Annual nitric and nitrous oxide emissions response to biochar amendment from an intensive greenhouse vegetable system in southeast China

Nitrogen use efficiency exhibits a trade-off relationship with soil N2O and NO emissions from wheat-rice rotations receiving manure substitution

Decreased N2O and NO emissions associated with stimulated denitrification following biochar amendment in subtropical tea plantations

Agricultural and forest soils with low organic C content and high alkalinity were studied over 17 days to investigate the potential response of the atmospheric pollutant nitric oxide (NO) and the greenhouse gas nitrous oxide (N2O) on (1) increased N deposition rates to forest soil; (2) different fertilizer types to agricultural soil and (3) a simulated rain event to forest and agricultural soils. Cumulative forest soil NO emissions (148–350 ng NO-N g−1) were ~ 4 times larger than N2O emissions (37–69 ng N2O-N g−1). Contrary, agricultural soil NO emissions (21–376 ng NO-N g−1) were ~ 16 times smaller than N2O emissions (45–8491 ng N2O-N g−1). Increasing N deposition rates 10 fold to 30 kg N ha−1 yr−1, doubled soil NO emissions and NO3− concentrations. As such high N deposition rates are not atypical in China, more attention should be paid on forest soil NO research. Comparing the fertilizers urea, ammonium nitrate, and urea coated with the urease inhibitor ‘Agrotain®,’ demonstrated that the inhibitor significantly reduced NO and N2O emissions. This is an unintended, not well-known benefit, because the primary function of Agrotain® is to reduce emissions of the atmospheric pollutant ammonia. Simulating a climate change event, a large rainfall after drought, increased soil NO and N2O emissions from both agricultural and forest soils. Such pulses of emissions can contribute significantly to annual NO and N2O emissions, but currently do not receive adequate attention amongst the measurement and modeling communities.

ABSTRACTChanges in weather and management practices such as manure and fertilizer applications have a major effect on nitrous oxide (N2O) and nitric oxide (NO) emissions from soils. N2O and NO emissions exhibit high intra- and inter-annual fluctuations, which are also highly influenced by land-use change. In this study we investigated how land-use change between grassland and cornfield affects soil N2O and NO emissions using long-term field measurements in a mollic andosol soil in Southern Hokkaido, Japan. Soil N2O and NO emissions were monitored for 5 years in a 30-year old grassland (OG), which was then plowed and converted to a cornfield for 3 years and then converted back to grassland (new grassland, NG) for another 3 years. We established four treatment plots: control, without any nitrogen (N) input (CT plot); chemical fertilizer only (F plot); chemical fertilizer and manure (MF plot); and manure only (M plot).Changing land use from OG to cornfield increased annual N2O emissions by 6–7 times, while the change from cornfield to NG resulted in a 0.3–0.6 times reduction in annual N2O emissions. N2O emissions in the newly established grassland were 2–5 times higher than those in the 30-year old grassland. Soil mineral N (NO3− and NH4+) was higher in cornfield, followed by NG and lowest in OG, while water extractable organic carbon (WEOC) did not significantly change with changing land use but tended to be higher in OG and NG than in cornfield. The ratio of WEOC to soil NO3− was the most important explanatory variable for differences in N2O emissions as land use changed. High N input, surplus soil N, and precipitation and low soil pH led to increased N2O emissions. N2O emissions in fertilizer- and/or manure-amended plots were 3–4, 2–5 and 1.4–2 times higher than those in the control treatment in OG, cornfield and NG, respectively. NO emissions were largely influenced by soil mineral N and N addition, and showed less response to changing land use. There were high inter-annual variations in both NO and N2O emissions in all plots, including the control treatment, highlighting the need for long-term measurements when determining local emission rates.

Spring thaw pulses decrease annual N2O emissions reductions by nitrification inhibitors from a seasonally frozen cropland

A European inventory of soil nitric oxide emissions and the effect of these emissions on the photochemical formation of ozone

Tropical soils are important sources of nitrous oxide (N2O) and nitric oxide (NO) emissions from the Earth’s terrestrial ecosystems. Clearing of tropical rainforest for pasture has the potential to alter N2O and NO emissions from soils by altering moisture, nitrogen supply or other factors that control N oxide production. In this review we report annual rates of N2O and NO emissions from forest and pastures of different ages in the western Brazilian Amazon state of Rondonia and examine how forest clearing alters the major controls of N oxide production. Forests had annual N2O emissions of 1.7 to 4.3 kg N ha −1 y −1 and annual NO emissions of 1.4 kg N ha −1 y −1 . Young pastures of 1–3 years old had higher N2O emissions than the original forest (3.1–5.1 kg N ha −1 y −1 ) but older pastures of 6 years or more had lower emissions (0.1 to 0.4 kg N ha −1 y −1 ). Both soil moisture and indices of soil N cycling were relatively poor predictors of N2O, NO and combined N2O + NO emissions. In forest, high N2O emissions occurred at soil moistures above 30% water-filled pore space, while NO emissions occurred at all measured soil moistures (18–43%). In pastures, low N availability led to low N2O and NO emissions across the entire range of soil moistures. Based on these patterns and results of field fertilization experiments, we concluded that: (1) nitrification was the source of NO from forest soils, (2) denitrification was not a major source of N2O production from forest soils or was not limited by NO − supply, (3) denitrification was a major source of N2O production from pasture soils but only when NO − was available, and (4) nitrification was not a major source of NO production in pasture soils. Pulse wettings after prolonged dry periods increased N2O and NO emissions for only short periods and not enough to appreciably affect annual emission rates. We project that Basin-wide, the effect of clearing for pasture in the future will be a small reduction in total N2O emissions if the extensive pastures of the Amazon continue to be managed in a way similar to current practices. In the future, both N2 Oa nd NO fluxes could increase if uses of pastures change to include greater use of N fertilizers or N-fixing crops. Predicting the consequences of these changes for N oxide production will require an understanding of how the processes of nitrification and denitrification interact with soil type and regional moisture regimes to control N2 Oa nd NO production from these new anthropogenic N sources.

Background:Fires burn roughly 3% of Earth’s land surface each year and are predicted to become more frequent and severe as human-caused climate change progresses. Fires can drive ecosystem N loss by volatilizing N bound in plant biomass to the atmosphere and by leaving behind ash rich in ammonium (NH4+) and organic N that can run off when it rains. While N volatilization and runoff account for a large fraction of N loss after fires, budget imbalances suggest soil emissions of nitric oxide (NO) and nitrous oxide (N2O) may also be significant N loss pathways after fire. Identifying sources of NO and N2O is important because NO is a precursor for tropospheric O3 which causes high rates of asthma hospitalizations,and N2O is a powerful greenhouse gas with 300× the warming potential of CO2. Soil emissions of NO and N2O are largely governed by the microbial processes of nitrification and denitrification. Under aerobic conditions typical of dry soils, nitrifying organisms such as ammonia-oxidizing bacteria (AOB) and ammonia-oxidizing archaea (AOA) oxidize NH4+ to nitrate (NO3-) and release NO and N2O as byproducts. AOA and AOB process N with different efficiencies, suggesting shifts in AOA:AOB ratios may change N emissions. Specifically, AOB are dominant in soils with high NH4+and pH and produce higher NO and N2O emissions. Since such soil conditions are frequently observed after fires, we hypothesize NO and N2O emissions will increase as AOB communities become dominant. To test this, we collected soil cores from 5 plots in the Sequoia National Park, CA over a time series starting two weeks after a high severity chaparral fire. We selectively inhibited AOA and AOB communities to measure their contributions to NO and N2O emissions. We also measured the isotopic composition of N2O emissions from these soils using an LGR isotopic N2O analyzer to better understand the processes responsible for post-fire N2O production.Results/ConclusionsOne month after the fire, soil bulk emissions of NO over 72hrs were 1.5 times higher in the burned plots (101.4 ± 22.4 µg N-NO/g soil burned; 67.1 ± 19.3 µg N-NO/g soil unburned; ±SE). Bulk soil emissions of N2O over 72hrs were 7.5 times lower in burned plots compared to before the fire (0.0616 ± 0.04 ng N-N2O/g soil burned; 0.463 ± 0.19 ng N-N2O/g soil unburned; ±SE). Although the effects of fire on nitrifier communities were not significant at one month post-fire (Control: p=0.14, AOA: p=0.09, AOB: p=0.162), both AOA and AOB contributions to NO emissions increased in response to fire. Results for nitrifier contributions to N2O emissions were highly variable and non-significant with no clear trends as all N2O emissions were near zero. Further analysis over the time series may yield clearer results as microbial communities have more time to recover. Pairing these data with isotopic information (in progress) may yield one of the most in-depth understandings of post-fire NO and N2O emissions to date.

Nitrous oxide (N2O) and nitric oxide (NO) are detrimental reactive gaseous oxides of nitrogen. Excessive application of nitrogen fertilizers in cropping systems has significantly increased the emissions of these gases, causing adverse environmental consequences. Previous studies have demonstrated that biochar amendment can regulate soil-N dynamics and mitigate N losses, but they lacked simultaneous assessments of soil N2O and NO emissions. Thus, the factors influencing the emissions of nitrogen oxides are still unclear. Therefore, this study examined the impact of biochar application on simultaneous N2O and NO emissions based on 18 peer-reviewed papers (119 paired observations). A machine learning model (boosted regression tree model) was adopted to assess the potential influencing factors, such as soil properties, biochar characteristics, and field management conditions. The addition of biochar reduced N2O and NO emissions by 16.2% and 14.7%, respectively. Biochar with a high total carbon content and pH, from woody or herbaceous feedstock, pyrolyzed at a high temperature, applied at a moderate rate and to soil with a high-silt content, a moderate pH, and coarse texture, could simultaneously reduce soil N2O and NO emissions. Biochar amendment, thus, has the potential to lower the environmental impact of crop production. Furthermore, the influence of soil properties, biochar characteristics, and field management should be considered in the future to enhance the efficacy of biochar.

Quantification of greenhouse gases [nitrous oxide (N2O) and methane (CH4)] and nitric oxide (NO) emissions from subtropical conventional vegetable systems through multi-site field measurements are needed to obtain accurate regional and global estimates. N2O, NO and CH4 emissions from subtropical conventional vegetable systems were simultaneously measured at two different sites with hilly topography in the Sichuan basin, southwest China by using the static chamber gas chromatography technique. Results showed that annual soil N2O and NO fluxes for the treatment receiving N fertilizer ranged from 6.34–7.71 kg N ha−1 yr−1 and 0.69–0.85 kg N ha−1 yr−1, respectively, while decreased soil CH4 uptakes by 26.4% as compared with no N fertilizer addition across our two sites of experiment. Overall, the average direct N2O and NO emission factor (EFd) were 0.71% and 0.12%, respectively, which were both lower than the available EFd for subtropical conventional vegetable systems. This finding indicates that current regional and global estimates of N2O and NO emissions from vegetable fields are likely overestimated. Background N2O emissions (3.42–3.62 kg N ha−1 yr−1) from the subtropical conventional vegetable systems were relatively high as compared with available field measurements worldwide, suggesting that background N2O emissions cannot be ignored for regional estimate of N2O emissions in subtropical region. Nevertheless, the significantly intra- and inter-annual variations in N2O, CH4 and NO emissions were also observed in the present study, which could be explained by temporal variations of environmental variables (i.e. soil temperature and moisture). The differences in N2O and NO EFd and CH4 emissions between various vegetable systems in particular under subtropical conditions should be taken into account when compiling regional or global inventories and proposing mitigation practices.

Biochar-enriched soil mitigated N2O and NO emissions similarly as fresh biochar for wheat production

Current understanding of greenhouse gas (GHG) fluxes associated with land-use change from forest to oil palm on mineral soil is not sufficient to provide reliable estimates of emission rates or advice on GHG mitigation strategies. Monocultures of oil palm have expanded in Southeast Asia, mostly replacing tropical forests. The limited data available have indicated that the land-use conversion is associated with a potentially aggravated GHG burden, including nitrous oxide (N2O) and nitric oxide (NO) emissions, with unclear underlying biological mechanisms. In this study, we investigated N2O and NO emission potentials of tropical soils with different land-uses from Sabah, Malaysian Borneo, under laboratory incubation. Under similar controlled conditions, logged forest and oil palm soils showed high and similar potentials of N2O and NO emissions following increase in soil moisture, while the emissions were negligible in a riparian reserve soil irrespective of moisture conditions. Soil N2O and NO emission rates from logged forest soils and oil palm (OP) plantations were of similar magnitude, with average fluxes over the 35 and 22 day incubation periods, respectively, of 11.5 and 1.6 ng N g−1 h−1 (OP) and 15.6 and 6.0 ng N g−1 h−1 (logged forest). Contrarily, the riparian reserve soil did not respond to rewetting and nitrogen application and fluxes were negligible. Furthermore, N2O fluxes were on average about 10 times higher than NO fluxes. The fact that forest soils also have the potential to emit large amounts of N2O and NO, has important implications for land-use change scenarios in the tropics, especially as some scenarios suggest atmospheric N deposition is likely to drastically increase in tropical regions due to biomass burning, increased N-fertilizer use and fossil fuel consumption. Quantification of related gene transcripts implied that Proteobacterial nirS and AniA-nirK (betaproteobacterial clade of Neisseria) containing denitrifiers might continuously contribute to the N2O emissions, while the nitrifiers (ammonia oxidizing archaea in this study) are conditionally active to produce N2O. This study therefore provides some evidence for N2O and NO emissions associated with phylogenetically diverse groups of microorganisms, which might be of importance in modulating the GHG emissions under different land-uses and field conditions.

Straw return reduces yield-scaled N2O plus NO emissions from annual winter wheat-based cropping systems in the North China Plain

A field experiment was conducted in a subtropical tea (Camellia sinensis (L.) O. Kuntze) plantation in Jiangsu Province, China, including the following treatments: no nitrogen (N) fertilizer (control), conventional mineral N fertilizer (urea) (CN), soybean cake fertilizer (SF), pig manure (PM), cattle manure (CaM), chicken manure (CM), and CM + biochar (CMB). Cumulative nitrous oxide (N2O) and nitric oxide (NO) emissions were 4.8 ± 0.1 and 3.7 ± 0.3 kg N ha−1 year−1 under CN, respectively, and increased to 5.4 ± 0.2 and 4.6 ± 0.3 kg N ha−1 year−1 under SF (P < 0.05), respectively. Treatments with livestock manures (PM, CaM, and CM) reduced N2O (41.4–49.6%) and NO (46.5–59.8%) emission in comparison to CN. Combined amendment of CM and biochar more effectively reduced N2O emissions than CM treatment alone. Based on a meta-analysis of 26 global paired measurements in acid soils, the threshold of C/N ratios of organic fertilizers between the positive and negative responses of N2O emissions to organic fertilizers was 8.6 with a range of 4.5–22.3 (95% confidence interval), indicating that reduced N2O emission under PM, CaM and CM was potentially due to their C/N ratios compared to the threshold. Organic fertilizer application did not influence tea yield, while combined application of CM and biochar increased tea yield and resulted in the least yield-scaled N2O emission. N2O and NO emission factors for N fertilizers applied under CN were 1.9 ± 0.1% and 1.5 ± 0.2%, respectively, and reduced to 0.08 ± 0.04% and 0.12 ± 0.04% under CMB, respectively. The results suggest that tea plantations in the subtropical region are hotspots for N2O and NO emissions. Combined application of chicken manure and biochar could mitigate N gas emissions and increase yield in the tea plantation systems.

Machine learning-based estimation and mitigation of nitric oxide emissions from Chinese vegetable fields