Modeling coupled nitrification–denitrification in soil with an organic hotspot
<p>The emission of nitrous oxide (N<span class="inline-formula"><sub>2</sub></span>O) from agricultural soils to the atmosphere is a significant contributor to anthropogenic greenhouse gas emissions. The recycling of organic nitrogen (N) in manure and crop res...
| Main Authors: | , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2023-09-01
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| Series: | Biogeosciences |
| Online Access: | https://bg.copernicus.org/articles/20/3895/2023/bg-20-3895-2023.pdf |
| Summary: | <p>The emission of nitrous oxide (N<span class="inline-formula"><sub>2</sub></span>O) from agricultural soils to the atmosphere is a significant contributor to anthropogenic greenhouse gas emissions. The recycling of organic nitrogen (N) in manure and crop residues may result in spatiotemporal variability in N<span class="inline-formula"><sub>2</sub></span>O production and soil efflux which is difficult to capture by process-based models. We propose a multi-species, reactive transport model to provide detailed insight into the spatiotemporal variability in nitrogen (N) transformations around such N<span class="inline-formula"><sub>2</sub></span>O hotspots, which consists of kinetic reactions of soil respiration, nitrification, nitrifier denitrification, and denitrification represented by a system of coupled partial differential equations. The model was tested with results from an incubation experiment at two different soil moisture levels (<span class="inline-formula">−30</span> and <span class="inline-formula">−100</span> hPa) and was shown to reproduce the recorded N<span class="inline-formula"><sub>2</sub></span>O and dinitrogen
(N<span class="inline-formula"><sub>2</sub></span>) emissions and the dynamics of important carbon (C) and N components in soil reasonably well. The simulation indicated that the four different
microbial populations developed in closely connected but separate layers,
with denitrifying bacteria growing within the manure-dominated zone and
nitrifying bacteria in the well-aerated soil outside the manure zone and
with time also within the manure layer. The modeled N<span class="inline-formula"><sub>2</sub></span>O production
within the manure zone was greatly enhanced by the combined effect of oxygen
deficit, abundant carbon source, and supply of nitrogenous substrates. In the
wetter soil treatment with a water potential of <span class="inline-formula">−30</span> hPa, the diffusive flux of nitrate (NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="78ed0f7e81615226176402cdd6a1afd5"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-3895-2023-ie00001.svg" width="9pt" height="16pt" src="bg-20-3895-2023-ie00001.png"/></svg:svg></span></span>) across the manure–soil interface was the main
source of NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="fa1148a5a7ab62133104fb46bf612014"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-3895-2023-ie00002.svg" width="9pt" height="16pt" src="bg-20-3895-2023-ie00002.png"/></svg:svg></span></span> for denitrification in the manure zone, while at a
soil water potential of <span class="inline-formula">−100</span> hPa, diffusion became less dominant and
overtaken by the co-occurrence of nitrification and denitrification in the
manure zone. Scenarios were analyzed where the diffusive transport of dissolved
organic carbon or different mineral N species was switched off, and they
showed that the simultaneous diffusion of NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M13" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="a192f22c747584054322d55d69a940ca"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-3895-2023-ie00003.svg" width="9pt" height="16pt" src="bg-20-3895-2023-ie00003.png"/></svg:svg></span></span>, ammonium
(NH<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M14" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="8pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="d0f05de3ef9fdb7d2948354df3a21cd8"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-3895-2023-ie00004.svg" width="8pt" height="15pt" src="bg-20-3895-2023-ie00004.png"/></svg:svg></span></span>), and nitrite (NO<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M15" display="inline" overflow="scroll" dspmath="mathml"><mrow><msubsup><mi/><mn mathvariant="normal">2</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="9pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="605864571c3dcb0b6e3cb32dc4ee1961"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-20-3895-2023-ie00005.svg" width="9pt" height="16pt" src="bg-20-3895-2023-ie00005.png"/></svg:svg></span></span>) was crucial to simulate the
dynamics of N transformations and N<span class="inline-formula"><sub>2</sub></span>O emissions in the model. Without
considering solute diffusion in process-based N<span class="inline-formula"><sub>2</sub></span>O models, the rapid
turnover of C and N associated with organic hotspots can not be accounted
for, and it may result in the underestimation of N<span class="inline-formula"><sub>2</sub></span>O emissions from soil
after manure application. The model and its parameters allow for new
detailed insights into the interactions between transport and microbial
transformations associated with N<span class="inline-formula"><sub>2</sub></span>O emissions in heterogeneous soil
environments.</p> |
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| ISSN: | 1726-4170 1726-4189 |