RESEARCH ARTICLE Fluxes of nitrous oxide from soil under different crop rotations and tillage systems in the South of Brazil Claudia P. Jantalia Æ Henrique P. dos Santos Æ Segundo Urquiaga Æ Robert M. Boddey Æ Bruno J. R. Alves Received: 11 January 2008 / Accepted: 9 April 2008 / Published online: 22 April 2008 Ó Springer Science+Business Media B.V. 2008 Abstract The zero tillage (ZT) system is used in a large area ( [ 24 Mha) of crop production in Brazil. This management system can contribute to soil C sequestration, but many studies in other countries have registered greater nitrous oxide emissions under ZT compared to conventional tillage (CT), which may reduce greenhouse gas mitigation benefits. The aim of this study was to estimate the emission of N 2 O from cropping systems under conventional and zero tillage in an 18-year-old experiment conducted on a Rhodic Ferralsol in the South of Brazil. Fluxes of N 2 O were measured over two years using static- closed chambers in the two tillage systems with three crop rotations. Soil water filled pore space (%WFPS) and soil mineral N were monitored along with rainfall and air temperature. Estimates of N 2 O emissions were obtained by integrating the fluxes with time and also by applying the IPCC direct emission factor (EF1 = 1%) to the amounts of N added as fertilisers and returned as crop residues. Fluxes of N 2 O were relatively low, apart from a short period at the beginning of measurements. No relationship between N 2 O fluxes and %WFPS or mineral N were observed. Nitrous oxide emissions were not influenced either by tillage system or crop rotation. For the crop rotation receiving high rates of N fertiliser in the second year, field-measured N 2 O emissions were significantly underestimated by the IPCC emission factor 1 (EF1). For the other treatments measured N 2 O emissions fell within the EF1 uncertainty range, but always considerably lower than the EF1 estimate, which suggests IPCC EF1 overestimates true N 2 O emissions for the Ferralsol under evaluation. Keywords Conventional tillage  Ferralsol  IPCC N 2 O Emission factors  Maize  Nitrous oxide emissions  Soybean  Vetch  Wheat  Zero tillage Introduction Of the total annual anthropogenic emissions of the radiatively-active gases, agriculture at present is considered to contribute approximately 20% to the greenhouse effect. Estimates for Brazil indicate that land-use and agriculture respond for 81% of the total national emissions of greenhouse gases (Teixeira et al. 2006). Part of this contribution is explained by nitrous oxide (N 2 O) emitted from N fertilizers and crop residue N (Prinn 2004). Compared to CO 2 ,N 2 O has a much smaller impact on annual greenhouse gas C. P. Jantalia  S. Urquiaga  R. M. Boddey (&)  B. J. R. Alves Embrapa-Agrobiologia, Rodovia BR 465, Km 7, Caixa Postal 75.505, Seropedica 23890-000, RJ, Brazil e-mail: bob@cnpab.embrapa.br H. P. dos Santos Embrapa Wheat Research Centre, Rodovia BR 285, km 294, Passo Fundo 99001-970, RS, Brazil 123 Nutr Cycl Agroecosyst (2008) 82:161–173 DOI 10.1007/s10705-008-9178-y