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Nitrogen is an essential nutrient that supports life, but excess N in the humanenvironment system causes multiple adverse effects from the local to the global scale. Sustainable N management in agroecosystems, therefore, has become more and more critical to address the increasing concern over food security, environmental quality and climate change. Australia is facing a serious challenge for sustainable N management due to its emission-intensive lifestyle (high level of animal-source foods and fossil fuels consumption) and its diversity of agricultural production systems, from extensive rainfed grain systems with mining of soil N to intensive crop and animal production systems with excessive use of N. This paper reviews the major challenges and future opportunities for making Australian agrifood systems more sustainable, less polluting and more profitable. [ABSTRACT FROM AUTHOR]

Un-fertilized rice paddies have shown maintained soil nitrogen (N) status, stable N supply to the rice plant and sustained rice yields at moderate levels for hundreds of years. Microbial N2 fixation is known to contribute N to un-fertilized paddies, but it cannot fully explain the maintained N nutrition, where favourable conditions exist for N loss by denitrification. We used 15N tracer, 15N2 uptake, acetylene reduction assay and qPCR to simultaneously investigate N2 fixation, dissimilatory nitrate reduction to ammonium (DNRA), denitrification and related microbial gene abundances in long-term low (or no) and high N input rice paddies of Myanmar. We also determined how varying soil organic carbon-to-nitrate (SOC/NO3−) ratios affect nitrate partitioning between DNRA and denitrification by manipulating these ratios through labile organic carbon addition. We observed more than 2.5 times higher N2 fixation (1.49–2.08 μg N g−1 soil day−1) and significantly higher N2 fixing gene (nifH) abundance in low compared with high N input paddies. Up to 60% of the soil nitrate (1.51–2.67 μg NO3−-N g−1 soil day−1) was ammonified through DNRA, and only 15% was lost as N2 through denitrification in low N input paddies, whereas denitrification exceeded DNRA in high N input paddies. The microbial gene related to DNRA activity (nrfA) was also higher in low input than in high input rice paddies. We found that nitrate retention can be improved in high N input rice paddies by maintaining a higher soil organic carbon-to-nitrate ratio. Our findings highlight the unique microbial N-cycling strategies in resource-limited paddies which support maintained N nutrition of the paddy system. [ABSTRACT FROM AUTHOR]

Abstract Dissimilatory nitrate reduction to ammonium (DNRA) and diazotrophic N 2 fixation contribute to nitrogen (N) supply in rice paddies, whereas denitrification contributes to N loss. Continuous N fertilization in rice paddies is known to increase denitrification and reduce N 2 fixation, however little is known about its effect on DNRA and the NO 3 − partitioning between DNRA and denitrification. Here, we investigated the rates of DNRA, denitrification and N 2 fixation, and their relevant microbial gene abundances, in long-term high and low N fertilized rice paddies using a 15NO 3 − tracer, an acetylene reduction assay and quantitative PCR analysis, in laboratory incubation studies. We observed that DNRA exceeded denitrification by a factor of eight in low N fertilized rice paddies, while DNRA was almost half of the denitrification rate in high N fertilized rice paddies. The nrfA gene abundance, related to DNRA, was significantly higher in the low N fertilized rice paddies and was positively correlated with DNRA rates. However, no clear difference in denitrifying gene (narG, nirK and nosZ) abundances was observed between the N fertilization regimes. The proportion of total NO 3 − reduced by DNRA had a significantly positive correlation with the soil organic carbon-to-NO 3 - ratio and negative correlation with the soil NO 3 − concentration. N 2 fixation added ten times more N in the low N input than in the high N input paddies. Our findings highlight the self-regulated microbial N cycling in low N input paddy systems which maintain long-term paddy soil N nutrition. Highlights • N 2 fixation added ten times more N to low N input than to high N input rice paddies. • DNRA retained the majority of nitrate in long-term low N input rice paddies. • Denitrification dominated nitrate reduction in long-term high N input rice paddies. • High SOC:NO 3 − ratio favours NO 3 − partitioning to DNRA in NO 3 − limited paddy soils. [ABSTRACT FROM AUTHOR]

Improving direct field measurement techniques to quantify gas emissions from cropped agricultural fields is challenging. We compared nitrous oxide (N2O) emissions measured with static closed chambers to those from a newly developed aerodynamic flux gradient (FG) approach. Measurements were made at a vegetable farm following chicken manure application. The FG calculations were made with a single open-path Fourier transform infrared (OP-FTIR) spectrometer (height of 1.45 m) deployed in a slant-path configuration, sequentially aimed at retro reflectors at heights of 0.8 and 1.8 m above ground. Hourly emissions were measured with the FG technique, but once a day between 10:00 and 13:00 with chambers. We compared the concurrent emission ratios (FG / chamber) of these two techniques and found N2O emission rates from a celery crop farm measured at midday by FG were statistically higher (1.22–1.40 times) than those from the chambers measured at the same time. Our results suggest the OP-FTIR slant-path FG configuration worked well in this study: it was sufficiently sensitive to detect the N2O gradients over our site, giving high temporal resolution N2O emissions corresponding to a large measurement footprint. [ABSTRACT FROM AUTHOR]

Abstract Urease and nitrification inhibitors are designed to mitigate ammonia (NH 3) volatilization and nitrous oxide (N 2 O) emission, but uncertainties on the agronomic and economic benefits of these inhibitors prevent their widespread adoption in pasture systems, particularly in subtropical regions where no such information is available. Here we report a field experiment that was conducted in a subtropical pasture in Queensland, Australia to examine whether the use of the urease inhibitor N -(n -butyl) thiophosphoric triamide (NBPT, applied as Green UreaNV®) and the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP, applied as Urea with ENTEC®) is environmentally, agronomically and economically viable. We found that Green UreaNV® and Urea with ENTEC® decreased NH 3 volatilization and N 2 O emission by 44 and 15%, respectively, compared to granular urea. Pasture biomass and nitrogen (N) uptake were increased by 22–36% and 23–32%, respectively, with application of the inhibitors compared to granular urea. A simple economic assessment indicates that the fertilizer cost for pasture production was 5.4, 4.4 and 6.0 Australian cents per kg dry matter for urea, Green UreaNV® and Urea with ENTEC®, respectively, during the experimental period. The mitigation of N loss using the inhibitors can reduce the environmental cost associated with pasture production. These results suggest that the use of these inhibitors can provide environmental, agronomic and economic benefits to a subtropical pasture. Graphical abstract Unlabelled Image Highlights • Effects of urease and nitrification inhibitors on N dynamics of a subtropical pasture were examined. • NBPT and DMPP decreased NH 3 volatilization by 44% and N 2 O emission by 15%, respectively. • The use of these inhibitors increased pasture biomass and N uptake by ~20–30%. • These inhibitors can provide environmental, agronomic and economic benefits. [ABSTRACT FROM AUTHOR]

Improving the direct field measurement techniques to quantify gases emissions from the large agriculture farm is challenging. We compared nitrous oxide (N2O) emissions measured with static chambers to those from a newly developed micrometeorological flux gradient (FG) approach. Measurements were made at a vegetable farm following chicken manure application. The FG calculations were made with a single open-path Fourier transform infrared (OP-FTIR) spectrometer (height of 1.45 m) deployed in a slant-path configuration: sequentially aimed at retro reflectors at heights of 0.8 and 1.8 m above ground. Hourly emissions were measured with the FG technique, but once a day between 10:00 and 13:00 with chambers. We compared the concurrent emission ratios (FG/Chambers) between these two techniques, and found N2O emission rates from celery crop farm measured at mid-day by FG were statistically higher (1.4 times) than those from the chambers measured at the same time. Our results suggest the OP-FTIR slant-path FG configuration worked well in this study: it was sufficiently sensitive to detect the N2O gradients over our site, giving high temporal resolution N2O emissions corresponding to a large measurement footprint. [ABSTRACT FROM AUTHOR]

Dissimilatory nitrate reduction to ammonium (DNRA), denitrification, anaerobic ammonium oxidation (anammox) and biological N2 fixation (BNF) can influence the nitrogen (N) use efficiency of rice production. Whilst the effect of N application on BNF is known, little is known about its effect on NO3 - partitioning between DNRA, denitrification and anammox. Here, we investigated the effect of N application on DNRA, denitrification, anammox and BNF, and on the abundance of relevant genes in three paddy soils in Australia. Rice was grown in the glasshouse with (150 kg N ha-1 ) and without N-fertiliser for 75 days, and the rhizosphere and bulk soils were collected separately for laboratory incubation and quantitative PCR analysis. Nitrogen application reduced DNRA rates by >16% in all the soils regardless of the rhizospheric zone but it did not affect the nrfA gene abundance. Without N, the amount and proportion of NO3 - reduced by DNRA (0.42-0.52 µg g-1 soil day-1 , 45-55%) was similar or higher than that by denitrification. However, with N the amount of NO3 - reduced by DNRA (0.32-0.40 µg g-1 soil day-1 ) was 40-50% lower than the NO3 - reduced by denitrification. Denitrification loss increased by >20% with N addition, and was affected by the rhizospheric zones. Nitrogen loss was minimal through anammox, while BNF added 0.02-0.25 µg N g-1 soil day-1. We found that DNRA plays significant positive role in paddy soil N retention as it accounts for up to 55% of the total NO3 - reduction, but this is reduced by N application. [ABSTRACT FROM AUTHOR]

A recently developed slant-path flux gradient (FG) technique, combined with open-path Fourier transform infrared (OP-FTIR) spectroscopy, was deployed to concurrently measure gas emissions of ammonia (NH 3 ), nitrous oxide (N 2 O), carbon dioxide (CO 2 ), and methane (CH 4 ) from an intensive vegetable farm in Australia. Gas fluxes were continuously measured for three weeks following chicken manure application to a celery crop, followed by intermittent measurements for three days a week for another three weeks. The average flux measured over the 41 day measurement period for NH 3 and N 2 O, was 5.2 and 2.9 mg N m −2  h −1 , respectively, CH 4 was 1.1 mg C m −2  h −1 , and CO 2 was 0.7 C g m −2  h −1 . Manure and fertilizer application substantially increased the emissions of these gases, by providing carbon (C) and nitrogen (N) substrates to the soil. The cumulative N losses as NH 3 and N 2 O following fertilizer application were 6.7% and 3.7% of total N applied, respectively. Using this FG/OP-FTIR technique, we demonstrated that the N 2 O emission factor for this vegetable farm is much higher than the IPCC default emission factor for manure applied to managed lands. These results highlight the need for large-scale measurements to quantify multiple gas losses from intensive agricultural systems. [ABSTRACT FROM AUTHOR]

Nitrification inhibitors are effective in decreasing direct nitrous oxide (N 2 O) emission from agricultural soils but may stimulate ammonia (NH 3 ) volatilization. Part of the NH 3 deposited to land is converted to N 2 O and emitted to the atmosphere, termed indirect N 2 O emission. While vegetable production systems entail a considerable risk of NH 3 and N 2 O loss from high nitrogen (N) input to the soil, the simultaneous effects of nitrification inhibitors on these N loss pathways have rarely been examined. We conducted paddock-scale (ca. four hectares) measurements using micrometeorological techniques to simultaneously quantify the effects of a nitrification inhibitor DMPP (3,4-dimethylpyrazole phosphate) on NH 3 and N 2 O emissions from two intensive vegetable farms. We found that DMPP decreased direct N 2 O emission by 37–38% (2.2–7.3 kg N ha −1 ) across the farms during the most intensive period of N input (18 days), but could increase NH 3 volatilization by 3–39% (1.6–4.8 kg N ha −1 ). The results highlight the importance of considering multiple N loss pathways when developing a strategy for mitigating agricultural greenhouse gas emissions. [ABSTRACT FROM AUTHOR]

Nitrification inhibitors show promise in decreasing nitrous oxide (N2O) emission from agricultural systems worldwide, but they may be much less effective than previously thought when both direct and indirect emissions are taken into account. Whilst nitrification inhibitors are effective at decreasing direct N2O emission and nitrate ( NO3-) leaching, limited studies suggest that they may increase ammonia ( NH3) volatilization and, subsequently, indirect N2O emission. These dual effects are typically not considered when evaluating the inhibitors as a climate change mitigation tool. Here, we collate results from the literature that simultaneously examined the effects of nitrification inhibitors on N2O and NH3 emissions. We found that nitrification inhibitors decreased direct N2O emission by 0.2-4.5 kg N2O-N ha−1 (8-57%), but generally increased NH3 emission by 0.2-18.7 kg NH3-N ha−1 (3-65%). Taking into account the estimated indirect N2O emission from deposited NH3, the overall impact of nitrification inhibitors ranged from −4.5 (reduction) to +0.5 (increase) kg N2O-N ha−1. Our results suggest that the beneficial effect of nitrification inhibitors in decreasing direct N2O emission can be undermined or even outweighed by an increase in NH3 volatilization. [ABSTRACT FROM AUTHOR]

A laboratory incubation experiment was conducted using the nitrification inhibitor acetylene and N isotope techniques in order to determine the relative significance of heterotrophic and autotrophic nitrification in three acid soils from different locations in Australia. The contribution of heterotrophic nitrification to total nitrification was found to vary from 20-88 % amongst the three soils. In the less acidic Glenormiston soil (pH 6.2, organic C content 5.6 %), nitrification was largely autotrophic with heterotrophic nitrification accounting for only 20 %. However, in the more acidic and higher organic C content Longworry soil (pH 4.8 and organic C content 9.3 %), heterotrophic nitrification was the predominant NO production pathway accounting for 88 % of total nitrification. [ABSTRACT FROM AUTHOR]

An open-path Fourier transform infrared (OP-FTIR) spectroscopic technique in combination with a backward Lagrangian stochastic (bLS) dispersion model (WindTrax) can be used to simultaneously measure gaseous emissions of N2O, NH3, CH4 and CO2. We assessed the capability of this technique for measuring NH3 and N2O emissions following the application of calcium nitrate (Ca(NO3)2), Nitrophoska (NPK) and chicken manure on a celery farm at Boneo, Victoria, during April and May 2013. We found that the OP-FTIR/WindTrax method was able to measure the diurnal variation in NH3 flux from the field site following application of chicken manure with measured emissions ranging from approximately 0.1-9.8 kg NH3-N ha-1 day-1. The OP-FTIR/WindTrax method also detected a diurnal variation in N2O flux of 1.5-6.2 kg N2O-N ha-1 day-1 and N2O flux increased in response to application of the Ca(NO3)2. We concluded that the OP-FTIR/WindTrax technique can quantify gaseous N loss from vegetable production systems. [ABSTRACT FROM AUTHOR]

Abstract: Laboratory incubation experiments were conducted to compare the effects of the nitrification inhibitors 3,4-dimethylpyrazole phosphate (DMPP) and 2-Chloro-6-(trichloromethyl)-pyridine (N-serve) on nitrification and nitrous oxide (N2O) emission from a Vertosol from southern Australia, under controlled moisture and temperature. Nitrification rates in the control soil were strongly influenced by the temperature and moisture, increasing by a factor of 3.6 for each 10 °C increase between 5 and 25 °C. DMPP inhibited nitrification effectively for 42 days at 5–15 °C and 40–60% water filled pore space (WFPS). DMPP also slowed nitrification appreciably at 25 °C when the soil was at 40% WFPS, but was less effective at 60% water filled pore space. N-serve inhibited nitrification effectively for 42 days under all test conditions. Emissions of N2O from the urea treatment (no inhibitors) significantly increased with increasing temperature and moisture. The ratio of total N2O emission to total nitrification was not constant and varied from around 0.03% at 5 °C and 40% WFPS to 0.12% at 25 °C and 60% WFPS. DMPP and N-serve reduced cumulative N2O emission over 42 days by more than 65% under all the imposed conditions. [Copyright &y& Elsevier]

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]

Land application of municipal wastewater is widely practised worldwide as a means of treating wastes and obtaining a benefit from the water and nutrients by growing pastures, trees, and sometimes edible crops such as vegetables, fruit and fibre, etc. Irrigation of pastures by treated and untreated sewage near Melbourne, Australia, for more than a century has increased heavy metals concentrations in the soil, but appears not to have increased their concentrations in the herbage and in animal tissues of animals grazed on these pastures. There seem to be sound reasons why this practice may be sustainable. [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]

Unlabelled Image • Enhanced efficiency fertilisers can be used to reduce N 2 O emissions but their impact on soil N reserves is not well known. • N 2 O emissions were measured from urea and enhanced efficiency fertilisers applied to pastures. • N 2 O emissions, but not emission factors, increased as N application rate increased. • Use of enhanced efficiency fertilisers reduced N 2 O emissions by 22–56%. • Using urease and nitrification inhibitors increased retention of N in soil. The effects of reducing nitrogen (N) rates or using enhanced efficiency fertilisers (EEFs) (i.e. urease and nitrification inhibitors, and controlled release fertilisers) on nitrous oxide (N 2 O) emissions and nitrogen use efficiency (NUE) are not well understood in temperate, rainfed pastures. A field experiment on rainfed ryegrass pasture in southern Australia examined the effect of granular urea N rate (0, 250 and 420 kg N ha−1 over 6 months) and EEF use (at 250 kg N ha−1 with NBPT, DMPP, or polymer coating (PCU)) on N 2 O emissions, NUE and fertiliser N recovery (using 15N techniques). Cumulative net-N 2 O emissions increased with N rate from 308 g N 2 O-N ha−1 (250 kg N ha−1) to 514 g N 2 O-N ha−1 (420 kg N ha−1). Using EEFs reduced N 2 O emissions by 22% (NBPT), 44% (DMPP) and 56% (PCU) compared to urea. The emission factor (EF) (kg net N 2 O-N per kg N applied) was 0.12 for both N rates (250 and 420 kg N ha−1) but reduced with the EEFs to 0.10 (NBPT) and 0.07 (DMPP and PCU) compared to urea. EEF use had no significant impact on biomass or apparent NUE but led to a greater recovery of N in the soil after one month (44.8% (DMPP) and 45.9% (NBPT) compared to urea (33.7%)). Within one month 42% of the N applied as urea (U50) was lost from the plant-soil system, which was reduced with DMPP (32% loss) and NBPT (33% loss). After six months, 52% (U50) to 59% (U84) of the urea N applied was lost. The positive effect of the EEFs on N 2 O emissions, and the increased recovery of N in the soil-plant system with the EEFs over one month indicates they could provide longer term benefits though soil N storage, and could be applied at lower N rates to achieve NUE benefit. [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]

Accurately monitoring Canopy Nitrogen Concentration (CNC) is a prerequisite for precision nitrogen (N) fertiliser management at the farm scale with carbon and N budgeting across the landscape and ecosystems. While many spectral indices have been proposed for CNC monitoring, their applicability and accuracy are often adversely affected by confounding factors such as aboveground biomass (AGB), crop type, growth stages, and environmental conditions, limiting their broader application and adoption; with AGB being one of the most dominant signals and confounding factors at canopy scale. The confounding effect can become more challenging as AGB is also physiologically linked with CNC across the growth stages. Additionally, the interplay between index form, selection of optimal wavebands and their bandwidths remains poorly understood for CNC index design. This study proposes robust and cost-effective 2- and 4-waveband multispectral (MS) CNC indices applicable across a wide range of crop conditions. We collected 449 canopy reflectance spectra (400–980 nm) together with corresponding CNC and AGB measurements across four growth stages of ryegrass (winter and summer), and five growth stages of barley (winter-spring) in Victoria, Australia, in 2018 and 2019. All possible waveband (400–980 nm) combinations revealed that the best combination varied between seasons and crop types. However, the visible spectrum, particularly the blue region, presented high and consistent performance. Bandwidths of 10–40 nm outperformed either very narrow (2 nm) or very broad bandwidths (80 nm). The newly developed 2-waveband index (416 and 442 nm with 10-nm bandwidth; R2 = 0.75 and NRMSE = 0.2) and 4-waveband index (512, 440, 414 and 588 nm with 40-nm bandwidth; R2 = 0.81 and NRMSE = 0.17) exhibited the best performance, while validation with an independent dataset (from a different growing period to those used in the model development) obtained NRMSE values of 0.25 and 0.24, respectively. The 4-waveband index provides enhanced performance and permits use of broader bandwidths than its 2-waveband counterpart. [ABSTRACT FROM AUTHOR]

The emission and mitigation of nitrous oxide (N2O) from high nitrogen (N) vegetable systems is not well understood. Nitrification inhibitors are widely used to decrease N2O emissions in many cropping systems. However, most N2O flux measurements and inhibitor impacts have been made with small chambers and have not been investigated at a paddock-scale using micrometeorological techniques. We quantified N2O fluxes over a four ha celery paddock using open-path Fourier Transform Infrared spectroscopy in conjunction with a backward Lagrangian stochastic model, in addition to using a closed chamber technique. The celery crop was grown on a sandy soil in southern Victoria, Australia. The emission of N2O was measured following the application of chicken manure and N fertilizer with and without the application of a nitrification inhibitor 3, 4-dimethyl pyrazole phosphate (DMPP). The two techniques consistently demonstrated that DMPP application reduced N2O emission by 37-44%, even though the N2O fluxes measured by a micrometeorological technique were more than 10 times higher than the small chamber measurements. The results suggest that nitrification inhibitors have the potential to mitigate N2O emission from intensive vegetable production systems, and that the national soil N2O emission inventory assessments and modelling predictions may vary with gas measurement techniques. [ABSTRACT FROM AUTHOR]

In recent years, identification of the microbial sources responsible for soil NO production has substantially advanced with the development of isotope enrichment techniques, selective inhibitors, mathematical models and the discoveries of specific N-cycling functional genes. However, little information is available to effectively quantify the NO produced from different microbial pathways (e.g. nitrification and denitrification). Here, a N-tracing incubation experiment was conducted under controlled laboratory conditions (50, 70 and 85% water-filled pore space (WFPS) at 25 and 35 °C). Nitrification was the main contributor to NO production. At 50, 70 and 85% WFPS, nitrification contributed 87, 80 and 53% of total NO production, respectively, at 25 °C, and 86, 74 and 33% at 35 °C. The proportion of nitrified N as NO ( P ) increased with temperature and moisture, except for 85% WFPS, when P was lower at 35 °C than at 25 °C. Ammonia-oxidizing archaea (AOA) were the dominant ammonia oxidizers, but both AOA and ammonia-oxidizing bacteria (AOB) were related to NO emitted from nitrification. AOA and AOB abundance was significantly influenced by soil moisture, more so than temperature, and decreased with increasing moisture content. These findings can be used to develop better models for simulating NO from nitrification to inform soil management practises for improving N use efficiency. [ABSTRACT FROM AUTHOR]

Interfacial modular assemblies of eco‐friendly metal–phenolic networks (MPNs) are of interest for surface and materials engineering. To date, most MPNs are assembled on water‐stable substrates; however, the self‐assembly of MPNs on highly water‐soluble substrates remains unexplored. Herein, a versatile approach is reported to engineer thickness‐tunable coatings (2–25 µm) on a water‐soluble substrate (i.e., urea) via the self‐assembly of MPNs in a nonaqueous solvent (i.e., acetonitrile). The coordination‐driven assembly of the MPN coatings in the nonaqueous solvent is distinct from that in aqueous systems, as the assembly is only achieved following the addition of urea granules into the iron–tannin solution. The coating occurs relatively rapidly (5–60 min), generating micrometer‐thick coatings from the adsorption of FeIII–TA complexes and micrometer‐sized FeIII–TA particles formed in solution. The straightforward nature of the present fabrication method in generating thick and robust coatings with high stability in nonaqueous environments (including at 60 °C) coupled with the broad range of available naturally abundant polyphenol–metal ion combinations expand the applicability of MPNs as coatings for water‐soluble materials, thus providing new opportunities for their broader application in a range of industrial processes and applications. [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]

Soil ecosystem represents the largest contributor to global nitrous oxide (N2O) production, which is regulated by a wide variety of microbial communities in multiple biological pathways. A mechanistic understanding of these N2O production biological pathways in complex soil environment is essential for improving model performance and developing innovative mitigation strategies. Here, combined approaches of the 15N-18O labelling technique, transcriptome analysis, and Illumina MiSeq sequencing were used to identify the relative contributions of four N2O pathways including nitrification, nitrifier-induced denitrification (nitrifier denitrification and nitrification-coupled denitrification) and heterotrophic denitrification in six soils (alkaline vs. acid soils). In alkaline soils, nitrification and nitrifier-induced denitrification were the dominant pathways of N2O production, and application of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) significantly reduced the N2O production from these pathways; this is probably due to the observed reduction in the expression of the amoA gene in ammonia-oxidizing bacteria (AOB) in the DMPP-amended treatments. In acid soils, however, heterotrophic denitrification was the main source for N2O production, and was not impacted by the application of DMPP. Our results provide robust evidence that the nitrification inhibitor DMPP can inhibit the N2O production from nitrifier-induced denitrification, a potential significant source of N2O production in agricultural soils. [ABSTRACT FROM AUTHOR]

Acetylene (C 2 H 2 ) is an effective nitrification inhibitor targeting autotrophic ammonia oxidizers, and has shown promise for improving nitrogen use efficiency by mitigating greenhouse gas nitrous oxide (N 2 O) emissions and reducing nitrate leaching. Its efficacy, however, varies considerably with edaphic and environmental conditions and remains largely less studied in dryland agricultural soils. Here we conducted two laboratory microcosm incubations to explore the efficacy of C 2 H 2 across various agricultural soils and under different conditions. The first incubation was with four agricultural soils at 25 °C and 60% water-filled pore space (WFPS), and the second incubation included one cropping soil under a range of conditions (15 °C, 25 °C, 35 °C and 50%, 70% WFPS). Our results showed that incubation of soil with 1% v/v C 2 H 2 resulted in complete or partial inhibition of nitrification, N 2 O emission, and AOA or AOB growth under the experimental conditions. Acetylene can totally inhibit nitrification in acidic cropping and dairy pasture soils through retarding both AOA and AOB growth, while C 2 H 2 partly inhibited nitrification and N 2 O emission in the alkaline vegetable soil through impeding only AOB growth. The highest inhibition effect of C 2 H 2 was achieved at 25 °C and 50% WFPS, while there was no inhibitory effect of C 2 H 2 when soil was incubated at 15 °C and 50% WFPS suggesting soil temperature may have a significant influence on C 2 H 2 effectiveness. The inhibition of C 2 H 2 on cumulative N 2 O emission increased with increasing temperature at 50% WFPS. In contrast, at 70% WFPS, the inhibition of C 2 H 2 on cumulative N 2 O emission decreased with increasing temperature. Since the effect of C 2 H 2 varied with soils and environmental conditions, this highlights the assumption that N 2 O production and nitrification can be affected by low concentrations of C 2 H 2 may be not appropriate in some occasions. [ABSTRACT FROM AUTHOR]

Real-time crop canopy nitrogen concentration (CNC) and aboveground biomass (AGB) sensing capability can enable precision agriculture with significant economic and ecological benefits. Canopy spectral response in visible near-infrared (VNIR, 400–979 nm) has been widely used to estimate CNC and AGB of canopies but is often confounded by the soil background, crop type, phenological changes and environmental conditions. Machine (ML) and deep learning (DL) have emerged as promising techniques for mapping CNC and AGB using canopy spectral reflectance in VNIR. However, ML and DL models' performance relies on extensive labelled training datasets, which are often limited due to being expensive and labour intensive. We estimated CNC and AGB using state-of-the-art hyperspectral (HS) modeling approaches using partial least squares regression (PLSR), random forest (RF), and one- and two-dimensional convolutional neural network (1D and 2D CNN). These models, together with multispectral (MS) approaches, were evaluated in the context of a small (422) dataset for model development collected from diverse fertilization and contrasting growth conditions. A handheld field spectroradiometer was used to collect spectral reflectance samples across a wide range (more than ten-fold difference in AGB) of canopy development stages in two seasons (winter and summer) in ryegrass, and across phenological stages (from GS-25 to GS-60) in barley. Results can be summarized in four components: (1) the median values of performance metrics in 1D CNN (R2 test =0.83, NRMSE test =0.15 for CNC; R2 test =0.79 (ryegrass), 0.61 (barley), NRMSE test = 0.29 (ryegrass), 0.30 (barley) for AGB) and PLSR (R2 test =0.71, NRMSE test = 0.20 for CNC; R2 test =0.62 (ryegrass), 0.70 (barley), NRMSE test = 0.38 (ryegrass), 0.27 (barley) for AGB) showed the best performance for CNC and AGB prediction in the test data; (2) when evaluated with the independent measurements, 1D CNN demonstrated the best (up to 56% decrease in NRMSE) performance for AGB and was comparable to PLSR for CNC (up to 25% decrease in NRMSE than their HS and MS counterparts); (3) predictive models underperformed at low canopy cover for CNC estimation and were adversely affected by the high biomass saturation effects for AGB prediction; and (4) visible spectrum is relatively more informative to CNC models whereas the red edge to NIR spectrum is more informative to AGB models. This study demonstrates the potential and limitations of commonly available field VNIR spectral reflectance data for CNC and AGB mapping across contrasting conditions in a small dataset (<500). • 1D convolutional neural network (CNN) exhibited the best and robust performance. • 1D CNN showed a relatively higher tolerance for biomass saturation effects. • Canopy nitrogen concentration (CNC) models underperformed at low canopy cover. • Visible spectrum was more informative for CNC prediction. • Red edge to NIR spectrum showed more relevance for aboveground biomass prediction. [ABSTRACT FROM AUTHOR]

The application of the nitrification inhibitor, 3,4-dimethylpyrazole-phosphate (DMPP), is considered as an effective strategy to mitigate agricultural nitrogen loss. However, the inhibitory effect of DMPP on nitrification is variable and the importance of the soil microbial community composition to the variability is poorly understood. In this study, nine soils were collected across three land uses to investigate the impact of DMPP on nitrification and associated dynamics of ammonia oxidizers in a 28-day microcosm incubation. The results showed that the efficacy of DMPP at inhibiting net nitrification rates varied highly from no effect to 63.6 % during the first week of incubation. The abundance of ammonia-oxidizing bacteria (AOB), rather than ammonia-oxidizing archaea (AOA), was significantly correlated with nitrate concentrations across three land uses and significantly inhibited by DMPP addition. DMPP had higher efficacy in neutral and alkaline wheat and vegetable soils, compared with pasture soils. Canonical correspondence analysis suggested that soil pH was the most influential factor explaining the community composition of AOB and AOA in the collected soils. However, neither ammonium nitrate nor DMPP addition had a significant effect on the community composition of AOB or AOA during the incubation indicated by non-metric multidimensional scaling ordination. Taken together, our findings indicated that DMPP slowed nitrification by inhibiting the growth of AOB, and DMPP application affected the abundance of AOB more than the ammonia oxidizer community composition. [ABSTRACT FROM AUTHOR]

The nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) is a powerful tool that can be used to promote nitrogen (N) use efficiency and reduce N losses from agricultural systems by slowing nitrification. Mounting evidence has confirmed the functional importance of ammonia-oxidizing archaea (AOA) and ammonia-oxidizing bacteria (AOB) in nitrification and N2O production; however, their responses to DMPP amendment and the microbial mechanisms underlying the variable efficiencies of DMPP across different soils remain largely unknown. Here we compared the impacts of DMPP on nitrification and the dynamics of ammonia oxidizers between an acidic pasture soil and an alkaline vegetable soil using a 15N tracing and 13CO2-DNA-stableisotope probing (SIP) technique. The results showed that DMPP significantly inhibited nitrification and N2O production in the vegetable soil only, and the transient inhibition was coupled with a significant decrease in AOB abundance. No significant effects on the community structure of ammonia oxidizers or the abundances of total bacteria and denitrifiers were observed in either soil. The 15N tracing experiment revealed that autotrophic nitrification was the predominant form of nitrification in both soils. The 13CO2-DNA-SIP results indicated the involvement of AOB in active nitrification in both soils, but DMPP inhibited the assimilation of 13CO2 into AOB only in the vegetable soil. Our findings provide evidence that DMPP could effectively inhibit nitrification through impeding the abundance and metabolic activity of AOB in the alkaline vegetable soil but not in the acidic pasture soil, possibly due to the low AOB abundance or the adsorption of DMPP by organic matter. [ABSTRACT FROM AUTHOR]

• Eighteen spectral indices are compared for their sensitivity to CNC and biomass. • Of these indices, PRI best correlates with CNC but it also correlates with biomass. • Regression relationships between CNC and all indices shift with growth stages. • CCCI exhibits stronger correlation to biomass than CNC. • A wide range of growth conditions are needed to develop a robust indicator for CNC. In precision farming, accurate estimation of canopy nitrogen concentration (CNC) is valuable for effective crop growth monitoring and nitrogen (N) fertiliser management. To date, many canopy multispectral indices have been proposed as indicators for CNC; however, many of these indices have also shown sensitivity to biomass and their performance drops at high biomass levels. Dependence on growth stage, season, or other environmental conditions limits their efficacy as generalized CNC indices. The objectives of this study were to assess the robustness of popular CNC indices across a wide range of biomass levels and fertiliser application levels; and for two contrasting seasons – winter and summer. To achieve this, we analysed the efficacy of seven canopy nitrogen indices, including canopy chlorophyll content index (CCCI), together with eleven other commonly used spectral indices. We used canopy level solar-induced hyperspectral reflectance data acquired using a hand-held optical spectroradiometer across four growth stages in winter (May-June 2018) and four in summer (January-February 2019) from an experimental field of irrigated perennial ryegrass with variable N application in Victoria, Australia. The field contained 40 plots, each with one of eight different N treatments. Almost all the indices exhibited similar correlation to CNC (%) when applied to individual stages (days) in both winter and summer; however, relationships between CNC and individual indices varied significantly between stages. We obtained similar results for canopy biomass. When the data across the entire range of growth stages and seasons were combined, the correlations between most canopy nitrogen indices and CNC became weak (R2 < 0.25, 0.9% ≤ RMSE ≤ 1.0%). PRI exhibited the highest correlation with CNC (R2 = 0.58, RMSE = 0.7%) for the combined data set. Even so, PRI's association with CNC and canopy biomass changed with the season. Most indices responded to both CNC and biomass simultaneously, and this confounds the estimation of CNC due to strong but growth stage-specific relationships between CNC and canopy biomass. This study shows that it is important to consider a wide range of conditions when evaluating multispectral CNC indices. [ABSTRACT FROM AUTHOR]

China has experienced a widespread increase in N deposition due to intensive anthropogenic activities, particularly in the subtropical regions. However, the effects of long-term N deposition on soil bacterial and fungal abundance, diversity, and community composition remain largely unclear. We assessed the effects of N deposition on soil microbial communities in summer and winter, using quantitative polymerase chain reaction and Illumina Miseq sequencing of bacterial 16S rRNA and fungal ITS genes from subtropical natural forest soils. The abundance of both soil bacteria and fungi exhibited a decreasing pattern with increasing N deposition rates. Nitrogen deposition increased bacterial diversity in both summer and winter, whereas fungal diversity was significantly decreased in summer, but greatly increased under the highest level of N deposition (150 kg N ha−1 yr−1) in winter. Nitrogen deposition significantly increased the relative abundance of bacterial phyla Actinobacteria, Chloroflexi, and WPS-2, but decreased that of Acidobacteria and Verrucomicrobia. In addition, N deposition significantly decreased the relative abundance of Ascomycetes, but did not exert any significant effect on Basidiomycetes. The bacterial and fungal community compositions were greatly influenced by N deposition, with soil N availability and soil pH identified as the two most influential soil properties. This study demonstrates that the fungal community was more sensitive than the bacterial community to N deposition, and further emphasizes the importance of simultaneously evaluating soil bacterial and fungal communities in response to global environmental changes. Unlabelled Image • The abundances of bacteria and fungi showed decreasing patterns with N deposition. • Nitrogen deposition increased bacterial diversity in summer and winter. • Fungal diversity decreased in summer, but increased under N deposition in winter. • Fungal community was more sensitive than the bacterial community to N deposition. [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]