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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. [ABSTRACT FROM AUTHOR]

• Urea broadcast and fertigation were applied at a commercial irrigated cotton farm. • Gas emissions were measured by micrometeorological technique and OP-FTIR technique. • NH 3 flux from anhydrous NH 3 was 24% higher than broadcasting urea with irrigation. • Daily fluxes of CH 4 and N 2 O were both negative following both fertilisation events. Abstract Agricultural systems use nitrogen (N) fertilizers to improve crop nutrition and yield, but applied N can negatively impact the environment and human health due to the gases emitted during and after N application. There are few direct measurements of multiple gaseous emissions from N fertiliser applied to irrigated cotton farms. This study was conducted in a commercial cotton farm in NSW, Australia to measure gaseous emissions from two N fertilisation strategies (urea broadcast onto dry soil followed by irrigation, anhydrous ammonia injected into water at the main irrigation channel), with the N fertilizer rate of 27 kg N ha−1 for each application. Gas fluxes of ammonia (NH 3), methane (CH 4), and nitrous oxide (N 2 O) were measured simultaneously using an inverse-dispersion technique coupled with open-path Fourier transform infrared (OP-FTIR) spectroscopic technique, located 150 and 800 m from the input source of the irrigation water. We found that anhydrous ammonia injected into the irrigation water contributed to higher peak NH 3 emissions (0.79 ± 0.09 kg N ha−1 day−1) than broadcasting urea onto dry soil (-0.06 ± 0.02 kg N ha−1 day−1). When daily NH 3 fluxes were accumulated over 8 − 10 days, 24% of the applied N was lost as NH 3 during anhydrous ammonia application, but no N loss was detected over the course of measurement period from the broadcast urea followed by irrigation. The daily fluxes of CH 4 and N 2 O were both negative following both fertilisation events. Our study suggests that cotton farm managers should avoid the use of anhydrous NH 3 in irrigation water to mitigate the environmental impact, as well as low efficiency of N fertiliser use. [ABSTRACT FROM AUTHOR]

• NH 3 emission was decreased by Green UreaNV® (45–55%) and polymer-coated urea (80%). • Extra cost of Green UreaNV® can be outweighed by reduced environmental cost of NH 3. • New fertilizer technology is needed to develop cost-effective polymer-coated urea. Mitigating ammonia (NH 3) volatilization from intensive pasture systems is critical for environmental sustainability. However, field-scale evaluation on the potential of enhanced efficiency fertilizers (e.g. urease inhibitors and controlled-release fertilizers) in mitigating NH 3 volatilization is limited. Using a micrometeorological technique, we conducted two field trials to investigate the effects of Green UreaNV® (urea coated with the urease inhibitor N -(n -butyl)thiophosphoric triamide, NBPT) and polymer-coated urea (a controlled-release fertilizer) on NH 3 volatilization from an intensive rainfed pasture in southern Australia. We found that NH 3 volatilization from urea was 5.8 and 5.6 kg N ha–1, respectively, in the autumn and spring trials, equivalent to 11–12% of the applied urea in each season. The use of Green UreaNV® and polymer-coated urea decreased the cumulative NH 3 volatilization by 45–55% and 80%, respectively. Taking into consideration the high environmental damage cost of NH 3 as found in the European Union, we hypothesize that both Green UreaNV® and polymer-coated urea can be cost-effective in mitigating NH 3 loss from this pasture. Our findings suggest that the extra cost of using these enhanced efficiency fertilizers for farmers is not compensated by the fertilizer N value of decreased NH 3 loss. However, from a societal perspective the extra cost for Green UreaNV® is likely outweighed by reduced environmental cost of NH 3. New fertilizer technology should be developed to improve the cost-effectiveness of polymer-coated urea to the farmers. [ABSTRACT FROM AUTHOR]

• Urea application reduced soil pH and increased soil total nitrogen (N), total carbon and nitrate; • Use of DMPP increased soil pH and reduced soil nitrate at a higher application rate of 120 kg Nha−1 relative to N alone; • Addition of N did not influence soil bacterial composition at phylum level but increased AOB abundance at application rate of 80 and 120 kg N ha−1. • DMPP addition did not influence soil bacterial composition at phylum level but reduced AOB and nirK abundance at an application rate of 120 kg N ha−1. Nitrification inhibitors have been reported to reduce nitrous oxide emission and nitrate leaching in agricultural systems. The effects of repeated applications of urea alone or in combination with nitrification inhibitors on nitrogen (N) cycling microbes involved in nitrification and denitrification together with non-targeted microbes are not well understood. Therefore, the objective of this study was to investigate the effects of repeated application of urea and DMPP on soil physio-chemistry, ammonia oxidizers and total bacteria in the soil. We collected soil samples from a 4.5-year field experiment under crop rotation with repeated application of seven treatments, namely control (CK), Urea (U), Urea + DMPP (UE) applied at 40, 80 and 120 kg N ha −1 , each treatment with three replicates. Ammonia-oxidizing bacteria (AOB) gene copy numbers increased as the N application rate increased (from 0 to 120 kg N ha −1). The use of DMPP significantly reduced AOB and nirK gene copy numbers compared to urea alone at an application rate of 120 kg N ha −1. There was no treatment effect on the abundance of ammonia-oxidizing archaea (AOA), Comammox clade A and B, nosZ and bacterial 16S rRNA genes. The community composition of AOB and AOA changed with N addition and use of DMPP but increasing N addition rate changed the composition of AOB only. Addition of N increased potential nitrification rates at 80 and 120 kg N ha −1. There was no significant treatment effect on the relative abundance of bacteria at the phylum level. This experiment demonstrated that the application of N (with or without DMPP) at rates lower than 120 kg N ha−1 would not result in significant impacts on soil archaeal and bacterial ecology. [ABSTRACT FROM AUTHOR]

• Volatilization from urea applied to grazed dairy pastures was modelled with DairyMod. • The complex process of volatilization was simulated by a simple modelling approach. • DairyMod is versatile for use across a range of scenarios with overall low model errors. • Modelling is attractive considering the difficulty, expense and uncertainty in field studies. Ammonia (NH 3) volatilization from fertilised agricultural soils is driven by complex interactions between edaphic, climatic and plant canopy factors that can be difficult to measure or predict. We developed a simplified approach using default parameters in the DairyMod model to predict daily NH 3 volatilization from urea applied to grazed dairy pastures. Several published datasets were used to validate the reliability of the model to reproduce key related soil processes in a whole farming systems framework. For the sites where monitoring for the experimental duration occurred, DairyMod simulated the main features of the observed NH 3 emissions, with an overall predicted median of 4.1 kg/ha or 7% of applied N, compared to the measured median of 6.1 kg/ha for 12% of applied N fertilizer. There was an overall root mean square error (RMSE) of 0.9 kg NH 3 N/ha/d and an overall mean prediction error (MPE) of 0.5 kg NH 3 N /ha/d. However, there was high uncertainty in several of the datasets used which made it difficult to be conclusive about the validation. The simulation accuracy was improved using daily wind speed (collected on-site in field campaigns) as input to the evapotranspiration calculations. In cases of high certainty in the volatilization data, it was concluded that the model was useful for the analysis of N cycling in situations used for dairy farming without the need for a more complex mechanistic method with difficult-to-obtain parameters. DairyMod presents a simple but readily reproducible prediction of NH 3 volatilization from urea application on pasture in intensive livestock farming systems compatible with the certainty of the model inputs and scale of model application. However, the collective understanding of NH 3 volatilization in pasture based dairy systems is currently based on a limited number of often uncertain, short term plot studies in the absence of animals. [ABSTRACT FROM AUTHOR]