Factors affecting N2O emissions in zero tilled loams cropped to soybean and maize Vanina R. N. Cosentino1,2, Miguel A. Taboada1,2,3 1 CONICET. (e-mail: cvanina@agro.uba.ar) 2 Facultad de Agronomía, Universidad de Agronomía, Av. San Martín 4453, Ciudad Autónoma de Buenos Aires, ABA, 3 INTA, Instituto de Suelos Castelar. Las Cabañas y De Los Reseros s/n (1686) Hurlingham, Provincia de Buenos Aires, Argentina. Despite the national greenhouse gas (GHG) inventory of Argentina shows nitrous oxide (N2O) to be the main GHG emitted from agricultural soils, field measurements on N2O emissions are almost inexistent in the country. This work reports the first results on N2O emissions and their affecting factors from zero tilled loams (Typic Argiudolls). These soils were subjected to a “wheat (Triticum aestivum L) / soybean (Glycine max, L. Merrill) - maize (Zea Mays L.) – soybean” rotation, in the subhumid Pampas region of Argentina (34 ° 57 '29''S, 60 ° 13' 11''W). Replicated (n = 3) field plots were sampled five times from November 2009 through December 2010 in a production farm of the region. Due the low topsoil temperatures (< 10ºC), N2O emissions were almost null during winter periods. During the rest of the year, when topsoil temperature increased, N2O emission rates were as high as 97 ugN-N2O*m-2*h-1 from a soil covered with soybean residues (October), or 85 ugN-N2O*m-2*h-1 from a soil covered with a recently N fertilized maize (February). In some dates N2O emission rates were related to nitrate concentration (0.2 m depth), and to a lesser extent to soil water filled pore space. These first field results show N2O emission rates to be highly variable in the studied soils, They were almost null during winter and seem to occur as pulses during the rest of the year.