BG3.20

To develop good mitigation strategies, estimates of nitrous oxide (N₂O) emissions from agricultural soils are needed. Process-based biogeochemical models have been used for such estimation but those have mainly been tested on field scaled measurement. Here we will explore how experimentally laboratory measurements can be used to to improve future model use. Based on a series of 43 days incubation experiments and a process model (CoupModel), we assessed the model’s sensitivity and uncertainty in estimating N₂O fluxes, CO₂ fluxes and soil mineral N. Our results suggested that the most sensitive parameters to N₂O flux estimates were related to the decomposibility of soil organic matter and related links to the denitrification processes. The model showed better performance in simulating low-magnitude daily and cumulative N₂O fluxes but a tendency to underestimate the fluxes as observed values increased. Residual analysis indicated that nitrification rate could be underestimated but did not sufficiently explain the model deviations. We also evaluated ancillary variables regarding N cycling, which indicates that additional types of observed data including soil oxygen concentrations and the sources of emitted N₂O, are required to evaluate model performance and possible biases. The modeled response to abiotic factors (e.g. soil moisture) did not reflect the measured values using consistent parameter sets, limiting the model application under constantly changing environmental conditions in reality. To conclude, the restricted description of N cycling process in the model may not be able to consistently simulate the denitrification and nitrification processes behind N₂O emissions and limits the extension of models beyond calibration. This calls for more frequent and more aspects of measurements in future experimental design for model evaluation and development. For the development of process models including CoupModel, there is a need to address crucial missing processes including solute diffusion and microscale heterogeneity, revisit current subrountines of moisture response functions and denitrifier growth dynamics, and report more aspects of simulated outputs for prediction and model.

How to cite: Zhang, J., Zhang, W., Jansson, P.-E., and Petersen, S. O.: Modelling nitrous oxide emissions from agricultural soil incubation experiments using CoupModel, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1266, https://doi.org/10.5194/egusphere-egu22-1266, 2022.

Denitrification is the main source of the greenhouse gas N₂O emitted from agricultural soils. While N₂O emissions and influencing factors have been very well studied in field experiments, there are hardly any reliable data for N₂ emissions on the field scale. However, these are essential to understand under which conditions complete denitrification occurs leading to N₂ formation and when N₂O is the main end product. Whether NO₃^- is reduced to N₂O or N₂ depends on several factors: the availability of NO₃^- and available organic C, as well as pH, oxygen availability, soil moisture, denitrifier community structure, and temperature. All of these parameters are highly dependent on crop development, as growing plants take up NO₃^- and water while increasing organic C availability via root exudates and dying roots, and alter soil pH as well as microbial communities by rhizosphere dynamics.

The objective of this field trial was to collect reliable measurement data on N₂ and N₂O emissions in typical German crops. Two crops were chosen that differ greatly in their temporal development: Winter wheat (Triticum aestivum L.) and sugar beet (Beta vulgaris subsp. vulgaris). Both crops were grown site-typically according to the rules of good agricultural practice. To measure N₂O and N₂ emissions, the improved ¹⁵N gas flux method including high enrichment ¹⁵N-labeled fertilizer was applied. Prior to gas sampling, chambers were purged with a mixture of helium and oxygen (80:20) to reduce the atmospheric N₂ background to < 2%. Soil samples were taken at regular intervals and analyzed for mineral N (NO₃^- and NH₄⁺) and water-soluble Corg content. In addition, we monitored crop development, plant N uptake, N transformation processes in soil, and N translocation to deeper soil layers.

How to cite: Rummel, P. S., Matson, A., Eckei, J., Well, R., and Dittert, K.: Effect of plant development and N uptake on denitrification in two contrasting crop species, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-6870, https://doi.org/10.5194/egusphere-egu22-6870, 2022.

Analysing isotopocule values of nitrous oxide (N₂O) produced in soil can be used to distinguish N₂O production pathways and to quantify N₂O reduction to N₂. In the field, this is typically accomplished by analysing gas samples collected from closed chambers and calculating the isotopocule values of soil-emitted N₂O taking into account the fraction of atmospheric N₂O. Accuracy of this approach is often limited when N₂O fluxes are low, leading to small fraction of soil-derived N₂O in the chamber gas. To overcome this limitation, some studies used N₂O isotopocules of soil air, assuming that these reflected N₂O produced in soil (Gallarotti et al., 2021, Zou et al., 2014). However, this can lead to inaccurate results because (i) due to bi-directional diffusive gas exchange with the atmosphere, soil air is a mixture of soil-derived and atmospheric N₂O and (ii) isotopic fractionation during diffusive flux to the atmosphere leads to enrichment of residual N₂O in soil air. To evaluate these confounding factors and develop an approach to determine isotopocules of N₂O produced in soil from soil air samples, we compared surface fluxes of N₂O isotopocules determined by the closed chamber method (Lewicka-Szczebak et al. 2020) with gas probe data. Moreover, a diffusion-reaction model (Maier et al., 2017, Well et al., 2019) will be extended to include isotopic fractionation in order to determine isotopocule values of produced N₂O from soil air data. Scenarios varying in depth–dependent N₂O production and diffusivity will be analyzed. Results will show to which extent soil air and production values differ, which bias is obtained by using uncorrected soil air values, how well values can be corrected by modeling, and under which conditions soil air sampling might lead to better performance than closed chamber sampling. We expect that soil air sampling can lead to improved sensitivity for isotopocule values of soil-derived N₂O in certain cases, but correction of data is obligate to obtain useful results.

End Text

@END_ABSTRACT@

Gallarotti N, Barthel M, Verhoeven E et al. (2021) In-depth analysis of N₂O fluxes in tropical forest soils of the Congo Basin combining isotope and functional gene analysis. The ISME Journal, 15, 3357-3374.

Lewicka-Szczebak D, Lewicki MP, Well R (2020) N₂O isotope approaches for source partitioning of N2O production and estimation of N₂O reduction – validation with the ¹⁵N gas-flux method in laboratory and field studies. Biogeosciences, 17, 5513-5537.

Maier M, Longdoz B, Laemmel T, Schack-Kirchner H, Lang F (2017) 2D profiles of CO₂, CH4, N₂O and gas diffusivity in a well aerated soil: measurement and Finite Element Modeling. Agricultural and Forest Meteorology, 247, 21-33.

Well R, Maier M, Lewicka-Szczebak D, Köster JR, Ruoss N (2019) Underestimation of denitrification rates from field application of the N-15 gas flux method and its correction by gas diffusion modelling. Biogeosciences, 16, 2233-2246.

Zou Y, Hirono Y, Yanai Y, Hattori S, Toyoda S, Yoshida N (2014) Isotopomer analysis of nitrous oxide accumulated in soil cultivated with tea (Camellia sinensis) in Shizuoka, central Japan. Soil Biology & Biochemistry, 77, 276-291.

How to cite: Well, R., Lewicka-Szczebak, D., Maier, M., and Matson, A.: Determination of nitrous oxide processes in soil from depth profiles of natural abundance stable isotope values by diffusion-reaction-fractionation modelling, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7043, https://doi.org/10.5194/egusphere-egu22-7043, 2022.

In this study we investigated the effect of mouldboard ploughing (MP), shallow cultivation (SC) and no-tillage (NT) methods on N₂O emission of a Central European long-term field experiment. We measured N₂O fluxes and environmental parameters (soil moisture and temperature) in three replicates per treatment on a biweekly to mounthly basis during two and a half year period. Besides regular measurements we carried out additional occasions timed to heavy rainfalls. N₂O fluxes occured after fertilization and on soils under high soil moisture conditions only, during spring and autumn. The average N₂O emission for the whole experimental period was the highest in NT (0.025±0.045 µg N₂O m^-2 s^-1), which was significantly higher (p<0.005) than in MP (0.004±0.003 µg N₂O m^-2 s^-1) or SC (0.003±0.003 µg N₂O m^-2 s^-1). Soil mositure was a significant (p<0.005) environmental driver of N₂O emissions in NT treatment.

How to cite: Dencső, M., Saliga, R., Molnár, S., and Tóth, E.: Effect of different tillage methods on soil N2O emission in an arable field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8376, https://doi.org/10.5194/egusphere-egu22-8376, 2022.

Prediction of liquid manure effects on N transformations in soils and associated N₂O and N₂ fluxes is poor because previous investigations mostly excluded N₂, the end product of denitrification. We address the questions, (1) how liquid manure fertilization and its application technique impact N₂, N₂O and CO₂ fluxes from agricultural soil, and (2) how the water, mineral N and dissolved organic carbon (DOC) content of the manure amended soil change between the soil layers. A sandy arable soil was used in a 10 days laboratory incubation at constant 15^oC, constant 40% and 60% water-filled pore space (WFPS) and 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. At 5^th and 10^th day, depth distribution of moisture, NH₄⁺, NO₃^-, DOC, pH and ¹⁵N enrichment of NO₃^- was determined with destructive sampling. The N₂+N₂O flux of the surface-applied and injected 40% WFPS treatments were 75% and 110% higher than the control and at 60% WFPS treatments were more than 610% and 1690% higher than the control. The product ratio of denitrification showed enhanced share of N₂ to the N₂+N₂O flux in the manure treatments, which we attribute to hot-spot dynamics of the manure layers. Our data demonstrate how the dynamics of moisture, labile C, NH₄⁺-N, formation of NO₃^--N by nitrification and pH following manure surface application or injection interact and result in N₂O cycling by various pathways. The data-set can thus be used to evaluate and further develop models to predict denitrification and respiration processes of the manure-soil hot-spots. Further progress in unravelling and modeling manure induced hot-spot dynamics can be achieved if temporal and spatial resolution of our measurements is improved and additional techniques to determine O₂ distribution and distinguish gross N transformations and their gaseous N fluxes are included.

How to cite: Grosz, B., Kemmann, B., Burkart, S., Petersen, S. O., and Well, R.: The impact of liquid organic fertilization and associated application techniques on N2, N2O and CO2 fluxes from agricultural soils, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-9113, https://doi.org/10.5194/egusphere-egu22-9113, 2022.

Denitrification is one of the major pathways of nitrogen (N) output from soil. In this process, soil nitrate (NO₃^-) is chemically reduced into dinitrogen (N₂) through microbial respiration. Incomplete denitrification leads to the emission of nitrous oxide (N₂O), a greenhouse gas 300 times more potent in inducing global warming than carbon dioxide (CO₂). Denitrification is highly variable in space and time, which makes it one of the most unconstrained processes in the global N cycle.

Measuring denitrification is challenging because it emits small amounts of N₂, hardly distinguishable from the high N₂ atmospheric background (78% in volume). The aim of this study was to increase the sensitivity of the ¹⁵N Gas Flux method (¹⁵NGF), which is considered today, the only suitable method for in situ measurement of denitrification. The ¹⁵NGF consists of injecting a stable isotopic tracer (¹⁵NO₃^-) in a pre-determined area of soil and quantifying N₂ production via its isotopic composition over time under an enclosed chamber. In order to increase the sensitivity of this method, we aimed to optimize two parameters: the quantity of tracer injected and the N₂ background concentration. Increasing the amount of available nitrate represents a risk of stimulating microbes. Reducing the atmospheric N₂ background in situ can be challenging because of leaks and diffusion issues.

Our study focused on three different types of agricultural land uses: Arable, Herbal-Rich ley and Grass Clover ley. All three land uses were part of the same experimental field and the leys were in a 3-year rotation with the Arable. We first incubated homogenised soil under lab conditions and under different treatments of added tracer in order to increase sensitivity and observe if a microbial stimulation occurred. Gravimetric moisture was raised to 45% (on a dry mass basis) to simulate a rainfall event and increase the magnitude of denitrification. First experiments showed no detectable amount of evolved N₂ and thus, a custom-made gas mix had to be used. This gas mix contained 20% of dioxygen (O₂), 5% of N₂ and 75% of Helium (He) and was used to replace the native atmosphere in the incubation chambers.

First results showed no significant difference in denitrified N for the ley soils treated with different amounts of tracer. The Arable soil however seemed to have been stimulated when using greater quantities of tracer but further results are expected to confirm this. The Arable treatment also had the highest potential of denitrification in the lab with a mean value of 6.26 x 10^-1 µgN/kg/h of emitted N₂, compared to the leys who both emitted 1.65 x 10^-1 µgN/kg/h. The theoretical sensitivity is increased 24 times for the detection ²⁹N₂ and 97 times for the detection of ³⁰N₂ when using the gas mix and a 50% tracer enrichment, compared to a 20% enrichment under atmospheric conditions.

Finally, we measured denitrification directly in-situ using higher quantities of tracer and the custom-made gas mix. This was done using either modified greenhouse gas chambers or sealed plastic liners.

How to cite: Micucci, G., Sgouridis, F., Krause, S., Lynch, I., McNamara, N. P., Dos Santos Pereira, G., Roos, F., and Ullah, S.: 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, 2022.

Accurate models of soil N cycling are an important tool for optimizing N use efficiency within agricultural systems and predicting N emissions to the environment. However, due to the methodological limitations for the measurement of N₂ emissions, in particular high atmospheric N₂, only a very limited number of soil N2 flux datasets are available to validate model estimates of denitrification. As part of the DFG-research unit “Denitrification in Agricultural Soils: Integrated Control and Modelling at Various Scales (DASIM)”, we are building on existing methods to take in situ measurements of denitrification under a variety of field conditions, with an emphasis on the detection of non-peak events. Using static chambers, we establish a low-N₂ background through headspace and soil flushing, and then use stable isotope techniques (natural abundance and ¹⁵N labeling of the soil mineral N pool) to assess the response of soil denitrification to combinations of climate, soil and plant factors found in the field. Here we present results of N₂ and N₂O fluxes from the field, which highlight both the potential and the challenges of using this combined method.  

How to cite: Matson, A., Lempio, D., Höppner, F., and Well, R.: Combining low-N2 background and 15N soil gas flux - lessons from the field, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13033, https://doi.org/10.5194/egusphere-egu22-13033, 2022.

Carbon dioxide (CO₂) and nitrous oxide (N₂O) are two of the most important greenhouse gases (GHG) resulting from agricultural activity. Production, emission and consumption of these gases are regulated by structural and chemical soil properties along with biological processes. Therefore, agricultural soils can act as GHG emitters but also as potential sinks.

Water scarcity added to a low soil quality, represent a challenge for agricultural sustainability in Mediterranean semiarid regions. Additionally, winter cereal cultivation followed by a summer fallow period has been the main extensive farming system in rainfed Mediterranean areas of Spain. No-tillage systems preserve more efficiently soil moisture and boost soil organic carbon storage in comparison with conventional tillage systems. Diversifying cropping systems may have several benefits on crop productivity and sustainability, such as an efficient control of weed seed bank, the prevention of possible crop diseases, the increase of the soil organic matter and the improvement of the soil water storage capacity. Due to the ability of legume crops to establish bacterial symbiosis for N fixation, crop rotations with cereal and legume crops may lead to a reduction of nitrogen fertilizers application. Minimizing N-fertilization is often associated with a decrease in GHG soil emissions. Henceforth, selecting adequate agricultural practices and cropping systems are key to minimize soil GHG emissions contributing to mitigate climate change. Accordingly, this study aims to evaluate the effect of diversified cropping systems compared to cereal monoculture systems on GHG soil emissions (CO₂ and N₂O) in Mediterranean semiarid conditions.

For this purpose, it was conducted a long-term field experiment in rainfed conditions located in Zaragoza, Spain. Two crop rotations under direct sowing system were compared (wheat-barley and barley-pea) for the evaluation of possible alternatives to the traditional barley monoculture. The soil CO₂ and N₂O emissions were quantified every two weeks since sowing (October) until harvest (June) and every three weeks from harvest to the next sowing (summer fallow) during three growing seasons: 2018-2019, 2019-2020 and 2020-2021. In addition, soil surface temperature and moisture were measured as well as bulk density.

During the first growing season, there was not effect of cropping diversification on CO₂ and N₂O emissions. However, in the following two seasons, the results obtained showed significative differences on the soil CO₂ and N₂O emission rates depending on the different cropping systems. A significant temporal variability was also observed in the soil emission rates of CO₂ and N₂O.The temporal variability found in the GHG emissions were mostly explained by the wide range of soil temperature and moisture found among years.

How to cite: Martin Brull, I., Cantero-Martínez, C., Bielsa Aced, A., Lafuente Rosales, V., Gómez Valenciano, F., and Álvaro-Fuentes, J.: Crop diversification effect on CO2 and N2O soil emissions in Mediterranean semiarid conditions, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4766, https://doi.org/10.5194/egusphere-egu22-4766, 2022.

The transition from conventional tillage (CT) to reduced tillage (RT) on cultivated lands to achieve carbon sequestration has shown variable impact on the greenhouse gas (GHG) balance at local sites from short to long-term studies. In this context, replicated automated closed chambers were set up on two plots from a long-term (since 2008) differentiated tillage trial (conventional CT vs. reduced tillage RT) on a loamy soil in Gembloux (Belgium) with the aim to analyse the temporal and spatial variabilities of N₂O fluxes and the impacts of tillage with regards to soil physical and chemical drivers in the soil profile.

Continuous measurements of CO₂ and N₂O emissions were performed with 8 chambers at four hours temporal resolution on each plot of 600 m², within 16 m² sampling square, during the growing season of sugar beet (April to October 2021), following a winter wheat crop with straw incorporation (crop residue). Soil physical (water content and tension, temperature, O₂ concentration, bulk density and gas diffusivity) and chemical (NO₃ and NH₄) drivers in the soil profile (5, 15, 25 cm) were also monitored.

Results show no significant difference between treatments on mean CO₂ and N₂O emissions. Nevertheless, a visible tendency of higher N₂O emissions on RT (>200%) echoes with previous experiment results over this site that indicated significantly higher mean N₂O emissions in the reduced tillage (RT) plot compared to conventional on a maize crop in 2015 and winter wheat in 2016. For each treatment, more than 70% of the N₂O emissions were measured during two peaks episodes that occurred after intense rainfall. A significant correlation was observed between the base-10 logarithm of N₂O and CO₂ fluxes, and it likely shows a link between N₂O production and mineralisation of organic matter, e.g. previous crop residues that were incorporated following previous summer wheat harvest. Soil relative gas diffusivity (D_p/D_o) in the first horizon (0-10 cm) was the best predictor of N₂O fluxes.

The N₂O emissions showed significant spatial variability within both treatments with coefficients of variation up to 400% between chamber measurements on the RT plot, especially during peak emissions, hampering statistical comparison between treatments. As replicated chambers are covering a limited surface, this suggests N₂O production in small-scale hotspots within the chambers sampling square. These results call for further work on local (sampling square) and plot scale spatial variabilities that need to be investigated to help the optimisation of the sampling strategy for a finer comparison between treatments.

How to cite: Boland, F., Delespesse, M., Chopin, H., Debacq, A., Dumont, B., Longdoz, B., and Heinesch, B.: Is shifting from conventional to reduced tillage worth the change in terms of greenhouse gas emissions: feedback from a long-term case study on a cultivated loamy soil in Belgium, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-11707, https://doi.org/10.5194/egusphere-egu22-11707, 2022.

Changes in agricultural management practices to enhance soil carbon (C) sequestration while maintaining crop productivity are a key opportunity to reduce the impact of humans on the environment, reducing greenhouse gas (GHG) fluxes to the atmosphere and nutrient leaching to aquatic ecosystems without compromising food and soil security. Amongst them, enhanced weathering (EW) of silicate minerals is a promising negative emission technology that can be associated with multiple co-benefits for crop production by spreading silicate minerals on arable soils (i.e. increase in crop yields, restoration of soil base cations and micro- and macronutrient stocks). A growing number of EW studies are focused on soil C sequestration and the effects on crop production. Yet, little is known about the impact of such management practices on GHG sink/source behaviour of agricultural soils and the soil bacterial communities involved.

In this context, winter wheat (Triticum aestivum) was grown in 20 mesocosms undergoing 4 different treatments: acid soil (pH ~5) with or without basalt addition (50 tones ha^-1) and alkaline soil (pH ~7) with or without basalt addition. Soil GHG emissions (CO₂, CH₄ and N₂O) were measured at six different time points spread over the growing season (from March to June). Measurements included anaerobic conditions (i.e. immediately after irrigation events) and aerobic condition (i.e. in-between events). Simultaneously, soil was sampled for the study of the soil bacterial community.

We found that basalt application led to an increase in crop yield in acid soils, while it decreased the yield in alkaline soils. GHG emissions were not reduced by the basalt amendment. Soil CO₂ fluxes peaked in-between irrigation events and were mainly influenced by the soil pH, being 2-fold higher in alkaline soils than in acid ones. Irrigation events increased both CH₄ and N₂O fluxes. Soils acted as CH₄ sink in-between irrigation events, but became sources shortly after those (up to 5-fold higher). While it was hypothesised that higher pH would result in an improved denitrification completion, the increase in pH induced by basalt application did not reduce soil N₂O fluxes. Higher N₂O fluxes were observed during irrigation events and in basalt-enriched mesocosms, as a result of combined enhanced nitrification and denitrification processes. Despite the modest effects of EW on soil GHG emissions, soil bacterial communities were very different for acid and alkaline soils, and varied significantly with basalt amendment and throughout time.

Overall, this study showed that EW resulted in an improved wheat yield and altered soil bacterial community in acid soils. However, the general effect of EW on soil GHG emissions was modest and complex.

How to cite: Poblador, S., Le Noir de Carlan, C., Verbruggen, E., and Vicca, S.: Enhanced weathering in acid and alkaline agricultural soils: greenhouse gas emissions and soil bacterial communities implications, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-13396, https://doi.org/10.5194/egusphere-egu22-13396, 2022.

Improved agricultural practices are considered as one of the potential solutions for mitigating global climate change. However, agricultural used landscapes are complex and their function as source and sink of greenhouse gases like CO₂, CH₄, and N₂O might differ substantially in time and space. Hence, accurate and precise information on the complex spatio-temporal gas flux pattern is needed to evaluate the effects/benefits of new agricultural practices aiming towards increasing soil organic carbon. Automatic chamber measurements are increasingly used in agricultural systems to determine emissions of greenhouse gases as well as the net ecosystem C balance (NECB). While the eddy covariance (EC) technique remains to be the most common method at field scale, automated chamber measurements might close a gap, by detecting small-scale spatial emission patterns, while still compromising a sufficient temporal resolution. Infrared gas analysers (IRGAs) have been available for decades and helped to facilitate CO₂ measurements substantially. In addition, further technical progress resulted in the development of multigas analysers, which are able to measure not only CO₂, but also CH₄, N₂O, as well as their isotopes. However, most of these analysers are rather cost-intensive and many of them are primary designed for use in the laboratory.

Here, we compare CO₂ fluxes and derived emission estimates, obtained using a widely applied IRGA (LI-850 CO₂/H₂O, Licor, Germany) with results of a new, medium cost, CO₂, CH₄, and N₂O gas analyser (ProCeas GENERAL, AP2E, France). Two of both sensors were mounted on a novel robotic chamber system (“CarboCrane”), which was installed in 2019 at an undulating summit position of the hummocky ground moraine landscape of NE Germany. The system is comprised of a gantry crane mounted on two tracks (110 m) transporting the sensors and two transparent closed chambers. Measurements of the net CO₂ exchange were performed by moving the system along the tracks with each chamber along one half of the covered area. Altogether, 36 measurement plots have been established. On each of these plots, an area for net CO₂ exchange measurement has been set up by inserting round iron frames (diameter=1.59 m) 5 cm deep into the soil on which the transparent chambers were deployed for measurements. CO₂ fluxes were determined by measuring the development of chamber headspace CO₂ concentrations (4 sec frequency; measurements of both sensors in parallel) over chamber deployment time (7 min; see 2.5) in a flow-through non-steady-state (FT-NSS) mode (Livingston and Hutchinson, 1995). CO₂ fluxes and emission estimates were derived for all four sensors for a test period of three month (April – June 2021) at six plots, covered with winter rye situated at a mineral fertilized, non-eroded Calcic Luvisol. To guarantee an enhanced variability in measured CO₂ fluxes, the six measured plots divide into topsoil diluted and non-diluted treatments. Our results show in general a great consistency between the results delivered by both sensors and support the assumption of a rather small error fraction of the sensor type for both, the calculated CO₂ flux and the emission estimates based on it.

How to cite: Kramp, K., Vaidya, S., Schmidt, M., Rakowski, P., Bonk, N., Buddrus, R., Verch, G., Sommer, M., Augustin, J., and Hoffmann, M.: Influence of sensor type on the error of automatic chamber derived CO2 fluxes and gap-filled emission estimates, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2175, https://doi.org/10.5194/egusphere-egu22-2175, 2022.

On arable land, C dynamics and storage are significantly influenced by tillage and N fertilization. Therefore, new practices such as the combination of topsoil dilution (e.g., through fractional deep tillage) and organic N fertilization may not only ameliorate soil's physical and chemical properties and promote root development but might also enhance soil organic carbon (ΔSOC) stocks. However, the impact of these practices depends on site-specific conditions as agricultural landscapes are often characterized by distinct small-scale soil heterogeneities. To upscale and evaluate the effects or benefits of these new farming practices, accurate and precise information on the complex spatio-temporal C flux pattern and their drivers are thus needed.

To investigate the impact of topsoil dilution and organic N fertilization on SOC storage, we performed a study in the strongly erosion affected arable landscape of NE Germany (Uckermark region, 53° 23' N, 13° 47' E; ~50-60 m a.s.l). The study area consisted of 36 measurement plots, of which each 12 covered one out of three erosion induced soil types; Calcic Luvisol (non-eroded), Nudiargic Luvisol (strongly eroded) and Calcaric Regosol (extremely eroded). During July 2020, a two factorial experimental design was established (topsoil dilution vs no topsoil dilution and mineral N fertilization vs organic N fertilization) through implementing topsoil dilution and organic N fertilization on three replicates of each of the three measured soil types. Topsoil dilution was achieved by removing the upper 6 cm of the topsoil layer adding/mixing equivalent weight of subsoil into it.

Subsequently, relevant C fluxes, especially the CO₂ exchange, were measured using a new robotic chamber system. C in plant biomass was measured by weekly biomass sampling on a nearby reference site and related to plot measurements of CO₂ through NDVI (normalized difference vegetation index) and RVI (ratio vegetation index) measurements. Here, we present our first results on the effect of soil type, topsoil dilution, and N-fertilization form on CO₂ and C exchange of winter rye. Our results show that there are not only differences between the distinct soil types but also differences between the non-diluted and diluted topsoil treatments. The latter show lower cumulated ecosystem respiration and gross primary productivity, as well as a lower RVI/NDVI  and above-ground biomass production, compared to the non-diluted soil. No substantial difference, however, was detected in the case of net ecosystem exchange. As a result, net ecosystem carbon balance was lower for diluted topsoil compared to the non diluted treatments.

How to cite: Vaidya, S., Schmidt, M., Kramp, K., Rakowski, P., Bonk, N., Buddrus, R., Verch, G., Sommer, M., Augustin, J., and Hoffmann, M.: Distinct short term response of C exchange to topsoil dilution and N-fertilization form at erosion affected arable land, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-2247, https://doi.org/10.5194/egusphere-egu22-2247, 2022.

As a result of globally strongly intensified N fertilization, agriculture is an important source not only for greenhouse gas (GHG) and especially gaseous N emissions but also N pollution through leaching. To increase nitrogen use efficiency and reduce gaseous N emissions and leaching, N inhibitors can be used. The use of N inhibitors, however, might directly affect crop growth and alter yield, which influences CO₂ exchange and might potentially change C sequestration. While the applicability of N inhibitors to reduce especially NH₃ and N₂O emissions is well recognized, to date, the influence of these inhibiters on CO₂ emissions and C sequestration is rather unclear.

We investigated the influence of urease (UI) and nitrification inhibitors (NI) when used with mineral fertilizer on GHG emissions and C sequestration for maize cropping in an on-farm, strip-field trial in NE Germany (Uckermark Region, “53°18'54.2"N, 13°40'15.2"E”). The on-farm field trial consists of four treatments, each implemented on a strip of 15m by 100m: non-fertilized (NF), fertilized (Urea Ammonium Sulfate (AS-HS)), with one (AS-HS + UI) and with two (AS-HS + UI + NI) inhibitors. On each treatment 5 PVC frames (0.5625 m²) for manual closed chamber measurements of GHG emissions were installed. Out of these 5 repetitive plots, one frame per treatment was kept clear of maize crops to obtain soil respiration (Rs). N₂O (and CH₄) emissions were measured using opaque chambers, evacuated glass bottles for sampling and subsequent GC analyses (Shimadzu GC-14B with ECD and FID detectors), while CO₂ exchange (Reco, Rs (opaque chamber) and NEE (transparent chamber)) were determined on-site by connecting the chambers with an infrared gas analyzer (LI-850, LI-COR Biosciences, Lincoln, USA). Crop growth was monitored through weekly measurements of plant height, NDVI and RVI as well as biomass samples. To obtain heterotrophic respiration (Rh), complementary to in-situ measurements, laboratory incubation experiment was conducted, using a fully automated incubation system (Rillig et al. 2021) and soil samples collected at distinct periods of maize cropping period and under different temperatures, to determine soil respiration. C sequestration was determined through calculating the net ecosystem C balance (NECB = NEE + C_import - C_export) as well as through repeated soil inventories.

The use of N inhibitors did reduce GHG emissions through reducing N₂O emissions, but also reduced maize biomass production (dry matter (t/ha): 18.2, 24.1, 19.9 and 19.5 for NF, AS-HS, AS-HS + UI, and AS-HS + UI + NI respectively). Consequently, Reco and gross primary productivity (GPP) were lower for the treatments with N inhibitors compared to the fertilized field without N inhibitors but higher than the non-fertilized treatment. No significant effect on NEE was found, while the C losses seemed to be slightly higher for the treatment without N inhibitor use.

How to cite: Monzon, O., Antonijevic, D., Vergara N, B., Verch, G., Lück, M., Augustin, J., and Hoffmann, M.: Influence of N inhibitors on carbon losses/sequestration in Maize cropping, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-4627, https://doi.org/10.5194/egusphere-egu22-4627, 2022.

Olive grove management entails environmental and socio-economic repercussions for the Mediterranean region. Maintaining bare soil in alleys is the most common management in this crop, but its implications for soil respiration (R_soil) are not well understood. Although previous studies have quantified R_soil at specific moments, soil respiration has not yet been continuously measured in olive groves. In this study a complete year of R_soil  measurements was taken in an irrigated olive grove in southeast of Spain. To avoid spontaneous weed growth a glyphosate-based herbicide was periodically applied. Six automated soil CO₂ efflux chambers with additional sensors of soil temperature (T) and soil water content (SWC) were controled by a multichamber monitoring system (Li-8100A, Li-cor). With the aim of know the spatial variability in R_soil and facilitate scaling up to estimate ecosystem soil respiration, 3 chambers were installed under the olive tree canopy and 3 chambers in the alleys.

Preliminary results show that R_soil increased in the warmer months and decreased in the colder months as expected. Also, daily R_soil values under the trees are normally several times higher than in the alleys but this ratio changed with the seasons. In warm months, daily R_soil under the tree was 2-3 times higher than daily R_soil in the alley, while in cold months (like January) it was 6 times higher. In the alleys, diurnal variability was detected in R_soil except in winter. While R_soil under the trees was practically constant throughout the day during the year except in summer when there appears to be a relationship with the decrease in the flux of photosynthates in environments with high VPD. In spring R_soil-alleys was double at midday versus night-time. Additionally, a positive and a negative relationship was established with temperature and SWC respectively. On the other hand, we found no clear relationship for R_soil under the tree with respect to T or SWC. These preliminary results suggest a considerable R_soil component of total ecosystem respiration influenced by the tree which does not depend on changes in T and SWC and that should be included in the partition models.

How to cite: Aranda-Barranco, S., Serrano-Ortiz, P., Kowalski, A. S., and Sanchez-Cañete, E.: Spatial and temporal variability of soil respiration in an irrigated olive grove in southeastern Spain, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-5747, https://doi.org/10.5194/egusphere-egu22-5747, 2022.

Soils in perennial cropping systems, such as vineyards, have good prospects for storing carbon since less management is required with minimum disturbance to the soil that might prevent rapid turnover of organic matter. In addition, incorporation of organic matter into the subsoil instead of conventional topsoil application might increase its resistance to decomposition through physical isolation and the buildup of organo-mineral complexes. However, the stability of organic matter in agricultural land could also be highly dependent on individual systems, soil properties and climatic conditions.

In our study, the stability of high carbon organic materials (i.e., compost and a Terra Preta-like material) after deep (30-60 cm) incorporation into the soil of a vineyard in western Germany was investigated with respect to greenhouse gas emissions. Portable gas analyzers were used for long-term in-situ monitoring of greenhouse gas emissions. Additional parameters quantified were soil redox potential using Pt electrodes and the concentration of greenhouse gases in the pore space of the soil using air samplers.

The deeply incorporated soil organic amendments showed good stability with respect to N₂O and CH₄ emission, whereas 30.4% and 51.7% of the compost and the Terra Preta-like material, respectively, was decomposed and released as atmospheric CO₂ after two years of observation. Oxygen availability at different soil depths throughout the sampling period, indicated by redox potential values of 300 to 700 mV, played a role in the turnover of organic matter in the treatments. Higher CO₂ concentration in the treatments in the deeper soil layer (30-50 cm) compared to the control was also consistent with higher CO₂ emission at the soil surface.

To investigate the site-specific influence on the stability of organic matter, the emission of greenhouse gases will also be quantified in different vineyards at different locations with similar management.  

How to cite: Islam, M. S., Pätzold, S., Wehrle, R., Bendel, N., Herzog, K., and Brüggemann, N.: Investigating the potential of vineyard soils for carbon sequestration and greenhouse gas emission mitigation after incorporation of organic matter into the subsoil, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-8111, https://doi.org/10.5194/egusphere-egu22-8111, 2022.

The Mediterranean region has a great surface of olive crops where about 98% of the world’s olive agricultural area is represented. Of these lands, 2.7 Mha are in Spain with more than half concentrated in the Southeastern Iberian Peninsula. In this type of crop, the maintenance of natural herbaceous-cover in the alleys from autumn to spring is a common practice to protect the soil against erosion, but little is known yet about its contribution to CO₂ and H₂O fluxes and their seasonal variability. The eddy covariance technique is used worldwide to measure GHG fluxes at the ecosystem level. Additionally, this technique has been used successfully to measure fluxes below the canopy in closed forests and pastures. In this regard, continuous monitoring of eddy covariance CO₂/H₂O fluxes above and below the trees canopy was carried out in an irrigated olive grove (Olea europaea L.) in the Southeastern Iberian Peninsula in the hydrological year 2020-2021. The olive trees are distributed in a plantation frame of 12×12 m and the area is divided into two plots: 1) with natural herbaceous-cover from autumn to spring, then cut and left on the surface (hereafter HC); and 2) kept herbaceous-free by glyphosate-based herbicide application (hereafter HF). Each plot has two eddy covariance towers, one above the canopy (ecosystem tower) and the other below the canopy (subcanopy tower).

A comparison between fluxes measured with the subcanopy towers and those measured with ecosystem towers showed the need for wind-direction filtering of the fluxes measured at the subcanopy level. Results show the relevance of selecting those fluxes coming from wind directions where the alleys are located in order to get accurate subcanopy CO₂/H₂O fluxes, avoiding those eddies coming from the olives. Regarding seasonal variability of the CO₂/H₂O fluxes measured at the subcanopy level, preliminary results showed that the HC plot behaved as a C light sink in winter (Dec., Jan., Feb.), being February the month with the most absorption averaging around 1.5 g C m^-2 day^-1 while HF behaved as C neutral. In the month before mowing (March), HC behaved as a sink, absorbing, on average, around 2.5 g C m^-2 day^-1, while HF acted as a light source emitting around 0.2 g C m^-2 day^-1. After mowing (from April to June) both HC and HF acted as sources, with HC yielding the largest values in April (around 2.1 g C m^-2 day^-1). Finally, in summer and autumn (from July to Nov.) both HC and HF appear to behave as weak C sources at the subcanopy level.

How to cite: Aguirre García, S. D., Callejas Rodelas, J. Á., Aranda Barranco, S., Sánchez-Cañete, E. P., Kowalski, A. S., and Serrano Ortiz, P.: Viability of Below-Canopy Eddy Covariance Measurements in Herbaceous-free and Herbaceous-cover Mediterranean olive crop, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-10515, https://doi.org/10.5194/egusphere-egu22-10515, 2022.

Methane (CH₄) has a global warming potential (GWP) 28-times that of carbon dioxide (CO₂) over a 100-year horizon. Riparian buffers strips are widely implemented for their water quality protection functions along agricultural land, but conditions prevailing within them may increase the emissions of greenhouse gases (GHGs), including CH₄. However,  only small amount of information is available regarding the dynamics of unintended emissions of soil CH₄ in these commonplace features of agroecosystems and how the dynamics compare to those for agricultural land not containing buffer strips. To understand the dynamics of soil CH₄ fluxes from a permanent upslope pasture and contiguous riparian buffer strips with different (grass, willow, and woodland) vegetation as well as controls with no buffer vegetation, field measurements were carried out using the static chamber technique on a replicated plot-scale facility. Gas fluxes were measured periodically with soil and environmental variables between June 2018 and February 2019 at Rothamsted Research, North Wyke, United Kingdom. Soils under all treatments were sinks of soil CH₄ with the willow riparian buffer (-2555 ± 318.7 g CH₄ ha^-1) having the lowest soil CH₄ flux followed by the grass riparian buffer (-2532 ± 318.7 g CH₄ ha^-1), woodland riparian buffer (-2318.0 ± 246.4 g CH₄ ha^-1), no-buffer control (-1938.0 ± 374.4 g CH₄ ha^-1), and lastly, the upslope pasture (-1328.0 ± 89.0 g CH₄ ha^-1) which had a higher flux. The three vegetated riparian buffers were more substantial soil CH₄ sinks, suggesting that they may help reduce soil CH₄ fluxes into the atmosphere in similar agroecosystems.

How to cite: Dlamini, J., Cardenas, L., Tesfamariam, E., Dunn, R., Hawkins, J., Blackwell, M., Evans, J., and Collins, A.: Soil methane (CH4) fluxes in cropland with permanent pasture and riparian buffer strips with different vegetation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1064, https://doi.org/10.5194/egusphere-egu22-1064, 2022.

Nitrogen emissions from agricultural soils have been increasing over the past century due to improved accessibility of nitrogen fertilisers. These fertilisers have unbalanced the global nitrogen (N) cycle, with far-reaching effects on soil acidification and biodiversity, eutrophication, and ozone depletion. The high yields achieved by modern agriculture must be maintained but this cannot come at the cost of the earth. Nanomaterials have been proposed as a viable alternative to improve conventional fertilisers and have been tested on a range of crops, with analysis of their effects on N cycling also common. Nanofertilisers have one or more dimensions on a nanoscale, and their high surface area to volume ratio causes them to adsorb to biomolecules around them, changing their reactivity and stability as they enter new environments. Previous work (Ramirez-Rodriguez et al. 2020) showed the nanocomposite, urea-doped amorphous calcium phosphate (U-ACP), was able to maintain wheat yield at a much lower concentration as compared to urea alone. Our study compared U-ACP to urea treatment on lettuce growth, N-cycle community size, N leachate concentration and reactive N-oxide (NO_Y) emissions. Urea and U-ACP treatment both produced more lettuce biomass than the control. However, U-ACP treatment significantly reduced NO_Y emissions from soil as compared to urea-treated soils, reducing emissions down to the same concentration as control soils. This pattern was also seen in aqueous emissions of reactive N species (ammonium, nitrite, and nitrate), with urea treated soils consistently producing higher concentrations than U-ACP treated soils. Denitrifying bacteria were more prevalent in U-ACP treated soils, potentially reflecting that the nanocomposite is able to aid in more complete denitrification, reducing production of intermediary, polluting N species. Our work focussed on NO_Y over other forms of volatile N, the high levels of NO_Y production by urea-treated soils indicate this may be an area of research that is deserving of greater attention in the future. This work illustrates that U-ACP, and other composite nanocarriers like it, may be good fertiliser candidates going into the future to reduce agricultural pollution, while maintaining crop yields.

How to cite: Chadwick, J., Zhang, P., Lynch, I., Ullah, S., and Mushinski, R.: Minimising nitrogen losses from agricultural soil using a nitrogen-doped nanocomposite, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-1299, https://doi.org/10.5194/egusphere-egu22-1299, 2022.

Ammonia (NH₃) emission is one of the dominant pathways of N loss from liquid manure fertilization with negative effects on environment and human health. It is still an unanswered question, how soil (e.g. pH, Corg, texture) and slurry factors (e.g. pH, Dm) interact in NH₃ emission processes and which of the two systems eventually dominates the other. A systematic incubation study was set up using soils with different soil textures, in which different soil pH levels were established by in two long-term fertilisation trials (Jyndevad, Denmark; Bad Lauchstädt, Germany). Two contrasting slurry types combined with two application techniques (surface banding, incorporation) were tested. Guiding hypotheses were that emissions from surface applied slurry are mainly governed by slurry characteristics while soil effects become dominant after slurry incorporation.

Dynamic chamber incubations (400 g dry soil, 60% WHC, 15 °C, exchange rate 10 head space Vol/min) were set up to determine NH₃ emissions after surface or incorporated application of pig slurry (PS, pH 6.6, DM 13.2%) and anaerobic digestate (AD, pH 8.1, DM 6.6%). Ammonia emissions were measured by photoacoustic gas monitor for a maximum of four days after fertilization. Soils investigated were a sandy soil with low clay content from Jyndevad in Denmark and a loamy loess-chernozem with high clay content from Bad Lauchstaedt in Saxony-Anhalt, Germany. From each location several soils (4 x Jyndevad and 7 x Bad Lauchstaedt) were collected from different experimental plots. The measured soil-pH-values of Jyndevad soils ranged between pH (CaCl₂) 3.62 – 6.17 and those from Bad Lauchstaedt between 5.29 – 7.22. Soil incorporation was done manually in the upper 2-3 cm soil layer immediately after slurry application. Data were analysed by ANOVA and multiple contrast tests or multiple mean comparisons.

A general relationship between soil-pH and NH₃ volatilization was not observed, although statistically significant differences occurred between different soils. Ammonia emissions for Bad Lauchstaedt were in the order ‘surface AD’ (44 % N applied) > ‘surface PS’ (12 %) > ‘incorporated PS’ (11 %) > ‘incorporated AD’ (7 %). Ammonia emissions for the location Jyndevad followed the same order though on a higher level, the emissions from incorporated AD tended to rise with increasing soil-pH-value and by contrast NH₃ emissions for incorporated PS at Jyndevad tended to decline with increasing soil-pH. For PS the effect of incorporation on emissions was only marginal while being very pronounced in AD. This was probably due to comparatively shallow incorporation in this pot trial and very high DM content of PS. Sand content was positively correlated with emissions, while clay and humus content showed negative relationships.

Lower NH₃ emissions occurred from PS compared to AD. Emissions were reduced due to factors ‘incorporation’ as well ‘clay and humus content’. Soil pH values had only effects on ammonia emissions from incorporated slurries. The results confirm the hypotheses that soil pH governs emissions from incorporated slurries while soil texture had a much more pronounced effect for both slurry application systems. Interactions with N₂O emissions will be discussed.

How to cite: Pacholski, A., Engel, F., and Seidel, A.: Soil texture and pH effects on NH3 emissions from pig slurry and anaerobic digestate with and without incorporation, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7188, https://doi.org/10.5194/egusphere-egu22-7188, 2022.

Ammonia emissions affect environment, climate and human health and concomitantly reduce fertilizer nitrogen use efficiency. Against the background of environmental and climate protection, the reduction of ammonia losses in the use of synthetic nitrogen fertilisers have become more important. However, there is a lack of data on simultaneous comparative evaluation of fertilizers in multiplot measurements for the assessment of fertilisation strategies and mitigation options. As a challenge, ammonia emission measurements from small plots in a randomized plot design are debated and uncertain.

The joint research project “NH₃-Min” focuses on the most common synthetic nitrogen fertilizers in Germany, i.e. urea (U), calcium ammonium nitrate (CAN), ammonium nitrate urea solution (UAN), ammonium sulphate urea (UAS) and evaluates different options for mitigation of ammonia emissions such as (i) choice of nitrogen form, (ii) use of urease and nitrification inhibitors (UI, NI) and (iii) ammonium sulfate urea injection (CULTAN).

In 2020 and the following 3 years a set of coordinated field trials is conducted in winter wheat, comprising 10 sites across Germany and covering different climatic regions and soil types. A combination of different sensors and flux calculation methods is tested and cross-validated on different spatial scales. In large circular plots (r = 20 m) two types of passive flux samplers, Leuning and Alpha samplers, are tested applying the IHF (integrated horizontal flux), ZINST and bLs (backward Lagrangian stochastic dispersion) flux calculations. Additionally, on one site (r = 70m) an Aerodyne QC-Laser is set-up using eddy covariance flux quantification. On the same field as the micrometeorological methods, Alpha samplers in combination with the bLs method, as well as acid traps in combination with dynamic chamber measurements with Dräger tubes (calibrated passive sampling) are used to determine ammonia fluxes in replicated small quadratic plots (81 m²).

First preliminary results showed that:

• IHF and ZINST were in close agreement for Leuning samplers.
• Alpha and Leuning samplers yielded similar results by ZINST flux quantification.
• Alpha samplers in combination with bLs method and acid traps were capable of significantly differentiating ammonia emissions between different fertilizer treatments in replicated plot measurements. Though, differences between the two plot approaches were observed.
• Concerning the different treatments, urea showed the highest emissions, however fertilizer injection (CULTAN) also yielded high ammonia emissions. Lowest emissions were recorded in the CAN treatment and urease-inhibited treatment.

More refined experimental results and project details will be presented and discussed.

How to cite: Kukowski, S., Götze, H., Kelsch, A., Frößl, J., Brüggemann, N., Ruser, R., Pacholski, A., Brümmer, C., and Flessa, H.: NH3-Min project: assessment of ammonia measurement methods and evaluation of synthetic nitrogen fertilizer ammonia emissions and nitrogen use efficiency, EGU General Assembly 2022, Vienna, Austria, 23–27 May 2022, EGU22-7434, https://doi.org/10.5194/egusphere-egu22-7434, 2022.