Loss Of NO Research Articles

Dry rainfed conditions are key drivers of the effect of conservation tillage and a nitrification inhibitor on N fate and N2O emissions: A field 15N tracing study

The sustainability of rainfed crops under semiarid conditions is threatened by low plant nitrogen (N) recovery as well as the potential loss of reactive N to the environment. A field 15N tracing experiment on barley (Hordeum vulgare L.) under rainfed conditions was carried out to study how different tillage management practices and the use of the nitrification inhibitor DMPSA affected the fate of N. The experiment consisted of a factorial combination of tillage (i.e., no tillage, NT, and conventional tillage, T) and fertilizer treatments (unfertilized control and ammonium nitrate, AN, with or without DMPSA). Single-labelled ammonium nitrate (15NH4NO3, 15AN, or NH415NO3, A15N) was applied at top-dressing to microplots at a rate of 80 kg N ha−1. Our results show out that DMPSA modulates the nitrification process from both fertilizer-N and endogenous soil-N (which was the main contributor to plant N uptake and N2O emissions), affecting soil residual N at the end of the cropping period (i.e., higher topsoil retention of 15AN in DMPSA-amended plots). Generally, cumulative N2O emissions from fertilizer were derived from 15AN rather than from A15N, thus confirming the site-specific choice of the source of synthetic N as an effective N2O mitigation strategy. Two months after harvest, a rewetting event produced a remarkable N2O emission peak that drove total cumulative N2O emissions and was also mainly derived from endogenous N. These results suggest that dry seasons could decrease N2O losses after fertilization while causing critical peaks after rewetting, thus potentially limiting the effectiveness of mitigation strategies. The average plant N recovery from the synthetic fertilizer was 22.6%, while the use of DMPSA combined with NT enhanced plant N uptake from endogenous soil-N. This could be a result of the improved crop development and plant N acquisition under NT, consistent with the decrease of soil N retention for A15N in the deeper layer at the end of the experiment in the nontilled plots. This study contributes to the mechanistic understanding of the effect of nitrification inhibitors and tillage on N2O emissions, soil N dynamics and N plant recovery, revealing relevant effects of both management strategies and a critical role of endogenous soil-N under dry rainfed conditions. It can be concluded that, under the conditions of our study, combining DMPSA with NT could help to improve plant N recovery, thus resulting in positive impacts on reactive N loss and climate change mitigation and adaptation.

Separating N2O production and consumption in intact agricultural soil cores at different moisture contents and depths.

Agricultural soils are a major source of the potent greenhouse gas and ozone depleting substance, N2O. To implement management practices that minimize microbial N2O production and maximize its consumption (i.e., complete denitrification), we must understand the interplay between simultaneously occurring biological and physical processes, especially how this changes with soil depth. Meaningfully disentangling of these processes is challenging and typical N2O flux measurement techniques provide little insight into subsurface mechanisms. In addition, denitrification studies are often conducted on sieved soil in altered O2 environments which relate poorly to in situ field conditions. Here, we developed a novel incubation system with headspaces both above and below the soil cores and field-relevant O2 concentrations to better represent in situ conditions. We incubated intact sandy clay loam textured agricultural topsoil (0-10 cm) and subsoil (50-60 cm) cores for 3-4 days at 50% and 70% water-filled pore space, respectively. 15N-N2O pool dilution and an SF6 tracer were injected below the cores to determine the relative diffusivity and the net N2O emission and gross N2O emission and consumption fluxes. The relationship between calculated fluxes from the below and above soil core headspaces confirmed that the system performed well. Relative diffusivity did not vary with depth, likely due to the preservation of preferential flow pathways in the intact cores. Gross N2O emission and uptake also did not differ with depth but were higher in the drier cores, contrary to expectation. We speculate this was due to aerobic denitrification being the primary N2O consuming process and simultaneously occurring denitrification and nitrification both producing N2O in the drier cores. We provide further evidence of substantial N2O consumption in drier soil but without net negative N2O emissions. The results from this study are important for the future application of the 15N-N2O pool dilution method and N budgeting and modelling, as required for improving management to minimize N2O losses.

Soil nitrogen transformation in different land use and implications for karst soil nitrogen loss controlling

A large amount of cropland in the Southwestern (SW) China karst area has been abandoned since the implementation of the Grain for Green project at the end of the last century, which significantly impacted the biogeochemistry cycle in soil. However, the effect of cropland abandonment on the soil nitrogen (N) cycle and the N loss process is still little understood. N content and isotope analysis were used to assess karst soil’s N fate and explore the N loss process in SW China. Soil samples were collected from four land uses, cropland (CR), abandoned CR (AC), shrubland and grassland (SG), and secondary forest (SF), by seasonal in a typically mixed land-use karst catchment at six soil depths. The results showed that the average soil particulate organic N (PON) content increased from 1.58 ± 0.49 g kg−1 to 2.70 ± 1.82 g kg−1, whereas average dissolved nitrate (NO3–-N) content decreased from 10.77 ± 8.87 mg kg−1 to 1.72 ± 1.84 mg kg−1 during revegetation. There was a decreasing amount of PON and dissolved N (NH4+-N、NO3–-N、TDN) content from surface to the bottom of the soil profile and large variation mainly occurred in 0 – 30 cm in the soil profiles of four different land uses, which suggests N transformation mainly occurred in topsoil (<30 cm). Mineralization was the major nitrogen transformation process that affected PON content and δ15N-PON values. The highest δ15N-PON fractionation (-5.0‰) in the soil profiles of the four types of land use caused by mineralization was detected in SF. Variation of N content and isotope values in soil profiles after cropland abandonment suggested that the loss of NO3–-N in karst catchment mainly came from the topsoil of cropland. Overall, N loss from the topsoil of cropland should pay more attention, while cropland abandonment can effectively reduce the loss of dissolved N from the thin karst soil layer.

Observationally constrained modelling of NO3 radical in different altitudes: Implication to vertically resolved nocturnal chemistry

Previous field observations have shown that NO3 and related species develop distinct vertical profiles in urban areas. In this study, we utilized the Platform for Atmospheric Chemistry and Vertical Transport (PACT) under observation constrains to simulate NO3 and related substances during field campaign in Beijing in the autumn of 2019. The simulations of NO3 for each layer have achieved a good agreement (R ≈ 0.92) with the LP-DOAS observations for the whole period. The vertical NO3 budget analysis concluded that direct loss dominates at the lowest layer (over 70%), while indirect loss is most significant at the upper layer. But what we found in this study is that direct NO3 loss is not only confined to the ground, but also has a vital proportion of 50% at high altitudes. What's more, case study of fast NO3 decay situation (Case II) shows that sometimes direct loss in the highest layer can account for more than 90% of the total NO3 loss, while indirect loss is more significant in the lowest layer than in the highest layer. In contrast, the poor NO3 simulation (Case III) indicates that the NO3 loss in the highest layer was all occupied by indirect loss. Loss pathway of NO3 in the high altitudes can be completely occupied by direct loss or indirect loss respectively, showing the complexity of the NO3 loss path. The sensitivity test on indirect NO3 loss rates via N2O5 heterogeneous reaction at highest layer suggested the importance of chemical equilibrium between NO3 and N2O5 on the budgets.

Alterations of ecosystem nitrogen status following agricultural land abandonment in the Karst Critical Zone Observatory (KCZO), Southwest China.

Secondary succession after agricultural land abandonment generally affects nitrogen (N) cycle processes and ecosystem N status. However, changes in soil N availability and NO3 - loss potential following secondary succession are not well understood in karst ecosystems. In the Karst Critical Zone Observatory (KCZO) of Southwest China, croplands, shrub-grass lands, and secondary forest lands were selected to represent the three stages of secondary succession after agricultural land abandonment by using a space-for-time substitution approach. The contents and 15N natural abundance (δ 15N) of leaves, soils, and different-sized aggregates at the three stages of secondary succession were analyzed. The δ 15N compositions of soil organic nitrogen (SON) in aggregates and soil to plant 15N enrichment factor (EF = δ 15Nleaf -δ 15Nsoil), combined with soil inorganic N contents and δ 15N compositions were used to indicate the alterations of soil N availability and NO3 -loss potential following secondary succession. Leaf N content and SON content significantly increased following secondary succession, indicating N accumulation in the soil and plant. The δ 15N values of SON also significantly decreased, mainly affected by plant δ 15N composition and N mineralization. SON content in macro-aggregates and soil NH4 + content significantly increased while δ 15N values of NH4 + decreased, implying increases in SON stabilization and improved soil N availability following secondary succession. Leaf δ 15N values, the EF values, and the (NO3 --N)/(NH4 +-N) ratio gradually decreased, indicating reduced NO3 - loss following secondary succession. Soil N availability improves and NO3 - leaching loss reduces following secondary succession after agricultural land abandonment in the KCZO.

Iron-rich sand promoted nitrate reduction in a study for testing of lignite based new slow-release fertilisers

The N losses and agronomic performances of newly developed slow-releasing fertilisers (SRFs; Epox5 and Poly5) were tested against conventional N fertilisers, urea and diammonium phosphate (DAP), in a climate-controlled lysimeter system. The dry matter (DM) yield and N losses of SRFs were not significantly different from urea and DAP. However, nitrate leaching and nitrous oxide (N2O) losses were unexpectedly low and therefore, it was inferred that nitrate underwent a chemical transformation. It was observed that a thick fibreglass wick interrupted drainage and created an anaerobic condition in the soil. The subsoil was found to have a high extractable total iron and it was postulated that iron played a role in the observed low level of N losses. An investigation was carried out with a factorial design using sand types and rates of N application as the main factors. Two types of sand; with high and low iron concentration and four levels of N applications; 0 (control), 50, 100 and 200 kg N ha−1 were employed in a leaching column and nitrate and N2O losses were measured. The nitrate leaching was significantly (P < 0.05) affected by sand types wherein a lower nitrate level was recorded for high‑iron concentration sand than for low-iron concentration sand at all N application levels. The N2O emission was significantly (P < 0.05) lower for high-iron sand than for low-iron sand for the 200 N treatment, but not significantly different between sand types for other treatments. These observations provide evidence for the involvement of iron in nitrate transformation under anaerobic conditions and it was hypothesised path was dissimilar nitrate reduction (DNR). Further studies are recommended, to identify the underlying mechanism responsible for nitrate reduction with iron-rich sand.

Changes in NO3 Radical and Its Nocturnal Chemistry in Shanghai From 2014 to 2021 Revealed by Long‐Term Observation and a Stacking Model: Impact of China's Clean Air Action Plan

AbstractNitrate radical (NO3), an important nocturnal tropospheric oxidant, was observed continuously in the eastern Chinese megalopolis of Shanghai from July 2018 to August 2021using differential optical absorption spectroscopy equipped with LED lamp. To assess changes in NO3 radical during the implementation of China's Clean Air Action Plan, a stacking model was developed to predict historical NO3 radical from 2014 to 2018 with good performance. Combining the observed and predicted data sets, the highest concentration of NO3 exceeded 300 pptv in 2021, while the highest monthly mean of 36.2 ± 30.9 pptv occurred in summer 2017. The impact of meteorology, precursors, and emissions on the evolution of nocturnal NO3 was quantified using the Kolmogorov‐Zurbenko filter. The rapid increase in annual NO3 from 2014 to 2017 was caused by a combination of persistently high precursor O3 concentrations, insufficient SO2‐represented primary pollutant reductions, and meteorological conditions favorable to NO3. As China's clean air actions advanced further, significant CO‐represented and SO2‐represented emission reductions overcame the impact of meteorological conditions and significantly lowered the NO3 levels between 2018 and 2021. These efforts drastically affected nocturnal NO3 chemistry, reducing NO3 loss rates by approximately 30% in both spring and summer in 2021 compared to 2014, although the NO3 levels were comparable between the 2 years. In addition, substantial reductions in CO‐represented and SO2‐represented primary pollutants, as well as effective management of NO2 and PM2.5, resulted in varying decreases in the rates of direct (removal by reactions with VOCs, etc.) and indirect (removal by heterogeneous consumption of N2O5) losses, thereby moderating secondary aerosol formation.

Nitrogen cycling in sediments on the NW African margin inferred from N and O isotopes in benthic chambers

Benthic nitrogen cycling in the Mauritanian upwelling region (NW Africa) was studied in June 2014 from the shelf to the upper slope where minimum bottom water O2 concentrations of 25 µM were recorded. Benthic incubation chambers were deployed at 9 stations to measure fluxes of O2, dissolved inorganic carbon (DIC) and nutrients (NO3-, NO2-, NH4+, PO43-, H4SiO4) along with the N and O isotopic composition of nitrate (δ15N-NO3- and δ18O-NO3-) and ammonium (δ15N-NH4+). O2 and DIC fluxes were similar to those measured during a previous campaign in 2011 whereas NH4+ and PO43- fluxes on the shelf were 2 – 3 times higher and possibly linked to a long-term decline in bottom water O2 concentrations. The mean isotopic fractionation of NO3- uptake on the margin, inferred from the loss of NO3- inside the chambers, was 1.5 ± 0.4 ‰ for 15/14N (15ϵapp) and 2.0 ± 0.5 ‰ for 18/16O (18ϵapp). The mean 18ϵapp:15ϵapp ratio on the shelf (&amp;lt; 100 m) was 2.1 ± 0.3, and higher than the value of 1 expected for microbial NO3-reduction. The 15ϵapp are similar to previously reported isotope effects for NO3- respiration in marine sediments but lower than determined in 2011 at a same site on the shelf. The sediments were also a source of 15N-enriched NH4+ (9.0 ± 0.7 ‰). A numerical model tuned to the benthic flux data and that specifically accounts for the efflux of 15N-enriched NH4+ from the seafloor, predicted a net benthic isotope effect of N loss (15ϵsed) of 3.6 ‰; far above the more widely considered value of ~0‰. This result is further evidence that the assumption of a universally low or negligible benthic N isotope effect is not applicable to oxygen-deficient settings. The model further suggests that 18ϵapp:15ϵapp trajectories &amp;gt; 1 in the benthic chambers are most likely due to aerobic ammonium oxidation and nitrite oxidation in surface sediments rather than anammox, in agreement with published observations in the water column of oxygen deficient regions.

Modelling the impacts of inhibitors and fertilizer placement on maize yield and ammonia, nitrous oxide and nitrate leaching losses in southwestern Ontario, Canada

Application of urease and nitrification inhibitors is an effective strategy for decreasing nitrogen (N) losses without negatively impacting yields, but the long-term impacts of inhibitors and N placement on N dynamics remains unclear. The objectives of this study were to 1) use a 3-year maize experiment in southwestern Ontario to evaluate the Denitrification-DeComposition (DNDC) model fitted with default and enhanced urea hydrolysis mechanisms, 2) determine the impacts of climate variability (30-year) on inhibitor performance on maize yield and N losses under a range of N treatments, and 3) estimate the optimal N application rates for maintaining high yield and minimizing N losses. The experiment treatments included a factorial arrangement of two N sources (urea, urea ammonium nitrate [UAN]), three N placement methods (broadcast urea [B-Urea], broadcast incorporated urea [BInc-Urea], injected UAN [Inj-UAN]), and three inhibitors (no inhibitor, urease inhibitor [UI], urease plus nitrification inhibitor [UI&NI]). Although both the default and improved model provided “fair” to “good” simulations of maize yield, N uptake, soil temperature, soil moisture, soil inorganic N content and nitrous oxide (N2O) emissions across treatments, more accurate simulations were obtained using the improved model. The default DNDC model indicated “poor” simulations of ammonia (NH3) volatilization according to the Nash-Sutcliffe efficiency (NSE <0) and index of agreement (d ≤ 0.38), whereas the improved DNDC produced “good” simulations (NSE = 0.22–0.39, d = 0.65–0.84) because of improved estimates of urea diffusion, hydrolysis and inhibitor efficiency. The 30-year simulation based upon 95% of the maximum yield resulted in annual NH3 losses of 35.4 kg N ha−1 for B-Urea and these losses were reduced by 40.1% with BInc-Urea and by 92.7% with Inj-UAN. When UI was added to either B-Urea or BInc-Urea, NH3 losses were reduced by 61.8–66.4%, whereas when UI&NI was added, losses were reduced by 41.0–49.4%. The Inj-UAN reduced annual N2O losses by 18.8% compared to B-Urea whereas two inhibitor treatments of B-Urea + UI&NI and BInc-Urea + UI&NI reduced N2O losses by 11.5–11.8% compared to B-Urea and BInc-Urea. Simulated annual N losses from Inj-UAN + UI&NI were reduced relative to Inj-UAN + UI because of decreased NO3− leaching. Simulated long-term average percentage of annual total N losses at the optimal N rate were 36.8, 30.8 and 22.0% from B-Urea, BInc-Urea and Inj-UAN, respectively, which reduced to 25.9–28.1, 24.9–25.5 and 21.2–21.9%, when inhibitors were added. Our study suggests that the DNDC model can be used to investigate the impacts of climate variability on inhibitor performance and determine the optimum range of N application rates for different inhibitor treatments.

Characterization of nutrient runoff from perennial and annual forages following broiler litter application.

Information on how forage species influence sediment and nutrient transport in runoff is required for limiting non-point source pollution from broiler litter applications. In this study, we examined the effects of five forage species (eastern gamagrass [Tripsacum dactyloides (L.) L.], Kernza [Thinopyrum intermedium (Host) Barkworth & D.R. Dewey], silphium [Silphium integrifolium Michx.], switchgrass [Panicum virgatum L.], and winter wheat [Triticum aestivum L.]) on runoff nutrient losses from broiler litter-amended (5.6 Mg ha-1 ) and non-amended plots (control) following four simulated rainfall (5cm h-1 ) events that were applied to these plots in late spring and early fall of 2019 and 2021. Runoff collected for 30min was analyzed for total suspended solids (TSS) and nutrients (total organic carbon [TOC], soluble reactive phosphorus [SRP], total dissolved phosphorus [TDP], total phosphorus [TP], total nitrogen [TN], ammonium-nitrogen [NH4 -N], and nitrate-nitrogen [NO3 -N]). Total sediment and nutrient losses increased 5- to 19-fold following litter application for all species, which reduced to background levels during fall rainfall events. Across the four simulated rainfall events, switchgrass resulted in lower cumulative losses of TSS, TOC, SRP, TDP, TP, and NO3 -N than gamagrass and wheat but did not differ from Kernza and silphium for litter-amended treatments. The performance of newly introduced perennial crops (Kernza and silphium) was similar or better than that of gamagrass in terms of cumulative runoff sediment and nutrient losses. Results show high potential for Kernza, silphium, and switchgrass to improve water quality when used in forage-vegetative filter strip systems.

Using DMPP with cattle manure can mitigate yield-scaled global warming potential under low rainfall conditions

Organic fertilisers can reduce the carbon (C) footprint from croplands, but adequate management strategies such as the use of nitrification inhibitors are required to minimise side-effects on nitrogen (N) losses to the atmosphere or waterbodies. This could be particularly important in a context on changing rainfall patterns due to climate change. A lysimeter experiment with maize (Zea mays L.) was set up on a coarse sandy soil to evaluate the efficacy of 3,4-dimethylpyrazole phosphate (DMPP) to mitigate nitrous oxide (N2O) emissions, nitrate (NO3−) leaching losses and net global warming potential from manure, with (R+) and without (R-) simulated rainfall events. Soil water availability was a limiting factor for plant growth and microbial processes due to low rainfall during the growing season. Nitrification was effectively inhibited by DMPP, decreasing topsoil NO3− concentrations by 28% on average and cumulative N2O losses by 82%. Most of the N2O was emitted during the growing season, with annual emission factors of 0.07% and 0.95% for manure with and without DMPP, respectively. Cumulative N2O emissions were 40% higher in R-compared to R+, possibly because of the higher topsoil NO3− concentrations. There was no effect of DMPP or rainfall amount on annual NO3− leaching losses, which corresponded to 12% of manure-N and were mainly driven by the post-harvest period. DMPP did not affect yield or N use efficiency (NUE) while R-caused severe reductions on biomass and NUE. We conclude that dry growing seasons can jeopardize crop production while concurrently increasing greenhouse gas emissions from a sandy soil. The use of nitrification inhibitors is strongly recommended under these conditions to address the climate change impacts.

Reactive Uptake of Gas-Phase NO2 by Urban Road Dust in the Dark.

Road dust constitutes a prominent source of anthropogenic particulate matter, making its heterogeneous interactions with common atmospheric gas-phase compounds important. Here, we show that three distinct samples of urban road dust-including dust samples collected from city streets in summer and winter, and an urban park in summer-react with NO2 in the dark, forming NO and surface nitrite. The loss of NO2 ranged from ∼2 to 13% of its gas-phase concentration and scaled with its concentration as well as with the mass of the road dust sample. The uptake of NO2 by the winter dust was ∼4 times greater than that seen from summer street dust, which was in turn greater than that by the park dust. The conversion ratio of NO2 → NO ranged from 0.06 to 0.8 NO produced per NO2 lost and was greatest for the summer park dust. Exposure of the summer road dust to NO2 roughly doubles the concentration of inorganic nitrite anion in the dust but does not produce nitrate. The formation of NO and photolabile nitrite products means that heterogeneous NO x reactions occurring on the surface of road dust in the dark could have wide implications for the oxidative potential of urban areas.

Normalizing time in terms of space: What drives the fate of spring thaw-released nitrogen in a sloping Arctic landscape?

In the Arctic tundra, snowmelt is followed by soil thaw allowing water and dissolved nutrients to move downslope. However, the fate of the released nitrogen (N) remains unclear, which includes the fraction of N that is lost to downslope transport or converted to N gasses.We have quantified the release of NO3− into the soil solution and the loss of gaseous N upon thaw and up to a month after first thaw in an Arctic hillslope in W Greenland. We further investigated which factors of the slope ecosystem that influence the NO3− concentrations and N2O fluxes throughout two snowmelt and growing seasons using a Structural Equation Model (SEM) linking physical, biological and biogeochemical characteristics across the slope.Snowmelt controls growing season onset, but varies in the landscape. To account for this, we normalized the spatiotemporal variation in snowmelt and soil thaw by measuring NO3− release and N2O loss in a controlled laboratory thaw experiment with topsoil cores from along the slope. We furthermore normalized seasonal progression of ecosystem variables in space based on the first day of soil thaw in the field. We tested the variable Day After Soil Thaw (DAST) as the temporal driver in our SEM, and found that season progression is the most important factor to describe patterns in NO3− concentrations and N2O fluxes. We conclude that DAST is a useful tool for analysing seasonal patterns in a spatially heterogeneous snowmelt landscape and between different snowmelt years.When normalizing based on first day of soil thaw, we saw that the decreasing NO3− content over the season did not control the increasing N2O emissions. Rather, nitrification replaced denitrification as the main N2O -source during the growing season, where soil temperatures increased and soil moisture decreased. The gaseous N loss from the slope during the first month of thaw was minor and amounted to 1% of the annual N deposition. A NO3− pulse released into solution after 24 h of thaw, when meltwater moves along the slope and connects upslope with downslope ecosystems, thus constituted a “hot moment” for interaction between landscape N pools, but the NO3− was immobilized by microorganisms or taken up by plants rather than denitrified and did thus not constitute a hot moment for N2O emissions. Thus, our results regarding what drives the fate of spring-thaw released N in the sloping Arctic landscape highlight the importance of snowmelt timing and the following number of Day After Soil Thaw as a normalizing factor for biogeochemical processes. This provides an analytical concept for reducing spatial and inter-annual variability to understand general seasonal patterns otherwise hidden.

Quantification of N and C cycling during aerobic composting, including automated direct measurement of N2, N2O, NO, NH3, CO2 and CH4 emissions

Closing the carbon (C) and nitrogen (N) balance has yet to be achieved in aerobic bioprocess due to current methodological drawbacks in the frequency of sampling and detection and the challenge in direct measurement of instantaneous N2 emission. To address this issue, a novel system was developed enabling simultaneous and online determination of gaseous C and N species (N2, N2O, NO, NH3, CO2 and CH4) from aerobic composting at a high frequency of 120 times·d−1. A helium‑oxygen gas mixture was used to replace the air in the system to enable direct measurement of N2 emission, and three different gas exchange methods were assessed in their ability to minimize atmospheric background N2: 1) the N2-free gas purging method; 2) one cycle of the evacuation-refilling procedure; 3) one cycle of evacuating and refilling followed by N2-free gas purging. Method 3 was demonstrated as an optimum N2-removal method, and background N2 concentrations decreased to ~66 μmol·mol−1 within 11.6 h. During the N2-free gas purging period, low temperature incubation at 15 °C reduced CO2, CH4, NO, N2O and NH3 losses by 80.5 %, 41-fold, 10-fold, 11,403-fold and 61.4 %, respectively, compared with incubation at 30 °C. Therefore, a fast and low-perturbation N2 removal method was developed, namely the evacuating/refilling-low temperature purging method. Notably, all C and N gases exhibited large within-day variations during the peak emission period, which can be addressed by high-frequency measurement. Based on the developed method, up to 97.8 % of gaseous C and 95.6 % of gaseous N losses were quantified over a 43-day compost incubation, with N2 emission accounting (on average) for 5.8 % of the initial total N. This system for high frequency measurement of multiple gases (including N2) provides a novel tool for obtaining a deeper understanding of C and N turnover and more accurate estimation of reactive N and greenhouse gas emissions during composting.

Combined effects of organic amendments and fertilization on cotton growth and yield

AbstractWith escalating fertilizer prices, interest in using poultry litter as a source of plant nutrients has increased. However, the rapid decomposition of litter, particularly in the hot and humid southern United States, makes poultry litter vulnerable to loss of nutrients. Biochar and lignite have been proposed to mitigate nutrient loss, particularly N. However, information on the integration of biochar and lignite with poultry litter on cotton (Gossypium hirsutum L.) growth and yield is limited under southeastern agro‐ecosystems. A field experiment was conducted on a Leeper silty clay loam soil from 2017 to 2020 to evaluate the combined effect of poultry litter and inorganic N fertilizer with biochar and lignite on cotton growth, yield, and nutrient utilization. The treatments consisted of a 3 × 3 full‐factorial arrangement of amendments and fertilization types organized in a randomized complete block design. Application rates were 6.7 Mg ha–1 for poultry litter, 6.7 Mg ha–1 for biochar and lignite, and 134 kg N ha–1 for inorganic fertilizer. Lignite and biochar were only added once. The combination of biochar and lignite with poultry litter and inorganic fertilizer was positively effective on yield and yield components. Integration of biochar with poultry litter and inorganic fertilizer increased lint yield by 42 and 44% as compared with fertilization alone. Cotton leaf area index increased by 34 and 51% when biochar and lignite were combined with inorganic fertilizer in 2020. The leaching loss of postharvest soil NO3–N was significantly reduced by 66 and 50% when biochar and lignite were combined with inorganic fertilizer, respectively.

Basin-scale control on N2O loss rate and emission in the Changjiang River network, China

Global riverine N2O emissions have been made by several studies with great uncertainty. However, the regional N2O budgets and patterns in large river networks is still unclear, due to the lacking understanding of in-river N2O emission rate and well-classified river network water areas. Furthermore, the mass ratio of N2O emission against nitrogen(N) load in river networks remains controversial. Here we report N2O emissions from the largest river of China, the Changjiang River network, emphasizing the basin-scale control on riverine N2O loss rate in response to increasing N loads and river size. We find the N2O emission rate is negatively related to Strahler river orders, and positively related to N loading. The velocity (Vf) of N conversion into N2O was 0.131-0.436 m yr-1, and N2O loss rate (ζ) was 0.27-37.64 ×10-4 d-1 and declined exponentially with water discharge. Both the loss rate and the mass ratio of N conversion into N2O varied significantly at basin scale, indicating the diminishing capacity of river ecosystems to convert excess DIN into N2O when N load increased as a direct result of human activities. Our study shows N2O emission was 0.66 Gg N2O-N (1Gg=109g) in 1986 and increased to 10.3 Gg N2O-N in 2014 for the whole Changjiang River network. We identified the headwater streams are hotspots of N2O emission across the headwater stream to the estuary aquatic continuum. N2O emission was about 0.82% - 5.31% of global riverine N2O budget during 2010-2014. Our study suggested that an integrated approach in view of the riverine N loads and river hydrology is needed to improve estimates of riverine N2O emissions.

Evaluation of correlated Pandora column NO2 and in situ surface NO2 measurements during GMAP campaign

Abstract. To validate the Geostationary Environment Monitoring Spectrometer (GEMS), the GEMS Map of Air Pollution (GMAP) campaign was conducted during 2020–2021 by integrating Pandora Asia Network, aircraft, and in situ measurements. In the present study, GMAP-2020 measurements were applied to evaluate urban air quality and explore the synergy of Pandora column (PC) NO2 measurements and surface in situ (SI) NO2 measurements for Seosan, South Korea, where large point source (LPS) emissions are densely clustered. Due to the difficulty of interpreting the effects of LPS emissions on air quality downwind of Seosan using SI monitoring networks alone, we explored the combined analysis of both PC-NO2 and SI-NO2 measurements. Agglomerative hierarchical clustering using vertical meteorological variables combined with PC-NO2 and SI-NO2 yielded three distinct conditions: synoptic wind-dominant (SD), mixed (MD), and local wind-dominant (LD). These results suggest meteorology-dependent correlations between PC-NO2 and SI-NO2. Overall, yearly daytime mean (11:00–17:00 KST) PC-NO2 and SI-NO2 statistical data showed good linear correlations (R=∼0.73); however, the differences in correlations were largely attributed to meteorological conditions. SD conditions characterized by higher wind speeds and advected marine boundary layer heights suppressed fluctuations in both PC-NO2 and SI-NO2, driving a uniform vertical NO2 structure with higher correlations, whereas under LD conditions, LPS plumes were decoupled from the surface or were transported from nearby cities, weakening correlations through anomalous vertical NO2 gradients. The discrepancies suggest that using either PC-NO2 or SI-NO2 observations alone involves a higher possibility of uncertainty under LD conditions or prevailing transport processes. However, under MD conditions, both pollution ventilation due to high surface wind speeds and daytime photochemical NO2 loss contributed to stronger correlations through a decline in both PC-NO2 and SI-NO2 towards noon. Thus, Pandora Asia Network observations collected over 13 Asian countries since 2021 can be utilized for detailed investigation of the vertical complexity of air quality, and the conclusions can be also applied when performing GEMS observation interpretation in combination with SI measurements.

Maize diversification and nitrogen fertilization effects on soil nitrous oxide emissions in irrigated mediterranean conditions

Maize is a major irrigated crop in Mediterranean areas and its typical intensive management may impact soil nitrous oxide (N2O) emissions. In these irrigated continuous maize systems, the legumes incorporation as well as adjusted nitrogen (N) fertilization might be interesting strategies to reduce soil N2O emissions. The objective of this study was to assess the impact of cropping diversification and different N rates on soil N2O emissions in flooded irrigated maize under Mediterranean conditions. To achieve this, two cropping systems (maize monoculture system, MC; and pea -maize rotation, MP) and 3N rates (unfertilized, 0N; medium rate, MN; and high rate, HN) were evaluated in a field experiment established in NE Spain during 2 years (2019; 2020). During the studied period, the N rate had a significant effect on soil N2O emissions, with a non-linear positive response of cumulative soil N2O emissions to N rates. In both systems, quick and high increases of soil N2O fluxes were observed immediately after the N application reaching 55 and 100 mg N2O-N m−2 day−1 in MC and MP, respectively. Both years, the pea phase of the MP rotation showed greater cumulative N2O emissions than the fallow of MC. However, N2O losses in the maize phase were similar (2019) or even higher (2020) in MC than in MP. Moreover, in both seasons, the MN treatments showed lower yield-scaled N2O emissions and N emission factor than the HN treatments, being this last lower than 1% in all cases. The results obtained showed that in irrigated Mediterranean conditions the replacement of a fallow by a legume, together with an adjusted N fertilization are favourable strategies to mitigate soil N2O emissions in high-yielding maize systems.

Variations of leachate CO2 and N2O concentrations on typical cultivated and natural hillslopes in southeastern hilly area of China

Greenhouse gases dissolved in the soil water and transported through subsurface flow were poorly understood in comparison to their emissions at the soil-atmosphere interface. In this study, leachate CO2 and N2O concentrations were monitored on a tea garden (TG) hillslope (cultivated) and a bamboo forest (BF) hillslope (naturally vegetated) from September 2019 to February 2022 in the south-eastern hilly area of China. Leachate CO2 and N2O concentrations ranged from 1.07 to 9.83 mg C L−1 and from 0.32 to 11.74 μg N L−1, respectively, on the TG hillslope, while they ranged from 0.64 to 25.95 mg C L−1 and from 0.23 to 5.68 μg N L−1, respectively, on the BF hillslope. On both hillslopes, leachate CO2 concentrations were the greatest in summer, while they were the lowest in winter. On the TG hillslope, the highest and the lowest leachate N2O concentrations were observed in spring and summer, respectively, while on the BF hillslope, they were observed in autumn and winter, respectively. On both hillslopes, soil temperature, precipitation during the previous 15 days, and matrix potential were positively related to the leachate CO2 concentrations but not related to the leachate N2O concentrations. Soil water content was positively related to both leachate CO2 and N2O concentrations, while such relationships with groundwater table depth were negative. Leachate total inorganic nitrogen and soil total inorganic nitrogen concentrations were positively related to the leachate N2O concentration on the TG hillslope, while such relationships were not observed on the BF hillslope. Spatial variations of leachate CO2 and N2O concentrations were mainly influenced by land covers, terrain attributes (slope, elevation), soil particle size distribution, bulk density and soil organic matter content. The findings of this study supplemented the knowledge of soil water dissolved CO2 and N2O in the cultivated and naturally vegetated land covers. Further researches are needed to quantify the CO2 and N2O losses through subsurface flow and their contributions to the total soil CO2 and N2O losses.

Reactivity and Loss Mechanisms of NO3 and N2O5 at a Rural Site on the North China Plain

NO3, NO2, O3, and relevant parameters were measured at a rural site on the North China Plain during June 2014. During the campaign, the average concentrations of NO3 and N2O5 were 4.8 ± 3.3 pptv and 30.5 ± 35.4 pptv, respectively. The average NO3 production rate was 1.03 ± 0.48 ppbvh−1, and the steady-state lifetimes of NO3 and N2O5 were 26 s and 162 s, respectively, indicating that the NOx chemistry in the rural site during summer was active. The uptake coefficient range of N2O5 was 0.023 to 0.118, with an average value of 0.062 ± 0.035. Meanwhile, the fitting for kNO3 was 0.013 ± 0.016 s−1, corresponding to the shorter NO3 lifetime below 1 min. The results show that the indirect loss pathways caused by the heterogonous uptake of N2O5 contributed 64–90% of the overall NO3 loss, with an average of 81%, suggesting that the N2O5 heterogeneous reaction dominated the nocturnal NOx loss over this region.