Cereal-legume intercrops are a promising way to combine high productivity and several ecological benefits in temperate agro-ecosystems. However the proportion of each species in the mixture at harvest is highly variable. N-fertilisation may be a mean for controlling these proportions (Naudin et al., 2010). Symbiotic N2 fixation (SNF) can be inhibited by nitrate exposure. Although the effect of nitrate on SNF has been extensively investigated different scales, few studies have highlighted the impact of different timings of nitrate exposure on the SNF apparatus (N2 fixation rate and nodule biomass) and on its ability to recover after nitrates removal. The aim of this study was to test the consequences on SNF of short-term exposure to nitrate at different growth stage of pea.