scholarly journals <sup>15</sup>N gas-flux method to determine N<sub>2</sub> emission and N<sub>2</sub>O pathways: a comparison of different tracer addition approaches

2019 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Reinhard Well
Keyword(s):  
15N Tracer ◽  
Homogeneous Distribution ◽  
Soil Cores ◽  
Flux Method ◽  
Gas Flux ◽  
N Transformations ◽  
Tracer Solution ◽  
Comparison Of The Results ◽  
Label Distribution ◽  
Intact Soil

Abstract. 15N gas flux method allows for quantification of N2 flux and tracing soil N transformations. An important requirement for this method is a homogeneous distribution of the 15N tracer added to soil. This is usually achieved by soil homogenization and admixture of the 15N tracer solution or multipoint injection of tracer solution to intact soil. Both methods may create artefacts. We aimed at comparing the results of the gas flux method using both tracer distribution approaches. Intact soil cores with injected 15N tracer solution show wider range of the results obtained. Homogenized soil shows better agreement between repetitions, but significant differences in 15N enrichment measured in soil nitrate and in emitted gases were also observed. For intact soil the wider variability of measured values rather results from natural diversity of non-homogenized soil cores than from inhomogeneous label distribution. Generally, comparison of the results of intact cores and homogenized soil did not reveal statistically significant differences in N2 flux determination. In both cases, pronounced dominance of N2 flux over N2O flux was noted. It can be concluded that both methods showed close agreement and homogenized soil is not necessarily characterized by more homogenous 15N label distribution.

scholarly journals The <sup>15</sup>N gas-flux method to determine N<sub>2</sub> flux: a comparison of different tracer addition approaches

SOIL ◽  
2020 ◽  
Vol 6 (1) ◽  
pp. 145-152 ◽  
Author(s):  
Dominika Lewicka-Szczebak ◽  
Reinhard Well
Keyword(s):  
15N Tracer ◽  
Homogeneous Distribution ◽  
Soil Cores ◽  
Flux Method ◽  
Gas Flux ◽  
N Transformations ◽  
Tracer Solution ◽  
Intact Soil Cores ◽  
Label Distribution ◽  
Intact Soil

Abstract. The 15N gas-flux method allows for the quantification of N2 flux and tracing soil N transformations. An important requirement for this method is a homogeneous distribution of the 15N tracer added to soil. This is usually achieved through soil homogenization and admixture of the 15N tracer solution or multipoint injection of tracer solution to intact soil. Both methods may create artefacts. We aimed at comparing the N2 flux determined by the gas-flux method using both tracer distribution approaches. Soil incubation experiments with silt loam soil using (i) intact soil cores injected with 15N label solution, (ii) homogenized soil with injected label solution, and (iii) homogenized soil with admixture of label solution were performed. Intact soil cores with injected 15N tracer solution show a larger variability of the results. Homogenized soil shows better agreement between repetitions, but significant differences in 15N enrichment measured in soil nitrate and in emitted gases were observed. For intact soil, the larger variability of measured values results rather from natural diversity of non-homogenized soil cores than from inhomogeneous label distribution. Generally, comparison of the results of intact cores and homogenized soil did not reveal statistically significant differences in N2 flux determination. In both cases, a pronounced dominance of N2 flux over N2O flux was noted. It can be concluded that both methods showed close agreement, and homogenized soil is not necessarily characterized by more homogenous 15N label distribution.

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;

scholarly journals Application of the <sup>15</sup>N gas-flux method for measuring in situ N<sub>2</sub> and N<sub>2</sub>O fluxes due to denitrification in natural and semi-natural terrestrial ecosystems and comparison with the acetylene inhibition technique

2016 ◽  
Vol 13 (6) ◽  
pp. 1821-1835 ◽  
Author(s):  
Fotis Sgouridis ◽  
Andrew Stott ◽  
Sami Ullah
Keyword(s):  
Terrestrial Ecosystems ◽  
15N Tracer ◽  
Acetylene Inhibition ◽  
Flux Method ◽  
Gas Flux ◽  
Acetylene Inhibition Technique ◽  
Land Use Types ◽  
N2o Fluxes ◽  
Inhibition Technique

Abstract. Soil denitrification is considered the most un-constrained process in the global N cycle due to uncertain in situ N2 flux measurements, particularly in natural and semi-natural terrestrial ecosystems. 15N tracer approaches can provide in situ measurements of both N2 and N2O simultaneously, but their use has been limited to fertilized agro-ecosystems due to the need for large 15N additions in order to detect 15N2 production against the high atmospheric N2. For 15N–N2 analyses, we have used an “in-house” laboratory designed and manufactured N2 preparation instrument which can be interfaced to any commercial continuous flow isotope ratio mass spectrometer (CF-IRMS). The N2 prep unit has gas purification steps and a copper-based reduction furnace, and allows the analysis of small gas injection volumes (4 µL) for 15N–N2 analysis. For the analysis of N2O, an automated Tracegas Preconcentrator (Isoprime Ltd) coupled to an IRMS was used to measure the 15N–N2O (4 mL gas injection volume). Consequently, the coefficient of variation for the determination of isotope ratios for N2 in air and in standard N2O (0.5 ppm) was better than 0.5 %. The 15N gas-flux method was adapted for application in natural and semi-natural land use types (peatlands, forests, and grasslands) by lowering the 15N tracer application rate to 0.04–0.5 kg 15N ha−1. The minimum detectable flux rates were 4 µg N m−2 h−1 and 0.2 ng N m−2 h−1 for the N2 and N2O fluxes respectively. Total denitrification rates measured by the acetylene inhibition technique in the same land use types correlated (r =  0.58) with the denitrification rates measured under the 15N gas-flux method, but were underestimated by a factor of 4, and this was partially attributed to the incomplete inhibition of N2O reduction to N2, under a relatively high soil moisture content, and/or the catalytic NO decomposition in the presence of acetylene. Even though relatively robust for in situ denitrification measurements, methodological uncertainties still exist in the estimation of N2 and N2O fluxes with the 15N gas-flux method due to issues related to non-homogenous distribution of the added tracer and subsoil gas diffusion using open-bottom chambers, particularly during longer incubation duration. Despite these uncertainties, the 15N gas-flux method constitutes a more reliable field technique for large-scale quantification of N2 and N2O fluxes in natural terrestrial ecosystems, thus significantly improving our ability to constrain ecosystem N budgets.

scholarly journals Application of the <sup>15</sup>N-Gas Flux method for measuring in situ N<sub>2</sub> and N<sub>2</sub>O fluxes due to denitrification in natural and semi-natural terrestrial ecosystems and comparison with the acetylene inhibition technique

2015 ◽  
Vol 12 (15) ◽  
pp. 12653-12689 ◽  
Author(s):  
F. Sgouridis ◽  
S. Ullah ◽  
A. Stott
Keyword(s):  
Gas Injection ◽  
Terrestrial Ecosystems ◽  
15N Tracer ◽  
Organic Soils ◽  
Acetylene Inhibition ◽  
Flux Method ◽  
Gas Flux ◽  
Acetylene Inhibition Technique ◽  
Inhibition Technique

Abstract. Soil denitrification is considered the most un-constrained process in the global N cycle due to uncertain in situ N2 flux measurements, particularly in natural and semi-natural terrestrial ecosystems. 15N tracer approaches can provide in situ measurements of both N2 and N2O simultaneously, but their use has been limited to fertilised agro-ecosystems due to the need for large 15N additions in order to detect 15N2 production against the high atmospheric N2. For 15N-N2 analyses, we have used an "in house" laboratory designed and manufactured N2 preparation instrument which can be interfaced to any commercial continuous flow isotope ratio mass spectrometer (CF-IRMS). The N2 prep unit has gas purification steps, a copper based reduction furnace, and allows the analysis of small gas injection volumes (4 μL) for 15N-N2 analysis. For the analysis of N2O, an automated Tracegas Pre-concentrator (Isoprime Ltd) coupled to an IRMS was used to measure the 15N-N2O (4 mL gas injection volume). Consequently, the coefficient of variation for the determination of isotope ratios for N2 in air and in standard N2O (0.5 ppm) was better than 0.5 %. The 15N Gas-Flux method was adapted for application in natural and semi-natural land use types (peatlands, forests and grasslands) by lowering the 15N tracer application rate to 0.04–0.5 kg 15N ha−1. For our chamber design (volume / surface = 8:1) and a 20 h incubation period, the minimum detectable flux rates were 4 μg N m−2 h−1 and 0.2 ng N m−2 h−1 for the N2 and N2O fluxes respectively. The N2 flux ranged between 2.4 and 416.6 μg N m−2 h−1, and the grassland soils showed on average 3 and 14 times higher denitrification rates than the woodland and organic soils respectively. The N2O flux was on average 20 to 200 times lower than the N2 flux, while the denitrification product ratio (N2O/N2 + N2O) was low, ranging between 0.03 and 13 %. Total denitrification rates measured by the acetylene inhibition technique under the same field conditions correlated (r = 0.58) with the denitrification rates measured under the 15N Gas-Flux method but were underestimated by a factor of 4 and this was attributed to the incomplete inhibition of N2O reduction to N2 under relatively high soil moisture content. The results show that the 15N Gas-Flux method can be used for quantifying N2 and N2O production rates in natural terrestrial ecosystems, thus significantly improving our ability to constrain ecosystem N budgets.

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 Denitrification Rate and Its Potential to Predict Biogenic N2O Field Emissions in a Mediterranean Maize-Cropped Soil in Southern Italy

Land ◽  
2019 ◽  
Vol 8 (6) ◽  
pp. 97 ◽  
Author(s):  
Annachiara Forte ◽  
Angelo Fierro
Keyword(s):  
Pore Space ◽  
Denitrification Rate ◽  
Linear Functions ◽  
N2o Emissions ◽  
Soil Cores ◽  
High Soil ◽  
N2o Fluxes ◽  
Intact Soil Cores ◽  
Intact Soil ◽  
Soil Nitrates

The denitrification rate in C2H2-amended intact soil cores and soil N2O fluxes in closed static chambers were monitored in a Mediterranean irrigated maize-cropped field. The measurements were carried out during: (i) a standard fertilization management (SFM) activity and (ii) a manipulation experimental (ME) test on the effects of increased and reduced application rates of urea at the late fertilization. In the course of the SFM, the irrigations following early and late nitrogen fertilization led to pulses of denitrification rates (up to 1300 μg N2O-N m−2 h−1) and N2O fluxes (up to 320 μg N2O-N m−2 h−1), thanks to the combined action of high soil temperatures and not limiting nitrates and water filled pore space (WFPS). During the ME, high soil nitrates were noted in all the treatments in the first one month after the late fertilization, which promoted marked N-losses by microbial denitrification (from 500 to 1800 μg N2O-N m−2 h−1) every time the soil WFPS was not limiting. At similar maize yield responses to fertilizer treatments, this result suggested no competition for N between plant roots and soil microbial community and indicated a probable surplus of nitrogen fertilizer input at the investigated farm. Correlation and regression analyses (CRA) on the whole set of data showed significant relations between both the denitrification rates and the N2O fluxes with three soil physical-chemical parameters: nitrate concentration, WFPS and temperature. Specifically, the response functions of denitrification rate to soil nitrates, WFPS and temperature could be satisfactorily modelled according to simple Michaelis-Menten kinetic, exponential and linear functions, respectively. Furthermore, the CRA demonstrated a significant exponential relationship between N2O fluxes and denitrification and simple empirical functions to predict N2O emissions from the denitrification rate appeared more fitting (higher concordance correlation coefficient) than the predictive empirical algorithm based on soil nitrates, WFPS and temperature. In this regard, the empirically established relationships between the denitrification rate on intact soil cores under field conditions and the soil variables provided local-specific threshold values and coefficients which may effectively work to calibrate and adapt existing N2O process-based simulation models to the local pedo-climatic conditions.

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.

Effects of Starch Encapsulation on Clomazone and Atrazine Movement in Soil and Clomazone Volatilization

Weed Science ◽  
1995 ◽  
Vol 43 (3) ◽  
pp. 445-453 ◽  
Author(s):  
Todd L. Mervosh ◽  
Edward W. Stoller ◽  
F. William Simmons ◽  
Timothy R. Ellsworth ◽  
Gerald K. Sims
Keyword(s):  
Unsaturated Flow ◽  
Soil Surface ◽  
Silty Clay ◽  
Silt Loam ◽  
Starch Granules ◽  
Soil Cores ◽  
Silty Clay Loam ◽  
Intact Soil Cores ◽  
Water Tension ◽  
Intact Soil

The effects of formulation on clomazone volatilization and transport through soil were studied. After 22 days of leaching under unsaturated flow in 49-cm long intact soil cores, greater clomazone movement was observed in Plainfield sand than in Cisne silt loam or Drummer silty clay loam soils. Soil clomazone concentrations resulting in injury to oats occurred throughout Plainfield soil cores but were restricted to the upper 14 cm of Cisne and Drummer soils. In addition, clomazone was detected in the leachate from Plainfield soil only. In a similar study with Plainfield sand cores, clomazone was less mobile than atrazine; encapsulation of the herbicides in starch granules did not affect clomazone movement but greatly decreased atrazine movement from the soil surface. Similarly, starch encapsulation did not affect bioavailability of clomazone but did reduce bioavailability of atrazine. In a laboratory study with continual air flow, volatilization of clomazone applied to the soil surface was reduced by encapsulation in starch and starch/clay granules. Clomazone volatilization was not affected by soil water content within a range of 33 to 1500 kPa water tension. Following soil saturation with water, clomazone volatilization from both liquid and granular formulations increased. Granule size appeared to have a greater impact than granule composition on clomazone volatilization.

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