Regulation of N<sub>2</sub>O emissions from acid organic soil drained for agriculture
<p>Organic soils drained for crop production or grazing land are agroecosystems with potentially high but variable emissions of nitrous oxide (<span class="inline-formula">N<sub>2</sub>O</span>). The present study investigated the regulation of <span class=...
| Main Authors: | , , , , , |
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| Format: | Article |
| Language: | English |
| Published: |
Copernicus Publications
2019-11-01
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| Series: | Biogeosciences |
| Online Access: | https://www.biogeosciences.net/16/4555/2019/bg-16-4555-2019.pdf |
| Summary: | <p>Organic soils drained for crop production or grazing land are agroecosystems
with potentially high but variable emissions of nitrous oxide (<span class="inline-formula">N<sub>2</sub>O</span>).
The present study investigated the regulation of <span class="inline-formula">N<sub>2</sub>O</span> emissions in a
raised bog area drained for agriculture, which is classified as potentially
acid sulfate soil. We hypothesised that pyrite (<span class="inline-formula">FeS<sub>2</sub></span>) oxidation was a
potential driver of <span class="inline-formula">N<sub>2</sub>O</span> emissions through microbially mediated reduction
of nitrate (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M7" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="a02883d0956e7dc256b9fe9fffa70b09"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4555-2019-ie00001.svg" width="25pt" height="16pt" src="bg-16-4555-2019-ie00001.png"/></svg:svg></span></span>). Two sites with rotational grass, and two sites
with a potato crop, were equipped for monitoring of <span class="inline-formula">N<sub>2</sub>O</span> emissions and
soil <span class="inline-formula">N<sub>2</sub>O</span> concentrations at the 5, 10, 20, 50 and 100 cm depth during weekly
field campaigns in spring and autumn 2015. Further data acquisition included
temperature, precipitation, soil moisture, water table (WT) depth, and soil
<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M10" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="dd23f13eb24280cbe650be4567ce8571"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4555-2019-ie00002.svg" width="25pt" height="16pt" src="bg-16-4555-2019-ie00002.png"/></svg:svg></span></span> and ammonium (<span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M11" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NH</mi><mn mathvariant="normal">4</mn><mo>+</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="24pt" height="15pt" class="svg-formula" dspmath="mathimg" md5hash="8cff18dc7544e09830abea500d71300b"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4555-2019-ie00003.svg" width="24pt" height="15pt" src="bg-16-4555-2019-ie00003.png"/></svg:svg></span></span>) concentrations. At all sites,
the soil was acidic, with pH ranging from 4.7 to 5.4. Spring and autumn
monitoring periods together represented between 152 and 174 d, with
cumulative emissions of 4–5 kg <span class="inline-formula">N<sub>2</sub>O</span>-N ha<span class="inline-formula"><sup>−1</sup></span> at sites with rotational
grass and 20–50 kg <span class="inline-formula">N<sub>2</sub>O</span>-N ha<span class="inline-formula"><sup>−1</sup></span> at sites with a potato crop.
Equivalent soil gas-phase concentrations of <span class="inline-formula">N<sub>2</sub>O</span> at grassland sites
varied between 0 and 25 <span class="inline-formula">µ</span>L L<span class="inline-formula"><sup>−1</sup></span> except for a sampling after
slurry application at one of the sites in spring, with a maximum of 560 <span class="inline-formula">µ</span>L L<span class="inline-formula"><sup>−1</sup></span> at the 1 m depth. At the two potato sites the levels of
below-ground <span class="inline-formula">N<sub>2</sub>O</span> concentrations ranged from 0.4 to 2270 <span class="inline-formula">µ</span>L L<span class="inline-formula"><sup>−1</sup></span> and from 0.1 to 470 <span class="inline-formula">µ</span>L L<span class="inline-formula"><sup>−1</sup></span>, in
accordance with the higher soil mineral N availability at arable sites.
Statistical analyses using graphical models showed that soil <span class="inline-formula">N<sub>2</sub>O</span>
concentration in the capillary fringe (i.e. the soil volume above the water
table influenced by tension saturation) was the strongest predictor of
<span class="inline-formula">N<sub>2</sub>O</span> emissions in spring and, for grassland sites, also in the autumn.
For potato sites in autumn, there was evidence that <span class="inline-formula"><math xmlns="http://www.w3.org/1998/Math/MathML" id="M28" display="inline" overflow="scroll" dspmath="mathml"><mrow class="chem"><msubsup><mi mathvariant="normal">NO</mi><mn mathvariant="normal">3</mn><mo>-</mo></msubsup></mrow></math><span><svg:svg xmlns:svg="http://www.w3.org/2000/svg" width="25pt" height="16pt" class="svg-formula" dspmath="mathimg" md5hash="da99f0b0265c157ce21f9580f34f8fd2"><svg:image xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="bg-16-4555-2019-ie00004.svg" width="25pt" height="16pt" src="bg-16-4555-2019-ie00004.png"/></svg:svg></span></span>
availability in the topsoil and temperature were the main controls on
<span class="inline-formula">N<sub>2</sub>O</span> emissions. Chemical analyses of intact soil cores from the 0 to 1 m depth,
collected at adjacent grassland and potato sites, showed that the total
reduction capacity of the peat soil (assessed by cerium(IV) reduction) was
much higher than that represented by <span class="inline-formula">FeS<sub>2</sub></span>, and the concentrations of
total reactive iron (TRFe) were higher than those of <span class="inline-formula">FeS<sub>2</sub></span>. Based on the
statistical graphical models and the tentative estimates of reduction
capacities, <span class="inline-formula">FeS<sub>2</sub></span> oxidation was unlikely to be important for <span class="inline-formula">N<sub>2</sub>O</span>
emissions. Instead, archaeal ammonia oxidation and either
chemodenitrification or nitrifier denitrification were considered to be
plausible pathways of <span class="inline-formula">N<sub>2</sub>O</span> production in spring, whereas in the autumn
heterotrophic denitrification may have been more important at arable sites.</p> |
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| ISSN: | 1726-4170 1726-4189 |