Rate Of Urea Hydrolysis Research Articles

A novel approach for stabilizing fresh urine by calcium hydroxide addition

In this study, we investigated the prevention of enzymatic urea hydrolysis in fresh urine by increasing the pH with calcium hydroxide (Ca(OH)2) powder. The amount of Ca(OH)2 dissolving in fresh urine depends significantly on the composition of the urine. The different urine compositions used in our simulations showed that between 4.3 and 5.8 g Ca(OH)2 dissolved in 1 L of urine at 25 °C. At this temperature, the pH at saturation is 12.5 and is far above the pH of 11, which we identified as the upper limit for enzymatic urea hydrolysis. However, temperature has a strong effect on the saturation pH, with higher values being achieved at lower temperatures. Based on our results, we recommend a dosage of 10 g Ca(OH)2 L−1 of fresh urine to ensure solid Ca(OH)2 always remains in the urine reactor which ensures sufficiently high pH values. Besides providing sufficient Ca(OH)2, the temperature has to be kept in a certain range to prevent chemical urea hydrolysis. At temperatures below 14 °C, the saturation pH is higher than 13, which favors chemical urea hydrolysis. We chose a precautionary upper temperature of 40 °C because the rate of chemical urea hydrolysis increases at higher temperatures but this should be confirmed with kinetic studies. By considering the boundaries for pH and temperature developed in this study, urine can be stabilized effectively with Ca(OH)2 thereby simplifying later treatment processes or making direct use easier.

Urea Hydrolysis Rate in Soil Toposequences as Influenced by pH, Carbon, Nitrogen, and Soluble Metals.

A simultaneous increase in the use of urea fertilizer and the incidence of harmful algal blooms worldwide has generated interest in potential loss pathways of urea from agricultural areas. The objective of this research was to study the rate of urea hydrolysis in soil profile toposequences sampled from the Coastal Plain (CP) and Piedmont (PM) regions of Maryland to understand native urea hydrolysis rates (UHRs) as well as the controls governing urea hydrolysis both across a landscape and with depth in the soil profile. A pH-adjustment experiment was conducted to explore the relationship between pH and urea hydrolysis because of the importance of pH to both agronomic productivity and microbial communities. Soils were sampled from both A and B horizons along transects containing an agricultural field (AG), a grassed field border (GB), and a perennially vegetated zone adjacent to surface water. On average, the A-horizon UHRs were eight times greater than corresponding B-horizon rates, and within the CP, the riparian zone (RZ) soils hydrolyzed urea faster than the agricultural soils. The pH adjustment of these soils indicated the importance of organic-matter-related factors (C, N, extractable metals) in determining UHR. These results suggest that organic-matter-rich RZ soils may be valuable in mitigating losses of urea from neighboring fields. Additional field-scale urea hydrolysis studies would be valuable to corroborate the mechanisms described herein and to explore the conditions affecting the fate and transport of urea in agroecosystems.

Isolation and identification of Pseudomonas azotoformans for induced calcite precipitation.

Biomineralization is a process by which living organisms produce minerals. The extracellular production of these biominerals by microbes has potential for various bioengineering applications. For example, crack remediation and improvement of durability of concrete is an important goal for engineers and biomineral-producing microbes could be a useful tool in achieving this goal. Here we report the isolation, biochemical characterization and molecular identification of Pseudomonas azotoformans, a microbe that produces calcite and which potentially be used to repair cracks in concrete structures. Initially, 38 bacterial isolates were isolated from soil and cements. As a first test, the isolates were screened using a urease assay followed by biochemical tests for the rate of urea hydrolysis, calcite production and the insolubility of calcite. Molecular amplification and sequencing of a 16S rRNA fragment of selected isolates permitted us to identify P. azotoformans as a good candidate for preparation of biotechnological concrete. This species was isolated from soil and the results show that among the tested isolates it had the highest rate of urea hydrolysis, produced the highest amount of calcite, which, furthermore was the most adhesive and insoluble. This species is thus of interest as an agent with the potential ability to repair cracks in concrete.

Estimation of a biofilm-specific reaction rate: kinetics of bacterial urea hydrolysis in a biofilm

Background/Objectives:Biofilms and specifically urea-hydrolysing biofilms are of interest to the medical community (for example, urinary tract infections), scientists and engineers (for example, microbially induced carbonate precipitation). To appropriately model these systems, biofilm-specific reaction rates are required. A simple method for determining biofilm-specific reaction rates is described and applied to a urea-hydrolysing biofilm.Methods:Biofilms were grown in small silicon tubes and influent and effluent urea concentrations were determined. Immediately after sampling, the tubes were thin sectioned to estimate the biofilm thickness profile along the length of the tube. Urea concentration and biofilm thickness data were used to construct an inverse model for the estimation of the urea hydrolysis rate.Results/Conclusions:It was found that urea hydrolysis in Escherichia coli MJK2 biofilms is well approximated by first-order kinetics between urea concentrations of 0.003 and 0.221 mol/l (0.186 and 13.3 g/l). The first-order rate coefficient (k1) was estimated to be 23.2±6.2 h−1. It was also determined that advection dominated the experimental system rather than diffusion, and that urea hydrolysis within the biofilms was not limited by diffusive transport. Beyond the specific urea-hydrolysing biofilm discussed in this work, the method has the potential for wide application in cases where biofilm-specific rates must be determined.

Whole cell kinetics of ureolysis by Sporosarcina pasteurii.

Ureolysis drives microbially induced calcium carbonate precipitation (MICP). MICP models typically employ simplified urea hydrolysis kinetics that do not account for cell density, pH effect or product inhibition. Here, ureolysis rate studies with whole cells of Sporosarcina pasteurii aimed to determine the relationship between ureolysis rate and concentrations of (i) urea, (ii) cells, (iii) NH4+ and (iv) pH (H(+) activity). Batch ureolysis rate experiments were performed with suspended cells of S.pasteurii and one parameter was varied in each set of experiments. A Michaelis-Menten model for urea dependence was fitted to the rate data (R(2) =0·95) using a nonlinear mixed effects statistical model. The resulting half-saturation coefficient, Km , was 305mmoll(-1) and maximum rate constant, Vmax , was 200mmoll(-1) h(-1) . However, a first-order model with k1 =0·35h(-1) fit the data better (R(2) =0·99) for urea concentrations up to 330mmoll(-1) . Cell concentrations in the range tested (1×10(7) -2×10(8) CFUml(-1) ) were linearly correlated with ureolysis rate (cell dependent Vmax'=6·4×10(-9) mmolCFU(-1) h(-1) ). Neither pH (6-9) nor ammonium concentrations up to 0·19moll(-1) had significant effects on the ureolysis rate and are not necessary in kinetic modelling of ureolysis. Thus, we conclude that first-order kinetics with respect to urea and cell concentrations are likely sufficient to describe urea hydrolysis rates at most relevant concentrations. These results can be used in simulations of ureolysis driven processes such as microbially induced mineral precipitation and they verify that under the stated conditions, a simplified first-order rate for ureolysis can be employed. The study shows that the kinetic models developed for enzyme kinetics of urease do not apply to whole cells of S.pasteurii.

Statistical Modeling of Environmental Factors on Microbial Urea Hydrolysis Process for Biocement Production

Calcium carbonate is a widely used raw material by many industries. It can be precipitated through microbial process within soil pores as cementitious bonding agent between grains for geotechnical applications. It is called microbially induced calcium carbonate precipitation (MICP). Designing an appropriate biogrout material for injection into soil is essential for controlling the amount, type, time, and place of the biocement production within pores. For this purpose, understanding the active reactions and the kinetics of bacterial growth and urea hydrolysis is necessary. A conductometric method and spectrophotometry were used in this study to, respectively, monitor the urea hydrolysis reaction progress and bacterial growth inS. pasteurii-inoculated urea-NB-NH4Cl solution at different level of the environmental factors that are initial cell concentration, urea concentration, and temperature. Variation in conductivity of the solution versus logarithmic scale of time was depicted as microbial ureolysis characteristic curve (MUCC) through which lag duration, specific rate, and potential of urea hydrolysis at each condition were obtained. Central composite face-centered (CCF) design, which is one of the response surface methodologies, was employed to statistically fit polynomial models explaining the bacterial growth and the characteristics obtained from MUCCs in terms of the environmental factors and their interactions. An optimization analysis based on the urea-normalized responses was also carried out.

Flexible film-type catalysts encapsulating urease within κ-carrageenan hydrogel network

Flexible film-type catalysts were synthesized by encapsulating urease within a κ-carrageenan gel network supported on a cellulose-acetate membrane filter. Synthesized film-type catalysts are flexible and can be easily formed into a shape that is suitable for a specific process configuration. The filter membrane has macropores about 200nm, which are formed by interconnected bead-shaped membrane material. Scanning electron microscopy shows that the surface of the membrane material is coated homogeneously with the κ-carrageenan hydrogel. Urease entrapped within the gel network hardly leaches out during urea hydrolysis catalysis conducted at 310K in a batch reactor and exhibits high catalytic performance. Analysis of the reaction data by the Michaelis–Menten equation shows that the film-type catalyst shows kinetic parameters (KM and Vmax) and apparent activation energy (24kJmol−1), which are all similar to those found for free urease. Estimation of the mass transfer rate of urea within the κ-carrageenan network and the urea hydrolysis rate show that the diffusion rate of urea within the thin film is five orders of magnitude higher than the reaction rate. The film catalyst can be recycled at least 7 times with <20% decrease in activity. High flexibility as well as high catalytic performance of the film catalyst shows prospective features of this catalyst for future applications.

Predicting Urea Hydrolysis in a Loblolly Pine Forest Floor

In a pine forest, urea hydrolysis rates can vary widely. The rate of urea hydrolysis is controlled by the amount of urease enzyme, temperature, pH, urea concentration, but at the soil surface, soil water potential is an especially critical factor because it may vary widely in short periods of time due to precipitation, dews, and rapid evaporation. The objective of this study was to describe the quantitative relationship between soil water and urea hydrolysis rates in a loblolly pine (Pinus taeda L.) forest floor. Hydrolysis rates were measured in a pine forest with time after urea was applied in seven studies performed at different times that varied widely in soil water content and temperature. Separately in a laboratory study, the urea hydrolysis rates were measured in pine needles and in the humified layer at different water potentials. Results showed that although well‐defined relationships were found between urea hydrolysis rates and forest floor water potentials, the urea hydrolysis rates measured in the field could not be predicted based on these relationships and the water potential of the forest floor pine needles at the time of urea application. However, the percent of urea hydrolyzed at 3 and 29 d could be predicted accurately from the initial water potential of new needles and an interaction between initial water potential and relative humidity days.

Excretion kinetics of 13C-urea breath test: influences of endogenous CO2 production and dose recovery on the diagnostic accuracy of Helicobacter pylori infection.

We report for the first time the excretion kinetics of the percentage dose of (13)C recovered/h ((13)C-PDR %/h) and cumulative PDR, i.e. c-PDR (%) to accomplish the highest diagnostic accuracy of the (13)C-urea breath test ((13)C-UBT) for the detection of Helicobacter pylori infection without any risk of diagnostic errors using an optical cavity-enhanced integrated cavity output spectroscopy (ICOS) method. An optimal diagnostic cut-off point for the presence of H. pylori infection was determined to be c-PDR (%) = 1.47% at 60min, using the receiver operating characteristic curve (ROC) analysis to overcome the "grey zone" containing false-positive and false-negative results of the (13)C-UBT. The present (13)C-UBT exhibited 100% diagnostic sensitivity (true-positive rate) and 100% specificity (true-negative rate) with an accuracy of 100% compared with invasive endoscopy and biopsy tests. Our c-PDR (%) methodology also manifested both diagnostic positive and negative predictive values of 100%, demonstrating excellent diagnostic accuracy. We also observed that the effect of endogenous CO2 production related to basal metabolic rates in individuals was statistically insignificant (p = 0.78) on the diagnostic accuracy. However, the presence of H. pylori infection was indicated by the profound effect of urea hydrolysis rate (UHR). Our findings suggest that the current c-PDR (%) is a valid and sufficiently robust novel approach for an accurate, specific, fast and noninvasive diagnosis of H. pylori infection, which could routinely be used for large-scale screening purposes and diagnostic assessment, i.e. for early detection and follow-up of patients.

CaCO3 Precipitation, Transport and Sensing in Porous Media with In Situ Generation of Reactants

Ureolytically driven calcite precipitation is a promising approach for inducing subsurface mineral precipitation, but engineered application requires the ability to control and predict precipitate distribution. To study the coupling between reactant transport and precipitate distribution, columns with defined zones of immobilized urease were used to examine the distribution of calcium carbonate precipitation along the flow path, at two different initial flow rates. As expected, with slower flow precipitate was concentrated toward the upstream end of the enzyme zone and with higher flow the solid was more uniformly distributed over the enzyme zone. Under constant hydraulic head conditions the flow rate decreased as precipitates decreased porosity and permeability. The hydrolysis/precipitation zone was expected to become compressed in the upstream direction. However, apparent reductions in the urea hydrolysis rate and changes in the distribution of enzyme activity, possibly due to CaCO3 precipitate hindering urea transport to the enzyme, or enzyme mobilization, mitigated reaction zone compression. Co-injected strontium was expected to be sequestered by coprecipitation with CaCO3, but the results suggested that coprecipitation was not an effective sequestration mechanism in this system. In addition, spectral induced polarization (SIP) was used to monitor the spatial and temporal evolution of the reaction zone.

Apparent Persistence of N‐(n‐butyl) Thiophosphoric Triamide Is Greater in Alkaline Soils

Recently completed NH3 volatilization field studies with urea suggest the urease inhibitor N‐(n‐butyl) thiophosphoric triamide (NBPT) has prolonged activity in alkaline relative to acidic soils. A laboratory incubation experiment was conducted at two temperatures (0.5 and 20°C) to determine whether NBPT degradation was affected by soil pH (alkaline vs. acidic) and to determine the impact on urea hydrolysis. Soil (10 g) from the surface horizon of a loam (pH 5.5) and a silt loam (pH 8.4) was placed in bottles and incubated up to 28 d in constant‐temperature chambers. A third soil was constructed by adding CaCO3 (0.3 g) to the loam soil (pH 8.2). Urea (20 mg) with and without NBPT (20 mg) was applied to each soil. High‐performance liquid chromatography–mass spectrometry analysis of KCl extracts revealed that NBPT degraded rapidly in the acidic soil compared with the alkaline soils (silt loam and loam with added CaCO3). Exponential decay constants for the acidic soil were 5.2 and 3.9 times larger than decay constants for the alkaline soils at 0.5 and 20°C, respectively. Urea hydrolysis rates were reduced by NBPT, and the response was greater for the alkaline soils (P &lt; 0.0001). Hydrolysis was inhibited by 17.0 and 86.2% at 20°C and by 53.3 and 92.1% at 0.5°C for the acidic and alkaline soils, respectively. This study confirmed field observations that NBPT persistence and activity is greater in alkaline soils. Additional studies, including chemical hydrolysis and sorption, are needed to clarify the processes responsible for the rapid disappearance of NBPT from extracts of acidic soils.

English

The faster urea hydrolyses process leads to high amount of ammonia gas emission from urea fertilized fields. Coating of urea with various materials is the most successful strategy to control N losses from urea fertilized fields. A laboratory study was conducted to evaluate the effects of uncoated urea, as compare to urea coated with hydroquinone and Cu on NH3 volatilization loss and rate of urea hydrolysis in soil. The coated urea treatments were prepared by using Cu and hydroquinone solutions with a fluidized bed coating machine. Two experiments were carried out to evaluate the coated urea treatments labelled as UCu (Cu coated urea) and UHY (Hydroquinon urea). Both experiments were carried out on a sandy soil named as Serdang series. The soil was characterized for its properties by standard methods. In the first experiment the coated urea was evaluated for ammonia volatilization loss by using closed chamber force draft technique. Simultaneously, an incubation experiment was conducted to evaluate the effect of hydroquinone and Cu coated urea treatments for their hydrolyses rate or mineralization process. It was estimated by the results that ammonia volatilization from Hydroquinon coated urea treated soil reduced 25% however, Cu coated urea showed 30% reduction in ammonia volatilization loss as compare to uncoated urea. In incubation experiment recovery of urea from soil was 50% more in coated urea as compare to uncoated urea. It is concluded that coating of urea with urease inhibitors can reduce successfully the ammonia volatilization loss and increased the recovery of urea either coated by Cu or hydroquinone. Key words:&nbsp;Urease inhibitor, urea, hydroquinone, Cu (Copper).

Reaction pathways and free energy profiles for spontaneous hydrolysis of urea and tetramethylurea: unexpected substituent effects

It has been difficult to directly measure the spontaneous hydrolysis rate of urea and, thus, 1,1,3,3-tetramethylurea (Me4U) was used as a model to determine the "experimental" rate constant for urea hydrolysis. The use of Me4U was based on an assumption that the rate of urea hydrolysis should be 2.8 times that of Me4U hydrolysis because the rate of acetamide hydrolysis is 2.8 times that of N,N-dimethyl-acetamide hydrolysis. The present first-principles electronic-structure calculations on the competing non-enzymatic hydrolysis pathways have demonstrated that the dominant pathway is the neutral hydrolysis via the CN addition for both urea (when pH < ~11.6) and Me4U (regardless of pH), unlike the non-enzymatic hydrolysis of amides where alkaline hydrolysis is dominant. Based on the computational data, the substituent shift of the free energy barrier calculated for the neutral hydrolysis is remarkably different from that for the alkaline hydrolysis, and the rate constant for the urea hydrolysis should be ~1.3 × 10(9)-fold lower than that (4.2 × 10(-12) s(-1)) measured for the Me4U hydrolysis. As a result, the rate enhancement and catalytic proficiency of urease should be 1.2 × 10(25) and 3 × 10(27) M(-1), respectively, suggesting that urease surpasses proteases and all other enzymes in its power to enhance the rate of reaction. All of the computational results are consistent with available experimental data for Me4U, suggesting that the computational prediction for urea is reliable.

尿素加水分解速度に基づく微生物固化技術の沿岸域への適用性評価

環境負荷の小さな新しい地盤改良技術として注目されている微生物固化の沿岸環境への適用を目的とし，尿素の加水分解速度と砂地盤の強度増加効果の関連性について検討した。陸域由来で固化効果が明らかとなっているBacillus pasteuriiを基準微生物とし，海水から単離され沿岸域での固化促進効果が期待されるSporosarcina aquimarinaを用いた比較検証試験を行った。試験は人工海水環境下で行うとともに，豊浦砂および天然プロセスで海砂の固化効果が報告されている場所で採取した2種類の砂を用いた。試験の結果から，1)菌体培養液と尿素溶液を用い，電気伝導度の変化により尿素の加水分解速度を定量的に評価できる， 2)海砂質量に対するカルサイトの析出率が同じであっても圧縮強さは微生物種により異なる，3)圧縮強さの増加効果と尿素の加水分解速度の間には正の相関が期待できる，ことがあきらかとなった。

Rate of Urea Application and NH3 Volatilization from Loblolly Pine

Surface application of urea to pine forests may lead to ammonia (NH3) volatilization, which can reduce forest production. The objective of this study was to characterize the effect of rate of urea application on urea hydrolysis rates and the loss of nitrogen (N) by NH3 volatilization under a range of environments in the field. Three field studies were performed in a mid‐rotation loblolly pine (Pinus taeda L.) plantation with treatments consisting of urea‐N application rates of 50, 100, and 200 kg N ha−1 applied to NH3 volatilization chambers that were designed to adjust the rate of air flow through the system based on wind speed at 1 cm above the soil surface. Overall, there was a tendency during some periods of measurement for urea hydrolysis to be slower at the high rate compared with the lower rates of application, but this effect was small. There was, however, no effect of rate of N application on NH3 loss, expressed as a percentage of the N applied, during any of the three studies. The main factor controlling NH3 loss was water availability as reflected by the interaction between pine needle water potential and relative humidity.

Kinetics and mechanism of jack bean urease inhibition by Hg2+.

BackgroundJack bean urease (EC 3.5.1.5) is a metalloenzyme, which catalyzes the hydrolysis of urea to produce ammonia and carbon dioxide. The heavy metal ions are common inhibitors to control the rate of the enzymatic urea hydrolysis, which take the Hg2+ as the representative. Hg2+ affects the enzyme activity causing loss of the biological function of the enzyme, which threatens the survival of many microorganism and plants. However, inhibitory kinetics of urease by the low concentration Hg2+ has not been explored fully. In this study, the inhibitory effect of the low concentration Hg2+ on jack bean urease was investigated in order to elucidate the mechanism of Hg2+ inhibition.ResultsAccording to the kinetic parameters for the enzyme obtained from Lineweaver–Burk plot, it is shown that the Km is equal to 4.6±0.3 mM and Vm is equal to 29.8±1.7 μmol NH3/min mg. The results show that the inhibition of jack bean urease by Hg2+ at low concentration is a reversible reaction. Equilibrium constants have been determined for Hg2+ binding with the enzyme or the enzyme-substrate complexes (Ki =0.012 μM). The results show that the Hg2+ is a noncompetitive inhibitor. In addition, the kinetics of enzyme inhibition by the low concentration Hg2+ has been studied using the kinetic method of the substrate reaction. The results suggest that the enzyme first reversibly and quickly binds Hg2+ and then undergoes a slow reversible course to inactivation. Furthermore, the rate constant of the forward reactions (k+0) is much larger than the rate constant of the reverse reactions (k-0). By combining with the fact that the enzyme activity is almost completely lost at high concentration, the enzyme is completely inactivated when the Hg2+ concentration is high enough.ConclusionsThese results suggest that Hg2+ has great impacts on the urease activity and the established inhibition kinetics model is suitable.

Enzyme kinetic characterization of microbe-produced urease for microbe-driven calcite mineralization

Just as calcite precipitation rate is equal to CO3 2− formation rate, this CO3 2− formation rate is equal to that of urea hydrolysis in microbial calcite precipitation. This formative rate of CO3 2− evolved a mode to assay the urea hydrolysis rate, which was influenced by urea and Ca2+ concentrations, pH, and temperature. To contrive the highest Vmax of the Michaelis–Menten enzyme kinetics equation for the fastest urea hydrolysis rate, 35 °C, pH 10, 2 M urea and 2 M Ca2+ were the optimal conditions based on the studies.

Comparison of rates of ureolysis between Sporosarcina pasteurii and an indigenous groundwater community under conditions required to precipitate large volumes of calcite

Ureolysis-driven calcite precipitation has potential to seal porosity and fracture networks in rocks thus preventing groundwater flow and contaminant transport. In this study urea hydrolysis and calcite precipitation rates for the model bacterium Sporosarcina pasteurii were compared with those of indigenous groundwater communities under conditions required to precipitate large volumes of calcite (up to 50 g L −1). We conducted microcosm experiments in oxic artificial and anoxic natural groundwaters (collected from the Permo-Triassic sandstone aquifer at Birmingham, UK) that were inoculated with aerobically grown S. pasteurii. The rate constants for urea hydrolysis, k urea, ranged between 0.06 and 3.29 d −1 and were only affected by inoculum density. Higher Ca 2+ concentration (50–500 mM Ca 2+) as well as differences in fO 2 did not inhibit the ureolytic activity of S. pasteurii and did not significantly impact k urea. These results demonstrate that S. pasteurii has potential to improve calcite precipitation in both oxic and anoxic groundwaters, especially if indigenous communities lack ureolytic activity. Urea hydrolysis by indigenous groundwater communities was investigated in anoxic, natural groundwaters amended with urea and CaCl 2. A notable increase in ureolysis rates was measured only when these communities were stimulated with dilute nutrients (with best results from blackstrap molasses). Furthermore, there was a considerable lag time (12–20 days) before ureolysis and calcite precipitation began. Calculated ureolysis rate constants, k urea, ranged between 0.03 and 0.05 d −1 and were similar to k urea values produced by S. pasteurii at low inoculum densities. Overall, this comparative study revealed that the growth of ureolytic microorganisms present within groundwaters can easily be stimulated to enhance rates of urea hydrolysis in the subsurface, and thus can be used to induce calcite precipitation in these environments. The time required for urea hydrolysis to begin is almost instantaneous if an inoculum of S. pasteurii is included, while it may take several weeks for ureolytic groundwater communities to grow and become ureolytically active.

Effect of Soil Water Contents on Urea Hydrolysis and Nitrification in a Newly Reclaimed Tidal Soils

The effect of soil water content on the transformation potential of N compounds derived from hydrolysis of urea applied in a reclaimed tidal soils which was saline-sodic was observed to evaluate nitrification rates of urea. Soil samples were collected from Moonpo series at the newly reclaimed area in Saemanguem. For the transformation potential of N compounds from urea (46% N), newly reclaimed tidal soils (RS) were amended with urea at the rates of 0, 10, and 20 kg 10a -1 . With leachate obtained from the incubated RS in a leaching tube at 25°C, urea hydrolysis and nitrification were measured for a total of 30days. The cumulative amounts of NO3 - -N in each of the four soils treated with urea was linear with time of incubation. Results showed that increase in pH occurred with increasing application rate of urea and volumetric water content due to hydrolysis of urea. The total N in the RS was decreased with incubation time, indicating that rates of urea hydrolysis was influenced by soil moisture conditions. Also, the cumulative amount of nitrate in RS gradually increased with increase in time of incubation.

Characterization of Kinetics of Urea Hydrolysis in A Newly Reclaimed Tidal Soils

It is imperative to study the hydrolysis of urea in high saline-sodic condition of a newly reclaimed tidal land in order to overcome the problems associated with use of urea fertilizer. The methodology adopted in this study tried to get a convenient way of estimating rate for N transformation needed in N fate and transport studies by reviewing pH and salt contents which can affect the microbial activity which is closely related to the rate of urea hydrolysis. The hydrolysis of urea over time follows first-order kinetics and soil urease activity in reclaimed soils will be represented by Michaelis-Menten-type kinetics. However, high pH and less microorganisms may delay the hydrolysis of urea due to decrease in urease activity with increasing pH. Therefore, the rate of urea hydrolysis should adopt V max referring enzyme activity (E 0 ) accounting for urease concentration which is indicative for urea hydrolysis, especially in a high saline and sodic soils.