Urea Hydrolysis In Soils Research Articles

Gibberellic acid and urease inhibitor optimize nitrogen uptake and yield of maize at varying nitrogen levels under changing climate.

Worldwide, nitrogen (N) deficiency is the main yield limiting factor owing to its losses via leaching and volatilization. Urease inhibitors slow down urea hydrolysis in soil by inhibiting urease enzyme activities whereas gibberellic acid is growth regulator. That is why, we evaluated the role of urease inhibitor [N-(n-butyl)thiophosphorictriamide (NBPT)] and gibberellic acid (GA3) in improving nitrogen uptake and yield of maize under different N levels (120 and 150 kg ha-1) along with control. Both N levels alone and in combination with GA3 and NBPT significantly increased yield and yield components of maize over control. In addition, 150 kg N ha-1 + NBPT + GA3 produced highest biological, grain, and stover yields, 1000 grain weight, plant height, and N uptake exhibiting 33.15%, 56.46%, 27.56%, 19.56%, 23.24%, and 78% increase over 150 kg N ha-1, respectively. The sole use of gibberellic acid or NBPT with each level of N also improved the yield and yield components of maize compared to sole N application and control. Furthermore, application of 120 kg N ha-1 along with NBPT and GA3 performed at par to 150 kg N ha-1 + NBPT + GA3 but it was superior than sole applied 150 kg N ha-1 for all the studied traits. These results imply that application of GA3 and/or NBPT can reduce dependence on urea and improve the yield and N uptake in maize by slowing urea hydrolysis in calcareous soils and shall be practiced.

An Evaluation of Maleic‐Itaconic Copolymers as Urease Inhibitors

Core Ideas Maleic‐Itaconic Polymers (MIPs) strongly and rapidly inactivate urease at pH 5.0. MIPs favour the release of the essential Ni(II) ions from the active site of urease. The urease inactivation by MIPs is comparable with that attained using NBPT. Urea hydrolysis in soil is accelerated 1015–fold by the nickel‐dependent enzyme urease to yield a source of N that can be assimilated by plants. This reaction determines an overall soil pH increase and significant ammonia volatilization, decreasing the efficiency of urea‐based fertilization. A control of urease activity is thus required for agronomic purposes. Maleic‐Itaconic Polymers (MIPs) have been claimed to decrease the N loss as ammonia volatilization by inhibiting urease activity. To investigate this matter, we performed an in vitro study using urease from jack bean (Canavalia ensiformis, JBU) at pH 7.5 and pH 5.0. Urease is not affected by MIPs at pH 7.5, but the enzyme is completely inactivated in 20 min at pH 5.0 using MIPs in the 0.4 to 2.4 μmol L–1 range. This inactivation is comparable to that attained using similar concentrations of N‐(n‐butyl)‐thiophosphoric triamide (NBPT). In vivo assays conducted using Sporosarcina pasteurii as a model for a widespread soil bacterium and urea, in the presence of either MIPs or NBPT at pH 7.5, revealed that NBPT significantly inhibits both cellular growth and urease activity, while MIPs have no effect. To elucidate the mechanism of extracellular urease inactivation by MIPs in vitro, their Ni(II) sequestration capability was investigated. The MIPs (50 μmol L–1) completely extract the essential Ni(II) ions from the active site of urease at pH 5.0, in 3 h. This phenomenon is related to the capability of MIPs to shift the Ni(II)‐urease dissociation equilibrium through binding and chelation of the Ni(II) ions off the active site.

Urease activity and urea hydrolysis rate under coupling effects of moisture content, temperature, and nitrogen application rate

The traditional qualitative analysis of the individual factors on the kinetic parameters cannot sufficiently reveal the mechanism underlying urea hydrolysis in soil. This study aimed at revealing the coupling effects of the three factors on urease activity (V0), hydrolysis rate constant (Ku), and activation energy (Ea) and establishing the quantitative model for Ku under the coupling condition. Laboratory culture experiments were conducted under different temperatures (T) (15°C, 20°C, 25°C, and 35°C), moisture contents (θ) (60%, 80%, and 100% of field capacities), and nitrogen application rates (F) (247 mg/kg, 309 mg/kg, 371 mg/kg, and 433 mg/kg). The urea content was measured daily. Results showed that the effects of moisture content, temperature, nitrogen application rate, and their interaction on V0 and Ku were in the descending order: T, F, T*F, θ, T*θ, F*θ, T*θ*F. The effect of single factor and two-factor coupling on V0 was extremely significant (p<0.01), whereas the effect of the three-factor coupling on V0 was negligible. The effects of three factors and their interaction on Ku were extremely significant (p<0.01). The effects of moisture content, nitrogen application rate, and their interaction on Ea were in the descending order: F, θ, F*θ. The effects of two factors and their interaction on Ea were not significant. The mean absolute percentage error (MAPE) values of the established Ku-1 (θ, T, F) and Ku-2(θ, T, F) models were 3.14% and 4.60%, respectively. The MAPE of the traditional Arrhenius model Ku-3(T) was 6.75%. The accuracy of the proposed three-factor interaction model was superior to that of the traditional single factor model. The results supplemented the mechanism of urea hydrolysis and improved the prediction accuracy of Ku. Keywords: urease activity, hydrolysis rate constant, Arrhenius model, activation energy, coupling effect DOI: 10.25165/j.ijabe.20181102.3784 Citation: Lei T, Gu Q Q, Guo X H, Ma J J, Zhang Y, Sun X H. Urease activity and urea hydrolysis rate under coupling effects of moisture content, temperature, and nitrogen application rate. Int J Agric & Biol Eng, 2018; 11(2): 132–138.

تأثير تغليف سماد اليوريا بمستخلصات النواتج الثانوية ( فينولات و زيوت طيارة ) من بعض النباتات على تثبيط نشاط أنزيم اليورييز في التربة = Effect of Coating Urea with Some Plant Secondary Products ( Phenolic and Votilized Oils ) on Urease Inhibition in Soil

An experiment was conducted to study the efficiency of coating urea with some secondary metabolism products extracted from plants to inhibit urease enzyme activity in silty loam soil. Phenolic substances and votilized oils were extrected from data palm fiber, eucalyptus leaves and myrtus leaves by applying standard methods.Urea fertilizer was coated with above extracts at ratios: 2.5, 5 and 10% (w/w) .Coated urea was applied to soils at rates of 30,90 and 270 mgN Kg-1soil.Fifty grames of soil were treated with coated urea and incubated at temperature of 37ᴼ C for 5 and 10 days.Then urease enzyme activity was measured and inhibition percentages were calculated. Results showed that coating urea fertilizer with phenolic or votilized oil compouned extracted from data palm fiber, eucalyptus and myrtus leaves reduced urease activity in soil. Highest urease inhibition (avg 63 % ) was obtained in soil treated with urea coated with phenole compouned (at ratio 5%)or votilized oil (at ratio 10%) extracted from eucalyptus leaves at 270 mg N Kg-1soil. Highest urease inhibition in soil treated with urea + ATS (Ammonium thiosulfate) at 270 mg N Kg-1soil was 56% . These results suggested a possibility of using urea coated with Phenolic substances and votilized oils extracted from some plants to reduced urea hydrolysis in soil and could be apotent substitute for ATS to increase urea efficiency.

Inhibitory Effects of Aqueous Extracts from Leaves of Common Tropical Green Plants on Urea Hydrolysis in Soils

Tropical plants contain a variety of secondary metabolites, and plant aqueous extracts can be used as urease inhibitors to improve nitrogen use efficiency and reduce the negative environmental effects. An incubation experiment was carried out to investigate the effects of aqueous extracts of 32 common tropical green plant species from 24 families on urea hydrolysis. The results indicated that the aqueous extracts from 3 of the common tropical green plants (Pterocarpus indicus, Callistemon rigidus, Terminalia mantaly) belonging to Leguminosae, Myrtaceae and Combretaceae respectively showed better inhibitory effects on urease than hydroquinone as a chemical inhibitor, and had more obvious potential applications. The inhibitory effects of active substances in plants were affected by extract temperature causing by solubility and thermal stability of active substances. T. mantaly had the most potential for development in this study as a fertilizer additive. The inhibitory effects of aqueous extracts of T. mantaly leaves on urea hydrolysis increased with increasing concentration of aqueous extracts, the strongest inhibitory effect on urease occurred after 2-3 d of incubation.

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).

Microbially Induced Calcium Carbonate Precipitation on Surface or in the Bulk of Soil

Microbial precipitation of calcium carbonate takes place in nature by different mechanisms. One of them is microbially induced carbonate precipitation (MICP), which is performed due to bacterial hydrolysis of urea in soil in the presence of calcium ions. The MICP process can be adopted to reduce the permeability and/or increase the shear strength of soil. In this paper, a study on the use of Bacillus sp., which was isolated from tropical beach sand, to perform MICP either on the surface or in the bulk of sand is presented. If the level of calcium salt solution was below the sand surface, MICP took place in the bulk of sand. On the other hand, if the level of calcium salt solution was above the sand surface, MICP was performed on the sand surface and formed a thin layer of crust of calcium carbonate. After six sequential batch treatments with suspension of urease-producing bacteria and solutions of urea and calcium salt, the permeability of sand was reduced to 14 mm/day (or 1.6×10−7 m/s) in both cases of bulk and surface MICP. Quantities of precipitated calcium after six treatments were 0.15 and 0.60 g of Ca per cm2 of treated sand surface for the cases of bulk or surface MICP, respectively. The stiffness of the MICP treated sand also increased considerably. The modulus of rupture of the thin layer of crust was 35.9 MPa which is comparable with limestone.

Effect of Mixing Urea with Humic Acid and Acid Sulphate Soil on Ammonia Loss, Exchangeable Ammonium and Available Nitrate

Problem statement: Ammonia loss due to rapid hydrolysis of urea in soil following surface application can be substantial. Ammonia loss in agriculture is estimated to be 1 to 60%. This laboratory study compared the effect of three different urea-humic acid-acid sulphate soil mixtures on NH3 loss and soil ammonium and nitrate contents, with loss from surface applied urea without additives (urea alone). Approach: Humic acid, acid sulfate soil and soil use in the incubation study was analyzed for selected soil physical-chemical properties. The fertilizers mixture and ammonia loss was done using standard methods. The treatments were evaluated in Randomized Complete block Design with 3 replications. The data obtained at the end of the study on total ammonia loss, soil pH, exchangeable ammonium and available nitrate were analyzed using analysis of variance and the means were compared using Duncan’s test using Statistical Analysis System (SAS) version 9.2. Results: The soil used to test treatments was a sandy clay loam Typic Paleudults (Nyalau series). The mixture significantly reduced NH3 loss by between 31.5 and 36.7% compare with urea alone with larger reductions with higher rate of humic acid (0.75 and 1 g Kg-1 of soil) and acid sulphate soil (0.75 g Kg-1 of soil). The impact of the treatment also showed significant effect on the soil pH and ammonium content at the end of study. Conclusion: Amending urea with acid sulphate soil and humic acid can reduce ammonia loss in acid soils by improving ammonium retention. This may in effect improve urea-N use efficiency as well as reducing environmental pollution in agriculture.

Free fatty acids from the pasture grass Brachiaria humidicola and one of their methyl esters as inhibitors of nitrification

The tropical pasture grass, Brachiaria humid- icola (Rendle) Schweick, produces nitrification inhib- itory compounds (termed biological nitrification inhibitors or BNIs) in its shoot and root tissues and releases BNIs from its roots. In the present study, two BNI compounds were isolated and identified from the shoot tissue of B. humidicola using activity-guided fractionation. The recombinant Nitrosomonas europaea containing luxAB genes derived from the biolumines- cent marine gram-negative bacterium Vibrio harveyi, were used to determine BNI activity. The BNI com- pounds in the shoot tissue were identified as linoleic acid (LA) and linolenic acid (LN) using authentic- chemicals obtained from ©Sigma (ED80 16.0 μ gm l −1 for both LA and LN) for verification. None of the other tested free fatty acids namely stearic acid, oleic acid, arachidonic acid, and cis-vaccenic acid showed any inhibitory effect on nitrification. Among the fatty acid methyl esters (FAME) evaluated (methyl oleate, methyl linoleate (LA-ME) and methyl linoleneate (LN-ME)), only LA-ME showed an inhibitory effect (ED80 8.0 μ gm l −1 ). The inhibitory effect of LA, LN and LA-ME in the soil was stable for 120 days at 20°C. Soil treated with LA, LN and LA-ME showed a very low accumulation of NO3 − and the maintenance of soil inorganic N in the NH4 + form. The inhibitory effect of LA-ME on soil nitrification was greater than that of LA or LN. In addition to BNI activity, both LA and LA- ME showed a suppressive effect on urea hydrolysis in soil. Both LA and LN blocked the AMO (ammonia monooxygenase) and HAO (hydroxylamino oxidoreduc- tase) enzymatic pathways in Nitrosomonas .S ince LA and LN can be produced from vegetable oils such as soybean, flax or sunflower, they have the potential for use as nitrification inhibitors in production agriculture.

Influence of Crop Residues and Organic Manures on the Hydrolysis of Urea in a Typic Haplustept

The emphasis on integrated use of organic amendments and fertilizers has made it imperative to study the effect of crop residues and organic manures on urea hydrolysis, which governs the release of N from urea fertilizer. Urea hydrolysis in soils is an enzymatic decomposition process facilitated by the extracellular enzyme urease. Our aim was to assess the influence of crop residues (rice straw, wheat straw) and organic manures (poultry manure, farm yard manure, cowpea, and sesbania) on urea hydrolysis by conducting a laboratory incubation experiment employing a Hasanpur silt loam soil (coarse loamy, mixed, hypothermic Typic Haplustept). The study was conducted at a constant temperature of 33 ± 1°C at two moisture levels (1:1 soil:water ratio and field capacity). The results showed that the rate of urea hydrolysis decreased with an increase in time of incubation (12 to 96 h), while the disappearance of urea N was associated with the corresponding increase in ( + )-N content in soils treated with crop residues and organic manures. In the nonamended soil, the time required 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, 60 to 72 h of incubation periods were required for urea hydrolysis. The rate of urea hydrolysis in the amended soil was of the following order: sesbania > cowpea > poultry manure > farmyard manure > rice straw and wheat straw, irrespective of the moisture regime. Urea hydrolysis followed first-order kinetics in all the treatments at both moisture levels. The rate constant value for urease activity was higher at field capacity, indicating that urea hydrolysis proceeded rapidly under the condition of field capacity rather than saturated conditions (1:1 soil:water ratio).

Urease and Nitrification Retardation Properties in Natural Essential Oils and Their By‐products

A laboratory incubation experiment was conducted with the natural essential oil of peppermint (Mentha spicata, MS), dementholized oil (DMO), terpenes, and a chemical inhibitor dicyandiamide (DCD), as coating materials for retardation of soil urea hydrolysis and nitrification. Retardation of nitrification was highest with DCD. The urea hydrolysis and nitrification processes were inhibited by all three natural products. Intensity of inhibition of both the processes increased with the level of application of the coating materials. With 0.50% level of coating, urea hydrolysis inhibition was in this decreasing order: DMO>terpenes>DCD>M. spicata oil; whereas at 1.00%, inhibition followed this order: terpenes>DMO>M. spicata oil>DCD. At 0.50% level of coating nitrification inhibition decreased in this order: M. spicata oil>DCD>DMO>terpenes; with 1.00%, the order was DCD>DMO>M. spicata oil>terpenes. All the three natural products (DMO, terpenes, and M. spicata oil) significantly retarded soil urease activity. These natural nitrification inhibitors significantly retarded Nitrosomonas. Nitrobacter, and total bacterial and actinomycete populations. Microbial activity retardation was more intense at a higher level of coating. We concluded that the different coating materials used could be used as potential retardants of urease activity as well as nitrification, unlike DCD, which is a potential retardant of nitrification and has little effect on the urea hydrolysis. The natural products, unlike chemical nitrification inhibitors, are less persistent, biodegradable, ecofriendly, and cheap.

Leaching and Transformation of Nitrogen Fertilizers in Soil After Application of N with Irrigation: A Soil Column Method

ABSTRACT A soil column method was used to compare the effect of drip fertigation (the application of fertilizer through drip irrigation systems, DFI) on the leaching loss and transformation of urea-N in soil with that of surface fertilization combined with flood irrigation (SFI), and to study the leaching loss and transformation of three kinds of nitrogen fertilizers (nitrate fertilizer, ammonium fertilizer, and urea fertilizer) in two contrasting soils after the fertigation. In comparison to SFI, DFI decreased leaching loss of urea-N from the soil and increased the mineral N (NH4+-N + NO3−N) in the soil. The N leached from a clay loam soil ranged from 5.7% to 9.6% of the total N added as fertilizer, whereas for a sandy loam soil they ranged between 16.2% and 30.4%. Leaching losses of mineral N were higher when nitrate fertilizer was used compared to urea or arrmonium fertilizer. Compared to the control (without urea addition), on the first day when soils were fertigated with urea, there were increases in NH4+-N in the soils. This confirmed the rapid hydrolysis of urea in soil during fertigation. NH4+-N in soils reached a peak about 5 days after fertigation, and due to nitrification it began to decrease at day 10. After applying NH4+-N fertilizer and urea and during the incubation period, the mineral nitrogen in the soil decreased. This may be related to the occurrence of NH4+-N fixation or volatilization in the soil during the fertigation process.

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 &gt; Dadupur loam &gt; Hisar sandy loam &gt; Jakhol silty clay loam &gt; Bawal loamy sand &gt; 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.

Efficiency of N-(n-butyl) thiophosphoric triamide in retarding hydrolysis of urea and ammonia volatilization losses in a flooded sandy loam soil amended with organic materials

Using a forced-draft chamber technique, the suppression of NH3 volatilization losses by applying N-(n-butyl) thiophosphoric triamide (NBPT) was studied in an alkaline sandy loam soil amended with green manure or wheat straw. Applied urea was completely hydrolysed in 12, 8 and 6 days in unamended, green manure and wheat straw amended soil, respectively. By applying 0.5% (w/w of urea) NBPT, complete hydrolysis of urea was delayed up to 16 days in the unamended soil, whereas in wheat straw amended soil urea hydrolysis was completed by the 12th day even when it was treated with 2% NBPT. Applied at 1 or 2% level, NBPT delayed the NH3 volatilization to the 4th day after application of urea in green manure or wheat straw amended soil. Hydrolysis of urea was more effectively retarded by applying NBPT in the unamended soil than in soil amended with green manure or wheat straw. In the unamended soil, 7.1% of the applied urea was lost through NH3 volatilization. The losses were reduced to 1.2 and 0.7% by applying 0.5 and 1% NBPT, respectively. Enhanced NH3 volatilization caused by the green manure or wheat straw was counteracted by applying NBPT.

Short-term effects of urea amended with the urease inhibitor N-(n-butyl) thiophosphoric triamide on perennial ryegrass

The current study investigated the short-term physiological implications of plant nitrogen uptake of urea amended with the urease inhibitor N-(n-butyl) thiophosphoric triamide (nBTPT) under both greenhouse and field conditions. 15N labelled urea amended with 0.0, 0.01, 0.1 and 0.5% nBTPT (w/w) was surface applied at a rate equivalent to 100 kg N ha−1 to perennial ryegrass in a greenhouse pot experiment. Root, shoot and soil fractions were destructively harvested 0.75, 1.75, 4, 7 and 10 days after fertilizer application. Urease activity was determined in each fraction together with 15N recovery and a range of chemical analyses. The effect of nBTPT amended urea on leaf tip scorch was evaluated together with the effect of the inhibitor applied on its own on plant urease activity. nBTPT-amended urea dramatically reduced shoot urease activity for the first few days after application compared to unamended urea. The higher the nBTPT concentration the longer the time required for shoot activity to return to that in the unamended treatment. At the highest inhibitor concentration of 0.5% shoot urease activity had returned to that of unamended urea by 10 days. Root urease activity was unaffected by nBTPT in the presence of urea but was affected by nBTPT in the absence of urea. Transient leaf tip scorch was observed approximately 7–15 days after nBTPT + urea application and was greatest with high concentrations of nBTPT and high urea-N application rates. New developing leaves showed no visual sign of tip necrosis. Urea hydrolysis of unamended urea was rapid with only 1.3% urea-N remaining in the soil after 1.75 days. N uptake and metabolism by ryegrass was rapid with 15N recovery from unamended urea, in the plant (shoot + root) being 33% after 1.75 days. Most of the 15N in the soil following the urea+0.5% nBTPT application was still as urea after 1.75 days, yet 15N plant recovery at this time was 25% (root+shoot). This together with other evidence, suggests that if urea hydrolysis in soil is delayed by nBTPT then urea can be taken up by ryegrass as the intact molecule, albeit at a significantly slower initial rate of uptake than NH4 +-N. Protein and water soluble carbohydrate content of the plant were not significantly affected by amending urea with nBTPT however, there was a significant effect on the composition of amino acids in the roots and shoots, suggesting a difference in metabolism. Although nBTPT-amended urea affected plant urease activity and caused some leaf-tip scorch the effects were transient and short-lived. The previously reported benefit of nBTPT in reducing NH3 volatilization of urea would appear to far outweigh any of the observed short-term effects, as dry-matter production of ryegrass is increased.

Metabolism of the urease inhibitor n-( n -butyl)thiophosphoric triamide (nbpt) in soils

An experiment was conducted to relate the effectiveness of N-( n-butyl)thiophosphoric triamide (NBPT) and its oxon analog N-( n-butyl)phosphoric triamide (BNPO) in controlling urea hydrolysis in soils to their corresponding soil concentrations. Both compounds were applied to an acid soil (pH 4.9) and to the same soil that had been neutralized (pH 7.1) by long-term liming or by the recent application of Ca(OH) 2. Hydrolysis of urea applied with the inhibitors was monitored along with the disappearance of the compounds themselves. Both compounds controlled urea hydrolysis much more effectively in the neutral soils than in the acid soil. HPLC analysis of soil extracts demonstrated that both compounds disappeared more rapidly in the acid soil, and that the compounds disappeared at similar rates for both neutral soils, indicating that pH governed disappearance rates in these soils. Disappearance rates were generally first-order for both compounds, although NBPT disappeared at an accelerated rate at low concentrations, presumably due to its simultaneous conversion to BNPO. The effectiveness of both compounds in controlling urea hydrolysis was closely related to the concentrations of BNPO found in the soil. BNPO was generally maintained at higher concentrations following NBPT application than when BNPO was applied directly to soil.

Fertilizer and temperature effects on urea hydrolysis in undisturbed soil

Few published studies have examined the effects of a continuous fertilizer application on urea hydrolysis. In the present study we investigated the effects of 9 years of continuous application of urea and P fertilizers on urea hydrolysis in undisturbed soil samples as affected by temperature (5–45°C). Undisturbed soil samples of surface horizons (0–7 cm) were obtained with cutting rings (50 cm3) from different fertilizer-treatment plots and inserted in polyethylene bottles (with cutting rings). Each soil sample (in the cutting ring) was treated with 10 ml urea solution (0.5 mmol urea N g-1 soil) and then broght to 90% field capacity. The samples were left to equilibrate for 30 min at a temperature of 4°C, then placed in an incubator at 37°C for 6 h. The results indicated that 9 years of continuous application of urea but not P had a significant effect on urea hydrolysis in soil. There was a good correlation between temperature and urea hydrolysis in soil. Q 10 was between 1.97 and 2.08 in the temperature range 5–45°C.

Urease activity and urea hydrolysis in soils treated with sewage

A laboratory experiment was conducted to study the relationship between soil urease activity and other soil properties in order to predict efficient utilization of urea fertilizer. Surface (0–15 cm) and sub-surface (15–30 cm) soil samples were collected from sewage-treated and untreated fields from 10 diverse sites in Haryana (India). Urease activity ranged from 2.48 to 15.91 μg urea N hydrolysed g −1 soil h −1 at 37°C. It was higher in surface and sewage-treated than in sub-surface and untreated soils. It was significantly correlated with soil organic carbon, cation exchange capacity, electrical conductivity, pH and total nitrogen, copper and manganese. Urea hydrolysis followed first-order kinetics, and the rate of hydrolysis increased with temperature in all the soils. It was faster in sewage-treated than in untreated soils. Controlled urea application is essential for better fertilizer use efficiency. Thermodynamic properties (energy of activation, enthalpy, entropy) were higher in untreated than in treated soils.

Thiosulfate Inhibition of Urea Hydrolysis in Soils: Tetrathionate as a Urease Inhibitor

AbstractAmmonium thiosulfate [ATS, (NH4)2S2O3, 12‐0‐0‐26S] added to urea‐ammonium nitrate (UAN) inhibits urea hydrolysis after application to soil. Thiosulfate itself does not inhibit purified jackbean urease, so products of S2O2‐3 oxidation in soil (tetrathionate [S4O2‐6], Fe2+, and Mn2+) are the probable urease inhibitor(s). The objectives of this study were to (i) identify the primary urease inhibitor produced by ATS in soil and (ii) determine why the efficacy of the inhibitor is improved by increasing UAN droplet size. Jackbean urease (urea amidohydrolase, Type III from jackbean, EC 3.5 1.5) was inhibited by Fe2+ (100% inhibition at 0.3 mM), Mn2+ (100% at 6.3 mM), Fe3+ (97% at 6.3 mM), and S4O2‐6 (39% at 7.8 mM). Thiosulfate did not inhibit jackbean urease at concentrations up to 18.8 mM. When applied in a simulated UAN fertilizer band, S4O2‐6 was as effective as S2O2‐3; it inhibited soil urease (24%) to the same extent as S2O2‐3 (26%) but more than FeSO4 (0%) in two soils. Urease inhibition by all species was low in unbuffered 5‐h soil incubations (Fe2+ [14%], Mn2+ [3%], S4O2‐6 [10%], and S2O3 [7%]) with 25 mmol S kg−1. Urease inhibition by S4O2‐6 increased from 9% at pH 7 to 30% at pH 8.5 in buffered incubations. Since pH during urea hydrolysis increases with UAN droplet size, the increased efficacy of ATS with application of large UAN droplets is probably due to greater activity of S4O2‐6 as a urease inhibitor at pH &gt; 7. Tetrathionate is the primary urease inhibitor produced by ATS in soil. Reaction of urease sulfhydryl groups with S4O2‐6 is proposed as an inhibitory mode of action.

Persistence of the inhibitory effects of phosphoroamides on urea hydrolysis in soils

Abstract The persistence of the inhibitory effects of three phosphoroamides [N‐(n‐butyl) thiophosphoric triamide (NBPT), phenylphosphorodiamidate (PPD), and thiophosphoryl triamide (TPT)] on urea hydrolysis in soils was assessed by measuring the ability of four soils to hydrolyze urea after they had been treated with 5 μg phosphoroamide/g soil and incubated at 15°C or 30°C for 0, 3, 7, 14, or 28 days. The soils used differed markedly in pH, texture, and organic‐matter content. The data obtained showed that the persistence of the effects of the phosphoroamides studied decreased with increase in soil temperature from 15°C to 30°C and that whereas the effect of PPD decreased with increase in the time of incubation, the effects of NBPT and TPT sometimes increased before decreasing with increased time of incubation. These observations are in harmony with the recent findings that PPD is a potent inhibitor of urease activity, but decomposes in soils with formation of phenol, which is a relatively weak inhibitor ...