Default Tier Research Articles

Biochar mitigation potential in Norway estimated by IPCC Tier 1 and Tier 2 methods

Biochar is a recalcitrant carbon-rich solid produced by pyrolysis of organic residues, and its application to soil is considered a promising approach to mitigate climate change, as biochar resists decomposition to readily contributes to soil carbon (C) sequestration. The IPCC provides a basis for future national-scale accounting of the changes in soil C stocks following biochar application to cropland soils. The IPCC Tier 1 approach for biochar is based on fixed emission factors to estimate biochar C sequestration. In contrast, the Tier 2 approach allows countries to use local emission factors and climate data to calculate the contribution of biochar to soil C sequestration. Accurate accounting of biochar C sequestration is essential for ensuring the credibility of C offsetting projects, as well as providing incentives for implementing biochar in C credit schemes, calling for comparative analyses of the different biochar Tier approaches. Here we retrieved biochar samples from local producers and measured their H/Corg to estimate the persistence of biochar in Norwegian croplands post application. Various feedstocks were considered, including forest residues, woody wastes, manure, sludge, and straw. For all biochar samples, the 100-year stable C fraction was calculated at ≥ 0.945, thus exceeding the default Tier 1 value (0.8). Biochar sourced from woody- and forestry residues had a Corg content above the default Tier 1 value (0.77). Based on this and data about national feedstock supplies, we compared the theoretical potential of biochar soil C sequestration to mitigate climate change in Norway, using the IPCC Tier 1 and Tier 2 approaches. Biochar C sequestration in soil was calculated at 0.79 Tg CO2-eq yr−1 and 0.92 to 0.96 Tg CO2-eq yr−1, respectively for the Tier 1 and Tier 2 approaches, thus, underlining that the choice of IPCC Tier approach can have a large impact on the estimated mitigation potential of biochar.

Comparison of methodologies for estimating enteric methane emission factors from sheep in smallholder systems in Africa: A case study from Ethiopia

In Ethiopia, enteric methane emissions from sheep contribute around 7 % to the national greenhouse gas (GHG) budget. This study examined the gross energy intake (GEI) and enteric methane emission factors (EFs) of sheep in smallholder systems in North Shewa, Ethiopia, using locally derived data via household surveys. The surveys encompassed two agroecological zones (AEZs) and analyzed various sheep classes across seasons. The study followed the Commonwealth Scientific Industrial Research Organization (CSIRO) Tier 2 methodology, which had previously been used in Kenya, and compared the results with those derived from the 2019 Refinement to the 2006 IPCC Guidelines for National Greenhouse Gas Inventories (IPCC Tier 2) methodology. The EFs from the two Tier 2 methodologies were compared with IPCC default Tier 1 EF. The ranges of GEI and EF estimated for the different sheep classes showed similarity with larger variations observed for IPCC Tier 2 estimates. The estimated GEI for the various sheep classes ranged from 11.1 to 13.8 MJ day−1 (‘CSIRO’ Tier 2) and 10.2–14.7 MJ day−1 (IPCC Tier 2). The estimated EFs ranged from 4.8 to 5.9 kg CH4 animal−1 year−1 (‘CSIRO’ Tier 2) and 4.5–6.5 kg CH4 animal−1 year−1 (IPCC Tier 2). The flock-level EF was computed by aggregating the EFs of the different sheep categories. The flock level EF estimated by the IPCC Tier 2 (6.0 ± 0.1 kg CH4 animal−1 year−1) was significantly higher compared to both the 'CSIRO' Tier 2 and IPCC Tier 1 methods. Based on the findings, we can say that variations in EF values emphasize the significance of taking different Tier 2 approaches into account when evaluating and comparing CH4 emissions estimates in smallholder sheep farming systems. However, there is a need for further investigations to compare the two Tier 2 methodologies against actual intake and emission measurements to decide which methodology is better.

Complete long-term monitoring of greenhouse gas emissions from a full-scale industrial wastewater treatment plant with different cover configurations

The greenhouse gas (GHG) emissions from wastewater treatment plants (WWTPs), consisting mainly of methane (CH4) and nitrous oxide (N2O), have been constantly increasing and become a non-negligible contributor towards carbon neutrality. The precise evaluation of plant-specific GHG emissions, however, remains challenging. The current assessment approach is based on the product of influent load and emission factor (EF), of which the latter is quite often a single value with huge uncertainty. In particular, the latest default Tier 1 value of N2O EF, 0.016 ± 0.012 kgN2O–N kgTN−1, is estimated based on the measurement of 30 municipal WWTPs only, without involving any industrial wastewater. Therefore, to resolve the pattern of GHG emissions from industrial WWTPs, this work conducted a 14-month monitoring campaign covering all the process units at a full-scale industrial WWTP in Shanghai, China. The total CH4 and N2O emissions from the whole plant were, on average, 447.7 ± 224.5 kgCO2-eq d−1 and 1605.3 ± 2491.0 kgCO2-eq d−1, respectively, exhibiting a 5.2- or 3.9-times more significant deviation than the influent loads of chemical oxygen demand (COD) or total nitrogen (TN). The resulting EFs, 0.00072 kgCH4 kgCOD−1 and 0.00211 kgN2O–N kgTN−1, were just 0.36% of the IPCC recommended value for CH4, and 13.2% for N2O. Besides, the parallel anoxic-oxic (A/O) lines of this industrial WWTP were covered in two configurations, allowing the comparison of GHG emissions from different odor control setup. Unit-specific analysis showed that the replacement of enclosed A/open O with enclosed A/O reduced the CH4 EF by three times, from 0.00159 to 0.00051 kgCH4 kgCOD−1, and dramatically decreased the N2O EF by an order of magnitude, from 0.00376 to 0.00032 kgN2O–N kgTN−1, which was among the lowest of all full-scale WWTPs.

Assessing nitrous oxide emissions and productivity of cropping systems for biogas production using digestate and mineral fertilisation in a coastal marsh site

Significant greenhouse gas emissions during substrate cultivation reduces the potential environmental benefits of biogas production. This study investigates the productivity of different cropping systems and their environmental impact in terms of nitrous oxide (N2O) emissions under the environmental conditions of the coastal marsh regions (Northern Germany) with heavy clay soils, in a 2-year field trial (April 2009-March 2011). Treatments included four cropping systems (perennial ryegrass (Lolium perenne, PR) ley, continuous maize (Zea mays), a rotation (CR1) of spring wheat (Triticum aestivum), Italian ryegrass (Lolium multiflorum, IR) and maize, and a rotation (CR2) of maize, winter wheat and IR; two sources of N (nitrogen) fertilizers (calcium ammonium nitrate, and biogas residue (BR)), and three levels of N fertilizer applications (control, moderate, high). Nitrous oxide emissions were determined for the unfertilized and highly fertilized cropping systems comprising PR ley, CR1 and CR2. Cumulative annual N2O emissions varied across the treatments, ranging from 0.82 to 3.4 kg N2O-N ha−1 year−1. Under high N fertilizer applications, PR ley incurred higher N2O-N losses compared to other tested cropping systems, and IR cover crop caused relatively high N2O-N emissions in a short vegetation period. The study observed wide range of yield-scaled emissions (0.00–5.60 kg N2O-N (Mg DM)−1) for different crops, emphasizing the variability in N2O emissions linked to cropping systems. The N2O-N emission factors for the three cropping systems were found to be low to moderate for all treatments, ranging from 0.03% to 0.53% compared to IPCC default Tier 1 N2O-N EFs. The lower emissions in the study were associated with prolonged high soil moisture conditions (water filled pore space >70%.), indicated by its negative correlation with N2O-N fluxes. Low dry matter and N yield of PR and of the wheat-IR sequence after BR application compared to other crops indicated a low N use efficiency. The estimation of N2O-N emissions based on N surplus was not promising specifically for the coastal study site where high groundwater level and organic matter in the soils were the predominant drivers for N2O-N emissions.

Improved accuracy and reduced uncertainty in greenhouse gas inventories by refining the IPCC emission factor for direct N2 O emissions from nitrogen inputs to managed soils.

Most national GHG inventories estimating direct N2O emissions from managed soils rely on a default Tier 1 emission factor (EF1) amounting to 1% of nitrogen inputs. Recent research has, however, demonstrated the potential for refining the EF1 considering variables that are readily available at national scales. Building on existing reviews, we produced a large dataset (n = 848) enriched in dry and low latitude tropical climate observations as compared to former global efforts and disaggregated the EF1 according to most meaningful controlling factors. Using spatially explicit N fertilizer and manure inputs, we also investigated the implications of using the EF1 developed as part of this research and adopted by the 2019 IPCC refinement report. Our results demonstrated that climate is a major driver of emission, with an EF1 three times higher in wet climates (0.014, 95% CI 0.011–0.017) than in dry climates (0.005, 95% CI 0.000–0.011). Likewise, the form of the fertilizer markedly modulated the EF1 in wet climates, where the EF1 for synthetic and mixed forms (0.016, 95% CI 0.013–0.019) was also almost three times larger than the EF1 for organic forms (0.006; 95% CI 0.001–0.011). Other factors such as land cover and soil texture, C content, and pH were also important regulators of the EF1. The uncertainty associated with the disaggregated EF1 was considerably reduced as compared to the range in the 2006 IPCC guidelines. Compared to estimates from the 2006 IPCC EF1, emissions based on the 2019 IPCC EF1 range from 15% to 46% lower in countries dominated by dry climates to 7%–37% higher in countries with wet climates and high synthetic N fertilizer consumption. The adoption of the 2019 IPCC EF1 will allow parties to improve the accuracy of emissions’ inventories and to better target areas for implementing mitigation strategies.

New N2O emission factors for crop residues and fertiliser inputs to agricultural soils in Germany

Direct agricultural N2O emissions in Germany have so far been estimated using the default Tier 1 emission factor of 1% (0.3–3%) in accordance with the IPCC’s default methodology. Since direct N2O emissions is a “key category” in the German National Greenhouse Gas Inventory, the IPCC recommends the use of country-specific emission factors or models. With the aim of deriving country-specific and stratified N2O emission factors, a meta-analysis was conducted using data collected from 71 individual studies comprising 676 separate emission measurements taken at 43 locations across Germany. A Bayesian generalised linear mixed-effects modelling approach was used to model N2O fluxes and derive emission factors. In contrast to what is suggested by the 2019 Refinement to the 2006 IPCC Guidelines, the model results did not support a distinction being made between emission factors for synthetic and organic fertilisers. Instead, a model based on four environmental zones roughly representing the north-west, north-east, south-east and south-west parts of the country was developed. It was used to derive district-wise emission factors for direct N2O emissions and revealed that northern districts had relatively lower emission factors than southern districts. The district-wise emission factors ranged from 0.38% to 0.92%. The national implied emission factor for direct N2O emissions from managed agricultural soils was 0.62% (0.43–0.85%). Accordingly, the estimate of German national GHG emissions from agriculture in 2015 is 8.59% (calculated with global warming potentials from IPCC’s fifth assessment report) lower than the estimate reported in the 2021 inventory submission to UNFCCC.

Abstract 249: Comparison of variant classification between molecular diagnostics experts and decision support software

Abstract INTRODUCTION: Assessing the actionability of variants identified in next-generation sequencing (NGS) of solid tumors is challenging. Recommendations from AMP/ASCO/CAP/ACMG (Li et al. JMD 2017) provide guidelines for prioritizing variants based on clinical significance and actionability. Sirohi et al. (JMD 2020) reported on interrater agreement with the AMP guidelines by distributing 51 variants from solid tumor NGS to 20 participants at 10 US academic molecular diagnostics laboratories. Initial agreement based on independent assessment amongst the 20 experts was fair (Cohen κ = 0.35). To explore the potential for decision support software to streamline interpretation and improve the reliability of tier classification, we evaluated the same variants with NAVIFY® Mutation Profiler*, a CE-IVD somatic variant interpretation tool that automatically assigns tiers based on curated public evidence. METHODS: Reverse annotation from protein or coding sequence changes was completed with TransVar (Zhou et al. Nat Methods 2015) to obtain hg38 genomic coordinates for the 51 variants. Variants were prepared in VCF files and uploaded to NAVIFY Mutation Profiler (v2.0.0.22e0193) for analysis. The software assigned tier classifications using evidence in Roche curation content version 2.33.0 (released Nov 10, 2020). The default tier for each variant was compared to the tier assigned by the most experts in Sirohi et al. If there was a tie, the higher tier was used for comparison (e.g. Tier II when there was a tie between Tier II and III). RESULTS: There was good agreement (Cohen κ = 0.61) in tier assignments for 37 variants with curation content in NAVIFY Mutation Profiler compared to consensus expert curation in Sirohi et al. Most disagreements could be explained by emerging biomedical evidence, such as phase II clinical trial results for NFE2L2 in squamous cell lung carcinoma, or recommendations in NCCN guidelines. For example, ERBB2 mutations were up-classified by NAVIFY Mutation Profiler to Tier I due to NCCN therapy recommendations, including trastuzumab in combination with lapatinib or pertuzumab for ERBB2-amplified colorectal cancer and trastuzumab emtansine for non-small cell lung cancer with ERBB2 exon 20 insertions. Of the 14 variants without curation in the database, none were actionable, and the experts had classified 11 as Tier III and 3 as Tier II. CONCLUSIONS: When curation content was available, there was high agreement between the assigned tier in NAVIFY Mutation Profiler and the most common tier assigned by 20 molecular diagnostics experts in a previously published study. The continuous growth in new biomedical evidence requires staying current with the latest guidelines and clinical trial results, or the use of regularly updated databases, to accurately interpret somatic cancer variants from NGS test results. * This product is for Research Use Only; Not for use in diagnostic procedures in the US. Citation Format: Stephanie J. Yaung, Shuba Krishna, Sidney Scudder, Maximilian Schmid, John F. Palma. Comparison of variant classification between molecular diagnostics experts and decision support software [abstract]. In: Proceedings of the American Association for Cancer Research Annual Meeting 2021; 2021 Apr 10-15 and May 17-21. Philadelphia (PA): AACR; Cancer Res 2021;81(13_Suppl):Abstract nr 249.

Soil carbon balance of afforested peatlands in the maritime temperate climatic zone

Drainage and conversion of natural peatlands into forestry increases soil CO2 emissions through decomposition of peat and modifies the quantity and quality of litter inputs and therefore the soil carbon balance. In organic soils, CO2 net emissions and removals, are reported using carbon emission factors (EF). The choice of specific default Tier 1 EF values from the IPCC 2013 Wetlands supplement depends on land use categories and climate zones. However, Tier 1 EF for afforested peatlands in the temperate maritime climate zone are based on data from eight sites, mainly located in the hemiboreal zone, and the uncertainty associated with these default values is a concern. In addition, moving from Tier 1 to higher-Tier carbon reporting values is highly desirable when large areas are affected by land use changes. In this study, we estimated site-specific soil carbon balance for the development of Tier 2 soil CO2 -C EFs for afforested peatlands. Soil heterotrophic respiration and aboveground litterfall were measured during two years at eight afforested peatland sites in Ireland. In addition, fine roots turnover rate and site-specific fine root biomass were used to quantify belowground litter inputs. Our findings found that draining of peatlands, and planting them with either Sitka spruce or lodgepole pine, resulted in soils being net carbon sources. The soil carbon balance at multi-year sites varied between 63 ± 92 and 309 ± 67 g C m-2 year-1 . Mean CO2 -C EF for afforested peatlands was 1.68 ± 0.33 tCO2 -Cha-1 year-1 . The improved CO2 -C EFs presented here for afforested peatlands are proposed as a basis to update national CO2 -C emissions from this land-use class in Ireland. Furthermore, new data from these sites will significantly contribute to the development of more reliable IPCC default Tier 1 CO2 -C EFs for afforested peatlands in the maritime temperate climate zone.

Apparent Nitrogen Recovery in Milk and Early Dry Season Nitrous Oxide Emission Factors for Urine Deposited by Dual-Purpose Cattle on Different Soil Types

Pasture conditions influence the nutrients use efficiency and nitrogen (N) losses from deposited excreta. Part of the N is lost as nitrous oxide (N2O), a potent greenhouse gas. The objective of this study was to characterize apparent N recovery in milk of dual-purpose cattle and to quantify N2O emissions from the urine they deposit following grazing on Megathyrsus maximus cv. Mombasa. The N content in the grass and the milk produced by the cattle and the milk urea N (MUN) content were quantified in two contrasting regions of Colombia (Casanare and Atlántico). Dry matter intake (DMI) by the cattle was estimated using the Cornell Net Carbohydrate and Protein System. We used a closed static chamber technique to measure N2O emissions from soils in areas with and without urine patches (21 days in Atlántico and 35 Days in Casanare). Estimated DMI values were 11.5 and 11.6 kg DM day−1, milk production was 6.5 and 5.9 L day−1, apparent N recovery in milk was 24 and 23%, and the MUN content was 4.4 and 17.2 mg N dl−1 in Casanare and Atlántico, respectively. N applied to soil in the form of urine corresponded at rates of 20 and 64 g N m−2 and net cumulative N2O emissions were 350 and 20 mg N2O-N m−2 in Casanare and Atlántico, respectively. Despite low digestibility of offered diet, N recovery in milk was above the values reported at dairy cattle in tropical conditions. High urine-N inputs at Atlántico site did not result in high N2O emissions suggesting that the default Tier 1 emission factor (EF) which is based on N inputs would have overestimated urine-based N2O emissions in Atlántico. Comparing previous studies conducted in Colombia, we observed inter-regional differences by urine-based N2O emissions. This observation suggests that to increase certainty in estimating urine-based N2O emissions, Colombia needs to move toward more region-specific Tier 2 EF and reduce its dependence on the default IPCC Tier 1 EF. In addition, the adoption of Tier 2 EF in the cattle sector will facilitate accounting for the effect of animal diets on N2O inventories.

Effect of sward management on the emissions of CH4 and N2O from faeces of sheep grazing Italian ryegrass pastures

Rotatinuous stocking (RN) management is based on animal ingestive behaviour responses, where optimal pre- and post-grazing sward heights are defined to increase nutrient intake per unit of grazing time. We hypothesized that the optimal sward structure and consequently, a high herbage nutritive value in RN treatment results in a greater faecal nitrogen (N) excretion by sheep and consequently, a greater faecal greenhouse gas (GHG) emissions compared with the traditional rotational stocking (RT) management, which is based on a maximum herbage accumulation and harvest. Therefore, the aim of this study was to evaluate the effect of two grazing management strategies (RN and RT) on the amount of dry matter (DM) faecal excretion, faecal N excretion and faecal GHG (CH4 and N2O) emissions from growing sheep grazing Italian ryegrass pastures. In order to evaluate faecal production and N excretion per animal and per ha, a first experiment (1) was carried out: RT - pre and post-grazing sward heights of 25 and 5 cm, respectively and, RN - pre and post-grazing sward heights of 18 and 11 cm, respectively. A second experiment (2) was carried out to measure the CH4 and N2O fluxes from faeces, using the static chamber method. Daily DM faecal and N excretion per animal were higher (P < 0.001) in RN compared with RT treatment. However, when considered daily DM faecal and N excretion per ha, results were lower (P < 0.001) for the RN than the RT treatment. CH4 and N2O emissions from faeces were higher (P < 0.001) in RN compared with RT treatment, both per animal and per hectare. In conclusion, our study showed that the RN grazing management, based on animal behaviour, resulted in a higher daily N excretion per animal and higher CH4 and N2O emissions from faeces of sheep grazing Italian ryegrass pastures. This study contributes to improve GHG national inventories for the subtropical Brazilian climatic conditions, where estimations from CH4 and N2O emissions factors for faeces from growing sheep grazing Italian ryegrass are markedly lower than the values reported by IPCC Default Tier 1.

Improving reporting of national greenhouse gas emissions from forest fires for emission reduction benefits: An example from Australia

Forest fires are a significant contributor to global greenhouse gas (GHG) emissions. Accurate reporting of GHG emissions from forest fires requires development of detailed methodologies and country specific data for estimating emissions. In recent years, Australia has updated its national methodology for reporting GHG emissions from fires on temperate forested lands, using a Tier 2 approach of the 2006 Intergovernmental Panel on Climate Change (IPCC) Guidelines for National Greenhouse Gas Inventories. This involved refinement of the equation for estimating GHG emissions from fires provided in the Guidance, and the revision of country specific data which was derived from a comprehensive literature review. The refinements were key to transparent reporting and evaluation of the climatic impacts of mitigation actions such as forest fire management. In this paper we describe the steps required to develop a Tier 2 method in reporting fire emissions using this Australian example, the lessons learnt, and the steps required to reduce uncertainties in estimates. This paper may assist other countries seeking to estimate and report GHG emissions from forest fires by moving from the default Tier 1 method to Tier 2 using country-specific information.

Nitrous Oxide and Methane Fluxes from Urine and Dung Deposited on Kenyan Pastures.

Livestock keeping is ubiquitous in tropical Africa. Urine and dung from livestock release greenhouse gases (GHGs), such as nitrous oxide (NO) and methane (CH), to the atmosphere. However, the extent of GHG's impact is uncertain due to the lack of in situ measurements in the region. Here we measured NO and CH emissions from cow urine and dung depositions in two Kenyan pastures that received different amounts of rainfall using static chambers across wet and dry seasons. Cumulative NO emissions were greater under dung+urine and urine-only patches ( 0.0001), more than three times higher in the wet compared with the dry season ( 0.0001), and higher in the farm receiving higher rainfall overall ( 0.0001). Cumulative CH emissions differed across treatments ( = 0.012), driven primarily by soil CH uptake from the urine-only treatment. Cumulative NO emissions were positively related to N input rate in excreta. However, the relationship was linear during the dry season ( 0.99; 0.001) and exponential during the wet season ( 0.99; < 0.0001). Nitrous oxide emission factors were 0.05% (dry season) and 0.18% (wet season) of N in urine and dung+urine, which is less than 10% of the IPCC Default Tier 1 emission factor of 2%. We predict that emissions from cattle urine in Kenya are approximately 1.7 Gg NO-N yr (FAO estimates 11.9 Gg NO-N yr). Our findings suggest that current estimates may overestimate the contribution of excreta to national GHG emissions and that emission factors from urine and dung need to account for agroecosystems with distinct wet and dry seasons.

Land use patterns and related carbon losses following deforestation in South America

Land use change in South America, mainly deforestation, is a large source of anthropogenic CO2 emissions. Identifying and addressing the causes or drivers of anthropogenic forest change is considered crucial for global climate change mitigation. Few countries however, monitor deforestation drivers in a systematic manner. National-level quantitative spatially explicit information on drivers is often lacking. This study quantifies proximate drivers of deforestation and related carbon losses in South America based on remote sensing time series in a systematic, spatially explicit manner. Deforestation areas were derived from the 2010 global remote sensing survey of the Food and Agricultural Organisation Forest Resource Assessment. To assess proximate drivers, land use following deforestation was assigned by visual interpretation of high-resolution satellite imagery. To estimate gross carbon losses from deforestation, default Tier 1 biomass levels per country and eco-zone were used. Pasture was the dominant driver of forest area (71.2%) and related carbon loss (71.6%) in South America, followed by commercial cropland (14% and 12.1% respectively). Hotspots of deforestation due to pasture occurred in Northern Argentina, Western Paraguay, and along the arc of deforestation in Brazil where they gradually moved into higher biomass forests causing additional carbon losses. Deforestation driven by commercial cropland increased in time, with hotspots occurring in Brazil (Mato Grosso State), Northern Argentina, Eastern Paraguay and Central Bolivia. Infrastructure, such as urban expansion and roads, contributed little as proximate drivers of forest area loss (1.7%). Our findings contribute to the understanding of drivers of deforestation and related carbon losses in South America, and are comparable at the national, regional and continental level. In addition, they support the development of national REDD+ interventions and forest monitoring systems, and provide valuable input for statistical analysis and modelling of underlying drivers of deforestation.

Managing fertiliser nitrogen to reduce nitrous oxide emissions and emission intensities from a cultivated Cambisol in Scotland

Emissions of nitrous oxide (N2O) were measured from an arable site in south east Scotland for twelve months during 2011–2012 using an intensive sampling strategy. This fully replicated and blocked field experiment aimed to provide accurate measurements of N2O emissions from one of the UK's principle geoclimatic zones supporting agricultural production and to produce robust N2O emission factors (EFs). Calculated EFs were compared to the IPCC's default Tier 1 EF of 1.25%, and the new value of 1%, to assess their suitability for use in locations throughout the UK. Emissions from ten treatments fertilised with either ammonium nitrate or urea at rates of 0kgNha−1 to 200kgNha−1, and sown with spring barley, were measured using the static closed chamber technique. Potential N2O mitigation options were investigated; these included the use of a nitrification inhibitor (NI), split fertiliser applications and variations in the form and quantity of fertiliser applied. Crop yields were measured to enable calculation of N2O emission intensities for each treatment; this is an important factor to consider when assessing N2O mitigation options due to the need to maintain crop yields. Cumulative N2O emissions varied between 1.32kg N2O-Nha−1 and 3.82kg N2O-Nha−1 with a mean 42% decrease in emissions associated with the use of the NI. Increases in crop yield were associated with increases in N fertiliser application, and the amendment of treatments with a NI and the use of a split fertiliser application significantly decreased crop yields by approximately 10% and 5% respectively. Annual EFs ranged between −0.28% to 1.35%. Emission intensities decreased with increasing fertiliser application at low N application rates, and the optimum fertiliser application rate to obtain minimum emissions but maximum crop yield was 160kgNha−1.

The challenge of modelling nitrogen management at the field scale: simulation and sensitivity analysis of N2O fluxes across nine experimental sites using DailyDayCent

The United Kingdom currently reports nitrous oxide emissions from agriculture using the IPCC default Tier 1 methodology. However Tier 1 estimates have a large degree of uncertainty as they do not account for spatial variations in emissions. Therefore biogeochemical models such as DailyDayCent (DDC) are increasingly being used to provide a spatially disaggregated assessment of annual emissions. Prior to use, an assessment of the ability of the model to predict annual emissions should be undertaken, coupled with an analysis of how model inputs influence model outputs, and whether the modelled estimates are more robust that those derived from the Tier 1 methodology. The aims of the study were (a) to evaluate if the DailyDayCent model can accurately estimate annual N2O emissions across nine different experimental sites, (b) to examine its sensitivity to different soil and climate inputs across a number of experimental sites and (c) to examine the influence of uncertainty in the measured inputs on modelled N2O emissions. DailyDayCent performed well across the range of cropland and grassland sites, particularly for fertilized fields indicating that it is robust for UK conditions. The sensitivity of the model varied across the sites and also between fertilizer/manure treatments. Overall our results showed that there was a stronger correlation between the sensitivity of N2O emissions to changes in soil pH and clay content than the remaining input parameters used in this study. The lower the initial site values for soil pH and clay content, the more sensitive DDC was to changes from their initial value. When we compared modelled estimates with Tier 1 estimates for each site, we found that DailyDayCent provided a more accurate representation of the rate of annual emissions.

CO2emissions from cropland in Norway estimated by IPCC default and Tier 2 methods

Monitoring changes in soil organic carbon is linked not only to atmospheric CO2 dynamics, but also to the sustainability of agricultural systems, maintaining food security, reducing water pollution and soil erosion. In accordance with the Intergovernmental Panel on Climate Change (IPCC) methodology, a Tier 2 method for estimating CO2 emissions from cropland on mineral soils in Norway was developed and the results were compared with those of the default Tier 1 method. A soil C balance model, the introductory carbon balance model (ICBM) was used to calculate country-specific soil organic carbon (SOC) stock change factors for cropland management systems for the Tier 2 method. Annual CO2 emissions from cropland management were substantially higher when estimated by the default Tier 1 method (313 Gg CO2 per year) compared with Tier 2 (149 Gg CO2 per year). The differences between the results were mainly due to the default Tier 1 stock change factors for crop rotations without manure application, which led to g...

Nitrous Oxide and Carbon Dioxide Emissions Following Green Manure and Compost Fertilization in Corn

Alternative N fertilizers that stimulate low greenhouse gas emissions from soil are needed to reduce the impact of agriculture on global warming. Corn (Zea mays L.) grown in a calcareous silt loam soil in northwestern Italy was fertilized with a municipal solid waste compost and vetch (Vicia villosa Roth.) green manure. Their potential to reduce N2O and CO2 emissions was compared with that of urea (130 kg N ha−1). Gaseous fluxes were measured for 2 yr in the spring (after soil incorporation of fertilizers) and in summer. In spring, the slow mineralization of compost reduced N2O emissions (0.11% of supplied N) relative to urea (3.4% of applied N), without an increase in CO2 fluxes. Nitrous oxide (2.31% of fixed N) and CO2 emissions from rapid vetch decomposition did not differ from urea. When N2O and CO2 fluxes were combined, compost reduced by 49% the CO2 equivalent emitted following urea application. Vetch did not show such an effect. In summer, no fertilizer effect was found on N2O and CO2 emissions. Compost proved to be potentially suitable to reduce the CO2 equivalent emitted after soil incorporation while vetch did not. For a thorough evaluation, net greenhouse gas emissions assessment should be extended to the entire N life cycle. Differences between calculated N2O emission factors and the default Tier 1 value of the Intergovernmental Panel on Climate Change (1%) confirmed the need for site‐ and fertilizer‐specific estimations.