Tools for quantifying N2O emissions from agroecosystems (original) (raw)
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Agriculture, Ecosystems & Environment, 2015
Biogeochemical models are useful tools for integrating the effects of agricultural management on GHG emissions; however, their development is often hampered by the incomplete temporal and spatial representation of measurements. Adding to the problem is that a full complement of ancillary measurements necessary to understand and validate the soil processes responsible for GHG emissions is often not available. This study presents a rare case where continuous N 2 O emissions, measured over seven years using a flux gradient technique, along with a robust set of ancillary measurements were used to assess the ability of the DNDC model for estimating N 2 O emissions under varying crop-management regimes. The analysis revealed that the model estimated soil water content more precisely in the normal and wet years (ARE 3.4%) than during the dry years (ARE 11.5%). This was attributed to the model's inability to characterize episodic preferential flow through clay cracks. Soil mineral N across differing management regimes (ARE 2%) proved to be well estimated by DNDC. The model captured the relative differences in N 2 O emissions between the annual (measured: 35.5 kg N 2 O-N ha À1 , modeled: 30.1 kg N 2 O-N ha À1 ) and annual-perennial (measured: 26.6 kg N 2 O-N ha À1 , modeled: 21.2 kg N 2 O-N ha À1 ) cropping systems over the 7 year period but overestimated emissions from alfalfa production and underestimated emissions after spring applied anhydrous ammonia. Model predictions compared well with the measured total N 2 O emissions (ARE À11%) while Tier II comparison to measurements (ARE À75%) helped to illustrate the strengths of a mechanistic approach in characterizing the site specific drivers responsible for N 2 O emissions. Overall this study demonstrated the benefits of having near continuous GHG flux measurements coupled with detailed ancillary measurements towards identifying soil process interactions responsible for regulating GHG emissions.
Nitrous oxide emissions at the landscape scale: spatial and temporal variability
Biogeosciences Discussions, 2011
Nitrous oxide (N 2 O) emissions from agricultural land are variable at the landscape scale due to variability in land use, management, soil type, and topography. A field experiment was carried out in a typical mixed farming landscape in Denmark, to investigate the main drivers of variations in N 2 O emissions, measured using static chambers. Measurements were made over a period of 20 months, and sampling was intensified during two weeks in spring 2009 when chambers were installed at ten locations or fields to cover different crops and topography and slurry was applied to three of the fields. N 2 O emissions during spring 2009 were relatively low, with maximum values below 20 ng N m −2 s −1 . This applied to all land use types including winter grain crops, grasslands, meadows, and wetlands. Slurry application to wheat fields resulted in short-lived two-fold increases in emissions. The moderate N 2 O fluxes and their moderate response to slurry application were attributed to dry soil conditions due to the absence of rain during the four previous weeks. Cumulative annual emissions from two arable fields that were both fertilized with mineral fertilizer and manure were large (17 kg N 2 O-N ha −1 yr −1 and 5.5 kg N 2 O-N ha −1 yr −1 ) during the previous year when soil water conditions were favourable for N 2 O production during the first month following fertilizer application. Our findings confirm the importance of weather conditions as well as nitrogen management on N 2 O fluxes.
Spatial variability of nitrous oxide emissions from croplands and unmanaged
Spatial variability of nitrous oxide emissions from croplands and unmanaged natural ecosystems across a large environmental gradient, 2024
Atmospheric nitrous oxide (N2O) is a potent greenhouse gas, with long atmospheric residence time and a global warming potential 273 times higher than CO2. N2Oemissions are mainly produced from soils and are influenced by biotic and abiotic factors that can be substantially altered by anthropogenic activities, such as land uses, especially when unmanaged natural ecosystems are replaced by croplands or other uses. In this study, we evaluated the spatial variability of N2O emissions from croplands (maize, soybean, wheat, and sugar cane crops), paired with the natural grasslands or forests that they replaced across a wide environmental gradient in Argentina, and identified the key drivers governing the spatial variability of N2O emissions using structural equation modeling. We conducted on-farm field measurements over 2 years at nine different sites, including a wide environmental gradient (mean rainfall from 679 to 1090 mm year−1 and mean temperatures from 13.8°C to 21.3°C), with diverse plant species life forms, and ecosystems, from the Semiarid Chaco forests in the Northwest of Argentina to the Pampas grasslands in the Southeast. On average, agricultural systems emitted more than twice N2O (+120%), had higher soil water content (+9%), higher soil temperatures (+3%), higher soil nitrate content (+19%) but lower ammonium (−33%) than natural ecosystems. We found that land use was the main driver of N2O emissions by directly affecting soil NO3 − contents in both natural ecosystems and croplands. Urgent management practices aimed at reducing N2O emissions from croplands are needed to mitigate their contributions to global climate change.
Nitrous Oxide Emissions from Agricultural Toposequences in Alberta and Saskatchewan
Soil Science Society of America Journal, 2004
sphere, most of it is converted to N 2 through a photolytic reaction that converts O 3 into O 2 thereby causing the Nitrous oxide fluxes from soils are inherently variable in time and stratosphere to lose some of its shielding properties space. An improved understanding of this variability is needed to make accurate estimates of N 2 O fluxes at a regional scale. The objec-against ultra violet rays (Schlesinger, 1997). Nitrous oxtives of this work were to (i) characterize the influence of soil-ide forms in soils primarily during the process of denitrilandscape combinations and N application rates on N 2 O emissions fication (Robertson and Tiedje, 1987) and, to a lesser and to (ii) determine the contribution of these influences on the extent, during nitrification (Tortoso and Hutchinson, estimation of N 2 O emissions at the field scale. We used static chambers 1990). Global annual N 2 O emissions from agricultural and gas chromatography methods to measure N 2 O fluxes and collected soils have been estimated to range between 1.9 and ancillary data (mineral N, water soluble C, soil water content, soil 4.2 Tg N, with about half arising from anthropogenic temperature) in Canada at Mundare (AB) in the aspen parkland sources (IPCC, 2001). ecoregion and at Swift Current (SK) in the short-grass prairie eco-The methodology proposed by Mosier et al. (1998) region. At Mundare, measurements were taken in 1995 and 1996 by relates N 2 O emissions to the agricultural N cycle through landscape position and land use. At Swift Current, data were collected the use of readily available FAO databases. In an effort in 1999 and 2000 by landscape position and N rate. At Mundare, to test the use of this methodology at a regional scale, landscape position affected N 2 O emissions but the pattern varied Lemke et al. (1998a) compared seasonal fluxes of measeasonally. During a 46-d period in summer 1995, a flux of 430 g N 2 ON ha Ϫ1 measured in a backslope was greater than the 60 g N 2 ON sured N 2 O at six sites in Alberta (Canada) against estiha Ϫ1 measured on average in shoulder and depressional areas. The mates made using the Mosier et al. (1998) procedure. flux pattern changed during a 43-d spring thaw of 1996 when fluxes Although the estimated fluxes compared fairly well with from depressional areas were greatest (1710 g N 2 ON ha Ϫ1). Nitrous the measured data, the procedure does not consider oxide emissions from natural areas were small. The emission pattern site-specific characteristics (e.g., soil texture) that may during summer 1996 was similar to that of 1995 but the fluxes were strongly influence N 2 O fluxes. an order of magnitude larger. At Swift Current, N 2 O fluxes in summer As a ratifying country of the Kyoto Protocol, 1 Canada 1999 were affected by topography and N rate. Fluxes were greatest is actively pursuing the development of protocols to in depressional areas receiving N at 110 kg ha Ϫ1 (3140 g N 2 ON ha Ϫ1). estimate greenhouse gas emissions from agriculture at Use of the area fraction occupied by each landscape position to calcua national scale, including N 2 O emissions from soils. late N 2 O flux increased the estimates of N 2 O fluxes at the field scale Brierley and Patterson (2002) recently advanced a hierin five out of six cases. Further research of N 2 O fluxes in variable archical ecological framework being developed in Canlandscapes should help elucidate factors controlling N 2 O fluxes from pedon to field scale and thus translate into improved flux estimates ada to scale up soil emissions of greenhouse gases from at regional scales. field to national levels. The framework classifies all lands hierarchically-from small-to large-scale spatial resolution-into ecozones, ecoregions, ecodistricts, and soil landscape polygons. Thus, predictions (through T he concentration of N 2 O in the atmosphere, estimodels or measurements) of N 2 O fluxes at the soil landmated at 2.68 ϫ 10 Ϫ2 mL L Ϫ1 around 1750, has scape level will be useful for scaling these fluxes to increased by about 17% as a result of human alterations regional and national level. of the global N cycle (IPCC, 2001). Nitrous oxide is a Nitrous oxide fluxes from soils are conspicuously varipotent greenhouse gas with much greater global warmable in time and space. An improved understanding of ing potential than CO 2. When N 2 O reaches the stratothis variability is needed to improve estimates of N 2 O fluxes at field and regional scales. The variability in N 2 O R.C. Izaurralde, Joint Global Change Research Institute, Univ. of fluxes can be partly explained by the complex interac
Environmental Modelling & Software, 2017
Greenhouse gas (GHG) emissions from agroecosystems, particularly nitrous oxide (N 2 O), are an increasing concern. To quantify N 2 O emissions from agroecosystems, which occur as a result of nitrogen (N) cycling, a new physically based routine was developed for the Soil and Water Assessment Tool (SWAT) model to predict N 2 O flux during denitrification and an existing nitrification routine was modified to capture N 2 O flux during this process. The new routines predict N 2 O emissions by coupling the carbon (C) and N cycles with soil moisture/temperature and pH in SWAT. The model uses reduction functions to predict total denitrification (N 2 + N 2 O) and partitions N 2 from N 2 O using a ratio method. The modified SWAT nitrification routine likewise predicts N 2 O emissions using reduction functions. The new denitrification routine and modified nitrification routine were tested using GRACEnet data at University Park, Pennsylvania, and West Lafayette, Indiana. Results showed strong correlations between plot measurements of N 2 O flux and the model predictions for both test sites and suggest that N 2 O emissions are particularly sensitive to soil pH and soil N, and moderately sensitive to soil temperature/moisture and total soil C levels.
Journal of Environmental Quality, 2003
Nitrous oxide (N 2 O) is a high-impact greenhouse gas. Due to the scarcity of unmanaged forests in Central Europe, its long-term natural background emission level is not entirely clear. We measured soil N 2 O emissions in an unmanaged, old-growth beech forest in the Hainich National Park, Germany, at 15 plots over a 1-year period. The average annual measured N 2 O flux rate was (0.49 ± 0.44) kg N ha -1 y -1 . The N 2 O emissions showed background-emission patterns with two N 2 O peaks. A correlation analysis shows that the distance between plots (up to 380 m) does not control flux correlations. Comparison of measured data with annual N 2 O flux rates obtained from a standard model (Forest-DNDC) without site-specific recalibration reveals that the model overestimates the actual measured N 2 O flux rates mainly in spring. Temporal variability of measured N 2 O flux was better depicted by the model at plots with high soil organic C (SOC) content. Modeled N 2 O flux rates were increased during freezing only when SOC was > 0.06 kg C kg -1 . The results indicate that the natural background of N 2 O emissions may be lower than assumed by most approaches.
Journal of Geophysical Research: Biogeosciences, 2019
With the addition of nitrogen (N), agricultural soils are the main anthropogenic source of N 2 O, but high spatial and temporal variabilities make N 2 O emissions difficult to characterize at the field scale. This study used flux-gradient measurements to continuously monitor N 2 O emissions at two agricultural fields under different management regimes in the inland Pacific Northwest of Washington State, USA. Automated 16-chamber arrays were also deployed at each site; chamber monitoring results aided the interpretation of the flux gradient results. The cumulative emissions over the six-month (1 April-30 September) monitoring period were 2.4 ± 0.7 and 2.1 ± 2 kg N 2 O-N/ha at the no-till and conventional till sites, respectively. At both sites, maximum N 2 O emissions occurred following the first rainfall event after N fertilization, and both sites had monthlong emission pulses. The no-till site had a larger N 2 O emission factor than the Intergovernmental Panel on Climate Change Tier 1 emission factor of 1% of the N input, while the conventional-till site's emission factor was close to 1% of the N input. However, these emission factors are likely conservative. We estimate that the global warming potential of the N 2 O emissions at these sites is larger than that of the no-till conversion carbon uptake. We recommend the use of chambers to investigate spatiotemporal controls as a complementary method to micrometeorological monitoring, especially in systems with high variability. Continued monitoring coupled with the use of models is necessary to investigate how changing management and environmental conditions will affect N 2 O emissions. Plain Language Summary Nitrous oxide (N 2 O) is a greenhouse gas and stratospheric ozone depleting substance that is emitted by soils. Agricultural soils tend to emit more N 2 O than natural soils due to the addition of nitrogen fertilizers. N 2 O emissions are not well understood on the scale of individual farms, as emissions are difficult to measure at this resolution because they are irregular over time and space. This variability is due to the dependence of N 2 O production and emission on soil properties, that is, moisture, nitrogen, and the microbiome. In this study we monitored N 2 O emissions from two agricultural fields under different tillage regimes using two complementary methods: the flux-gradient technique and automated chambers. The flux-gradient technique measures N 2 O emissions at the field scale, which is relevant to agronomic management. Using both techniques together improves confidence in our results, which give us information on total N 2 O emissions from these fields, as well as the relationships between N 2 O emissions and rainfall, temperature, and carbon dioxide respiration.
Model estimates of nitrous oxide emissions from agricultural lands in the United States
Global Biogeochemical Cycles, 1996
The Denitrification-Decomposition (DNDC) model was used to elucidate the role of climate, soil properties, and farming practices in determining spatial and temporal variations in the production and emission of nitrous oxide (N20) from agriculture in the United States. Sensitivity studies documented possible causes of annual variability in N20 flux for a simulated Iowa corn-growing soil. The 37 scenarios tested indicated that soil tillage and nitrate pollution in rainfall may be especially significant anthropogenic factors which have increased N20 emissions from soils in the United States. Feedbacks to climate change and biogeochemical manipulation of agricultural soil reflect complex interactions between the nitrogen and carbon cycles. A 20% increase in annual average temperature in øC produced a 33% increase in N20 emissions. Manure applications to Iowa corn crops enhanced carbon storage in soils, but also increased N20 emissions. A DNDC simulation of annual N20 emissions from all crop and pasture lands in the United States indicated that the value lies in the range 0.9 -1.2 TgN. Soil tillage and fertilizer use were the most important farming practices contributing to enhanced N20 emissions at the national scale. Soil organic matter and climate variables were the primary determinants of spatial variability in N20 emissions. Our results suggest that the United States Government, and possibly the Intergovernmental Panel on Climatic Change (IPCC), have underestimated the importance of agriculture as a national and global source of atmospheric N20. The coupled nature of the nitrogen and carbon cycles in soils results in complex feedbacks which complicate the formulation of strategies to reduce the global warming potential of greenhouse gas emissions from agriculture.
Environmental Science & Policy, 1999
The IPCC Guidelines for National Greenhouse Gas Inventories provide default methodologies for estimating emissions of the most important greenhouse gases at a national scale. The methodology for estimating emissions of nitrous oxide (N 2 O) from agriculture was revised in 1996 by an international working group. Here we summarize this new methodology and apply it to the global data. The new method aims at assessing the full nitrogen cycle and takes into account N 2 O formation in agricultural ®elds (direct emissions), animal waste management systems (AWMSs) as well as indirect emissions taking place at remote places after nitrogen is lost from the agricultural ®elds. Using the IPCC method, we estimated that global agricultural N 2 O emissions almost doubled between 1960 (3.5 Tg N 2 ON) and 1994 (6.2 Tg N 2 ON). Direct emissions, animal waste management systems and indirect emissions make about equal contribution to total current emissions.