Spatial and temporal variability of nitrous oxide emissions in a mixed farming landscape of Denmark

Biogeosciences, 9, 2989–3002, 2012 www.biogeosciences.net/9/2989/2012/ doi:10.5194/bg-9-2989-2012 © Author(s) 2012. CC Attribution 3.0 License. Biogeosciences Spatial and temporal variability of nitrous oxide emissions in a mixed farming landscape of Denmark K. Schelde1 , P. Cellier2,3 , T. Bertolini4 , T. Dalgaard1 , T. Weidinger5 , M. R. Theobald6 , and J. E. Olesen1 1 Aarhus University, Institute of Agroecology, P.O. Box 50, 8830 Tjele, Denmark UMR1091 Environnement et Grandes Cultures, 78850 Thiverval-Grignon, France 3 AgroParisTech, UMR Environnement et Grandes Cultures, 78850 Thiverval-Grignon, France 4 Euromediterranean Center for Climate Change (CMCC), Division Climate Change Impacts on Agriculture, Forests and Natural Ecosystems, 73100 Lecce, Italy 5 Eötvös Loránd University, Department of Meteorology, 1117 Budapest, Hungary 6 Technical University of Madrid, E.T.S.I. Agrónomos, Dept. Agricultural Chemistry and Analysis, Madrid 28040, Spain 2 INRA, Correspondence to: K. Schelde () Received: 2 December 2011 – Published in Biogeosciences Discuss.: 14 December 2011 Revised: 29 June 2012 – Accepted: 11 July 2012 – Published: 7 August 2012 Abstract. Nitrous oxide (N2 O) emissions from agricultural land are variable at the landscape scale due to variability in land use, management, soil type, and topography. A field experiment was carried out in a typical mixed farming landscape in Denmark, to investigate the main drivers of variations in N2 O emissions, measured using static chambers. Measurements were made over a period of 20 months, and sampling was intensified during two weeks in spring 2009 when chambers were installed at ten locations or fields to cover different crops and topography and slurry was applied to three of the fields. N2 O emissions during spring 2009 were relatively low, with maximum values below 20 ng N m−2 s−1 . This applied to all land use types including winter grain crops, grasslands, meadows, and wetlands. Slurry application to wheat fields resulted in short-lived two-fold increases in emissions. The moderate N2 O fluxes and their moderate response to slurry application were attributed to dry soil conditions due to the absence of rain during the four previous weeks. Cumulative annual emissions from two arable fields that were both fertilized with mineral fertilizer and manure were large (17 kg N2 O-N ha−1 yr−1 and 5.5 kg N2 ON ha−1 yr−1 ) during the previous year when soil water conditions were favourable for N2 O production during the first month following fertilizer application. Our findings confirm the importance of weather conditions as well as nitrogen management on N2 O fluxes. 1 Introduction Atmospheric nitrous oxide (N2 O) concentrations have increased during the industrial era due to increased anthropogenic emissions (Smith, 2004). Nitrous oxide acts as a potent greenhouse gas and is also involved in the destruction of stratospheric ozone. There has been an increasing effort towards quantifying and identifying the sources and sinks of N2 O, in order to better predict and possibly mitigate future emissions by improved management of land and resources. Approximately 65 % of atmospheric emissions of N2 O originate from soils (Smith, 2004). N2 O is produced in soils as an intermediate in the two contrasting microbial processes: autotrophic nitrification and heterotrophic denitrification. The contributions of these two processes to N2 O emissions vary with climate, soil conditions and soil management (Skiba and Smith, 2000). Land use type and changes in the crop rotation are also particularly important in determining the rate of N2 O emissions from agricultural land. For a specific crop type and soil type, it is typically found that fertilization rate, fertilizer type, timing, and cultivation play an important role in the processes controlling N2 O emission from soils (Kavdir et al., 2008). N2 O fluxes can be sporadic and short-lived, depending on the environmental conditions of the soil, particularly the temperature and moisture content (Smith et al., 1998; Frolking et al., 1998). Schaufler et al. (2010) observed a positive correlation of N2 O fluxes with Published by Copernicus Publications on behalf of the European Geosciences Union. 2990 K. Schelde et al.: Spatial and temporal variability of nitrous oxide emissions Grass Arable2 Wheat1 Wheat3 08 Meadow Wh1Slope Arable1 Wheat2 Meadow 09 Wetland 1 Figure 1 Fig. 1. Aerial photograph showing the ten locations for manual chamber measurements within the Bjerringbro landscape. Arable1 and Arable2 were studied throughout the period 2007–2008 and the 2009 campaign. Meadow08 was studied during 2007–2008, and remaining sites were only monitored during the intensive campaign in 2009. The aerial photograph was taken in early summer of 2010. soil moisture but found no significant relationship between emissions and N fertilization or N deposition level when analyzed over all soil moisture conditions. In short, several factors influence N2 O flux patterns, and the interactions between factors make it difficult to predict emissions on a short or long time scale (Machefert et al., 2002). Many previous inventories or measurement studies on N2 O flux dynamics have focused on ecosystems or landuse types such as forests (Pihlatie et al., 2005; Kesik et al., 2005), wetland/organic soils (Maljanen et al., 2003), grasslands (Flechard et al., 2007; Chatskikh et al., 2005), or arable crop rotations in experimental plots (Petersen et al., 2006; Chirinda et al., 2010). However, there have been few attempts (Dunmola et al., 2010) to cover the mosaic of land use types encountered at the landscape scale within a single study. Pattey et al. (2006) demonstrated how micrometeorological measurement techniques can be used for the upscaling from field to landscape. While these techniques provide valuable integrated information at the landscape scale, they do not easily distinguish between contributions from individual areas. Emissions of N2 O most often form a heterogeneous signal with local hotspots contributing significantly to the total flux (Matthews et al., 2010). Laville et al. (2011) concluded that the uncertainty in cumulated N2 O emissions due to infrequent sampling was less than the uncertainty due to spatial variability of the sampling sites. The current study was designed as a component of a measurement programme to estimate nitrogen fluxes and land management at the landscape level (Theobald et al., 2011) and to support modelling of the landscape-scale N fluxes Biogeosciences, 9, 2989–3002, 2012 (Duretz et al., 2011). The objective of the study was to examine the major drivers of N2 O emissions in a diverse agricultural landscape. Chamber measurements were made over a 20-month period at 10 sites in a Danish landscape to identify variations in emissions due to topography, land use or crop type, and management. During a limited period, more intensive measurements were made using add (...truncated)