SSS8.6

The factors that control the soil CO₂ concentration are not yet well understood. Therefore, the objective of this study was to explore what factors control the soil CO₂ concentration and its dynamic in a desert soil. For this purpose, CO₂ concentration and temperature were measured in six soil depths (ranging from 15 to 185 cm) in a deeply weathered, coarse-textured desert soil in the North of Chile at high frequency (every 60 minutes) together with precipitation and air temperature for one year. The mean CO₂ concentration calculated across the whole measuring period increased linearly with soil depth from 463 ppm in 15 cm to 1542 ppm in 185 cm soil depth. We observed a diel oscillation of the CO₂ concentration that decreased with soil depth and a hysteretic relationship between the topsoil CO₂ concentration and both air and soil temperature. A small precipitation event increased the CO₂ concentrations in 15, 30, and 50 cm soil depths for several days but did not alter the amplitude of the diel oscillation of the CO₂ concentration. The diel oscillation was very likely caused by strong differences between the soil and the air temperature at night, in particular in summer, causing transport of topsoil air to the atmosphere by thermal convection. Our results have important implications as they show that the soil CO₂ concentration can be controlled by air temperature through thermal convection, rather than by soil temperature, and that the hysteretic relationship between soil CO₂ concentration and temperature can be caused by physical factors alone.

How to cite: Spohn, M. and Holzheu, S.: Air temperature controls diel oscillation of the CO2 concentration in a desert soil, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-434, https://doi.org/10.5194/egusphere-egu21-434, 2021.

Biological soil crusts (biocrusts) have been reported to play a considerable role in the global carbon budget through CO₂ uptake by photosynthesis. However, it is still unclear if ecosystems dominated by biocrusts are net carbon sinks. That is mainly because so far, most research have focused on characterizing photosynthesis ex-situ, neglecting the underlying soil component, and particularly the in-situ spatio-temporal variability of soil CO₂ fluxes, which can be substantial. Moreover, it is still unknown how those CO₂ fluxes evolve during the ecological succession of biocrusts and which are the biophysical and geochemical factors that control them. Therefore, this research aimed to (1) identify those factors and (2) describe and explain the evolution of annual cumulative soil CO₂ fluxes over ecological succession in a dryland.

To this end, we conducted continuous measurements over 2 years of the topsoil CO₂ molar fraction (χ_s) in association with below- and aboveground microclimatic variables in 21 locations representative of the ecological succession of biocrusts, characterized by 5 stages: (1) physical depositional crust; (2) incipient cyanobacteria; (3) mature cyanobacteria; (4) lichen community dominated by Squamarina lentigera and Diploschistes diacapsis and (5) lichen community of Lepraria isidiata. Those measurements were also conducted under plants (Macrochloa tenacissima, Salsola genistoides, and Lygeum spartum). Using spatio-temporal statistics, an explanatory model of χ_s dynamics was calibrated on the first year of data and cross-validated to test prediction on the second year. An explanatory model of annual cumulative fluxes was also developed.

The biocrust type, soil water content (ϑ) and temperature (T_s) and interactions between those variables explained and predicted efficiently the χ_s dynamics. Among those factors, the effect of ϑ was preponderant and dependent on T_s and antecedent soil moisture conditions. The magnitude of the ϑ effect tended to increase in late successional stages, producing greater CO₂ emissions, most likely as a result of progressive soil organic carbon accumulation resulting in greater substrate availability for microbial respiration, and higher porosity enhancing CO₂ diffusion. The calcite content (and potentially indirectly the pH through a buffering effect of CaCO₃) also played a role in explaining annual cumulative CO₂ fluxes. Those fluxes were particularly mitigated where CaCO₃ was abundant, apparently due to a substantial nocturnal uptake of atmospheric CO₂ by soil (influx) throughout the study. The cumulative annual influx represented up to 115% of the cumulative annual efflux, generating a net annual carbon uptake by soil in some locations. Influxes have been increasingly reported recently from drylands soils, which are now regarded as potential carbon sinks. Those influxes have been attributed to different abiotic processes which are still debated. In this ecosystem, in the light of our observations, we assume that a geochemical process of CO₂ dissolution in soil water followed by CaCO₃ dissolution that consumes CO₂ might be involved. If this assumption could be verified, this geochemical process consuming CO₂ would need to be separated from biocrust photosynthesis and respiration, when measuring soil surface CO₂ fluxes, to not overestimate and underestimate respectively the biotic contribution to the global carbon budget.

How to cite: Lopez-Canfin, C., Lázaro, R., and Pérez Sánchez-Cañete, E.: Biophysical and geochemical processes control antagonistically the soil-atmosphere CO2 exchange during biocrust ecological succession in the Tabernas Desert, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-2487, https://doi.org/10.5194/egusphere-egu21-2487, 2021.

Soil CO₂ and O₂ are coupled in some processes (e.g. respiration) but uncoupled in others (e.g. mineral weathering), such that simultaneous measurement of these two gases can yield insight into an array of soil chemical reactions and biogeochemical processes. Because soil CO₂ production and O₂ consumption are tightly coupled when aerobic respiration and diffusion persist in the soil system, the deviations from that coupling can be interpreted to signify various biotic and abiotic reactions. Here, we used such measurements as a function of depth to understand mineral, hillslope, and seasonal controls on soil pCO₂ relative to pO₂ in three watersheds of different bedrock lithology. We made our measurements over a growing season in three neighboring humid, temperate watersheds underlain by three different sedimentary bedrocks – acidic shale, calcareous shale, and acidic sandstone. Across these three watersheds, we expected to observe different soil pCO₂ vs. pO₂ patterns. For example, in calcareous soils we anticipated to observe a greater signature of soil CO₂ consumption through weathering reactions than in silicate-dominated systems. Additionally, based on prior work, we anticipated a strong metal oxidation signature in the acidic soils.

Our results point to the strong control of parent material on the deviation of soil pCO₂ from the theoretical values for aerobic respiration and diffusion. In the two acidic parent materials we observed a signature of seasonal metal redox cycling, with metal oxidation in the early growing season as soils drain and reoxygenate, and metal reduction in the late growing season when warm moist soils drive soil respiration rates to higher than the diffusion rate of O₂. On the other hand, in the calcareous watershed, soil pCO₂ and pO₂ measurements did not suggest a seasonal redox cycle and instead indicate a consistent deficit of CO₂ relative to the O₂ consumed through aerobic respiration. Corresponding measurements of porewater chemistry indicate that this deficit is not solely attributable to carbonate mineral weathering, but also from consistent dissolution and transport downslope of respired CO₂. We calculate that the effects of these processes can impact soil CO₂ efflux to the atmosphere by up to 35%. Such results challenge our understanding of the soil carbon cycle. Employing coupled pCO₂ and pO₂ measurements in other systems will deepen understanding of soil C fluxes by identifying where and when factors other than aerobic respiration and diffusion control C flux out of the soil.

How to cite: Hodges, C., Brantley, S., and Kaye, J.: Soil carbon dioxide and oxygen concentrations indicate mineralogy plays a key role in controlling soil pCO2, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-8036, https://doi.org/10.5194/egusphere-egu21-8036, 2021.

Soil oxygen has been recognized as a potential limiting factor in plant production second only to water and nutrients. While it is widely accepted that soil gaseous oxygen levels below 10% V/V are detrimental to plant production, there are currently no accepted indices to quantify the effect of different agricultural practices on soil oxygen supply and availability. To address this challenge, a new approach is introduced, whereby indices describing the soil oxygen dynamics are determined using data from continuous in-situ soil oxygen measurements. To give the measurements a mechanistic interpretation, we developed a conceptual model describing the soil oxygen dynamics as a simplified mass balance between oxygen supply rate and oxygen consumption rate. The approach was applied to analyze field measurements of soil oxygen and water tension at 35 cm depth in avocado orchards irrigated with either Fresh Water (FW) or Treated Wastewater (TWW) in clay soil (~60% clay). The reliability of the method was shown, as soil respiration rates equivalent to 1-2 g O₂m^-2 d^-1 were established, in line with previous reports for evergreen trees. The model defines the soil water tension at which oxygen supply to the measurement depth after irrigation surpasses the oxygen consumption rate as the critical soil water tension, and a value of ~50 mbar was established for the experiment site, again within the range described in the literature for soils with similar properties using other methodologies. Using the new approach, it was established that more hypoxic conditions occur in TWW irrigated plots as compared to FW irrigated plots due to a difference in the time required to reach the critical soil water tension – TWW irrigated plots took nearly 50% longer to reach a soil water tension of 50 mbar after each irrigation in the height of the irrigation season. This delay in TWW irrigated plots was directly related to the soil drying rate, which was lower in the TWW irrigated soils in both night and day periods, indicating both a hindering of drainage and of plant water uptake. In a second study site, the values describing the soil oxygen dynamics were found to relate to the soil stone content (particles>2mm), a known effector of soil aeration. By utilizing in-situmeasurements, the method aims to represent the intricate interrelations occurring in the field which may be missed using methods focusing on the individual factors affecting soil oxygen. The insights gained can provide the basis for designing management techniques to resolve unfavorable low oxygen levels in agriculture, as well as in natural environments where hypoxia affects soil carbon turnover, the evolution of greenhouse-gasses, and the fate of toxic elements in soils.

How to cite: Shenker, M. and Yalin, D.: Analysis of soil oxygen dynamics as a diagnostic tool of the soil oxygen status in-situ, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-9996, https://doi.org/10.5194/egusphere-egu21-9996, 2021.

Appropriate application of organic fertilizer is required to reduce environmental impact from grassland and to achieve sustainable livestock production. However, N₂O fluxes from soil increase mainly due to changes in soil environmental factors such as temperature, moisture, soil pH and soil mineral nitrogen content, immediately just after fertilization, and it may be different among the types of fertilizer. In this study, we investigated that how N₂O fluxes are influenced by the application of three types of organic fertilizer (manure, slurry, and digestive fluid) for 4 years in a grassland on Andosol in southern Hokkaido, Japan. Five treatment plots: no fertilizer, chemical fertilizer, manure, slurry, and digestive fluid were established in a managed grassland in Shizunai Livestock farm, Hokkaido University. Fertilizers were applied in late April every year from 2017 to 2020. Organic fertilizers were applied such that the NPK not exceed the regional recommendation rate, and the shortage was compensated by chemical fertilizer. N₂O flux was measured by using a closed chamber method. At the same time of the flux measurements, soil temperature at 5 cm soil, and soil moisture (WFPS), soil pH, NO₃-N contents in 0-5 cm soil were measured to see the relationship with N₂O fluxes.

In 2017, a large peak of N₂O flux was observed in slurry plot (195.8μg m^-2h^-1) and digestive fluid plot (347.8 μg m^-2h^-1), whereas in 2018 and 2019, there were no large peak after the fertilization at all plots, however, in 2020, a large peak of N₂O flux was observed in manure plot (472.7 and 475.7μg m^-2h^-1) and slurry plot (194.9μg m^-2h^-1). These peaks of N₂O flux were significantly larger than those in no fertilizer and chemical fertilizer plots. All N₂O flux peaks were observed when the soil temperature ranged 10-14 ℃. In 2017 and 2020, a large peak of N₂O flux was observed although WFPS was always above 80% which is the soil moisture level leading to the complete denitrification. There was a negative relationship between N₂O flux and soil pH. Low soil pH might reduce the N₂O reductase activity, leading to the large peak of N₂O flux at high WFPS above 80%. In addition, there was a positive relationship between N₂O flux and soil NO₃^--N contentin 2017 and 2020. However, in 2018 and 2019, when WFPS was below 80% in most days, there was no positive relationship between N₂O flux and soil NO₃^--N content. In conclusion, the peak of N₂O flux was different depending on the year and fertilizer, In order to reduce N₂O flux just after fertilization, it is especially important not to lower the soil pH and not to increase the WFPS.

How to cite: Kitamura, R., Sugiyama, C., Yasuda, K., Nagatake, A., Yuan, Y., Du, J., Yamaki, N., Taira, K., Kawai, M., and Hatano, R.: Influence of soil environmental factors on N2O fluxes just after application of three types of organic fertilizers - 4 years study in a grassland on Andosol in southern Hokkaido, Japan, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1948, https://doi.org/10.5194/egusphere-egu21-1948, 2021.

Nitrous oxide (N₂O) is a powerful greenhouse gas (GHG) with a global warming potential about 300 times that of carbon dioxide (CO₂). In Switzerland, N₂O emissions contribute to about 6% of the total GHG emissions, agriculture being responsible for more than 60% of the former. Understanding the processes driving N₂O emissions from agricultural land is therefore of paramount importance for developing national GHG emissions inventories. Of relevance in this respect is the fact that about two-thirds of the agricultural lands are grasslands, part of which are managed as pastures.

Urine deposited by grazing animals has high N loads and induce increased nitrification and denitrification. Urine patches are hence hotspots for N₂O emissions. In the IPCC Tier 1 method still in use in Switzerland for quantifying N₂O emissions, a default EF₃ value of 2% is assumed for excreta (dung and urine). This does not properly account for the spatial heterogeneity of N returns from grazing animals. Recent studies have indeed shown that country-specific EF₃ are typically much lower than the default IPCC value. These results suggest that the use of IPCC Tier 2 and Tier 3 methods, that rely on the application of process-based models, is to be preferred for estimating countrywide N₂O emissions.

In this work, we will apply the comprehensive process-based model ecosys to simulate N₂O emissions from urine patches in a Swiss grazing system. We report on preliminary results from experiments aiming at modelling artificially applied urine patches. After showing that the model is able to reproduce the emission rates measured in a companion field trial, we use ecosys to examine N fractions lost to direct (N₂O emissions) and indirect (ammonia volatilization, nitrate leaching and runoff) pathways for urine-N input rates varying from 500-2000 kg N ha^-1. We also apply the model to understand the effects of seasonal variations in the environmental drivers on N₂O EF. This work is part of a PhD conducted by the first author that aims at developing the scientific basis for establishing country-specific EFs for grazing-related N₂O emissions in Switzerland.

How to cite: Kuntu-Blankson, K., Six, J., Barczyk, L., Ammann, C., and Calanca, P.: Process-based model estimation of N2O Emission factors for urine patches in a Swiss grazing system, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-13220, https://doi.org/10.5194/egusphere-egu21-13220, 2021.

Common field methods for measuring soil denitrification in situ include monitoring the accumulation of ¹⁵N labelled N₂ and N₂O evolved from ¹⁵N labelled soil nitrate pool in soil surface chambers. Bias of denitrification rates derived from chamber measurements results from subsoil diffusion of ¹⁵N labelled denitrification products, but this can be corrected by diffusion modeling (Well et al., 2019). Moreover, precision of the conventional ¹⁵N gas flux method is low due to the high N₂ background of the atmosphere. An alternative to the closed chamber method is to use concentration gradients of soil gas to quantify their fluxes (Maier &  Schack-Kirchner, 2014). Advantages compared to the closed  chamber method include the facts that (i) time consuming work with closed chambers is replaced by easier sampling of soil gas probes, (ii) depth profiles yield not only the surface flux but also information on the depth distribution of gas production and (iii) soil gas concentrations are higher than chamber gas concentration, resulting in better detectability of ¹⁵N-labelled denitrification products. Here we use this approach for the first time to evaluate denitrification rates derived from depth profiles of ¹⁵N labelled N₂ and N₂O in the field by closed chamber measurements published previously (Lewicka-Szczebak et al., 2020).

We compared surface fluxes of N₂ and N₂O from ¹⁵N labelled microplots using the closed chamber method. Diffusion–based soil gas probes (Schack-Kirchner et al., 1993) were used to sample soil air at the end of each closed chamber measurement. A diffusion-reaction model (Maier et al., 2017) will be  used to fit measured and modelled concentrations of ¹⁵N labelled N₂ and N₂O. Depth-specific values of denitrification rates and the denitrification product ratio will be obtained from best fits of depth profiles and chamber accumulation, taking into account diffusion of labelled denitrification products to the subsoil (Well et al., 2019).

Depending on the outcome of this evaluation, the gradient method could be used for continuous monitoring of denitrification in the field based on soil gas probe sampling. This could replace or enhance current approaches by improving the detection limit, facilitating sampling and delivering information on depth-specific denitrification.  

References:

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.

Maier M, Schack-Kirchner H (2014) Using the gradient method to determine soil gas flux: A review. Agricultural and Forest Meteorology, 192, 78-95.

Schack-Kirchner H, Hildebrand EE, Wilpert KV (1993) Ein konvektionsfreies Sammelsystem für Bodenluft. Zeitschrift Fur Pflanzenernahrung Und Bodenkunde, 156, 307-310.

Well R, Maier M, Lewicka-Szczebak D, Koster 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.

How to cite: Well, R., Lewicka-Szczebak, D., Maier, M., and Matson, A.: Quantifying soil denitrification in situ from depth profiles of 15N labelled denitrification products by diffusion-reaction modelling, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-7835, https://doi.org/10.5194/egusphere-egu21-7835, 2021.

The exchange of the climate-relevant greenhouse gases (GHGs) at the soil-atmospheric interface is regulated by both abiotic and biotic controls. However, evidence on nutrient limitations of soil GHG fluxes from African tropical forest ecosystems is still rare. Therefore, an ecosystem-scale nutrient manipulation experiment (NME) consisting of nitrogen (N), phosphorus (P), N + P, and control treatments was set up in a tropical forest in northwestern Uganda. Soil carbon dioxide (CO₂), methane (CH₄), and nitrous oxide (N₂O) fluxes were measured monthly using static vented chambers for 14 months. A root trenching treatment was also done in all the experimental plots in order to disentangle the contribution of root and microbial respiration to total soil CO₂ effluxes. In parallel to soil GHG flux measurements, soil temperature, soil moisture, and mineral N were determined. Lifting the N limitation on the soil nitrifiers and denitrifiers through N fertilization significantly increased N₂O fluxes in N, and N + P addition plots in the transitory phase (0-28 days after N fertilization, p < 0.01). However, sustained N fertilization did not significantly affect background (measured more than 28 days after fertilization) N₂O fluxes. Alleviation of the P limitation on soil methanotrophs through P fertilization marginally and significantly increased CH₄ consumption in the transitory (p = 0.052) and background (p = 0.010) phases, respectively. Simultaneous addition of N and P (N + P) significantly affected transitory soil CO₂ effluxes (p = 0.010), suggesting a possible co-limitation of N and P on soil respiration. Microbial CO₂ effluxes were significantly larger than root CO₂ effluxes (p < 0.001) across all treatment plots so was the contribution of microbial respiration to the total soil CO₂ effluxes (about 70 %, p < 0.001). Despite the fact that soil respiration was affected through N + P fertilization, neither heterotrophic nor autotrophic respiration significantly differed in either the N + P or the other treatments. Overall, the study findings suggest that the contribution of tropical forests to the global soil GHG budget could be altered by changes in N and P availability in these biomes.

Key words: Soil greenhouse gas fluxes, nutrient manipulation experiment, soil nutrient limitation, and Ugandan tropical pristine forest.

How to cite: Tamale, J., Hüppi, R., Griepentrog, M., Turyagyenda, L. F., Barthel, M., Doetterl, S., Fiener, P., and van Straaten, O.: Evaluating the role soil nutrients play in regulating soil greenhouse gas fluxes from the pristine tropical forests: evidence from a nutrient manipulation experiment in Uganda, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-1415, https://doi.org/10.5194/egusphere-egu21-1415, 2021.

Static chambers are frequently used to evaluate greenhouse gas (GHG) emissions from agro-systems. However, the effects of such chambers on water and nutrient distribution within and under the chamber’s base (i.e., anchor) in drip irrigation and its effects on GHG emissions is not well understood. This study aimed to shed some light on the topic by using field measurements and physically based, three-dimensional (3-D) simulations of flow transport and nitrogen transformations in variably saturated, spatially heterogeneous flow domain. GHG fluxes [methane (CH₄), carbon dioxide (CO₂), and nitrous oxide (N₂O)] were measured in the field for two years using a portable FTIR gas analyzer. The main findings of this study suggest that: (i) the chamber’s base modifies the water and nutrient distribution within it. Placement of the dripper inside the base leads to higher water contents, higher nitrate and ammonium concentrations, and higher N₂O fluxes relative to an undisturbed area. In contrast, placement of the dripper outside the chamber base reduces all of these parameters, including the N₂O fluxes, relative to an undisturbed area. (ii) The dripper’s location relative to the chamber’s base had minor to no effect on CO₂ fluxes. The effect on the CH₄ fluxes was not conclusive, yet suggested higher emissions when the dripper was located inside the base. (iii) A minimal disturbance is achieved when the dripper is located within a base, and the base’s radius equals the capillary length of the soil.

How to cite: Baram, S., Bar-Tal, A., Gal, A., and Russo, D.: The use of static chambers in drip irrigation: what should be considered?, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-16474, https://doi.org/10.5194/egusphere-egu21-16474, 2021.

A common method to measure radon exhalation rates relies on the accumulation chamber technique. Usually, this approach only considers one-dimensional gas transport within the soil that neglects lateral diffusion. However, this lateral transport could reduce the reliability of the method. In this work, several cylindrical- shaped accumulation chambers were built with different heights to test if the insertion depth of the chamber into the soil improves the reliability of the method and, in that case, if it could limit the radon lateral diffusion effects. To check this hypothesis in laboratory, two reference exhalation boxes were manufactured using phospho- gypsum from a repository located nearby the city of Huelva, in the southwest of Spain. Laboratory experiments showed that insertion depth had a deep impact in reducing the effective decay constant of the system, extending the interval where the linear fitting can be applied, and consistently obtaining reliable exhalation measurements once a minimum insertion depth is employed. Field experiments carried out in the phosphogypsum repository showed that increasing the insertion depth could reduce the influence of external effects, increasing the re- peatability of the method. These experiments provided a method to obtain consistent radon exhalation mea- surements over the phosphogypsum repository.

How to cite: Gutiérrez Álvarez, I., Guerrero, J. L., Martín, J. E., Adame, J. A., and Bolívar, J. P.: Influence of the accumulation chamber insertion depth to measure surface radon exhalation rates, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-4222, https://doi.org/10.5194/egusphere-egu21-4222, 2021.

 Generally, during the paddy rice cultivation period, CH₄ produced in the soil is reported to be released to the atmosphere through three pathways: diffusion (<1%), bubbles (<10%), and via rice (> 90%). However, there are few studies have measured gas diffusion coefficient for soil below surface of the water, and there is no study has provided an accurate understanding of CH₄ dynamics in paddy fields. Furthermore, there are few studies that understanding the CH₄ dynamics in fertilizer-free and pesticide-free paddy fields, which is mainly controlled by inter-tillage practices. Therefore, this study aimed to clarify the effects of tillage and the number of inter-tillage and the presence or absence of fertilizer and pesticide on the CH₄ dynamics in rice paddy soil. This study compared three types of CH₄ flux, which were total CH₄ flux from rice paddy field measured by transparent chamber with plants, and soil derived CH₄ flux measured by dark chamber without plants, and gas diffusion flux calculated as a product of the gas diffusion coefficient and measured soil gas concentration gradient at the depths of 0-5 and 5-10cm. And they were compared with in the five rice cultivation periods (flooding, mid-drying, intermittent irrigation, drainage, and fallowing) and in the four treatment plots (conventional farming (CF), and fertilizer- and pesticide-free farming with zero-inter-tillage(T0), two-inter-tillage(T2), and five-inter-tillage (T5)). The CF was conducted according to the regional recommendation for tillage, fertilization and pest and weed control. The results showed that the peak of total CH₄ flux was observed in the mid-drying and intermittent irrigation periods in all treatments, and that the CH₄ flux via rice plant accounted for 60-90% of the total CH₄ flux. The CF showed significantly highest CH₄ emission during the periods, and the increase of the number of inter-tillage tended to increase the CH₄ emission. In the drainage period, the CH₄ flux by bubbles in the CF and T5 accounted for more than 80% of the total CH₄ flux. In the fallowing period, the diffusion CH₄ flux at the depth of 5-10cm increased in all treatments, but the low total CH₄ emission and increased CO₂ emission. This study revealed that incorporation of organic matter into soil in conventional rice farming tended to increase CH₄ emission. The main pathway of CH₄ emission from rice paddy field was via rice, and it was influenced by tillage significantly. The decomposition of organic matter from rice straw and weeds incorporated into soil was the source of the bubble of CH₄. Furthermore, it seemed that the most of diffusively transferred CH₄ was easily oxidized to CO₂.

How to cite: Namie, H., Shimada, K., Zhao, S. S., Ishiguro, M., and Hatanano, R.: Influence of tillage practice on major pathways of CH4 emission in rice paddy field, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-3912, https://doi.org/10.5194/egusphere-egu21-3912, 2021.

Understanding the soil-gas migration in unsaturated soil is important in a number of problems that include carbon loading to the atmosphere from the bio-geochemical activity and leakage of gases from subsurface sources from carbon storage unconventional energy development. The soil water dynamics in the vadose zone control the soil-gas pathway development and, hence, the gas flux's spatial and temporal distribution at the soil surface. The spatial distribution of soil-water content depends on soil water characteristics. The dynamics are controlled by the water flux at the land surface and water table fluctuations. Physical properties of soil give a better understanding of the soil gas dynamics and migration from greater soil depths. The fundamental process of soil gas migration under dynamic water content was investigated in the laboratory using an intermediate-scale test system under controlled conditions that is not possible in the field. The experiments focus on observing the methane gas migration in relation to the physical properties of soil and the soil moisture patterns. A 2D soil tank with dimensions of 60 cm × 90 cm × 5.6 cm (height × length × width) was used.  The tank was heterogeneously packed with sandy soil along with a distributed network of soil moisture, temperature, and electrical conductivity sensors. The heterogeneous soil configuration was designed using nine uniform silica sands with the effective sieve numbers #16, #70, #8, #40/50, #110, #30/40, #50, and #20/30 (Accusands, Unimin Corp., Ottawa, MN), and a porosity ranging in values from 0.31 to 0.42. Four methane infrared gas sensors and a Flame Ionization detector (HFR400 Fast FID) were used for the soil gas sampling at different depths within the soil profiles and at the land surface.  A complex transient soil moisture distribution and soil gas migration patterns were observed in the 2D tank. These processes were successfully captured by the sensors. These preliminary experiments helped us to understand the mechanism of soil moisture sensor response and methane gas migration into a heterogeneous sandy soil with a view to developing a large-scale test in a 3D tank (4.87 m × 2.44 m × 0.40 m) and finally transition to field deployment.

How to cite: Ilie, A. M. C., Illangasekare, T. H., Soga, K., and Whalley, W. R.: A laboratory study of the effect of soil-water dynamics on the migration of gases from subsurface sources, EGU General Assembly 2021, online, 19–30 Apr 2021, EGU21-6101, https://doi.org/10.5194/egusphere-egu21-6101, 2021.