Seasonal N2O Research Articles

Local variation of PM2.5 and NO2 concentrations within metropolitan Beijing

Studies on long-term effects of air pollutants in China are limited, in part due to a lack of appropriate spatial exposure models. Elsewhere, Land Use Regression (LUR) models have been used extensively to estimate individual-level air pollutant exposure variation within urban areas by combining air pollution measurements with geospatial predictors. Here, LUR models were developed to estimate spatial variation in fine particulate matter (PM2.5) and nitrogen dioxide (NO2) concentrations during the heating and non-heating seasons in Beijing, China. Daily routine PM2.5 and NO2 measurements at 35 monitoring stations from October 2012 to December 2013 were collected as dependent variables, with 191 geospatial measures generated as potential independent variables. The PM2.5 LUR model included latitude and forest land (within a 5000m buffer) in the heating season; and latitude, residential land use (5000m) and main road length (100m) in the non-heating season. The NO2 LUR model included latitude, population density (5000m), water bodies (2000m) and road network factors in the heating season; and residential land use (5000m), water bodies (1000m) and road network factors in the non-heating season. Adjusted R2 and cross validation R2 values of all seasonal models were above 0.80, except for the heating season NO2 model (adjusted R2 = 0.87, cross validation R2 = 0.77). Different spatial patterns between NO2 and PM2.5 were evident in Beijing, with a more distinct local pattern for NO2 than PM2.5 and during the non-heating season, when regional pollution was less dominant. These 250m resolution LUR models can be used for health impact assessment or to estimate PM2.5 and NO2 concentrations at the residential addresses of participants in epidemiological cohorts of Beijing.

Nitrous oxide and nitric oxide emissions from lowland rice cultivation with urea deep placement and alternate wetting and drying irrigation

Urea deep placement (UDP) and the alternate wetting and drying (AWD) irrigation method are two promising rice production technologies. However, studies on the impact of UDP under AWD irrigation on nitrous oxide (N2O) and nitric oxide (NO) emissions are limited. In this study, the effects of UDP with AWD irrigation on these emissions, nitrogen use efficiency (NUE), and rice yields are investigated, compared to conventional broadcast application. N2O and NO emissions from three fertilizer treatments – no nitrogen, UDP, and broadcast application of prilled urea (PU) – were measured. Measurements were taken using an automated gas sampling and analysis system continuously for two consecutive Boro (dry) rice seasons. N2O emission peaks were observed after broadcast application of PU but not after UDP. In contrast, large spikes in N2O emission were observed after UDP, compared to broadcast application, during dry periods. Despite differences in emission peaks, seasonal cumulative N2O emissions from UDP and broadcast treatments were similar. However, NO emissions were minimal and unaffected by UDP or AWD. UDP increased rice yields by 28% and N recovery efficiency by 167%, compared to broadcast urea. This study demonstrates that UDP with AWD irrigation can increase yields and NUE without increasing N2O and NO emissions.

Pinto peanut cover crop nitrogen contributions and potential to mitigate nitrous oxide emissions in subtropical coffee plantations

Many coffee (Coffea arabica L) production systems are characterised by high use of nitrogen (N) fertilisers, which can result in N leaching and emissions of nitrous oxide (N2O). We investigated the potential for legume cover crops grown inter-row to provide N for coffee trees and lower seasonal N2O emissions compared to poultry litter amendment at two subtropical field sites over 12 months, with unfertilised traditional grass groundcover used as a control treatment. Groundcovers (legume and grass treatments) were slashed from the inter-row into the tree line every 2–6 weeks as per normal farming operations. The prostrate ground cover legume Pinto peanut (Arachis pintoi) produced 4–5 t ha−1 biomass at both sites over the 12 month period, and fixed 146 kg N ha−1 year−1 at one site as estimated using the 15N natural abundance method. Background emissions from soil were lower at site 1 (0.38 kg N2O-N ha−1 year−1) than site 2 (2.26 kg N2O-N ha−1 year−1) reflecting differences in soil N and C levels at the sites. The use of Pinto peanut residues as an N amendment didn't result in any N2O flux events beyond those observed in the traditional groundcover control treatment across the season at either site, while the application of poultry litter to match farmer practice at these sites led to a major emission event. Ultimately, the Pinto peanut cover crop treatment led to a lower emission factor than for poultry litter at both sites, and resulted in significantly lower cumulative seasonal emissions for the legume cover crop (0.34 kg N2O-N ha−1 season−1) than poultry litter amendment (0.68 kg N2O-N ha−1 season−1) at site 1 despite similar inputs of N into the system. These findings suggest cover crop legumes could be integrated into coffee plantations to offset a portion of external N inputs, while lowering N2O emissions.

Linking soil N2O emissions with soil microbial community abundance and structure related to nitrogen cycle in two acid forest soils

Tree species and seasonal change influence N2O flux and microbial communities, but the mechanisms are unclear. We studied N2O flux in soils planted with slash pine and oil-seed camellia trees. We sampled on typical days of the four seasons. We tested whether N-cycling communities respond more to tree species or seasonal change. We assessed how tree species affect N2O flux. We used qPCR and RFLP to determine abundance and community composition of amoA-containing bacteria (AOB) and archaea (AOA), and denitrifiers that contain the narG, nirK, nirS, and nosZ genes. N2O flux rate and soil characteristics varied significantly between forest soils and sampling seasons. Abundance of all detected genes, but not of the nirS gene, was significantly affected by tree species. Differences in gene abundance between days in different seasons were found only for narG, nirK, and nosZ. Functional microbial community composition in the soil varied between the tree species for most of the genes studied, but varied, not significantly, slightly among sampling days. Differences in the abundance and community composition of nitrifiers and denitrifiers between tree species depended on soil concentration of NH4+, NO3−, and dissolved organic carbon (DOC). N2O flux rate was affected by community composition, but not abundance of nitrifiers and denitrifiers. Temperature, NO3−, and DOC concentrations significantly affected N2O flux. Tree species influenced N2O flux more than seasonal change, by altering community composition and environmental factors rather than nitrifier/denitrifier abundance.

Effects of Plastic Film Mulching Patterns and Irrigation on Yield of Summer Maize and Greenhouse Gas Emissions Intensity of Field

In order to evaluate the effect of different treatments on yield and greenhouse gas emissions during the summer maize growing season, a two-year film mulching experiment was conducted in 2014 and 2015. In this experiment, the two main experimental factors were rainfed treatment (R) and irrigated treatment (I), and the secondary experimental factors included control treatment (CK), half film mulching treatment (HM), and full film mulching treatment (FM). The emissions of soil greenhouse gases (CO2, CH4, and N2O) were monitored using a static opaque chamber and chromatography method. Moreover, the greenhouse gas emissions intensity (GHGI) was used to evaluate the effect of carbon sequestration in different treatments. The results of this study showed that the yields of the RHM and RFM treatments did not differ significantly in 2014, but increased by 19.6% and 26.8%, respectively, in 2015 compared with that of RCK. The yield of IHM was not improved, and that of IFM significantly increased by 14.1% and 55.8% in 2014 and 2015, respectively, compared with that of ICK. The irrigated treatments only promoted CO2 emissions in 2015 (P<0.01), and all film mulching treatments (regardless of HM and FM treatments) had no effect on CO2 emissions under rainfed and irrigated conditions (P>0.05). Irrigated treatments had no effect on the absorption of CH4 (P>0.05), whereas the film mulching treatments had an inhibitory effect. Compared with values of RCK, the amount of seasonal N2O emissions for ICK showed a significant difference in 2015 with a decrease of 22.3%. Compared with values of RCK, the amounts of N2O emissions for RHM and RFM had no significant differences in 2014, but significantly decreased by 50.7% and 51.4% in 2015, respectively. Compared with ICK, IHM and IFM significantly decreased the amounts of N2O emissions by 47.5% and 54.2% in 2014, and by 9.6% and 52.2% in 2015, respectively. The GHGIs of RHM and RFM were significantly reduced by 60.1% and 61.7% in 2015, respectively, compared with values of RCK, and the GHGIs of IHM and IFM were significantly reduced by 39.7% and 53.2% in 2014, and reduced by 22.2% and 67.5% in 2015, respectively, compared with that of ICK. This means that the effect of FM on reducing GHGI was better than that of HM. It was also found that the significantly reduced GHGI in irrigated treatments may be attributed to the increased yields. Therefore, FM under irrigation conditions was recommended for summer maize for stabilizing the yield and reducing the GHGI.

Greenhouse gas footprint of diversifying rice cropping systems: Impacts of water regime and organic amendments

Increasing water scarcity and Asia’s rapid economic and social development, specifically the growing demand for animal products and biofuels, is forcing farmers to transform their traditional lowland double-rice cropping systems [R-R] to mixed lowland-upland systems where upland crops such as aerobic rice [R-A] or maize [R-M] are grown instead of paddy rice during the dry period. Such changes have implications on the C and N cycling in the soil-plant system, including major shifts in soil greenhouse gas (GHG) emissions from CH4 to N2O once paddies are used for upland cropping. Moreover, soil organic carbon stocks are decreasing, thereby jeopardizing soil fertility. In this study, we investigated if straw residue incorporation and/or catch crop cultivation impairs the greenhouse gas footprint of diversifying rice cropping systems and thus, presents an alternative to open-field straw burning and intensive mineral N fertilization. For this, we calculate annual global warming potentials (GWP) and yield-scaled GWPs of three different rice systems (R-R: rice-rice, R-A: rice- aerobic rice, R-M: rice maize) without (control) or with additions of straw (+6 Mg ha−1 [S]) or + straw + mungbean as catch crop ([M + S]) on the basis of high-temporal-resolution GHG emissions (CH4 and N2O), and measurements of yield parameters. The field trial was carried out at the International Rice Research Institute (IRRI), Philippines, covering two full years. Although dry season N2O emissions increased twice- to threefold in the diversified systems (R-A, R-M), the strong reduction of CH4 emissions during this period resulted in significantly lower annual yield-scaled GWP as compared to the traditional R-R system. The same pattern was observed after application and incorporation of organic material (straw and mungbean), but led to higher substrate availability for methanogens during the following season. Therefore, the GWP was 9–39% higher in treatments including straw incorporation as compared to a control treatment without organic substrate amendments. Additional incorporation of mungbeans further increased GWPs, whereby the increment was highest in R-R rotation (88%) and lowest in R-M rotation (55%), with annual GHG emissions of 11.8 and 5.6 Mg CO2-eq ha−1, respectively. Our study shows that the yield-scaled GWP, as well as irrigation water demand, is lowest for rice-maize (R-M) cropping systems, followed by R-A and R-R systems. This ranking persists even with the incorporation of crop residues, a requirement for farmers as the ban of open-field burning is increasingly enforced. Our work also calls for a refinement of IPCC emission factors for lowland-upland rotations and the inclusion of the land-preparation period within the GHG balance of rice cropping systems.

Evaluation of four modelling approaches to estimate nitrous oxide emissions in China's cropland

Process-based models are useful tools to integrate the effects of detailed agricultural practices, soil characteristics, mass balance, and climate change on soil N2O emissions from soil - plant ecosystems, whereas static, seasonal or annual models often exist to estimate cumulative N2O emissions under data-limited conditions. A study was carried out to compare the capability of four models to estimate seasonal cumulative N2O fluxes from 419 field measurements representing 65 studies across China's croplands. The models were 1) the DAYCENT model, 2) the DNDC model, 3) the linear regression model (YLRM) of Yue et al. (2018), and 4) IPCC Tier 1 emission factors. The DAYCENT and DNDC models estimated crop yields with R2 values of 0.60 and 0.66 respectively, but both models showed significant underestimation for all measurements. The estimated seasonal N2O emissions with R2 of 0.31, 0.30, 0.21 and 0.17 for DAYCENT, DNDC, YLRM, and IPCC, respectively. Based on RMSE, modelling efficiency and bias analysis, YLRM performed well on N2O emission prediction under no fertilization though bias still existed, while IPCC performed well for cotton and rapeseed and DNDC for soybean. The DAYCENT model accurately predicted the emissions with no bias across other crop and fertilization types whereas the DNDC model underestimated seasonal N2O emissions by 0.42 kg N2O-N ha−1 for all observed values. Model evaluation indicated that the DAYCENT and DNDC models simulated temporal patterns of daily N2O emissions effectively, but both models had difficulty in simulating the timing of the N2O fluxes following some events such as fertilization and water regime. According to this evaluation, algorithms for crop production and N2O emission should be improved to increase the accuracy in the prediction of unfertilized fields both for DAYCENT and DNDC. The effects of crop types and management modes such as fertilizations should also be further refined for YLRM.

Nitrous oxide emissions from soils under traditional cropland and apple orchard in the semi-arid Loess Plateau of China

The conversions of cropland to forest, or other tree-based systems, are considered to be important processes affecting regional and global greenhouse gas budgets, especially for nitrous oxide (N2O). From April 2007 to March 2009, in the rain-fed semi-arid climate of the Loess Plateau, China, soil N2O emissions were measured using static chambers from a winter wheat field and an apple orchard, which had been established in part of the wheat field 23 years earlier.Annual average N2O emissions from the apple orchard (2.40 kg N2O ha−1yr−1) were 12.15% higher than those in the wheat field (2.14 kg N2O ha−1yr−1). Seasonal rainfall, in combination with higher nitrogen fertilization, had a promoting effect on N2O emissions in the apple orchard compared with the wheat field. The amounts and patterns of summer rainfall and winter snowfall were the principal controllers of seasonal and annual N2O fluxes in these rain-fed semi-arid regions, likely through their influence on soil moisture content. Since there may be a moisture threshold associated with summer rainfall and winter snowfall triggering higher N2O emissions, climatic regimes should be taken into account when assessing the effects of land use on N2O emissions in the Loess Plateau.

Microbial explanations for field-aged biochar mitigating greenhouse gas emissions during a rice-growing season.

Knowledge about the impacts of fresh and field-aged biochar amendments on greenhouse gas (CH4, N2O) emissions is limited. A field experiment was initiated in 2012 to study the effects of fresh and field-aged biochar additions on CH4 and N2O emissions and the associated microbial activity during the entire rice-growing season in typical rice-wheat rotation system in Southeast China. CH4 and N2O fluxes were monitored, and the abundance of methanogen (mcrA), methanotrophy (pmoA), ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB), nitrite reductase (nirS, nirK), N2O reductase (nosZ), and potential soil enzyme activities related to CH4 and N2O were simultaneously measured throughout different rice developmental stages. There were three treatments: control (urea without biochar), fresh BC (urea with fresh biochar added in 2015), and aged BC (urea with 3-year field-aged biochar added in 2012). Results showed that field-aged biochar significantly decreased seasonal CH4 emissions by 16.8% in relation to the fresh biochar, though no significant differences were detected between biochars and control treatment. The structural equation model indicated that soil pH, microbial biomass carbon (MBC), pmoA, and mcrA were the main factors directly influenced by fresh and aged biochar amendments; aged biochar showed a negative effect while fresh biochar showed positive effects on CH4 fluxes. Both fresh and field-aged biochar obviously increased AOA and AOB abundances and reduced the (nirS+nirK)/nosZ ratio during the entire rice-growing season, although no significant effects were observed on seasonal N2O emissions. Therefore, biochar amendment produced long-term effects on total CH4 and N2O emissions through observed influences of soil pH and functional gene abundance. The figure shows how fresh and field-aged biochar differentially affected CH4 production and oxidation and N2O production and reduction through related functional gene abundances. Blue arrows indicate suppressing while pink arrows indicate promoting effect.

Seasonal N2O emissions respond differently to environmental and microbial factors after fertilization in wheat–maize agroecosystem

Biogeochemical processes regulating cropland soil nitrous oxide (N2O) emissions are complex, and the controlling factors need to be better understood, especially for seasonal variation after fertilization. Seasonal patterns of N2O emissions and abundances of archaeal ammonia monooxygenase (amoA), bacterial amoA, nitrate reductase (narG), nitrite reductase (nirS/nirK), and nitrous oxide reductase (nosZ) genes in long-term fertilized wheat–maize soils have been studied to understand the roles of microbes in N2O emissions. The results showed that fertilization greatly stimulated N2O emission with higher values in pig manure-treated soil (OM, 2.88 kg N ha−1 year−1) than in straw-returned (CRNPK, 0.79 kg N ha−1 year−1) and mineral fertilizer-treated (NPK, 0.90 kg N ha−1 year−1) soils. Most (52.2–88.9%) cumulative N2O emissions occurred within 3 weeks after fertilization. Meanwhile, N2O emissions within 3 weeks after fertilization showed a positive correlation with narG gene copy number and a negative correlation with soil NO3− contents. The abundances of narG and nosZ genes had larger direct effects (1.06) than ammonium oxidizers (0.42) on N2O emissions according to partial least squares path modeling. Stepwise multiple regression also showed that log narG was a predictor variable for N2O emissions. This study suggested that denitrification was the major process responsible for N2O emissions within 3 weeks after fertilization. During the remaining period of crop growth, insufficient N substrate and low temperature became the primary limiting factors for N2O emission according to the results of the regression models.

An Explanation for the Nitrous Oxide Layer Observed in the Mesopause Region

AbstractRecent satellite measurements of a layer of enhanced nitrous oxide (N2O) in the mesosphere‐lower thermosphere (MLT) from the Atmospheric Chemistry Experiment‐Fourier Transform Spectrometer have suggested an unexpected, minor high‐altitude production source. Here we report the development of a mechanism and the first model simulations, which can explain the formation of this MLT N2O layer. N2O production occurs primarily via a reaction route involving the excitation of N2 from secondary electrons. Simulations using the Whole Atmosphere Community Climate Model, with external forcing from the Global Airglow model, quantitatively reproduce the observed vertical, latitudinal, and seasonal N2O variations. Sensitivity results indicate that photoelectrons are far more important than previously predicted, causing approximately two thirds of global N2O production in the MLT. Energetic electron precipitation over high latitudes provides the remaining contribution. Solar cycle analysis reveals N2O enhancements of up to ×2 at solar maximum compared to solar minimum.

Prediction of N2O emissions under different field management practices and climate conditions

Due to the contributions of nitrous oxide (N2O) to global climate change and stratospheric ozone destruction, it is important to understand how climate and agricultural management affect N2O emissions. Although the process-based Denitrification Decomposition (DNDC) model is often used for quantifying emissions of N2O, the accuracy of these predictions remains in question, and it is not clear which input variables, environmental or field management, have the greatest effect on model performance. In this study, DNDC was evaluated for prediction of N2O fluxes from two climatically-different corn-field sites in the United States (a Colorado irrigated field and a Minnesota rainfed field). Besides climate, these sites offer the additional advantage that measurements are available for multiple field management practices, including fertilizer application, tillage, and crop rotation. This evaluation found that DNDC did not consistently, correctly predict daily-scale N2O fluxes. Cumulative growing season N2O fluxes were significantly under-predicted in Colorado and were both under- and over-predicted in Minnesota. Model calibration of four soil input parameters did not significantly improve N2O emission predictions at either site or time scale. Modeled and measured N2O fluxes and model error were all strongly correlated with precipitation. Over-predictions of N2O fluxes were associated with heavy precipitation and high modeled denitrification. Based on our results, model improvements to decrease model error for corn cropping systems in temperate climate zones should focus on better accounting for the effects of precipitation on denitrification. Despite discrepancies in daily and cumulative growing season N2O fluxes, DNDC correctly identified the only field management (fertilizer application rate) that significantly influenced the measured N2O fluxes.

A seasonal source and sink of nitrous oxide in mangroves: Insights from concentration, isotope, and isotopomer measurements

Mangrove forests can be a source or a sink of nitrous oxide (N2O) to the atmosphere, but seasonal mangrove N2O dynamics are not well understood. We used continuous high-resolution N2O concentration data to construct seasonal budgets of N2O in two tropical mangrove-lined creeks for both the wet and dry seasons. Furthermore we used N stable isotope analysis to constrain the pathways of N2O production and consumption within these creeks. Calculated water-air fluxes were within a range typical of undisturbed mangroves, however obvious seasonal differences in N2O dynamics were observed at the two sites. The mangrove systems were a net source of N2O to the atmosphere during the dry season and a net sink during the wet season. In the wet season we propose that increased allochthonous carbon enhances N2O consumption by denitrification. Combining the seasonal fluxes, the Fitzroy mangrove system, which received a continual input of allochthonous nitrate (NO3−), was a net source of N2O, while the Burdekin mangrove system was close to a net N2O balance. Interpreted in the context of DIN and N2O concentrations, the N2O isotopic values observed in the dry season point to fungal denitrification as the most likely pathway of N2O production. This study shows that subtle shifts in seasonal nutrient supply regulate mangrove N2O production and consumption.

Incorporation of rice straw mitigates CH4 and N2O emissions in water saving paddy fields of Central Vietnam

ABSTRACTThis study evaluated the effects of rice straw and water regimes on CH4 and N2O emissions from paddy fields for two rice growing seasons (summer 2014 and spring 2015). Water regimes included alternating wet–dry irrigation (AWD) maintained at three levels (–5 cm, – 10 cm and –15 cm) in comparison to continuous flooding irrigation (CF). Rice straw (5 t ha–1) was incorporated into the top soil (0 – 15 cm), distributed and burned in situ. Results showed that using burned in situ rice straw was found to reduce seasonal cumulative CH4 emission (24–34% in summer; 18–28% in spring), N2O emission (21–32% in summer; 22–29% in spring) and lower rice yield (8–9%) than rice straw incorporation into top soil. AWD methods reduced the amount of CH4 production (22.6–41.5%) and increased N2O emission (25–26%) without any decrease in rice yield. Rice straw incorporation into the top soil with AWD had higher water productivity (23–37%) than rice straw when burned in situ with CF. The results conclude that AWD and rice straw management can be employed as mitigation strategy for CH4 and N2O emissions from paddy fields in Central Vietnam.

Effects of light-felling on non-growing season greenhouse gas emission from soils in Korean pine forests in Maoer Mountains, China.

Non-growing season soil greenhouse gas emission may play an important role in the forest ecosystem carbon and nitrogen cycle. However, it is not clear about the effects of the cutting distur-bance on soil greenhouse gas emissions during non-growing season. The CO2, CH4 and N2O fluxes and related environmental factors (soil temperature, water content, carbon and nitrogen, etc.) were monitored in the Korean pine plantation (fifty year-old) under different light-felling manners (control, no cutting; the half light-felling, cutting 50% of broad-leaved trees in canopy; the whole light-felling, cutting 100% of broad-leaved trees in canopy), using static chamber technique and gas chromatography during non-growing season in Maoer Mountains of China. The main aim was to reveal the influence of cutting disturbance on soil greenhouse gases emission during non-growing season and its controlling factors. The results showed that the whole and half light-felling manners significantly decreased CO2emission flux by 21.0% and 22.8%, and N2O by 23.5% and 11.2%, and decreased CH4uptake by 16.0% and 16.4%. The contribution of non-growing season CO2, CH4 and N2O emission to annual total was 11.7%-14.2%, 13.1%-17.0% and 63.9%-72.6%, respectively. Light-felling manners decreased annual cumulative contribution of CO2 by 1.4%-2.5%, that of CH4 by 0.7%-3.9%, but increased that of N2O by 2.4%-8.7%. Furthermore, light-felling increased the correlations of soil CO2 fluxes with soil temperature, soil water content, nitrate and ammonium, and decreased its correlation with soil organic carbon content. Light-felling increased the correlations of soil CH4 flux with soil water content, soil pH, soil organic carbon, ammonium, and decreased its correlation with nitrate. Light-felling increased the correlations between soil N2O flux and soil temperature, decreased the correlations with nitrate and ammonium, and changed the positive correlation with soil pH to negative. Therefore, light-felling had significant effects on the emission fluxes of the greenhouse gas during non-growing season, with the whole light-felling decreased more soil N2O emission flux than the half light-felling.

Urea fertigation sources affect nitrous oxide emission from a drip-fertigated cotton field in northwestern China

Drip-fertigated systems are widely used for crop production in arid regions to improve water and nutrient use efficiency. However, the effect of fertilizer nitrogen (N) sources on nitrous oxide (N2O) emissions from such systems is not well understood. A field experiment was conducted in 2015 and 2016 on a sandy loam soil in Xinjiang, China with plastic-mulch, drip-fertigated cotton (Gossypium hirsutum L.) to determine N2O emissions from different fertilizer N sources. Treatments were established in a factorial design consisting of a 0 N control and three treatments receiving 240 kg N ha−1 as (1) polymer-coated urea (ESN), (2) urea alone, or (3) urea with both urease (NBPT) and nitrification (DCD) inhibitors. ESN was banded in the row at planting, whereas the two urea treatments were applied through banding and fertigation. In these treatments, 20% of the urea was banded in the row at planting and the remaining 80% was applied with six fertigation events over the growing season. Seasonal cumulative N2O emissions (ƩN2O) for urea alone were 330 g N ha−1 and were 27% greater than the control. Compared to urea alone, the ESN treatment increased ƩN2O by 43% due to the one-time application at planting that resulted in high soil N availability and high N2O emissions shortly after planting. Compared to urea alone, urea plus the two inhibitors decreased ƩN2O by 21%. Cotton seed yield and total N uptake was not affected by N sources, while ESN had significantly higher yield-based emission intensity compared to the other N treatments. In general, the seasonal N2O emissions and N-applied emission factors under the drip-fertigated system were lower than those reported for other agricultural systems. This was likely because of low soil moisture preventing appreciable N2O emissions. These results demonstrated that addition of urease and nitrification inhibitors could further reduce already low N2O emissions with soluble urea with drip-fertigation and under plastic mulch condition.

Effects of precipitation exclusion on N2O emissions in a savanna ecosystem in SW China

Savanna ecosystems play a crucial role in global N2O emissions. However, our understanding of N2O emissions under limiting precipitation conditions is lacking. This study evaluates the effects of precipitation reduction on soil N2O fluxes from a woody savanna ecosystem in Yunnan Province, Southwest China. Precipitation exclusion shelters were installed above the tree canopy, and four total treatments were established as follows: a control (CK) and precipitation exclusions of 30% (PE3), 50% (PE5), and 70% (PE7). Two years (2015–2016) of N2O fluxes, soil temperature and soil water content data were collected. The N2O fluxes were generally low, ranging from 0.039 to 0.245 mg N m−2 day−1, and they were strongly linked to precipitation events. Additionally, the N2O fluxes during the rainy season were significantly greater than those during the dry season. The maximum N2O flux was observed in August, and the minimum flux occurred in December. Precipitation exclusion had a significant negative influence on the N2O fluxes. The N2O emissions of CK, PE3, PE5, and PE7 were 0.20, 0.17, 0.13, and 0.12 kg N ha−1 yr−1, respectively. With the exacerbation of precipitation exclusion, the decrease rate of precipitation exclusion on the N2O emissions increased over the entire year (eventually reaching 41.8% in PE7), but the decrease rate of precipitation exclusion on the soil N2O emission during the dry season was stronger than that during the rainy season. Additionally, the proportion of dry season N2O emissions to total annual emissions decreased (from 45% to 41%), and that of rainy season N2O emissions to total annual emissions increased (from 55% to 59%) over the year, whereas they exhibited a stable trend from PE5. The data show that the Yuanjiang savanna is a net source of N2O; precipitation reduction decreases the N2O emissions in the savanna regions, indicating that precipitation reduction can only slow the increase in the N2O concentration in the atmosphere and can therefore slow global warming. In addition, the N2O emissions during the dry season may play a significant role in total N2O emissions and be more sensitive to precipitation reduction than those during rainy season. These possibilities should be considered in future studies, especially in those ecosystems that experience substantial inter-annual climatic fluctuations.

N2O and CH4 emissions from N-fertilized rice paddy soil can be mitigated by wood vinegar application at an appropriate rate

To understand the impacts of wood vinegar (WV), a by-product of biochar production, on N2O and CH4 emissions and their total global warming potential (GWPt) from N-fertilized rice paddy soil, a soil column experiment was conducted using three treatments: 240 kg urea-N ha−1 accompanied with 0, 5, and 10 t WV ha−1, respectively. Results showed that N2O and CH4 emission flux patterns were dominated by water regime of rice growth cycle, which was independent with WV application. The total N2O, CH4 emission loads and GWPt over rice season of three N received treatments were 6.41–8.85 kg ha−1, 127.7–405.0 kg ha−1, and 5.24–12.03 t CO2-e ha−1, respectively. Rice seasonal N2O and CH4 emissions were synchronously mitigated by 22.4% and 36.4%, respectively, when WV was applied at 5 t ha−1. Consequently, 5 t ha−1 WV treatment reduced 31.5% of GWPt compared with the urea treatment. In addition, 10 t ha−1 WV treatment exerted a more positive effect on suppressing N2O with 27.6% reduction. However, it increased GWPt by 57.2% because its CH4 emission load was increased by 101.8%. In conclusion, WV amendment applied at an appropriate rate (5 t ha−1) or combination with other CH4 control technologies were suggested to reduce both N2O and CH4 emissions and thereby the GWPt in N-fertilized rice paddy soil.

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

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

On Upscaling of Soil Microbial Processes and Biogeochemical Fluxes From Aggregates to Landscapes

AbstractSoil microbial communities respond to spatial and temporal variations in environmental conditions (e.g., saturation and ambient temperatures) as reflected in the dynamics of microbially produced greenhouse gas (GHG) fluxes (primarily CO2, N2O, and CH4) emitted from soil surfaces. Despite considerable progress in resolving key soil microbial processes, their quantification remains largely empirical with limited predictability. We report a mechanistic and analytical modeling framework for integrating local environmental effects on GHG‐producing microbial processes primarily in soil aggregates (or other hot spots) and the upscaling of these to regional GHG fluxes. The mechanistic model enables systematic evaluation of how soil structural features (e.g., aggregation and layers), spatial variability, and dynamic ambient conditions (e.g., temperature and hydration) affect soil microbial functioning. The upscaling of microbial processes from aggregates of different sizes to soil profiles and landscapes implements mechanistically derived microbial response functions with spatial information on soil type, land cover, and resource distribution. The modeling framework was evaluated using reported field data for seasonal N2O emissions from subarctic regions resulting in reasonable agreement. The proposed analytical framework offers a practical compromise balancing a simplified representation of dynamic microbial processes that respond to local conditions with an upscalable representation of soil GHG fluxes over landscapes under changing environmental conditions.