Soil N<Subscript>2</Subscript>O fluxes in integrated production systems,continuous pasture and Cerrado

The objective of this study was to evaluate N₂O fluxes from integrated crop-livestock (ICL) and integrated crop-livestock forest (ICLF) systems, continuous pasture and native Cerrado. The experiment was conducted at Embrapa Cerrados, Planaltina-DF, in a Red Oxisol, between February 2012 and April 2014, following the transition of crop to livestock, which began in March 2012, with the sowing of Brachiaria brizantha cv. Piatã, intercropped with sorghum. The experimental design was a randomized block with three replications. The treatments were: cultivated area intercropped with rows of Eucalyptus, spaced 2 × 2 m between plants and 22 m between rows (ICLF); and an area cultivated without tree species (ICL), and also two adjacent reference areas: native Cerrado and continuous pasture. N₂O productions were characterized by fluxes below 20 μg N m^?2 h^?1. The ICL system had the highest cumulative flux with 2.84 kg N ha^?1, while the ICLF system obtained cumulative fluxes of 2.05 kg N ha^?1. The native Cerrado showed a negative balance, with –0.05 kg N ha^?1. The dry season was mostly characterized by low N₂O fluxes ranging between 10 μg N m^?2 h^?1 and negative values, whereas higher N₂O fluxes were observed after precipitation events, especially those following a long drought period. The water filled pore space was the factor that best explained N₂O fluxes, but higher fluxes were observed after the application of nitrogen fertilizer. There was a positive correlation between microbial biomass carbon and N₂O fluxes in the ICL and ICLF systems.     

Nitrous oxide emissions as influenced by legume cover crops and nitrogen fertilization

In this study, we measured nitrous oxide (N₂O) fluxes from plots of fall-planted hairy vetch (HV, Vicia villosa) and spring-planted broadleaf vetch (BLV, Vicia narbonensis) grown as nitrogen (N) sources for following summer forage crabgrass (Digitaria sanguinalis). Comparisons also included 60 kg ha^?1 inorganic N fertilizer for crabgrass at planting (60-N) and a control without N fertilizer. Each treatment had six replicated plots across the slope. Fluxes were measured with closed chamber systems during the period between spring growth of cover crops and first-cut of crabgrass in mid-July. HV had strong stand and aboveground biomass had 185?±?50 kg N ha^?1 (mean?±?standard error, n?=?6) at termination. However, BLV did not establish well and aboveground biomass had only 35?±?15 kg N ha^?1. Ratio vegetation index of crabgrass measured as proxy of biomass growth was highest in HV treatment. However, total aboveground biomass of crabgrass was statistically similar to 60-N plots. Fluxes of N₂O were low prior to termination of cover crops but were as high as 8.2 kg N₂O ha^?1 day^?1 from HV plots after termination. The fluxes were enhanced by large rainfall events recorded after biomass incorporation. Rainfall enhanced N₂O fluxes were also observed in other treatments, but their magnitudes were much smaller. The high N₂O fluxes from HV plots contributed to emissions of 30.3?±?12.4 kg N₂O ha^?1 within 30 days of biomass incorporation. Emissions were only 2.0?±?0.7, 3.4?±?1.3 and 1.0?±?0.4 kg N₂O ha^?1 from BLV, 60-N and control plots, respectively.     

Integrated management practices significantly affect N2O emissions and wheat–maize production at field scale in the North China Plain

In the North China Plain, a field experiment was conducted to measure nitrous oxide (N₂O) and methane (CH₄) fluxes from a typical winter wheat–summer maize rotation system under five integrated agricultural management practices: conventional regime [excessive nitrogen (N) fertilization, flood irrigation, and rotary tillage before wheat sowing; CON], recommended regime 1 (balanced N fertilization, decreased irrigation, and deep plowing before wheat sowing; REC-1), recommended regime 2 (balanced N fertilization, decreased irrigation, and no tillage; REC-2), recommended regime 3 (controlled release N fertilizer, decreased irrigation, and no tillage; REC-3), and no N fertilizer (CK). Field measurements indicated that pulse emissions after N fertilization and irrigation contributed 19–49 % of annual N₂O emissions. In contrast to CON (2.21 kg N₂O-N ha^?1 year^?1), the other treatments resulted in significant declines in cumulative N₂O emissions, which ranged from 0.96 to 1.76 kg N₂O-N ha^?1 year^?1, indicating that the recommended practices (e.g., balanced N fertilization, controlled release N fertilizer, and decreased irrigation) offered substantial benefits for both sustaining grain yield and reducing N₂O emissions. Emission factors of N fertilizer were 0.21, 0.22, 0.23, and 0.37 % under CON, REC-1, REC-3, and REC-2, respectively. Emissions of N₂O during the freeze–thaw cycle period and the winter freezing period accounted for 9.7 and 5.1 % of the annual N₂O budget, respectively. Thus, we recommend that the monitoring frequency should be increased during the freeze–thaw cycle period to obtain a proper estimate of total emissions. Annual CH₄ fluxes from the soil were low (?1.54 to ?1.12 kg CH₄-C ha^?1 year^?1), and N fertilizer application had no obvious effects on CH₄ uptake. Values of global warming potential were predominantly determined by N₂O emissions, which were 411 kg CO₂-eq ha^?1 year^?1 in the CK and 694–982 kg CO₂-eq ha^?1 year^?1 in the N fertilization regimes. When comprehensively considering grain yield, global warming potential intensity values in REC-1, REC-2, and REC-3 were significantly lower than in CON. Meanwhile, grain yield increased slightly under REC-1 and REC-3 compared to CON. Generally, REC-1 and REC-3 are recommended as promising management regimes to attain the dual objectives of sustaining grain yield and reducing greenhouse gas emissions in the North China Plain.     

Nitrous oxide fluxes in a Brazilian clayey oxisol after 24 years of integrated crop-livestock management

Integrated crop-livestock systems have been recently adopted in several agricultural regions of Brazil. Studies involving the effect of adopting integrated systems on greenhouse gas mitigation are essential for choosing sustainable agricultural systems. In this study, the emissions of nitrous oxide in a crop-livestock system (4-year crop/pasture rotation) compared with two continuous crop (CC) areas under conventional and no-tillage management were investigated. The treatments consisted of continuous cropping under no-tillage (CC-NT), continuous cropping with annual heavy disc harrow (CC-CT), an integrated crop-livestock system under no-tillage (CLS-NT) and native Cerrado as a reference. Considering the cumulative N₂O emissions in a year, the CC-CT emitted 2.55 kg N-N₂O ha^?1, higher than the Cerrado, which emitted 0.55 kg N-N₂O ha^?1. All the agricultural systems emitted more N₂O than the Cerrado, however, the two conservation systems CC-NT and CLS-NT had lower emissions than the CC-CT, and were responsible for 1.90 and 1.52 kg N-N₂O ha^?1, respectively. In the agroecosystems, the highest N₂O fluxes were observed after fertilization and rainfall events. In the CC systems, N₂O emissions were greater than in the integrated system during the sorghum/off-season period, but in the CC-CT emissions were greater than in CC-NT. During the soybean cycle no differences in emissions were observed between both CC systems, which surpassed that in CLS-NT that was occupied by Brachiaria pasture. The annual cumulative N₂O emissions in CLS-NT were close to that observed in the Cerrado indicating this system to be an agricultural practice with potential to mitigate N₂O emissions.     

Soil organic matter,greenhouse gases and net global warming potential of irrigated conventional,reduced-tillage and organic cropping systems

Reducing tillage intensity and diversifying crop rotations may improve the sustainability of irrigated cropping systems in semi-arid regions. The objective of this study was to compare the greenhouse gas (GHG) emissions, soil organic matter, and net global warming potential (net GWP) of a sugar beet (Beta vulgaris L.)-corn (Zea mays L,) rotation under conventional (CT) and reduced-tillage (RT) and a corn-dry bean (Phaseolus vulgaris L.) rotation under organic (OR) management during the third and fourth years of 4-year crop rotations. The gas and soil samples were collected during April 2011–March 2013, and were analyzed for carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) emissions, water-filled pore space (WFPS), soil nitrate (NO₃ ^?–N) and ammonium (NH₄ ⁺–N) concentrations, soil organic carbon (SOC) and total nitrogen (TN), and net global warming potential (net GWP). Soils under RT had 26% lower CO₂ emissions compared to 10.2 kg C ha^?1 day^?1 and 43% lower N₂O emissions compared to 17.5 g N ha^?1 day^?1 in CT during cropping season 2011, and no difference in CO₂ and N₂O emissions during cropping season 2012. The OR emitted 31% less N₂O, but 74% more CO₂ than CT during crop season 2011. The RT had 34% higher SOC content than CT (17.9 Mg ha^?1) while OR was comparable with CT. Net GWP was negative for RT and OR and positive for CT. The RT and OR can increase SOC sequestration, mitigate GWP and thereby support in the development of sustainable cropping systems in semiarid agroecosystems.     

Performance of wearable ionization air cleaners: Ozone emission and particle removal

Wearable ionization air cleaners are compact in size and marketed for personal respiratory protection by removing air pollutants from users' breathing zone. In this study, ozone emission and particle removal rates of four wearable ionization air cleaners (namely, AC1 through AC4) were evaluated inside a 0.46 m³ stainless steel chamber. Continuous measurements were conducted for ozone concentration, PM_2.5 concentration, and particle size distribution in the size range of 18.1–289 nm. Two of the four wearable air cleaners (i.e., AC1 and AC2) had detectable ozone emissions. The 10-h average ozone emission rates were quite different (i.e., 0.67 mg·h^?1 for AC1 and 3.40 × 10^?2 mg·h^?1 for AC2); however, the ozone emissions were negligible for AC3 and AC4. The number removal rates for particles within the measured size range were highly variable (i.e., 2.20 h^?1, 0.52 h^?1, 8.10 h^?1, and 27.9 h^?1 for AC1 through AC4, respectively). The corresponding mass removal rates of PM_2.5 were 1.85 h^?1, 0.48 h^?1_,1.52 h^?1, and 5.37 h^?1, respectively. Regulatory guidelines are needed to assure these devices can effectively remove particles without ozone emissions to protect public health.

Copyright © 2016 American Association for Aerosol Research     

Net ecosystem CO2 exchange and carbon cycling in tropical lowland flooded rice ecosystem

The seasonal fluxes of CO₂ and its characteristics with relation to environmental variables were investigated under tropical lowland flooded rice paddies employing the open path eddy covariance technique. The seasonal net ecosystem carbon budget was quantified by empirical modelling approach. The integrated net ecosystem exchange (NEE), gross primary production (GPP) and ecosystem respiration (RE) in the flooded rice field was ?448, 811 and 363 g C m^?2 in wet season. Diurnal variations of mean NEE values during the season varied from +3.99 to ?18.50 μmol CO₂ m^?2 s^?1. The daily average NEE over the cropping season varied from +2.73 to ?7.74 g C m^?2 day^?1. The net ecosystem CO₂ exchange reached its maximum in heading to flowering stage of rice with an average value of ?5.67 g C m^?2 day^?1. On daily basis the flooded rice field acted as a net sink for CO₂ during most of the times in growing season except few days at maturity when it became a net CO₂ source. The rate of CO₂ uptake by rice as observed from negative NEE values increased proportionally with air temperature up to 34 °C. The carbon distribution in different component of soil-plant system namely, soil organic carbon, dissolved organic carbon, methane emission, rhizodeposition, carbon in algal biomass, crop harvest and residues were quantified and carbon balance sheet was prepared for the wet season in tropical rice. Carbon balance sheet for tropical rice revealed 7.12 Mg C ha^?1 was cycled in the system in wet season.     

Nitrous oxide (N2O) emissions in response to increasing fertilizer addition in maize (Zea mays L.) agriculture in western Kenya

National and regional efforts are underway to increase fertilizer use in sub-Saharan Africa, where attaining food security is a perennial challenge and mean fertilizer use in many countries is <10 % of nationally recommended rates. Increases in nitrogen (N) inputs will likely cause increased emissions of the greenhouse gas nitrous oxide (N₂O). We established experimental plots with different rates of N applied to maize (Zea mays) in a field with a history of nutrient additions in western Kenya and measured N₂O fluxes. Fertilizer was applied by hand at 0, 50, 75, 100, and 200 kg N ha^?1 in a split application on March 22 and April 20, 2010. Gas sampling was conducted daily during the week following applications, and was otherwise collected weekly or biweekly until June 29, 2010. Cumulative fluxes were highest from the 200 kg N ha^?1 treatment, with emissions of 810 g N₂O–N ha^?1; fluxes from other treatments ranged from 620 to 710 g N₂O–N ha^?1, but with no significant differences among treatments. Emissions of N₂O during the 99-day measurement period represented <0.1 % of added fertilizer N for all treatments. Though limited to a single year, these results provide further evidence that African agricultural systems may have N₂O emission factors substantially lower than the global mean.     

VOLATILE ORGANIC COMPOUND (VOC) REMOVAL BY ADSORPTION ONTO ACTIVATED CARBON FIBER CLOTH AND ELECTROTHERMAL DESORPTION: AN INDUSTRIAL APPLICATION

ABSTRACT

Previous studies have shown good adsorption of volatile organic compounds (VOC) present in air onto activated carbon fiber cloths (ACFCs). In a chemical plant, a treatment process was carried out to control a gaseous emission (flow close to 100 m³ h^?1) loaded with methylene chloride at concentrations ranging between 3 and 30 g m^?3. A final mass flow lower than 100 g h^?1 was required in the outlet emission. Two identical cylindrical ACFC modules worked alternately in an adsorption-desorption cycle. The outlet pollutant mass flow was found to be less than 4 g h^?1. After saturation of the adsorbent, the module was electrothermally regenerated. Desorbed methylene chloride was recovered in a cryogenic trap and reused in the chemical processes of the plant. This system worked continuously for more than 18 months (24 h per day) with no operating problems and giving good performance in terms of VOC outlet emission concentrations.     

Nitrous oxide emissions from a fertile grassland in Western Norway following the application of inorganic and organic fertilizers

In Norway, 65 % of the agricultural land is under grassland for feeding ruminants. The objective of the present study was to quantify N₂O emissions from grassland on a fertile sandy loam in Western Norway, and to estimate the response of seasonal N₂O emissions to added inorganic N, cattle slurry (CS) N and clover N. Ammonium nitrate (AN) and CS were applied manually at annual rates of 0, 100, 150, 200 and 250 kg AN-N ha^?1, 80 kg CS-N ha^?1 or as a combination of 200 kg AN-N ha^?1 and 80 kg CS-N ha^?1. Background N₂O emissions were five times higher in summer season 2009 than in 2010, but the relative amount of N₂O derived from AN was constant in both periods, amounting to 0.11 % of applied N. CS had no measurable impact on N₂O emissions in 2009, but 0.15 % of CS-N was emitted as N₂O during summer 2010. In the warm year of 2009, which included a drought period, 1–24 % of the N₂O emissions were attributed to the effect of clover depending on fertilization. Clover had no effect on N₂O fluxes in the cool and moist year 2010. Our results suggest that N₂O emissions in fertile Norwegian grasslands are to a great extent controlled by inter-annual variations in background emissions and variable contribution of biologically fixed N and CS-N.     

Erratum to: Electrochemical dissolution of metallic platinum in ionic liquids

The electrochemical dissolution of Pt in several ionic liquids (ILs) was studied. Different ILs were tested assessing their potential to dissolve Pt. Dissolution rate and current efficiency were evaluated. The main focus was on Cl containing ILs: first generation, eutectic-based ILs and second generation ILs with discrete anions. Pt dissolution only occurred in type 1 eutectic-based ILs with a max. dissolution rate of 192.2 g m^?2 h^?1 and a max. current efficiency of 99 % for the ZnCl₂–1-ethyl-3-methylimidazolium chloride IL, and 9.090 g m^?2 h^?1 and 96 % for the 1:1 ZnCl₂–choline chloride IL. The dissolution occurred through the formation of [PtCl_x]^y? complexes. To form these complexes, addition of a metal chloride was necessary. Furthermore, an IL with an electrochemical window of 1.5 V, preferably 2.0 V was required to achieve Pt dissolution. The added metal salt needed to have a higher decomposition potential than 1.5 V or should be a Pt salt.     

Effects of the herbicides butachlor and bensulfuron-methyl on N2O emissions from a dry-seeded rice field

Independent field and laboratory incubation experiments were conducted to investigate the effects of two commonly used herbicides butachlor and bensulfuron-methyl on N₂O emissions from a dry-seeded rice field. Three treatments were applied in field experiments: a fertilized control without herbicide, fertilized plots amended with butachlor equivalent to 2.55 L ha^?1 of 60 % by weight active ingredient and fertilized plots amended with bensulfuron-methyl equivalent to 300 g ha^?1 of 10 % by weight active ingredient. Herbicides were applied twice in the rice growing season according to local farming practices. The same treatments were used in laboratory incubation experiments, i.e., a fertilized control without herbicide and fertilized soil amended with the herbicide butachlor or bensulfuron-methyl. The soil moisture was adjusted to 0.55 g g^?1 in the lab incubation experiments based on the average water content determined in the dry-seeded rice field. The field and laboratory simulation experiments all showed that the butachlor applications led to significantly increased N₂O emissions (p < 0.05), whereas bensulfuron-methyl had no effect on N₂O emissions (p > 0.05). Butachlor enhanced the N₂O emissions by up to 177.5 % over the entire rice growing season. Moreover, butachlor and bensulfuron-methyl treatment led to a marginal stimulation of the soil respiration rates. A further investigation in the field experiments suggested that the butachlor-enhanced N₂O emissions resulted from increased soil ammonium nitrogen and nitrate nitrogen contents and the more abundance of ammonia-oxidizing and denitrifying bacteria in the late stage after the herbicide application. The bensulfuron-methyl treatment had no influence on N₂O emissions during the rice growing season, which was attributed to the low soil nitrate nitrogen contents during this period.     

Electrochemical dissolution of metallic platinum in ionic liquids

The electrochemical dissolution of Pt in several ionic liquids (IL’s) was studied. Different IL’s were tested assessing their potential to dissolve Pt. Dissolution rate and current efficiency were evaluated. The main focus was on Cl containing IL’s: first generation, eutectic based IL’s and second generation IL’s with discrete anions. Pt dissolution only occurred in type 1 eutectic-based IL’s with a max. dissolution rate of 192.2 g m^?2 h^?1 and a max. current efficiency of 99 % for the ZnCl₂-1-ethyl-3-methylimidazolium chloride IL, and 9.090 g m^?2 h^?1 and 96 % for the 1:1 ZnCl₂–choline chloride ionic liquid. The dissolution occurred via the formation of [PtCl _x ] ^y? complexes. To form these complexes, addition of a metal chloride was necessary. Furthermore, an IL with an electrochemical window of 1.5 V, preferably 2.0 V is required to achieve Pt dissolution. The added metal salt needed to have a higher decomposition potential than 1.5 V or should be a Pt salt.     

Greenhouse gas emissions in an agroforestry system of the southeastern USA

Agroforestry systems may provide diverse ecosystem services and economic benefits that conventional agriculture cannot, e.g. potentially mitigating greenhouse gas emissions by enhancing nutrient cycling, since tree roots can capture nutrients not taken up by crops. However, greenhouse gas emission data from agroforestry systems are not available in the southeastern USA, thus limiting our ability to optimize agroforestry management strategies for the region. We hypothesized that tree-crop interactions could prevent excess N from being released to the atmosphere as nitrous oxide (N₂O). We determined N₂O and carbon dioxide (CO₂) emissions, soil temperature, water content, and surface-soil inorganic N in an 8-year-old agroforestry site at the Center for Environmental Farming Systems in Goldsboro, North Carolina, USA. The experimental design was a factorial arrangement of soil texture (loamy sand, sandy loam, and clay loam) and canopy cover (cropped alley, margin between crops and trees, and under Pinus palustris, Pinus taeda, and Quercus pagoda) with three replications. Sampling occurred 42 times within a year using static, vented chambers exposed to the soil for 1-h periods. Soil N₂O emission was lower under tree canopies than in cropped alleys, and margin areas were intermediate. Soil texture, water content, and inorganic N were key determinants of the magnitude of N₂O emission. Soil CO₂ emission was controlled by temperature and water content as expected, but surprisingly not by their interaction. Soil temperature was 1.8 ± 1.3 °C lower and soil water content was 0.043 ± 0.15 m³ m^?3 lower under tree canopy than in cropped alleys, which helped to reduce CO₂ emission under trees relative to that in cropped alleys. Our results provide a foundation for reducing greenhouse gas emissions in complex agricultural landscapes with varying soil texture by introducing timber production without abandoning agricultural operations.     

Measurement and modeling of nitrous and nitric oxide emissions from a tea field in subtropical central China

Tea fields represent an important source of nitrous oxide (N₂O) and nitric oxide (NO) emissions due to high nitrogen (N) fertilizer applications and very low soil pH. To investigate the temporal characteristics of N₂O and NO emissions, daily emissions were measured over 2½ years period using static closed-chamber/gas chromatograph and chemiluminescent measurement system in a tea field of subtropical central China. Our results revealed that N₂O and NO fluxes showed similar temporal trends, which were generally driven by temporal variations in soil temperature and soil moisture content and were also affected by fertilization events. The measured average annual N₂O and NO emissions were 10.9 and 3.3 kg N ha^?1 year^?1, respectively, highlighting the high N₂O and NO emissions from tea fields. To improve our understanding of N-cycling processes in tea ecosystems, we developed a new nitrogenous gas emission module for the water and nitrogen management model (WNMM, V2) that simulated daily N₂O and NO fluxes, in which the NO was simulated as being emitted from both nitrification and nitrite chemical decomposition. The results demonstrated that the WNMM captured the general temporal dynamics of N₂O (NSE = 0.40; R² = 0.52, RMSE = 0.03 kg N ha^?1 day^?1, P < 0.001) and NO (NSE = 0.41; R² = 0.44, RMSE = 0.01 kg N ha^?1 day^?1, P < 0.001) emissions. According to the simulation, denitrification was identified as the dominant process contributing 76.5% of the total N₂O emissions, while nitrification and nitrite chemical decomposition accounted for 52.3 and 47.7% of the total NO emissions, respectively.     

Recovery of groundwater N2O at the soil surface and its contribution to total N2O emissions

Production and accumulation of the major greenhouse gas nitrous oxide (N₂O) in surface groundwater might contribute to N₂O emissions to the atmosphere. We report on a ¹⁵N tracer study conducted in the Fuhrberger Feld aquifer in northern Germany. A K¹⁵NO₃ tracer solution (60 atom%) was applied to the surface groundwater on an 8 m² measuring plot using 45 injection points in order to stimulate production of ¹⁵N₂O by denitrification and to detect its contribution to emissions at the soil surface. Samples from the surface groundwater, from the unsaturated zone and at the soil surface were collected in regular intervals over a 72-days period. Total N₂O fluxes at the soil surface were low and in a range between ?7.6 and 29.1 μg N₂O-N m^?2 h^?1. ¹⁵N enrichment of N₂O decreased considerably upwards in the profile. In the surface groundwater, we found a ¹⁵N enrichment of N₂O between 13 and 42 atom%. In contrast, ¹⁵N enrichment of N₂O in flux chambers at the soil surface was very low, but a detectable ¹⁵N enrichment was found at all sampling events. Fluxes of groundwater-derived ¹⁵N-N₂O were very low and ranged between 0.0002 and 0.0018 kg N₂O-N ha^?1 year^?1, indicating that indirect N₂O emissions from the surface groundwater of the Fuhrberger Feld aquifer occurring via upward diffusion are hardly significant. Due to these observations we concluded that N₂O dynamics at the soil–atmosphere interface is predominantly governed by topsoil parameters. However, highest ¹⁵N enrichments of N₂O throughout the profile were obtained in the course of a rapid drawdown of the groundwater table. We assume that such fluctuations may enhance diffusive N₂O fluxes from the surface groundwater to the atmosphere for a short time.     

Fertiliser timing and use of inhibitors to reduce N<Subscript>2</Subscript>O emissions of rainfed wheat in a semi-arid environment

Nitrogen (N) management is critical to the profitability of grain production systems, however careful management of fertiliser is needed to minimise environmental impacts. We investigated the effect of five N fertilisation strategies on nitrous oxide (N₂O) emissions and nitrogen use efficiency (NUE) of rainfed wheat grown on a clay soil in a temperate, semi-arid environment of south eastern Australia during 2013 and 2014. Treatments included urea application (50 kg N/ha) at sowing with and without nitrification inhibitor (3,4–dimethylpyrazole phosphate) and surface broadcasting of urea with and without urease inhibitor (n-butyl thiophosphoric triamide) at the end of tillering plus an unfertilised control. Daily N₂O emissions were low and responsive to in-season rainfall and fertiliser addition at sowing. Cumulative emissions from sowing until harvest were highest where N was applied at sowing in 2013; 160 g N₂O-N/ha, while the 0 N control emitted 28 g N₂O-N/ha (over 201 days). Emissions during 2014 were 77% lower than 2013 due to dry seasonal conditions; cumulative emissions were 49 g N₂O-N/ha where N was applied at sowing, with background emissions of around 0 g N₂O-N/ha (over 177 days). Inhibitors showed limited scope for reducing N₂O emissions in this environment, however deferring N application until the end of tillering reduced N₂O emissions. Grain yield responses to fertiliser were significant; increasing grain yield by 11–31% and NUE was generally high (recovery efficiency?>?68%). However, deferring N application until the end of tillering in 2014 reduced yield (??19%) and recovery of applied N (??74%).     

Emissions of CH4, N2O, NH3 and odorants from pig slurry during winter and summer storage

Manure storage contributes significantly to greenhouse gas (GHG), NH₃ and odour emissions from intensive livestock production. A pilot-scale facility with eight 6.5-m³ slurry storage units was used to quantify emissions of CH₄, N₂O, NH₃, and odorants from pig slurry during winter and summer storage. Pig slurry was stored with or without a straw crust, and with or without interception of precipitation, i.e., four treatments, in two randomized blocks. Emissions of total reduced S (mainly H₂S) and p-cresol, but not skatole, were reduced by the straw crust. Total GHG emissions were 0.01–0.02 kg CO₂ eq m^?3 day^?1 during a 45-day winter storage, and 1.1–1.3 kg CO₂ eq m^?3 day^?1 during a 58-day summer storage period independent of storage conditions; the GHG balance was dominated by CH₄ emissions. Nitrous oxide emissions occurred only during summer storage where, apparently, emissions were related to the water balance of the surface crust. An N₂O emission factor for slurry storage with a straw crust was estimated at 0.002–0.004. There was no evidence for a reduction of CH₄ emissions with a crust. Current Intergovernmental Panel on Climate Change recommendations for N₂O and CH₄ emission factors are discussed.     

Symbiotic nitrogen fixation by legumes in two Chinese grasslands estimated with the 15N dilution technique

Symbiotic nitrogen (N) fixation by legumes was investigated using the ¹⁵N dilution technique in two Chinese grasslands: one in the north-eastern Tibetan Plateau and the other in Inner Mongolia in China. A small amount (0.03 g N m^?2) of ¹⁵N labelled (NH₄)₂SO₄ fertilizer was evenly distributed in two soils. One month after the ¹⁵N addition, four legumes (Astragalus sp., Gueldenstaedtia diversifolia, Oxytropis ochrocephala and Trigonella ruthenica) in the alpine meadow and two legumes (Thermopsis lanceolata and Melissitus ruthenica) in the temperate steppe were collected. Several non-legume plant species were harvested as the reference. Above-ground biomass of legumes ranged from 8 to 24 g m^?2 in the alpine meadow and from 11 to 35 g m^?2 in the temperate steppe. The reference plants showed distinctly higher ¹⁵N atom% excess than legumes (0.08% vs. 0.02% in the alpine meadow, 0.10% vs. 0.02% in the temperate steppe). The N derived from atmosphere (%Ndfa) ranged from 50 to 90% N in the alpine meadow, while it ranged from 85 to 92% in the temperate steppe. Based on the legume above-ground biomass, total symbiotic N₂-fixation rate was estimated to be 1.00 g N m^?2 year^?1 in the alpine meadow and 1.15 g N m^?2 year^?1 in the temperate steppe. These N inputs by legumes can account for 9% of the gap between the N demand and the seasonal N release by mineralization in the alpine Kobresia grassland and 20% in the temperate Leymus grassland, respectively. Considering additional contribution of the root biomass, we suggest that biological N₂-fixation by legumes plays an important role in the cycling of N in both Kobresia and Leymus grasslands on an annual scale.     

Season and location–specific nitrous oxide emissions in an almond orchard in California

Almonds are an important commodity in California and account for around 15% of the state’s fertilizer nitrogen (N) consumption. Motivated by strong correlations typically observed between fertilizer N inputs and emissions of the potent greenhouse gas and ozone depleting molecule nitrous oxide (N₂O), this study aimed to characterize spatial and temporal patterns in N₂O emissions in an almond orchard under typical agronomic management. N₂O fluxes were measured for a total of 2.5 years, including 3 growing seasons and 2 dormant seasons. Measurements targeted two functional locations, defined as tree rows and tractor rows. In conjunction with the flux measurements, we determined driving variables including soil ammonium (NH₄ ⁺) and nitrate (NO₃ ^?), dissolved organic carbon (DOC), soil water-filled pore space (WFPS), soil pH, air temperature and precipitation. Cumulative annual N₂O emissions were low (0.65 ± 0.07 and 0.53 ± 0.19 kg N₂O–N ha^?1 year^?1 in year 1 and 2, respectively), likely due to the coarse soil texture and microject sprinkler irrigation and fertigation system. Emission factors (EF), conservatively calculated as the ratio of N₂O emitted to fertilizer N applied, were 0.25 ± 0.03% and 0.19 ± 0.07% for year 1 and 2, respectively, which is below the IPCC EF range of 0.3–3%. Correlation analyses between N₂O and driving variables suggested that overall N₂O production was limited by microbial activity and nitrification was likely the major source process, but specific drivers of N₂O emissions varied between seasons and functional locations.