Effects of urease inhibitors on nitrification in soils

The effects of 10 urease inhibitors on nitrification in soils were studied by determining the effects of 10 and 50 parts/10⁶ (soil basis) of each inhibitor on the amounts of nitrate and nitrite produced when soils treated with ammonium sulfate (200 μg of ammonium N/g of soil) were incubated (30°C) under aerobic conditions for 14 days. The urease inhibitors used (catechol. hydroquinone, p-benzoquinone, 2,3-dimethyl-p-benzoquinone, 2,5-dimethyl-p-benzoquinone. 2,6-dimethyl-p-benzoquinone. 2,5-dichloro-p-benzoquinone, 2,6-dichloro-p-benzoquinone. sodium p-chloromercuribenzoate, and phenylmercuric acetate) were those found most effective in previous work to evaluate more than 130 compounds as soil urease inhibitors. Their effects on nitrification were compared with those of three compounds patented as soil nitrification inhibitors (N-Serve. AM. and ST).Most of the urease inhibitors studied had little effect on nitrification when applied at the rate of 10 μg/g of soil. but had marked inhibitory effects when applied at the rate of 50 μg/g of soil. None inhibited nitrification as effectively as N-Serve. but phenylmercuric acetate inhibited nitrification more effectively than did AM or ST when applied at the rate of 10 μg/g of soil. Phenylmercuric acetate, 2,5-dimethyl-p-benzoquinone, and 2,6-dimethyl-p-benzoquinone had very marked effects on nitrification when applied at the rate of 50 μg/g of soil.     

Release and recovery of nitrogen from winter annual cover crops in no‐till corn production

Abstract

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

Problems in the use of urea as a nitrogen fertilizer

Abstract. N -( n -butyl) thiophosphoric triamide (NBPT) is the most effective compound currently available for retarding hydrolysis of urea fertilizer in soil and for decreasing ammonia volatilization and nitrite e accumulation in soils treated with urea. It is a poor inhibitor of plant or microbial urease, but decomposes quite rapidly in soil with formation of N -( n -butyl) phosphoric triamide, which is a potent inhibitor of urease activity.
The adverse effects of urea fertilizers on seed germination and seedling growth in soil are due to ammonia produced through hydrolysis of urea by soil urease. They can be eliminated by addition of a urease inhibitor to these fertilizers.
The leaf-burn commonly observed after foliar fertilization of soybeans with urea results from accumulation of toxic amounts of urea in the soybean leaves rather than formation of toxic amounts of ammonia through urea hydrolysis by leaf urease. Leaf-burn is accordingly increased rather than decreased by addition of a urease inhibitor to the urea fertilizer applied.     

Production of urease by microbial activity in soils under aerobic and anaerobic conditions

Summary Several workers have reported that O₂ has little, if any, effect on hydrolysis of urea by soil urease, but others have reported that it has a marked effect, hydrolysis being significantly faster in soils under aerobic conditions than in O₂-depleted soils. In studies to account for these divergent results, we found that whereas plant residues and other readily decomposable organic materials markedly stimulated microbial production of urease in soils under aerobic conditions, they did not greatly stimulate production of urease in soils under anaerobic conditions. We also found that although anaerobic conditions retarded production of urease by soil microorganisms, they did not inhibit hydrolysis of urea by soil urease. These observations suggest that the divergent findings concerning the effect of O₂ on hydrolysis of urea by soil urease may have resulted from differences in the amounts of readily decomposable organic materials in the soils studied.     

Use of p-benzoquinone and hydroquinone for retardation of urea hydrolysis in soils

Studies to evaluate p-benzoquinone (PBQ) and hydroquinone (HQ) for retardation of urea hydrolysis in soils showed that the effects of these compounds increase markedly with the amount of PBQ or HQ added and decrease markedly with time and with increase in temperature from 10 to 40°C. They also indicated that PBQ and HQ inhibit soil urease activity by identical mechanisms. The effects of various soil properties on the effectiveness of PBQ and HQ for retardation of urea hydrolysis in soils were investigated by studies with 25 surface soils selected to obtain a wide range in pH, texture and organic-matter content. Simple correlation analyses showed that the inhibitory effects of PBQ or HQ on urea hydrolysis in these soils were correlated very highly significantly with organic C content ($\text{r}\text{= ? 0.76}{}^{71}$), total N content ($\text{r}\text{= ? 0.74}{}^{71}$), urease activity ($\text{r = ? 0.70}{}^{71}$) andcation-exchange capacity ($\text{r}\text{= ? 0.62}{}^{71}$). The effects of these compounds also were highly significantly correlated with sand content ($\text{r}\text{= 0.57}{}^7$) and were significantly correlated with silt content ($\text{r}\text{= ? 0.421}$), clay content ($\text{r}\text{= ? 0.491}$) and surface area ($\text{r}\text{= ? 0.491}$), but were not significantly correlated with pH or CaCO₃ equivalent. Multiple-regression analyses indicated that the effectiveness of PBQ and HQ for retardation of urea hydrolysis in soils tends to increase with decrease in soil organicmatter content.     

Urease Inhibition by Metals and its Relation to Nitrogen Transformations

The inhibitory effects of twelve metallic cations on urease activity in three soil types were evaluated. Four of these metals Cu⁺², Fe⁺³, Al⁺³ and Co⁺² in their sulphate forms were tested for retarding the urea hydrolysis in soils. They reduced the accumulation of NH₄-N, nitrite and gaseous losses of ammonia between 35 and 50%.     

Urea hydrolysis in soils: Factors influencing the effectiveness of phenylphosphorodiamidate as a retardant

Studies to determine the factors influencing the effectiveness of phenylphosphorodiamidate (PPD) to retard urea hydrolysis in soils showed that the inhibitory effect of PPD on hydrolysis of urea by soil urease increased markedly with the amount of PPD added and decreased markedly with time and with increase in temperature from 10 to 40°C. They also showed that the ability of PPD to retard urea hydrolysis in 15 surface soils selected to obtain a wide range in properties was significantly correlated with organic C content (r = ?0.68⁷), total N content (r = ?0.74⁷), cation-exchange capacity (r = ?0.65⁷), sand content (r=0.66⁷), clay content (r = ?0.64⁷) and surface area (r = ?0.60¹), but was not significantly correlated with pH, silt content, urease activity or CaCO₃ equivalent. Multiple-regression analyses indicated that the effectiveness of PPD to retard urea hydrolysis in soils tends to increase with decrease in soil organic-matter content.     

Urea Hydrolysis of Tea Soils as Influenced by Incubation Period,Soil pH,and Nitrification Inhibitor

Abstract

Laboratory incubation studies were conducted with south Indian tea soils to investigate the influence of soil pH, incubation period, and nitrification inhibitor on urea hydrolysis. The soils used in this experiment were sampled from six different regions of south India. The physicochemical properties, urea hydrolysis as influenced by soil pH, incubation period, and nitrification inhibitor were determined. There was a strong positive correlation between urease activity and organic‐matter content of tea soils, whereas physicochemical properties failed to show any relationship with urease activity. The urease activity was highest in Munnar soils. At 25°C, the activity reached maximum within 15 days after fertilizer application, and it was considerably high up to 36 days in the soils of Anamallais, 18 days in Munnar, and 27 days in other zones studied, which revealed the minimum interval between two successive urea fertilizer applications. Soils of different zones showed a different pattern of urease activity when the soil pH was changed artificially between 4 and 5.5. Addition of nitrification inhibitor [dicyandiamide, DCD] to urea prevented nitrate ion formation, resulting in the accumulation of desirable ammonium ions.     

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 of urease activity, whereas NBPT and TPT do not inhibit urease activity but decompose in soil with formation of their oxon analogs, which are potent inhibitors of urease activity. The inhibitory effect of NBPT on urea hydrolysis was considerably more persistent than that of PPD or TPT and was significant even after incubation of NBPT‐treated soil at 15°C or 30°C for 28 days.     

Effects of phosphoroamides on ammonia volatilization and nitrite accumulation in soils treated with urea

Summary We compared the effects of N-(n-butyl) thiophosphoric triamide (NBPT), N-(diaminophosphinyl)-cyclohexylamine (DPCA), phenylphosphorodiamidate (PPD), and hydroquinone on transformations of urea N in soils. The ability of these urease inhibitors to retard urea hydrolysis, ammonia volatilization, and nitrite accumulation in soils treated with urea-decreased in the order NBPT > DPCA PPD > HQ. When five soils were incubated at 30°C for 14 days after treatment with urea (1 mg urea N g^–1 soil), on average, the gaseous loss of urea N as ammonia and the accumulation of urea N as nitrite were decreased from 52 to 5 % and from 11 to 1%, respectively, by addition of NBPT at the rate of 10 g g^–1 soil (0.47 parts of NBPT per 100 parts of urea). The data obtained support previous evidence that NBPT is more effective than PPD for reduction of the problems encountered in using urea as a fertilizer and deserves consideration as a fertilizer amendment for retarding hydrolysis of urea fertilizer in soil.     

Soil urease activity and kinetics

The activity and kinetic properties of urease in several Malaysian soils were examined. The values for K_m and V_max of the soils computed according to the Hanes equation were in general agreement with other reports as far as magnitudes were concerned. A significant correlation between K_m and V_max was also obtained. The urease activity of the soils was variable, and it was noted that expression of the activity as the time required to hydrolyze half of the applied urea has limited use in soils of low activity. In all soils studied, inhibition of urease activity was effectively achieved using Ag⁺, while Cu²⁺ was only effective in two soils, and marginally effective in the other two soils. Urease inhibitors have potential applications in reducing volatilization losses of ammonia derived from urea applied to soils.     

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

Abstract

Work reported showed that N‐butyl phosphorothioic triamide (NBPT) is considerably more effective than phenylphosphorodiamidate (PPD) as a soil urease inhibitor and merits consideration as a fertilizer amendment for retarding hydrolysis of urea fertilizer in soil. Studies to determine the factors influencing the effectiveness of NBPT for retardation of urea hydrolysis in soil showed that the inhibitory effect of NBPT on hydrolysis of urea by soil urease increased markedly with the amount of NBPT added and decreased markedly with time and with increase in temperature from 10 to 40°C. They also showed that the ability of NBPT to retard urea hydrolysis in 13 surface soils selected to obtain a wide range in properties was significantly correlated with organic C content (r = ‐0.70**), total N content (r = ‐0.76**), cation‐exchange capacity (r = ‐0.67* ), sand content (r = 0.61*), clay content (r = ‐0.63*), and surface area (r = ‐0.66*), but was not significantly correlated with pH, silt content, urease activity, or CaCO₃ equivalent. Multiple‐regression analyses indicated that the effectiveness of NBPT for retardation of urea hydrolysis in soil tends to increase with decrease in soil organic‐matter content.     

Transformations and effects of urea derivatives in soil

The application of urea phosphate, urea nitrate and thoiurea to a silty clay soil from Nile Delta (pH 7.4, 1,9% CaCO₃) inhibited soil urease activity if compared to urea. The nitrification process of ammonia formed from urea hydrolysis was retarded. The use of these urea derivatives eliminated nitrite accumulation and greatly retarded nitrate formation with increased recovery of urea-N throughout the experimental period. Gaseous losses of urea-N as ammonia or by denitrification were reduced. These derivatives may be much more advantageous than urea if fertilizer effeciency is to be increased.     

添加脲酶抑制剂NBPT对麦秆还田稻田氨挥发的影响

氨挥发是稻田氮素损失的重要途径,为探明脲酶抑制剂NBPT对小麦秸秆还田稻田中氨挥发的影响,采用密闭室通气法,在太湖地区乌珊土上,研究了脲酶抑制剂n-丁基硫代磷酰三胺(NBPT)对小麦秸秆还田稻田中施肥后尿素水解和氨挥发动态变化的影响。结果表明:稻田氨挥发损失主要集中在基肥和分蘖肥时期。添加NBPT可明显延缓尿素水解,推迟田面水NH4+-N峰值出现的时间,并降低NH4+-N峰值,降低了田面水氨挥发速率和挥发量。NBPT的效果在基肥和分蘖肥施用后尤为明显,不加NBPT时施入的尿素在2~3 d内基本水解彻底,NH4+-N和氨挥发速率在第2 d即达到峰值,两次施肥后NH4+-N峰值分别为132.3 mg·L-1和66.3mg·L-1,氨挥发峰值为15.6 kg·hm-2·d-1和10.4 kg·hm-2·d-1;而添加NBPT后,NH4+-N峰值推迟至施肥后第4 d出现,NH4+-N峰值降至70.7 mg·L-1和51.6 mg·L-1,氨挥发峰值降至4.7 kg·hm-2·d-1和2.6 kg·hm-2·d-1。添加NBPT使稻田氨挥发损失总量从73.3 kg(N)·hm-2(占施氮量的24.4%)降低至34.5 kg(N)·hm-2(占施氮量的11.5%),降低53%。在添加小麦秸秆稻田中添加NBPT通过延缓尿素水解而显著降低了氨挥发损失。     

Effect of N-(n-butyl) thiophosphoric triamide on hydrolysis of urea by plant,microbial, and soil urease

Summary Comparison of the effects of N-(n-butyl) thiophosphoric triamide (NBPT) and phenylphosphorodiamidate (PPD) on hydrolysis of urea by plant (jackbean), microbial (Bacillus pasteurii), and soil urease showed that whereas NBPT was considerably more effective than PPD for inhibiting hydrolysis of urea added to soil, it was much less effective than PPD for inhibiting hydrolysis of urea by plant or microbial urease. Studies to account for this observation indicated that NBPT is rapidly decomposed in soil to a compound that is much more effective than NBPT for inhibition of urease activity and that this compound is N-(n-butyl) phosphoric triamide.     

Hydrolysis of urea in two sandy soils under citrus production as influenced by rate and depth of placement

Abstract

The use of urea as a nitrogen (N) source is increasing in citrus production on sandy soils in Florida. Entisol and Spodosol are the two major soil orders used for citrus production. This study was conducted to examine the difference in rate of urea hydrolysis as influenced by depth of placement in a Candler fine sand (Typic Quartzipsamment) and a Wabasso sand (Alfic Haplaquod). These two soils represent the contrasting soils typically found in the citrus growing region of central, southern, and east coast regions of Florida. The rate of urea hydrolysis was faster in a Candler fine sand than that in a Wabasso sand and was greater for the low (0.25 g N/kg) than that for the increased (0.50 or 1.00 g/kg) rates of urea applications in both soils. In a parallel experiment, the rate of urea hydrolysis was examined at various depths (0 to 15‐, 15 to 30‐, 30 to 45‐, and 45 to 60‐cm) in the Candler fine sand using in situ and laboratory incubation studies. The rate of urea hydrolysis decreased with an increase in depth of placement of urea. Increased content of organic matter and higher soil temperature in the surface soil may contribute to increase in urease activity thus resulting in increased rate of urea hydrolysis than that in the lower depth soil.     

Effects of thiosulfate and tetrathionate on urease activity and seedling growth

Abstract

Interest in use of ammonium thiosulfate (ATS) in conjunction with urea as a fertilizer has been stimulated by reports that ATS retards hydrolysis of urea by soil urease. We recently found, however, that ATS significantly retarded urea hydrolysis in soil only when applied at very high rates (>2,500 (μg/g soil) that adversely affected seedling development. Because ATS is rapidly oxidized in soil, we compared the effects of thiosulfate and its oxidation products (tetrathionate, sulfite, and sulfate) on urea hydrolysis and seedling development in soil and hydrolysis of urea by jackbean urease. We found that the inhibitory effect of thiosulfate on urea hydrolysis in soil is due to tetrathionate formed by oxidation of thiosulfate and that both thiosulfate and tetrathionate have an adverse effect on seedling growth of wheat and corn in soil. Tetrathionate at concentrations of 2,500 and 5,000 μ.g/mL inhibited hydrolysis of urea by jackbean urease, whereas thiosulfate had no inhibitory effect at these concentrations. We could not confirm a hypothesis that the inhibitory effect of ATS on soil urease is due to Fe²⁺ and Mn²⁺ formed during oxidation of thiosulfate in soil.     

铅对两个红壤中酶活性的影响

Enzyme activities have the potential to indicate biological functioning of soils. In this study, soil urease, dehydrogenase, acid phosphatase and invertase activities and fluorescein diacetate（FDA） hydrolysis were measured in two red soils spiked with Pb^2＋ ranging from 0 to 2 400 mg kg^-1 to relate the enzyme activity values to both plant growth and the levels of available and total Pb^2＋ concentrations in soils, and to examine the potential use of soil enzymes to assess the degrees of Pb contamination. Soil samples were taken for enzyme activities assaying during 3 month’s incubation and then after planting of celery（Apium graveolens L.） and Chinese cabbage（Brassica chinensis L.）. Enzyme activities in the red soil derived from arenaceous rock（RAR） were generally lower than those in the red soil developed on Quaternary red earths（REQ）. At high Pb^2＋ loadings, in both incubation and greenhouse studies, urease activity and FDA hydrolysis were significantly inhibited. But there were no significant relationships between soil dehydrogenase, acid phosphatase or invertase activity and soil Pb^2＋ loadings in both RAR and REQ soils. The growth of celery and Chinese cabbage increased soil urease activity and FDA hydrolysis, but had minimal effect on dehydrogenase and invertase activities. There were positive correlations between celery biomass and soil urease activity and FDA hydrolysis. These results demonstrate that urease activity and FDA hydrolysis are more sensitive to Pb^2＋ than acid phosphatase, dehydrogenase and invertase activities in the RAR and REQ soils.     

Ureolytic microorganisms and soil fertility: A review

Abstract

Soil microorganisms play an important role in increasing soil fertility and recycling of nutrients within the soil. Different microorganisms including filamentous fungi, yeasts, mycorrhiza, bacteria, cyanobacteria, and actinomycetes possess the urease enzymes. Urease plays a role in soil enrichment through degradation or hydrolysis of organic nitrogen (N). Urea is an important fertilizer and may enter the soil with the excretions of higher animals and through destruction of the nitrogenous bases contained in the nucleic acids of plant and animal tissues. These products increase soil fertility by an urease. Ureolytic production and activity, and fertility of soil are affected by chemical propertes of soil, environmental factors, sources of urea, and soil microorganism. Problems encountered in use of urea as a fertilizer result from its rapid hydrolysis to ammonium carbonate by soil urease activity and the concomitant rise in pH and accumulation of ammonium. These problems include damage to germinating seedlings and young plants and gaseous loss of urea N as ammonia. The technologies and management practices that can be used to improve urea efficiency and reduce losses include coating of granules, soil incorporation, and use of new slow‐release fertilizers by forming sparingly soluble urea‐aldehyde compounds as ureaforms, crotonylidene diurea, isobutylidene diurea or using natural N‐containing compounds such as composted sludges of municipal and animal wastes. The degradative process of the ureolytic microorganims on animal and plant organic N wastes could help to satisfy condition of eliminating excessive wastes and pollution and simultaneously supply plant with available N.     

Effect of soil on urease inhibition by substituted urea herbicides

The effects of some substituted urea herbicides, fenuron, monuron, diuron and linuron, on soil urease were investigated. All herbicides are soil urease mixed inhibitors and the same inhibition mechanism is presumed. A kinetic relationship, which takes into account herbicide adsorption, is developed in order to calculate the inhibition constants of soil urease from adsorption constants. A linear relationship between Hammett sigma values and log K_i for fenuron, monuron and diuron is obtained, from which the formation of a complex between herbicides and enzyme is proposed By comparing kinetic constants for soil urease with those obtained for jack bean, in the presence of the same herbicides, a possible effect of the soil matrix on the enzyme-herbicide complex is also suggested.