Towards improved N2O budgets estimation from 10 site-years measurement and analysis of key drivers
Authors: Bigaignon Laurent , Le Dantec Valérie , Zawilski Bartosz , Granouillac Franck , Fieuzal Rémy , Claverie Nicole , Lemaire Baptiste , Brut Aurore , Ceschia Eric , Mordelet Patrick , Delon Claire , Tallec Tiphaine 
Published: March 2021

&lt;p&gt;Agriculture represents 14% of global anthropogenic greenhous gases (GHG) emissions, 46% of this amount being due to N&lt;sub&gt;2&lt;/sub&gt;O emissions from soils (UNEP, 2012). N&lt;sub&gt;2&lt;/sub&gt;O is a powerful GHG (IPCC, 2013) and its emissions from agricultural soils are related to physical-chemical parameters which depend on climate (temperature, rain&amp;#8230;), soil properties (Robertson et al., 1989) and farming practices (irrigation, tillage, fertilization&amp;#8230;) (Tellez-Rio et al., 2015). The IPCC Tier 1 emission factor remains widely used to estimate annual N&lt;sub&gt;2&lt;/sub&gt;O budgets from agricultural soils by taking into account the annual amount of N input only. However, not taking into account the environmental controlling factors may introduce high uncertainty in N&lt;sub&gt;2&lt;/sub&gt;O budget estimation. Our study aims at highlighting the key drivers of N&lt;sub&gt;2&lt;/sub&gt;O emissions from two agricultural sites in the South West of France and at proposing an improved, simple and accessible methodology to estimate N&lt;sub&gt;2&lt;/sub&gt;O budget at crop plot and seasonal scale. For this purpose, we benefited from a unique long time series of daily N&lt;sub&gt;2&lt;/sub&gt;O fluxes (from 2011 to 2016) measured with 6 closed automated chambers on two ICOS sites with contrasted agricultural management (FR-Lam and FR-Aur).&lt;/p&gt;&lt;p&gt;N&lt;sub&gt;2&lt;/sub&gt;O annual budget vary from 1.04 to 7.96 kgN ha&lt;sup&gt;-1&lt;/sup&gt; yr&lt;sup&gt;-1 &lt;/sup&gt;for winter wheat and maize crop, respectively. The effects of fertilization, rain and irrigation, plant development, spring mineralization and deep tillage on N&lt;sub&gt;2&lt;/sub&gt;O emissions were investigated. Significant correlations between rain combined with fertilization and plant development, deep tillage or spring mineralisation was found with R&amp;#178; of 0.91, 0.99 and 0.85, respectively. &amp;#160;We took advantage of these results to develop an empirical model, including N input quantity, residual N, leaf area index and water input in order to estimate seasonal and annual N&lt;sub&gt;2&lt;/sub&gt;O budget. At the seasonal scale, the model output matched well with the observed budget, with a R&amp;#178; and a RMSE of 0.87 and 0.33 kgN ha&lt;sup&gt;-1&lt;/sup&gt; at FR-Lam and of 0.92 and 0.12 kgN ha&lt;sup&gt;-1&lt;/sup&gt; at FR-Aur, respectively.&amp;#160; It also gave good statistical scores at the crop year scale with a R&amp;#178; of 0.96 and a low RMSE of 0.43 kgN ha&lt;sup&gt;-1&lt;/sup&gt; when binding data from both sites. Using the IPCC Tiers 1 methodology gave lower and more scattered results with a R&amp;#178; of 0.46 and a RMSE of 1.46 kgN ha&lt;sup&gt;-1&lt;/sup&gt;. For sites where N&lt;sub&gt;2&lt;/sub&gt;O fluxes are not monitored,&amp;#160; that new methodology may be an alternative and a more precise methodology than the IPCC Tiers 1 approach. It has also the advantage to require only few and accessible input variables.&lt;/p&gt;&lt;p&gt;&amp;#160;&lt;/p&gt;&lt;p&gt;REFERENCES&lt;/p&gt;&lt;p&gt;IPCC, 2013. Climate Change 2013: The Physical Science Basis. Cambridge University Press, Cambridge.&lt;/p&gt;&lt;p&gt;Robertson et al., 1989. Aerobic denitrification in various heterotrophic nitrifiers. Antonie van Leeuwenhock., 56, 289-299.&lt;/p&gt;&lt;p&gt;Tellez-Rio et al., 2015. N2O and CH4 Emissions from a Fallow&amp;#8211;wheat Rotation with Low N Input in Conservation and Conventional Tillage under a Mediterranean Agroecosystem. Sci. Total Environ., 508, 85&amp;#8211;94.&lt;/p&gt;&lt;p&gt;UNEP, 2012. Growing greenhouse gas emissions due to meat production.&lt;/p&gt;