Search

According to the available guidelines, good practices for calculating nitrous oxide (N 2 O) emission factors (EFs) for livestock excreta and manure application include that sampling duration should be of at least one year after the nitrogen (N) application or deposition. However, the available experimental data suggest that in many cases most emissions are concentrated in the first months following N application. Therefore resources could be better deployed by measuring more intensively during a shorter period. This study aimed to assess the contribution of the N 2 O flux in the period directly after N application to the annual net emission. We used a database of 100 year-long plot experiments from different excreted-N sources (dung, urine, farmyard manure and slurry) used to derive EFs for the UK and Ireland. We explored different shorter potential measurement periods that could be used as proxies for cumulative annual emissions. The analysis showed that the majority of emissions occur in the first months after application, especially in experiments that i) had urine as the N source, ii) had spring N application, iii) were conducted on fine-textured soils, or iv) showed high annual emissions magnitude. Experiments that showed a smaller percentage of emissions in the first months also had a low magnitude of annual net emissions (below 370 gN 2 O-N ha -1 year -1 ), so the impact of measuring during a shorter period would not greatly influence the calculated EF. Accurate EF estimations were obtained by measuring for at least 60 days for urine (underestimation: 7.1%), 120 days for dung and slurry (4.7 and 5.1%) and 180 days for FYM (1.4%). At least in temperate climates, these results are promising in terms of being able to estimate annual N 2 O fluxes accurately by collecting data for less than 12 months, with significant resource-saving when conducting experiments towards developing country-specific EFs., Competing Interests: Declaration of competing interest The authors declare that they have no known competing financial interests or personal relationships that could have appeared to influence the work reported in this paper., (Copyright © 2022 Elsevier Ltd. All rights reserved.)

Grazed grassland systems are an important component of the global carbon cycle and also influence global climate change through their emissions of nitrous oxide and methane. However, there are huge uncertainties and challenges in the development and parameterisation of process-based models for grazed grassland systems because of the wide diversity of vegetation and impacts of grazing animals. A process-based biogeochemistry model, DeNitrification-DeComposition (DNDC), has been modified to describe N(2)O emissions for the UK from regional conditions. This paper reports a new development of UK-DNDC in which the animal grazing practices were modified to track their contributions to the soil nitrogen (N) biogeochemistry. The new version of UK-DNDC was tested against datasets of N(2)O fluxes measured at three contrasting field sites. The results showed that the responses of the model to changes in grazing parameters were generally in agreement with observations, showing that N(2)O emissions increased as the grazing intensity increased., (Copyright © 2011 Elsevier Ltd. All rights reserved.)

Background: Brachiaria humidicola (Bh) has the ability to produce biological nitrification inhibitors (NIs) and release NIs from the root to the soil. Aims: To compare the effects of growing Bh with Brachiaria ruziziensis (Br, which is not able to produce NIs) on soil nitrogen (N) dynamics, N gases and carbon dioxide (CO2) emissions and nitrifiers and denitrifiers following sheep urine application, a laboratory incubation was conducted in a He/O2 continuous flow denitrification system (DENIS). This incubation was conducted in the absence of light. Hence the measured effects of Bh and Br on N cycling were the residual effect of biological NIs released into the soil prior to the incubation and released via root death. Methods: The treatments were: (1) Bh with water application (Bh + W); (2) Bh with sheep urine (Bh + U); (3) Br with water application (Br + W); (4) Br with sheep urine (Br + U). Results: Results showed that soil NO3– concentration increased significantly in the soil with sheep urine application after the incubation. Soil nitrous oxide (N2O) and nitric oxide (NO) emissions increased immediately after the sheep urine application and peaked twice during the incubation. Cumulative emissions for the first peak were significantly lower from the Bh + U treatment (0.054 kg N ha–1) compared with the Br + U treatment (0.111 kg N ha–1), but no significant differences were observed in the total cumulative N2O and NO emissions between the Bh + U and Br + U treatment at the end of the incubation. Sheep urine addition did not affect the AOA, nirS and nosZ gene copies, but significantly increased the AOB gene copies after the incubation. Conclusions: We conclude that the residual effect of Bh to mitigate N2O emissions in a highly nitrifying soil is short‐lived. [ABSTRACT FROM AUTHOR]

Biological nitrification inhibition is a plant‐mediated rhizosphere process where natural nitrification inhibitors can be produced and released by roots to suppress nitrifier activity in soil. Nitrification is one of the critical soil processes in the nitrogen (N) cycle, but unrestricted and rapid nitrification in agricultural systems can result in major losses of N from the plant–soil system (i.e., by NO3− leaching and gaseous N emissions). In this study, we explored the potential efficacy of biological nitrification inhibitors (linoleic acid [LA] and linolenic acid [LN]) and a proven efficient synthetic (dicyandiamide [DCD]) nitrification inhibitor on N dynamics, nitrous oxide (N2O) and carbon dioxide (CO2) emissions in a highly nitrifying soil. 14C‐labelled LA, LN and DCD mineralization was determined in a parallel experiment to explore the fate of inhibitors after application. We found that LA and LN had no effect on soil NH4+ concentrations, but significantly decreased NO3− concentrations. Soil that received DCD had lower NO3− and higher NH4+ concentrations than the control (soil without nitrification inhibitors). LA and LN increased the cumulative N2O and CO2 emissions when they were applied at high concentrations (635 or 1,270 mg kg−1 dry soil). LA and LN had a much greater mineralization rate than that of DCD: 47–56%, 37–61% and 2.7–5.5%, respectively, after 38 days incubation. We conclude that in contrast to the direct inhibition of nitrification caused by DCD, addition of LA and LN may cause apparent nitrification inhibition by promoting microbial immobilization of soil NH4+ and/or NO3−. Future studies on nitrification inhibitors need to clearly differentiate between the direct and indirect effects that result from addition of these compounds to soil. Highlights: The efficacy and stability of nitrification inhibitors in a highly nitrifying soil were explored.This study supports efforts to mitigate N losses and improve nitrogen use efficiency of inputs.Addition of LA, LN and DCD can decrease NO3− concentration, but their modes of action may be different.The apparent effect of LA and LN on soil NO3− concentration could be indirect. [ABSTRACT FROM AUTHOR]

The application of organic materials to soil can recycle nutrients and increase organic matter in agricultural lands. Digestate can be used as a nutrient source for crop production but it has also been shown to stimulate greenhouse gas (GHG) emissions from amended soils. While edaphic factors, such as soil texture and pH, have been shown to be strong determinants of soil GHG fluxes, the impact of the legacy of previous management practices is less well understood. Here we aim to investigate the impact of such legacy effects and to contrast them against soil properties to identify the key determinants of soil GHG fluxes following digestate application. Soil from an already established field experiment was used to set up a pot experiment, to evaluate N2O, CH4 and CO2 fluxes from cattle‐slurry‐digestate amended soils. The soil had been treated with farmyard manure, green manure or synthetic N‐fertilizer, 18 months before the pot experiment was set up. Following homogenization and a preincubation stage, digestate was added at a concentration of 250 kg total N/ha eq. Soil GHG fluxes were then sampled over a 64 day period. The digestate stimulated emissions of the three GHGs compared to controls. The legacy of previous soil management was found to be a key determinant of CO2 and N2O flux while edaphic variables did not have a significant effect across the range of variables included in this experiment. Conversely, edaphic variables, in particular texture, were the main determinant of CH4 flux from soil following digestate application. Results demonstrate that edaphic factors and current soil management regime alone are not effective predictors of soil GHG flux response following digestate application. Knowledge of the site management in terms of organic amendments is required to make robust predictions of the likely soil GHG flux response following digestate application to soil. [ABSTRACT FROM AUTHOR]

Drying and rewetting cycles are known to be important for the dynamics of carbon (C), phosphorus (P), and nitrogen (N) in soils. This study reports the short‐term responses of these nutrients to consecutive drying and rewetting cycles and how varying soil moisture content affects microbial biomass C and P (MBC and MBP), as well as associated carbon dioxide (CO2) and nitrous oxide (N2O) emissions. The soil was incubated for 14 d during which two successive drying–rewetting episodes were imposed on the soils. Soils subjected to drying (DRW) were rewetted on the seventh day of each drying period to return them to 60% water holding capacity, whilst continually moist samples (M), with soil maintained at 60% water holding capacity, were used as control samples. During the first seven days, the DRW samples showed significant increases in extractable ammonium, total oxidized nitrogen, and bicarbonate extractable P concentrations. Rewetting after the first drying event produced significant increases only in CO2 flux (55.4 µg C g−1 d−1). The MBC and MBP concentrations fluctuated throughout the incubation in both treatments and only the second drying–rewetting event resulted in a significantly MBC decrease (416.2 and 366.8 mg kg−1 in M and DRW soils, respectively). The two drying–rewetting events impacted the microbial biomass, but distinguishing the different impacts of microbial versus physical impacts of the perturbation is difficult. However, this study, having a combined approach (C, N, and P), indicates the importance of understanding how soils will react to changing patterns of drying–rewetting under future climate change. [ABSTRACT FROM AUTHOR]

In grassland systems, cattle and sheep urine patches are recognized as nitrous oxide (N2O) emission hot spots due to the high urinary nitrogen (N) concentrations. Hippuric acid (HA) is one of the constituents of ruminant urine that has been reported as a natural inhibitor of soil N2O emissions. The aim of this study was to examine the potential for elevated ruminant urine HA concentrations to reduce N2O emissions, in situ, on an acidic heavy clay soil under poorly drained conditions (WFPS > 85%). A randomized complete block design experiment with three replications and four treatments was conducted using the closed‐static‐flux chamber methodology. The four treatments were applied inside the chambers: control with no artificial urine application (C), control artificial urine (U), and enriched artificial urine with two rates of HA (55.8 and 90 mM, U+HA1, U+HA2). Soil inorganic‐N, soil dissolved organic carbon (DOC), soil pH as well as N2O and methane (CH4) fluxes were monitored over a 79‐d period. Although N2O emissions were not affected by the HA enriched urine treatments, U+HA2 positively affected the retention of N as NH4+ until day 3, when the soil pH dropped to values < 5. Subsequently, as a consequence of rainfall events and soil acidification, it is likely that leaching or sorption onto clay reduced the efficacy of HA, masking any treatment differential effect on N2O emissions. Moreover, CH4 fluxes as well as DOC results reflected the soil anaerobic conditions which did not favour nitrification processes. Further research is needed to determine the fate of HA into the soil which might clarify the lack of an in situ effect of this compound. [ABSTRACT FROM AUTHOR]

Unravelling the impacts of climate change on agriculture becomes increasingly important, as the rates and magnitude of its effects are accelerating. Current estimates of the consequences of climate change on nitrous oxide (N 2 O) emissions remain largely uncertain; there is a need for more consistent and comprehensive assessments of this impact. In this study we explored the implications of two IPCC climate change projections (high and medium emissions scenarios) on N 2 O emissions from South West England grasslands for the time slices of a baseline, the 2020s, the 2050s and the 2080s, employing a process-based model (SPACSYS). The model was initially calibrated and validated using datasets collected from three grassland sites of the region. Statistical analysis showed that simulated results had no significant total error or bias compared to measured values. We found a consistent increase in N 2 O emissions of up to 94% under future climate change scenarios compared to those under the baseline, and warming rather than precipitation variability was the overriding factor controlling the N 2 O rise. Modelling fertilizer forms showed that replacing ammonium-nitrate fertilizers with urea or slurry significantly reduced N 2 O emissions (c. 30%). Our study highlights the urgent necessity to adopt viable N 2 O mitigation measures now in order to avoid higher emissions in the future. [ABSTRACT FROM AUTHOR]

Abstract: A detailed inventory framework was developed to estimate nitrous oxide (N2O) and methane (CH4) emissions from UK agriculture using the IPCC approach. The inventory framework model was illustrated by combining relevant emission factors with agricultural census data for England, Wales, Scotland and Northern Ireland for the year 2000 to derive country-specific emission estimates which were summed to derive the UK total. The framework enables simple assessment to be made of the impact on national emissions of using different emission factors (EFs) (e.g. site- or local-specific compared with IPCC default factors). The framework was used to calculate the average annual emissions of nitrous oxide (N2O) and methane (CH4) for specific livestock and crops, and amounts lost through volatilisation, leaching and runoff for each country in the UK. The framework provides a simple, realistic and transparent approach to estimating national emissions and can easily be updated. [Copyright &y& Elsevier]

This study argues that several metrics are necessary to build up a picture of yield gain and nitrogen losses for ryegrass sheep pastures. Metrics of resource use efficiency, nitrous oxide emission factor, leached and emitted nitrogen per unit product are used to encompass yield gain and losses relating to nitrogen. These metrics are calculated from field system simulations using the DAYCENT model, validated from field sensor measurements and observations relating to crop yield, fertilizer applied, ammonium in soil and nitrate in soil and water, nitrous oxide and soil moisture. Three ryegrass pastures with traditional management for sheep grazing and silage are studied. As expected, the metrics between long-term ryegrass swards in this study are not very dissimilar. Slight differences between simulations of different field systems likely result from varying soil bulk density, as revealed by a sensitivity analysis applied to DAYCENT. The field with the highest resource use efficiency was also the field with the lowest leached inorganic nitrogen per unit product, and vice versa. Field system simulation using climate projections indicates an increase in nitrogen loss to water and air, with a corresponding increase in biomass. If we simulate both nitrogen loss by leaching and by gaseous emission, we obtain a fuller picture. Under climate projections, the field with the lowest determined nitrous oxide emissions factor, had a relatively high leached nitrogen per product amongst the three fields. When management differences were investigated, the amount of nitrous oxide per unit biomass was found to be significantly higher for an annual management of grazing only, than a silage harvest plus grazing, likely relating to the increased period of livestock on pasture. This work emphasizes how several metrics validated by auto-sampled data provide a measure of nitrogen loss, efficiency and best management practise. Unlabelled Image • Provides yield-nitrogen metrics for ryegrass sheep pastures • Combination of climate, sensor and sampling data applied to agri-system modelling • Highest resource use efficiency coincides with lowest leaching per unit product. • N 2 O per unit biomass significantly lower for silage & grazing than grazing only. • Several related metrics reveal info about the system, hidden by using one metric. [ABSTRACT FROM AUTHOR]

Agricultural soils are a major source of nitric oxide (NO) and nitrous oxide (N 2 O), which are produced and consumed by biotic and abiotic soil processes. The dominant sources of NO and N 2 O are microbial nitrification and denitrification. While N 2 O emissions have been attributed to both processes, depending on the environmental conditions such as substrate availability, pH and water filled pore space (WFPS), NO emissions are thought to predominantly derive from nitrification. Although attributing gaseous emissions to specific processes is still difficult, recent findings challenge the latter of those assumptions. Using the gas-flow-soil-core method, i.e soil cores incubated under a He/O 2 atmosphere at constant surface gas flow, combined with 15 N labelled isotopic techniques, the present study investigated the role of denitrification on NO, N 2 O and N 2 emissions in a UK grassland soil under high soil moisture and an aerobic headspace atmosphere. With the application of KNO3 and glucose to support denitrification, denitrification was the source of N loss of between 0.61 and 0.67% of the added N via NO emissions, 1.60–1.68% via N 2 O and 0.03–0.05% via N 2 emissions. Overall, our study showed that denitrification has been overlooked as a source of NO emissions. [ABSTRACT FROM AUTHOR]

China accounts for a third of global nitrogen fertilizer consumption. Under an International Panel on Climate Change (IPCC) Tier 2 assessment, emission factors (EFs) are developed for the major crop types using country-specific data. IPCC advises a separate calculation for the direct nitrous oxide (N 2 O) emissions of rice cultivation from that of cropland and the consideration of the water regime used for irrigation. In this paper we combine these requirements in two independent analyses, using different data quality acceptance thresholds, to determine the influential parameters on emissions with which to disaggregate and create N 2 O EFs. Across China, the N 2 O EF for lowland horticulture was slightly higher (between 0.74% and 1.26% of fertilizer applied) than that for upland crops (values ranging between 0.40% and 1.54%), and significantly higher than for rice (values ranging between 0.29% and 0.66% on temporarily drained soils, and between 0.15% and 0.37% on un-drained soils). Higher EFs for rice were associated with longer periods of drained soil and the use of compound fertilizer; lower emissions were associated with the use of urea or acid soils. Higher EFs for upland crops were associated with clay soil, compound fertilizer or maize crops; lower EFs were associated with sandy soil and the use of urea. Variation in emissions for lowland vegetable crops was closely associated with crop type. The two independent analyses in this study produced consistent disaggregated N 2 O EFs for rice and mixed crops, showing that the use of influential cropping parameters can produce robust EFs for China. [ABSTRACT FROM AUTHOR]

Bacteria and fungi have been shown to produce nitrous oxide (N 2 O) during denitrification, but their contribution after nitrate (NO 3 −) application to soil is not clearly established. In a microcosm experiment, the relative contribution of bacteria and fungi to N 2 O and carbon dioxide (CO 2) production by four contrasting soils representing different land uses after KNO 3 addition was studied. The soils were daily wetted to 80% water-filled pore space (WFPS) and kept under greenhouse conditions for 10 days. The fungicide cycloheximide and the bactericide streptomycin were used to determine the possible microbial origin of the N 2 O and CO 2 emissions. Non-target effects of the antibiotics on the emission of N 2 O and CO 2 were evaluated using the inhibitor additivity ratio (IAR). The abundance of the bacterial and fungal communities was estimated by quantitative PCR (qPCR) of the bacterial 16S rRNA gene and the fungal internal transcribed spacer (ITS) region, respectively. The gene copy number of bacterial denitrifiers was calculated after quantification of the nirK , nirS , norB , nosZ I and nosZ II genes. After 10 d, regardless of the soil type, the cumulative N 2 O emission from the soils treated with cycloheximide or streptomycin were similar. In all the four soils, N 2 O fluxes were greater (on average 1.8 ± 0.3 times) in soils amended with the fungicide than with the bactericide during incubation for the first 48–96 h. Greater N 2 O emissions (on average 1.7 ± 0.2 times) were detected in soils where bacteria were inhibited in comparison to those treated with the fungicide from 96 to 240 h. On average, 68.5% of the total CO 2 emitted during the 10-d incubation period was produced in soils treated with the fungicide and 31.5% in those treated with the bactericide. The greater contribution of bacteria to the production of N 2 O than fungi during the first 48–96 h was possibly due to a faster used of nitrate. Variations in the abundance of bacterial 16S rRNA genes, the ITS region, and the nirK , nirS , norB and nosZ I bacterial denitrification genes indicated that the antibiotics used to prevent the growth of bacteria and fungi were effective during incubation. These results suggest that both bacteria and fungi should be considered when designing and applying greenhouse gas mitigation strategies in soils and that their relative contribution to produce N 2 O and CO 2 can vary with time and nitrate availability. • In a 10-d microcosm experiment, bacteria dominated fungi for N 2 O emissions during the first 3 d after N-fertilisation. • Fungi dominated bacteria for N 2 O emissions during the remaining 7-d of treatment. • After 10-d, bacteria and fungi similarly contributed to N 2 O production in the four soils analysed. • Bacteria were greater CO 2 producers than fungi after the 10-d treatment in the four soils analysed. • Bacteria and fungi should be considered when designing greenhouse gas mitigation strategies. [ABSTRACT FROM AUTHOR]

• Heterotrophic nitrification is an important source of N 2 O at low WFPS. • Similar contributions of nitrification, heterotrophic nitrification and denitrification occurred at medium WFPS level. • High N 2 O emissions result via nitrification coupled denitrification at medium & high WFPS. • Abiotic factors need to be considered as well as biotic factors to understand the cause of emissions. To identify the production and consumption pathways and temporal dynamics of N 2 O emitted from soil, this study uses 15N-labelled substrate-N to quantify the underlying gross N transformation rates using the Ntrace analysis tool and link them to N-emissions. In three experiments twelve soil cores each were incubated in a lab incubation system to measure gaseous emissions, while parallel incubations under the same conditions were set up for destructive soil sampling at 7 time points. Using the triple labelling technique (applying NH 4 NO 3 with either the NH 4 +-N or the NO 3 −-N, or both being 15N labelled), this study investigated the effects of 55, 70 and 85% water filled pore space (deemed to promote nitrification, both nitrification and denitrification, and denitrification, respectively) in a clay soil on gaseous N emissions and investigates the source and processes leading to N 2 O emissions. To assess the utilisation of applied NO 3 − vs. nitrified NO 3 − from applied NH 4 +, the 15N tracing tool Ntrace was used to quantify the rates of immobilisation of NO 3 − and NH 4 +, oxidation of NH 4 +, mineralisation of organic N and subsequent nitrification by the analysis of the 15N in the soil. Gross transformation rates were calculated, indicating the relative importance of added NO 3 − and NO 3 − derived from nitrified added NH 4 +. Results show an important contribution of heterotrophic nitrification (organic N oxidation to NO 3 −) which was highest at the 55% water filled pore space (WFPS), decreasing in its contribution to N-transformation processes with increasing WFPS, while nitrification (NH 4 + oxidation to NO 3 −) was contributing the most at 70% WFPS. The contribution of denitrification increased with increasing WFPS, but only became dominant at 85% WFPS. While denitrification still showed to be most important at high and nitrification at lower WFPS, the actual % WFPS values were not as expected and highlight the fact that WFPS is a contributor, but not the sole/most important parameter determining the type of N-transformation processes taking place. [ABSTRACT FROM AUTHOR]