N-butyl Thiophosphoric Triamide Research Articles

The Effect of Urease Inhibitors Coated Urea on the Growth, Physiological Activities and Yield of Maize (Zea mays L.) in Inceptisol Jogonalan, Klaten

An approach to minimize the loss of nitrogen (N) evaporating from urea is by inhibiting urease activity by urea coating with N- (n-butyl) thiophosphoric triamide (NBPT) and N- (n-propyl) thiophosphoric triamide (NPPT). The effect of urease inhibitor to minimize N loss has not been done in inceptisol soil. The purpose of this study was to study the effect of urease inhibitor coated urea on growth, physiological activity and yield of maize in Inceptisol Jogonalan, Klaten, Indonesia. The treatment was laid out in a Randomized Complete Block Design with 4 replications namely N0 (without fertilizer), N1 (urea + NBPT 348 kg ha-1) and N2 (urea + NBPT 278 kg ha-1). All treated plants was fertilized once in one growing season 3 weeks after planting (WAP). Observations were done on several variables: soil physicochemical characteristics, plant physiological activity as well as growth and yield of maize. Data were analyzed using Analysis of Variance (ANOVA), and then the mean comparisons were done by using Least Significance Difference (LSD) test at 5%. The results showed that fertilization affected all observed variables. The effect of urea-coated urea inhibitor urease (NBPT+NPPT) compared with N0 (control) showed very optimum result, especially in N2 treatment. The urea coated with NBPT + NPPT (urease inhibitors) was more effective at lower dose of 278 kg ha-1 and tended to provide better results indicated by the growth and yield of maize in Inceptisol, Jogonalan, Klaten. The better growth as well as the higher yield of maize that was indicated by seed weight of 11,45 tons ha-1 and 100-seed weight of 37.75 g were obtained from N2 treatment as compared to other treatments. The hybrid maize (P35) has an optimum yield potential of 12.1 tons of dry pipes per hectare.

Effects of Urease Inhibitor and Nitrification Inhibitor on the Nitrogen Losses, Physiological Activity, and Oil Palm Yield on Red-Yellow Podzolic

Nitrogen (N) fertilizer efficiency can increase by adding N-(n-butyl) thiophosphoric triamide (NBPT) and N-(n-propyl) thiophosphoric triamide (NPPT) as urease inhibitor in urea fertilizer and adding 3,4-dimethyl pyrazole phosphate (DMPP) as nitrification inhibitor in ammonium sulfate (ZA) fertilizer. The research objectives were to examine the effectiveness of urease inhibitor (NBPT and NPPT) and nitrification inhibitor (DMPP) on the physiological activity and oil palm yield on red-yellow podzolic. Field experiment was done using a Randomized Complete Block Design (RCBD) of single factor and three replications as block. The single factor was nine fertilization treatments of urea with or without urease inhibitor, and ZA with or without nitrification inhibitor. The use of urease inhibitors decreases the amount of volatilization and N loss fertilizer. The higher dose of broadcasting N fertilizer (on the same type of fertilizer) resulted in the higher amount of N loss and volatilization. All fertilization treatments did not have any significant influence to the width and the length of opening stomata, nitrate reductase activity (NRA), N concentration in oil palm leaf, Oil Extraction Rate (OER), and Free Fatty Acid (FFA). Meanwhile, The oil palms at yellow red podzolic applied with urea 195 kg/ha combined with 0.12% of NBPT-NPPT resulting in higher fresh fruit bunch productivity.

Ammonia Volatilization Loss and Corn Nitrogen Nutrition and Productivity with Efficiency Enhanced UAN and Urea under No-tillage

New urease and nitrification inhibitors and polymer coatings were introduced in recent years, but their effects on N loss and plant N nutrition were scarcely examined in agronomic no-tillage production systems. A field experiment of urea treated with efficiency enhancers was conducted on no-tillage corn (Zea mays L.) in Tennessee, the USA during 2013–2015. A field experiment on urea and ammonium nitrate (UAN) treated with efficiency enhancers was carried out on no-tillage corn in Tennessee in 2014 and 2015. Urea treated with N-(n-butyl) thiophosphoric triamide (NBPT) at concentrations of 20% (NBPT1), 26.7% (NBPT2), or 30% (NBPT3) and polymer coated urea (PCU) were effective but maleic-itaconic copolymer treated urea was ineffective in reducing ammonia volatilization loss and improving N nutrition, grain yield, and N agronomic use efficiency of corn compared with untreated urea. Specifically, NBPT1, NBPT2, or NBPT3 treated urea and PCU reduced the total ammonia volatilization loss by 29.1–78.8%, 35.4–81.9%, 77.3–87.4%, and 59.1–83.3% during the 20 days after N applications, but increased grain yield by 15.6–31.4%, 12.9–34.8%, 18.7–19.9%, and 14.6–41.1%, respectively. The inhibitory effect of NBPT on ammonia volatilization did not improve with NBPT concentration increased from 20% to 30%. UAN treated with NBPT3 or a combination of urease and nitrification inhibitors resulted in 16.5–16.6% higher corn yield than untreated UAN only when they were surface applied. In conclusion, when urea-containing fertilizers are surface applied without any incorporation into the soil under no-tillage, their use efficiencies and performances on corn can be enhanced with an effective urease inhibitor in areas and years with noticeable urea N losses.

Chemical Attributes of a Dystrophic Red Latosol of Brazilian Cerrado After Poultry Litter Application Associated to a Urea Inhibitor

Poultry waste recycling is now a globally practice consolidated in agriculture. However, the proper disposal of poultry waste should enable to reduce N losses and to decrease pollution potential from the high concentrations of poultry litter applied to soil. In this context, the aim of the present study was to evaluate poultry litter doses and the effect of an urease inhibitor on the chemical attributes of a dystrophic Red Latosol. Two experiments were carried out, one in a greenhouse and another in a eucalyptus forest area, both applying completely randomized design with a 2 × 6 + 1 factorial arrangement, applying two types and six doses of poultry litter (5, 10, 20, 40, 80 and 160 t ha-1) plus the controls, with four replicates, total of 52 pots. The application of poultry litter doses altered soil chemical attributes, except for potential acidity. Soil pH, cation exchange capacity (CEC), sum of bases (SB) and electric conductivity (EC) values and Ca, Mg, K, P, S, organic matter (OM), Mn, Zn and Cu levels increased with increasing poultry litter doses, while Fe and B contents decreased. The 40, 80 and 160 t ha-1 poultry litter doses led to contamination potential of the soil due to salinity and alkalinity, and also raised the EC of the percolate at levels limiting to plants. The NBPT (N-butyl thiophosphoric triamide) urease inhibitor exhibited no influence on soil chemical attributes.

Ammonia losses following surface application of enhanced-efficiency nitrogen fertilizers and urea

The so-called “enhanced-efficiency N fertilizers” were developed to mitigate ammonia losses from surface-applied urea (UR) and thereby increase N use efficiency and crop yield. However, research is needed to assess the efficiency of these products in mitigating ammonia emission. The aim of this study was to compare volatilization losses of ammonia following application of UR treated with B and Cu (B-Cu-UR), UR treated with dicyandiamide (DCD) and N-(n-butyl) thiophosphoric triamide (NBPT) (DCD-NBPT-UR), UR treated with humic substances (HS-UR), UR treated with NBPT (NBPT-UR), polymer S-coated UR (PSCUR), S-coated UR (SCUR), and untreated and uncoated UR (UR). Fertilizers (at a rate of 2355 mg N kg−1) were applied over the soil surface, and volatilized ammonia was quantified for 60 d under controlled conditions using a static closed chamber. Use of DCD-NBPT-UR increased ammonia emissions in comparison to UR by blocking nitrification and keeping the soil pH high, the latter resulting from UR hydrolysis. Urease complexation by the inhibitor and gradual N release resulted in low losses of ammonia by NBPT-UR and PSCUR, respectively. Compared to UR, BCu-UR delayed and slightly decreased ammonia volatilization. HS-UR, SCUR, and UR fertilizers had similar ammonia losses. Humic substances most likely did not act on urea-N complexation or even on decreasing urease activity, whereas immediate release of the nutrient by SCUR was noted. NBPT-UR and PSCUR could substitute for UR, aiming to mitigate ammonia volatilization.

Insights into Urease Inhibition by N-( n-Butyl) Phosphoric Triamide through an Integrated Structural and Kinetic Approach.

The nickel-dependent enzyme urease represents a negative element for the efficiency of soil nitrogen fertilization as well as a virulence factor for a large number of pathogenic and antibiotic-resistant bacteria. The development of ever more efficient urease inhibitors demands knowledge of their modes of action at the molecular level. N-( n-Butyl)-phosphoric triamide (NBPTO) is the oxo-derivative of N-( n-butyl)-thiophosphoric triamide (NBPT), which is extensively employed in agriculture to increase the efficiency of urea-based fertilizers. The 1.45 Å resolution structure of the enzyme-inhibitor complex obtained upon incubation of Sporosarcina pasteurii urease (SPU) with NBPTO shows the presence of diamido phosphoric acid (DAP), generated upon enzymatic hydrolysis of NBPTO with the release of n-butyl amine. DAP is bound in a tridentate binding mode to the two Ni(II) ions in the active site of urease via two O atoms and an amide NH2 group, whereas the second amide group of DAP points away from the metal center into the active-site channel. The mobile flap modulating the size of the active-site cavity is found in a disordered closed-open conformation. A kinetic characterization of the NBPTO-based inhibition of both bacterial (SPU) and plant ( Canavalia ensiformis or jack bean, JBU) ureases, carried out by calorimetric measurements, indicates the occurrence of a reversible slow-inhibition mode of action. The latter is characterized by a very small value of the equilibrium dissociation constant of the urease-DAP complex caused, in turn, by the large rate constant for the formation of the enzyme-inhibitor complex. The much greater capability of NBPTO to inhibit urease, as compared with that of NBPT, is thus not caused by the presence of a P═O moiety versus a P═S moiety, as previously suggested, but rather by the readiness of NBPTO to react with urease without the need to convert one of the P-NH2 amide moieties to its P-OH acid derivative, as in the case of NBPT. The latter process is indeed characterized by a very small equilibrium constant that reduces drastically the concentration of the active form of the inhibitor in the case of NBPT. This indicates that high-efficiency phosphoramide-based urease inhibitors must have at least one O atom bound to the central P atom in order for the molecule to efficiently and rapidly bind to the dinickel center of the enzyme.

Can split or delayed application of N fertiliser to grain sorghum reduce soil N2O emissions from sub-tropical Vertosols and maintain grain yields?

Most soil nitrous oxide (N2O) emissions from rain-fed grain sorghum grown on sub-tropical Vertosols in north-west New South Wales, Australia, occur between fertiliser nitrogen (N) application at sowing and booting growth stage. At three experiments, we investigated the potential for deferring some (split-N) or all (delayed) fertiliser N until booting to mitigate N2O produced without compromising optimum crop yields. N products included urea, 3,4-dimethyl pyrazole phosphate (DMPP)-urea, polymer-coated urea (PCU) and N-(n-butyl)thiophosphoric triamide (NBPT)-urea. For a fourth experiment, the N fertiliser rate was varied according to pre-sowing soil mineral N stocks left by different previous crops. All experiments incorporated 15N mini-plots to determine whether delayed or split-N affected crop N uptake or residual soil N. Compared to urea applied at-sowing, delayed applications of urea, DMPP-urea or NBPT-urea at booting reduced the N2O emission factor (EF, percentage of applied N emitted) by 67–81%. Crop N uptake, grain yield and protein tended to be lower with delayed N than N at-sowing due to dry mid-season conditions. Much of the unused N remained in the soil at harvest. Split-N (33% sowing:67% booting) using urea, reduced EF by 59% compared to at-sowing urea, but maintained crop N uptake, grain yield and protein. Using DMPP-urea or PCU for the at-sowing portion of the split reduced EF by 84–86%. Grain yield was maintained using PCU, but was lower with DMPP-urea, which had more N in vegetative biomass. Using NBPT-urea for the in-crop portion of the split did not affect N2O emissions or crop productivity. Nitrogen budgeting to account for high pre-sowing soil mineral N nullified urea-induced N2O emissions. An N-budgeted, split-N strategy using urea offers the best balance between N2O mitigation, grain productivity and provision of a soil mineral N buffer against dry mid-season conditions. Split-N using DMPP-urea or PCU further enhanced N2O mitigation but there was no yield response to justify the extra expense.

The Effect of Granular Commercial Fertilizers Containing Elemental Sulfur on Wheat Yield under Mediterranean Conditions.

The demand to develop fertilizers with higher sulfur use efficiency has intensified over the last decade, since sulfur deficiency in crops has become more widespread. The aim of this study was to investigate whether fertilizers enriched with 2% elemental sulfur (ES) via a binding material of organic nature improve yield when compared to the corresponding conventional ones. Under the scanning electron microscope, the granules of the ES-containing fertilizer were found to be covered by a layer of crystal-like particles, the width of which was found to be up to 60 μm. Such a layer could not be found on the corresponding conventional fertilizer granules. Several fertilization schemes with or without incorporated ES were tested in various durum wheat varieties, cultivated in commercial fields. The P-Olsen content of each commercial field was found to be correlated with the corresponding relative change in the yields (YF/YFBES) with a strong positive relationship. The content of 8 ppm of available soil phosphorus was a turning point. At higher values the incorporation of ES in the fertilization scheme resulted in higher yield, while at lower values it resulted in lower yield, compared with the conventional one. The experimental field trials that established following a randomized block design, were separated in two groups: One with P-Olsen ranging between 18–22 ppm and the other between 12–15 ppm, the results of which corroborated the aforementioned finding. The use of ES in all portions of fertilization schemes provided higher relative yields. The coexistence of ES with sulfate in the granule was more efficient in terms of yield, when compared to the granule enriched with ES alone under the same fertilization scheme and agronomic practice. The application of fertilizer mixtures containing the urease inhibitor N-(n-butyl) thiophosphoric triamide (NBPT), ES and ammonium sulfate resulted in even higher relative yields. Yield followed a positive linear relationship with the number of heads per square meter. In this correlation, the P-Olsen content separated the results of the two groups of blocks, where the applied linear trend line in each group presented the same slope.

Simultaneous quantification of N‐butylthiophosphoric triamide and dicyandiamide in urea formulation by liquid chromatography with tandem mass spectrometry

A new liquid chromatography with tandem mass spectrometry method employing a mixed-mode zwitterionic stationary phase was developed for simultaneous determination of urease inhibitor (N-butylthiophosphoric triamide) and nitrification inhibitor (dicyandiamide) in urea fertilizer. Molecular modeling based on density functional theory calculations was employed to provide an insight into the interaction mechanism of urea, dicyandiamide, and N-butylthiophosphoric triamide with zwitterionic stationary phase in chromatographic separation system. The detection of analytes was performed on a triple quadrupole tandem mass spectrometer in multiple reaction monitoring mode using positive electrospray ionization. The ion transitions monitored were m/z 85→68 for dicyandiamide and m/z 168.2→74 for N-butylthiophosphoric triamide, respectively. The standard calibration curves of dicyandiamide and N-butylthiophosphoric triamide were linear over the range of 1.0 ̶ 15ppm (coefficient of determination=0.9984), 0.05 ̶ 1ppm (coefficient of determination=0.9995), with limit of detection of 25 and 5ppb, respectively. The recoveries of low, middle, and high concentrations were from 96.7 to 105.8% for N-butylthiophosphoric triamide and 94.4 to 105.8% for dicyandiamide with accuracy (relative error %) of ≤5.8% and ≤5.8%, the precision (coefficients of variation) was ≤2.0% and ≤2.9%, respectively. The validated method was successfully applied on real urea samples to determine N-butylthiophosphoric triamide and dicyandiamide simultaneously.

Evaluation of Nutrisphere‐N as an Inhibitor of Urease in Soils with pH Values Near Five

Core IdeasA recent paper showed that Nutrisphere‐N inhibits purified urease at pH 5.0.Nutrisphere‐N was tested as a urease inhibitor with soils near pH 5.0.Nutrisphere‐N did not inhibit urease activity in soils near pH 5.0.Nutrisphere‐N is a maleic‐itaconic polymer (MIP) marketed as a soil urease inhibitor. Recently, it was shown that the MIP in Nutrisphere‐N was able to inhibit purified urease at a pH of 5.0. Furthermore, Ni was removed from purified urease by MIP at a pH of 5.0. The objective of this study was to determine if these findings with purified urease at pH 5.0 could be replicated with soils with pH values near 5.0. Three soils with pH values of 4.5, 5.2, and 5.7 were incubated with 5 μg g–1ofN‐(n‐butyl) thiophosphoric triamide (NBPT) as Agrotain Ultra, and 5 and 50 μg g–1of MIP as Nutrisphere‐N. The inhibitors were allowed to react with the soil for 1 d before application of urea (sequential application) or applied at the same time as urea (simultaneous application). For the sequential application, 5 μg g–1of NBPT as Agrotain Ultra inhibited soil urease activity by 49%, versus –3 and –1% for 5 and 50 μg g–1of MIP as Nutrisphere‐N (average of three soils). For the simultaneous application, averaged across the three soils, 5 μg g–1of NBPT inhibited soil urease activity by 59%, versus –1 and −4% for 5 and 50 μg g–1of MIP. The observation that MIP inhibits purified urease at a pH of 5.0 could not be repeated with soils with pH values near 5.0. It remains to be demonstrated that Nutrisphere‐N functions as a soil urease inhibitor at the concentrations likely to be applied to soil.

Impacts of N‐stabilizers and Biochar on Nitrogen Losses, Nitrogen Phytoavailability, and Cotton Yield in Poultry Litter‐Fertilized Soils

Core Ideas Effect of nitrogen stabilizers were evaluated on nitrogen uptake and yield of cotton in poultry litter fertilized soils. Nitrogen stabilizers effect on nitrogen losses as NH3 and N2O were evaluated from poultry litter fertilized soils. Effect of pine hardwood biochar on nitrogen uptake, yield of cotton, and nitrogen losses were evaluated from poultry litter fertilized soils. Poultry litter (PL) serves as a multi‐nutrient fertilizer. However, compared to inorganic fertilizers, PL requires high rate of application to meet crop nutrient requirements due to relatively low concentration and easy loss of nutrients. A 4‐yr field experiment was conducted with cotton (Gossypium hirsutum L.) to examine the effect of the N‐stabilizers [N‐(n‐butyl) thiophosphoric triamide (NBPT) and dicyandiamide (DCD)], and pine hardwood biochar (PBC) on minimizing N‐losses through NH3 volatilization and N2O emissions, plant nutrient content and agronomic yield in PL applied soils. Application of NBPT to PL was evaluated at 1, 2, and 4 kg ha−1, and NBPT+DCD at 0.22 kg NBPT+2.72 kg DCD and 0.44 kg NBPT+5.44 kg DCD ha−1 with PL only and untreated control treatments. PBC applied to PL was evaluated at 2 and 4 Mg ha−1 along with PBC only at 4 Mg ha−1. The results showed that N‐stabilizers were useful in mitigating PL N‐losses via reducing NH3 volatilization and N2O emissions by up to 12 and 64%, respectively, compared to PL only treatment. N‐stabilizers also improved plant tissue‐N content by up to 5.5% and cotton yields by about 6% over PL treatment. The application of NBPT at 2 kg ha−1 with PL produced higher cotton yield along with lower N losses. For NBPT+DCD, 0.44 kg NBPT+5.44 kg DCD ha−1 with PL performed better than 0.22 kg NBPT+2.72 kg DCD ha−1. PBC was effective in reducing N‐losses through NH3 volatilization and N2O emissions, compared to PL and the untreated control. However, PBC led to reduced N‐availability to plants, as evidenced by lower tissue N‐content and lower cotton yields.

Fertiliser timing and use of inhibitors to reduce N2O emissions of rainfed wheat in a semi-arid environment

Nitrogen (N) management is critical to the profitability of grain production systems, however careful management of fertiliser is needed to minimise environmental impacts. We investigated the effect of five N fertilisation strategies on nitrous oxide (N2O) emissions and nitrogen use efficiency (NUE) of rainfed wheat grown on a clay soil in a temperate, semi-arid environment of south eastern Australia during 2013 and 2014. Treatments included urea application (50 kg N/ha) at sowing with and without nitrification inhibitor (3,4–dimethylpyrazole phosphate) and surface broadcasting of urea with and without urease inhibitor (n-butyl thiophosphoric triamide) at the end of tillering plus an unfertilised control. Daily N2O emissions were low and responsive to in-season rainfall and fertiliser addition at sowing. Cumulative emissions from sowing until harvest were highest where N was applied at sowing in 2013; 160 g N2O-N/ha, while the 0 N control emitted 28 g N2O-N/ha (over 201 days). Emissions during 2014 were 77% lower than 2013 due to dry seasonal conditions; cumulative emissions were 49 g N2O-N/ha where N was applied at sowing, with background emissions of around 0 g N2O-N/ha (over 177 days). Inhibitors showed limited scope for reducing N2O emissions in this environment, however deferring N application until the end of tillering reduced N2O emissions. Grain yield responses to fertiliser were significant; increasing grain yield by 11–31% and NUE was generally high (recovery efficiency > 68%). However, deferring N application until the end of tillering in 2014 reduced yield (− 19%) and recovery of applied N (− 74%).

Nitrogen Recovery and Loss from Kentucky Bluegrass Fertilized by Conventional or Enhanced-Efficiency Urea Granules

Easy handling and low unit N cost make prilled urea (46-0-0) a popular fertilizer. While incomplete recovery of granular urea applications by turfgrass is documented, field evaluations of NH3 volatilization mitigation by coatings or bioinhibitor efficiency enhancements are limited. Meanwhile, NH3 emissions reduce air quality and contribute to nutrient loading of water resources. Our objectives were to quantify 3- and 6-d ammonia emission and 9-week turfgrass recovery of unincorporated granular fertilizer application to turfgrass. In 2014 and 2015, commercial urea-N fertilizers were broadcast over a mature Kentucky bluegrass (Poa pratensis L. ‘Midnight’) lawn at 43 kg ha−1. Treatments included conventional urea and three enhanced-efficiency fertilizers; a blended fertilizer with 25% of its urea-N supplanted by polymer- and polymer-/sulfur-coated prills, or two stabilized urea fertilizers both amended by N-(n-butyl) thiophosphoric triamide (NBPT) and dicyandiamide (DCD) inhibitors. Using a 51% ‘trapping-efficiency’ flux chamber system under the field conditions described, 23.1 or 33.5% of the conventional urea-N was lost as NH3 over the respective 3- or 6-d period following application. Alternatively, dual amendment by NBPT and DCD resulted in approximately 10.3 or 19.6% NH3-N loss over the respective 3- or 6-d periods, and greater fertilizer-N recovery by the turfgrass over the 9-week experiments.

Tillage and Coated-Urea Effects on Nitrous Oxide Emissions from Direct-Seeded, Delayed-Flood Rice Production in Arkansas

Rice (Oryza sativa L.) is a key component of the diet of billions of humans, thus rice is a main agricultural product in many regions, particularly in eastern Arkansas, USA. Rice production is known to be a source of greenhouse gases, namely methane (CH4), but, under certain conditions, nitrous oxide (N2O) as well. The objective of this study was to evaluate the effects of tillage practice [conventional tillage (CT) and no-tillage (NT)] and urea fertilizer type [N-(n-butyl) thiophosphoric triamide (NBPT)-coated and non-coated urea] on N2O fluxes, season-long N2O emissions, and the global warming potential (GWP) from rice grown in eastern Arkansas in a direct-seeded, delayed-flood production system on a silt-loam soil.

Urea-based fertilization strategies to reduce yield-scaled N oxides and enhance bread-making quality in a rainfed Mediterranean wheat crop

Urea fertilizer applications to calcareous soils can result in significant nitrous oxide (N2O) and nitric oxide (NO) emissions, predominantly via nitrification rather than denitrification. To address this, we explored several mitigation strategies based on improved urea management in a rainfed winter wheat (Triticum aestivum L.) crop during two consecutive cropping seasons with contrasting rainfall quantities and distribution. The strategies we investigated included the split application of urea at top dressing, the use of nitrification inhibitors (e.g. 2-(3,4-dimethyl-1H-pyrazol-1-yl) succinic acid isomeric mixture, DMPSA, and nitrapyrin), the urease inhibitor N-butyl thiophosphorictriamide (NBPT), or the double inhibitor DMPSA + NBPT. Emissions of N2O, NO, methane (CH4), as well as measurements of grain and straw yield and bread-making quality (protein content, reserve protein composition: glutenins and gliadins) were measured. Nitrogen (N) use efficiency (NUE) and N surplus were also calculated. Results were affected by rainfall, since the first cropping season experienced typical rainfall quantity and distribution, whilst the second cropping season was very dry, thus increasing significantly the yield-scaled emissions and N surplus, and markedly decreasing the NUE. In comparison to the single application of urea without inhibitors, all treatments generally decreased surface-scaled and yield-scaled emissions, with urea+DMPSA being the most effective and consistent mitigation option. Split urea and NBPT did not mitigate surface-scaled emissions in the dry cropping season, because of the marked peaks in N oxides after flowering, caused by inefficient crop N uptake. In the typical rainfall cropping season, the use of the double NBPT+DMPSA inhibitor led to the best balance between mitigation of yield-scaled N oxides emissions, N efficiency, crop yield and bread-making quality (i.e. increments in total protein, gliadins and glutenins). We did not observe any effect of nitrification inhibitors on grain yield (except in the dry cropping season) or the composition of gluten proteins. Our results suggest that the use of DMPSA with or without NBPT should be recommended to mitigate yield-scaled emissions of N oxides in rainfed semi-arid crops.

Profitability of Enhanced Efficiency Urea Fertilizers in No‐Tillage Corn Production

Core Ideas Urea + NBPT and PCU provided significantly higher mean yields and net returns than conventional urea. Urea + NBPT and PCU provided significantly lower yields and net returns than ammonium nitrate. Urea + NBPT and PCU offer greater potential to improve net returns than urea + MICP. This study determined the effects of enhanced efficiency (EE) urea fertilizers relative to ammonium nitrate (AN) on no‐tillage (NT) corn (Zea mays L.) yields and net returns (NRs) in Tennessee. Corn yields were from experiments conducted at two N fertilization rates of 123 and 168 kg ha−1 with four replications in a split‐plot design from 2013 through 2015 at three locations in middle (Springfield) and west Tennessee (Milan and Jackson). ANOVA analyses were used to identify differences in EE urea treatment yields and NRs. Breakeven and sensitivity analysis was used to compare yield and identify the threshold of positive NR of EE urea fertilizers relative to AN for a given premium price over conventional urea. Results indicated that urea + 20% or 26.7% N‐(n‐butyl)‐thiophosphoric triamide (NBPT) and polymer‐coated urea (PCU) provided significantly higher mean yields (2.0 Mg ha−1 more on average) and NRs ($283 ha−1 more) than conventional urea. Notwithstanding, these EE urea fertilizers had lower yields and produced lower benefits than AN in the course of this study. On the other hand, mean yield (8.7 Mg ha−1) and NR ($1012 ha−1) for urea + maleic–itaconic acid copolymer (MICP) were not significantly different from conventional urea (8.3 Mg ha−1 and $959 ha−1). In general, N fertilizer sources behaved similarly among N rates and locations. Given the growing reliance on urea fertilizer in NT corn production in Tennessee, urea + NBPT and PCU offer the greatest potential to improve expected NRs relative to conventional urea.

Advanced Agronomic Practices to Maximize Feed Barley Yield, Quality, and Standability in Alberta, Canada. II. Responses to Supplemental Post‐Emergence Nitrogen

Agronomic solutions such as supplemental post‐emergence N may increase yield of feed‐barley grain. Grain yield, grain N yield, and grain protein generally increased as post‐emergence N rate increased. Largest grain yield increases occurred in environments with >300 mm of growing season precipitation. Yields decreased when N was applied as urea ammonium nitrate in hot and low‐precipitation conditions. There were no adverse negative effects to maturity, lodging, or grain quality in ‘Amisk’ feed barley. Small yield gains and decreasing feed barley (Hordeum vulgare L.) acreage in Alberta may be addressed with agronomic solutions. Field experiments were conducted from 2014 to 2016 at 3 irrigated and 11 rain‐fed environments in Alberta, Canada, to determine the effects of supplemental post‐emergence N on ‘Amisk’ feed barley growth, grain yield, and grain quality. At the time of seeding, urea N was applied at rates suitable for targeting average yield potential in each environment. Just prior to BBCH 30 (beginning of stem elongation), this was supplemented with additional 0, 34, and 68 kg N ha−1 in the form of undiluted urea ammonium nitrate (UAN), and 34 kg N ha−1 with the urease inhibitor N‐(n‐butyl) thiophosphoric triamide (NBPT). In most environments, grain yield, grain N yield (grain yield × percentage grain N), and grain protein increased with post‐emergence N rate. The largest positive grain yield responses (up to 19%) usually occurred in environments with more than 300 mm of growing season precipitation. Grain yield and grain N yield were significantly reduced when post‐emergence N was applied in high temperatures with low precipitation. Post‐emergence N increased height, but did not markedly change lodging or days to maturity. The grain quality parameters of test weight, starch, and fiber had minor responses to post‐emergence N application. The addition of NBPT to post‐emergence N had little effect on any response variables. Supplemental post‐emergence N provided an agronomic solution for increasing feed barley grain yield, but consistent increases were limited to irrigated or high precipitation environments.

No evidence for higher agronomic N use efficiency or lower nitrous oxide emissions from enhanced efficiency fertilisers in aerobic subtropical rice

Enhanced efficiency nitrogen (N) fertilisers (EENFs) contain chemical urease or nitrification inhibitors, or physical barriers (e.g. polymer coating) to minimise the rapid build-up of nitrate (NO3−) in soils. They have the potential to improve N use efficiency and lower N2O emissions from soils. However, evidence of the efficacy of EENFs in warm, wet subtropical conditions is lacking. We therefore developed N response curves (0, 30, 60, 90, 120 and 150 kg N ha-1) for urea, polymer coated urea (PCU), 3,4-dimethylpyrazole phosphate (DMPP)-urea (Entec®), N-(n-butyl) thiophosphoric triamide (NBPT)-urea (Green urea®) and a carbon-coated urea (Black urea®) in subtropical, aerobic rice (Oryza sativa L) crops in two fields with contrasting soils (Gleysol and Histosol), and quantified N2O emissions from nil-N and 90 kg N ha-1 treatments for all EENFs and urea. In the Gleysol, cumulative in-crop N2O emissions were relatively high (approximately 2 kg N2O-N ha-1 season-1 with 90 kg N ha-1 applied) with no significant mitigation from any EENFs compared to urea. Grain yield data fitted with an exponential model indicated that 95% of the estimated maximum grain yield (6.8 t ha-1 at 14% moisture) was achieved with 81 kg N ha-1 for the urea treatment. The yield response curves for all tested EENF products did not differ significantly from the urea-N yield response curve. In the Histosol, cumulative in-crop N2O emissions were negligible (around 0.05 kg N2O-N ha-1 season-1), with no significant difference (p < 0.05) between N fertiliser or nil-N treatments, and 95% of the estimated maximum grain yield (5.63 t ha-1 at 14% moisture) was achieved with only 11 kg N ha-1 for urea. There was no evidence that EENFs could achieve the maximum yield at a lower applied N rate. We hypothesised that the low soil pH of 4.9 (1:5 CaCl2 extract) may have inhibited nitrification in the Histosol, leading to low N2O emissions and a limited response to N fertiliser. Ultimately, the results of this study found no evidence that EENF products could improve agronomic N use efficiency or lower N2O emissions in the two aerobic rice crops studied.

The contrasting effects of N-(n-butyl) thiophosphoric triamide (NBPT) on N2O emissions in arable soils differing in pH are underlain by complex microbial mechanisms

The urease inhibitor, N-(n-butyl) thiophosphoric triamide (NBPT), has been proposed to reduce synthetic fertilizer-N losses, including nitrous oxide (N2O) emissions from agricultural soils. However, the response of N2O emission to NBPT amendment is inconsistent across soils and associated microbial mechanisms remain largely unknown. Here we performed a meta-analysis of the effects of NBPT on N2O emissions and found NBPT significantly reduced N2O emissions in alkaline soils whereas no obvious effects exhibited in acid soils. Based on the finding of meta-analysis that pH was a key modifier in regulating the effect of NBPT on N2O emissions, we selected two arable soils differing in pH and conducted a microcosm study. In conjunction with measurement of N2O emission, community structure and abundance of functional guilds were assessed using T-RFLP and qPCR. Our results showed NBPT retarded urea hydrolysis and inhibited nitrification, but stimulated N2O emission in alkaline soil, whereas it exhibited no remarkable effects in acid soil, thereby only partly confirming the results of meta-analysis. Abundances of AOB and ureC-containing bacteria decreased, while abundance of AOA increased in both soils with NBPT addition. For acid soil, N2O emissions were significantly correlated with both abundances and community structures of AOA and ureC-containing bacteria, as well as abundance of AOB; for alkaline soil, abundances and community structures of AOB were correlated with N2O emission, as well as community structures of ureC-containing bacteria and archaea, indicating an inconsistent response pattern of community traits of N2O emissions-related functional guilds to NBPT between alkaline soil and acid soil. Our findings suggest that (i) efficacy of NBPT in N2O emission was mainly influenced by soil pH and (ii) variable effects of NBPT on N2O emission might originate not only from the direct effect of NBPT on community traits of urease-positive microbes, but from the indirect effect on ammonia oxidizers.

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.