In clay soils with poor drainage two trials were carried out with the objective of determining the effect of nitrogen application on maize (Zea mays L.) for silage on forage yield and protein content. In Trial 1, the treatments were two corn silage hybrids of different growing periods, SX-43 and INIA-150, sown at 90.000 plants ha-1 and four N rates: 0, 100, 200 and 400 kg N ha-1. In Trial 2, the treatments were two N rates: 200 and 400 kg of N ha-1, and three forms of N application: a) 1/2 at sowing + 1/2 at 30 cm plant height; b) 1/3 at sowing + 1/3 at 30 cm plant height + 1/3 at 60 cm plant height; and c) 1/4 at sowing + 1/4 at 30 cm plant height + 1/4 at 60 cm plant height +1/4 at flowering. One treatment was without N. In Trial 1 N application increased DM yield (P < 0.05), but no significant response was observed with N rates between 100 and 400 kg N ha-1, due to soil limitations. Forage production and protein percentage increased significantly with N application. In Trial 2, DM production in corn silage increased with higher N rates (P < 0.05). Forage protein percentage was increased by higher N rates and partitioning of the application. On increasing the partitioning of N from two to four applications, protein percentage of forage was increased by 23 and 37% for 200 and 400 kg of N ha-1, respectively.