Estimating Agricultural Nitrous Oxide Emissions

Better information on greenhouse gas (GHG) emissions and mitigation potential in the agricultural sector is necessary to manage these emissions and identify responses that are consistent with the food security and economic development priorities of countries. Critical activity data (what crops or livestock are managed in what way) are poor or lacking for many agricultural systems, especially in developing countries. In addition, the currently available methods for quantifying emissions and mitigation are often too expensive or complex or not sufficiently user friendly for widespread use.The purpose of this focus issue is to capture the state of the art in quantifying greenhouse gases from agricultural systems, with the goal of better understanding our current capabilities and near-term potential for improvement, with particular attention to quantification issues relevant to smallholders in developing countries. This work is timely in light of international discussions and negotiations around how agriculture should be included in efforts to reduce and adapt to climate change impacts, and considering that significant climate financing to developing countries in post-2012 agreements may be linked to their increased ability to identify and report GHG emissions (Murphy et al 2010, CCAFS 2011, FAO 2011).

Impacts of nitrogen management and organic matter application on nitrous oxide emissions and soil organic carbon from spring maize fields in the North China Plain

Background Agricultural soils contribute towards the emission of CH4 (mainly from paddy fields) and N2O (from N-fertilizer application), the two important greenhouse gases causing global warming. Most studies had developed the inventories of CH4 and N2O emission at the country level (larger scale) for India, but not many studies are available at the local scale (e.g. district level) on these greenhouse gases (GHGs). Assam is an important state in the North Eastern region of India. In addition to being the regional economic hub for the entire region, agriculture is the major contributor to the state’s gross domestic product. In Assam about three-fourths of the area is under paddy cultivation and rice is the staple food. With this background, a district wise inventory of CH4 and N2O emission in the North Eastern state of Assam, India was carried out using different emission factors, viz., IPCC, Indian factors and others, to highlight the discrepancies that arose in the emission estimation of these important GHGs while used at the smaller scale i.e. district level. This study emphasizes the need for better methodologies at the local level for GHGs inventories. This study also reiterates the fact that no emission factor is universally applicable across all regions. The GHGs like CH4 and N2O are highly site and crop specific and the factors required for their inventory are driven by cultural practices, agronomic management, soil resources and socio-economic drivers. Material and methods In this study, Intergovernmental Panel on Climate Change (IPCC) methodology was used for the estimation of CH4 and N2O emission. In case of N2O emission, both direct and indirect emission from agricultural soil was estimated for the various districts of Assam. Results The CH4 (base year 2000–2001) and N2O (base year 2001–2002) emission was estimated to be 121 Gg and 1.36 Gg from rice paddy and agricultural fields of Assam state respectively. Conclusions This study is the first report on the estimation of the GHG emission at the district level from the entire state of Assam, agriculturally one very important state of North Eastern India. This state is also considered as remote due to its geographical location. The study clearly elucidates that there is large variation in the emission inventory of CH4 and N2O at the district level (local scale) when different emission factors are used. This calls for detailed and comprehensive data collection and mapping at the micro level for accurate inventory of greenhouse gases in future from agriculture fields.

Operationalizing marketable blue carbon

The Ecology of Meat

Bioenergy from perennial grasses mitigates climate change via displacing fossil fuels and storing atmospheric CO2 belowground as soil carbon. Here, we conduct a critical review to examine whether increasing plant diversity in bioenergy grassland systems can further increase their climate change mitigation potential. We find that compared with highly productive monocultures, diverse mixtures tend to produce as great or greater yields. In particular, there is strong evidence that legume addition improves yield, in some cases equivalent to mineral nitrogen fertilization at 33–150 kg per ha. Plant diversity can also promote soil carbon storage in the long term, reduce soil N2O emissions by 30%–40%, and suppress weed invasion, hence reducing herbicide use. These potential benefits of plant diversity translate to 50%–65% greater life-cycle greenhouse gas savings for biofuels from more diverse grassland biomass grown on degraded soils. In addition, there is growing evidence that plant diversity can accelerate land restoration.

Nitrous oxide (N2 O) emissions from inland waters remain a major source of uncertainty in global greenhouse gas budgets. N2 O emissions are typically estimated using emission factors (EFs), defined as the proportion of the terrestrial nitrogen (N) load to a water body that is emitted as N2 O to the atmosphere. The Intergovernmental Panel on Climate Change (IPCC) has proposed EFs of 0.25% and 0.75%, though studies have suggested that both these values are either too high or too low. In this work, we develop a mechanistic modeling approach to explicitly predict N2 O production and emissions via nitrification and denitrification in rivers, reservoirs and estuaries. In particular, we introduce a water residence time dependence, which kinetically limits the extent of denitrification and nitrification in water bodies. We revise existing spatially explicit estimates of N loads to inland waters to predict both lumped watershed and half-degree grid cell emissions and EFs worldwide, as well as the proportions of these emissions that originate from denitrification and nitrification. We estimate global inland water N2 O emissions of 10.6-19.8GmolNyear-1 (148-277GgNyear-1 ), with reservoirs producing most N2 O per unit area. Our results indicate that IPCC EFs are likely overestimated by up to an order of magnitude, and that achieving the magnitude of the IPCC's EFs is kinetically improbable in most river systems. Denitrification represents the major pathway of N2 O production in river systems, whereas nitrification dominates production in reservoirs and estuaries.

دراینمقاله،میزانو ارزش انتشارگازهایگلخانه‌ای اکسید‌نیتروس(N2O) و دی‌اکسید‌کربن(CO2)حاصلازتولید حبوبات منتخب ایران (شامل نخود، لوبیا و عدس) با استفاده از مدل GHGE،برایسالزراعی91-90برآورد شده است.نتایج نشان‌داد که استان‌هایفارسوبوشهر، به‌ترتیبباتولیدسالانه271/79 و 004/0 تنN2O، بیشترینوکمترینمیزانتولیدگاز گلخانه‌ایN2Oرا دارامی‌باشند. همچنین استان‌هایلرستانوبوشهر نیز به‌ترتیب باتولیدسالانه83/10327 و33/1‌تنCO2،بیشترینوکمترینمیزانتولیدگاز گلخانه‌ایCO2را به‌خود اختصاص داده‌اند. مجموعهزینه‌هایزیست‌محیطی انتشار گازهای گلخانه‌ای N2O و CO2 کلکشورنیزحدود705/32‌میلیاردریالبرآوردگردید. باتوجهبه یافته‌ها، مدیریت کودهای نیتروژنه مصرفی در مزارعوتوسعهسیاست‌کاهشمیزانانتشاربه‌همراه مالیات زیست‌محیطی انتشار گازهای گلخانه‌ای بر سطوح مختلف تولید پیشنهاد شده ‌است. واژه‌های کلیدی: اکسید‌نیتروس، دی‌اکسید‌کربن، حبوبات، گازهای گلخانه‌ای

Effects of urea form and soil moisture on N2O and NO emissions from Japanese Andosols

The objective of the project is to provide a systematic review of the literature on GHG emissions from swine operations, including both a qualitative review and a meta-analysis that integrates results of various independent studies. Results showed that variation of the CH4 and N2O emission rates from swine operations has not been adequately captured by the Intergovernmental Panel on Climate Change (IPCC) approaches. For CH4 emissions, the differences between the IPCC estimated emission rates and measured values were significantly influenced by type of emission source, geographic region and measurement methods. In North American studies, the results indicated an overestimation by the IPCC approaches for CH4 emissions from lagoons and the discrepancy mainly occurred at lower temperatures. In European studies, the results indicated an overestimation of the IPCC approaches in swine buildings with pit systems. For N2O emissions, an overall underestimation of the IPCC approaches was observed in European studies but not in North American studies. Swine buildings generated much higher CO2 emissions than manure storage facilities while CH4 and N2O emissions were not different. Lagoons generated significantly higher N2O emissions than slurry storage basin/tanks, while CH4 and CO2 emissions were not different. Farrowing swine emitted more CH4 and CO2 emissions as compared with other swine categories, while gestating swine had greater N2O emissions. North American studies reported significantly higher CH4 emissions from swine operations than European and Asian studies. Diet CP was not significant on GHG emissions, while temperature were significant on CH4 emissions from lagoons or slurry storage facilities.

Agricultural soils contribute toward the emission of methane (CH4) and nitrous oxide (N2O), the two important greenhouse gases (GHGs) causing global warming. A state‐wise inventory of CH4 and N2O emissions from agricultural soils of India was prepared for the base year 2007 using the Intergovernmental Panel on Climate Change (IPCC) national inventory preparation guidelines. For CH4 inventory, state‐specific emission coefficients were used for rice grown under upland, rain‐fed, irrigated, and deepwater, the four major rice ecosystems of the country. In case of N2O, both direct and indirect emissions from agricultural soils in different states were calculated using indigenous country specific emission factors. The change in annual emission of CH4 and N2O during the period 1980 to 2007 was estimated using the same emission coefficients. Indian rice fields covering an area of 43.86 million ha under the different rice ecosystems emitted 3.37 million tons of CH4 (84.25 Tg CO2 equivalents) in 2007. The annual direct and indirect N2O‐N emissions from Indian agricultural soils was estimated to be 118.67 Gg (55.5 Tg CO2 equivalent) and 19.48 Gg (9.1 Tg CO2 equivalent), respectively. The global warming potential of the agricultural soils was estimated to be 148 Tg for the year 2007. Emissions from field burning of agricultural residues resulted in an annual emission of 250 Gg of CH4 (6.2 Tg CO2 equivalent) and 6.5 Gg of N2O (1.9 Tg CO2 equivalent). Emission of CH4 from Indian rice fields has remained almost constant during this period whereas there has been an increase of 176% in N2O emissions from agricultural soils due to increased inorganic fertilizer application, however the greenhouse gas emission intensity has declined over the years due to increase in food production.

[ACCESS RESTRICTED TO THE UNIVERSITY OF MISSOURI AT AUTHOR'S REQUEST.] Agricultural soils are responsible for a majority of human caused greenhouse gas (GHG) production, such as N₂O and carbon dioxide (CO₂). Nitrous oxide is a potent GHG that stays in the atmosphere for at least 100 years. It is also an ozone-depleting gas. Carbon dioxide is problematic due to its abundance in the atmosphere. These GHGs, along with methane, have had a significant impact on climate change. Claypan soils are characterized as having a significantly higher clay content deeper in the soil profile compared to the layers directly above it. The goal of this research was to investigate the impact N fertilizer placement has on GHG emissions and corn growth. The specific research objectives were to determine the effects of urea fertilizer placement with and without a nitrification inhibitor (NI) on cumulative soil GHG emissions (N₂O and CO₂) and to assess the effects of urea fertilizer placement with and without a NI on plant N uptake, N use efficiency (NUE), and corn (Zea mays L.) production, on a poorly drained claypan soil in Northeastern Missouri. A NI helps reduce the amount of nitrous oxide produced. Field studies were conducted in 2014 and 2015. Soil greenhouse gas emissions were measured frequently throughout the growing season to determine flux and cumulative N₂O and CO₂ emissions. Soil water content and soil temperature were also assessed at each gas sampling event. Rainfall was higher than the 10-year average over the growing season for both 2014 and 2015 and possibly resulted in increased environmental N loss. Soil N₂O and CO₂ emissions were higher during the 2015 growing season. The UDB treatment produced the greatest amount of cumulative soil N₂O emissions during both growth seasons at 100 and 354 g N₂O-N ha⁻¹. Deep banded urea without a NI resulted in the highest soil CO₂ production in 2014 and UAA had the greatest cumulative CO₂ emissions in 2015 at approximately 11 and 17 kg CO₂-C ha⁻¹, respectively. Incorporating urea to a depth of 8 cm, deep banding urea, and deep banding urea with a NI all resulted in significantly higher yields of corn by as much as much as 10%. Deep banding urea with a NI provided as high as a 48% increase in grain yield compared to other treatments in 2015. The highest yields occurred in 2014 when there were lower N₂O emissions. In 2015, there were higher N₂O emissions and lower yields. This research suggests that urea fertilizer placement has an impact on GHG emissions and corn growth and this information should be provided to farmers who are interested in producing more corn and losing less N. The amount of rainfall during the growing season may also influence soil GHG emissions and corn growth. More research should be conducted to understand to what extent climatic variability impacts GHG and crop production.

The emission factor method (Tier 1) recommended by the Intergovernmental Panel on Climate Change (IPCC) is commonly used to estimate greenhouse gas (GHG) emissions from livestock and poultry farms. However, the estimation accuracy may vary due to practical differences in manure management across China. The objectives of this study were to estimate the direct and indirect nitrous oxide (N2O) emissions from dairy manure management between 1990 and 2021 in China and characterize its spatial and temporal variations following IPCC guideline Tier 2. The N2O emission factor (EF) of dairy cow manure management systems was determined at the national level and regional level as well. The results showed that the national cumulative N2O emission of manure management from 1990 to 2021 was 113.1million tons of CO2 equivalent, ranging from 90.3 to 135.9 million tons with an uncertainty of ±20.2%. The annual EF was 0.021 kg N2O-N (kg N)−1 for total emissions, while it was 0.014 kg N2O-N (kg N)−1 for direct emissions. The proportions of N2O emissions in North China, Northeast China, East China, Central and Southern China, Southwest China and Northwest China were 32.3%, 18.6%, 11.4%, 5.8%, 6.1% and 25.8%, respectively. In addition, N2O emissions varied among farms in different scales. The respective proportions of total N2O emissions from small-scale and large-scale farms were 64.8% and 35.2% in the past three decades. With the improvement in farm management and milk production efficiency, the N2O emissions per unit mass of milk decreased from 0.77 × 10−3 kg to 0.48 × 10−3 kg in 1990–2021. This study may provide important insights into compiling a GHG emission inventory and developing GHG emission reduction strategies for the dairy farming system in China.

Fertilizer nitrogen use is estimated to be a significant source of nitrous oxide (N2O) emissions in western Canada. These estimates are based primarily on modeled data, as there are relatively few studies that provide direct measures of the magnitude of N2O emissions and the influence of N source on N2O emissions. This study examined the influence of nitrogen source (urea, coated urea, urea with urease inhibitor, and anhydrous ammonia), time of application (spring, fall) and method of application (broadcast, banded) on nitrous oxide emissions on two Black Chernozemic soils located near Winnipeg and Brandon Manitoba. The results of this 3-yr study demonstrated consistently that the rate of fertilizer-induced N2O emissions under Manitoba conditions was lower than the emissions estimated using Intergovernmental Panel on Climate Change (IPCC) coefficients. The Winnipeg site tended to have higher overall N2O emissions (1.7 kg N ha-1) and fertilizer-induced emissions (~0.8% of applied N) than did the Brandon site (0.5 kg N ha-1), representing ~0.2% of applied N. N2O emissions in the first year of the study were much higher than in subsequent years. Both the site and year effects likely reflected differences in annual precipitation. The N2O emissions associated with the use of anhydrous ammonia as a fertilizer source were no greater than emissions with urea. Fall application of nitrogen fertilizer tended to result in marginally greater N2O emissions than did spring application, but these differences were neither large nor consistent. Key words: Nitrogen fertilizer, nitrous oxide emissions, nitrate intensity, anhydrous ammonia, urea

Anthropogenic activities cause the introduction of nitrogen (N) into aquatic environments where these N inputs drive the biological synthesis of nitrous oxide (N2O), a potent and ozone-depleting greenhouse gas. To assess the significance of N2O emissions to climate change, the Intergovernmental Panel on Climate Change (IPCC) estimates indirect N2O emissions from rivers, lakes, and estuaries by multiplying the amounts of N received by these ecosystems with specific emission factors. Interestingly, the IPCC recently increased the N2O emission factor associated with wastewater discharge into “nutrient-impacted (eutrophic) aquatic receiving environments” nearly four times based on experimental evidence of high N2O emissions from N-receiving eutrophic ecosystems. As microalgae can produce N2O, these organisms may contribute to the N2O emissions frequently reported in eutrophic aquatic bodies. If that is the case, estimating N2O emissions solely based on nitrogen inputs to water bodies might lead to inaccurate N2O budgeting as microalgae growth is often limited by phosphorus in these environments. Establishing the significance of microalgal N2O synthesis in eutrophic environments is, therefore, critical and may lead to considerable changes on how to budget and mitigate N2O emissions and eutrophication.