Total Annual N2O Research Articles

Effects of Controlled-release Blended Fertilizer on Crop Yield and Greenhouse Gas Emissions in Wheat-maize Rotation System

The increasing use of nitrogen fertilizers exerts extreme pressure on the environment (e.g., greenhouse gas emissions, GHGs) for winter wheat-summer maize rotation systems in the North China Plain. The application of controlled-release fertilizers is considered as an effective measure to improve crop yield and nitrogen fertilizer utilization efficiency. To explore the impact of one-time fertilization of controlled-release blended fertilizer on crop yield and GHGs of a wheat-maize rotation system, field experiments were carried out in Dezhou Modern Agricultural Science and Technology Park from 2020 to 2022. Five treatments were established for both winter wheat and summer maize, including no nitrogen control (CK), farmers' conventional nitrogen application (FFP), optimized nitrogen application (OPT), CRU1 (the blending ratio of coated urea and traditional urea on winter wheat and summer maize was 5:5 and 3:7, respectively), and CRU2 (the blending ratio of coated urea and traditional urea on winter wheat and summer maize was 7:3 and 5:5, respectively). The differences in yield, nitrogen fertilizer utilization efficiency, fertilization economic benefits, and GHGs among different treatments were compared and analyzed. The results showed that nitrogen application significantly increased the single season and annual crop yields of the wheat-maize rotation system (P < 0.05). Compared with those of FFP, the CRU1 and CRU2 treatments increased the yields of summer maize by 0.4% to 5.6%, winter wheat by -5.4% to 4.1%, and annual yields by -1.1% to 3.9% (P > 0.05). N recovery efficiency (NRE), N agronomic efficiency (NAE), and N partial factor productivity (NPFP) were increased by -8.6%-43.4%, 2.05-6.24 kg·kg-1, and 4.24-10.13 kg·kg-1, respectively. Annual net income increased by 0.2% to 6.3%. Nitrogen application significantly increased the annual emissions of soil N2O and CO2 in the rotation system (P < 0.05) but had no effect on the annual emissions of CH4 (except for in the FFP treatment in the first year). The annual total N2O emissions under the CRU1 and CRU2 treatments were significantly reduced by 23.4% to 30.2% compared to those under the FFP treatment (P < 0.05). Additionally, nitrogen application significantly increased the annual global warming potential (GWP) of the rotation system (P < 0.05), but the intensity of greenhouse gas emissions was reduced due to the increase in crop yields. Compared with that under FFP, the annual GWP under the CRU1 and CRU2 treatments decreased by 9.6% to 11.5% (P < 0.05), and the annual GHGs decreased by 11.2% to 13.8% (P > 0.05). In summary, the one-time application of controlled-release blended fertilizer had a positive role in improving crop yield and economic benefits, reducing nitrogen fertilizer input and labor costs, and GHGs, which is an effective nitrogen fertilizer management measure to promote cleaner production of food crops in the North China Plain.

Methane and Nitrous Oxide Fluxes with Different Land Uses in the Temperate Meadow Steppe of Inner Mongolia, China

Background and aims: Grazing and mowing are widely adopted management practices for the semiarid steppe in China that profoundly affect the greenhouse gas (GHG) flux in grassland ecosystems. However, the general mechanisms for CH4 and N2O fluxes in response to grazing and mowing remain poorly understood. Thus, we conducted year-round flux measurements of CH4 and N2O fluxes to investigate the effect of grazing and mowing on CH4 and N2O fluxes. Methods: Using manual static chamber and gas chromatography, we measured the fluxes of CH4 and N2O from grazing-exclusion, grazing and mowing sites from June 2019 to June 2020 in the Hulunbuir Grassland, Inner Mongolia. Results: Grazing and mowing increased soil temperature and reduced soil water content and soil inorganic N content. Compared with grazing and mowing, lower mean CH4 uptake (−67.58 ± 8.9 μg m−2 h−1) and higher mean N2O emissions (29.17 ± 6.8 μg m−2 h−1) were found at the grazing-exclusion site. No pulse emissions of N2O were found for all sites during the spring thaw period (STP), and only two small N2O emission peaks due to soil thawing were captured on April 2nd and 5th. The contribution of the spring thaw to the total annual N2O budget was small and accounted for only 10%, 13% and 12% of the annual fluxes at the grazing-exclusion, grazing and mowing sites, respectively. Conclusion: Our results indicate that grazing and mowing enhance CH4 uptake and inhibit N2O emissions, primarily due to the increased soil temperature and reduced soil water content and soil inorganic N content. No apparent pulse N2O emissions were observed at any of the three sites during the STP in the Hulunbuir grassland.

Response of N2O emissions to biochar amendment on a tea field soil in subtropical central China: A three-year field experiment

High inputs of fertilizer nitrogen (N) in tea fields lead to declining soil pH and high emissions of N2O. Amending the soil with biochar can potentially reduce N2O emissions and alleviate soil acidification. To assess the multi-year effects of wheat straw-derived biochar on N2O emissions and tea yield in tea fields, a three-year (2014–2016) field trial following the wheat straw-derived biochar addition was conducted in a tea plantation in southern China under three treatments, namely, conventional treatment (CON, application of conventional organic-chemical fertilizer without biochar), and treatments with conventional organic-chemical fertilizer + straw-derived biochar addition at 10 t ha−1 (BC10) and 40 t ha−1 (BC40) applied once at the beginning of the experiment. Compared to BC10 treatment, the annual total N2O emissions of BC40 were increased by 32.0–46.2% in 2015 and 2016 (p ＜ 0.05) while no significant difference was found between BC10 and CON (p = 0.32–0.97), and N2O emissions of BC10 showed a declined trend during the three years. An increase in tea yield of 24.2–26.0% (p ＜ 0.05) was also observed in BC10 treatment in 2015 and 2016 relative to CON. Differences between treatments in NH4+-N were mostly significant (p ＜ 0.05) but not in NO3--N and DOC (p = 0.16–0.81). The BC40 treatment significantly raised soil pH relative to the CON (p < 0.05). Our collective data indicated that N2O fluxes were positively correlated with the abundance of nirK-denitrification gene during the tea-growing season (p ＜0.05). Long-term impact of straw-derived biochar amendment on N2O was inconsistent with previous short-term biochar studies in tea field soil. Our results indicated that wheat straw-derived biochar amendment at a low rate (BC10) into tea field soil is more feasible for reducing yield-scale N2O emissions in the studied tea field system.

Effects of Nitrogen Fertilizer and Straw Returning Methods on N2O Emissions in Wheat-Maize Rotational Soils

In order to explore the impacts of nitrogen fertilizer and straw returning methods on N2O emissions, a two-factor split-zone design was adopted for experimentation under the winter wheat-summer maize rotation model in the Guanzhong area of Shanxi, China. The main areas of interest were conventional nitrogen (G) and reduced nitrogen (70% G); the sub-areas were straw no return (N), straw return (S), and straw return + biochar (SB); we analyzed their impacts on N2O emissions and crop yield, and the relationships with related impact factors. The results showed that the N2O emissions peaks appeared in the wheat season and maize season treatments within 5-16 days after fertilization, and also appeared after rainfall. The N2O flux was significantly and positively correlated with soil temperature and NH4+-N content. Regardless of the wheat season, maize season, or annual total N2O emissions, the 70% GSB treatment was the lowest and the GS treatment was the highest. At the same level of nitrogen application, S treatment increased N2O emissions, SB treatment could reduce N2O emissions, both S and SB treatments could significantly increase crop yields, and SB production increased more; 70%G-level annual N2O emissions, when compared with the G level, had been reduced by 40% to 48%, while the yield has not decreased significantly. Through comprehensive consideration, a reduction of nitrogen by 30% was achieved through the combination of straw + biochar on the basis of conventional nitrogen application, while ensuring high crop yields and the best N2O emissions reduction.

Effects of Different Rotation Patterns of Oil-Rice on Methane and Nitrous Oxide Emissions in Rice Fields

A field experiment was carried out to investigate the effects of different rice-rape rotation systems on methane and nitrous oxide emissions, which were measured using the static chamber/gas chromatography method, prediction of their global warming potentials (GWP), and greenhouse gas intensity (GHGI) in paddy fields. The results showed that the average cumulative emissions of CH4from a double cropping paddy field, single season rice field (including middle or late), rape field, and leisure land were 135.25, 55.64, 5.05, and 1.89 kg ·hm-2, respectively. The CH4 emission during the rice season accounted for 91.8%-98.5% of the annual CH4 emission in different rotation years, and the contents of dissolved organic carbon in paddy soil exhibited a significantly positive correlation with CH4 emission. The CH4 emission in conventional late rice paddy was 18.7% higher than that of hybrid late rice paddy (P<0.05). The average cumulative emissions of N2O from double cropping paddy field, single season rice field (including middle or late), rape field, and leisure land were 0.94, 0.64, 1.38, and 0.24 kg ·hm-2, respectively. Out of the total annual N2O emission, 57.2% to 70.2% was from the rape field; 17.8% and 30.6% was due to the winter fallow treatments with previous crop type of double corpping rice and single season rice, respectively. There was no significant difference in N2O emission between hybrid rice and conventional rice paddy fields. The GWP of double cropping rice-winter fallow and double cropping rice-rape was higher than that of rice-rape and rice-winter fallow, and the GWP of CH4 in rice season accounted for 71.2% to 90.9% of the annual GWP of rotation. The highest treatment of GHGI was rice-rice-rape, and the treatment of rice-oil and rice-winter slack was lower. According to the comprehensive environmental and economic benefits, the late hybrid rice-rape patterns should be selected to reduce greenhouse gases in multiple cropping rice fields of South China.

Nitrous oxide (N&amp;lt;sub&amp;gt;2&amp;lt;/sub&amp;gt;O) and methane (CH&amp;lt;sub&amp;gt;4&amp;lt;/sub&amp;gt;) in rivers and estuaries of northwestern Borneo

Abstract. Nitrous oxide (N2O) and methane (CH4) are atmospheric trace gases which play important roles in the climate and atmospheric chemistry of the Earth. However, little is known about their emissions from rivers and estuaries, which seem to contribute significantly to the atmospheric budget of both gases. To this end concentrations of N2O and CH4 were measured in the Rajang, Maludam, Sebuyau and Simunjan rivers draining peatland in northwestern (NW) Borneo during two campaigns in March and September 2017. The Rajang River was additionally sampled in August 2016 and the Samunsam and Sematan rivers were additionally sampled in March 2017. The Maludam, Sebuyau, and Simunjan rivers are typical “blackwater” rivers with very low pH (3.7–7.8), very high dissolved organic carbon (DOC) concentrations (235–4387 mmol L−1) and very low O2 concentrations (31–246 µmol L−1; i.e. 13 %–116 % O2 saturation). The spatial and temporal variability of N2O and CH4 concentrations (saturations) in the six rivers or estuaries was large and ranged from 2.0 nmol L−1 (28 %) to 41.4 nmol L−1 (570 %) and from 2.5 nmol L−1 (106 %) to 1372 nmol L−1 (57 459 %), respectively. We found no overall trends of N2O with O2 or NO3-, NO2- or NH4+, and there were no trends of CH4 with O2 or dissolved nutrients or DOC. N2O concentrations showed a positive linear correlation with rainfall. We conclude, therefore, that rainfall is the main factor determining the riverine N2O concentrations since N2O production or consumption in the blackwater rivers themselves seems to be low because of the low pH. CH4 concentrations were highest at salinity = 0 and most probably result from methanogenesis as part of the decomposition of organic matter under anoxic conditions. CH4 in the concentrations in the blackwater rivers showed an inverse relationship with rainfall. We suggest that CH4 oxidation in combination with an enhanced river flow after the rainfall events might be responsible for the decrease in the CH4 concentrations. The rivers and estuaries studied here were an overall net source of N2O and CH4 to the atmosphere. The total annual N2O and CH4 emissions were 1.09 Gg N2O yr−1 (0.7 Gg N yr−1) and 23.8 Gg CH4 yr−1, respectively. This represents about 0.3 %–0.7 % of the global annual riverine and estuarine N2O emissions and about 0.1 %–1 % of the global riverine and estuarine CH4 emissions. Therefore, we conclude that rivers and estuaries in NW Borneo – despite the fact their water area covers only 0.05 % of the global river/estuarine area – contribute significantly to global riverine and estuarine emissions of N2O and CH4.

Nitrous oxide emissions from China's croplands based on regional and crop-specific emission factors deviate from IPCC 2006 estimates

Calculated N2O emission factors (EFs) of applied nitrogen (N) fertilizer are currently based upon a single, universal value advocated by the IPCC (Inter-governmental Panel on Climate Change) even though EFs are thought to vary with climate and soil types. Here, we compiled and analyzed 151 N2O EF values from agricultural fields across China. The EF of synthetic N applied to these croplands was 0.60%, on average, but differed significantly among six climatic zones across the country, with the highest EF found in the north subtropical zone for upland fields (0.93%) and the lowest in the middle subtropical zone for paddy fields (0.20%). Precipitation and soil pH, which showed non-linear relationships with EF, are among the factors governing it, explaining 7.0% and 8.0% of the regional variation in EFs, respectively. Annual precipitation was the key factor regulating N2O emissions from synthetic N fertilizers. Among crop types, legume crops had the highest EFs, which were significantly (P < 0.05) higher than those of cereals. Total soil N2O emissions from fertilized croplands with maize, rice, wheat, and vegetables in China, calculated using the climatic zone (regional) EFs, were estimated to be 239 Gg N yr−1 with an uncertainty of 21%. Importantly, this value was substantially (33%) lower than that (357 Gg N yr−1) derived from the IPCC default EF but close to the 253 Gg N yr−1 estimated using crop-specific EFs. N2O emissions from applied synthetic N fertilizer accounted for 66.5% of the total annual N2O emissions from China's maize, rice, wheat and vegetable fields. Taken together, our study's results strongly suggest that regional EFs should be included for accurate N2O inventories from croplands across China.

Effects of biochar amendment on net greenhouse gas emissions and soil fertility in a double rice cropping system: A 4-year field experiment

A 4-year field experiment was conducted to investigate the effects of biochar amendment on the net greenhouse gas emission (NGHGE), greenhouse gas intensity (GHGI), soil fertility and crop yield in a typical double rice cropping system in the central subtropics of China, from April 2012 to April 2016. Three biochar treatments were studied in this experiment, with application rates of 0, 24 and 48 t ha−1 (named CK, LB and HB, respectively) using straw-derived biochar applied once at the beginning of the experiment. In each treatment, the fluxes of methane (CH4), nitrous oxide (N2O) and soil heterotrophic respiration (Rh) were measured using a static chamber/gas chromatography method. Major soil fertility properties were also determined throughout the experimental period. Biochar amendment was found to persistently decrease annual total CH4 emissions by 20 to 51% in the four years, but increased the annual total N2O emissions and Rh by 150 to 190% and 2 to 19% in the first year and the following three years, respectively. On a 4-year average, biochar addition significantly reduced annual NGHGE and GHGI by 156 to 264% and 159 to 278%, respectively (p < 0.05), with much higher reduction in the first year than those in the following three years (916 to 1911% vs 24 to 51%) due to soil carbon sequestration from biochar addition in the first year. The reduction of NGHGE and GHGI was mainly caused by the decrease of CH4 emissions (71 to 74% contribution), and the increase of soil carbon sequestration (25 to 29% contribution) in biochar treatments. Biochar amendment also significantly and persistently increased soil pH, total organic carbon (TOC), total nitrogen (TSN), and total phosphorus (TSP) by 6 to 14%, 33 to 61%, 11 to 15%, and 9 to 12%, respectively (p < 0.05), in the four years. Significant increases (p < 0.05) of microbial biomass carbon and nitrogen contents were found only in the first year after biochar amendment. Soil pH was also increased significantly (p < 0.05) with biochar amendment, but showed a declining trend in the four years. Annual grain yields for the biochar treatments were enhanced by 1 to 13%, with an average of 4 to 7% in the four years, compared to CK (p = 0.07–0.26). Compared to the LB treatment, the HB treatment significantly decreased average NGHGE and GHGI, and significantly increased average soil pH value and TOC content, but there was no significantly difference in average TSN, TSP, and yield between LB and HB treatments (p < 0.05). The gross margin analysis by considering the profit from rice grain, gain for NGHGE, and cost for biochar indicated that the economical profit for the LB treatment might be higher than that for the CK and HB treatments. Our results suggest that addition of biochar at 24 t ha−1 can be regarded as a consistently effective and economic measure for greenhouse gas emission mitigation, and soil fertility improvement, in the double rice cropping system.

Assessing Short‐Term Impacts of Management Practices on N2O Emissions From Diverse Mediterranean Agricultural Ecosystems Using a Biogeochemical Model

AbstractCroplands are important sources of nitrous oxide (N2O) emissions. The lack of both long‐term field measurements and reliable methods for extrapolating these measurements has resulted in a large uncertainty in quantifying and mitigating N2O emissions from croplands. This is especially relevant in regions where cropping systems and farming management practices (FMPs) are diverse. In this study, a process‐based biogeochemical model, DeNitrification‐DeComposition (DNDC), was tested against N2O measurements from five cropping systems (alfalfa, wheat, lettuce, vineyards, and almond orchards) representing diverse environmental conditions and FMPs. The model tests indicated that DNDC was capable of predicting seasonal and annual total N2O emissions from these cropping systems, and the model's performance was better than the Intergovernmental Panel on Climate Change emission factor approach. DNDC also captured the impacts on N2O emissions of nitrogen fertilization for wheat and lettuce, of stand age for alfalfa, as well as the spatial variability of N2O fluxes in vineyards and orchards. DNDC overestimated N2O fluxes following some heavy rainfall events. To reduce the biases of simulating N2O fluxes following heavy rainfall, studies should focus on clarifying mechanisms controlling impacts of environmental factors on denitrification. DNDC was then applied to assess the impacts on N2O emissions of FMPs, including tillage, fertilization, irrigation, and management of cover crops. The practices that can mitigate N2O emissions include reduced or no tillage, reduced N application rates, low‐volume irrigation, and cultivation of nonleguminous cover crops. This study demonstrates the necessity and potential of utilizing process‐based models to quantify N2O emissions from regions with highly diverse cropping systems.

Annual N2O emissions from conventionally grazed typical alpine grass meadows in the eastern Qinghai–Tibetan Plateau

Annual nitrous oxide (N2O) emissions from high-altitude alpine meadow grasslands have not been effectively characterized because of the scarcity of whole-year measurements. The authors performed a year-round measurement of N2O fluxes from three conventionally grazed alpine meadows that represent the typical meadow landscape in the eastern Qinghai–Tibetan Plateau (QTP). The results showed that annual N2O emissions averaged 0.123±0.053 (2SD, i.e., the double standard deviation indicating the 95% confidence interval) kgNha−1yr−1 across the three meadow sites. N2O flux pulses during the spring freezing-thawing period (FTP) were observed at only one site, indicating a large spatial variability in association with soil moisture differences. Approximately 34–57% (mean: 46%) of the annual N2O emissions occurred in the non-growing season, highlighting the substantial importance of accurate flux observations during this period. The simultaneous observations showed conservative, marginal nitric oxide (NO) fluxes of 0.058±0.032 (2SD) kgNha−1yr−1. The N2O fluxes across the three field sites correlated negatively with the soil nitrate concentrations during the entire year-round period (P<0.05). Furthermore, a significant joint regulatory effect of topsoil temperature and moisture on the N2O and NO fluxes was observed during the relatively warm periods. Based on the results of the present and previous studies, a simple extrapolation roughly estimated the annual total N2O emission from Chinese grasslands to be 73±15 (2SD) GgNyr−1 (1Gg=109g). A linear dependence of the annual N2O fluxes on the aboveground net primary productivity (ANPP) was also found. This result may provide a simple approach for estimating the N2O emission inventories of frigid alpine or temperate grasslands that are ungrazed either in the summer or year round. However, further confirmation of this relationship with a wider ANPP range is still needed in the future studies.

Impact of CULTAN fertilization with ammonium sulfate on field emissions of nitrous oxide

Agricultural soils have a great share on global nitrous oxide (N2O) emissions. The method of nitrogen fertilization is a manageable control parameter of N2O production in soil. Controlled uptake long-term ammonia nutrition (CULTAN) intends to aliment field growing crops mainly with ammonium instead of nitrate, aiming at a better N use efficiency and less N leaching by placing ammonium-based N fertilizer in highly concentrated depots in the soil. In this two years field study, we analyzed N2O flux rates and dynamics of mineral N in soils after injection of ammonium sulfate solution (CULTAN) and conventional surface application of the same fertilizer type (ammonium sulfate at a rate of 130kgNha−1) to winter wheat at two sites with different soil texture. Using 15N-ammonium as a tracer, we additionally measured fertilizer-derived emissions and fertilizer N uptake at one CULTAN plot.Grain yields were higher after CULTAN fertilization than after surface application of N fertilizer; significantly so in one year at each site. Neither N uptake nor N use efficiency were consistently different between fertilization methods. Nitrate accumulation in CULTAN treated plots occurred after fertilizer injection, showing that the concentrated NH4+ depots did not sufficiently inhibit nitrification. Total annual N2O emission ranged from 0.29 to 1.9kgNha−1yr−1, with higher emissions from fertilized than unfertilized plots, but no significant difference between fertilizer application methods. N2O emission was higher at the loam than the sandy loam site, with twice as high annual emission at the loam site (1.2±0.5kgNha−1yr−1) compared to the sandy loam site (0.6±0.2kgNha−1yr−1) after CULTAN fertilization. Temporal N2O emission dynamics were influenced by weather conditions (i.e., thawing of soil) and irrigation and could partly be explained by changes in soil moisture and soil mineral N. With only 1–17% of total annual fluxes at the 15N CULTAN plot, fertilizer-derived N2O emissions were small, highlighting the dominance of soil N for N2O emission.In terms of N2O emission, CULTAN fertilization did thus not proof beneficial over surface application of the same fertilizer.

Nitrous oxide emissions from an agro-pastoral ecotone of northern China depending on land uses

Overgrazing and intensive farming have led to severe land degradation in the past half century in the agro-pastoral ecotone of northern China. Currently, complete and periodical exclusions of grazing are commonly adopted for the restoration of these degraded grasslands. However, little is known about the effects of such land uses on nitrous oxide (N2O) emission in this region. Using static chamber technique, we quantified annual N2O emissions (from May 2012 to September 2013) from four land uses: summer-grazed grassland (SG), winter-grazed grassland (WG), ungrazed grassland since 1997 (UG) and oat cropland (OC). N2O emissions occurred mainly after farmyard manure fertilization and during spring thaw periods. Annual N2O fluxes from the SG, WG, UG and OC were 0.19, 0.15, 0.43 and 0.98kg Nha−1yr−1, respectively. The spring–thaw N2O emissions from UG and OC dominated the annual emission and accounted for 70% and 65% of the annual fluxes, respectively. In contrast, the contributions of spring thaw fluxes to total annual N2O emissions for SG and WG were only 32%. N2O fluxes during spring thaw season were positively related to soil NH4++ NO3− content accounting for 80% of N2O flux variability across all land uses. Land use conversion from the native grassland to cropland increased N2O flux both during growing and spring thaw seasons due to farmyard manure application. Instead, grazing has the potential to decrease annual N2O losses mainly through reducing spring–thaw N2O emissions.

Comparison of Net Global Warming Potential and Greenhouse Gas Intensity Affected by Management Practices in Two Dryland Cropping Sites

Little is known about the effect of management practices on net global warming potential (GWP) and greenhouse gas intensity (GHGI) that account for all sources and sinks of greenhouse gas (GHG) emissions in dryland cropping systems. The objective of this study was to compare the effect of a combination of tillage, cropping system, and N fertilization on GWP and GHGI under dryland cropping systems with various soil and climatic conditions from 2008 to 2011 in western North Dakota and eastern Montana, USA. Treatments in western North Dakota with sandy loam soil and 373 mm annual precipitation were conventional till malt barley (Hordeum vulgarie L.) with 67 kg N ha-1 (CTB/N1), conventional till malt barley with 0 kg N ha-1 (CTB/N0), no-till malt barley-pea (Pisum sativum L.) with 67 kg N ha-1 (NTB-P/N1), no-till malt barley with 67 kg N ha-1 (NTB/N1), and no-till malt barley with 0 kg N ha-1 (NTB/N0). In eastern Montana with loam soil and 350 mm annual precipitation, treatments were conventional till malt barley-fallow with 80 kg N ha-1 (CTB-F/N1), conventional till malt barley-fallow with 0 kg N ha-1 (CTB-F/N0), no-till malt barley-pea with 80 kg N ha-1 (NTB-P/N1), no-till malt barley with 80 kg N ha-1 (NTB/N1), and no-till malt barley with 0 kg N ha-1 (NTB/N0). Carbon dioxide sink as soil C sequestration rate at the 0 - 10 cm depth was greater in NTB-P/N1 and NTB/N1 than the other treatments at both sites and greater in eastern Montana than western North Dakota. Carbon dioxide sources were greater with N fertilization than without and greater with conventional till than no-till. Soil total annual N2O and CH4 fluxes varied among treatments, years, and locations. Net GWP and GHGI were lower in NTB-P/N1 than the other treatments in western North Dakota and lower in NTB-P/N1 and NTB/N1 than the other treatments in eastern Montana. Net GWP across similar treatments was lower in eastern Montana than western North Dakota, but GHGI was similar. Annualized crop yield was greater in the treatments with N fertilization than without. Because of greater grain yield but lower GWP and GHGI, no-till malt barley-pea rotation with adequate N fertilization can be used as a robust management practice to mitigate net GHG emissions while sustaining dryland crop yields, regardless of soil and climatic conditions. Loam soil reduced GWP and crop yields compared with sandy loam soil.

Nitrous oxide and methane emissions from a vetch cropping season are changed by long-term tillage practices in a Mediterranean agroecosystem

Lower greenhouse gas (GHG) emissions from legume-based cropping systems have encouraged their use to deliver mitigation in agricultural systems. Considerable uncertainties remain about the interaction of legumes with long-term tillage systems on GHG emissions under rainfed agroecosystems. In this context, a field experiment was undertaken under a rainfed vetch crop to evaluate the effect of three long-term tillage systems (i.e. no tillage (NT), minimum tillage (MT) and conventional tillage (CT)) on nitrous oxide (N2O) and methane (CH4) emissions for 1 year. Different N2O flux patterns were observed among tillage systems during the growth period of vetch, which depended on the soil conditions favouring nitrification and denitrification. The NT system maintained a higher sink for N2O than MT and CT from January to mid-April, which significantly reduced N2O emissions at this stage. In this period, denitrification capacity and nirK gene numbers were higher for MT than NT and CT. Additionally, an increase in soil NO3− content and more favourable denitrification conditions in MT and NT than in CT for the last crop period increased N2O emissions in conservation tillage systems. Total annual N2O losses were significantly higher in MT (124.2 g N2O–N ha−1) than NT (51.1 g N2O–N ha−1) and CT (54 g N2O–N ha−1) in a vetch crop. Low net uptake of CH4 was observed for all tillage systems. These results suggested that long-term NT may be a better option than MT to mitigate GHG emissions in rainfed legume-cereal rotation.

Two-year simultaneous records of N2O and NO fluxes from a farmed cropland in the northern China plain with a reduced nitrogen addition rate by one-third

Given the common problem of fertilizer overuse, agronomists are calling for a reduction of the high nitrogen dose by 1/3. We carried out a field experiment over two full winter wheat–summer maize rotations in the North China Plain (NCP) to determine whether this degree of nitrogen reduction will significantly reduce the emissions of nitrous oxide (N2O) and nitric oxide (NO). Three treatments were investigated in the field trial: a control with no nitrogen application, the conventional practice with nitrogen over-application and the optimal practice with a reduced dose of nitrogen by 1/3. Our observations across all treatments over the experimental period reveal significant correlations of the fluxes of either gas with soil temperature and moisture as well as the concentrations of soil ammonium, nitrate and dissolvable organic carbon. There were strong correlations within the functions of the dual Arrhenius and Michaelis–Menten kinetics, giving apparent activation energy values of 40–97 and 59–92kJmol−1 for N2O and NO fluxes, respectively. Our results provide annual direct emission factors of 0.48–0.96% for N2O and 0.15–0.47% for NO and demonstrate a significant correlation between N2O emission induced by fertilization and fertilizer nitrogen use efficiency (NUE). The correlation indicates a significant potential of N2O mitigation via enhancing NUEs. A reduction in the nitrogen dose did not obviously mitigate either the annual NO emission in both rotations or the annual N2O emission in the second one. However, nitrogen reduction significantly decreased the annual total N2O emission by 38% during the first rotation. These inconsistencies in the responses of N2O emission to the reduced nitrogen dose can be attributed to improper fertilization practices, such as broadcasting urea prior to heavy rainfalls or irrigation events during the maize season, which implies a need for further fertilization practice options/techniques in addition to the reduction of nitrogen doses.

Effects of flooding-induced N2O production, consumption and emission dynamics on the annual N2O emission budget in wetland soil

Rapid flooding of wetland soil promotes subsurface N2O production in the soil and potential emission to the atmosphere in distinctive emission pulses. Changes in flooding frequency of wetland soil following future climate change will likely affect the timing and magnitude of nitrous oxide (N2O) emissions from the soil to the atmosphere. From October 2009 to October 2010, rapid flooding of a natural Danish wetland was observed twice in response to high precipitation events. A flooding-induced N2O emission pulse (delay ∼16 h; duration ∼12 h; total emission 1.83 mg N2O–N m−2, max. emissions ∼250 μg N2O–N m−2 h−1) was observed when the soil conditions in the top soil had been oxidized for more than 2–3 weeks prior to flooding. This flooding-induced N2O emission pulse constituted ∼2.5% of the annual net N2O emissions of 0.74 kg N2O–N ha−1 yr−1. A net uptake of atmospheric N2O was observed during mid-summer when the WL was at its seasonally lowest counterbalancing ∼6.4% of the total annual net N2O emission budget. Main surface emission periods of N2O were observed when the water level and associated peaks in subsurface N2O concentrations were gradually decreasing to soil depths down to 40 cm below the surface. These surface emission patterns are predominantly linked to variations in plant-mediated gas transport via Phalaris arundinacea and N2O producing/consuming processes in the root zone. Soil flooding experiments using high-resolution N2O microsensors demonstrate very large N2O production and consumption capacities where >500 nmol N2O cm−3 were sequentially produced and consumed in less than 24 h. It is concluded that a higher future frequency of flooding-induced N2O emissions will have a very limited effect on the net annual N2O emission budget as long as NO3− availability in the soil prior to rapid flooding is not dramatically increased.

No significant nitrous oxide emissions during spring thaw under grazing and nitrogen addition in an alpine grassland

AbstractA recent study (Wolf et al., 2010) suggests that short—lived pulses of N2O emission during spring thaw dominate the annual N2O budget and that grazing decreases N2O emissions during the spring thaw. To verify this we conducted year—round N2O flux measurements from June 2010 to May 2011 in Tianshan alpine grassland in central Asia. No pulse emissions of N2O were found at grazing management sites and nitrogen addition sites during the spring thaw. The contribution of the spring thaw to the total annual N2O budget was small and accounted for only 6.6% of the annual fluxes, with winter emissions accounting for 16.7% and growing season emissions accounting for 76.7%. The difference in N2O emissions attributable to grazing management was not significant (P &gt; 0.05). Nitrogen input tended to increase N2O emissions at N addition sites during the grass growing season compared with those at unfertilized sites. N2O fluxes showed a significant correlation with air temperature and also with both soil temperature and soil water content at 10 cm depth.

Regional sources of nitrous oxide over the United States: Seasonal variation and spatial distribution

This paper presents top‐down constraints on the magnitude, spatial distribution, and seasonality of nitrous oxide (N2O) emissions over the central United States. We analyze data from tall towers in 2004 and 2008 using a high resolution Lagrangian particle dispersion model paired with both geostatistical and Bayesian inversions. Our results indicate peak N2O emissions in June with a strong seasonal cycle. The spatial distribution of sources closely mirrors data on fertilizer application with particularly large N2O sources over the US Cornbelt. Existing inventories for N2O predict emissions that differ substantially from the inverse model results in both seasonal cycle and magnitude. We estimate a total annual N2O budget over the central US of 0.9–1.2 TgN/yr and an extrapolated budget for the entire US and Canada of 2.1–2.6 TgN/yr. By this estimate, the US and Canada account for 12–15% of the total global N2O source or 32–39% of the global anthropogenic source as reported by the Intergovernmental Panel on Climate Change in 2007.

Non-growing season nitrous oxide fluxes from an agricultural soil as affected by application of liquid and composted swine manure

Kariyapperuma, K. A., Furon, A. and Wagner-Riddle, C. 2012. Non-growing season nitrous oxide fluxes from an agricultural soil as affected by application of liquid and composted swine manure. Can. J. Soil Sci. 92: 315–327. Agricultural soils have been recognized as a significant source of anthropogenic nitrous oxide (N2O) emissions, an important greenhouse gas and contributor to stratospheric ozone destruction. Application of liquid swine manure (LSM) has been reported to increase direct N2O emissions from agricultural soils. Composting of LSM with straw under forced aeration has been suggested as a mitigation practice for emissions of N2O. In cold climates, up to 70% of total annual soil N2O emissions have been observed during winter and spring thaw. Non-growing season soil N2O emissions after field application of composted swine manure (CSM) versus LSM have not been directly compared in past studies. A 2-yr field experiment was conducted at the Arkell Research Station, Ontario, Canada, as a part of a larger study to evaluate composting as a mitigation strategy for greenhouse gases (GHGs). The objectives were to quantify and compare non-growing season N2O fluxes from agricultural soils after fall application of LSM and CSM. Nitrous oxide fluxes were measured using the flux-gradient method. Compared with LSM, CSM resulted in 57% reduction of soil N2O emissions during February to April in 2005, but emissions during the same period in 2006 were not affected by treatments. This effect was related to fall and winter weather conditions with the significant reduction occurring in the year when soil freezing was more pronounced. Compared with LSM, CSM resulted in a reduction of 37% (CO2-eq) of estimated N2O emissions per liter of treated manure and of 50% in the emission factor for the non-growing season.

Nitrous oxide emissions from a typical northern Chinese municipal wastewater treatment plant

Nitrous oxide (N2O) emissions from a typical full-scale tertiary municipal wastewater treatment plant (WWTP) in northern China were investigated during spring and summer of 2010. Results showed that the major emission sources of N2O performed the following descending order: oxic tanks, final clarifier tanks, anoxic tanks, sludge concentration tanks and anaerobic tanks. The total annual N2O flux from the oxic tanks was the highest and accounted for the majority of total N2O emissions of this WWTP. The emission factors derived from the field measurements included per capita emissions of 1.73–2.19g of N2O person–1 y–1 and flow based emissions of 2.37×10–5–3.01×10–5 g of N2O (L of wastewater) –1. The N2O emissions accounted for approximately 0.10%–0.13% of the total nitrogen removed in this WWTP. The most significant factors influencing N2O emissions in this plant were dissolved oxygen concentration and nitrite concentration in the oxic tanks.