scholarly journals Supplementary material to "Underestimation of denitrification rates from field application of the <sup>15</sup>N gas flux method and its correction by gas diffusion modelling"

2018 ◽  
Author(s):  
Reinhard Well ◽  
Martin Maier ◽  
Dominika Lewicka-Szczebak ◽  
Jan-Reent Köster ◽  
Nicolas Ruoss
Keyword(s):  
Gas Diffusion ◽  
Field Application ◽  
Flux Method ◽  
Gas Flux ◽  
Diffusion Modelling ◽  
Supplementary Material

scholarly journals Underestimation of denitrification rates from field application of the <sup>15</sup>N gas flux method and its correction by gas diffusion modelling

2019 ◽  
Vol 16 (10) ◽  
pp. 2233-2246 ◽  
Author(s):  
Reinhard Well ◽  
Martin Maier ◽  
Dominika Lewicka-Szczebak ◽  
Jan-Reent Köster ◽  
Nicolas Ruoss
Keyword(s):  
Field Experiments ◽  
Pore Space ◽  
Soil Surface ◽  
Gas Diffusion ◽  
Surface Fluxes ◽  
Soil Gas ◽  
Total Production ◽  
Concentration Gradients ◽  
Flux Method ◽  
Gas Flux

Abstract. Common 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 closed chambers that are placed on the soil surface. Gas diffusion is considered to be the main transport process in the soil. Because accumulation of gases within the chamber decreases concentration gradients between soil and the chamber over time, the surface efflux of gases decreases as well, and gas production rates are underestimated if calculated from chamber concentrations without consideration of this mechanism. Moreover, concentration gradients to the non-labelled subsoil exist, inevitably causing downward diffusion of 15N-labelled denitrification products. A numerical 3-D model for simulating gas diffusion in soil was used in order to determine the significance of this source of error. Results show that subsoil diffusion of 15N-labelled N2 and N2O – and thus potential underestimation of denitrification derived from chamber fluxes – increases with chamber deployment time as well as with increasing soil gas diffusivity. Simulations based on the range of typical soil gas diffusivities of unsaturated soils showed that the fraction of N2 and N2O evolved from 15N-labelled NO3- that is not emitted at the soil surface during 1 h chamber closing is always significant, with values up to >50 % of total production. This is due to accumulation in the pore space of the 15N-labelled soil and diffusive flux to the unlabelled subsoil. Empirical coefficients to calculate denitrification from surface fluxes were derived by modelling multiple scenarios with varying soil water content. Modelling several theoretical experimental set-ups showed that the fraction of produced gases that are retained in soil can be lowered by lowering the depth of 15N labelling and/or increasing the length of the confining cylinder. Field experiments with arable silt loam soil for measuring denitrification with the 15N gas flux method were conducted to obtain direct evidence for the incomplete surface emission of gaseous denitrification products. We compared surface fluxes of 15N2 and 15N2O from 15N-labelled micro-plots confined by cylinders using the closed-chamber method with cylinders open or closed at the bottom, finding 37 % higher surface fluxes with the bottom closed. Modelling fluxes of this experiment confirmed this effect, however with a higher increase in surface flux of 89 %. From our model and experimental results we conclude that field surface fluxes of 15N-labelled N2 and N2O severely underestimate denitrification rates if calculated from chamber accumulation only. The extent of this underestimation increases with closure time. Underestimation also occurs during laboratory incubations in closed systems due to pore space accumulation of 15N-labelled N2 and N2O. Due to this bias in past denitrification measurements, denitrification in soils might be more relevant than assumed to date. Corrected denitrification rates can be obtained by estimating subsurface flux and storage with our model. The observed deviation between experimental and modelled subsurface flux revealed the need for refined model evaluation, which must include assessment of the spatial variability in diffusivity and production and the spatial dimension of the chamber.

scholarly journals Underestimation of denitrification rates from field application of the <sup>15</sup>N gas flux method and its correction by gas diffusion modelling

2018 ◽  
Author(s):  
Reinhard Well ◽  
Martin Maier ◽  
Dominika Lewicka-Szczebak ◽  
Jan-Reent Köster ◽  
Nicolas Ruoss
Keyword(s):  
Field Experiments ◽  
Pore Space ◽  
Soil Surface ◽  
Gas Diffusion ◽  
Surface Fluxes ◽  
Soil Gas ◽  
Total Production ◽  
Concentration Gradients ◽  
Flux Method ◽  
Gas Flux

Abstract. Common 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 closed chambers that are placed on the soil surface. Gas diffusion is considered to be the main transport process in the soil. Because accumulation of gases within the chamber decreases concentration gradients between soil and chamber over time, the surface efflux of gases decreases as well and gas production rates are underestimated if calculated from chamber concentrations without consideration of this mechanism. Moreover, concentration gradients to the non-labelled subsoil exist, inevitably causing downward diffusion of 15N labelled denitrification products. A numerical 3-D model for simulating gas diffusion in soil was used in order to determine the significance of this source of error. Results show that subsoil diffusion of 15N-labelled N2 and N2O – and thus potential underestimation of denitrification derived from chamber fluxes – increases with chamber deployment time as well as with increasing soil gas diffusivity. Simulations based on the range of typical soil gas diffusivities of unsaturated soils showed that the fraction of N2 and N2O evolved from 15N-labelled NO3 that is not emitted at the soil surface during one hour chamber closing is always significant with values up to > 50 % of total production due to accumulation in the pore space of the 15N-labelled soil and diffusive flux to the unlabelled subsoil. Empirical coefficients to calculate denitrification from surface fluxes were derived by modelling multiple scenarios with varying soil water content. Field experiments with arable silt loam soil for measuring denitrification with the 15N gas flux method were conducted to obtain direct evidence for the incomplete surface emission of gaseous denitrification products. We compared surface fluxes of 15N2 and 15N2O from 15N–labelled micro-plots confined by cylinders using the closed chamber method with cylinders open or closed at the bottom, finding 37 % higher surface fluxes with bottom closed. Modeling fluxes of this experiment confirmed this effect, however with a higher increase in surface flux of 89 %. From our model and experimental results we conclude that field surface fluxes of 15N-labelled N2 and N2O severely underestimate denitrification rates if calculated from chamber accumulation only. The extent of this underestimation increases with closure time. Underestimation also occurs during laboratory incubations in closed systems due to pore space accumulation of 15N-labelled N2 and N2O. Due to this bias in past denitrification measurements, denitrification in soils might be more relevant than assumed to date. Corrected denitrification rates can be obtained by estimating subsurface flux and storage with our model. The observed deviation between experimental and modeled subsurface flux revealed the need for refined model evaluation which must include assessment of the spatial variability in diffusivity and production and the spatial dimension of the chamber.

Improvement of the 15 N gas flux method for in situ measurement of soil denitrification and its product stoichiometry

2019 ◽  
Vol 33 (5) ◽  
pp. 437-448 ◽  
Author(s):  
Reinhard Well ◽  
Stefan Burkart ◽  
Anette Giesemann ◽  
Balázs Grosz ◽  
Jan Reent Köster ◽  
...  
Keyword(s):  
In Situ Measurement ◽  
Flux Method ◽  
Gas Flux

scholarly journals Quantifying N<sub>2</sub>O reduction to N<sub>2</sub> based on N<sub>2</sub>O isotopocules – validation with independent methods (helium incubation and <sup>15</sup>N gas flux method)

2017 ◽  
Vol 14 (3) ◽  
pp. 711-732 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Jürgen Augustin ◽  
Anette Giesemann ◽  
Reinhard Well
Keyword(s):  
Isotopic Fractionation ◽  
Isotopic Signature ◽  
Residual Fraction ◽  
Simultaneous Estimation ◽  
Site Preference ◽  
Isotopic Enrichment ◽  
Flux Method ◽  
Gas Flux ◽  
Isotopic Analyses

Abstract. Stable isotopic analyses of soil-emitted N2O (δ15Nbulk, δ18O and δ15Nsp = 15N site preference within the linear N2O molecule) may help to quantify N2O reduction to N2, an important but rarely quantified process in the soil nitrogen cycle. The N2O residual fraction (remaining unreduced N2O, rN2O) can be theoretically calculated from the measured isotopic enrichment of the residual N2O. However, various N2O-producing pathways may also influence the N2O isotopic signatures, and hence complicate the application of this isotopic fractionation approach. Here this approach was tested based on laboratory soil incubations with two different soil types, applying two reference methods for quantification of rN2O: helium incubation with direct measurement of N2 flux and the 15N gas flux method. This allowed a comparison of the measured rN2O values with the ones calculated based on isotopic enrichment of residual N2O. The results indicate that the performance of the N2O isotopic fractionation approach is related to the accompanying N2O and N2 source processes and the most critical is the determination of the initial isotopic signature of N2O before reduction (δ0). We show that δ0 can be well determined experimentally if stable in time and then successfully applied for determination of rN2O based on δ15Nsp values. Much more problematic to deal with are temporal changes of δ0 values leading to failure of the approach based on δ15Nsp values only. For this case, we propose here a dual N2O isotopocule mapping approach, where calculations are based on the relation between δ18O and δ15Nsp values. This allows for the simultaneous estimation of the N2O-producing pathways' contribution and the rN2O value.

Quantifying soil denitrification in situ from depth profiles of 15N labelled denitrification products by diffusion-reaction modelling 

2021 ◽  
Author(s):  
Reinhard Well ◽  
Dominika Lewicka-Szczebak ◽  
Martin Maier ◽  
Amanda Matson
Keyword(s):  
Soil Gas ◽  
Diffusion Reaction ◽  
Flux Method ◽  
Closed Chamber ◽  
Gas Flux ◽  
Depth Profiles ◽  
Chamber Method ◽  
Chamber Measurements ◽  
Closed Chamber Method

&lt;p&gt;Common field methods for measuring soil denitrification in situ include monitoring the accumulation of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O evolved from &lt;sup&gt;15&lt;/sup&gt;N labelled soil nitrate pool in soil surface chambers. Bias of denitrification rates derived from chamber measurements results from subsoil diffusion of &lt;sup&gt;15&lt;/sup&gt;N labelled denitrification products, but this can be corrected by diffusion modeling (Well et al., 2019). Moreover, precision of the conventional &lt;sup&gt;15&lt;/sup&gt;N gas flux method is low due to the high N&lt;sub&gt;2&lt;/sub&gt; background of the atmosphere. An alternative to the closed chamber method is to use concentration gradients of soil gas to quantify their fluxes (Maier &amp;&amp;#160; Schack-Kirchner, 2014). Advantages compared to the closed &amp;#160;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 &lt;sup&gt;15&lt;/sup&gt;N-labelled denitrification products. Here we use this approach for the first time to evaluate denitrification rates derived from depth profiles of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O in the field by closed chamber measurements published previously (Lewicka-Szczebak et al., 2020).&lt;/p&gt;&lt;p&gt;We compared surface fluxes of N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O from &lt;sup&gt;15&lt;/sup&gt;N labelled microplots using the closed chamber method. Diffusion&amp;#8211;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 &amp;#160;used to fit measured and modelled concentrations of &lt;sup&gt;15&lt;/sup&gt;N labelled N&lt;sub&gt;2&lt;/sub&gt; and N&lt;sub&gt;2&lt;/sub&gt;O. 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).&lt;/p&gt;&lt;p&gt;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. &amp;#160;&lt;/p&gt;&lt;p&gt;References:&lt;/p&gt;&lt;p&gt;Lewicka-Szczebak D, Lewicki MP, Well R (2020) N2O isotope approaches for source partitioning of N2O production and estimation of N2O reduction &amp;#8211; validation with the 15N gas-flux method in laboratory and field studies. Biogeosciences, &lt;strong&gt;17&lt;/strong&gt;, 5513-5537.&lt;/p&gt;&lt;p&gt;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, &lt;strong&gt;247&lt;/strong&gt;, 21-33.&lt;/p&gt;&lt;p&gt;Maier M, Schack-Kirchner H (2014) Using the gradient method to determine soil gas flux: A review. Agricultural and Forest Meteorology, &lt;strong&gt;192&lt;/strong&gt;, 78-95.&lt;/p&gt;&lt;p&gt;Schack-Kirchner H, Hildebrand EE, Wilpert KV (1993) Ein konvektionsfreies Sammelsystem f&amp;#252;r Bodenluft. Zeitschrift Fur Pflanzenernahrung Und Bodenkunde, &lt;strong&gt;156&lt;/strong&gt;, 307-310.&lt;/p&gt;&lt;p&gt;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, &lt;strong&gt;16&lt;/strong&gt;, 2233-2246.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;

Applying slurry with different techniques in spring – which pathway does the nitrogen take?

2021 ◽  
Author(s):  
Caroline Buchen-Tschiskale ◽  
Heinz Flessa ◽  
Reinhard Well
Keyword(s):  
Passive Samplers ◽  
Plant Residues ◽  
N Recovery ◽  
Nitrification Inhibitors ◽  
Soil Cores ◽  
Flux Method ◽  
Undisturbed Soil ◽  
Gas Flux ◽  
N Transformation ◽  
Application Techniques

&lt;p&gt;One of the most important measures to reduce ammonia (NH&lt;sub&gt;3&lt;/sub&gt;) and nitrous oxide (N&lt;sub&gt;2&lt;/sub&gt;O) fluxes from crop production is the adoption of low-emission application techniques for slurry. Application techniques may also impact dinitrogen (N&lt;sub&gt;2&lt;/sub&gt;) emission, as they can influence denitrification activity by changing slurry and soil aeration (e.g. by injection techniques), nitrate formation (e.g. by adding nitrification inhibitors) and the pH value (e.g. by slurry acidification). However, measuring N&lt;sub&gt;2&lt;/sub&gt; emissions and following pathways of slurry nitrogen (N) transformation under field conditions is still challenging.&lt;/p&gt;&lt;p&gt;Thus, we set up a field experiment using undisturbed soil cores with growing winter wheat as small lysimeters. Cattle slurry treatments include the following application techniques: trailing hose with and without acidification (H&lt;sub&gt;2&lt;/sub&gt;SO&lt;sub&gt;4&lt;/sub&gt;), slot injection with and without nitrification inhibitor (DMPP). Soil cores without slurry application were used as control. In a first step, soil nitrate was &lt;sup&gt;15&lt;/sup&gt;N labelled by homogeneous injection of a K&lt;sup&gt;15&lt;/sup&gt;NO&lt;sub&gt;3&lt;/sub&gt; solution (98 at% &lt;sup&gt;15&lt;/sup&gt;N, equal to 4 kg N ha&lt;sup&gt;-1&lt;/sup&gt;). One week later, we applied 72 kg N ha&lt;sup&gt;-1&lt;/sup&gt;&lt;sup&gt;15&lt;/sup&gt;N-labelled slurry (NH&lt;sub&gt;4&lt;/sub&gt;&lt;sup&gt;+&lt;/sup&gt; labelled at 65 at% &lt;sup&gt;15&lt;/sup&gt;N). NH&lt;sub&gt;3&lt;/sub&gt; emissions were measured by Dr&amp;#228;ger-Tube method (Pacholski, 2016). N&lt;sub&gt;2&lt;/sub&gt;O and N&lt;sub&gt;2&lt;/sub&gt; emission were measured using the &lt;sup&gt;15&lt;/sup&gt;N gas flux method with N&lt;sub&gt;2&lt;/sub&gt;-depleted atmosphere (Well et al., 2018). To close the N balance and follow the different N transformation pathways, &lt;sup&gt;15&lt;/sup&gt;N losses by leaching, &lt;sup&gt;15&lt;/sup&gt;N uptake by plant and residual &lt;sup&gt;15&lt;/sup&gt;N in roots, plant residues, microbial biomass and soil were analysed by IRMS.&lt;/p&gt;&lt;p&gt;N&lt;sub&gt;2&lt;/sub&gt;O emission were very low (up to 0.1 kg N&lt;sub&gt;2&lt;/sub&gt;O-N ha&lt;sup&gt;-1&lt;/sup&gt;) and not significantly different between treatments during the experimental period of 60 days. Since the N&lt;sub&gt;2&lt;/sub&gt;O/(N&lt;sub&gt;2&lt;/sub&gt;+N&lt;sub&gt;2&lt;/sub&gt;O) ratio of denitrification (N&lt;sub&gt;2&lt;/sub&gt;Oi) was also very low, most labelled N was lost via N&lt;sub&gt;2&lt;/sub&gt; (up to 3 kg N ha&lt;sup&gt;-1&lt;/sup&gt;). Nevertheless, the major gaseous loss pathway was NH&lt;sub&gt;3&lt;/sub&gt; with up to 8 kg N ha&lt;sup&gt;-1&lt;/sup&gt; in the trailing hose treatment. Slot injection significantly reduced NH&lt;sub&gt;3&lt;/sub&gt; emission, while N leaching losses were up 5 kg N ha&lt;sup&gt;-1&lt;/sup&gt;. Recovery of &lt;sup&gt;15&lt;/sup&gt;N was higher in the soil N pool (32-48 %) than in plants (19-37 %) and roots (5-7 %). Total &lt;sup&gt;15&lt;/sup&gt;N recovery was almost complete, indicating that the experiment was able to catch the relevant N pathways.&lt;/p&gt;&lt;p&gt;&lt;strong&gt;References:&lt;/strong&gt;&lt;/p&gt;&lt;p&gt;Pacholski, A., 2016. Calibrated passive sampling-multi-plot field measurements of NH&lt;sub&gt;3&lt;/sub&gt; emissions with a combination of dynamic tube method and passive samplers. Journal of visualized experiments: JoVE 109, e53273.&lt;/p&gt;&lt;p&gt;Well, R., Burkart, S., Giesemann, A., Grosz, B., K&amp;#246;ster, J., Lewicka-Szczebak, D., 2018. Improvement of the &lt;sup&gt;15&lt;/sup&gt;N gas flux method for in situ measurement of soil denitrification and its product stoichiometry. Rapid Communications in Mass Spectrometry 33, 437&amp;#8211;448.&lt;/p&gt;

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