea persistence in soil owing to minimum urea hydrolysis, probably, the extracts of V. nilotica and E. camaldulensis showed their urease inhibition potential. The results of this study provide a base line for the identification of new soil urease inhibitor compounds from plant materials in future.

Organosulfur Compounds as Soil Urease Inhibitors and Their Effect on Kinetics of Urea Hydrolysis

Organosulfur Compounds as Soil Urease Inhibitors and Their Effect on Kinetics of Urea Hydrolysis

Degradation of Allicin as Urease Inhibitor Affected by Soil Conditions and Its Effect on Kinetic Properties of Soil Urease

ABSTRACT Allicin is an organosulfur compound from garlic that has shown potential as a soil urease inhibitor. However, little information was available on the degradation of allicin in different soil conditions and its effect toward kinetic properties of urease enzyme. Degradation of allicin was quantified by measuring the remaining concentration of allicin using high performance liquid chromatography (HPLC). The outcomes of the study showed allicin is able to retain longer than 24 h when moisture of soil was at 30% compared to 50 and 100% soil moisture levels. Meanwhile, when the temperature increased from 25 to 35ºC, the percentage of allicin decreased significantly. Contrary to this, as pH of soil increased to 6.5, the rate degradation of allicin was slower compared to pH 4.5 and 5.5. The Michaelis constant (Km ) is increased while the maximum enzyme reaction velocity (Vmax ) decreases after 24 h incubation compared to control showing inhibition of urease enzymes by allicin. Overall results revealed that the effectiveness of allicin as urease inhibitor was significantly related to its degradation rate in soil.

Evaluation of Nutrisphere‐N as an Inhibitor of Urease in Soils with pH Values Near Five

Core IdeasA recent paper showed that Nutrisphere‐N inhibits purified urease at pH 5.0.Nutrisphere‐N was tested as a urease inhibitor with soils near pH 5.0.Nutrisphere‐N did not inhibit urease activity in soils near pH 5.0.Nutrisphere‐N is a maleic‐itaconic polymer (MIP) marketed as a soil urease inhibitor. Recently, it was shown that the MIP in Nutrisphere‐N was able to inhibit purified urease at a pH of 5.0. Furthermore, Ni was removed from purified urease by MIP at a pH of 5.0. The objective of this study was to determine if these findings with purified urease at pH 5.0 could be replicated with soils with pH values near 5.0. Three soils with pH values of 4.5, 5.2, and 5.7 were incubated with 5 μg g–1ofN‐(n‐butyl) thiophosphoric triamide (NBPT) as Agrotain Ultra, and 5 and 50 μg g–1of MIP as Nutrisphere‐N. The inhibitors were allowed to react with the soil for 1 d before application of urea (sequential application) or applied at the same time as urea (simultaneous application). For the sequential application, 5 μg g–1of NBPT as Agrotain Ultra inhibited soil urease activity by 49%, versus –3 and –1% for 5 and 50 μg g–1of MIP as Nutrisphere‐N (average of three soils). For the simultaneous application, averaged across the three soils, 5 μg g–1of NBPT inhibited soil urease activity by 59%, versus –1 and −4% for 5 and 50 μg g–1of MIP. The observation that MIP inhibits purified urease at a pH of 5.0 could not be repeated with soils with pH values near 5.0. It remains to be demonstrated that Nutrisphere‐N functions as a soil urease inhibitor at the concentrations likely to be applied to soil.

Evaluation of Allicin as Soil Urease Inhibitor

Urea is the most widely used form of N fertilizer in agriculture. However, if it is not incorporated into soil soon after application, urea has the disadvantage of undergoing considerable losses as ammonia gas due to hydrolysis in the presence of soil urease. Urease inhibitors are some of the most commonly used approaches to overcome nitrogen losses in fields, as they delay urea hydrolysis and thus increase the chances of urea incorporation into soil. Among the known soil urease inhibitors is the chemical based N(butyl) thiophosphoric triamide (NBPT) but it is found to cause some phytotoxic effect on plants among assimilation issues. Allicin, a natural based bio-inhibitor from garlic (Allium sativum L.), has shown potential to inhibit urease activity. In this context, laboratory experiments were conducted to examine the effect of different allicin concentrations on soil urease inhibition period. The loss of applied urea was quantified, using diacetylmonoxime (DAM) calorimetric method, following application of urea with and without allicin. Urea and a mixture of urea and allicin at different concentrations (5%, 10% and 15% w allicin/w urea) were surface-applied at a rate of 1000μg Urea N/kg soil to small circular containers. The soil was irrigated to maintain the moisture content between 25-30% throughout the study. This study suggest that prilled form urea application gave more consistent results than when urea was dissolved and added to the soil as a solution. Through this study, it was shown that allicin exerts inhibitory effects on urease in soil for agricultural applications, where 5% weight allicin to weight urea applied resulted in the best urease inhibition. At the given operating parameters, allicin inhibition was about 75% less than NBPT at steady state. While this study demonstrated the potential of allicin as a viable bio-inhibitor to retard the loss of urea in soil and thus it may be used along with urea for improved utilization of the applied –N by plants.

A Comparison of a Maleic‐Itaconic Polymer and N‐(n‐butyl) Thiophosphoric Triamide as Urease Inhibitors

A maleic‐itaconic polymer (MIP) is claimed to inactivate soil urease by nickel removal from the enzyme. Four studies were conducted to compare the urease inhibition properties of two commercial formulations of MIP with a commercial formulation of N‐(n‐butyl) thiophosphoric triamide (NBPT). In the first study, addition of MIP at 1, 5, or 50 mg kg–1 provided 0 to 2% inhibition of urea hydrolysis, averaged across three soils. At 500 mg kg–1, MIP inhibited urea hydrolysis by 7 to 9%, averaged across three soils. By contrast, addition of NBPT at 1 or 5 mg kg–1 inhibited urea hydrolysis by an average of 64 and 72%, respectively. In a second study, 13 carboxylic acids of known nickel sequestration properties, two MIP formulations, and NBPT were evaluated as soil urease inhibitors. Averaged across three soils, MIP and the other carboxylic acids provided <5% inhibition of urea hydrolysis when applied at 50 mg kg–1. Addition of NBPT at 1 and 5 mg kg–1 provided an average of 62 and 72% inhibition. In two additional studies using purified jackbean [Canavalia ensiformis (L.) DC.] urease in the absence of soil, NBPT provided complete inhibition at a concentration of 1 mg L–1 in the reaction mixture. Adding MIP at rates up to 100 mg L–1 either did not inhibit urease, or stimulated urea hydrolysis. It was concluded that MIP was not an effective inhibitor of soil or jackbean urease. It was also concluded that nickel sequestration by carboxylic acids is an unlikely mode of action for soil urease inhibition.

Evaluation of ammonium thiosulfate as a soil urease inhibitor

Interest in use of ammonium thiosulfate (ATS) in conjunction with urea as a fertilizer has been stimulated by recent reports that this compound retards hydrolysis of urea by soil urease and thereby reduces volatilization of urea N as ammonia from soils fertilized with urea. We evaluated ATS as a soil urease inhibitor by studying its effects on urea hydrolysis, seed germination, and early seedling growth in soil. We found that ATS significantly retarded urea hydrolysis only when applied at rates as high as 2,500 or 5,000µg g−1 soil, whereasN-(n-butyl) thiophosphoric triamide (NBPT) (a patented inhibitor of urea hydrolysis in soil) caused substantial retardation of urea hydrolysis when applied at rates as low as 1µg g−1 soil. We also found that ATS had an adverse effect on germination of corn or wheat seeds in soil when applied at the rate of 2,500 or 5,000µg g−1 soil and caused a dramatic reduction of early seedling growth of corn or wheat when applied at the rate of 1,000, 2,500, or 5,000µg g−1 soil. These findings indicate that ATS has little, if any, potential value for retarding hydrolysis of urea fertilizer in soil.

Potential phytotoxicity associated with the use of soil urease inhibitors

Recent work in our laboratory showed that the adverse effect of urea fertilizer on seed germination and seedling growth in soil is due to ammonia produced through hydrolysis of urea by soil urease (NH(2)CONH(2) + H(2)O --> 2NH(3) + CO(2)) and can be eliminated by amending the fertilizer with a small amount of a urease inhibitor such as N-(n-butyl)thiophosphoric triamide or phenylphosphorodiamidate. Continuation of this work showed that these inhibitors can induce leaf-tip necrosis in plants. Research to account for this phytotoxicity indicated that it resulted from an accumulation of toxic amounts of urea in plants through inhibition of urease activity by N-(n-butyl)thiophosphoric triamide and phenylphosphorodiamidate. Support for this conclusion was provided by experiments showing that these urease inhibitors increased both leaf-tip necrosis and urea concentrations in wheat (Triticum aestivum L.) and sorghum [Sorghum bicolor(L.) Moench] plants grown in soils treated with urea and that the necrotic areas of such plants had a much higher concentration of urea than did the nonnecrotic areas. The potential of urease inhibitors for inducing phytotoxicity should not preclude their use to eliminate the adverse effects of urea fertilizers on seed germination and seedling growth in soil because the ammonia produced through hydrolysis of urea fertilizer by urease is much more detrimental to plant growth than is the urea accumulation induced by urease inhibitors.

Evaluation of phenoxyaminocyclotriphosphazatrienes as sustained-action soil urease inhibitors

Evaluation of phenoxyaminocyclotriphosphazatrienes as sustained-action soil urease inhibitors

Effect of soil bulk density on inhibition of hydrolysis of surface‐applied granular urea containing phenyl phosphorodiamidate in unsaturated soil

Abstract Soil bulk density markedly influences hydrolysis of surface‐applied granular urea that is vulnerable to serious ammonia volatilization losses. In order to decrease the ammonia losses by retarding urea hydrolysis, several chemicals have been tested for their soil urease inhibition properties. Phenyl phosphorodiamidate (PPDA) is a potent soil urease inhibitor. Laboratory studies using soil column incubations were conducted to investigate the effect of soil bulk density on inhibition of hydrolysis of surface‐applied urea granules (=20 mg of urea/granule) containing 1% PPDA in unsaturated soils. The increase in soil bulk density (from 0.69 to 1.50 Mg/m3) markedly increased the rate of hydrolysis of surface‐applied urea granules and significantly decreased the apparent urease inhibition by PPDA present in the granules. These results are attributed to the probable spatial separation of urea and PPDA because of the differences in diffusive transports in unsaturated soils caused in part by differences in...

Evaluation of some phosphoroamides as soil urease inhibitors

The effectiveness of six phosphoroamides for retardation of urea hydrolysis in soils was studied by determining the effects of 10 μg g−1 soil of each compound on the amounts of urea hydrolyzed when soils treated with urea were incubated at 10°, 20°, 30°, and 40°C for 3, 7, and 14 days. The phosphoroamides used wereN-(diaminophosphinyl)-cyclohexylamine,N-benzyl-N-methyl phosphoric triamide, diethyl phosphoric triamide, trichloroethyl phosphorodiamidate, dimethyl phosphoric triamide, andN-butyl phosphorothioic triamide [N-(n-butyl) thiophosphoric triamide]. The soils used were selected to obtain a range in properties, and the effects of the six phosphoroamides studied were compared with those of two compounds known to be among the most effective compounds thus far proposed for retardation of urea hydrolysis in soils (phenylphosphorodiamidate and hydroquinone). The data obtained showed that all six of the phosphoroamides evaluated compared favorably with hydroquinone as soil urease inhibitors and that two of them [N-butyl phosphorothioic triamide andN-(diaminophosphinyl)-cyclohexylamine] were superior to phenylphosphorodiamidate for retardation of urea hydrolysis in soils at 20°, 30°, or 40°C.

Evaluation of N‐butyl phosphorothioic triamide for retardation of urea hydrolysis in soil

Abstract Work reported showed that N‐butyl phosphorothioic triamide (NBPT) is considerably more effective than phenylphosphorodiamidate (PPD) as a soil urease inhibitor and merits consideration as a fertilizer amendment for retarding hydrolysis of urea fertilizer in soil. Studies to determine the factors influencing the effectiveness of NBPT for retardation of urea hydrolysis in soil showed that the inhibitory effect of NBPT on hydrolysis of urea by soil urease increased markedly with the amount of NBPT added and decreased markedly with time and with increase in temperature from 10 to 40°C. They also showed that the ability of NBPT to retard urea hydrolysis in 13 surface soils selected to obtain a wide range in properties was significantly correlated with organic C content (r = ‐0.70**), total N content (r = ‐0.76**), cation‐exchange capacity (r = ‐0.67* ), sand content (r = 0.61*), clay content (r = ‐0.63*), and surface area (r = ‐0.66*), but was not significantly correlated with pH, silt content, urease...

Inhibition of Urease Activity by Heterocyclic Sulfur Compounds

AbstractThe inhibition of both jack bean urease and soil urease by several heterocyclic mercaptans was investigated. The following compounds not previously tested as urease inhibitors were found to be effective inhibitors of jack bean urease: 1,3,4‐thiadiazole‐2,5‐dithiol; 5‐mercapto‐3‐phenyl‐1,3,4‐thiadiazole‐2‐thione; and 5‐amino‐1,3,4‐thiadiazole‐2‐thiol. The disulfides of the latter two compounds were found to be very potent inhibitors of jack bean urease. The results are consistent with an inhibition mechanism involving a thiol‐disulfide exchange reaction between a disulfide and one or more of the sulfhydryl groups of urease. The results also imply that inhibition of urease by the heterocyclic mercaptans was due to trace amounts of the corresponding disulfides or polysulfides in the mercaptan preparations. A number of heterocyclic mercaptans, two disulfides, and a number of known urease inhibitors were evaluated as soil urease inhibitors, and the following compounds were the most effective: 1,4‐benzoquinone ∼ hydroquinone > 2,5‐dimethyl‐1,4‐benzoquinone ∼ catechol ∼ 1,3,4‐thiadiazole‐2,5‐dithiol ∼ 2,6‐dimethyl‐1,4‐benzoquinone.

Germination of Wheat and Alfalfa Seeds as Affected by Some Soil Urease Inhibitors1

AbstractThe use of urease inhibitors has been proposed as a means of controlling the rate of urea hydrolysis in soils. However, application of enzyme inhibitors to soils may affect other soil processes in addition to urea hydrolysis.The purpose of this study was to determine whether soil urease inhibitors would affect the germination of wheat (Triticum aestivum L.) and alfalfa (Medicago sativa L) seeds. Soil urease inhibitors included in this study were; catechol, p‐benzoquinone, 2,5‐dimethyl‐p‐benzoquinone, hydroquinone, 1,2‐napthoquinone, benzohydroxamic acid, and phenylmercuric acetate.In the initial study, 0.003, 0.015 or 0.03 g of each inhibitor was applied to wheat or alfalfa seeds that had been placed on moist paper towelling. Germination percentage was recorded after incubating the seeds for 8 days at 20 C. At the highest rate of inhibitor application all inhibitors caused a noticeable decrease in the germination percentages of seeds of both species. Only catechol and 1,2‐napthoquinone had no effect on seed germination at the low rate of 0.003 g/plate. In a second experiment, seeds were germinated in moist soil in the presence of inhibitors applied at the rates of 100, 50, or 10 ppm of soil. No compounds affected germination when applied at 10 ppm of soil and at the higher rates, only 2,5‐dimethyl‐p‐benzoquinone caused severe reduction in the germination percentages recorded for both species.

Effects of urease inhibitors on nitrification in soils

The effects of 10 urease inhibitors on nitrification in soils were studied by determining the effects of 10 and 50 parts/10 6 (soil basis) of each inhibitor on the amounts of nitrate and nitrite produced when soils treated with ammonium sulfate (200 μg of ammonium N/g of soil) were incubated (30°C) under aerobic conditions for 14 days. The urease inhibitors used (catechol. hydroquinone, p-benzoquinone, 2,3-dimethyl- p-benzoquinone, 2,5-dimethyl- p-benzoquinone. 2,6-dimethyl- p-benzoquinone. 2,5-dichloro- p-benzoquinone, 2,6-dichloro- p-benzoquinone. sodium p-chloromercuribenzoate, and phenylmercuric acetate) were those found most effective in previous work to evaluate more than 130 compounds as soil urease inhibitors. Their effects on nitrification were compared with those of three compounds patented as soil nitrification inhibitors (N-Serve. AM. and ST). Most of the urease inhibitors studied had little effect on nitrification when applied at the rate of 10 μg/g of soil. but had marked inhibitory effects when applied at the rate of 50 μg/g of soil. None inhibited nitrification as effectively as N-Serve. but phenylmercuric acetate inhibited nitrification more effectively than did AM or ST when applied at the rate of 10 μg/g of soil. Phenylmercuric acetate, 2,5-dimethyl- p-benzoquinone, and 2,6-dimethyl- p-benzoquinone had very marked effects on nitrification when applied at the rate of 50 μg/g of soil.

Inhibition of urease activity in soils

Studies to evaluate more than 100 compounds as inhibitors of urease activity in soils showed that dihydric phenols and quinones were the most effective organic compounds tested and that silver and mercury salts were the most effective inorganic compounds. When the most potent inhibitors were compared using 50 μg of inhibitor per g of soil, their effectiveness decreased in the order: catechol > phenylmercuric acetate > hydroquinone > p-benzoquinone and 2,5-dichloro- p-benzoquinone > 2,6-dichloro- p-benzoquinone > silver sulfate > 1,2-naphthoquinone > phenol > mercuric chloride > sodium p-chloromercuribenzoate and 4-chlorophenol > 2,5-dimethyl- p-benzoquinone > N-ethylmaleimide > gold chloride > aceto-hydroxamic acid and copper sulfate. The inhibitory effects of most of these compounds on soil urease activity decreased markedly with time, but the effect of 2,5-dimethyl- p-benzoquinone increased, presumably because this compound is decomposed in soils to a relatively stable product more effective than the parent compound as a soil urease inhibitor. The findings concerning the rates of inactivation of urease inhibitors in soils indicate that, of the various compounds tested, 2,5-dimethyl- p-benzoquinone, 2,5-dichloro- p-benzoquinone, and 2,6-dichloro- p-benzoquinone are likely to prove the most effective for retardation of urea decomposition in soils and reduction of the problems caused by the normally rapid hydrolysis of fertilizer urea by soil urease. N-Serve and other compounds used to inhibit nitrification in soils have very little, if any, effect on soil urease activity.