Ecology & Safety ISSN 1314-7234, Volume 10, 2016 Journal of International Scientific Publications www.scientific-publications.net Page 43 TESTING THE DNDC MODEL FOR NITROUS OXIDE EMISSIONS (N 2 O) FROM CROPLAND IN SLOVAKIA Ján Horák 1 , Irina Mukhina 2 , Viliam Bárek 3 1 Department of Biometeorology and Hydrology, Slovak University of Agriculture, Hospodárska 7, 94976 Nitra, Slovakia 2 Agrophysical Research Institute of the Russian Academy of Agricultural Sciences, 14 Grazhdansky prospect, St. Petersburg, Russia 3 Department of Landscape Engineering, Slovak University of Agriculture, Hospodárska 7, 94976 Nitra, Slovakia Abstract The measured data of N 2 O emissions were used to test the DNDC model from cropland during the growing season of spring barley (April-July in 2012) in Slovakia. There wasn’t found a good agreement with seasonal N 2 O emissions. The relative deviation between observed and simulated total seasonal N 2 O emissions (kg N ha -1 ) from two treatments were 91% and 281% for treatment without and with N fertilizer (N0 and N1), respectively. Also some discrepancies were found between observed and simulated emissions when evaluating the daily N 2 O emissions, especially when looking at the magnitude of N 2 O emissions peaks. The correlation between observed and simulated daily N 2 O emissions was r = 0.72 (n = 18, P < 0.01) and r = 0.56 (n = 18, P < 0.05) for N0 and N1 treatment, respectively. Key words: soil N 2 O emission, DNDC model, testing, spring barley 1. INTRODUCTION A global climate change caused by anthropogenic emission of greenhouse gases (CO 2 , CH 4 , N 2 O) is one of the most important environmental problems in the latest human history. Nitrous oxide (N 2 O) emissions from agriculture reach approximately 70% of annual global N 2 O emissions (Mosier, 2001) and approximately 75% of all N 2 O emissions in Slovakia (Šiška, Igaz, 2005). Great efforts have been done to measure N 2 O from cropland in recent years and lots of field and lab measurements have been collected. However, estimates of N 2 O from cropland are still far from being reliable due to large spatial and temporal variability of the N 2 O fluxes in response to climatic and soil conditions which make it very difficult to quantify them from cropland or other agricultural sources. Total N 2 O emissions are divided into direct and indirect emissions. Direct N 2 O emissions from cultivating have natural source and come into existence in consequence of microbial processes – nitrification and denitrification. They depend on N inputs from: fertilizers, organic fertilizers from livestock production, plant residues and symbiotic fixation of leguminous. Indirect N 2 O emissions are a result of processes of atmospheric ammonia and NOx deposition and transformation of N loosing by soil washing and run off (IPCC 1996). Nitrification is the aerobic microbial oxidation of ammonium ions to nitrite via NH 2 OH, and then to nitrate:       3 2 2 4 NO NO OH NH NH (1) N 2 O is also formed in the course of denitrification, the anaerobic microbial (mainly bacterial) reduction of nitrate successively to nitrite and then to the gases NO, N 2 O and N 2 : 2 2 2 3 N O N NO NO NO       (2) The Slovak Republic as one of the signatory states of the United Nations Framework on Climate Change (UNFCC) and according to the Kyoto protocol is required to quantify an annual national