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\hypersetup{pdftitle={\textit{In sit}u Determination of CO$_{2}$ and N$_{2}$O Emissions and Isotopic Composition in Agricultural Soils Following a Precipitation Pulse Using Real"=Time CO$_{2}$ and N$_{2}$O Isotope Analysers},pdfauthor={Janet Chen, Christian Resch, Leopold Mayr, Maria Heiling, Gerd Dercon},pdfsubject={Tropentag 2016: Abstract},pdfkeywords={13C, 15N, farming, greenhouse gas, mulch, soil},pdfpagemode=None,colorlinks=true}
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\parbox[b]{13.4cm}{\centering \large{\textbf{Tropentag, September 18-21, 2016, Vienna, Austria}}\\[1ex] \Large{``Solidarity in a competing world ---\\fair use of resources''\\[2ex]}}
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\Large{\textbf{\textit{In sit}u Determination of CO$_{2}$ and N$_{2}$O Emissions and Isotopic Composition in Agricultural Soils Following a Precipitation Pulse Using Real"=Time CO$_{2}$ and N$_{2}$O Isotope Analysers\footnote{\textbf{Contact Address:} Janet Chen, International Atomic Energy Agency (IAEA), Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Reaktorstrasse 1, 2444~Seibersdorf, Austria, \mbox{e-mail}: \email{j.chen@iaea.org}}\\[0.8ex]}}
\normalsize{\textsc{Janet Chen, Christian Resch, Leopold Mayr, Maria Heiling, Gerd Dercon}}
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\begin{itemize*}
\item[]{\small{\textit{International Atomic Energy Agency (IAEA), Joint FAO/IAEA Division of Nuclear Techniques in Food and Agriculture, Austria}}}
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\index[author]{Chen, Janet}
\index[author]{Resch, Christian}
\index[author]{Mayr, Leopold}
\index[author]{Heiling, Maria}
\index[author]{Dercon, Gerd}
\begin{center}
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\textbf{Abstract}
\begin{abstract}
\normalsize{
Agricultural soils cover \mbox{12.6\,\%} of the Earth's surface and are essential in food production. Additionally, this land can either serve as storage of greenhouse gases (GHGs) belowground, or further release GHGs into the atmosphere. Accurately estimating GHGs fluxes from agricultural soils is difficult, however, due to the dynamic pattern of emissions that are largely driven by environmental factors such as water availability. Farming practices, such as mulch application, also affect soil GHG emissions. We measured effects of mulch application on emissions and isotopic composition of the GHGs, CO$_{2}$ and N$_{2}$O, in agricultural soils in greenhouse meso"=cosms (\mbox{70\,cm} deep and \mbox{50\,cm} diameter, soybean"=maize crop rotation since 2012) following an artificial 5 mm precipitation pulse using a novel closed"=loop method in real"=time. Both CO$_{2}$ and N$_{2}$O emissions increased in mulch"=covered soils immediately after the precipitation pulse by roughly 30 mg·m$^{-2}$·h$^{-1}$ and 0.56 $\mu$g·m$^{-2}$·h$^{-1}$, respectively. N$_{2}$O emissions were reduced in bare soils following the precipitation pulse to roughly 0.13 $\mu$g·m$^{-2}$·h$^{-1}$ and CO$_{2}$ gas was absorbed by soil at roughly 10 mg·m$^{-2}$·h$^{-1}$. Response of CO$_{2}$ emissions in mulch"=covered soils to precipitation was rapid and decreased exponentially over a 4--7 h period and CO$_{2}$ absorption into bare soils also persisted after the precipitation pulse for a similar time period. Response of N$_{2}$O emissions to precipitation in both soils was also rapid and returned to pre"=precipitation pulse rates within 1 h. Only CO$_{2}$ emissions from mulch"=covered soils exhibited a change in isotopic composition after the precipitation pulse, decreasing by approximately 2\permil{}. This decrease in $\delta$$^{13}$C indicates an increase in respiration of a relatively $^{13}$C-depleted C source following precipitation, such as a larger proportion of C3 compared to C4 plant material. The high temporal resolution of our continuous CO$_{2}$ and N$_{2}$O gas measurements allowed us to more accurately measure GHG gas flux and isotopic composition compared to estimates that are overestimated using intermittent gas sampling. Our results indicate that CO$_{2}$ emissions are predominant in agricultural soils and that bare soils can temporarily serve as a sink of CO$_{2}$ following a precipitation event while mulch"=covered soils function as a CO$_{2}$ source.



}

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\end{abstract}
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\noindent \textbf{Keywords:} $^{13}$C, $^{15}$N, farming, greenhouse gas, mulch, soil
\index[key]{Farming}
\index[key]{Greenhouse gas}
\index[key]{Mulch}
\index[key]{Soil}
\end{document}
