N-butyl Thiophosphoric Triamide Research Articles

Urea- Versus Ammonium Nitrate–Based Fertilizers for Green Sugarcane Cultivation

This study tested the hypothesis that enhanced-efficiency fertilizers, such as urea treated with NBPT, are a feasible substitute for ammonium nitrate–based fertilizers for green sugarcane cultivation. The experimental design included six N sources applied over sugarcane straw at two sites in Central-South Brazil. Treatments included ammonium nitrate, urea, and four urea-based fertilizers treated with different rates of the urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT) at two rates of N (50 and 100 kg ha−1), plus an additional control. Nitrogen status in the plant, the activity of glutamine synthetase (GS) and nitrate reductase (NR) in the leaves, and sugarcane stalk yield and quality were evaluated. At site 1, N rates increased the SPAD index, stalk yield, N uptake, and sugar yield. At site 2, N rates increased GS activity, N content, the SPAD index, and N uptake, but stalk and sugar yield were not increased due to large variability in these parameters. All N sources resulted in similar yields at both sites. These results were compared with those in the literature. Among 27 studies surveyed, the average sugarcane yield was 97.8 or 97.4 Mg ha−1 under ammonium nitrate or urea fertilization, respectively, and these averages did not differ by the Kruskal-Wallis test. The results of this study demonstrate that enhanced-efficiency fertilizers have the potential to reduce NH3 emissions from urea-based fertilizers in green sugarcane fields without affecting sugarcane yield.

Temporal response of ureolytic and ammonia-oxidizing microbes and pasture yield to urea and NBPT at Leigh Creek of Victoria in Australia

The urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT) has been reported to effectively reduce nitrogen (N) losses by inhibiting urea hydrolysis. However, the effect of NBPT on soil ureolytic and ammonia-oxidizing microbes is not well understood, with inconsistent effects on crop yield and nitrogen use efficiency (NUE). Further, repeated use or overuse of chemical fertilizers can have environmental implications like soil acidification. A field experiment was conducted at Leigh Creek, Victoria at a site with a history of repeated application of urea alone (40U) or with NBPT (as Green Urea NV® (40GU)) at 40 kg N ha−1, and urea applied at 80 kg N ha−1 (80U), to perennial ryegrass (Lolium perenne L.). We aimed to investigate the temporal effects of NBPT applied with urea on ureolytic and ammonia-oxidizing microbes, pasture dry matter (DM) yield, and NUE within a season following treatment applications. The abundance of ureolytic microbes was higher in the control (CK) compared to all N treatments on all sampling days. The ureC gene copy numbers in 40 GU were significantly lower than in 40U on sampling days seven and 45. There was no significant effect of NBPT on the abundance of ammonia oxidizers, but increasing urea application rate to 80 kg N ha−1 (80U) significantly increased the abundance of ammonia-oxidizing bacteria (AOB) on days 7 and 45, and complete ammonia oxidizers (comammox Nitrospira) clade B on day 7 compared to 40U. There was no significant effect of NBPT on pasture DM yield, N-uptake, or NUE. Increasing N application rate significantly increased pasture DM yield and N- uptake but this did not influence the pasture NUE.

Ammonia volatilization from fertilizer sources on a loam soil in Idaho

AbstractOptimizing crop N uptake while minimizing NH3 volatilization from N fertilizer sources is a critical part of agricultural best management practices. Urea is the most widely used N fertilizer but is also one of the most susceptible to losses as NH3. Fertilizer sources and additives can be used to reduce NH3 volatilization. Specifically, urease inhibitors [e.g., N‐(n‐butyl) thiophosphoric triamide (NBPT)] can reduce NH3 volatilization from urea. A novel fused ammonium sulfate nitrate (ASN) product has recently been developed as another potential alternative N fertilizer source but has not been studied widely. A field study was performed to quantify NH3 volatilization from the newly available ASN fertilizer as compared with various N fertilizers (ammonium sulfate [AS] and urea) including urea treated with the urease inhibitor NBPT in an alkaline calcareous loam soil in Idaho. Further, we assessed NH3 volatilization from surface applied and incorporated N fertilizers from these various N sources. Untreated surface‐applied urea volatilized the highest amount of NH3, whereas incorporation of N fertilizers was effective in reducing volatilization as compared with untreated surface‐applied urea. Our study indicated that the N fertilizer sources (AS, ASN, and urea+NBPT) were equally effective in reducing NH3 volatilization when compared with surface‐applied urea. Our study will help refine N fertilizer management under multiple field situations and traditional management practices of crop producers in the western United States. Further, site‐years and study locations would be needed to provide evidence of the effectiveness of ASN in reducing NH3 volatilization under a wider range of soil and environmental conditions.

Benefits from enhanced-efficiency nitrogen fertilisers in rainfed temperate pastures are seasonally driven

Context Enhanced-efficiency nitrogen (N) fertilisers (EEFs) can reduce N loss, but productivity and environmental benefits vary. A field experiment on rainfed ryegrass dominant pastures in southern Australia examined the effect of EEFs combined with reduced N rate on agronomic N efficiency (AE) (additional biomass per unit N applied) and apparent NUE (ApNUE) (additional plant N uptake per unit N applied) relative to urea. Methods EEFs examined were granular urea coated with (i) urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT), (ii) nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) or (iii) polymer coating (PCU). Nitrogen was applied five times over 9 months at 0–84 kg N ha−1 per application. Key results AE varied with season from –0.5 to 22.3 kg DM kg N−1 in late (dry conditions) and early spring (ideal conditions), respectively. AE of PCU was significantly lower than urea for the first harvest due to slow N release. Using DMPP led to higher AE than equivalent urea rates in August (at 34 and 50 kg N ha−1) and early October (34 kg N ha−1). At the lowest rate (17 kg N ha−1), NBPT generally led to higher AE than at higher N rates. Using NBPT at 17 kg N ha−1 led to higher AE than urea at the same rate in July, August and February. The ApNUE ranged from 3.6% (summer) to 68% (early spring), and decreased with increasing N rate. Using DMPP did not significantly change cumulative ApNUE (entire experiment) (34%) due to limited leaching and denitrifying conditions. Cumulative ApNUE was lowest with PCU (23%) due to initial slow N release. Conclusion Seasonal variations in pasture responses to fertiliser N affected the efficiency outcomes from using EEFs. Implications Benefits in ApNUE and AE from using EEFs rely on their seasonal strategic use combined with reduced N inputs. The initial slow release of N from the PCU could be overcome by strategies such as combining the PCU with uncoated urea, to improve ApNUE.

Joint application of urease and nitrification inhibitors to diminish gaseous nitrogen losses under different tillage systems

Urea fertilization is a widely spread source of nitrogen (N) for agriculture because of its easy accessibility. However, its use is highly inefficient, since a large amount of the applied N is lost to the environment mainly in the form of ammonia (NH3) volatilization, causing serious environmental and economic damages. Although there are simple strategies to reduce these losses, as the subsurface application, this practice cannot be adopted in all types of cultivations and tillage systems. To address this problem, combinations of urease and nitrification inhibitors (double inhibitors) have been developed to close all possible N escape routes, which is not achieved when these inhibitors are applied individually. The objective of this work was to evaluate the potential of a new double inhibitor combining N-(n-butyl) thiophosphoric triamide (NBPT) and 2-(3,4-dimethylpyrazole-1-YL)-succinic acid (DMPSA) to mitigate N losses in a rapeseed crop established in conventional tillage (CT) and no-tillage (NT) soils under Humid Mediterranean conditions. To do so, N losses in form of NH3 volatilization and nitrous oxide (N2O) emissions were determined through the Dräger-Tube method (DTM) and closed chamber method respectively. The specific weather conditions present during the experiment promoted great losses, mostly in form of NH3 volatilization. The treatments receiving urea without inhibitors or urea with DMPSA lost up to 57.3 and 59.9 kg N ha−1 in CT and NT respectively. Nonetheless, the application of the double inhibitor was able to diminish these losses by more than 50%, reducing the losses to a minimum of 18.8 kg N ha−1 (CT) and 25 kg N ha−1 (NT). As a whole, a CT system fertilized with a single application of urea with the double inhibitor showed the lowest global warming potential (GWP) (3.93 Mg CO2-eq ha−1), at the same level of the unfertilized treatment.

Current knowledge on urease and nitrification inhibitors technology and their safety.

Urea is one of the most widely used commercial fertilisers worldwide due to its high N density and cost effectiveness. However, it can be lost in the form of gaseous ammonia and other greenhouse gas (GHG) emissions which can potentially lead to environmental pollution. Farmers are compelled to apply more urea to account for those losses, thereby increasing their expenditure on fertilization. The objective of this paper is to present a literature review on current knowledge regarding inhibitor technologies such as urease inhibitor; n-(N-butyl) thiophosphoric triamide (NBPT), and nitrification inhibitor; dicyandiamide (DCD). A thorough review of all the scientific literature was carried out and a proposed risk assessment framework developed. The study showed that the urease inhibitor NBPT significantly reduced NH3 loss from urea. However, concerns about NBPT safety to human health had been raised when the nitrification inhibitor DCD appeared as a residue in milk. This article presents a risk assessment framework for evaluating human exposure to chemicals like NBPT or DCD, following the consumption of foods of animal origin (e.g. milk) from cows grazing on inhibitor-treated pasture. The EU's target of a 40% reduction of greenhouse gas emissions by 2030 can be aided by using NBPT as part of an overall suite of solutions. A comprehensive risk assessment is advised for effective evaluation of potential risks from exposure to these inhibitors.

Kinetics and thermodynamics of urea hydrolysis in the presence of urease and nitrification inhibitors

Urease inhibitor [N-(n-butyl) thiophosphoric triamide (NBPT)] and nitrification inhibitor (NI) (3,4-dimethylpyrazole phosphate) have been used to reduce nitrogen (N) losses from urea-based fertilizers. This study evaluated the effect of temperature, NBPT, and NI on kinetic and thermodynamic properties of urea hydrolysis in six soils. Soils were amended (250 kg N·ha−1) with urea (UR), NBPT treated urea (URNBPT), or NBPT + NI treated urea (URDI), incubated at 5, 15, or 25 °C, and destructively sampled eight times during an 18 d incubation. We measured urea hydrolysis rate by the disappearance of urea with time and determined the rate constant (k; d−1) assuming first-order kinetics. Our results showed that k increased with temperature in the order of 0.07 (5 °C), 0.12 (15 °C), and 0.20 (25 °C) across soils and inhibitor treatments. In addition, k declined in the order of UR (0.19) > URDI (0.11) > URNBPT (0.08) across soils and temperatures. Although urease inhibitor, NBPT, increased the half-life of urea from 3.8 to 8.3 d across soil–temperature, the addition of a NI significantly reduced the half-life of NBPT treated urea by approximately 2 d across soil–temperature. Thermodynamics parameters showed that urea hydrolysis was nonspontaneous, and enthalpy and entropy changes were not significantly different among inhibitor treatments in five of the six soils. We conclude that the often-reported greater ammonia volatilization from URDI than URNBPT may not only be due to the persistence of ammonium in the presence of NI but also because NI reduced the inhibitory effect of NBPT on urea hydrolysis.

N-(n-Butyl) Thiophosphoric Triamide (NBPT)-Coated Urea (NCU) Improved Maize Growth and Nitrogen Use Efficiency (NUE) in Highly Weathered Tropical Soil

Nitrogen (N) fertilizer is commonly used to supply sufficient N for plant uptake, for which urea is one of the highly preferred synthetic N fertilizers due to its high N content. Unfortunately, N provided by urea is rapidly lost upon urea application to soils through ammonia volatilization, leaching, and denitrification. Thus, treatment of urea with urease inhibitor (N-(n-Butyl) Thiophosphoric Triamide (NBPT)) is among the solutions to slow down urea hydrolysis, therefore reducing loss of NH3 and saving N available for plant uptake and growth. A field study was carried out to evaluate the effects of NBPT-coated urea (NCU) at varying rates on growth, yield, and nitrogen use efficiency (NUE) of maize in tropical soil. The experiment was conducted at Field 15, Universiti Putra Malaysia, Serdang, Selangor, Malaysia, and maize (Zea mays var. Thai Super Sweet) was used as the test crop. The results showed that all maize grown in soils applied with urea coated with NBPT (NCU) (T2, T3, T4, and T5) had significantly (P ≤ 0.05) higher chlorophyll content compared to the control (T0 and T1). The surface leaf area of maize grown in NCU-treated soils at 120 kg N h−1 (T3) was recorded as the highest. NCU at and 96 kg N ha−1 (T3 and T4) were relatively effective in increasing maize plant dry weight, yield, and N uptake. Improvement of NUE by 45% over urea was recorded in the treatment of NCU at 96 kg N ha−1. NBPT-coated urea (NCU) at 96 kg N ha−1 had potential to increase the growth, yield, nitrogen uptake, and NUE of maize by increasing the availability of N for plant growth and development.

Biochemical changes and distribution of nitrogen from bands of stabilised N-fertilizers in contrasting soils

‘Stabilised’ nitrogen (N) represents an important category of enhanced efficiency fertilizers (EEFs) in which chemicals added to urea granules inhibit target soil N transformation processes in order to optimize N availability for crop uptake. However the mechanistic understanding of how these inhibitors perform when urea-based fertilizers are banded, causing substantial modifications to the soil chemical environment, is poorly understood. In a 16-day laboratory incubation, the efficacies of the nitrification inhibitor (NI), 3,4-dimethylpyrazole phosphate (DMPP), and the urease inhibitor (UI), N-(n-butyl) thiophosphoric triamide (NBPT), were investigated in two soils by incubating two commercially available urea-based products containing these additives in bands at concentrations equivalent to 150 kg N ha−1 at row spacing of 1.8 m. When compared to a granular urea standard, DMPP did not provide any inhibitory benefits except when the inhibitor was able to diffuse beyond the zone affected by urea-N hydrolysis, within which considerable nitrification inhibition occurred because of the chemical conditions. The benefit of the NI was most significant in the soil with higher clay, organic matter and pH buffering capacity, with these properties confining the ureolytic-induced chemical changes and N transformations inhibitory zone closer to the fertilizer band. In contrast, the UI provided some benefit by slowing the rapid rise in pH, electrical conductivity and aqueous ammonia observed in standard urea bands, although the effects of NBPT were temporary (ca. 9 days) in both soils. The benefit of NI and UI technology relative to urea alone is likely to vary considerably between soils and fertilizer application methods. This study provides a physico-chemical approach to determining under what conditions the benefits of banded ‘stabilising’ EEF technology may be realised.

Nitrification inhibitor reduces the inhibitory effect of N‐(n‐butyl) thiophosphoric triamide (NBPT) on the hydrolysis of urea

AbstractThe addition of nitrification inhibitor (NI) with a urease inhibitor, N‐(n‐butyl) thiophosphoric triamide (NBPT), has been reported to offset the reduction of ammonia volatilization by NBPT. An incubation study was conducted to investigate the interaction between NBPT and NI (3,4‐dimethyl pyrazole phosphate) on hydrolysis of urea in five soils with a range of physico‐chemical properties. Untreated urea (UR), NBPT treated urea (URNBPT), or NBPT+NI treated urea (URDI) were surface‐applied (250 kg N ha−1) to each soil. The soils were incubated (21 °C) and destructively sampled nine times during a 22‐day period. Urea hydrolysis rate (k; d−1) was measured by the disappearance of urea with time and modeled with a first‐order kinetic. The value of k was in the order of UR (0.321) > URDI (0.183) > URNBPT (0.151) across the five soils. While the urease inhibitor, NBPT, significantly reduced k in each soil, the addition of a NI with NBPT significantly decreased the ability of NBPT to inhibit urea hydrolysis by an average of 21% across the soils. We found that NI significantly reduced the half‐life of urea by about 1 d when compared with NBPT alone. Principal component analysis showed that k did not depend on any of the soil properties, rather, it depended on the type of treatment. Net nitrification rate constant was significantly greater in UR than URNBPT in loam and clay soils but not different in sandy loam soils. We conclude that the often‐reported increase in ammonia volatilization with the double inhibitor relative to NBPT alone may not only be due to the persistence of ammonium but may also be due to an increased rate of urea hydrolysis in the presence of a NI.

Vertical distribution of fertilizer nitrogen from surface water flooding of a silt loam and clay soil used for rice production

AbstractNitrogen (N) fertilizer retention and short‐term vertical redistribution into soil affect N balance and N‐use efficiency in rice (Oryza sativa L.) production systems. A series of experiments was conducted on intact soil cores obtained from rice production fields to track floodwater and soil ammonium‐ and nitrate‐N concentrations up to 96 hr after urea and ammonium sulphate fertilizer amendments to dry, silt loam soil (a) as compared to clay soil, (b) with and without a delay before floodwater establishment and (c) at two initial soil water conditions (dry and muddy). The impact of a 5‐day delay before flood establishment was also compared between untreated and N‐(n‐butyl)thiophosphoric triamide (NBPT)‐treated urea‐N concentrations. Urea‐derived N generally moved deeper into dry, silt loam soil than ammonium sulphate. Ammonium sulphate‐derived N concentration was greatest in the surface 2 cm of soil, decreased with depth, and was unaffected by floodwater duration. A 5‐day delay between fertilization and flooding resulted in urea behaving similarly to ammonium sulphate, although NBPT treatment resulted in vertical N distributions similar to those for untreated urea applied to dry, immediately flooded soil. When urea was applied to muddy soil, no fertilizer N was observed below 2 cm, while large concentrations of ammonium‐N remained in the floodwater. Results collectively demonstrate the importance of immediate downward movement of fertilizer‐applied N into dry soil for retention, and the use of a urease inhibitor to maximize urea‐derived N downward movement into soil when a delay in flood establishment cannot be avoided.

Utility of stabilized nitrogen fertilizers to reduce nitrate leaching under optimal management practices

AbstractBackground: The inadequate application of nitrogen (N) to crops has increased the reactive N in the atmosphere and in the surface and ground waters. Stabilized N‐fertilizers with nitrification (NI) and urease (UI) inhibitors have been proposed to reduce these environmental problems without affecting or even increasing crop productivity.Aim: The objective of this study was to evaluate, in a maize–maize–wheat rotation, if the use of the NI 3,4‐dimethylpyrazole phosphate (DMPP) and the UIs N‐(n‐butyl) thiophosphoric triamide (NBPT) and monocarbamide dihydrogen sulfate (MCDHS) reduces N leaching without compromising yield under optimal management of N and water.Methods: The experiment was conducted in 24 drainage lysimeters with two soil types with contrasting water holding capacity under Mediterranean irrigated conditions. The fertilizer treatments were urea, urea with DMPP, urea with NBPT, and urea with MCDHS. For the maize crop, conventional fertilizer application was split into 6‐ and 13‐leaf stages, whereas stabilized fertilizers were applied as a single application at the 6‐leaf stage. All fertilizer treatments were applied at late tillering in the wheat crop.Results: The soil mineral N was measured at the beginning and the end of each crop season, but no differences were found among fertilizer treatments. Differences in the volume of water drained or the cumulative mass of nitrate depending on the fertilizer were not significant (three‐year treatment average of 200 L m−2 and 22 kg N ha−1 in the Deep soil, and 334 L m−2 and 40 kg N ha−1 in the Shallow type, respectively). No consistent significant differences were found in agronomic parameters (chlorophyll measurements, yield, and total N uptake) between the fertilizer treatments.Conclusion: Based on the results, the use of stabilized N‐fertilizer could be recommended to reduce the number of N applications in maize without compromising grain yield but with no advantages to reduce nitrate‐leaching losses if N rates are managed properly under efficient irrigation management practices.

Volatilization of ammonia from conventional sources of nitrogen and compacted urea under controlled conditions

Urea is the most used nitrogen fertilizer in tropical agriculture, but when applied to the soil surface, it can promote nitrogen (N) losses by volatilization of ammonia (NH3). The present study aimed to evaluate, under controlled laboratory conditions, the N-NH3 losses from conventional N sources and compacted urea . Fertilizers were applied on the surface of a eutrophic Red Latosol of clayey texture (Oxisol), previously moistened to 60% of its maximum water-retention capacity. Conduction of the experiment was in a completely randomized design with six replicates . The treatments were four N sources in doses equivalent to 100 kg ha-1 of N (urea, urea + N-(N-butyl) thiophosphoric triamide (NBPT), ammonium nitrate and urea compacted with additives and polymers), and the additional control groups (soil with no fertilizer and empty chamber). We evaluated the N-NH3 losses by volatilization for a period of 20 days with the aid of hermetically sealed chambers. The results demonstrated the importance of using compacted urea for reducing nitrogen losses via volatilization. These results suggest that choosing the N source can reduce its volatilization and thus improve the harnessing of N from the nitrogen fertilization, when performed with a urea basis.

Turnover of Urea in a Soil from the North China Plain as Affected by the Urease Inhibitor NBPT and Wheat Straw

In the North China Plain (NCP), urea is applied to predominantly high-pH soils and high gaseous losses of N are observed in the forms of ammonia (NH3) and nitrous oxide (N2O). The production of N2O and N2 is further stimulated by the addition of fresh organic materials. The urease inhibitor (UI) N-(n-butyl) thiophosphoric triamide (NBPT) restricts the loss of N by reducing the rate of urea hydrolysis and limiting the substrates for NH3 and N2O emission. We investigated the turnover of N—as well as the emissions of NH3, N2O and CO2—as affected by the addition of wheat straw and urea +NBPT in an incubation experiment using soil from a farmer’s field, typical for the NCP. Added wheat straw prolonged the persistence of NH4+ after the application of both urea and urea +NBPT, while reducing the formation of nitrate. Wheat straw may therefore either act as a stimulant of hydrolysis or as an inhibitor of nitrification. Urea increased soil respiration and the emission of N2O, possibly acting as a primer for microbial activity as described in earlier studies. In combination with the application of organic C sources, this effect of urea may be a main driver of gaseous N loss.

Nitrification and urease inhibitors improve rice nitrogen uptake and prevent denitrification in alkaline paddy soil

Increasing evidence indicates that nitrification is a vital factor in crop growth and nitrous oxide emission. Nitrification and urease inhibitors have been demonstrated to be effective in inhibiting the nitrification process and are widely used as fertilizer additives in agricultural soils. However, the effects of these inhibitors on rice N uptake and N2O production through denitrification in paddy soils remain unclear. In the present work, we compared the influences of nitrification inhibitors dicyandiamide (DCD), nitrapyrin (2-chloro-6-(trichloromethyl) pyridine; NP) and N-(n-butyl) thiophosphoric triamide (NBPT) on rice growth, the fate of urea nitrogen (N), and the abundances and activities of ammonia oxidizers and denitrifiers. The fate of urea N was determined by the 15N isotope labeling technique, and the abundances of ammonia oxidizers and denitrifiers were determined using qPCR. All three inhibitors improved rice growth mainly due to the increase in urea N use efficiency. Urea N uptake was negatively correlated with nitrification. The growth of ammonia-oxidizing bacteria (AOB), important in nitrification, was directly blocked by DCD. Additionally, NP and NBPT impeded the growth of ammonia-oxidizing archaea (AOA). In addition, NP significantly increased the microbial biomass to promote more residual urea N in soil and increased soil N transformation. NBPT significantly inhibited urea hydrolysis indirectly affecting nitrification. All three inhibitors decreased the potential denitrification rate (PDR) at the rice heading stage but had little effect on the denitrifier gene abundance except for nitrapyrin, which decreased the nirK gene abundance. DCD and NBPT may reduce the denitrification activity by decreasing the denitrification substrate (NO3−) concentration. These results suggest that DCD, NP and NBPT have a beneficial effect on improving rice N uptake and have the potential to reduce N2O generation through denitrification.

Joint mitigation of NH3 and N2O emissions by using two synthetic inhibitors in an irrigated cropping soil

Ammonia (NH3) emissions from cropping systems are a major pathway of nitrogen (N) loss thus strongly affecting nitrogen use efficiency (NUE). The agriculture sector is responsible for ca. 94% of global NH3 emissions, mostly associated with manure management (56%), animal manure applied to soil (18%) and inorganic N fertilization (21%). Furthermore, N fertilization enhances N2O emissions from cropping systems. The assessment of NH3, and also N2O, abatement strategies on a regional basis has, therefore, become a strategic priority for sustainable food production worldwide.A field experiment, under Mediterranean conditions, was carried out to assess the N2O and NH3 mitigation efficiency of different synthetic inhibitors in an irrigated maize crop fertilized with urea (U). The nitrification inhibitor (NI) 3,4 dimethylpyrazole succinic acid (DMPSA), and the combination of the DMPSA and the urease inhibitor (UI), N-(n-butyl) thiophosphoric triamide (NBPT), were used in the experiment. Our findings indicate that, following top-dressing N fertilization, the highest NH3 emissions were observed after U + NI and U applications (12.2 and 11.1 kg N ha−1, respectively), with no significant differences between them. The application of urea with both inhibitors (U + 2I) significantly reduced these emissions down to 3.3 kg N ha−1. During canopy senescence, NH3 emissions were not negligible and were statistically similar between treatments, with an average value of 2.3 kg N ha−1. In addition, the treatments with NI were effective in reducing cumulative N2O losses (ca. 79%).

Efficiency of fall versus spring applied urea‐based fertilizers treated with urease and nitrification inhibitors I. Ammonia volatilization and mitigation by NBPT

AbstractMid‐ or late‐fall N fertilization is usually recommended on the Canadian prairies to reduce N losses from fall‐applied N. Yet, N fertilizers are less efficient when applied in mid‐ or late fall than in spring on crop yield. Ammonia volatilization from N fertilizers is one of the reasons for the low N use efficiency. We conducted a 2‐yr study to quantify and contrast the efficacy of a urease inhibitor, N‐(n‐butyl) thiophosphoric triamide (NBPT), with and without a nitrification inhibitor, 3,4‐ dimethylpyrazole phosphate (NI), in reducing NH3 volatilization from fall‐ and spring‐applied urea‐based fertilizers in two contrasting soils. Treatments consisted of surface‐applied urea and urea–NH4NO3 (UAN) with and without NBPT or NBPT + NI (double inhibitor, DI). We measured NH3 volatilization with acid‐charged disks during 21 (fall) or 28 (spring) d. Total NH3 volatilization (percentage of applied N) from untreated urea and UAN across sites ranged from 7 to 22% with fall application and from 3 to 29% with spring application. Addition of NBPT only or DI to urea or UAN reduced NH3 volatilization by 61 to 74% in the fall and 4 to 69% in the spring across site‐years. We found that the reduction of NH3 volatilization by NBPT was significantly greater in the fall (65%) than in the spring (40%) and with urea (61%) than with UAN (43%). Our study showed that (a) significant NH3 volatilization could occur from surface‐applied urea‐based fertilizers even under late‐fall temperatures and (b) NBPT reduced NH3 volatilization from fall‐ as well as spring‐applied urea‐based fertilizers. Therefore, farmers are encouraged to treat their urea‐based fertilizers with NBPT when considering surface application.

Nitrogen fertilisers with urease inhibitors reduce nitrous oxide and ammonia losses, while retaining yield in temperate grassland

Nitrogen fertilisation, although a cornerstone of modern agricultural production, negatively impacts the environment through gaseous losses of nitrous oxide (N2O), a potent greenhouse gas (GHG), and ammonia (NH3), a known air pollutant. The aim of this work was to assess the feasibility of urea treated with urease inhibitors to reduce gaseous N losses in temperate grassland, while maintaining or improving productivity compared to conventional fertiliser formulations. Urease inhibitors were N-(n-butyl)-thiophosphoric triamide (NBPT) (urea + NBPT) and N-(n-propyl)-thiophosphoric triamide (NPPT) (urea+ NBPT + NPPT), while conventional fertilisers were urea and calcium ammonium nitrate (CAN). N2O emission factors were 0.06%, 0.07%, 0.09% and 0.58% from urea + NBPT, urea, urea + NBPT + NPPT and CAN, respectively, with CAN significantly higher than all the urea formulations, which were not significantly different from each other. Ammonia loss measured over one fertiliser application was significantly larger from urea, at 43%, compared with other formulations at 13.9%, 13.8% and 5.2% from urea + NBPT, urea + NBPT + NPPT and CAN, respectively. Changing fertiliser formulation had no significant impact on grass yield or N uptake in four out of five harvests. In the last harvest urea + NBPT significantly out-yielded urea, but not CAN or urea + NBPT + NPPT. Overall, urea treated with either one or both urease inhibitors significantly reduced emissions of N2O and NH3, while preserving yield quantity and quality. Therefore, changing fertiliser formulation to these products should be encouraged as a strategy to reduce GHG and air pollution from agricultural practices in temperate climate.

Stability of stored N-(n-butyl) thiophosphoric triamide (NBPT) treated urea-based fertilizers

ABSTRACTThe effectiveness of N-(n-butyl) thiophosphoric triamide (NBPT) in reducing ammonia volatilization from urea-based fertilizers has been thoroughly investigated. However, the stability of this inhibitor during storage of NBPT treated urea and urea ammonium nitrate (UAN) needs further investigation. We compared ammonia volatilization from NBPT treated urea (360 mg NBPT kg−1 urea) and UAN (180 mg NBPT L−1 UAN) that were stored at room temperature for 6, 3 and 0 months. We measured ammonia volatilization with cylindrical chambers fitted with acid-charged discs at five times for 21 d. Total ammonia volatilization (measured as a % of applied nitrogen) was significantly greater in untreated urea and UAN (32% to 33%) than those in NBPT treated urea and UAN (6% to 12%). Reduction of ammonia volatilization was not significantly different among NBPT treated urea (73% to 81%) and UAN (63% to 73%) irrespective of storage time. This implies that farmers can mix their urea-based fertilizers with NBPT formulation 6 months prior to fertilization without compromising the ammonia volatilization reducing property of the NBPT.

Can NBPT urease inhibitor in combination with Azospirillum brasilense inoculation improve wheat development?

This research was developed to investigate the use of Azospirillum brasilense to enhance N use in wheat cropping systems and to assess the potential interactions between inoculation and urease inhibitor N-(n-butyl)thiophosphoric triamide (NBPT). The study was set up under a no-till system in a Rhodic Hapludox. The experimental design was a randomized completely block design with four replicates arranged in a two N source (urea with and without NBPT) × five N rate applied as side dress (0–200 kg ha−1) × two inoculation (with and without A. brasilense) factorial scheme. Inoculation with A. brasilense in combination with application of 100 and 150 kg N ha−1 was found to increase grain yield by 19.6 and 18.8%, respectively. Inoculation also increased biomass N uptake by 66.9% when N was omitted. Inoculation and NBPT application were found to increase NUE by 23.7% compared to inoculation in combination with conventional urea and by 140% compared to NBPT without inoculation. In addition, inoculation increased plant height and NUE by 13.2 and 49%, respectively, compared with non-inoculated plots. Conventional urea and urea with NBPT had a similar effect on nutrient concentration, N uptake, leaf chlorophyll index, biomass weight and wheat grain yield. This study showed positive improvements in wheat production parameters as a result of inoculation, but the potential benefits of NBPT use were less evident. Further research should be conducted under growing conditions that provide increased N volatilization to better study the potential of NBPT application.