BG1.4 | Nitrogen Cycling in the Anthropocene: Microbiological Processes, Land-atmosphere- Interactions, and advances in quantification and process-based modelling of Denitrification in soils

BG1.4

Nitrogen Cycling in the Anthropocene: Microbiological Processes, Land-atmosphere- Interactions, and advances in quantification and process-based modelling of Denitrification in soils

Anthropogenic disturbance of the global nitrogen (N) cycle has more than doubled the amount of reactive N circulating in the terrestrial biosphere alone. Exchange of reactive/non-reactive nitrogen gases between land and atmosphere are strongly affecting Earth’s atmospheric composition, air quality, global warming, climate change and human health.
Soil denitrification as a key process of terrestrial N cycle is poorly quantified despite a long research history, but progress is expected from focused effort in recent decades to improve techniques for measuring and modelling N2 and N2O fluxes. Yet we still lack a comprehensive, quantitative understanding of denitrification rates in soils due to methodical limitation, its complex controls and the spatio-temporal variability on a field or landscape scale. Due to the lack of suitable data-sets, process-based denitrification models have rarely been validated and results of their application on site and regional scales are highly uncertain.
This session seeks to improve our understanding of a) how intensification of reactive N use, land management and climate change affects the pools and fluxes of nitrogen in terrestrial and aquatic ecosystems, b) how reactive N enrichment of land and water will affect the future carbon sink of natural ecosystems as well as atmospheric exchanges of reactive (NO, N2O, NH3, HONO, NO2 and non-reactive N (N2) gases with implications for global warming, climate change and air quality, and c) how quantification and prediction of soil denitrification can be improved.
We welcome contributions covering a wide range of experimental and modelling studies, which covers microbes-mediated and physico-chemical transformations and transport of nitrogen across the land-water-air continuum in natural ecosystems from local to regional and global scales. We also invite contributions on methodical advances in measuring denitrification in soils addressing N2 and N2O fluxes with a focus on controlling factors; reports on novel methods; process-based modelling of denitrification at various scales; linking denitrification rates to parameters of the denitrifying community.

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Convener: Sami Ullah | Co-conveners: Reinhard Well, Balázs Grosz, Peter Dörsch, Tuula Larmola, Lena RoheECSECS, Dianming Wu

Orals

| Tue, 25 Apr, 14:00–15:45 (CEST)

Room 1.15/16

Posters on site

| Attendance Tue, 25 Apr, 16:15–18:00 (CEST)

Hall A

Orals: Tue, 25 Apr | Room 1.15/16

The oral presentations are given in a hybrid format supported by a Zoom meeting featuring on-site and virtual presentations. The button to access the Zoom meeting appears just before the time block starts.

Chairpersons: Tuula Larmola, Balázs Grosz, Sami Ullah

14:00–14:05

5-minute convener introduction

14:05–14:15

EGU23-4780

solicited

Highlight

Virtual presentation

Ammonia oxidation as the engine to induce denitrification to produce N2O in alkaline agricultural soils

Xiaotang Ju and Xiaotong Song

Ammonia oxidation contributes to global N₂O emissions both by direct production and by fueling denitrification (provision of nitrite or nitrate to denitrifiers). Urea or ammonia-based fertilizers account for approximately 70% of annual nitrogen fertilizer inputs globally. This means that the subsequent coupling processes driven by ammonia oxidation are of great significance to N₂O emissions. However, for this important source of N₂O production, direct evidence at the process- and microorganism- level is highly lacking, leading to that the systematic mechanism of the coupling processes and microbial activities in response to environmental changes (especially O₂ changes) remains unknown. Here, we investigated ammonia oxidation, other soil N transformation processes, N₂O emissions and related environmental changes (e.g., O₂ consumption) and microbial activities in a calcareous upland soil in Northern China, which has a strong ammonia oxidizing rate and is a global N₂O hotspot, by combining field observations, microcosm, molecular and isotope techniques. The results showed that the soil has a far (5-30 times) higher nitrification potential and gross nitrification rate than other cropland soils in the world. The strong ammonia oxidation led to rapid O₂ consumption and NO₂^- accumulation in soil matrix, causing strong emission peaks of N₂O, which was in line with the N₂O yield from denitrifiers. The N₂O ¹⁵N site preference and ¹⁵N labeling data further revealed a major role of nitrification-induced denitrification in high N₂O emissions. A higher AOB/AOA gene abundance ratio correlated the higher nitrification potential, higher NO₂^- transition and higher N₂O emissions. A coupling expression of nitrifying and denitrifying genes (amoA, narG, nirS, nirK, nosZ) and a significant structural alteration of the soil microbiota along with the O₂ consumption driven by ammonia oxidation linked to higher N₂O emissions. All the evidence points to ammonia oxidation-linked denitrification being the major process generating N₂O. In consequence, reducing N surplus, slowing down nitrification rate using nitrification inhibitors, and avoiding high ammonium microzones using slow-release or organic fertilizers are main measures to reduce N₂O emissions per unit of urea or NH₄⁺-based N input in intensively managed alkaline soils globally.

How to cite: Ju, X. and Song, X.: Ammonia oxidation as the engine to induce denitrification to produce N2O in alkaline agricultural soils, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4780, https://doi.org/10.5194/egusphere-egu23-4780, 2023.

14:15–14:25

EGU23-2124

On-site presentation

Denitrification in dry soils: Unexpected N emissions under environmental extremes

Peter Homyak

Moisture is a key factor governing soil nitrogen (N) biogeochemistry; it controls microbial activity and, therefore, the cycling of N. Ongoing climate change is altering precipitation regimes, increasing the frequency and intensity of droughts with implications for ecosystem N retention and loss. In particular, wetting dry soils can produce large emission pulses of nitrous oxide (N₂O), a potent greenhouse gas, but the mechanisms governing the N losses remain elusive. Especially because denitrification, arguably the most important process producing N₂O, is thermodynamically unfavorable in dry soils. Disentangling how drought can alter the balance between ecosystem N retention and loss is further challenged by the multiple biotic and abiotic processes that interact to control N availability and emissions, requiring multiple analytical approaches.

To advance understanding of N cycling in dry soils, we studied drylands in southern California that can experience >6 months without rain and whose contrasting soils developing under shrub canopies (soils known as “islands of fertility”), or in the bare interspaces between shrubs, allow us to interrogate biotic–abiotic interactions. Using isotopologues of N₂O coupled with chloroform fumigations to slow microbial activity, we found that N retention and loss trade off as dry conditions intensify. In particular, N₂O emissions were undetectable from soils in the interspaces between plants, but exceeded 1000 ng N-N₂O m^-1 s^-1 in islands of fertility, rivaling emissions observed in global hotspots like tropical forests and temperate agroecosystems. Despite the hot and dry conditions, isotope tracers and natural abundance isotopologues of N₂O indicated NO₃^- was reduced to N₂O within 15 minutes of wetting dry desert soils, and that both denitrification and N₂O reduction to N₂ contributed to the observed patterns, with δ¹⁵N^SP-N₂O values averaging 12.8 ± 3.9 ‰. Consistent with isotope values, fumigating soils in the lab with chloroform decreased NO₃^--derived N₂O emissions by 59%, suggesting denitrifiers were able to reduce NO₃^- immediately after wetting these summer-dry desert soils. In contrast to NO₃^-, the ¹⁵N-NH₄⁺ tracer was not found in N₂O, suggesting nitrification is not an important pathway governing N₂O emissions in these systems. Despite the hot and dry conditions known to make denitrification thermodynamically unfavorable in many drylands, denitrifiers can endure through hot and dry summers and are key to producing the surprisingly large N₂O emissions when dry desert soils wet up.

How to cite: Homyak, P.: Denitrification in dry soils: Unexpected N emissions under environmental extremes, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2124, https://doi.org/10.5194/egusphere-egu23-2124, 2023.

14:25–14:35

EGU23-4849

ECS

Highlight

On-site presentation

Importance of in-situ measurements of both N2O and N2 emissions to calibration of biogeochemical models to simulate N budgets

Naoya Takeda, Johannes Friedl, David Rowlings, Clemens Scheer, Edwin Haas, David Kraus, and Peter Grace

Denitrification is a key process in the global nitrogen (N) cycle, causing nitrous oxide (N₂O) and dinitrogen (N₂) emissions. Even though denitrification is assumed to be a major N loss pathway from agroecosystems, field-scale estimates of both N₂O and N₂ are scarce, reflecting methodological difficulties in measuring and upscaling N₂ emissions. Mechanistic biogeochemical models allow estimates of seasonal denitrification losses at the field scale, extrapolating important yet often limited experimental results. However, such predictions rely mostly on N₂O data, meaning that the lack of N₂ data hinders the validation of overall denitrification rates, which remain a major uncertainty for N budgets.

This study investigated denitrification losses and N budgets in two subtropical sugarcane systems using Agricultural Production Systems sIMulator (APSIM) with unique datasets of both N₂O and N₂ emissions measured in the field with the ¹⁵N gas flux method and upscaled over the growing season. Five key soil N parameters in APSIM were identified as influential on N₂O and N₂ emissions via global sensitivity analysis, followed by generalised likelihood uncertainty estimation to determine their posterior distributions using (i) both N₂O and N₂ data and (ii) N₂O data only.

For both approaches, the calibration of APSIM led to larger denitrification (N₂O+N₂) losses and a shift towards N₂ compared to the use of default parameters. Simulated N₂O emissions did not differ between the different calibration approaches. However, simulated N₂ emissions were larger and agreed better with the observed values when calibrated with both N₂O and N₂ consistently across sites. This approach also improved the simulation of fertiliser N losses via denitrification, leaching and runoff, compared to the observed fertiliser ¹⁵N loss at harvest.

These findings indicate that biogeochemical models commonly used with default soil N parameters or calibration limited to N₂O data are likely to underestimate denitrification losses, producing a bias in simulations of N budgets. Our findings also highlight the importance to integrate in-situ measurements of N₂O and N₂in simulation exercises, and demonstrate how innovative isotope methods can be used to inform biogeochemical models, ensuring more accurate N budget estimates across scales.

How to cite: Takeda, N., Friedl, J., Rowlings, D., Scheer, C., Haas, E., Kraus, D., and Grace, P.: Importance of in-situ measurements of both N2O and N2 emissions to calibration of biogeochemical models to simulate N budgets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4849, https://doi.org/10.5194/egusphere-egu23-4849, 2023.

14:35–14:45

EGU23-11088

ECS

Virtual presentation

Sources and sinks of atmospheric nitrous acid (HONO) in the megacity of Shanghai during COVID-19

Yue Wang and Dianming Wu

The COVID-19 global pandemic has significantly affected air quality due to changes in human behavior. Gaseous nitrous acid (HONO) is a significant precursor of the hydroxyl radicals (OH), powerfully influencing atmospheric oxidization capacity and air quality. However, the impacts on the sources and sinks of HONO during COVID-19 are not well understood. Here, we observed the concentrations of HONO, nitric oxide (NO), and nitrogen dioxide (NO₂) in the suburb of Shanghai during May 2020 (P1), August 2020 (P2), and April 2021 (P3) to analyze seasonal variations of HONO chemistry and also clarify how different pandemic phases influence HONO sources and sinks. The average concentration of HONO during P1, P2 and P3 showed an increasing trend (0.292 ± 0.0078、0.358 ± 0.0115, and 0.415 ± 0.0115 ppb, respectively), with direct emission from vehicles was the most essential source of the nocturnal HONO concentration (38.14%, 47.52%, and 50.95%, respectively), followed by heterogeneous conversion of NO₂. The daytime HONO sources presented noticeable discrepancy among three study periods. In spring, homogeneous reaction was the primary HONO source with a mean production rate of 0.2 ppb h⁻¹, while there was almost no unknown source (P_unknown). In summer, however, the average production rate of homogeneous reaction decreased to 0.15 ppb h⁻¹, while P_unknown was up to 58% of the whole HONO production, demonstrating some strongly enhanced source(s) in the summer season. By comparing HONO budgets between different pandemic phases, the contributions of vertical and horizontal transport doubled from P1 to P3, with the average production rates increasing from 0.03 to 0.06 ppb h⁻¹. Our results also showed that the strict lockdown measures reduced the unknown sources of HONO (P1), and correspondingly, as Shanghai implemented regular epidemic prevention and control measures, the relatively high rate of P_unknownwas observed during P3, making up 35% of the whole HONO production. What is more, through the strong correlation with J(HNO₃) (r = 0.9) and J(NO₂) (r = 0.89), it can be argued that the photolysis of nitric acid and photo-enhanced heterogeneous conversion may be a vital production pathway. The HONO photolysis was the major loss pathway, occupying approximately 85% of HONO loss during all campaigns. During noontime, the average photolysis loss rate was 1.07、2.40 and 1.86 ppb h⁻¹, accounting for up to 96% of the HONO sinks. Dry deposition was the second important loss pathway, especially in the morning and before sunset. This study indicates remarkable seasonal variations of HONO and the effects of COVID-19, and has significant implications on controlling measures of air pollutants in megacity.

How to cite: Wang, Y. and Wu, D.: Sources and sinks of atmospheric nitrous acid (HONO) in the megacity of Shanghai during COVID-19, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11088, https://doi.org/10.5194/egusphere-egu23-11088, 2023.

14:45–14:55

EGU23-6382

ECS

On-site presentation

Modeling coupled nitrification-denitrification in manure-amended soil

Jie Zhang, Elisabeth Larsen Kolstad, Wenxin Zhang, Per-Erik Jansson, Iris Vogeler Cronin, and Søren O. Petersen

The flux of nitrous oxide (N₂O) from the soil to the atmosphere is an important contributor to the global greenhouse effect. Spatial variation in the distribution of factors that drive N₂O producing processes often creates hotspots within soil that are difficult to quantify and model, and this is particularly the case after manure amendment. In the stagnant soil matrix, solute diffusion is crucial in supplying the nitrate (NO₃^-)to nearby zones, i.e., hotspots, to maintain a locally high NO₃^-reduction. To provide detailed insight into the spatiotemporal variability of nitrogen (N) transformations around N₂O hotspots, we propose a multi-species, reactive transport model containing kinetic reactions of soil respiration, nitrification, nitrifier denitrification, and denitrification, built on a system of partial differential equations. The model was used to simulate the amount of N₂O, dinitrogen (N₂) and carbon dioxide (CO₂) emitted from a 10 cm soil profile with time, and concentration profiles of crucial intermediates. The measured N₂O and N₂ fluxes correlate well with the model simulations, with a simulated stratification of growing nitrifying and denitrify activities in and around the manure hotspot which is consistent with previous incubation experiments. N₂O evolution was sensitive to the initial setup of oxygen (O₂) availability, and anaerobic condition was maintained in the saturated manure zone throughout the simulation period, demonstrating the necessity of simulating the heterogeneity within soil in N₂O models. Simulation experiments will be conducted to assess the effects of solute diffusion on N transformations. We anticipate that diffusive NO₃^- transport to be crucial to facilitate the coupled nitrification-denitrification around the manure zone. Neglecting such a process in process models may make it difficult to reflect the rapid turnover of nitrogen pool around organic hotspots and underestimate N₂O emissions. The model and its parameters allows for new detailed insight into N₂O formation processes in heterogeneous environments.

How to cite: Zhang, J., Kolstad, E. L., Zhang, W., Jansson, P.-E., Cronin, I. V., and Petersen, S. O.: Modeling coupled nitrification-denitrification in manure-amended soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6382, https://doi.org/10.5194/egusphere-egu23-6382, 2023.

14:55–15:05

EGU23-13402

ECS

Highlight

On-site presentation

In situ measurement of denitrification (N2 and N2O) and greenhouse gas emissions (CO2, N2O, CH4) in conservation agriculture

Gianni Micucci, Fotis Sgouridis, Stefan Krause, Iseult Lynch, Niall P. McNamara, Gloria Dos Santos Pereira, Felicity Roos, and Sami Ullah

Over the last 80 years, intensive agriculture has had numerous consequences globally. In particular, it has led to a loss of soil organic carbon (SOC) and a decline in soil fertility, resulting in higher nitrogen (N) fertilizer application. Excess of fertilizer has driven the emissions of N₂O, a greenhouse gas (GHG) 298 times more potent in inducing global warming than CO₂. Under the UK target of net zero emissions by 2050 and considering the recent increase in fertilizer price, conservation agriculture appears a viable solution to sustain food production whilst reducing global warming. Along with species diversification and reduction (or absence) of tillage, a permanent soil organic cover is the third pillar of conservation agriculture. In particular, “leys” consist in temporary pastures planted in between crops or to restore exhausted soils. These leys are planted with a mix of N fixing plants, which have a unique symbiotic relationship with soil bacteria collectively called “Rhizobia” that transform atmospheric N₂ into organic nitrogen. The mineralization of this organic nitrogen is expected to reduce dependence on N fertilizer. In contrast with the traditional grass/clover mix, herbal leys have recently gained popularity amongst UK farmers. They consist in a more complex mixture of grasses, legumes and herbs, bringing a range of benefits to forage, livestock health and soil fertility.

Here we report a year’s worth of measurement of soil mineral N and SOC contents, N mineralization potential, in situ measurement of denitrification (which transforms N fertilizer into N₂O and N₂) and total GHG emissions (CO₂, N₂O, CH₄) from a 4-year-old herbal ley in comparison with an arable field. We measured denitrification with our newly developed method (see Micucci et al., 2022) and GHG with conventional GHG chambers. First results show that during the early growing season (April to June), total N₂O emissions measured from GHG chambers were 10 to 60 times higher in the arable field than in the herbal ley, due to N fertilizer application. Similarly, a high loss of this N fertilizer was observed during April in the form of denitrified N₂.

Micucci, G., Sgouridis, F., Krause, S., Lynch, I., McNamara, N. P., Dos Santos Pereira, G., Roos, F., and Ullah, S. (2022). Towards enhanced sensitivity of the 15N Gas Flux method for quantifying denitrification in soil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-585, https://doi.org/10.5194/egusphere-egu22-585

How to cite: Micucci, G., Sgouridis, F., Krause, S., Lynch, I., McNamara, N. P., Dos Santos Pereira, G., Roos, F., and Ullah, S.: In situ measurement of denitrification (N2 and N2O) and greenhouse gas emissions (CO2, N2O, CH4) in conservation agriculture, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13402, https://doi.org/10.5194/egusphere-egu23-13402, 2023.

15:05–15:15

EGU23-6652

ECS

Virtual presentation

The production of N2O from sheep urine patches is influenced by soil properties.

Danielle Hunt, Laura Cardenas, Davey Jones, and David Chadwick

The urine patch from livestock creates an active hotspot of soil nitrogen (N) cycling due to the intrinsically high N and carbon (C) loading rates. These N hotspots frequently result in N losses to the atmosphere or leaching from soil. N losses vary due to climate conditions, soil conditions, and management practices. However, we do not fully understand how these factors influence N cycling and nitrous oxide (N₂O) emissions from urine patches. Intensive lowland grazing systems on mineral soils have been relatively well studied in this context, however, other grazing systems such as extensive upland systems on organic soils have been much less studied.

To investigate the effect of soil type on N cycling and N₂O emissions in the urine patch, soil was collected from pastures in an altitudinal gradient, from an improved lowland mineral soil with coastal influence to unimproved organic soil under acid grassland. Depending on the position along the gradient, the soils change in properties such as pH, bulk density, organic matter content, cation exchange capacity and nutrient availability. Soil was collected for a laboratory incubation study from four sites including two lowland sites (Cambisol and Cambisol with coastal influence) and two upland sites (Podzol and Histosol). Soils were sieved and divided into four replicates of each treatment. Sheep urine from Welsh Mountain ewes was applied at an equivalent loading rate of 150 kg N ha^-1 to half of the soil and the remaining half received the equivalent volume of water as a control. All the treatments were held at 70% water-filled pore space to optimise both moisture conditions for nitrification and denitrification to occur. Over 100 days, greenhouse gas emissions were monitored along with soil pore water nitrate and ammonium concentrations.

Soil type had an overall significant effect on N₂O emissions with the highest cumulative emissions during this period being from the Podzol and the lowest cumulative emissions being from the Histosol. The two lowland sites showed no significant differences. There was a delay in nitrification in the Podzol, with the majority of the N₂O being emitted a month after urine application. The Histosol showed no evidence of nitrification as there was no build-up of nitrate concentrations over the experiment. This was probably due to differences in soil pH in the soils. There were no differences in carbon dioxide or methane emissions from the four soils, but there was a spike in methane flux on the Podzol which corresponded with increases in N₂O fluxes from this soil type.

This experiment has shown that certain upland soils have the potential to produce N₂O emissions and cycle N under optimal conditions, although this is at a much slower rate than the lowland sites. Results from this incubation study helps improve our understanding of how soil properties in organic soils affect N cycling and contribute to knowledge gaps on the sustainability of upland grazing systems.

How to cite: Hunt, D., Cardenas, L., Jones, D., and Chadwick, D.: The production of N2O from sheep urine patches is influenced by soil properties., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-6652, https://doi.org/10.5194/egusphere-egu23-6652, 2023.

15:15–15:25

EGU23-8168

ECS

On-site presentation

Cross-Comparisons of Sediment Incubation Methods to Bound Stochastic Influences on Denitrification of Natural Waters from Mississippi River Floodplain Wetlands

Stony S. Samberg, Marjorie L. Brooks, Scott D. Hamilton-Brehm, Joseph M. Krienert, and Jonathan W.F. Remo

Flood regimes in large river systems such, as the Mississippi River, are inherently stochastic meaning that floodplain wetlands experience varying hydrostatic pressures of groundwater upwelling (exfiltration) and infiltration from overland flooding. Distinctions in water delivery can drastically alter the oxygen levels and groundwater delivery into wetland sediments where anaerobic microbes remove nitrates through denitrification. Our findings bound conditions for modeling denitrification rates across oxic flood waters versus exfiltration by anoxic groundwaters. Four-by-four factorial laboratory incubation treatments included oxic versus anoxic waters (degassed with helium) introduced by exfiltration or infiltration (Figs. 1A, 1B).

Sediments collected in triplicate from four floodplain wetlands located along Dogtooth Bend segment of the Mississippi River near the Ohio River confluence were incubated with river water. Sediments were incubated at 29 ^oC for 96 h. Nitrogen gas production was measured by membrane inlet mass spectrometry (MIMS). Inflow and outflow waters were analyzed for nitrate, ammonia, phosphate, and dissolved organic carbon while sediments were characterized for their physical traits. In contrast to most studies, that estimate denitrification relative to surface area in incubations only (i.e. address conditions of surface flooding), we also present our findings relative to sediment volumes (i.e. evaluate denitrification rates from exfiltration of groundwater). Regression analyses compared denitrification from surface area versus volume calculations (R² values > 0.89); consequently providing an excellent tool for converting estimates from surface area alone to varying sediment saturation for more rigorous assessments of subsurface interactions.

Average denitrification rates relative to sediment volume were significantly higher in anoxic-deep-injection cores (“AD cores”; 23.83 + 1.94 N mg/m³/d) compared to anoxic-surface-delivery cores (“AS cores”; 19.98 + 1 N mg/m³/d), that also exceeded oxic-deep-injection cores (“OD cores"; 14.96 + 1.78 N mg/m³/d) and oxic-surface-delivery cores (“OS cores”; 10.23 + 1.04 N mg/m³/d). Thus, average denitrification followed an anoxic-injection hierarchy of AD > AS > OD > OS (p-values < 0.003), which was maintained for denitrification relative to surface area. Regarding site-specific distinctions, for sandy sites this hierarchy persisted, and each treatment differed significantly. Sites with clayey sediments had very-low permeability regardless of injection type; thus only oxic versus anoxic treatments differed significantly irrespective of water delivery. By contrast sites with loamy sediments, injection type significantly influenced denitrification rates while neither oxic nor anoxic water treatments differed. An AICc model showed that phosphate, ammonia, temperature variation, dissolved oxygen, and sand content explained 33% (p-value < 0.05) of the variation in denitrification rates across all cores and treatments.

Our findings highlight the greater insights provided from cross-comparison incubation designs to better inform landscape-scale models of denitrification rates across floodplain wetlands depending on the magnitude and duration of flooding.

How to cite: Samberg, S. S., Brooks, M. L., Hamilton-Brehm, S. D., Krienert, J. M., and Remo, J. W. F.: Cross-Comparisons of Sediment Incubation Methods to Bound Stochastic Influences on Denitrification of Natural Waters from Mississippi River Floodplain Wetlands, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8168, https://doi.org/10.5194/egusphere-egu23-8168, 2023.

15:25–15:35

EGU23-15598

Highlight

On-site presentation

Effect of residue management and nitrification inhibitor on N2O and N2 emissions from an intensive sugarcane cropping system in sub-tropical Australia

Clemens Scheer, Johannes Friedl, Daniel Warner, David Rowlings, Weijin Wang, and Peter Grace

Sugarcane is typically produced under conditions that are known to stimulate soil denitrification, i.e. high fertiliser inputs in combination with high levels of crop residue (trash) retention and a warm and humid climate, and high levels of fertiliser N losses from intensive sugarcane systems have been reported. However, there is still insufficient reliable data on N₂losses from sugarcane soils based on field measurements since it is inherently challenging to measure N₂ emissions against the high atmospheric N₂ background. This study investigated the effect of cane trash removal and the use of the nitrification inhibitor 3,4-dimethylpyrazole phosphate (DMPP) on N₂ and N₂O emissions on a commercial sugarcane farm in sub-tropical Australia using the ¹⁵N gas flux method. Substantial gaseous N losses were observed under current management practice where cane trash retention and N fertiliser application (145 kg N ha^-1 as urea) resulted in elevated losses of N₂O and N₂ from a subsurface N fertiliser band, with more than 50% of these gaseous N losses emitted as N₂O. Cane trash retention increased the magnitude of N₂O and N₂emissions reflecting overlapping effects of increased soil water content and labile C supply from residues, but had no effect on the N₂O/(N₂+N₂O) ratio. The NI DMPP was extremely effective in reducing overall N₂O and N₂ losses and also promoted complete denitrification of N₂O to environmentally benign N₂, with only 4% of total N₂O and N₂losses emitted as N₂O. This shows that DMPP might be especially effective in reducing N₂O emissions from banded fertiliser were localized zones of high NO₃^- concentration around the fertiliser band are created that are particularly vulnerable to denitrification. Consequently, the use of DMPP in sugarcane systems with banded fertiliser does not only offer environmental benefits by reducing N₂O emissions but also substantially reduces overall denitrification losses, providing an effective strategy to improve NUE and reduce N₂O emissions for the Australian sugarcane industry.

How to cite: Scheer, C., Friedl, J., Warner, D., Rowlings, D., Wang, W., and Grace, P.: Effect of residue management and nitrification inhibitor on N2O and N2 emissions from an intensive sugarcane cropping system in sub-tropical Australia, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-15598, https://doi.org/10.5194/egusphere-egu23-15598, 2023.

15:35–15:45

EGU23-12416

ECS

On-site presentation

Nitrogen losses from food production in the North China Plain compared to environmental targets

Fanlei Meng, Mengru Wang, Reinder Ronda, Maryna Strokal, Carolien Kroeze, Lin Ma, Wen Xu, and Fusuo Zhang

North China Plain (NCP) is a region in China, with highly intensive food production and a hotspot of nitrogen (N) losses to the environment. Region-specific N management is, therefore, required to effectively reduce agricultural N losses. For this it is important to identify the N flows and environmental targets in the food chain (including crop production, animal production, food processing, and human consumption) at the county scale. We developed an integrated assessment N framework. It combines a food chain approach with an air quality model and groundwater model. We apply this method to quantify the relative contributions from parts of the food chain to N losses. We identify environmental targets to air and water in Quzhou, a typical agricultural county in the NCP. We found that N losses to the environment from the food chain were ~11 kt in Quzhou in 2017. Approximately 80% of this amount is from crop and animal production, which is primarily caused by the low N use efficiency in crop production (28%) and animal production (18%). Ammonia (NH₃) emissions to air (4.1 kt N) and N leaching (2.1 kt N), and direct discharges of manure to water (1.9 kt N) are the main contributors to the N losses in Quzhou. To meet the environmental targets for air quality (PM_2.5) and groundwater quality, the NH₃ emissions and N leaching need to be reduced by 55%, and 21-50%, respectively. Our findings indicate that better nutrient management is urgently needed to reduce agricultural N losses and to support Agriculture Green Development in NCP.

How to cite: Meng, F., Wang, M., Ronda, R., Strokal, M., Kroeze, C., Ma, L., Xu, W., and Zhang, F.: Nitrogen losses from food production in the North China Plain compared to environmental targets, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-12416, https://doi.org/10.5194/egusphere-egu23-12416, 2023.

Posters on site: Tue, 25 Apr, 16:15–18:00 | Hall A

The posters scheduled for on-site presentation are only visible in the poster hall in Vienna. If authors uploaded their presentation files, these files are linked from the abstracts below, but only on the day of the poster session.

Chairpersons: Peter Dörsch, Reinhard Well, Lena Rohe

A.222

EGU23-5834

ECS

On-site presentation

Prolonged Flooding followed by drying increase greenhouse gas emissions differently from soils under grassland and arable land uses

Yafei Guo, Ernesto Saiz, Aleksandar Radu, and Sami Ullah

Abstract

Under the predicted climate change scenarios, heavy precipitation could result in prolonged flooding (PF) and flooding-drying (FD) of soils in agriculture. The influence of PF and FD on soil greenhouse gas fluxes and nitrogen (N) dynamics of arable and grassland soils, which are the dominant land use types in UK soil, is still unclear. Two months of soil incubation experiments were conducted to find out the impact of PF and FD on soil nitrogen dynamics and greenhouse gas fluxes from arable and grassland soil. The result showed the developed ion selective electrodes (ISE) sensor was working to measure NH₄⁺ in the first 5 days of real-life application under both grassland and arable soil. There were less N₂O-N emissions in grassland and arable soil when soil moisture was higher than 100% water-holding capacity (WHC). Arable soil had more N₂O-N emissions when soil moisture was higher than 100% WHC compared to grassland soil due to a low pH. Grassland soil had more N₂O-N emissions when soil moisture was lower than 100% WHC compare to arable soil due to a high carbon and nitrogen source. When soil moisture was greater than 100% WHC, the available NO₃^--N in the soil controlled N₂O-N emissions of grassland more effectively. The N₂O-N emissions of grassland soil were more controlled by soil stable NH₄⁺-N and NO₃^--N when soil moisture was lower than 100% WHC. The emissions of N₂O-N and CO₂-C were increased with the time of FD. FD significantly increased N₂O-N, CO₂-C, and CH₄-C emissions in grassland soil compared to arable soil by 0.93, 2.15, and 37.29 times, respectively. Converting arable land use to grassland could increase the greenhouse gas (GHG) emissions under climate change (heavy rain). Further research needs to be done to find out how to reduce the GHG emissions under climate change after transfer arable to grassland.

How to cite: Guo, Y., Saiz, E., Radu, A., and Ullah, S.: Prolonged Flooding followed by drying increase greenhouse gas emissions differently from soils under grassland and arable land uses, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5834, https://doi.org/10.5194/egusphere-egu23-5834, 2023.

A.223

EGU23-5324

ECS

On-site presentation

Low-cost in-field determination of soil ion concentration using a portable 3D printed device based on ion-selective electrodes and textile threads

Ernesto Saiz, Yafei Guo, Sami Ullah, Sameer Sonkusale, and Aleksandar Radu

Population keeps growing so as the need for food production. The increase in energy prices is putting a lot of pressure in energy intensive industrial processes such as the production of fertilizers. Farmers need to fine-tune the amount of fertilizer needed by the soil, so that they do not add in excess, elevating costs and polluting the environment, or do not fall short, suffering sub-optimal crop yields.

This work reports the fabrication and characterization of a low-cost device for the continuous monitoring of the concentration of plant nutrients based on ion-selective electrodes and textile threads that work in direct contact with soils. Here, as proof of concept, we developed a thread-based, microfluidic sensor platform. We utilized traditional polymer membrane-based ion-selective electrodes (ISEs) for potassium, nitrate, ammonium and pH were drop-casted directly on top of a miniaturized, 3D-printed holder. Electrical contact is established via graphite-based contacts link to the electrochemical signal reader via electrical wires. The sensor platform was enhanced by the addition of five 30 cm long textile threads connected to an absorption pad on the opposite side. This is the key innovation as these threads mimic the roots and via capillary action wick the moisture from the soil to the sensing area. The entire sensor platform contained 4 ISEs for each chemical species and one reference electrode and was encased into a 3D printed housing. The device is placed next to the soil that is going to be analysed inserting the threads in the soil sampling area.

Preliminary results show that thread-based sensor system is reproducible and consistently provides a near-Nernstian sensitivity of 55±5 and 50±3 for potassium, -58±1 and -63±2 for nitrate, and 60±1 and 60±12 (mV/decade) for ammonium between 2.8x10^-6 and 1.3x10^-2 M without (directly in solution) and with textile threads respectively. Analysis of soil samples with different soil moisture content (100%, 75%, 50% and 40%) using our low cost device gave a correlation coefficient of R² = 0.91 for potassium and R² = 0.92 for ammonium when compared to the values measured using traditional methods such as inductively coupled plasma optical emission spectroscopy (ICP-OES) and flow injection analysis (FIA), respectively. The promising performance of this low-cost device is encouraging towards its use as an extended network to measure soil ion concentration at high temporal and spatial resolution.

How to cite: Saiz, E., Guo, Y., Ullah, S., Sonkusale, S., and Radu, A.: Low-cost in-field determination of soil ion concentration using a portable 3D printed device based on ion-selective electrodes and textile threads, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5324, https://doi.org/10.5194/egusphere-egu23-5324, 2023.

A.224

EGU23-2623

On-site presentation

Which N2O production processes are relevant when converting from grassland to cropland?

Caroline Buchen-Tschiskale, Dominika Lewicka-Szczebak, Greta Nicolay, Mirjam Helfrich, Heinz Flessa, and Reinhard Well

During the last decades, large areas of grassland were converted to cropland across Europe, mainly due to the increasing demand of cropland following the expansion of biogas plant production (e.g. maize). However, the conversion to cropland bears a risk of nitrous oxide (N₂O) emission due to enhanced nitrogen (N) mineralization. Until now, knowledge about N₂O production pathways due to grassland conversion and in particular N₂O reduction to N₂ is very limited (Buchen et al., 2018), even though understanding of N₂O processes and identification of sources are needed in order to devise mitigation options.

N₂O samples were collected periodically from manual chambers following chemical and mechanical conversion from permanent grassland to cropland (maize) at two sites with different texture (clayey loam and sandy loam) and fertilization regime (with and without mineral N-fertilization) in north-western Germany (Helfrich et al., 2020). Samples were analysed for natural abundance stable isotope signatures of soil-emitted N₂O (δ¹⁵N^bulk_N2O, δ¹⁸O_N2O and δ¹⁵N^SP_N2O = intramolecular distribution of ¹⁵N in the N₂O molecule) by isotope ratio mass spectrometry (IRMS) and dual-isotope of N₂O isotopic signatures (plotting δ¹⁵N^SP_N2O vs. δ¹⁸O_N2O) were used for data evaluation (Lewicka-Szczebak et al., 2017). Although, isotopic signatures were very variable throughout the year at both sites, the clayey loam site exhibited a close correlation between δ¹⁵N^sp_N2O and δ¹⁸O_N2O suggesting that values were mainly controlled by N₂O reduction to N₂. At the sandy loam site this pattern was less pronounced, possibly because processes other than bacterial denitrification (e.g. fungal denitrification and nitrification) also significantly influence isotopocule values. Altogether, bacterial denitrification was found to be the most important process following grassland conversion to maize cropping.

References:

Buchen, C., Lewicka‐Szczebak, D., Flessa, H., Well, R., 2018. Estimating N₂O processes during grassland renewal and grassland conversion to maize cropping using N₂O isotopocules. Rapid Communications in Mass Spectrometry 32, 1053-1067.

Helfrich, M., Nicolay, G., Well, R., Buchen-Tschiskale, C., Dechow, R., Fuß, R., Gensior, A., Paulsen, H., Berendonk, C., Flessa, H., 2020. Effect of chemical and mechanical grassland conversion to cropland on soil mineral N dynamics and N₂O emission. Agriculture, Ecosystems & Environment 298, 106975.

Lewicka-Szczebak, D., Augustin, J., Giesemann, A., Well, R., 2017. Quantifying N₂O reduction to N₂based on N₂O isotopocules – validation with independent methods (helium incubation and ¹⁵N gas flux method). Biogeosciences 14, 711-732.

How to cite: Buchen-Tschiskale, C., Lewicka-Szczebak, D., Nicolay, G., Helfrich, M., Flessa, H., and Well, R.: Which N2O production processes are relevant when converting from grassland to cropland?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-2623, https://doi.org/10.5194/egusphere-egu23-2623, 2023.

A.225

EGU23-3413

Highlight

On-site presentation

Hot-spots of denitrification in soil depending on crop residue and liquid manure incorporation – models and experiments

Reinhard Well, Rene Dechow, and Balazs Grosz

Soil denitrification is known to be affected by incorporation of crop residues due to supply of reductants and oxygen (O₂) consumption by decomposition. The formation of anoxic microsites where denitrification can occur thus depends on quality, particle size and spatial distribution of incorporated residues in interaction with physical and chemical soil properties. Current biogeochemical models typically assume homogeneity of soil layers and thus don’t consider the size and distribution of crop residue particles. Until now, dinitrogen (N₂) and nitrous oxide (N₂O) fluxes related to residue incorporation patterns have been rarely studied and are poorly represented by current models. Here we present synergetic concepts and results of two projects addressing the spatial modelling of anoxic hot-spots („Modeling the impact of liquid organic fertilization and associated application techniques on N₂O and N₂ emissions from agricultural soils”, MOFANE) and measures to mitigate denitrification in soil („Measures to reduce direct and indirect climate-impacting emissions caused by denitrification in agriculturally used soils”, MinDen).

To test the incorporation of harvest residues and catch crops on denitrification, a full-factorial laboratory incubation will be carried out in MinDen, assessing incorporation methods and pre-crushing of catch crops, and how these interact with soil type and water content.

Based on a static model to take into account spatial hot-spots induced by liquid manure (Baral et al., 2016) a dynamic model was developed in MOFANE and tested using lab experiments (Grosz et al., 2022). This model can also be applied to evaluate the aforementioned crop residue effects.

We present a conceptual model of denitrification in dependence of size and distribution of crop residues, soil type, soil moisture and soil structure. It predicts that pre-shredding and homogenous incorporation favours denitrification at low gas diffusivity given by high moisture and/or high clay content or bulk density, since small organic hot-spots suffice to create anoxia. For high gas diffusivity (e.g. due to sandy texture and/or dry conditions) it predicts that denitrification is favoured if incorporated crop residues are large, since anoxic microsites can only develop if the size of organic hot-spots is large enough so that the O₂ sink strength exceeds O₂ diffusion from the atmosphere.

Scenarios of the conceptual model will be tested using the dynamic hot-spot model and results will be presented.

Baral, K.R., Arthur, E., Olesen, J.E., Petersen, S.O., 2016. Predicting nitrous oxide emissions from manure properties and soil moisture: An incubation experiment. Soil Biology & Biochemistry 97, 112-120.

Grosz, B., Kemmann, B., Burkart, S., Petersen, S.O., Well, R., 2022. Understanding the Impact of Liquid Organic Fertilisation and Associated Application Techniques on N2, N2O and CO2 Fluxes from Agricultural Soils. Agriculture 12, 692.

How to cite: Well, R., Dechow, R., and Grosz, B.: Hot-spots of denitrification in soil depending on crop residue and liquid manure incorporation – models and experiments, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-3413, https://doi.org/10.5194/egusphere-egu23-3413, 2023.

A.226

EGU23-4359

ECS

On-site presentation

The effect of fertilisation and crops on nitrogen sequestration based on microbial analysis and N2O emissions

Laura Kuusemets

EGU General Assembly 2023

23-28 April 2023

THE EFFECT OF FERTILISATION AND CROPS ON NITROGEN SEQUESTRATION BASED ON MICROBIAL ANALYSIS AND N₂O EMISSIONS

Laura Kuusemets¹, Ülo Mander¹, Jordi Escuer Gatius², Alar Astover ², Mikk Espenberg¹

¹ University of Tartu, Institute of Ecology and Earth Sciences, Vanemuise 46, 51014 Tartu, Estonia

²Estonian University of Life Sciences, Institute of Agricultural and Environmental Sciences, Kreutzwaldi 5, 51014 Tartu, Estonia

Contact: laura.kuusemets@ut.ee

Nitrogen (N) is an essential nutrient in crop production as N is used to make amino acids (make the proteins that construct cells), is one of the building blocks for DNA, and is a significant component of chlorophyll (photosynthesis). The input of N in the form of fertilisers increases crop yield. On the other hand, agricultural nitrogen inputs can cause N leaching and the loss of biologically active N to the atmosphere, contributing to global warming. Thus, excessive and inefficient use of N fertiliser results in enhanced crop production costs and pollution of water bodies and the atmosphere. Agricultural landscapes are an important source of nitrous oxide (N₂O), a highly active greenhouse gas and stratospheric ozone depleter. The main objectives of the study were to evaluate whether and how different crop species and fertilisation norms affect nitrous oxide (N₂O) emissions and soil microbiome using the closed chamber method and quantitative polymerase chain reaction (qPCR) analysis.

The study was done in the IOSDV (International Organic Nitrogen Long-term Fertilisation Experiment) experimental field located in the southern part of Estonia. The crop species studied were barley (cultivar “Elmeri”), sorgo (cultivar “Susu”), and wheat (cultivar “Mistral”). The fertiliser treatment is constituted of mineral nitrogen fertilisation and fertilisation with farmyard manure. Three nitrogen fertiliser treatment rates were used: 0, 80 and 160 kg ha⁻¹. Samples were collected over seven months, from April 2022 to October 2022. qPCR was used to quantify the abundance of bacteria- and archaea-specific 16S rRNA, nitrification (bacterial, archaeal and comammox (complete ammonia oxidation) amoA) denitrification (nirK, nirS, nosZI and nosZII) and dissimilatory nitrate reduction to ammonium (DNRA; nrfA gene) marker genes from the soil samples.

The results of this study indicate that different fertilisation influence N₂O emissions and the highest N₂O emissions are emitted from the highest N fertilizer treatment (160 kg ha⁻¹). On average, sorgo fields fertilised with farmyard manure had slightly higher N₂O emissions compared to fertilisation with mineral fertiliser. In addition, on average, the highest and smallest N₂O emissions occurred with wheat and barley, respectively. The N₂O emissions among all crop species decreased during drought in the summer. The preliminary microbial analysis shows that nitrification was the primary process resulting in N₂O emissions, but the different groups of nitrifiers showed different trends under different fertilisation and crops.

How to cite: Kuusemets, L.: The effect of fertilisation and crops on nitrogen sequestration based on microbial analysis and N2O emissions, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-4359, https://doi.org/10.5194/egusphere-egu23-4359, 2023.

A.227

EGU23-5282

On-site presentation

Shifting China’s rice fields from nitrogen source to sink by innovative agricultural management

Weichen Huang, Wenjun Jiang, and Feng Zhou

Rice field has been traditionally considered as a nonpoint source of reactive nitrogen (N) for the environment, while it, with surrounding ditches and ponds, also contributes to receiving N inputs from atmosphere and waterbodies and intercepting N outputs from rice field. However, due to the paucity of multi-site, long-term observation and control experiment data, as well as robust process-based model for nitrogen budget, a comprehensive assessment of the N source (i.e., outputs > inputs) or sink (i.e., inputs > outputs) of rice field for the environment, from site to regional scale, is lacking. Here, a 2-year systematic observation and process-based simulations of N budget across China, covering typical annual rice cropping systems including single rice, double rice and rotation, were conducted to identify the roles of rice field in nitrogen cycling in China. The cost-benefit analysis for shifting China’s rice fields from nitrogen source to sink in different climatic scenarios (wet, normal and dry year) by innovative agricultural management, without compromising crop yield or soil fertility, were further evaluated. Rice fields, with surrounding ditches and ponds, perform as a nitrogen sink for atmosphere but a source for waterbody, which was confirmed by both the observational data and regional assessment by process-based model, regardless of rice types or climatic scenarios. With the adoption of sustainable N and water regulation measures, single rice field across China could be shifted to N sink (12.9-29.9 kg N ha^-1) while the N source of double rice would be reduced by 51%-66%. For middle rice field (rotation with other crops), N sink would be achieved in dry year, while 31%-55% would shift to sink in wet and normal year. However, with such great benefits, the costs only accounted for 41%-49% of the expenditure for waste water treatment. Furthermore, through sorting all the measures and adopting economic ones (lower cost with higher benefit) in priority, we found that rice fields across China have great space for source-to-sink regulation with zero cost, which means the benefits would exceed the regulation costs, and even achieve overall N sink in dry year. Together these findings help us to update scientific knowledge to the role of rice fields in ecosystems, as well as highlight the significance and possibility for achieving environmental-friendly rice field, by improving agricultural management technologies.

How to cite: Huang, W., Jiang, W., and Zhou, F.: Shifting China’s rice fields from nitrogen source to sink by innovative agricultural management, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5282, https://doi.org/10.5194/egusphere-egu23-5282, 2023.

A.228

EGU23-5440

ECS

On-site presentation

Microbial and environmental factors affecting nitrate removal in bio-electrochemical systems (BES)

Sharvari Sunil Gadegaonkar, Ülo Mander, and Mikk Espenberg

Excess nitrogen has caused environmental issues by polluting the air and water. Many different processes help remove nitrogen compounds from contaminated soils and waters, and the presence of oxygen is one of the most decisive factors. Denitrification in anaerobic conditions is considered the main removal processes of excessive nitrogen, although lately discovered anaerobic ammonium oxidation (ANAMMOX) and dissimilatory nitrate reduction to ammonium (DNRA) may also have an important role in nitrogen elimination of different systems. To a lesser extent, also nitrification can contribute to nitrogen elimination in watery systems. All previously pointed out removal mechanisms occur in the constructed wetlands and could even be enhanced with the bio-electrochemical systems (BES). BES exploit the ability of the electroactive microorganisms to reduce the oxides of nitrogen.

We analyzed various articles treating nitrate (NO₃) polluted water in BES and normalized their NO₃ removal efficiencies to a common unit (mg liter⁻¹ day⁻¹). We analyzed the effect of various factors such as electrode materials, working mode, type of inoculum, number of chambers, systems’ capacity and the microbial community structure on the NO₃ removal efficiencies. The highest removal efficiencies were displayed by granular carbon and carbon cloth used as cathode and anode material, respectively. The electrode materials and operational parameters, such as working mode and number of chambers, were deemed important by the random forest classification algorithm. Continuous mode of operation, denitrifying microbes as inoculum type, and two chamber systems have displayed optimum NO₃ removal efficiencies. Feature selection using random forest classification showed the type of inoculum and capacity of the BES were unimportant factors. Proteobacteria and Firmicute were the prominent phyla observed in BES treating NO₃ polluted water. Besides the denitrification (abundance of narG, nirS, nirK, nosZI, and nosZII genes) process in BES, there is evidence of electrochemical support for anaerobic ammonium oxidation (ANAMMOX) (abundance of hzsB or ANAMMOX specific 16S rRNA gene) and dissimilatory NO₃ reduction to ammonium (DNRA) (abundance of nrfA gene) processes. The results of this work aid in understanding the prevalent processes in the BES and help to build efficient BES for optimum NO₃ removal.

How to cite: Gadegaonkar, S. S., Mander, Ü., and Espenberg, M.: Microbial and environmental factors affecting nitrate removal in bio-electrochemical systems (BES), EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5440, https://doi.org/10.5194/egusphere-egu23-5440, 2023.

A.229

EGU23-5615

Highlight

On-site presentation

Crop plant effects on denitrification – what have we learned in six years DASIM project?

Pauline Sophie Rummel, Reinhard Well, Johanna Pausch, Paulina Englert, Amanda Matson, Lukas Beule, Sebastian Floßmann, Jonas Eckei, Birgit Pfeiffer, and Klaus Dittert

Denitrification in agricultural crop production is one of the main sources of gaseous N₂O and N₂ losses to the environment. To successfully develop mitigation strategies, it is crucial to understand N₂O production pathways, but also to quantify all other gaseous N losses, especially N₂ emissions. Therefore, this project aimed (1) to identify the main drivers of denitrification during plant growth and in the post-harvest period, (2) to quantify denitrification derived N₂O and N₂ losses during the cropping season, and (3) to assess the interactions between plant litter quality, initial litter degradation, and formation of hotspots of N₂O and N₂ production. We conducted experiments on the laboratory, greenhouse, and field plot scale using the ¹⁵N gas flux method and HeO₂ atmosphere to directly measure N₂O and N₂ losses and to determine the fraction of denitrification derived N losses. We worked with soils, crops, temperature and moisture conditions that are typical for our central German humid-temperate climate.

Plant growth affected all controlling factors of denitrification, especially soil moisture, NO₃⁻ and C_org availability. Crop species differed in their growing patterns and N uptake throughout the growing season controlling both N and C availability in soil. Accordingly, N₂O and N₂ emission patterns differed between crop species. Overall, emissions were highest when plant N uptake was low, i.e., during early growth stages and ripening, and after harvest. On the field scale, soil moisture and temperature were major controls of N₂O+N₂ losses.

In a climate chamber study under controlled temperature conditions, N₂O and N₂ fluxes mainly derived from denitrification of labeled ¹⁵NO₃⁻ in anoxic microsites, while nitrification simultaneously occurred in more oxic parts of the soil, potentially contributing to formation of unlabeled N₂O. Increasing soil moisture with irrigation increased denitrification rates in anoxic hotspots, which corresponded with increasing N₂O and especially N₂ fluxes. At the same time, it restricted nitrification and thus decreased the share of nitrification-dependent processes contributing to N₂O formation.

Incorporation of plant litter increased CO₂, N₂O, and N₂ losses irrespective of litter quality, soil moisture or soil type/SOM content. We found that under O₂ limiting conditions (70 % WFPS), the fraction of easily degradable C controlled the magnitude of N₂O and N₂ losses after litter incorporation. Under moderate soil moisture (50-60 % WFPS), interactions between litter degradation and SOM turnover affected the time course and processes contributing to N₂O formation. Overall, our high-resolution gas flux measurements showed that N₂O+N₂ emissions from harvest residues can contribute significantly to the total N loss.

How to cite: Rummel, P. S., Well, R., Pausch, J., Englert, P., Matson, A., Beule, L., Floßmann, S., Eckei, J., Pfeiffer, B., and Dittert, K.: Crop plant effects on denitrification – what have we learned in six years DASIM project?, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-5615, https://doi.org/10.5194/egusphere-egu23-5615, 2023.

A.230

EGU23-7971

On-site presentation

Contrasting effects of increase in water and nutrients availability on soil respiration and soil nitric and nitrous oxide emissions in desert.

Ilya Gelfand and Martha Osei-Yeboah

Soil microbial processes in drylands are limited by multiple abiotic factors, the most important being water and macronutrients (nitrogen (N) and phosphorus (P)). Understanding of relative importance of different abiotic factors for soil microbial processes is important because drylands are important regulators of global carbon (C) cycle and there is close connection between water, N, and C cycles. To assess how soil activity is affected by removing multiple nutrient limitations and manipulating water availability we conducted a short-term, multifactorial field experiment. We manipulated water, N, and P availability by application of the nutrients and water in the field. We evaluated how soil respiration, nitrous oxide, and nitric oxide emissions responded to increasing water, N and P availability individually and interactively in the Negev Desert. We hypothesized that neither water nor nutrient addition alone will enhance the activity of desert soils. On the other hand, removing multiple limitations will accelerate soil nutrient cycling. Further we hypothesized that acceleration of soil nutrient cycling will be reflected in high soil emissions of N₂O, NO, and CO₂ as proxies for the N cycle and respiration, respectively. We found that increasing water availability in desert soils significantly accelerated soil respiration rates but not the N cycle. Nitrogen availability affected soil NO production but not soil respiration. Soil emissions of N₂O were unaffected by neither water nor nutrients additions. Phosphorus additions had no effect on soil microbial activity either alone or synergistically together with N and water.

How to cite: Gelfand, I. and Osei-Yeboah, M.: Contrasting effects of increase in water and nutrients availability on soil respiration and soil nitric and nitrous oxide emissions in desert., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-7971, https://doi.org/10.5194/egusphere-egu23-7971, 2023.

A.231

EGU23-8878

ECS

On-site presentation

Low vs. upland - copper addition regulates denitrification in cropland soils from N2O emissions hotspots in Denmark

Yujia Liu, Daniel Mika-Nsimbi Poultney, Florian Wichern, Per Ambus, and Carsten W. Müller

Agricultural land-use makes up around 38% of the total global land surface. Farming activities are a major source of greenhouse gas emissions (carbon dioxide, methane and nitrous oxide) worldwide. Nitrous oxide (N₂O) emissions from agricultural land are an important contributor to the overall greenhouse gas budget. The high spatial and temporal variation of N₂O emissions in agricultural lands makes it more challenging and important to quantify the actual emissions. Denmark’s glacial landscape is characterized by a high abundance of topographic depressions. These are typically flooded for 1-3 months per year, mainly during late winter and spring season. As these depressions are frequent in agricultural areas, their soils are exposed to an increased nitrate availability due to regular fertilization. The combination of high-water saturation and high nitrate availability results in distinct landscape denitrification and thus N₂O emission “hotspots”.

The reduction of N₂O to N₂ by N₂O reductase can be an important mechanism to mitigate N₂O emissions. The N₂O reductase is both Cu and pH sensitive. Studies have showed Cu-modified organic fertilizer have the potential to enhance the reduction from N₂O to N₂, and therefore decrease N₂O emissions from fields.

In this study, we aimed to elucidate if Cu addition alters the emission of N₂O from upland and depression soils in a different way. Therefore, we conducted an incubation experiment with both upland and depression soils, testing how different levels of Cu addition and two different water levels affect the emission of N₂O. In order to differentiate the N₂O production pathways (nitrification or denitrification), we applied ¹⁵N tracer in the form of ¹⁵NH₄¹⁵NO₃ or ¹⁴NH₄¹⁵NO₃. We also added ¹³C labelled maize residues to be able to trace the consumption of fresh substrate in the course of denitrification as affected by different Cu and water levels.

Interestingly, although the soils were homogenized and incubated at the same water availability, we demonstrated a clearly higher N₂O emission from the depression soils compared to the upland soils. In general, we were able to demonstrate that Cu addition clearly reduces the level of N₂O emissions from upland soils, which is clearly more pronounced at higher soil water levels.

How to cite: Liu, Y., Poultney, D. M.-N., Wichern, F., Ambus, P., and Müller, C. W.: Low vs. upland - copper addition regulates denitrification in cropland soils from N2O emissions hotspots in Denmark, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-8878, https://doi.org/10.5194/egusphere-egu23-8878, 2023.

A.232

EGU23-13010

On-site presentation

Advancing the realistic simulations of N2O emissions in cold climate watersheds using Soil and Water Assessment Tool

Prasad Daggupati, Uttam Ghimere, and Asim Biswas

Nitrous Oxide (N₂O) emissions in Soil and Water Assessment Tool (SWAT) is heavily dependent on soil temperature and moisture. However, SWAT has been known to highly under-estimate soil temperature which limits movement of water and nutrients throughout the soil profile and does not replicate freeze-thaw cycles which is of paramount importance in the N₂O emissions. Thus, we integrated modules developed by individual researchers pertaining to energy balanced snow melt, rain-on-snow, energy balanced soil temperature and N₂O emission into a single SWAT model and termed in SWAT Cold Climate N₂O (SWAT-CCN2O). SWAT-CCN2O was then tested for flows, sediments, soil temperature and N2O emission simulation in a representative watershed in Ontario, Canada, the Speed River basin. Compared with the unaltered SWAT model, SWAT-CCN2O was able to significantly capture the pre-spring snowmelt induced flows. A more realistic simulation of soil temperature (soil temperatures did not go below -4^oC) and a satisfactory simulation of sediments and N₂O emissions were observed in the basin, which highlights the potential to use SWAT-CCN2O for streamflow and N₂O simulation in cold climatic catchments. This version of SWAT is made publicly available for further improvements and applications in similar watersheds.

How to cite: Daggupati, P., Ghimere, U., and Biswas, A.: Advancing the realistic simulations of N2O emissions in cold climate watersheds using Soil and Water Assessment Tool, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13010, https://doi.org/10.5194/egusphere-egu23-13010, 2023.

A.233

EGU23-17035

On-site presentation

Comammox Nitrospira contributed nitrification and N2O production activity in coastal wetland

Ping Han and Dongyao Sun

Specific nitrification inhibitors (NIs) have been widely used to disentangle the contribution of ammonia-oxidizing archaea (AOA), ammonia-oxidizing bacteria (AOB) as well as nitrite oxidizers to the nitrification process in specific environments. However, if these previously reported NIs can also be used to evaluate the activity of the newly discovered complete ammonia oxidizers (comammox) Nitrospira, remains understudied. Here we evaluated various NIs for their impact and specificity regarding inhibition of comammox Nitrospira in batch cultures of pure and mixed strains of AOA, AOB and comammox. Using these batch cultures, we observed that chlorate could specifically inhibit the ammonia oxidation and nitrite oxidation activity of comammox Nitrospira, while it had no effect on the tested AOA and AOB strains. This inhibitory effect of chlorate on comammox Nitrospira was subsequently confirmed based on ¹³CO₂-DNA-stable isotope probing (¹³C-DNA-SIP) analysis. Furthermore, by applying a set of specific NIs, the nitrification and nitrous oxide (N₂O) production rates of comammox Nitrospira in coastal wetlands were estimated as 17.45 ng N g^-1 h^-1(26.9 % of the total rate) and 0.0083 µmol^-1 L h^-1(28.5%). Altogether, we identified and applied an effective and specific inhibitor of comammox Nitrospira, which allowed quantifying comammox activity in wetlands of the Yangtze Estuary, shedding new light on the ecological roles of comammox bacteria in coastal wetland environments.

How to cite: Han, P. and Sun, D.: Comammox Nitrospira contributed nitrification and N2O production activity in coastal wetland, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-17035, https://doi.org/10.5194/egusphere-egu23-17035, 2023.

A.234

EGU23-13162

On-site presentation

Modeling hot-spot of N2 and N2O production in agricultural soils as introduced by liquid organic fertilization

Balázs Grosz, Rene Dechow, and Reinhard Well

Prediction of liquid organic fertilizer effects by biogeochemical models on denitrification and associated N₂O and N₂ fluxes in soils is inappropriate, because previous studies mostly excluded N₂, and the calibration of the models without N₂ data is inaccurate. Besides, the models mostly homogenize the substrate content of the applied manure with the corresponding substrate pools of the soil, without the consideration of the effects of the liquid manure induced hot-spots in the soil. Therefore, the main goal of the MOFANE Project was to develop a new approach dealing with hot spot effects in manure amended soils. A simple and static model approach (Sommer et al., 2004) was improved and developed for a dynamic model to consider the effect of the manure induced hot-spots in the soils. It contemplates the effect of the application technique of the liquid manure (surface or injected), the ammonium and labile organic carbon content of the manure, the water content and the structure of the soil to calculate the NH₃ loss, the N mineralization and O₂ consumption of the degradable organic content, the nitrification and the denitrification in the manure-soil hot-spot region. The substrate exchange and flow are calculated based on the water potential difference between the liquid manure and soil. A laboratory experiment was conducted to provide proper input and output data for the model testing. A sandy (Grosz et al., 2022) and a loamy arable soil were investigated in 10 days laboratory incubations. The temperature was constant 15^oC and the water-filled pore space (WFPS) were constant 40% and 60%. The soils were amended with and without artificial slurry in three manure treatments (control, surface-applied, injected). N₂O and CO₂ fluxes were quantified by gas chromatography. N₂ and source-specific N₂O flux was quantified by isotope-ratio mass spectrometry. The results of laboratory experiments will be used for testing the model accuracy.

Grosz, B., Kemmann, B., Burkart, S., Petersen, S. O., and Well, R.: Understanding the Impact of Liquid Organic Fertilisation and Associated Application Techniques on N₂, N₂O and CO₂ Fluxes from Agricultural Soils, Agriculture, 12, 692, https://doi.org/10.3390/agriculture12050692, 2022.

Sommer, S. G., Petersen, S. O., and Møller, H. B.: Algorithms for calculating methane and nitrous oxide emissions from manure management, Nutrient Cycling in Agroecosystems, 69, 143–154, https://doi.org/10.1023/B:FRES.0000029678.25083.fa, 2004.

How to cite: Grosz, B., Dechow, R., and Well, R.: Modeling hot-spot of N2 and N2O production in agricultural soils as introduced by liquid organic fertilization, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-13162, https://doi.org/10.5194/egusphere-egu23-13162, 2023.

A.235

EGU23-14831

ECS

On-site presentation

Microscale oxygen distribution to predict denitrification in structured soil

Maik Lucas, Lena Rohe, Hans-Jörg Vogel, Reinhard Well, and Steffen Schlüter

Different microbial species are capable of producing N₂O through multiple pathways, and these can coexist within short distances due to different microenvironmental conditions in the heterogeneous soil structure. Denitrification in soil occurs predominantly in microbial hotspots where denitrifiers use nitrate as an alternative electron acceptor. Soil water content has a profound influence on denitrification because it determines the diffusion lengths of oxygen through air- and water-filled pores, as well as the diffusion of denitrification products from the source in the soil to the atmosphere. Predicting N₂O emissions resulting from denitrification, however, is notoriously difficult without quantifying microscale hotspots.

In this experiment we evaluated results from an incubation experiment with undisturbed cores from two different soils having contrasting structures (cropland vs. meadow) at three different water contents. In addition to high-resolution gas chromatography, ¹⁵N-labeled nitrate solution allowed information on denitrification and its product ratios to be gained through IRMS measurements at selected time points. On the other hand, 7 needle-type optodes per core in combination with image analysis of images derived by X-ray tomography are used to quantify small scale diffusion distances and hotspots around POM. Last, a previous experiment, with the same but sieved soil and without particulate organic matter (POM), is used as a comparison to further investigate the influence local structure heterogeneity and POM on denitrification.

First results indicate that the reduction of diffusion pathways during sieving in the arable soil resulted in significantly lower emissions after sieving compared to the structured soil, while N₂O+N₂ emissions in the meadow soil were only slightly affected by sieving. For the first time, we were able to generate 3D images of O₂ saturation by combining image-derived diffusion length information with the measured O₂ concentrations. These allowed to explain high variabilities of N₂O+N₂emissions from the field structured cores.

How to cite: Lucas, M., Rohe, L., Vogel, H.-J., Well, R., and Schlüter, S.: Microscale oxygen distribution to predict denitrification in structured soil, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14831, https://doi.org/10.5194/egusphere-egu23-14831, 2023.

A.236

EGU23-14663

ECS

On-site presentation

Effect of various fertilizer doses on soil N2O and CO2 emissions in cropland soils in Hungary

Ádám Mészáros, Boglárka Magyar, Nicholas Omoding, János Balogh, Szilvia Fóti, Krisztina Pintér, Attila Percze, Giulia De Luca, and Zoltán Nagy

Quantifying greenhouse gas emissions has been a priority for climate scientists for decades. As a result, the spatial and temporal dynamics of emissions have been widely studied, but to date, we still do not fully understand the main drivers of the variation in patterns. The aim of our research is to quantify the spatio-temporal variability of these greenhouse gases under various nutrient supply conditions and different tillage practices (plow or cultivator) on sandy-clay and loam soils.

Our measurements took place near Kartal on loam soil and near Gödöllő on sandy-clay soil, in Central Hungary, in 2022 on winter wheat. CO₂ and N₂O fluxes are analyzed with Li-cor gas analyzers (LI-870 CO₂/H₂O Analyzer and LI-7820 N₂O/H₂O Trace Gas Analyzer) connected to the 8200-01S Smart Chamber. We can track both modest changes brought on by natural factors (precipitation, temperature variations) and the impact of more significant artificial factors (fertilization, type of tillage) on the N₂O and CO₂ flux using these rather sensitive devices. In Kartal, 24, and in Gödöllő 40 KG-PVC rings with a diameter of 20 cm were placed in the study areas and measured on a weekly basis. In Kartal half of the collars received fertilizer, and the other half was covered during the application. In Gödöllő, 8 different treatments can be distinguished, resulting from a combination of 3 different fertilizer doses (0kg/ha, 75kg/ha, and 150kg/ha), 2 tillage methods (plow and cultivator), and soil conditioners. The collars protrude 4 cm from the soil and the inner soil surface has been cleared of vegetation. The gas exchange between soil and air is measured for 3 minutes on each collar, while simultaneously measuring soil moisture, temperature, and vegetation cover (LAI) near the collars. Soil samples were taken monthly to a depth of 15 cm, and 50 cm from the collars.

Based on our observation, in the case of N₂O emission, there are significant differences between the two study areas. On average N₂O emissions in Gödöllő were higher than in Kartal. Cumulative N₂O emissions were significantly higher in areas receiving higher doses of fertilizer. For 150kg/ha, the highest value was 42 g N m², while for 0kg/ha and 75kg/ha, lower values of around 16-20 g N m² were observed. With average emissions of 420–500 g C m², there are no discernible variations in cumulative CO₂ emission across treatments. However, the temporal variation of both GHG emissions shows differences due to the persistent drought in summer. During the rainy season, spring and autumn, a more intense N₂O and CO₂ flux were observed due to soil respiration.

How to cite: Mészáros, Á., Magyar, B., Omoding, N., Balogh, J., Fóti, S., Pintér, K., Percze, A., De Luca, G., and Nagy, Z.: Effect of various fertilizer doses on soil N2O and CO2 emissions in cropland soils in Hungary, EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-14663, https://doi.org/10.5194/egusphere-egu23-14663, 2023.

A.237

EGU23-11325

ECS

On-site presentation

Inputs of reactive nitrogen from wet deposition and fertilization in a tropical montane catchment characterised by smallholder farming.

Miriam Kasebele, Suzanne Jacobs, and Lutz Breuer

Reactive nitrogen from anthropogenic inputs such as fertilizers and its changes in the transport and fate in the environment as a consequence of changes in land management may alter the nitrogen balance of a catchment and thus its concentrations in water bodies. This can be enhanced by increased wet and dry deposition of nitrogen from anthropogenic activities. In the Mau Forest Complex in Kenya, the annual export of nitrogen from a catchment dominated by smallholder agriculture was reported to be almost double those from the native forest. Fertilization and livestock management are assumed to have contributed to this shift, but no empirical evidence is available to support this. Furthermore, the contribution of the nitrogen wet deposition through rainfall and throughfall to the nitrogen balance has not been quantified yet. This study aims at determining the contribution of nitrogen wet deposition and anthropogenic inputs to the nitrogen balance of a 27 km² headwater catchment characterized by smallholder farming in the Mau Forest Complex. Rainfall and throughfall samples were collected from precipitation collectors in 10 different locations within 24 hours after 11 rainfall events in the span of 9 weeks. Anthropogenic inputs were estimated from a household survey (n=185).

Median and Interquartile range (IQR) concentrations of total dissolved nitrogen (TDN) were slightly higher in rainfall i.e. 0.7 (0.4–0.9) mg N L⁻¹ than in throughfall i.e. 0.6 (0.4–0.8) mg N L⁻¹, resulting in median wet deposition of 0.04 (0.02–0.06) kg N ha⁻¹ from rainfall and 0.03 (0.01–0.06) kg N ha⁻¹ from throughfall per sampled rainfall event (4.7 mm; 2.5–8.1 mm). Extrapolated to the full year, this leads to an estimated nitrogen input from wet deposition of 11.7 (9.5-12.5) kg N ha⁻¹ yr⁻¹from rainfall and 6.4 (5.7-9.6) kg N ha⁻¹ yr⁻¹from throughfall, although this estimate does not consider seasonal changes in TDN concentrations in rain- and throughfall. Median inputs of nitrogen from inorganic fertilizer was 25 (15.2–40.2) kg N ha⁻¹ yr⁻¹, whereas annual inputs from livestock were 76 (49-125) kg N ha^-1 yr⁻¹.

Reactive nitrogen inputs from farming and livestock are higher than the estimated wet deposition and could therefore significantly impact the catchment nitrogen balance. It follows therefore that a continual and increase use of nitrogen inputs from manures and fertilization with inorganic fertilizers, as well as further forest cover loss for agricultural expansion may lead to future elevated levels of nitrogen in the environment, leading to risks of progressive enrichment of water bodies and further nitrogen imbalances. To keep these in check, appropriate manure management strategies, fertilizer application and control of forest conversion cannot be overemphasized.

How to cite: Kasebele, M., Jacobs, S., and Breuer, L.: Inputs of reactive nitrogen from wet deposition and fertilization in a tropical montane catchment characterised by smallholder farming., EGU General Assembly 2023, Vienna, Austria, 23–28 Apr 2023, EGU23-11325, https://doi.org/10.5194/egusphere-egu23-11325, 2023.