Soil Biology & Biochemistry 38 (2006) 2782–2793 Nitrogen oxides emission from soils bearing a potato crop as influenced by fertilization with treated pig slurries and composts Antonio Vallejo a,Ã , Ute M. Skiba b , Lourdes Garcı´a-Torres a , Augusto Arce a , Susana Lo´pez-Ferna´ndez a , Laura Sa´nchez-Martı´n a a Escuela Te´cnica Superior de Ingenieros Agro´nomos, Universidad Polite´cnica de Madrid, Ciudad Universitaria, 28040 Madrid, Spain b Centre for Ecology and Hydrology, Edinburgh, Bush Estate, Penicuik, Midlothian EH26 QB,UK Received 21 December 2005; received in revised form 13 April 2006; accepted 19 April 2006 Available online 22 May 2006 Abstract Nitrous oxide, nitric oxide and denitrification losses from an irrigated soil amended with organic fertilizers with different soluble organic carbon fractions and ammonium contents were studied in a field study covering the growing season of potato (Solanum tuberosum). Untreated pig slurry (IPS) with and without the nitrification inhibitor dicyandiamide (DCD), digested thin fraction of pig slurry (DTP), composted solid fraction of pig slurry (CP) and composted municipal solid waste (MSW) mixed with urea were applied at a rate of 175 kg available N ha 1 , and emissions were compared with those from urea (U) and a control treatment without any added N fertilizer (Control). The cumulative denitrification losses correlated significantly with the soluble carbohydrates, dissolved N and total C added. Added dissolved organic C (DOC) and dissolved N affected the N 2 O/N 2 ratio, and a lower ratio was observed for organic fertilizers than from urea or unfertilized controls. The proportion of N 2 O produced from nitrification was higher from urea than from organic fertilizers. Accumulated N 2 O losses during the crop season ranged from 3.69 to 7.31 kg N 2 O–N ha 1 for control and urea, respectively, whereas NO losses ranged from 0.005 to 0.24 kg NO–N ha 1 , respectively. Digested thin fraction of pig slurry compared to IPS mitigated the total N 2 O emission by 48% and the denitrification rate by 33%, but did not influence NO emissions. Composted pig slurry compared to untreated pig slurry increased the N 2 O emission by 40% and NO emission by 55%, but reduced the denitrification losses (34%). DCD partially inhibited nitrification rates and reduced N 2 O and NO emissions from pig slurry by at least 83% and 77%, respectively. MSW+U, with a C:N ratio higher than that of the composted pig slurry, produced the largest denitrification losses (33.3 kg N ha 1 ), although N 2 O and NO emissions were lower than for the U and CP treatments. This work has shown that for an irrigated clay loam soil additions of treated organic fertilizers can mitigate the emissions of the atmospheric pollutants NO and N 2 O in comparison with urea. r 2006 Elsevier Ltd. All rights reserved. Keywords: Nitrous oxide; Nitric oxide; Denitrification; Organic fertilizer; Compost; Pig slurry; Dissolved organic C; Dicyandiamide 1. Introduction Organic and mineral fertilizers are known to be key variables in the regulation of nitrous oxide (N 2 O) and nitric oxide (NO) emissions from soils (Mosier et al., 1998). These gases are formed in the soil during biological denitrification and nitrification (Firestone and Davidson, 1989). Although the overall impact of most parameters affecting these processes is largely known, the fine process details, for example how the composition of organic N fertilizers affects denitrification, nitrifica- tion and emission rates are still insufficiently understood. When an organic N fertilizer is incorporated into the soil, degradable organic compounds join the ammonium ðNH þ 4 Þ and nitrate ðNO  3 Þ pool and the added carbon influences the proportion of N 2 O produced in relation to dinitrogen (N 2 ) during denitrification (Scholefield et al., 1997). However, little information of the impact of increased C input on the generation of N 2 O, N 2 and NO is available (Dendooven et al., 1998; De Wever et al., 2002). ARTICLE IN PRESS www.elsevier.com/locate/soilbio 0038-0717/$ - see front matter r 2006 Elsevier Ltd. All rights reserved. doi:10.1016/j.soilbio.2006.04.040 Ã Corresponding author. Tel.: +34 913 365 652; fax: +34 913 365 639. E-mail address: antonio.vallejo@upm.es (A. Vallejo).