Figure 1. Cumulative N 2 O fluxes from soils in the intercropping period. N 2 O emission from a maize cropping system influenced by replacing fallow with cover crops and its subsequent incorporation into the soil. García-Marco, S. a , Sanz-Cobeña, A. a , Gabriel, J.L. b , Almendros, P. a , Quemada, M. b and Vallejo, A. a a Dpto. Química y Análisis Agrícola, ETSI Agrónomos, Technical University of Madrid, Ciudad Universitaria, 28040 Madrid, Spain b Dpto. Producción Vegetal: Fitotecnia, ETSI Agrónomos, Technical University of Madrid, Ciudad Universitaria, 28040 Madrid, Spain 1. Background & Objectives Application of nitrogen (N) fertilizers in agricultural soils increases the risk of N loss to the atmosphere in the form of ammonia (NH 3 ), nitrous oxide (N 2 O) and nitric oxide (NO) and the water bodies as nitrate (NO 3 - ). The implementation of agricultural management practices can affect these losses. In Mediterranean irrigation systems, the greatest losses of NO 3 - through leaching occur within the irrigation and the intercrop period. One way to abate these losses during the intercrop period is the use of cover crops that absorb part of the residual N from the root zone (Gabriel and Quemada, 2011). Moreover, during the following crop, these species could be applied as amendments to the soil, providing both C and N to the soil. This effect of cover and catch crops on decreasing the pool of N potentially lost has focused primarily on NO 3 - leaching. The aim of this work was to evaluate the effect of cover crops on N 2 O emission during the intercrop period in a maize system and its subsequent incorporation into the soil in the following maize crop. 2. Materials & Methods Fifteen plots were set in the field and five cover cropping treatments, barley (Hordeum vulgare L.), vetch (Vicia villosa L.), rape (Brassica napus L.), bare fallow and bare fallow without previously N fertilization as a control soil, were arranged in a fully randomized design with three replicates. Cover crops were broadcast in October 2009 and treated with glyphosate in March 2010. The cover crop residue was incorporated by ploughing to the soil in half of each plot and removed in the other half. Maize was sowed in April 2011 and harvested in September 2010. Irrigation during the maize crop was applied according to crop evapotranspiration. Each plot received 120 kg ha -1 of P and K (before sowing maize) and 150 kg N ha -1 as NH 4 NO 3 split in two applications (2/3 at the end of May and 1/3 at the end of June) except in the bare fallow soil without N application. N 2 O emissions were sampled using the chamber technique (Roelle et al., 1999) and analyzed by gas chromatography using a HP-6890 gas chromatograph equipped with a Plot-Q capillary column and a 63 Ni micro electron-capture detector (μECD). 3. Results & Discussion In the intercrop period, N 2 O emissions from soil were influenced by the presence of cover crops (Figure 1). The presence of barley and rape decreased N 2 O emission but not significantly (P>0.05).