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.

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;

scholarly journals Combination of photoacoustic detector with gas diffusion probes for the measurement of methane concentration gradients in submerged paddy soil

Chemosphere ◽  
1996 ◽  
Vol 33 (12) ◽  
pp. 2487-2504 ◽  
Author(s):  
F. Rothfuss ◽  
F.G.C. Bijnen ◽  
R. Conrad ◽  
F.J.M. Harren ◽  
J. Reuss
Keyword(s):  
Paddy Soil ◽  
Methane Concentration ◽  
Gas Diffusion ◽  
Concentration Gradients

A Synthesis of Knowns, Unknowns, and Policy Recommendations from the Sea Lamprey International Symposium

1980 ◽  
Vol 37 (11) ◽  
pp. 2202-2208 ◽  
Author(s):  
Carl J. Walters ◽  
George Spangler ◽  
W. J. Christie ◽  
Patrick J. Manion ◽  
James F. Kitchell
Keyword(s):  
International Symposium ◽  
Large Scale ◽  
Fishery Management ◽  
Field Experiments ◽  
Lake Trout ◽  
Sea Lamprey ◽  
Future Research ◽  
Fish Stock ◽  
Total Production ◽  
Pilot Studies

The Sea Lamprey International Symposium (SLIS) has provided a broad spectrum of facts and speculations for consideration in future research and management programs. Many aspects of the laboratory biology and field life history of the sea lamprey (Petromyzon marinus) are now well understood. There is little question that it can now be controlled by chemical larvicides, and perhaps in the future by more efficient integrated control programs. There is correlative evidence (wounds, scars, catch curves) that lamprey caused major mortalities in some fish species, and that control in conjunction with stocking has lead to remarkable recoveries of salmonid stocks in the Great Lakes. However, there are great gaps in understanding about just what the lamprey does under field conditions, and it is not yet possible to reject several hypotheses that assign lamprey a minimum or transient role in fish stock changes. Further studies on details of lamprey biology are, in themselves, unlikely to fill the gaps; one alternative is to conduct a large-scale field experiment involving cessation of lamprey control while holding other factors (fishing, stocking) as steady as possible. If it is decided to proceed with management on the assumption that lamprey are important, without the major field experiments to confirm it, then at least the following steps should be taken: (1) the chemical treatment program should be reviewed in detail, with a view to finding treatment schedules that will minimize frequency and dose rates for lampricide applications; (2) pilot studies on alternative control schemes (sterile male, attractants, barriers) should only be funded if they are statistically well designed (several replicate and control streams), and involve quantitative monitoring of lamprey spawning success and subsequent total production of transforming larvae; (3) the lake trout (Salvelinus namaycush) stocking program should be maintained at its present level, and should involve diverse genotypes rather than a few hatchery strains; (4) growth in the sport fisheries for lake trout should be curtailed, and commercial fisheries should not yet be permitted; (5) a multispecies harvesting policy should be designed that takes into account the buffering effect of each species on lamprey mortality suffered by others (i.e. should some species not be harvested at all, and viewed instead as buffers for more valuable species?); and (6) a program should be developed for restoring, by culture if necessary, native forage species in case the introduced smelt and alewife should collapse under pressure from fishing and prédation by the growing salmonid community.Key words: sea lamprey, proposed research, fishery management, mathematical models, population dynamics

scholarly journals A field perspective on effects of fire and temperature fluctuation on Cerrado legume seeds

2017 ◽  
Vol 27 (2) ◽  
pp. 74-83 ◽  
Author(s):  
L. Felipe Daibes ◽  
Talita Zupo ◽  
Fernando A.O. Silveira ◽  
Alessandra Fidelis
Keyword(s):  
Temperature Fluctuation ◽  
Field Experiments ◽  
Seed Viability ◽  
Soil Surface ◽  
Temperature Fluctuations ◽  
Fire Effects ◽  
Fuel Load ◽  
Physical Dormancy ◽  
Legume Seeds ◽  
Field Perspective

AbstractInformation from a field perspective on temperature thresholds related to physical dormancy (PY) alleviation and seed resistance to high temperatures of fire is crucial to disentangle fire- and non-fire-related germination cues. We investigated seed germination and survival of four leguminous species from a frequently burned open Neotropical savanna in Central Brazil. Three field experiments were conducted according to seed location in/on the soil: (1) fire effects on exposed seeds; (2) fire effects on buried seeds; and (3) effects of temperature fluctuations on exposed seeds in gaps and shaded microsites in vegetation. After field treatments, seeds were tested for germination in the laboratory, together with the control (non-treated seeds). Fire effects on exposed seeds decreased viability in all species. However, germination of buried Mimosa leiocephala seeds was enhanced by fire in an increased fuel load treatment, in which we doubled the amount of above-ground biomass. Germination of two species (M. leiocephala and Harpalyce brasiliana) was enhanced with temperature fluctuation in gaps, but this condition also decreased seed viability. Our main conclusions are: (1) most seeds died when exposed directly to fire; (2) PY could be alleviated during hotter fires when seeds were buried in the soil; and (3) daily temperature fluctuations in gaps also broke PY of seeds on the soil surface, so many seeds could be recruited or die before being incorporated into the soil seed banks. Thus seed dormancy-break and germination of legumes from Cerrado open savannas seem to be driven by both fire and temperature fluctuations.

Technologies of drop irrigation of young almond garden on terraces in foothland conditions of the Kyzylsu-Yuzhnaya river basin

2021 ◽  
Vol 0 (1) ◽  
pp. 12-15
Author(s):  
Daler Domullodzhanov
Keyword(s):  
River Basin ◽  
Drip Irrigation ◽  
Field Experiments ◽  
Soil Surface ◽  
Perennial Grasses ◽  
Minimum Amount ◽  
Almond Orchard

The article presents the results of field experiments on the study of the technology of drip irrigation of a young almond orchard on terraces with clear cover with tillage soil surface, with use of mulching and overseeding of perennial grasses. In the variant with mulching, the minimum amount of irrigation observed – 24, with the irrigation norm – 1904 litre per tree. In other cases, the number of irrigation events increases from 8 to 23, respectively, the irrigation norms are 1.39 and 2.06 times.

scholarly journals Crop residues on short-term CO2 emissions in sugarcane production areas

2013 ◽  
Vol 33 (4) ◽  
pp. 699-708 ◽  
Author(s):  
Mariana M. Corradi ◽  
Alan R. Panosso ◽  
Marcílio V. Martins Filho ◽  
Newton La Scala Junior
Keyword(s):  
Co2 Emissions ◽  
Field Experiments ◽  
Crop Residues ◽  
Soil Surface ◽  
Dry Mass ◽  
Agricultural Crop ◽  
Short Term ◽  
Sugarcane Production ◽  
Soil Temperatures ◽  
Production Areas

The proper management of agricultural crop residues could produce benefits in a warmer, more drought-prone world. Field experiments were conducted in sugarcane production areas in the Southern Brazil to assess the influence of crop residues on the soil surface in short-term CO2 emissions. The study was carried out over a period of 50 days after establishing 6 plots with and without crop residues applied to the soil surface. The effects of sugarcane residues on CO2 emissions were immediate; the emissions from residue-covered plots with equivalent densities of 3 (D50) and 6 (D100) t ha-1 (dry mass) were less than those from non-covered plots (D0). Additionally, the covered fields had lower soil temperatures and higher soil moisture for most of the studied days, especially during the periods of drought. Total emissions were as high as 553.62 ± 47.20 g CO2 m-2, and as low as 384.69 ± 31.69 g CO2 m-2 in non-covered (D0) and covered plot with an equivalent density of 3 t ha-1 (D50), respectively. Our results indicate a significant reduction in CO2 emissions, indicating conservation of soil carbon over the short-term period following the application of sugarcane residues to the soil surface.

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
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