A proteomic and metabolomic approach was conducted to decipher the biochemical bases of silage maize N utilization and metabolism in relation to growth and productivity. Leaf samples were collected on plants cultivated in the field, where they were subjected to optimal and low N fertilization treatments. The proteomic and metabolomic responses to low N was thus analyzed in 29 hybrids (29 different dent inbred lines crossed with the same flint inbred line). Ecophysiological and agronomic traits were measured on plants cultivated in the same fields. Multivariate analyses allowed us to connect the data obtained at these different levels of integration and to analyse the genetic variation of susceptibility to low N.