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Reducing nitrogen losses can be accomplished by mixing fertilizers with nitrification inhibitors (NI). In some agricultural systems, increasing soil N supply capacity by the use of NI could lead to improved N use efficiency (NUE) and increased crop yields. This study examined the effect of different N rates and NI in maize in the north of Iran. The maize was fertilized with urea at three levels (69, 115 and 161 kg N.ha -1 ) alone or with nitrapyrin as NI. Increasing the N application rate resulted in a considerable rise in growing-season N 2 O emissions. When nitrapyrin was used, N 2 O emissions were dramatically reduced. NI treatment reduced N 2 O emissions in the growth season by 88%, 88%, and 69% in 69, 115, and 161 kg of N.ha -1 , respectively. NI treatment reduced yield-scaled N 2 O emissions; the lowest quantity of yield-scaled N 2 O was found in 69 N + NI (0.09 g N 2 O-N kg -1  N uptake). Additionally, grain yield increased by 19%, 31% and 18.4% after applying NI to 69 N, 115 N, and N69, N115 and N161. Results showed that 115 N + NI and N69 treatments showed the highest (65%) and lowest (29%) NUEs, respectively. Finally, our findings show that NI can reduce N 2 O emissions while increasing NUE and yield, but that the application method and rate of nitrapyrin application need to be improved in order to maximize its mitigation potential., (© 2022. The Author(s).)

Emissions of the critical ozone-depleting and greenhouse gas nitrous oxide (N 2 O) from soils and industrial processes have increased considerably over the last decades 1-3 . As the final step of bacterial denitrification, N 2 O is reduced to chemically inert N 2 (refs. 1,4 ) in a reaction that is catalysed by the copper-dependent nitrous oxide reductase (N 2 OR) (ref. 5 ). The assembly of its unique [4Cu:2S] active site cluster Cu Z requires both the ATP-binding-cassette (ABC) complex NosDFY and the membrane-anchored copper chaperone NosL (refs. 4,6 ). Here we report cryo-electron microscopy structures of Pseudomonas stutzeri NosDFY and its complexes with NosL and N 2 OR, respectively. We find that the periplasmic NosD protein contains a binding site for a Cu + ion and interacts specifically with NosL in its nucleotide-free state, whereas its binding to N 2 OR requires a conformational change that is triggered by ATP binding. Mutually exclusive structures of NosDFY in complex with NosL and with N 2 OR reveal a sequential metal-trafficking and assembly pathway for a highly complex copper site. Within this pathway, NosDFY acts as a mechanical energy transducer rather than as a transporter. It links ATP hydrolysis in the cytoplasm to a conformational transition of the NosD subunit in the periplasm, which is required for NosDFY to switch its interaction partner so that copper ions are handed over from the chaperone NosL to the enzyme N 2 OR., (© 2022. The Author(s), under exclusive licence to Springer Nature Limited.)

The aim of this study was to evaluate the effectiveness of nitrification inhibitor (nitrapyrin; NI) as a mitigation option for yield-scaled emissions of nitrous oxide (N 2 O) under tillage management and urea fertilization in the irrigated maize fields in northern Iran. A split-plot experiment was performed based on a randomized completed blocks design with three replicates. The main plots were the levels of tillage practices (conventional tillage (CT) and minimum tillage (MT), and the subplots were the fertilizer treatments (control, urea, and urea + NI). The gas samples for measuring N 2 O emissions were collected during the maize growing season from June to September, using opaque manual circular static chambers. Soil samples were taken at 0-10 cm to determine water-filled pore space, ammonium (NH 4 + ), and nitrate (NO 3 - ) concentrations in the soil. When the crop reached physiological maturity, maize was harvested to measure grain yield, biomass production, N uptake of aboveground, and nitrogen use efficiency (NUE). The results showed that the applying NI in combination with urea reduced the total N 2 O emissions by up to 58% and 64% in MT and CT, respectively. In the urea + NI treatment, mean soil concentrations of NH 4 + and NO 3 - were significantly higher (20%) and lower (23.5%), respectively, compared with other treatments. The NI reduced the yield-scaled N 2 O-N emission up to 79% and 55% for CT and MT, respectively. Furthermore, compared to treatment with urea alone, the application of NI increased the NUE of the MT and CT systems by an average of 55% and 46%, respectively. This study emphasized that the application of nitrapyrin should be encouraged in irrigated maize fields, in order to minimize N 2 O emissions and improve NUE and biomass production., (© 2021. The Author(s), under exclusive licence to Springer-Verlag GmbH Germany, part of Springer Nature.)

The properties of agricultural soils in various regions of the world are variable and can have a significant but poorly understood impact on soil nitrogen (N) transformations and nitrous oxide (N 2 O) emissions. For this reason, we undertook a study of gross N transformations and related N 2 O emissions in contrasting agricultural soils from China and the UK. Seven Chinese and three UK agricultural soils were collected for study using a 15 N tracing approach. The soil pH ranged from 5.4 to 8.7, with three acidic soils collected from Jinjing, Lishu and Boghall; one neutral soil collected from Changshu, and the other six alkaline soils collected from Quzhou, Zhangye, Changwu, Jinzhong, Boxworth and Stetchworth. Our results showed that the main N transformation processes were oxidation of ammonium (NH 4 + ) to nitrate (NO 3 - ) (O NH4 ), and mineralization of organic N to NH 4 + . The gross autotrophic nitrification rates calculated in the three acidic soils were between 0.25 and 4.15 mg N kg -1  d -1 , which were significantly lower (p < 0.05) than those in the remaining neutral and alkaline soils ranging from 6.94 to 14.43 mg N kg -1  d -1 . Generally, soil pH was positively correlated (p < 0.001) with gross autotrophic nitrification rate and cumulative N 2 O emissions, indicating that soil pH was an important factor regulating autotrophic nitrification and N 2 O emissions. There was also a significant positive correlation between the gross autotrophic nitrification rate and cumulative N 2 O emissions, highlighting the importance of this process for producing N 2 O emissions in these agricultural soils under aerobic conditions. Gross NH 4 + immobilization rates were very low in most soils except for the Jinjing soil with the lowest pH. In conclusion, the gross autotrophic nitrification rates and related N 2 O emissions were controlled by soil pH irrespectively of the soil's origin in these agricultural soils., (Copyright © 2019 Elsevier B.V. All rights reserved.)

Rising atmospheric CO 2 concentrations are expected to increase nitrous oxide (N 2 O) emissions from soils via changes in microbial nitrogen (N) transformations. Several studies have shown that N 2 O emission increases under elevated atmospheric CO 2 (eCO 2 ), but the underlying processes are not yet fully understood. Here, we present results showing changes in soil N transformation dynamics from the Giessen Free Air CO 2 Enrichment (GiFACE): a permanent grassland that has been exposed to eCO 2 , +20% relative to ambient concentrations (aCO 2 ), for 15 years. We applied in the field an ammonium-nitrate fertilizer solution, in which either ammonium ( NH 4 + ) or nitrate ( NO 3 - ) was labelled with 15 N. The simultaneous gross N transformation rates were analysed with a 15 N tracing model and a solver method. The results confirmed that after 15 years of eCO 2 the N 2 O emissions under eCO 2 were still more than twofold higher than under aCO 2 . The tracing model results indicated that plant uptake of NH 4 + did not differ between treatments, but uptake of NO 3 - was significantly reduced under eCO 2 . However, the NH 4 + and NO 3 - availability increased slightly under eCO 2 . The N 2 O isotopic signature indicated that under eCO 2 the sources of the additional emissions, 8,407 μg N 2 O-N/m 2 during the first 58 days after labelling, were associated with NO 3 - reduction (+2.0%), NH 4 + oxidation (+11.1%) and organic N oxidation (+86.9%). We presume that increased plant growth and root exudation under eCO 2 provided an additional source of bioavailable supply of energy that triggered as a priming effect the stimulation of microbial soil organic matter (SOM) mineralization and fostered the activity of the bacterial nitrite reductase. The resulting increase in incomplete denitrification and therefore an increased N 2 O:N 2 emission ratio, explains the doubling of N 2 O emissions. If this occurs over a wide area of grasslands in the future, this positive feedback reaction may significantly accelerate climate change., (© 2018 John Wiley & Sons Ltd.)

Nitrous oxide (N2O) is a potent greenhouse gas and the dominant anthropogenic stratospheric ozone-depleting emission. The tropospheric concentration of N2O continues to increase, with animal production systems constituting the largest anthropogenic source. Stable isotopes of nitrogen (N) provide tools for constraining emission sources and, following the temporal dynamics of N2O, providing additional insight and unequivocal proof of N2O source, production pathways and consumption. The potential for using stable isotopes of N is underutilised. The intent of this article is to provide an overview of what these tools are and demonstrate where and how these tools could be applied to advance the mitigation of N2O emissions from animal production systems. Nitrogen inputs and outputs are dominated by fertiliser and excreta, respectively, both of which are substrates for N2O production. These substrates can be labelled with 15N to enable the substrate-N to be traced and linked to N2O emissions. Thus, the effects of changes to animal production systems to reduce feed-N wastage by animals and fertiliser wastage, aimed at N2O mitigation and/or improved animal or economic performance, can be traced. Further 15N-tracer studies are required to fully understand the dynamics and N2O fluxes associated with excreta, and the biological contribution to these fluxes. These data are also essential for the new generation of 15N models. Recent technique developments in isotopomer science along with stable isotope probing using multiple isotopes also offer exciting capability for addressing the N2O mitigation quest.

With a growing world population and global warming, we are challenged to increase food production while reducing greenhouse gas (GHG) emissions. We studied the effects of biochar (BC) and hydrochar (HC) produced via pyrolysis or hydrothermal carbonization, respectively, on GHG fluxes in three laboratory incubation studies. In the first experiment, ryegrass was grown in sandy loam mixed with equal amounts of a nitrogen-rich peanut hull BC, compost, BC+compost, double compost, or no addition (control); wetting-drying cycles and N fertilization were applied. Biochar with or without compost significantly reduced NO emissions and did not change the CH uptake, whereas ryegrass yield was significantly increased. In the second experiment, 0% (control) or 8% (w/w) of BC (peanut hull, maize, wood chip, or charcoal) or 8% HC (beet chips or bark) was mixed into a soil and incubated at 65% water-holding capacity (WHC) for 140 d. Treatments included simulated plowing and N fertilization. All BCs reduced NO emissions by ∼60%. Hydrochars reduced NO emissions only initially but significantly increased them after N fertilization to 302% (HC-beet) and 155% (HC-bark) of the control emissions, respectively. Large HC-associated CO emissions suggested that microbial activity was stimulated and that HC was less stable than BC. In the third experiment, nutrient-rich peanut hull BC addition and incubation over 1.5 yr at high WHCs did not promote NO emissions. However, NO emissions were significantly increased with BC after NHNO addition. In conclusion, BC reduced NO emissions and improved the GHG-to-yield ratio under field-relevant conditions. However, the risk of increased NO emissions with HC addition must be carefully evaluated., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

Biochar is the product of pyrolysis produced from feedstock of biological origin. Due to its aromatic structure and long residence time, biochar may enable long-term carbon sequestration. At the same time, biochar has the potential to improve soil fertility and reduce greenhouse gas (GHG) emissions from soils. However, the effect of biochar application on GHG fluxes from soil must be investigated before recommendations for field-scale biochar application can be made. A laboratory experiment was designed to measure carbon dioxide (CO) and nitrous oxide (NO) emissions from two Irish soils with the addition of two different biochars, along with endogeic (soil-feeding) earthworms and ammonium sulfate, to assist in the overall evaluation of biochar as a GHG-mitigation tool. A significant reduction in NO emissions was observed from both low and high organic matter soils when biochars were applied at rates of 4% (w/w). Earthworms significantly increased NO fluxes in low and high organic matter soils more than 12.6-fold and 7.8-fold, respectively. The large increase in soil NO emissions in the presence of earthworms was significantly reduced by the addition of both biochars. biochar reduced the large earthworm emissions by 91 and 95% in the low organic matter soil and by 56 and 61% in the high organic matter soil (with and without N fertilization), respectively. With peanut hull biochar, the earthworm emissions reduction was 80 and 70% in the low organic matter soil, and only 20 and 10% in the high organic matter soil (with and without N fertilization), respectively. In high organic matter soil, both biochars reduced CO efflux in the absence of earthworms. However, soil CO efflux increased when peanut hull biochar was applied in the presence of earthworms. This study demonstrated that biochar can potentially reduce earthworm-enhanced soil NO and CO emissions. Hence, biochar application combined with endogeic earthworm activity did not reveal unknown risks for GHG emissions at the pot scale, but field-scale experiments are required to confirm this., (Copyright © by the American Society of Agronomy, Crop Science Society of America, and Soil Science Society of America, Inc.)

The influence of soil phosphorous (P) content on the N-cycling communities and subsequent effects on N2O emissions remains unclear. Two laboratory incubation experiments were conducted on soils collected from a long-term (est. 1995) P-addition field trial sampled in summer 2018 and winter 2019. Incubations were treated with a typical field amendment rate of N as well as a C-amendment to stimulate microbial activity. Throughout both incubations, soil subsamples were collected prior to fertiliser amendment and then throughout the incubations, to quantify the abundance of bacteria (16S rRNA), fungi (ITS) and Thaumarcheota (16S rRNA) as well as functional guilds of genes involved in nitrification (bacterial and archaeal amoA, and comammox) and denitrification (nirS, nirK, nosZ clade I and II) using quantitative PCR (qPCR). We also evaluated the correlations between each gene abundance and the associated N2O emissions depending on P-treatments. Our results show that long-term P-application influenced N-cycling genes abundance differently. Except for comammox, overall nitrifiers' genes were most abundant in low P while the opposite trend was found for denitrifiers' genes. C and N-amendments strongly influenced the abundance of most genes with changes observed as soon as 24 h after application. ITS was the only gene correlated to N2O emissions in the low P-soils while microbes were mostly correlated to emissions in high P, suggesting possible changes in the organisms involved in N2O production depending on soil P-content. This study highlights the importance of long-term P addition on shaping the microbial community function which in turn stimulates a direct impact on the subsequent N emissions. [ABSTRACT FROM AUTHOR]

Nutrient-poor organic soils under maritime grassland are often located in remote wet locations in the landscape. Leaving these soils without drainage maintenance often raise the water table but continuous management (grazing) means they could remain a source of carbon dioxide (CO 2 ) while also turning into a small source of methane (CH 4 ). Due to geographical and socio-economic reasons, removing these sites from agricultural production may be an option to mitigate greenhouse gas (GHG) emissions. To test this hypothesis we measured GHG fluxes over a four year period, at a drained and a rewetted organic soil under grassland, which were both grazed for the first two years and not grazed for the following two years. Statistical response functions estimated for gross primary production (GPP) and ecosystem respiration ( R eco ) were used to reconstruct annual CO 2 –C balances using site-specific models driven by soil temperature, solar radiation, soil water table (WT) and leaf area index (LAI). Annually, soil CO 2 emissions were comparable when grazed, although the rewetted site had a lower net ecosystem carbon balance (NECB) despite displaying higher CH 4 emissions. Both sites have lower CO 2 emissions than typical drained organic soils due to management practices: extensive grazing, no fertilisation and mean annual water tables above −25 cm. When grazing stopped, GPP and R eco increased dramatically driven by vigorous growth of vegetation at both sites. The shallow drained site remained a source of CO 2 and small source of CH 4 while the rewetted site became either neutral or a small sink of CO 2 with decreased CH 4 emissions compared to the grazing period. Nitrous oxide (N 2 O) emissions were negligible at either site. Removing grazing significantly reduced the NECB at both sites but in terms of global warming potential (GWP), the greatest GHG mitigation was in the rewetted site which exerted a cooling effect in the second year after the management shift. [ABSTRACT FROM AUTHOR]

A field study was conducted to determine the effect of the nitrification inhibitor dicyandiamide (DCD) on N2O and N2 emissions after cattle slurry (CS) application in the presence of nitrate (NO3) fertiliser on seven different occasions (between March 2009 and March 2011). N2O emissions from CS in the presence of NO3 fertiliser were very high (0.4-8.7% of applied N) over a 20-day period, under mild moist conditions. Emissions were significantly larger from the CS treatment compared to an NH4+-N source, supplying the same rate of N as in the slurry. This study supports the view that organic fertilisers should not be applied at the same time as nitrate-based fertilisers, as significant increases in N2O emissions occur. The average N2O mole fraction (N2O/(N2O+N2)) over all seven application dates was 0.34 for CSNO3 compared to 0.24 for the NH4ClNO3 treatment, indicating the dominance of N2 emissions. The rate of nitrification in CSNO3 was slower than in NH4ClNO3, and DCD was found to be an effective nitrification inhibitor in both treatments. However, as N2O emissions were found to be predominantly associated with the NO3 pool, the effect of DCD in lowering N2O emissions is limited in the presence of a NO3 fertiliser. To obtain the maximum cost-benefit of DCD in lowering N2O emissions, under mild moist conditions, it should not be applied to a nitrate containing fertiliser (e.g. ammonium nitrate or calcium ammonium nitrate), and therefore the application of DCD should be restricted to ammonium-based organic or synthetic fertilisers. [ABSTRACT FROM AUTHOR]

Methane (CH) emissions following surface application of liquid digestate were measured on agricultural grassland. The total extent of emissions was estimated by curve fitting and integration. The temporal pattern of the CH efflux was well described by fitting double-phase decay curves ( $$ J(T) = B \times {\text{EXP}}( - iT) + C \times {\text{EXP}}( - jT) $$). Total emissions were found to be small in all cases (7.3-11.5 mg CH L). From a greenhouse gas perspective, this level of CH emissions represents only a few per cent of the global warming potential of the nitrous oxide emissions which may occur following application of the digestate. [ABSTRACT FROM AUTHOR]

The aim of the present study was to separate and quantify process-specific gross nitrite (NO2−) production in a permanent grassland soil and separate the observed NO2− concentration into process-specific sub-pools. We re-analysed data from a laboratory experiment where either the nitrate and/or ammonium ions were labelled with 15N. The simultaneously occurring N transformations were quantified with a 15N tracing tool in combination with a Monte Carlo sampling technique which has been extended by a NO2− sub-model. Three pathways of NO2− production were identified, that is autotrophic nitrification, denitrification and the oxidation of organic N. The full model contained nine pools and 14 N transformations. This is the first report where such a complex 15N tracing model has been used and where all parameters have been optimized simultaneously. Our analysis shows that on average 52.4% of the total soil NO2− concentration was directly derived from oxidation of organic N. Nitrification and denitrification contributed on average 18.1 and 29.5%, respectively, to the total NO2− pool. However, more than 99% of the gross NO2− production was related to the NH4+ oxidation, which was rapidly further oxidized to NO3−. Our re-analysis using a Monte Carlo sampling technique resulted in parameter profiles that differed from the original analysis. As the new technique is able to optimize all parameters in one optimization run we regard this technique as superior to the previous one. A process-based understanding of NO2− dynamics in soils has important implications for the understanding of the production of the greenhouse gas nitrous oxide (N2O), which is tightly linked to NO2− turnover. [ABSTRACT FROM AUTHOR]

Denitrifying enzyme activity (DEA) and flux rates of nitrous oxide (N2O) and dinitrogen (N2) were studied in DEA assays on soils treated with 3,4-dimethylpyrazole phosphate (DMPP). Nitrous oxide and N2 fluxes were quantified by 15N gas-flux method with no additional enzymatic inhibitors, thus, overcoming problems associated with the use of chloramphenicol and acetylene. The nitrification inhibitor DMPP did not affect DEA or the measured gas emissions even when applied in concentrations 14 times higher than the recommended concentration. [Copyright &y& Elsevier]

• Strip tillage with residue retention increases N 2 O emission in wheat. • N fertilizer application rates linearly increases N 2 O emissions. • N 2 O emission factor in strip tillage is higher than the IPCC default value. • Soil larger aggregates are more conducive to produce and transport N 2 O. • Medium-term strip tillage with residue retention reduces N requirement for wheat. Nitrous oxide (N 2 O) emissions were measured in irrigated wheat (Triticum aestivum) in an annual wheat- mungbean (Vigna radiata)-rice (Oryza sativa L) rotation that had been running for seven consecutive years. Effect of two soil disturbance levels (strip vs. conventional tillage; ST vs. CT both with 30 % residue retention) and three nitrogen (N) fertilizer rates (60, 100 and 140 % of the recommended N fertilizer dose, RD; called hereafter 60RD, 100RD and 140RD, respectively) were assessed. Mean N 2 O fluxes were about 110 % higher in ST than in CT. The rate of N fertilizer application influenced the mean and cumulative N 2 O fluxes with significantly higher fluxes in ST than in CT. Based on the respective maximum grain yields (CT: 140RD, 3.52 t ha−1; ST: 60RD, 3.19 t ha−1) yield-scaled N 2 O emissions were higher in ST than those in CT. However, tillage vs. N rate interactions showed both the highest and lowest yield-scaled N 2 O fluxes in ST with 140RD and 60RD, respectively. Soil microbial biomass carbon (MBC), organic carbon (SOC), total N (TN), nitrate (NO 3 - -N), aggregate mean weight diameter (MWD) and larger aggregate size classes (2.0‒0.85 and >2.0 mm) were significantly higher in ST and positively correlated with N 2 O fluxes. Our results highlight that, despite increased N 2 O emissions, ST with residue can trade-off emissions to improve soil macro aggregation, C sequestration and retention of N and crop yield with the lower N fertilizer and other energy inputs. Reduction of the recommended N fertilization rate could be considered if ST is adopted. [ABSTRACT FROM AUTHOR]

• Intensification scenarios increased absolute N emissions compared to baseline. • Intensification scenarios may result in reduced N emission intensity. • Mitigation methods ameliorate increased emissions associated with intensification. • Mitigation methods may not offset absolute increase in N loss due to intensification. Increased global demand for dairy produce and the abolition of EU milk quotas have resulted in expansion in dairy production across Europe and particularly in Ireland. Simultaneously, there is increasing pressure to reduce the impact of nitrogen (N) losses to air and groundwater on the environment. In order to develop grassland management strategies for grazing systems that meet environmental targets and are economically sustainable, it is imperative that individual mitigation measures for N efficiency are assessed at farm system level. To this end, we developed an excel-based N flow model simulating an Irish grass-based dairy farm, to evaluate the effect of farm management on N efficiency, N losses, production and economic performance. The model was applied to assess the effect of different strategies to achieve the increased production goals on N utilization, N loss pathways and economic performance at farm level. The three strategies investigated included increased milk production through increased grass production, through increased concentrate feeding and by applying a high profit grass-based system. Additionally, three mitigation measures; low ammonia emission slurry application, the use of urease and nitrification inhibitors and the combination of both were applied to the three strategies. Absolute N emissions were higher for all intensification scenarios (up to 124 kg N ha−1) compared to the baseline (80 kg N ha−1) due to increased animal numbers and higher feed and/or fertiliser inputs. However, some intensification strategies showed the potential to reduce the emissions per ton milk produced for some of the N-loss pathways. The model showed that the assessed mitigation measures can play an important role in ameliorating the increased emissions associated with intensification, but may not be adequate to entirely offset absolute increases. Further improvements in farm N use efficiency and alternatives to mineral fertilisers will be required to decouple production from reactive N emissions. [ABSTRACT FROM AUTHOR]

This research investigated the effect of long-term phosphorus (P) addition relative to carbon (C) availability on nitrous oxide (N 2 O) emissions from an ungrazed grassland soil via two incubation experiments. No significant effect of soil P on N 2 O was found under C-limited conditions, while under added-C, cumulative N 2 O was significantly higher from low-P (p < 0.05) rather than high-P soils. CO 2 was not significantly different between P-levels. This highlights the influence of soil P on N 2 O emissions under non C-limiting conditions. This is one of the first studies demonstrating available-C moderating the effect of P on N 2 O emissions from temperate grassland soils. • Phosphorus effects on N 2 O emissions from soils are poorly understood. • Carbon limitation masks effects of phosphorus on nitrous oxide emissions. • When soil not C-limited, N 2 O reduced at higher P concentrations. • Manipulation of C:N:P ratio can reduce N 2 O emissions from grassland. [ABSTRACT FROM AUTHOR]