N2O Emission Peaks Research Articles

Nitrous oxide emission in autotrophic partial nitritation system: Macro- and microanalyses

A laboratory-scale sequencing batch reactor fed with synthetic high-ammonium wastewater was operated for autotrophic partial nitritation, and the characteristics of N2O emission were investigated by both macro- and microanalysis. A N2O emission quantity of 5.98±1.24mg (n=17) was observed, accounting for 0.997%±0.408% of the influent nitrogen. The N2O level in the off-gas first increased to a maximum of 91.5 ppmv in the initial 50min, and then decreased and remained around 34.8 ppmv until the end of aeration. An asymptotic function (y=14.3-14.2×0.992(x), R(2)=0.997) could be used to estimate the quantity of N2O emitted. Microelectrodes were used to explore the variations in the nitrogen distribution and consumption rate within sludge flocs as the reaction proceeded. During the aeration phase, partial nitritation occurred mainly in the surface layer of flocs. This is where most N2O was produced, indicating that N2O was generated as a byproduct of the nitritation. During the settling phase, the N2O concentration and volumetric production rate were much higher than those in the aeration phase, suggesting that the settling phase contributes to the initial N2O emission peak.

Response of N2O emission to water and nitrogen addition in temperate typical steppe soil in Inner Mongolia, China

The Chinese steppe is undergoing a drastic increase in nitrogen (N) deposition, and the precipitation in this region is predicted to increase. However, the response of soil N2O emissions to the coupling changes of precipitation and N deposition in grassland ecosystem has been seldom discussed. A manipulative field experiment was conducted to investigate the individual and interactive effects of precipitation increase and N deposition on soil N2O efflux in semi-arid temperate grassland in Inner Mongolia during the growing seasons of 2010 and 2011.The treatments included four N addition levels [20gNm−2y−1 (N20), 10gNm−2y−1 (N10), 5gNm−2y−1 (N5), and a zero-N control (CK)] and two water application levels [natural precipitation for dry (D) and 15% increase of long-term mean annual precipitation for wet (W) treatments]. Results indicated that N and water addition both significantly increased soil N2O effluxes (P<0.01). The maximum N2O emissions were observed within 2–3 days after N addition to all treatments, and the N2O effluxes in W treatments were generally higher than in D treatments for the same N input level. For the treatments without N inputs, the N2O emission peak of WCK was 9.8% higher than DCK in 2010. The effect of water addition on N2O emission was more evident when more N fertilizer was applied. For the high N input treatments, the maximum N2O emission of WN20 treatment was 222.6% higher than DN20 in 2010. The changes in N and water availabilities accounted for 91.3% (2010) and 75.6% (2011) of the N2O cumulative efflux variation among different treatments (P<0.01). The N2O effluxes were significantly affected by the interactive effect between N and water in 2010 and 2011 (P<0.05). Significant interannual variability in the cumulative N2O emissions was observed, the cumulative N2O emissions in 2011 were significantly lower than those in 2010 even though the summer of 2011 experienced higher rainfall (P<0.01). Temperature also significantly influenced soil N2O emission apart from the effects of water and N. The temperature change accounted for 41.3% (W) to 47.2% (D) of the temporal variations in N2O emission during the relatively dry 2010. The combined changes in soil moisture, NH4+-N, and temperature accounted for 43.1% (D) to 54.5% (W) of the temporal variations in N2O emission in the relatively wet year of 2011.

Influence mechanism of controlled irrigation on N&amp;#60;sub&amp;#62;2&amp;#60;/sub&amp;#62;O emissions from paddy fields

In order to study the effects of controlled irrigation (CI) on seasonal variations of N2O emissions from paddy fields, N2O emissions from CI paddy fields were investigated by the method of static chamber/gas chromatography. Soil moisture, soil temperature and soil redox potential (Eh) were also measured. The quantitative relationships between N2O emissions and affecting factors were analysed. Soil drying incurred substantial N2O emissions, while no substantial N2O emission was observed after the soil was re-wetted following the drying phase. The peaks of N2O emissions from the CI paddy fields were all observed 8-10 days after soil drying with the WFPS ranging from 78.1% to 85.3%. However, no significant correlation was found between soil temperature and N2O emissions (p > 0.05), indicating that soil temperature is not a critical factor in N2O emission. N2O peaks were observed at soil Eh values ranging from +207.5 to +275.2 mV in CI paddy fields. No significant N2O emission occurred at Eh values higher than +300 mV or lower than +120 mV. These results suggest that N2O emissions may be reduced obviously by keeping the WFPS higher than 83.5% after each fertilizer application.

Characteristics of nitrous oxide emissions and the affecting factors from vegetable fields on the North China Plain

Nitrous oxide (N2O) is one of the most important greenhouse gases emitted from fertilized agricultural soils. Vegetable fields, mostly managed under intensive mode with higher rate nitrogen application, frequent irrigation, and multiple planting-harvest cycles, does contribute to national GHG inventory greatly due to the increasing planting area in China. N2O emissions from four different fields – a maize field (maize), a newly established open-ground vegetable field converted from a maize field four years earlier (OV4), an established open-ground vegetable field converted from a maize field more than 20 years ago (OV20), and an established sunlight heated greenhouse vegetable field converted from a maize field more than 20 years ago (GV20) with four different fertilization treatments for the OV4 field were measured using the closed chamber method between March 15th, 2012 and March 14th, 2013 in suburban area of Beijing, North China Plain. Results showed that the annual N2O emissions from vegetable fields were 3.1–4.6 times higher than the typical maize field. All the N2O emission peaks were occurred after fertilization and the fertilization associated emissions accounted for 81.1% (ranging from 77.0% to 87.2%) of the annual N2O emission with 22.2% time duration in the whole year for vegetable fields. Both the occurrence data and duration of N2O emission peaks were associated with N input type (chemical or manure) and the application rate. The N2O emission peaks appeared earlier (on the 3rd day after application) and lasted shorter when only chemical N was applied; while they appeared later (on the 7th to 10th day after application) and lasted longer when the combination of manure and chemical N were applied. The magnitudes of N2O emission peaks increased when the N application rate was higher. Dicyandiamide (DCD) decreased N2O emissions by 30.1% and 21.1% in the spring cucumber and autumn cabbage seasons respectively (averaged of 24.7% over the whole year). Calculations showed that it is critical to estimate the emission factor (EF) by N type in order to decrease the uncertainty of regional N2O emissions when using EF as calculation method. EFs were 0.20% and 0.42% for manure N in the cucumber and cabbage seasons respectively; and were 0.55–1.30% and 0.8–1.59% for chemical N in the cucumber and cabbage seasons respectively.

京郊典型设施蔬菜地土壤N2O排放特征

PDF HTML阅读 XML下载 导出引用 引用提醒 京郊典型设施蔬菜地土壤N2O排放特征 DOI: 10.5846/stxb201306091534 作者: 作者单位: 中国农业科学院农业资源与农业区划研究所/农业部面源污染控制重点实验室,中国农业科学院农业资源与农业区划研究所/农业部面源污染控制重点实验室,中国农业科学院农业资源与农业区划研究所/农业部面源污染控制重点实验室,中国农业科学院农业资源与农业区划研究所/农业部面源污染控制重点实验室 作者简介: 通讯作者: 中图分类号: 基金项目: 国家自然科学青年基金（41201287）；公益性行业（农业）科研专项（201103039）；中央级公益性科研院所基本科研业务费（302-30，402-15） Characteristics of nitrous oxide emissions from typical greenhouse vegetable fields in Beijing suburbs Author: Affiliation: Key Laboratory of Non-point Source Pollution Control, Ministry of Agriculture / Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences,,Key Laboratory of Non-point Source Pollution Control, Ministry of Agriculture / Institute of Agricultural Resources and Regional Planning, Chinese Academy of Agricultural Sciences, Fund Project: 摘要 | 图/表 | 访问统计 | 参考文献 | 相似文献 | 引证文献 | 资源附件 | 文章评论 摘要:利用静态暗箱-气相色谱法对北京郊区设施蔬菜地典型种植模式（番茄-白菜-生菜）下土壤N2O排放特征进行了周年（2012年2月22日-2013年2月23日）观测，探讨了不同处理下（即不施氮肥处理（CK）、农民习惯施肥处理（FP）、减氮优化施肥处理（OPT）和减氮优化施肥+硝化抑制剂处理（OPT+DCD））N2O排放特征及土壤温度、土壤湿度、土壤无机氮含量对土壤N2O排放的影响。结果表明：每次施肥+灌溉之后设施蔬菜地会出现明显的N2O排放高峰，持续时间一般为3-5 d。不同处理N2O排放通量变化范围在-0.21-14.26 mg N2O m-2 h-1，平均排放通量0.03-0.36 mg N2O m-2 h-1。整个蔬菜生长季各处理N2O排放与土壤孔隙含水率（WFPS）均表现出极显著的正相关关系（P < 0.01）；不施氮处理5 cm深度土壤温度与N2O排放通量呈现显著的正相关关系（P < 0.05）；各处理N2O排放与土壤表层硝态氮含量具有较一致变化趋势。不同处理下N2O年度排放总量差异显著，依次顺序为FP（（20.66±0.91）kg N/hm2） > OPT（（12.79±1.33）kg N/hm2） > OPT+DCD（（8.03±0.37）kg N/hm2）。与FP处理相比，OPT处理和OPT+DCD处理N2O年排放总量分别减少了38.09%和61.13%。各处理N2O排放系数介于0.36%-0.77%，低于IPCC 1.0%的推荐值。在目前的管理措施下，合理减少施氮量和添加硝化抑制剂是减少设施蔬菜地N2O排放量的有效途径。 Abstract:Nitrous oxide (N2O) has been recognized as one of the most important trace gases in the atmosphere that causes global warming and stratospheric ozone depletion. Nitrogen (N) fertilizer is considered as the primary source of N2O emissions from agricultural soils. As a large agricultural country, China consumes the greatest amount of synthetic N fertilizer which accounts for 30% of the world consumptions. Therefore, quantifying N2O emissions from agricultural soils and seeking suitable mitigation measures have become a relatively hot issue in international global climate change studies. However, the task has proved to be uneasy because N2O production and emission processes are very complex and are influenced by a number of soil and environmental variables, interacting soil water and N processes, crop uptake and management practices. Especially the N2O emissions from the greenhouse vegetable systems are more complex because the system obtain relatively higher inputs of fertilizer (e.g., N fertilizer application rate can be as high as 1,500 kg N/hm2), more water irrigation and cultivation disturbance. This paper reported a field experiment with intensive measurements of N2O fluxes from a greenhouse vegetable system with varied management treatments in Fangshan District located in the western suburbs of Beijing, China. N2O fluxes in conjunction with the main environmental drivers (i.e., soil temperature, soil moisture, soil NO3--N and soil NH4+-N) were observed from Feb. 2012 to Feb. 2013. Four treatments, i.e., the control treatment (CK), the farmers' practice treatment (FP), the optimized fertilization treatment (OPT), and the OPT treatment with nitrification inhibitor amendment treatment (OPT+DCD), were implemented during the experimental period to test the impacts of fertilization on N2O fluxes from the agroecosystem. The CK had no fertilizer applied; FP consisted of 2,470 kg N/hm2 with 1,270 and 1,200 kg N/hm2 from synthetic fertilizer and manure, respectively; the OPT reduced synthetic fertilizer rate to 573 kg N/hm2. The field was planted with tomato, cabbage and lettuce rotation during the two experimental years. The results indicated that large amount of N2O emissions were observed in the spring and summer periods when the soil had relatively high temperatures and moisture. N2O emission peaks were measured following each event of fertilization or irrigation. The high peaks usually lasted for 3-5 days. During the experimental period, N2O emission rates ranged from -0.21-14.26 mg N2O m-2 h-1 with daily means ranging from 0.03-0.36 mg N2O m-2 h-1. The annual cumulative N2O emissions ranged from 1.69-20.66 kg N hm-2, based on which the annual emission factor was calculated to be 0.36%-0.77% of the fertilizer N. Compared to the FP treatment, the OPT and OPT+DCD treatments both significantly reduced the annual N2O emissions by 38.09% and 61.3%(P < 0.05), respectively. The N2O emissions during the tomato, lettuce, cabbage and fallow periods accounted for 60.65%, 26.32%, 10% and 3.3% of annual cumulative emissions, respectively. The fertilizer-induced N2O emissions varied across the N application rates, the crop growing periods and the management treatments. N2O fluxes were positively related to the soil water filled pore space (WFPS) when the WFPS values varied between 48.88%-79.88%(P < 0.05). There was no consistent correlation between N2O fluxes and the soil temperature at soil depth of 5 cm. Higher soil available nitrogen, especially nitrate, contributed higher N2O emissions. In conclusion, alternative management practices such as reduced fertilizer application rate and amendment of DCD could effectively reduce N2O emissions from the greenhouse vegetable field which usually emitted more N2O than other croplands in China. 参考文献 相似文献 引证文献

Nitrous oxide emission factors for urine and dung patches in a subtropical Brazilian pastureland

Cattle urine and dung (faeces) patches are nitrous oxide (N2O) sources in pasturelands with impacts in the global N2O budget, but specific information about those emissions are still missing for Brazilian subtropical and tropical regions. We conducted a sequence of 3 field-trials (summer, winter and spring, 90 days each) to evaluate the N2O emission and emission factor (EF) after the deposition of 3 volumes of cattle urine or 3 weights of dung (½, 1 and 1½ time the mean urination volume or defecation weight of Friesian cows) on a free-drained Cambisol of a subtropical pastureland of Brazil. The N2O emission peaks (3198μgN2O-Nm−2h−1 after urine in summer was the highest) occurred on average 17±9 days after application (DAA), both for urine and dung, and dropped to the background levels 41±10 DAA of urine and 49±10 DAA of dung. The highest contents of NH4+-N in soil (200–250mgNkg−1) occurred one day after urine application and 10–14 days later for dung (100–200mgNkg−1). Nitrate peaks occurred from 23 to 26 DAA in urine patches (∼40–50mgNkg−1) and 19–50 DAA in dung patches (∼40–50mgNkg−1). The N2O emission peaks for urine coincided with soil NH4+-N peak in winter but with soil NO3−-N peak in spring. For dung, the emission peak seemed to be more associated with soil NO3−-N than to NH4+-N, either in winter or spring (inorganic-N was not assessed in summer). It was not possible to conclude whether nitrification or denitrification was the dominant process in N2O production, but it seemed that both played relevant roles. The EF for urine, averaged across the seasons, diminished with increments in urine volume, from 0.33% in ½ volume to 0.19% in 1½ volume, possibly because urine percolated deeper into the soil and proportionally less N remained available for N2O production in the top layer. The EF for dung was 0.19%, 0.12% and 0.14% for ½, 1 and 1½ weight, respectively, showing no clear trend with increment in dung weight. The lowest EFs for urine and dung occurred in winter, possibly because of lowest temperatures and soil water-filled pore space. The average EF for dung (0.15%) was lower than that of urine (0.26%), because urea-N of urine is more readily available for the hydrolysis than organic N forms of dung. This result suggests that these two excreta should be addressed separately in national greenhouse gases inventories or communications. Our results suggest that the default 2% EF proposed in IPCC Guidelines for cattle excreta are overestimated for subtropical Brazil.

Measurements of N2O emissions from different vegetable fields on the North China Plain

Few studies have measured the N2O emission fluxes from vegetable fields. In order to identify the characteristics and the influencing factors of N2O emissions from different vegetable fields, we measured N2O emissions for a full year from four typical fields, including an open-ground vegetable field that has produced vegetables for over 20 years (OV20), a recently developed open-ground vegetable field that was converted from a maize field three years earlier (OV3), a recently developed greenhouse vegetable field that was converted from a maize field 3 years earlier (GV3) and a typical local maize field (Maize). Four different fertilization treatments were set additionally in the recently developed open-ground vegetable field. These were: no fertilizer or manure (OV3_CK), manure only (OV3_M) and the combination of manure with different rates of chemical fertilizer application (OV3_MF1 and OV3_MF3). The results showed that N2O emission fluxes fluctuated between 0.3 ± 0.1 and 912.4 ± 80.0 mg N2O–N m−2 h−1 with the highest emission peak occurring after fertilization followed by irrigation. Nitrogen application explained 64.6–84.5% of the N2O emission in the vegetable fields. The magnitude of the emission peaks depended on the nitrogen application rate and the duration of the emission peaks was mainly associated with soil temperature when appropriate irrigation was given after fertilization. The N2O emission peaks occurred later and lasted for a longer period when the soil temperature was <24 °C in May. However, emission peaks occurred earlier and lasted for a shorter period when the soil temperature was around 25–33 °C from June to August. The annual N2O emissions from the fertilized vegetable fields were 1.68–2.38 times higher than that from the maize field, which had an emission value of 2.88 ± 0.10 kg N ha−1 a−1. The N2O emission factor (EF) of manure nitrogen was 0.07% over the whole year, but was 0.11% and 0.02% in the spring cucumber season and the autumn cabbage season, respectively. The EF of chemical nitrogen was 1.10–1.78% for the vegetable field over the whole year and it was higher in recently developed vegetable field than in the established field (1.54–1.78% vs. 1.10%). Vegetable fields may contribute greatly to the national greenhouse gas inventories due to the high fertilizer application rates, frequent irrigation and an increased number of tillage–planting cycles.

Nitrous oxide emissions from paddy fields under different water managements in southeast China

Water management is recognized as one of the most important factors in regulating nitrous oxide (N2O) emissions from paddy fields. In China, controlled irrigation (CI) is widely applied because it has been proved highly effective in saving water. During the rice-growing season, the soil in CI paddy fields remains dry 60–80% of the time compared with soil irrigated by traditional methods. This study aims to assess N2O emissions from paddy fields under CI, with traditional irrigation (TI) as the control. The cumulative N2O emission from CI paddy fields was 2.5 kg N ha−1, which was significantly greater than that from TI paddy fields (1.0 kg N ha−1) (P < 0.05). Soil drying caused substantial N2O emissions. The majority (73.9%) of the cumulative N2O emission from CI paddy fields was observed during the drying phase, whereas no substantial N2O emissions were observed when the soil was re-wetted after the drying phase. More and significantly higher peaks of N2O emissions from CI paddy fields (P < 0.05) were also detected. These peaks were observed ~8 days after fertilizer application at water-filled pore spaces (WFPS) ranging from 78.0 to 83.5%, soil temperature ranging from 29.1 to 29.4°C, and soil redox potential (Eh) values ranging from +207.5 to +256.7 mV. The highest N2O emission was measured 8 days after the application of base fertilizer at a WFPS of 79.0%, soil temperature of 29.1°C, and soil Eh value of +207.5 mV. These results suggest that N2O emissions may be reduced obviously by keeping the WFPS higher than 83.5% within 10 days after each fertilizer application, especially when the soil temperature is suitable.

Greenhouse gas fluxes in a drained peatland forest during spring frost-thaw event

Abstract. Fluxes of greenhouse gases (GHG) carbon dioxide (CO2), methane (CH4) and nitrous oxide (N2O) were measured during a two month campaign at a drained peatland forest in Finland by the eddy covariance (EC) technique (CO2 and N2O), and automatic and manual chambers (CO2, CH4 and N2O). In addition, GHG concentrations and soil parameters (mineral nitrogen, temperature, moisture content) in the peat profile were measured. The aim of the measurement campaign was to quantify the GHG fluxes during freezing and thawing of the top-soil, a time period with potentially high GHG fluxes, and to compare different flux measurement methods. The forest was a net CO2 sink during the two months and the fluxes of CO2 dominated the GHG exchange. The peat soil was a small sink of atmospheric CH4 and a small source of N2O. Both CH4 oxidation and N2O production took place in the top-soil whereas CH4 was produced in the deeper layers of the peat, which were unfrozen throughout the measurement period. During the frost-thaw events of the litter layer distinct peaks in CO2 and N2O emissions were observed. The CO2 peak followed tightly the increase in soil temperature, whereas the N2O peak occurred with a delay after the thawing of the litter layer. CH4 fluxes did not respond to the thawing of the peat soil. The CO2 and N2O emission peaks were not captured by the manual chambers and hence we conclude that high time-resolution measurements with automatic chambers or EC are necessary to quantify fluxes during peak emission periods. Sub-canopy EC measurements and chamber-based fluxes of CO2 and N2O were comparable, although the fluxes of N2O measured by EC were close to the detection limit of the system. We conclude that if fluxes are high enough, i.e. greater than 5–10 μg N m−2 h−1, the EC method is a good alternative to measure N2O and CO2 fluxes at ecosystem scale, thereby minimizing problems with chamber enclosures and spatial representativeness of the measurements.

The fluxes and controlling factors of N2O and CH4 emissions from freshwater marsh in Northeast China

Nitrous oxide (N2O) and methane (CH4) emissions were measured using a static chamber method in two adjacent plots of freshwater marsh predominated by Calamagrostis angustifolia, one is seasonal waterlogged (SW) and the other without surface water accumulation (NW), in Sanjiang Plain wetland (47°35’N, 133°31’E), northeast China, during 2002–2004. The diurnal and seasonal flux variations of both gases were significantly correlated with 5-cm-soil temperature. The NW marsh is a source of N2O and sink of CH4, while the SW marsh is sink of N2O and source of CH4. Remarkably, we observed a N2O emission peak under Eh of −300 to −100 mV, and CH4 emission peak under Eh of +300 to +400 mV, which indicate additional sources of N2O and CH4 for the freeze-thaw induced emission peaks of N2O and CH4 observed between late July and early August. Further study shows that the additional N2O and CH4 were emitted under the frozen soil after thawing.

Simulation of N2O fluxes from Irish arable soils: effect of climate change and management

Emissions of nitrous oxide (N2O) from an Irish arable soil were simulated using the DeNitrification–DeComposition (DNDC) model. The soil chosen was a free-draining sandy loam typical of the majority of cereal growing land in Ireland, and one that has been previously used to test and validate DNDC-model. DeNitrification–DeComposition model was considered suitable to estimate N2O fluxes from Irish arable soils however, underestimated the flux by 24%. The objectives of this study were to estimate future N2O fluxes from a spring barley field under conventional (moulboard plowing) and reduced (chisel plowing) tillage and different N-fertilzer application rates. Three climate scenarios, a baseline of measured climatic data from the weather station at Kilkenny and a high- and low-temperature-sensitive scenarios predicted by the Hadley Global Climate Model (HadCM4) based on the AB1 emission scenario of the Intergovernment Panel on Climate Change (IPCC) were investigated. For conventional tillage under all scenarios, three peaks of N2O emissions were predicted; an early spring peak coinciding mostly with soil plowing, a mid/late spring peak coinciding with fertilizer application and an early autumn peak coinciding with residue incorporation and onset of autumn rainfall. Under reduced tillage, due to the less amount of soil disturbance, the early spring peak was not predicted. In all cases, the total amount of N2O emitted in the late spring peak due to fertilizer application was less than the sum of the other peaks. Under climate change, using the high-temperature-increase scenario, DNDC predicted an increase in N2O emissions from both conventional and reduced tillage, ranging from 58% to 88% depending upon N application rate. In contrast, annual fluxes of N2O either decreased or increased slightly in the low temperature increase scenario relative to N application (−26 to +16%). Outputs from the model indicate that elevated temperature and precipitation increase N mineralization and total denitrification leading to greater fluxes of N2O. Annual uncertainties due to the use of two different future climate scenarios were significantly high, ranging from 74% to 95% and from 71% to 90% for the conventional and reduced tillage.

Effects of N and P fertilization on the greenhouse gas exchange in two northern peatlands with contrasting N deposition rates

Abstract. Peatlands are important ecosystems in the context of biospheric feedback to climate change, due to the large storage of organic C in peatland soils. Nitrogen deposition and increased nutrient availability in soils following climate warming may cause changes in these ecosystems affecting greenhouse gas exchange. We have conducted an N and P fertilization experiment in two Swedish bogs subjected to high and low background N deposition, and measured the exchange of CO2, CH4 and N2O using the closed chamber technique. During the second year of fertilization, both gross primary production and ecosystem respiration were significantly increased by N addition in the northernmost site where background N deposition is low, while gross primary production was stimulated by P addition in the southern high N deposition site. In addition, a short-term response in respiration was seen following fertilization in both sites, probably associated with rapid growth of nutrient-limited soil microorganisms. No treatment effect was seen on the CH4 exchange, while N2O emission peaks were detected in N fertilized plots indicating the importance of taking N2O into consideration under increased N availability. In a longer term, increased nutrient availability will cause changes in plant composition, which will further act to regulate the peatland greenhouse gas exchange.

Nitrogen Removal, N2O Emission, and NH3 Volatilization Under Different Water Levels in a Vertical Flow Treatment System

Two series of laboratory-scale vertical flow systems (flooded and nonflooded columns) were designed to compare nitrogen removal performance, nitrous oxide emission, and ammonia volatilization under different water levels upon treating diluted digested livestock liquid. In these systems, influent was supplied at three hydraulic loading rates (HLRs of 1.25, 2.5, and 5 cm day−1) during stage 1 and the rates were doubled during stage 2 when the water levels of nonflooded columns were elevated from zero to half the height of the soil column. After hydraulic loading rates doubled, the average removal rates of total nitrogen in flooded columns varied from 1.27 to 2.94 g−2 day−1 and those in nonflooded columns ranged from 1.23 to 3.88 g−2 day−1. The T-N removal at an HLR of 10 cm day−1 in the nonflooded column with an elevated water table level had higher efficiency than that in the flooded column, suggesting T-N removal is enhanced in the nonflooded column probably due to the improved coupled nitrification–denitrification process under the elevated water table level condition. On the other hand, there was a significant correlation (r2 = 0.532, p < 0.001) between the N2O flux and redox potential that mainly corresponded to water levels and HLRs, suggesting anoxic or aerobic conditions stimulate N2O emission by enhancing the nitrification (nitrification–denitrification) process. In contrast, NH3 volatilization had a high flux in the anaerobic condition mainly because of flooding. Based on the experimental results, it is hypothesized a nonflooded condition with higher water table level (Eh range of −160 to +260 mV) would be suitable to reduce N2O emission and NH3 volatilization peak value by at least half while maintaining relatively efficient nitrogen removal performance.

Soil greenhouse gas fluxes and global warming potential in four high‐yielding maize systems

AbstractCrop intensification is often thought to increase greenhouse gas (GHG) emissions, but studies in which crop management is optimized to exploit crop yield potential are rare. We conducted a field study in eastern Nebraska, USA to quantify GHG emissions, changes in soil organic carbon (SOC) and the net global warming potential (GWP) in four irrigated systems: continuous maize with recommended best management practices (CC‐rec) or intensive management (CC‐int) and maize–soybean rotation with recommended (CS‐rec) or intensive management (CS‐int). Grain yields of maize and soybean were generally within 80–100% of the estimated site yield potential. Large soil surface carbon dioxide (CO2) fluxes were mostly associated with rapid crop growth, high temperature and high soil water content. Within each crop rotation, soil CO2 efflux under intensive management was not consistently higher than with recommended management. Owing to differences in residue inputs, SOC increased in the two continuous maize systems, but decreased in CS‐rec or remained unchanged in CS‐int. N2O emission peaks were mainly associated with high temperature and high soil water content resulting from rainfall or irrigation events, but less clearly related to soil NO3‐N levels. N2O fluxes in intensively managed systems were only occasionally greater than those measured in the CC‐rec and CS‐rec systems. Fertilizer‐induced N2O emissions ranged from 1.9% to 3.5% in 2003, from 0.8% to 1.5% in 2004 and from 0.4% to 0.5% in 2005, with no consistent differences among the four systems. All four cropping systems where net sources of GHG. However, due to increased soil C sequestration continuous maize systems had lower GWP than maize–soybean systems and intensive management did not cause a significant increase in GWP. Converting maize grain to ethanol in the two continuous maize systems resulted in a net reduction in life cycle GHG emissions of maize ethanol relative to petrol‐based gasoline by 33–38%. Our study provided evidence that net GHG emissions from agricultural systems can be kept low when management is optimized toward better exploitation of the yield potential. Major components for this included (i) choosing the right combination of adopted varieties, planting date and plant population to maximize crop biomass productivity, (ii) tactical water and nitrogen (N) management decisions that contributed to high N use efficiency and avoided extreme N2O emissions, and (iii) a deep tillage and residue management approach that favored the build‐up of soil organic matter from large amounts of crop residues returned.

Effects of charcoal addition on N2O emissions from soil resulting from rewetting air-dried soil in short-term laboratory experiments

Laboratory experiments were conducted to examine the effect of charcoal addition on N2O emissions resulting from rewetting of air-dried soil. Rewetting the soil at 73% and 83% of the water-filled pore space (WFPS) caused a N2O emission peak 6 h after the rewetting, and the cumulative N2O emissions throughout the 120-h incubation period were 11 ± 1 and 13 ± 1 mg N m−2, respectively. However, rewetting at 64% WFPS did not cause detectable N2O emissions (−0.016 ± 0.082 mg N m−2), suggesting a severe sensitivity to soil moisture. When the soils were rewetted at 73% and 78% WFPS, the addition of charcoal to soil at 10 wt% supressed the N2O emissions by 89% . In contrast, the addition of the ash from the charcoal did not suppress the N2O emissions from soil rewetted at 73% WFPS. The addition of charcoal also significantly stimulated the N2O emissions from soil rewetted at 83% WFPS compared with the soil without charcoal addition (P < 0.01). Moreover, the addition of KCl and K2SO4 did not show a clear difference in the N2O emission pattern, although Cl− and SO2− 4, which were the major anions in the charcoal, had different effects on N2O-reducing activity. These results indicate that the suppression of N2O emissions by the addition of charcoal may not result in stimulation of the N2O-reducing activity in the soil because of changes in soil chemical properties.

N2O, CH4 and CO2 emissions from seasonal tropical rainforests and a rubber plantation in Southwest China

The main focus of this study was to evaluate the effects of soil moisture and temperature on temporal variation of N2O, CO2 and CH4 soil-atmosphere exchange at a primary seasonal tropical rainforest (PF) site in Southwest China and to compare these fluxes with fluxes from a secondary forest (SF) and a rubber plantation (RP) site. Agroforestry systems, such as rubber plantations, are increasingly replacing primary and secondary forest systems in tropical Southwest China and thus effect the N2O emission in these regions on a landscape level. The mean N2O emission at site PF was 6.0 ± 0.1 SE μg N m−2 h−1. Fluxes of N2O increased from <5 μg N m−2 h−1 during dry season conditions to up to 24.5 μg N m−2 h−1 with re-wetting of the soil by the onset of first rainfall events. Comparable fluxes of N2O were measured in the SF and RP sites, where mean N2O emissions were 7.3 ± 0.7 SE μg N m−2 h−1 and 4.1 ± 0.5 SE μg N m−2 h−1, respectively. The dependency of N2O fluxes on soil moisture levels was demonstrated in a watering experiment, however, artificial rainfall only influenced the timing of N2O emission peaks, not the total amount of N2O emitted. For all sites, significant positive correlations existed between N2O emissions and both soil moisture and soil temperature. Mean CH4 uptake rates were highest at the PF site (−29.5 ± 0.3 SE μg C m−2 h−1), slightly lower at the SF site (−25.6 ± 1.3 SE μg C m−2 h−1) and lowest for the RP site (−5.7 ± 0.5 SE μg C m−2 h−1). At all sites, CH4 uptake rates were negatively correlated with soil moisture, which was also reflected in the lower uptake rates measured in the watering experiment. In contrast to N2O emissions, CH4 uptake did not significantly correlate with soil temperature at the SF and RP sites, and only weakly correlated at the PF site. Over the 2 month measurement period, CO2 emissions at the PF site increased significantly from 50 mg C m−2 h−1 up to 100 mg C m−2 h−1 (mean value 68.8 ± 0.8 SE mg C m−2 h−1), whereas CO2 emissions at the SF and RP site where quite stable and varied only slightly around mean values of 38.0 ± 1.8 SE mg C m−2 h−1 (SF) and 34.9 ± 1.1 SE mg C m−2 h−1 (RP). A dependency of soil CO2 emissions on changes in soil water content could be demonstrated for all sites, thus, the watering experiment revealed significantly higher CO2 emissions as compared to control chambers. Correlation of CO2 emissions with soil temperature was significant at the PF site, but weak at the SF and not evident at the RP site. Even though we demonstrated that N and C trace gas fluxes significantly varied on subdaily and daily scales, weekly measurements would be sufficient if only the sink/ source strength of non-managed tropical forest sites needs to be identified.

Overwinter greenhouse gas fluxes in two contrasting agricultural habitats

Mid-day field fluxes of nitrous oxide (N2O), carbon dioxide (CO2) and methane (CH4) were measured during late winter/early spring in an arable field and an adjacent fallow in southern Germany. On the arable field, 2 dm high ridges, drawn as seed-beds for potato, were exposed to mild, partly diurnal freezing–thawing. Substantially elevated N2O emission rates (6–750 µg N2O-N m–2 h–1) were observed throughout the investigation period which coincided with freezing–thawing events in the surface soil (0–5 cm). Soil temperatures in the densely vegetated fallow were more isothermal due to an insulating snow/ice cover, resulting in much lower N2O emission rates (0–57 µg N2O-N m–2 h–1). CH4 uptake rates were low in both habitats during soil frost (+2 to −7.5 µg CH4-C m–2 h–1) but increased markedly in the fallow after spring thaw. Our data suggest that N2O emission peaks may occur recurrently throughout the winter when soils are subjected to diurnal surface thawing. We concluded that microclimatic conditions strongly control N2O winter loss, thus overriding ecosystem-level differences in off-season nutrient cycling. To further characterize winter-time nutrient cycling and habitat functioning in our sites, we determined NO3 – and NH4 + contents, fumigation-extractable carbon (Cmic) and nitrogen (Nmic) and enumerated protozoa and nematoda throughout the investigation period. Cmic and microbial C:N ratios in the fallow were higher in winter than during the rest of the year as indicated by a 2-year study, reflecting favorable conditions for microbial C assimilation at low temperatures in the absence of freeze–thaw perturbation. In the arable soil, Cmic contents were significantly reduced during soil freezing but recovered quickly upon warming of the soil. Dynamics of Cmic in the arable soil were paralleled by protozoan biomass and transient shifts in functional composition of the nematode community, indicating that microfaunal predation played an important role in nutrient cycling after freeze–thaw perturbation. Only minor microfaunal dynamics were observed in the climatically more stable fallow, essentially confirming the absence of perturbation at this site. Our findings provide strong evidence that overwinter N2O formation is regulated by both the physical freeze–thaw susceptibility of the soil and the ecological functioning of the habitat.

N2O and NO emissions from soils after the application of different chemical fertilizers

Three nitrogen chemical fertilizers were applied to soil – controlled-release urea (CU), a mixture of ammonium sulfate and urea with nitrification inhibitor (AM), and a mixture of ammonium sulfate and urea with no nitrification inhibitor (UA). N2O and NO fluxes from an Andosol soil in Japan were measured six times a day for three months with an automated flux monitoring system in lysimeters. The total amount of nitrogen applied was 20 g N m−2. The total N2O emissions from CU, AM and UA were 1.90, 12.7, and 16.4 mg N m−2, respectively. The total NO emissions from CU, AM and UA were 231, 152, and 238 mg N m−2, respectively. The total NO emission was 12–15 times higher than the total N2O emission. High peaks in N2O and NO emissions from UA occurred for one month after the basal fertilizer application. The N2O emissions from CU and AM during the peak period were 50% of those from UA, and the NO emissions were less than 50% of those from UA. After the peak period, the N2O and NO emissions from CU were the highest for two months. A negative correlation was found between the flux ratio of NO–N to N2O–N and the water-filled pore space. A diel pattern with increased N2O and NO fluxes during the day and with decreased fluxes during the night was observed.