Nitrous oxide emissions during establishment of eight alternative cellulosic bioenergy cropping systems in the North Central United States

Greenhouse gas (GHG) emissions from soils are a key sustainability metric of cropping systems. During crop establishment, disruptive land‐use change is known to be a critical, but under reported period, for determining GHG emissions. We measured soil N₂O emissions and potential environmental drivers of these fluxes from a three‐year establishment‐phase bioenergy cropping systems experiment replicated in southcentral Wisconsin (ARL) and southwestern Michigan (KBS). Cropping systems treatments were annual monocultures (continuous corn, corn–soybean–canola rotation), perennial monocultures (switchgrass, miscanthus, and poplar), and perennial polycultures (native grass mixture, early successional community, and restored prairie) all grown using best management practices specific to the system. Cumulative three‐year N₂O emissions from annuals were 142% higher than from perennials, with fertilized perennials 190% higher than unfertilized perennials. Emissions ranged from 3.1 to 19.1 kg N₂O‐N ha^?1 yr^?1 for the annuals with continuous corn > corn–soybean–canola rotation and 1.1 to 6.3 kg N₂O‐N ha^?1 yr^?1 for perennials. Nitrous oxide peak fluxes typically were associated with precipitation events that closely followed fertilization. Bayesian modeling of N₂O fluxes based on measured environmental factors explained 33% of variability across all systems. Models trained on single systems performed well in most monocultures (e.g., R² = 0.52 for poplar) but notably worse in polycultures (e.g., R² = 0.17 for early successional, R² = 0.06 for restored prairie), indicating that simulation models that include N₂O emissions should be parameterized specific to particular plant communities. Our results indicate that perennial bioenergy crops in their establishment phase emit less N₂O than annual crops, especially when not fertilized. These findings should be considered further alongside yield and other metrics contributing to important ecosystem services.     

Impacts of monoculture cropland to alley cropping agroforestry conversion on soil N2O emissions

Monoculture croplands are a major source of global anthropogenic emissions of nitrous oxide (N₂O), a potent greenhouse gas that contributes to ozone depletion. Agroforestry has the potential to reduce N₂O emissions. Presently, there is no systematic comparison of soil N₂O emissions between cropland agroforestry and monoculture systems in Central Europe. We investigated the effects of converting the monoculture cropland system into the alley cropping agroforestry system on soil N₂O fluxes at three sites (each site has paired agroforestry and monoculture) in Germany, where agroforestry combined crop rows and poplar short-rotation coppice (SRC). We measured soil N₂O fluxes monthly over 2 years (March 2018–January 2020) using static vented chambers. Annual soil N₂O emissions from agroforestry ranged from 0.21 to 2.73 kg N ha⁻¹ year⁻¹, whereas monoculture N₂O emissions ranged from 0.34 to 3.00 kg N ha⁻¹ year⁻¹. During the rotation of corn crop, with high fertilization rates, agroforestry reduced soil N₂O emissions by 9% to 56% compared to monocultures. This was mainly caused by low soil N₂O emissions from the unfertilized agroforestry tree rows. Soil N₂O fluxes were predominantly controlled by soil mineral N in both agroforestry and monoculture systems. Our findings suggest that optimized fertilizer input will further enhance the potential of agroforestry for mitigating N₂O emissions.     

Nitrogen turnover in fresh Douglas fir litter directly after additions of moisture and inorganic nitrogen

The effects of wetting and drying and inorganic nitrogen (N) addition on carbon (C) and N turnover in fresh Douglas fir litter (Speuld forest, the Netherlands) were investigated. Litter was incubated for 9 days in the laboratory, receiving different moisture and N addition treatments. Following the additions, a series of reactions were observed of which most notable were a rapid retention of added ammonium and nitrate (NO ₃ ^- ) and a sudden increase in CO₂ respiration. For the rewetted-and-moist incubations, respiration levels remained elevated, N was net immobilized and nitrous oxide (N₂O) production increased throughout the experiment. About 80% of the NO ₃ ^- produced was lost again as N₂O. In the rewetted-and-dried incubations, respiration decreased during the drying phase; no clear patterns in N mineralization were detected; and N₂O production remained at constant levels, but still resulted in gaseous loss for half of the NO ₃ ^- net produced. The experiments thus revealed two important NO ₃ ^- sinks in LF1 litter, namely rapid retention of added NO ₃ ^- and gaseous loss as N₂O. The maximum NO ₃ ^- loss via these sinks was estimated at 2 kg-N ha^-1 yr^-1, which is small compared to annual NO ₃ ^- leaching at 90 cm soil depth (31 kg-N ha^-1 yr^-1).     

Greenhouse Gas Emissions, Nitrate Leaching, and Biomass Yields from Production of Miscanthus × giganteus in Illinois, USA

Understanding the effects of nitrogen (N) fertilization on Miscanthus × giganteus greenhouse gas emissions, nitrate leaching, and biomass production is an important consideration when using this grass as a biomass feedstock. The objective of this study was to determine the effect of three N fertilization rates (0, 60, and 120?kg?N?ha^?1 using urea as the N source) on nitrous oxide (N₂O) and carbon dioxide (CO₂) emissions, nitrogen leaching, and the biomass yields and N content of M. × giganteus planted in July 2008, and evaluated from 2009 through early 2011 in Urbana, Illinois, USA. While there was no biomass yield response to N fertilization rates in 2009 and 2010, the amount of N in the harvested biomass in 2010 was significantly greater at the 60 and 120?kg?N?ha^?1?N rates. There was no significant CO₂ emission response to N rates in 2009 or 2010. Similarly, N fertilization did not increase cumulative N₂O emissions in 2009, but cumulative N₂O emissions did increase in 2010 with N fertilization. During 2009, nitrate (NO ₃ ^? ) leaching at the 50-cm soil depth was not related to fertilization rate, but there was a significant increase in NO ₃ ^? leaching between the 0 and 120?kg?N?ha^?1 treatments in 2010 (8.9 and 28.9?kg?NO₃?CN?ha^?1?year^?1, respectively). Overall, N fertilization of M. × giganteus led to N₂O releases, increased fluxes of inorganic N (primarily NO ₃ ^? ) through the soil profile; and increased harvested N without a significant increase in biomass production.     

Polymer Coated Urea in Turfgrass Maintains Vigor and Mitigates Nitrogen's Environmental Impacts

Polymer coated urea (PCU) is a N fertilizer which, when added to moist soil, uses temperature-controlled diffusion to regulate N release in matching plant demand and mitigate environmental losses. Uncoated urea and PCU were compared for their effects on gaseous (N₂O and NH₃) and aqueous (NO₃^-) N environmental losses in cool season turfgrass over the entire PCU N-release period. Field studies were conducted on established turfgrass sites with mixtures of Kentucky bluegrass (Poa pratensis L.) and perennial ryegrass (Lolium perenne L.) in sand and loam soils. Each study compared 0 kg N ha^-1 (control) to 200 kg N ha^-1 applied as either urea or PCU (Duration 45CR®). Application of urea resulted in 127–476% more evolution of measured N₂O into the atmosphere, whereas PCU was similar to background emission levels from the control. Compared to urea, PCU reduced NH₃ emissions by 41–49% and N₂O emissions by 45–73%, while improving growth and verdure compared to the control. Differences in leachate NO₃^- among urea, PCU and control were inconclusive. This improvement in N management to ameliorate atmospheric losses of N using PCU will contribute to conserving natural resources and mitigating environmental impacts of N fertilization in turfgrass.     

Methane and nitrous oxide fluxes in annual and perennial land-use systems of the irrigated areas in the Aral Sea Basin

Land use and agricultural practices can result in important contributions to the global source strength of atmospheric nitrous oxide (N₂O) and methane (CH₄). However, knowledge of gas flux from irrigated agriculture is very limited. From April 2005 to October 2006, a study was conducted in the Aral Sea Basin, Uzbekistan, to quantify and compare emissions of N₂O and CH₄ in various annual and perennial land-use systems: irrigated cotton, winter wheat and rice crops, a poplar plantation and a natural Tugai (floodplain) forest. In the annual systems, average N₂O emissions ranged from 10 to 150 μg N₂O-N m⁻² h⁻¹ with highest N₂O emissions in the cotton fields, covering a similar range of previous studies from irrigated cropping systems. Emission factors (uncorrected for background emission), used to determine the fertilizer-induced N₂O emission as a percentage of N fertilizer applied, ranged from 0.2% to 2.6%. Seasonal variations in N₂O emissions were principally controlled by fertilization and irrigation management. Pulses of N₂O emissions occurred after concomitant N-fertilizer application and irrigation. The unfertilized poplar plantation showed high N₂O emissions over the entire study period (30 μg N₂O-N m⁻² h⁻¹), whereas only negligible fluxes of N₂O (<2 μg N₂O-N m⁻² h⁻¹) occurred in the Tugai. Significant CH₄ fluxes only were determined from the flooded rice field: Fluxes were low with mean flux rates of 32 mg CH₄ m⁻² day⁻¹ and a low seasonal total of 35.2 kg CH₄ ha⁻¹. The global warming potential (GWP) of the N₂O and CH₄ fluxes was highest under rice and cotton, with seasonal changes between 500 and 3000 kg CO₂ eq. ha⁻¹. The biennial cotton–wheat–rice crop rotation commonly practiced in the region would average a GWP of 2500 kg CO₂ eq. ha⁻¹ yr⁻¹. The analyses point out opportunities for reducing the GWP of these irrigated agricultural systems by (i) optimization of fertilization and irrigation practices and (ii) conversion of annual cropping systems into perennial forest plantations, especially on less profitable, marginal lands.     

Greenhouse gas fluxes respond to different N fertilizer types due to altered plant-soil-microbe interactions

The application of inorganic nitrogen (N) fertilizers strongly influences the contribution of agriculture to the greenhouse effect, especially by potentially increasing emissions of nitrous oxide (N₂O), carbon dioxide (CO₂) and methane (CH₄) from soils. The present microcosm-study investigates the effect of different forms of inorganic N fertilizers on greenhouse gas (GHG) emissions from two different agricultural soils. The relationship between greenhouse gas emissions and soil microbial communities, N transformation rates and plant (Hordeum vulgare L. cv. Morex) growth were investigated. Repeated N fertilization led to increased N₂O emissions. In a parallel survey of functional microbial population dynamics we observed a stimulation of bacterial and archaeal ammonia oxidisers accompanied with these N₂O emissions. The ratio of archaeal to bacterial ammonium monooxygenase subunit A (amoA) gene copies (data obtained from Inselsbacher et al., 2010) correlated positively with N₂O fluxes, which suggests a direct or indirect involvement of archaea in N₂O fluxes. Repeated N fertilization also stimulated methane oxidation, which may also be related to a stimulation of ammonia oxidizers. The fertilizer effects differed between soil types: In the more organic Niederschleinz soil N-turnover rates increased more strongly after fertilization, while in the sandy Purkersdorf soil plant growth and soil respiration were accelerated depending on fertilizer N type. Compared to addition of NH ₄ ⁺ and NO ₃ ^? , addition of NH₄NO₃ fertilizer resulted in the largest increase in global warming potential as a summary indicator of all GHG related effects. This effect resulted from the strongest increase of both N₂O and CO₂ emission while plant growth was not equally stimulated, compared to e.g. KNO₃ fertilization. In order to decrease N losses from agricultural ecosystems and in order to minimize soil derived global warming potential, this study points to the need for interdisciplinary investigations of the highly complex interactions within plant-soil-microbe-atmosphere systems. By understanding the microbial processes underlying fertilizer effects on GHG emissions the N use efficiency of crops could be refined.     

Spatial variability of nitrous oxide emissions from an Australian irrigated dairy pasture

Understanding spatial variability of emissions of nitrous oxide (N₂O) is essential to understanding of N₂O emissions from soils to the atmosphere and in the design of statistically valid measurement programs to determine plot, farm and regional emission rates. Two afternoon, ‘snap-shot’ experiments were conducted; one in the summer and one in the autumn of 2004, to examine the statistics and soil variables affecting the spatial variability of N₂O emissions at paddock scale. Small, static chambers (mini-chambers) were placed at 100 locations over an 8,100 m² area of irrigated dairy pasture in northern Victoria, Australia. Chamber headspace was sampled for N₂O and soil samples taken below each mini-chamber were analysed for soil nitrate (NO₃ ^-), ammonium (NH₄ ⁺) and other chemical and physical properties known to affect N₂O emissions. The experiments took place immediately after the sequence of grazing, urea application and irrigation. Nitrous oxide emissions and soil variables were analysed using classical statistics to investigate the effect of soil variables on N₂O emissions. Geostatistics were used to investigate spatial patterns of N₂O emissions and soil variables over the measurement area. Nitrous oxide emissions were extremely variable; 45–765 ng N₂O–N m^?2 s^?1 and 20–953 ng N₂O–N m^?2 s^?1 for the two experiments with corresponding averages of 165 and 138 ng N₂O–N m^?2 s^?1. Nitrous oxide emissions showed spatial dependence up to 73 and 51 m for the two experiments. Nitrous oxide emissions showed significant correlation with soil nutrients in decreasing order of NO₃ ^-, NH₄ ⁺ and available-P concentrations. There was no significant correlation of N₂O emissions with measured soil physical properties.     

Determination of 15N Abundance in Nanogram Pools of NO3- and NO2- by Denitrification Bioassay and Mass Spectrometry

Suspensions of two strains of Pseudomonas aeruginosa (ON12 and ON12-1) were used to reduce NO₃^- and NO₂^-, respectively, to N₂O. The evolved N₂O was quantified by gas chromatography with electron capture detection, and the ¹⁵N abundance was determined by mass spectrometry with a special inlet system and triple-collector detection. Sample gas containing unknown N₂O pools as small as 0.5 ng of N was analyzed by use of a spike technique, in which a reference gas of N₂O of natural ¹⁵N abundance was added to obtain enough total N for the mass spectrometer. In NO₃^- or NO₂^- pools, the ¹⁵N abundance could be determined in samples as small as approximately 3.5 ng of N. No cross-contamination took place between the NO₃^- and NO₂^- pools. The excellent separation of NO₃^- and NO₂^- pools, small sample size required, and low contamination risk during N₂O analysis offer great advantages in isotope studies of inorganic N transformations by, e.g., nitrifying or denitrifying bacteria in the environment.     

京郊典型设施蔬菜地土壤N_2O排放特征

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-2h-1,平均排放通量0.03—0.36 mg N2O m-2h-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(P0.01);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(P0.05);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。     

Nitrogen–climate interactions in US agriculture

Agriculture in the United States (US) cycles large quantities of nitrogen (N) to produce food, fuel, and fiber and is a major source of excess reactive nitrogen (Nr) in the environment. Nitrogen lost from cropping systems and animal operations moves to waterways, groundwater, and the atmosphere. Changes in climate and climate variability may further affect the ability of agricultural systems to conserve N. The N that escapes affects climate directly through the emissions of nitrous oxide (N₂O), and indirectly through the loss of nitrate (NO₃ ^?), nitrogen oxides (NO _x ) and ammonia to downstream and downwind ecosystems that then emit some of the N received as N₂O and NO _x . Emissions of NO _x lead to the formation of tropospheric ozone, a greenhouse gas that can also harm crops directly. There are many opportunities to mitigate the impact of agricultural N on climate and the impact of climate on agricultural N. Some are available today; many need further research; and all await effective incentives to become adopted. Research needs can be grouped into four major categories: (1) an improved understanding of agricultural N cycle responses to changing climate; (2) a systems-level understanding of important crop and animal systems sufficient to identify key interactions and feedbacks; (3) the further development and testing of quantitative models capable of predicting N-climate interactions with confidence across a wide variety of crop-soil-climate combinations; and (4) socioecological research to better understand the incentives necessary to achieve meaningful deployment of realistic solutions.     

Soil‐derived trace gas fluxes from different energy crops – results from a field experiment in Southwest Germany

Willow coppice, energy maize and Miscanthus were evaluated regarding their soil‐derived trace gas emission potential involving a nonfertilized and a crop‐adapted slow‐release nitrogen (N) fertilizer scheme. The N application rate was 80 kg N ha^?1 yr^?1 for the perennial crops and 240 kg N ha^?1 yr^?1 for the annual maize. A replicated field experiment was conducted with 1‐year measurements of soil fluxes of CH₄, CO₂ and N₂O in weekly intervals using static chambers. The measurements revealed a clear seasonal trend in soil CO₂ emissions, with highest emissions being found for the N‐fertilized Miscanthus plots (annual mean: 50 mg C m^?² h^?1). Significant differences between the cropping systems were found in soil N₂O emissions due to their dependency on amount and timing of N fertilization. N‐fertilized maize plots had highest N₂O emissions by far, which accumulated to 3.6 kg N₂O ha^?1 yr^?1. The contribution of CH₄ fluxes to the total soil greenhouse gas subsumption was very small compared with N₂O and CO₂. CH₄ fluxes were mostly negative indicating that the investigated soils mainly acted as weak sinks for atmospheric CH₄. To identify the system providing the best ratio of yield to soil N₂O emissions, a subsumption relative to biomass yields was calculated. N‐fertilized maize caused the highest soil N₂O emissions relative to dry matter yields. Moreover, unfertilized maize had higher relative soil N₂O emissions than unfertilized Miscanthus and willow. These results favour perennial crops for bioenergy production, as they are able to provide high yields with low N₂O emissions in the field.     

Predicting soils and environmental impacts associated with switchgrass for bioenergy production: a DAYCENT modeling approach

Switchgrass (Panicum virgatum L.) production has the potential to improve soils and the environment. However, little is known about the long‐term future assessment of soil and environmental impacts associated with switchgrass production. In this study, soil organic carbon (SOC), soil nitrate (), water‐filled pore space (WFPS), carbon dioxide (CO₂) and nitrous oxide (N₂O) fluxes, and biomass yield from switchgrass field were predicted using DAYCENT models for 2016 through 2050. Measured data for model calibration and validation at this study site managed with nitrogen fertilization rates (N rates) (low, 0 kg N ha^?1; medium, 56 kg N ha^?1; and high, 112 kg N ha^?1) and landscape positions (shoulder and footslope) for switchgrass production were collected from the previously published studies. Modeling results showed that the N fertilization can enhance SOC and soil NO₃^?, but increase soil N₂O and CO₂ fluxes. In this study, medium N fertilization was the optimum rate for enhancing switchgrass yield and reducing negative impact on the environment. Footslope position can be beneficial for improving SOC, , and yield, but contribute higher greenhouse gas (GHG) emissions compared to those of the shoulder. An increase in temperature and decrease in precipitation (climate scenarios) may reduce soil , WFPS, and N₂O flux. Switchgrass production can improve and maintain SOC and , and reduce N₂O and CO₂ fluxes over the predicted years. These findings indicate that switchgrass could be a sustainable bioenergy crop on marginally yielding lands for improving soils without significant negative impacts on the environment in the long run.     

Exchange of gaseous nitrogen compounds between agricultural systems and the atmosphere

Crop and livestock agricultural production systems are important contributors to local, regional and global budgets of NH₃, NO_x (NO + NO₂) and N₂O. Emissions of NH₃ and NO_x (which are biologically and chemically active) into the atmosphere serve to redistribute fixed N to local and regional aquatic and terrestrial ecosystems that may otherwise be disconnected from the sources of the N gases. The emissions of NO_x also contribute to local elevated ozone concentrations while N₂O emissions contribute to global greenhouse gas accumulation and to stratospheric ozone depletion.Ammonia is the major gaseous base in the atmosphere and serves to neutralize about 30% of the hydrogen ions in the atmosphere. Fifty to 75% of the 55 Tg N yr^–1 NH₃ from terrestrial systems is emitted from animal and crop-based agriculture from animal excreta and synthetic fertilizer application. About half of the 50 Tg N yr^–1 of NO_x emitted from the earth surface annually arises from fossil fuel combustion and the remainder from biomass burning and emissions from soil. The NO_x emitted, principally as nitric oxide (NO), reacts rapidly in the atmosphere and in a complex cycle with light, ozone and hydrocarbons, and produces nitric acid and particulate nitrate. These materials can interact with plants and the soil locally or be transported form the site and interact with atmospheric particulate to form aerosols. These salts and aerosols return to fertilize terrestrial and aquatic systems in wet and dry deposition. A small fraction of this N may be biologically converted to N₂O. About 5% of the total atmospheric greenhouse effect is attributed to N₂O from which 70% of the annual global anthropogenic emissions come from animal and crop production.The coupling of increased population with a move of a large sector of the world population to diets that require more energy and N input, will lead to continued increases in anthropogenic input into the global N cycle. This scenario suggests that emissions of NH₃, NO_x and N₂O from agricultural systems will continue to increase and impact global terrestrial and aquatic systems, even those far removed from agricultural production, to an ever growing extent, unless N resources are used more efficiently or food consumption trends change.     

Nitrous oxide emissions from agricultural fields: Assessment, measurement and mitigation

In this paper we discuss three topics concerning N₂O emissions from agricultural systems. First, we present an appraisal of N₂O emissions from agricultural soils (Assessment). Secondly, we discuss some recent efforts to improve N₂O flux estimates in agricultural fields (Measurement), and finally, we relate recent studies which use nitrification inhibitors to decrease N₂O emissions from N-fertilized fields (Mitigation).To assess the global emission of N₂O from agricultural soils, the total flux should represent N₂O from all possible sources; native soil N, N from recent atmospheric deposition, past years fertilization, N from crop residues, N₂O from subsurface aquifers below the study area, and current N fertilization. Of these N sources only synthetic fertilizer and animal manures and the area of fields cropped with legumes have sufficient global data to estimate their input for N₂O production. The assessment of direct and indirect N₂O emissions we present was made by multiplying the amount of fertilizer N applied to agricultural lands by 2% and the area of land cropped to legumes by 4 kg N₂O-N ha^-1. No regard to method of N application, type of N, crop, climate or soil was given in these calculations, because the data are not available to include these variables in large scale assessments. Improved assessments should include these variables and should be used to drive process models for field, area, region and global scales.Several N₂O flux measurement techniques have been used in recent field studies which utilize small and ultralarge chambers and micrometeorological along with new analytical techniques to measure N₂O fluxes. These studies reveal that it is not the measurement technique that is providing much of the uncertainty in N₂O flux values found in the literature but rather the diverse combinations of physical and biological factors which control gas fluxes. A careful comparison of published literature narrows the range of observed fluxes as noted in the section on assessment. An array of careful field studies which compare a series of crops, fertilizer sources, and management techniques in controlled parallel experiments throughout the calendar year are needed to improve flux estimates and decrease uncertainty in prediction capability.There are a variety of management techniques which should conserve N and decrease the amount of N application needed to grow crops and to limit N₂O emissions. Using nitrification inhibitors is an option for decreasing fertilizer N use and additionally directly mitigating N₂O emissions. Case studies are presented which demonstrate the potential for using nitrification inhibitors to limit N₂O emissions from agricultural soils. Inhibitors may be selected for climatic conditions and type of cropping system as well as the type of nitrogen (solid mineral N, mineral N in solution, or organic waste materials) and applied with the fertilizers.     

Methane and nitrous oxide emissions from direct-seeded and seedling-transplanted rice paddies in southeast China

Background and aims

The rice production is experiencing a shift from conventionally seedling-transplanted (TPR) to direct-seeded (DSR) cropping systems in Southeast Asia. Besides the difference in rice crop establishment, water regime is typically characterized as water-saving moist irrigation for DSR and flooding-midseason drainage-reflooding and moist irrigation for TPR fields, respectively. A field experiment was conducted to quantify methane (CH₄) and nitrous oxide (N₂O) emissions from the DSR and TPR rice paddies in southeast China.

Methods

Seasonal measurements of CH₄ and N₂O fluxes from the DSR and TPR plots were simultaneously taken by static chamber-GC technique.

Results

Seasonal fluxes of CH₄ averaged 1.58 mg m^?2 h^?1 and 1.02 mg m^?2 h^?1 across treatments in TPR and DSR rice paddies, respectively. Compared with TPR cropping systems, seasonal N₂O emissions from DSR cropping systems were increased by 49 % and 46 % for the plots with or without N application, respectively. The emission factors of N₂O were estimated to be 0.45 % and 0.69 % of N application, with a background emission of 0.65 and 0.95 kg N₂O-N ha^?1 under the TPR and DSR cropping regimes, respectively. Rice biomass and grain yield were significantly greater in the DSR than in the TPR cropping systems. The net global warming potential (GWP) of CH₄ and N₂O emissions were comparable between the two cropping systems, while the greenhouse gas intensity (GHGI) was significantly lower in the DSR than in the TPR cropping systems.

Conclusions

Higher grain yield, comparable GWP, and lower GHGI suggest that the DSR instead of conventional TPR rice cropping regime would weaken the radiative forcing of rice production in terms of per unit of rice grain yield in China, and DSR rice cropping regime could be a promising rice development alternative in mainland China.     

氮素类型和剂量对寒温带针叶林土壤N2O排放的影响

大气氮沉降输入会增加森林生态系统氮素有效性,进而改变土壤N_2O产生与排放,然而有关不同氮素离子(氧化态NO_3~--N与还原态NH_4~+-N)沉降对土壤N_2O排放的影响知之甚少。以大兴安岭寒温带针叶林为研究对象,构建了3种类型(NH_4Cl、KNO_3、NH_4NO_3)和4个施氮水平(0、10、20、40 kg N hm~(-2)a~(-1))的增氮控制试验,利用流动化学分析仪和静态箱-气相色谱法4次/月测定凋落物层和矿质层土壤无机氮含量、土壤-大气界面N_2O净交换通量以及相关环境因子,分析施氮类型和剂量对土壤氮素有效性、土壤N_2O通量的影响探讨氮素富集条件下土壤N_2O通量的环境驱动机制。结果表明:施氮类型和剂量均显著影响土壤无机氮含量,土壤NH_4~+-N的积累效应显著高于NO_3~--N。施氮一致增加寒温带针叶林土壤N_2O排放,NH_4NO_3促进效应最为明显,增幅为442%-677%,高于全球平均水平(134%)。土壤N_2O通量与土壤温度、凋落物层NH_4~+-N含量正相关,且随着施氮水平增加而增加。结果表明大气氮沉降短期内不会导致寒温带针叶林土壤NO_3~--N大量流失,但会显著促进土壤N_2O的排放。此外,外源性NH_4~+和NO_3~-输入对土壤N_2O排放的促进作用具有协同效应,在未来森林生态系统氮循环和氮平衡研究中应该区分对待。     

Tillage and Nitrogen Application Effects on Nitrous and Nitric Oxide Emissions from Irrigated Corn Fields

A 2-year study was conducted to investigate the potential of no-till cropping systems to reduce N₂O and NO emissions under different N application rates in an irrigated corn field in northeastern Colorado. Flux measurements were begun in the spring of 2003, using vented (N₂O) and dynamic (NO) chambers, one to three times per week, year round, within plots that were cropped continuously to corn (Zea mays L.) under conventional-till (CT) and no-till (NT). Plots were fertilized at planting in late April with rates of 0, 134 and 224 kg N ha⁻¹ and corn was harvested in late October or early November each year. N₂O and NO fluxes increased linearly with N application rate in both years. Compared with CT, NT did not significantly affect the emission of N₂O but resulted in much lower emission of NO. In 2003 and 2004 corn growing seasons, the increase in N₂O-N emitted per kg ha⁻¹ of fertilizer N added was 14.5 and 4.1 g ha⁻¹ for CT, and 11.2 and 5.5 g ha⁻¹ for NT, respectively. However, the increase in NO-N emitted per kg ha⁻¹ of fertilizer N added was only 3.6 and 7.4 g ha⁻¹ for CT and 1.6 and 2.0 g ha⁻¹ for NT in 2003 and 2004, respectively. In the fallow season (November 2003 to April 2004), much greater N₂O (2.0–3.1 times) and NO (13.1–16.8 times) were emitted from CT than from NT although previous N application did not show obvious carry-over effect on both gas emissions. Results from this study reveal that NT has potential to reduce NO emission without an obvious change in N₂O emission under continuous irrigated corn cropping compared to CT.     

Influence of integrated weed management system on N-cycling microbial communities and N2O emissions

Aims

Integrated weed management, which allows reducing the reliance of cropping systems on herbicides, is based on the use of specific combinations of innovative agricultural practices. However the impact of the introduction of these practices in cropping systems may influence soil functioning such as biogeochemical cycling. Here, we investigated N₂O emissions and the abundances of N-cycling microorganisms in 11-year old cropping systems (i.e. conventional reference and integrated weed management) in order to estimate the environmental side-effects of long-term integrated weed management.

Methods

N₂O emissions were continuously measured using automated chambers coupled with infrared analysers. Abundances of ammonia oxidizers and denitrifiers together with total bacteria and archaea were determined monthly from 0 to 10 and 10–30 cm soil layer samples by quantitative Polymerase Chain Reaction (qPCR). The relationship between N₂O emissions and microbial abundances during the study were investigated as were their relationships with soil physicochemical parameters and climatic conditions.

Results

Over 7 months, the system with integrated weed management emitted significantly more N₂O with cumulated measured emissions of 240 and 544 g N-N₂O ha^?1 for conventional and integrated systems, respectively. Abundances of microbial guilds varied slightly between systems, although ammonia-oxidizing bacteria were more abundant in the reference system (1.7 10⁶ gene copies g^?1 dry weight soil) compared to the integrated system (1.0 10⁶ gene copies g^?1 dry weight soil). These differences revealed both the long-term modification of soil biogeochemical background and the functioning of microbial processes due to 11 years of alternative field management, and the short-term impacts of the agricultural practices introduced as part of weed management during the cropping year.

Conclusions

The abundances of the different microbial communities involved in N cycling and the intensity of N₂O emissions were not related, punctual high N₂O emissions being more dependent on favourable soil conditions for nitrifying and denitrifying activities. Future studies will be performed to check these findings for other pedoclimatic conditions and to examine the impact of such cropping systems.     

A Review of Spatial Variation of Inorganic Nitrogen (N) Wet Deposition in China

Atmospheric nitrogen (N) deposition (N_dep), an important component of the global N cycle, has increased sharply in recent decades in China. Although there were already some studies on N_dep on a national scale, there were some gaps on the magnitude and the spatial patterns of N_dep. In this study, a national-scale N_dep pattern was constructed based on 139 published papers from 2003 to 2014 and the effects of precipitation (P), energy consumption (E) and N fertilizer use (F_N) on spatial patterns of N_dep were analyzed. The wet deposition flux of NH₄⁺-N, NO₃^--N and total N_dep was 6.83, 5.35 and 12.18 kg ha^-1 a^-1, respectively. N_dep exhibited a decreasing gradient from southeast to northwest of China. Through accuracy assessment of the spatial N_dep distribution and comparisons with other studies, the spatial N_dep distribution by Lu and Tian and this study both gained high accuracy. A strong exponential function was found between P and N_dep, F_N and N_dep and E and N_dep, and P and F_N had higher contribution than E on the spatial variation of N_dep. Fossil fuel combustion was the main contributor for NO₃^--N (86.0%) and biomass burning contributed 5.4% on the deposition of NO₃^--N. The ion of NH₄⁺ was mainly from agricultural activities (85.9%) and fossil fuel combustion (6.0%). Overall, N_dep in China might be considerably affected by the high emissions of NO_x and NH₃ from fossil fuel combustion and agricultural activities.