Transformation Of Urea Research Articles

Research on the Influence of Irrigation Amount on Dynamic Changes and Accumulation of Soil Nitric Nitrogen under Film Hole Irrigation

Through the experiment of different Irrigation Amounts with urea applied, the paper studied the influence of Irrigation Amounts on soil nitric nitrogen dynamical changes under film hole irrigation and the nitric nitrogen content of the growing period was determined. The result showed: different irrigation amount in the profiles being 3cm and 8cm away from the film hole center, it appeared nitric nitrogen accumulation peaks, increased the irrigation amount promoted the transformation of urea, increased the transformed nitric nitrogen content and distribution of nitric nitrate and the risk of nitric nitrate leaching. In the profiles being 3cm away from the film hole center, the nitric nitrogen accumulation peak significantly reduced at harvest stage, but it reduced in the profiles being 8cm away from the film hole center at milky stage. The milky stage was the maximum period when the corn uptook nitrogen at different irrigation amount. Increased irrigation amount lower the accumulation content of nitric nitrogen near the film hole center after harvest, and higher the accumulation content of nitric nitrogen far away from the film hole center. Above researches could provide the basis for rational fertilization of farmland and nitrate environmental impacts on assessment.

Study on Heat and Mass Transfer During Urea Prilling Process

Urea prills are produced in the prilling towers where a solidification-cooling process takes place. The ambient air is used as the cooling air stream for this process. In hot days, the temperature of the product at the bottom of the tower are hot that cannot be packed directly. In addition, in hot/ humid days, the prills form lamps and cakes with each other and on the scrubber. A mathematical model based on the hydrodynamics, heat, and mass transfer between the urea and the cooling air is developed. A numerical technique with an explicit scheme is used to solve the model. The model results describe the variation of the temperature and moisture along the radius of the particle. Hence, the model results introduce an interpretation of the problem of caking and lamps formation appears because of the incomplete solidification of the prills at the bottom of the tower. In addition, the results predict the quality of the product under different operating conditions of the ambient cooling air. Urea is marketed as a solution or in the solid form. Urea in solid form is produced in the final process stage by either granulation or prilling. Transformation of urea from melt to solid prills takes place in the urea prilling tower. In the prilling process, urea melt is pumped to the top of 50 to 60 meter (above ground) cylindrical concrete tower where it is fed to the prilling device that called rotating bucket. The rotating bucket is a sieve-like cylindrical or conical drum that rotates about its axis. Liquid jets emerge from the various holes on the curved surface of the drum, and break up due to centrifugal and capillary instability. The liquid urea droplets formed fall downward the prilling tower. A countercurrent cooling air stream enters from intake openings located around the circumference of the tower at a height approximately 7 meters from the ground level of the tower. Heat and mass transfer between the downward urea droplets and the upward cooling air stream along the height of the tower occurs, and thus a solidification-cooling process takes place. The product, urea prills, goes from the tower base to a conveyor belt where it has collected and packed. The air stream exhaust from the tower through the exhausted stakes located at the top of the tower where it spreads in the surrounding environment. As ambient air is used in the process of cooling and solidification of the prills inside the tower, thus both the dry bulb temperature and humidity of the ambient air highly affect the quality of the final product. In this study, a case study of a prilling process in Abu Qir Fertilizers Co, Alexandria, Egypt is considered. Based on the reported information from the company that is in some days in summer session, the prills are hot to the limit that cannot be packed directly. The delay in the packing process leads to a decrease in the yearly company production. In addition, in humid/ hot days, the lamp of prills forms at the bottom of the tower that also is not desired for the product quality.

Hugoniot curve of urea

Various approaches to describing the Hugoniot curve for urea were considered. A satisfactory agreement with experimental data was obtained under the assumption that a polymorphous transformation of urea occurred behind the shock wave front.

Impact of land-use types on soil nitrogen net mineralization in the sandstorm and water source area of Beijing, China

Abstract Changes of land-use type (LUT) can affect soil nutrient pools and cycling processes that relate long-term sustainability of ecosystem, and can also affect atmospheric CO2 concentrations and global warming through soil respiration. We conducted a comparative study to determine NH4+ and NO3− concentrations in soil profiles (0–200 cm) and examined the net nitrogen (N) mineralization and net nitrification in soil surface (0–20 cm) of adjacent naturally regenerated secondary forests (NSF), man-made forests (MMF), grasslands and cropland soils from the windy arid and semi-arid Hebei plateau, the sandstorm and water source area of Beijing, China. Cropland and grassland soils showed significantly higher inorganic N concentrations than forest soils. NO3−-N accounted for 50–90% of inorganic N in cropland and grassland soils, while NH4+-N was the main form of inorganic N in NSF and MMF soils. Average net N-mineralization rates (mg kg−1 d−1) were much higher in native ecosystems (1.51 for NSF soils and 1.24 for grassland soils) than in human disturbed LUT (0.15 for cropland soils and 0.85 for MMF soils). Net ammonification was low in all the LUT while net nitrification was the major process of net N mineralization. For more insight in urea transformation, the increase in NH4+ and, NO3− concentrations as well as C mineralization after urea addition was analyzed on whole soils. Urea application stimulated the net soil C mineralization and urea transformation pattern was consistent with net soil N mineralization, except that the rate was slightly slower. Land-use conversion from NSF to MMF, or from grassland to cropland decreased soil net N mineralization, but increased net nitrification after 40 years or 70 years, respectively. The observed higher rates of net nitrification suggested that land-use conversions in the Hebei plateau might lead to N losses in the form of nitrate.

Synthesis of pyrrole urea and pyrrole carbonylurea derivatives

A series of urea and carbonylurea distamycin analogs whereby the linker has two NH groups for hydrogen bonding with base pairs of DNA were synthesized. The urea and carbonylurea derivatives are prepared from the in situ generation of pyrrole isocyanate (prepared from compound 3) and acyl isocyanate (compound 9), followed by the reaction with an amine. The synthetic feasibility for the further transformations of the pyrrole urea and pyrrole carbonylurea derivatives was also addressed. The binding abilities of these molecules to calf thymus DNA were evaluated by DNA melting temperature ( T m) analysis.

Effect of organics on nitrogen transformations in soil under different moisture regimes

Awareness of the environmental aspects of the quality of crop production has increased in recent decades, leading to renewed interest in organics such as crop residues, green manures and organic manures. The effect of organics on urea transformation was investigated by conducting a laboratory incubation experiment in alluvial clay loam soil (Typic Ustifluvents) at 33±1°C with two moisture levels (1:1 soil:water ratio and field capacity). The rate of urea hydrolysis decreased as the time of incubation increased and the disappearance of urea N was associated with a corresponding increase in the (NH 4+ + NO 3− )-N content in soils treated with crop residues (rice straw and wheat straw), organic manures (poultry manure and farmyard manure) and green manures (cowpea and sesbania). In untreated soil, the time taken for the complete hydrolysis of the applied urea (200 μg urea N g −1 soil) was more than 96 h at both the moisture levels, whereas in amended soils it was completed in 48 h. The rate of urea hydrolysis was more rapid at field capacity than at the 1:1 soil:water ratio. Urea hydrolysis was higher in sesbaniatreated soils, followed by cowpea, poultry manure, farmyard manure, rice straw and wheat straw at both the moisture levels. At field capacity, 85.5% urea was hydrolysed in sesbania-treated soil as compared to 32% in untreated soil after 24 hours of incubation, while at the 1:1 soil:water ratio the corresponding values were 81.5 and 27.5%. Urea hydrolysis followed first order reaction kinetics at both the moisture levels.

Investigation into Photocatalytic Degradation of Gaseous Ammonia in CPCR

Addition of urea-based antifreeze admixtures during cement mixing in construction of buildings has led to increasing indoor air pollution because of continuous transformation and emission of urea to gaseous ammonia on indoor concrete walls. To control ammonia pollution from indoor concrete walls, a circulated photocatalytic reactor (CPCR) was designed to intensify the performance for the decomposition of gaseous ammonia in the present study and TiO2 film photocatalysts were prepared by the sol−gel method and coating onto the inner wall of this reactor using a bonder of polyacrylic ester emulsion, which was characterized by FTIR, TEM, and SEM. In particular, the influences of initial concentration of ammonia on the degradation conversion (Dp), apparent reaction rate constants (kr), initial degradation rate (r), deactivation, and regeneration of catalyst in CPCR were investigated. Furthermore, a designed equation of surface catalytic kinetics was developed for describing the decomposition of ammonia in CPCR. The total number of adsorption sites available for the gas molecules NT and the adsorption equilibrium constant Kads values were determined through a linear-fitting method. Finally, undesirable NO2− and NO3− were detected as the intermediates in the process of photodegradation at different initial concentration of ammonia, which was detected by catalytic kinetic spectrophotometry. The results indicated that the degradation conversion (Dp), initial degradation rate (r), degraded products, and half-life (t1/2) were closely correlated to the initial concentration of ammonia. It was found that the reaction kinetics fixed the pseudofirst-order kinetic equation of photocatalytic degradation of gaseous ammonia in CPCR, and the kinetic results are discussed in terms of adsorption of ammonia and products degraded.

Urea Transformation of Wetland Microbial Communities

Transformation of urea to ammonium is an important link in the nitrogen cycle in soil and water. Although microbial nitrogen transformations, such as nitrification and denitrification, are well studied in freshwater sediment and epiphytic biofilm in shallow waters, information about urea transformation in these environments is scarce. In this study, urea transformation of sedimentary, planktonic, and epiphytic microbial communities was quantified and urea transformation of epiphytic biofilms associated with three different common wetland macrophyte species is compared. The microbial communities were collected from a constructed wetland in October 2002 and urea transformation was quantified in the laboratory at in situ temperature (12 degrees C) with the use of the 14C-urea tracer method, which measures the release of 14CO2 as a direct result of urease activity. It was found that the urea transformation was 100 times higher in sediment (12-22 mmol urea-N m(-2) day(-1)) compared with the epiphytic activity on the surfaces of the submerged plant Elodea canadensis (0.1-0.2 mmol urea-N m(-2) day(-1)). The epiphytic activity of leaves of Typha latifolia was lower (0.001-0.03 mmol urea-N m(-2) day(-1)), while urea transformation was negligible in the water column and on the submerged leaves of the emergent plant Phragmites australis. However, because this wetland was dominated by dense beds of the submerged macrophyte E. canadensis, this plant provided a large surface area for epiphytic microbial activity-in the range of 23-33 m2 of plant surfaces per square meter of wetland. Thus, in the wetland system scale at the existing plant distribution and density, the submerged plant community had the potential to transform 2-7 mmol urea-N m(-2) day(-1) and was in the same magnitude as the urea transformation in the sediment.

Petiole and Soil Nitrogen Concentrations during the Growing Season of Two Potato Cultivars as Influenced by Different Nitrogen‐Management Practices

Fine‐tuning potato nitrogen (N) management for irrigated sandy soils is a desirable goal to optimize the production and minimize negative impacts on the environment. Effects of different rates of preplant N (PP‐N) applications and different rates and frequencies of in‐season N (IS‐N) for two potato cultivars were evaluated for 2 years (2001 and 2002) in a Quincy fine sand (mixed, mesic, Xeric Torripsamments) in the Pacific Northwest (PNW). In the 2001 experiment, the petiole nitrate (NO3‐N) concentrations in both the cultivars were in the optimum range in the samples taken 22 days after emergence (DAE). In the subsequent sampling, the petiole NO3‐N concentrations showed a wide range proportional to the rates of IS‐N. In the 2002 experiment, the petiole NO3‐N concentrations were in the excess range in most treatments until about 51 DAE in both the cultivars, followed by a decline in concentrations to the low range. The petiole phosphorus (P) and potassium (K) concentrations were mostly above the excess range in both the cultivars over the entire sampling period. The soil N data showed that the transformation of urea N was quite rapid and that the extractable ammonium (NH4‐N) and NO3‐N concentrations in the soil returned to the background levels within 90 days after the PP‐N application. The results of this study demonstrate a rapid transformation of preplant applied urea N into NH4‐N and NO3‐N and depletion of the available N in the top 120 cm of soil. This, in turn, supports the need for IS‐N applications to meet the crop N requirement during the later growing period.

Effect of Lead on the Transformation of Urea-N in Fly Ash-Contaminated Soils under Different Moisture Regimes

Urea is applied to soil for plant growth and undergoes various changes while in the soil. The mobility of heavy metals changes with the transformation of urea applied to the soil that, in turn, affects the activity of microbial biomass. The objective of this study was to determine the interaction between lead (Pb) and urea under two moisture regimes (60% and saturated water contents). At 60% water content, the amount of NH4-N decreased with the incubation time, irrespective of Pb and urea applied, while the amount of NO3-N content in the soil gradually increased with the incubation period to 28 days, and such an increase was counteracted by application of Pb. The amount of NO3-N content was higher than that of NH4-N, however, under saturated moisture condition, the amount of NH4-N was increased with the incubation time regardless of the levels of Pb application. The amount of NO3-N content in the soil gradually decreased with the advance of incubation at saturated condition. Although application of urea increased the NO3-N content in the soil, such an increase was suppressed by the application of different levels of Pb at water saturated condition throughout the incubation period.

Decomposition of indoor ammonia with TiO 2-loaded cotton woven fabrics prepared by different textile finishing methods

Addition of urea-based antifreeze admixtures during cement mixing in construction of buildings has led to increasing indoor air pollution due to continuous transformation and emission of urea to gaseous ammonia in indoor concrete wall. In order to control ammonia pollution from indoor concrete wall, the aqueous dispersion was firstly prepared with nano-scale TiO 2 photocatalysts and dispersing agent, and then mixed with some textile additives to establish a treating bath or coating paste. Cotton woven fabrics were used as the support materials owing to their large surface area and large number of hydrophilic groups on their cellulose molecules and finished using padding and coating methods, respectively. Two TiO 2-loaded fabrics were obtained and characterized by X-ray diffractometer (XRD) and scanning electron microscopy (SEM). Moreover, a specifically designed ammonia photocatalytic system consisting of a small environmental chamber and a reactor was used for assessing the performance of these TiO 2-loaded fabrics as the wall cloth or curtains used in house rooms in the future and some factors affecting ammonia decomposition are discussed. Furthermore, a design equation of surface catalytic kinetics was developed for describing the decomposition of ammonia in air stream. The results indicated that increasing dosage of the TiO 2 aqueous dispersion in treating bath or coating paste improved the ammonia decomposition. And ammonia was effectively removed at low ammonia concentration or gas flow rate. When relative humidity level was 45%, ammonia decomposition was remarkably enhanced. It is the fact that ammonia could be significantly decomposed in the presence of the TiO 2-padded cotton fabric. Whereas, the TiO 2-coated cotton fabric had the reduced photocatalytic decomposition of ammonia and high adsorption to ammonia owing to their acrylic binder layer. Finally, the reaction rate constant k and the adsorption equilibrium constant K values were determined through a curve-fitting method and the TiO 2-padded cotton fabric had the higher k value and lower K value than the TiO 2-coated cotton fabric.

Molecular rearrangement of 1-substituted 3-aminoquinoline-2,4-diones in their reaction with urea and nitrourea synthesis and transformations of reaction intermediates

1-Substituted 3-alkyl/aryl-3-amino-1H,3H-quinoline-2,4-diones (6) react with nitrourea to give 3-ureido-1H,3H-quinoline-2,4-diones (10), 9b-hydroxy-3,3a,5,9b-tetrahydro-1H-imidazo[4,5-c]quinoline-2,4-diones (11), and 3,3a-dihydro-5H-imidazo[4,5-c]quinoline-2,4-diones (12). Compounds 11 were dehydrated to 12 by the action of phosphorus pentoxide. All three types of compounds rearrange in boiling acetic acid to give three different types of products of molecular rearrangement. A proposed reaction mechanism is discussed.

Short-term alleviation of aluminum phytotoxicity by urea application in acid soils from south China

A laboratory experiment was conducted to study effects of urea fertilizer on the chemical composition of soil solutions over time, and to determine Al toxicity as a function of rates of urea application. The experiment revealed that addition of urea fertilizer to soils caused drastic changes in soil pH during the hydrolysis and nitrification stages of urea transformation in the experiment. These pH changes, depending on the N rate of urea application and time courses, had variable effects on soil exchangeable Al, extracted with artificial solutions containing 1 mol l −1 KCl. The Al mobilization rate could be resolved into two phases: A declining phase for Al was attributed to the urea-induced hydrolysis while a second rising phase was dependent with the nitrification of added N fertilizer. The decreases in exchangeable Al reached the greatest in 4–7 days after fertilization, consistent with soil pH increase. Decreased Al availability had been observed as a consequence of increasing urea addition and soil pH when using Root elongation of maize seedlings as the estimators. Results from the present study demonstrate that urea fertilizer to the surface of soils may lead to a temporary immobilization of Al and, therefore, alleviated Al toxicity to plant seedlings.

Thermolysis of Urea Complexes of Uranyl Nitrate

Quantitative parameters of thermolysis of uranyl nitrate urea complexes, [UO2(NO3)2{(NH2)2·CO}2], [UO2(H2O){(NH2)2CO}4](NO3)2, and [UO2(H2O){(NH2)2CO}5](NO3)2 at 175, 200, and 225°C were measured. Thermolysis of [UO2(NO3)2{(NH2)2CO}2] at 200°C affords the biuret complex of uranyl nitrate in a 90% yield. The urea ligands in the hydrated complexes completely transform into biuret at 175°C. Thermolysis of [UO2(H2O){(NH2)2CO}5](NO3)2 yields the biuret-cyanurate complexes of uranyl nitrate. The features of thermolysis of the uranyl nitrate complexes originate from the chemical transformations of urea at elevated temperatures.

Transport and transformation of de-icing urea from airport runways in a constructed wetland system

Urea, NH2-CO-NH2, is used as a de-icing agent at Kalmar Airport, southeast Sweden. During 1998-2001, urea contributed on average 30% of the yearly nitrogen (N) transport of 41,000 kg via Törnebybäcken stream to the coastal zone of the Baltic Sea. In order to reduce stream transport of N from airport, agricultural and other diffuse sources, a wetland was constructed in 1996. Annual wetland retention of total-N varied in the range of 2,500-8,100 kg (6-36% of influent) during 1998-2001, according to mass balances calculated from monthly sampling. During airport de-icing, January-March 2001,660 kg urea-N out of 2,600 kg applied urea-N reached the wetland according to daily sampling. This indicated that 75% of the urea was transformed before entering the wetland. Urea was found to be only a minor part (8%) of total-N in the wetland influent. Calculations of cumulative urea-N loads at the wetland inlet and outlet respectively, showed a significant urea transformation during February 2001 with approximately 40% of the incoming urea-N being transformed in the wetland system. These results show that significant amounts of urea can be transformed in a wetland system at air temperatures around 0 degree C.

Presubmergence and green manure affect the transformations of nitrogen‐15‐labeled urea under lowland soil conditions

AbstractThe effect of presubmergence and green manuring on various processes involved in [15N]‐urea transformations were studied in a growth chamber after [15N]‐urea application to floodwater. Presubmergence for 14 days increased urea hydrolysis rates and floodwater pH, resulting in higher NH3 volatilization as compared to without presubmergence. Presubmergence also increased nitrification and subsequent denitrification but lower N assimilation by floodwater algae caused higher gaseous losses. Addition of green manure maintained higher NH4+‐N concentration in floodwater mainly because of lower nitrification rates but resulted in highest NH3 volatilization losses. Although green manure did not affect the KCl extractable NH4+‐N from applied fertilizer, it maintained higher NH4+‐N content due to its decomposition and increased mineralization of organic N. After 32 days about 36.9 % (T1), 23.9 % (T2), and 36.4 % (T3) of the applied urea N was incorporated in the pool of soil organic N in treatments. It was evident that the presubmergence has effected the recovery of applied urea N.

Effect of soil type, exchangeable sodium percentage, water content, and organic amendments on urea hydrolysis in some tropical Indian soils

Urea has emerged as one of the most extensively used sources of nitrogen fertiliser in recent years because of its low cost per unit nitrogen. Urea hydrolysis in soils is an enzymatic decomposition process by the enzyme urease. The effects of soil type, exchangeable sodium percentage, moisture regime, and organic manures and their levels on the kinetics of urea hydrolysis were studied in a series of laboratory incubation experiments at 25 ± 1�C. Urea transformation followed first-order kinetics, and the first-order rate constants for soils varied from 0.0321 to 0.1182/h. The rate of urea hydrolysis in the different soils increased with greater clay content and followed the order: Gulkani clay loam > Dadupur loam > Hisar sandy loam > Jakhol silty clay loam > Bawal loamy sand > Balsamand sand. Increasing the exchangeable sodium percentage in soils decreased the rate of urea hydrolysis both at field capacity and flooded conditions (2 cm standing water). Application of vermicompost, sheep manure, poultry manure, pig manure, and urban waste to soil at the 1% level increased the rate of hydrolysis over the untreated soil.

Transformation of urea during the growth of some blue-green (Cyanoprocaryota) and green (Chlorophyta, Chlorococcales) algae

The accumulation of ammonium nitrogen in the culture medium of green and blue-green algae of the genera The accumulation of ammonium nitrogen in the culture medium of green and blue-green algae of the genera Acutodesmus (Hedew.) Tsar. (1 species), Chlorella Beijer, (1), Coelastrum Nag. (1), and Desmodesmus (Chod.) An, Friedl et Hegew. (5) was studied in the process of their growth on urea. It has been revealed that a sharp increase in the NH4+ concentration in the culture of blue-green algae due to the high activity of urease leads to their inhibition, and eventually to their death. Chlorococcal algae containing urea amidase differed in a low intensity of urea hydrolysis and in the absence of the inhibitory effect of NH4+ ions on their growth. In addition, it has been shown that the character of urea decomposition depends on the biological peculiarities of the species, which is the most distinct in representatives of the order Chlorococcales. The presence of accompanying (associated) bacteria in their culture leads to a decrease in the ammonium nitrogen quantity in the medium.

Fate of urea nitrogen applied to a banana crop in the wet tropics of Queensland

This paper reports a study in the wet tropics of Queensland on the fate of urea applied to a dry or wet soil surface under banana plants. The transformations of urea were followed in cylindrical microplots (10.3 cm diameter × 23 cm long), a nitrogen (N) balance was conducted in macroplots (3.85 m × 2.0 m) with 15N labelled urea, and ammonia volatilization was determined with a mass balance micrometeorological method. Most of the urea was hydrolysed within 4 days irrespective of whether the urea was applied onto dry or wet soil. The nitrification rate was slow at the beginning when the soil was dry, but increased greatly after small amounts of rain; in the 9 days after rain 20% of the N applied was converted to nitrate. In the 40 days between urea application and harvesting, the macroplots the banana plants absorbed only 15% of the applied N; at harvest the largest amounts were found in the leaves (3.4%), pseudostem (3.3%) and fruit (2.8%). Only 1% of the applied N was present in the roots. Sixty percent of the applied N was recovered in the soil and 25% was lost from the plant-soil system by either ammonia volatilization, leaching or denitrification. Direct measurements of ammonia volatilization showed that when urea was applied to dry soil, and only small amounts of rain were received, little ammonia was lost (3.2% of applied N). In contrast, when urea was applied onto wet soil, urea hydrolysis occurred immediately, ammonia was volatilized on day zero, and 17.2% of the applied N was lost by the ninth day after that application. In the latter study, although rain fell every day, the extensive canopy of banana plants reduced the rainfall reaching the fertilized area under the bananas to less than half. Thus even though 90 mm of rain fell during the volatilization study, the fertilized area did not receive sufficient water to wash the urea into the soil and prevent ammonia loss. Losses by leaching and denitrification combined amounted to 5% of the applied N.

MODELING UREA, AMMONIUM, AND NITRATE TRANSPORT AND TRANSFORMATIONS IN FLOODED SOIL COLUMNS

Understanding the fate of organic nitrogen (urea, ammonium, and nitrate) introduced into wetlands is important for wetland restoration and environmental quality. However, the transformation of nitrogen in wetlands is complicated by the coexistence of oxidized and reduced soil conditions. In this study, we investigated the transport and transformations of 15 N-urea, and its degradation products ( 15 NH 4 and 15 NO 3 ) in laboratory columns packed with Crowley silt loam, a major rice soil in southwest Louisiana. A 2-centimeter floodwater layer was maintained during the experiments to simulate wetland conditions. Sterilized soil columns with the addition of urease inhibitor [N-(n-butyl) thiophosphoric triamide] were used to measure urea diffusion in the soil. Urea transformations were studied using 15 N-urea, and the degradation products (ammonium and nitrate) were measured at 0.5, 1, 2, 4, and 6 days after urea application. Adsorption isotherms for urea and NH 4 were determined using batch experiments under sterile conditions. A system of diffusion equations (DEs) was formulated to describe urea, NH 4 , and NO 3 diffusion and transformation in soil. Urea hydrolysis was assumed to take place in the soil profile only, and nitrification in the floodwater and the surface soil layer. Denitrification may take place in both the floodwater and soil profile depending on oxygen depletion. Predicted urea and ammonium distributions in the soil profile following urea application were highly correlated to their experimental values (r 2 > 0.91). Although nitrate concentrations at each sampling time were underpredicted, the model overpredicted by 8.7% the amount of nitrate denitrified during the 6-day experimental period.