No-tillage systems, associated with black oat as preceding cover crop, have been increasingly adopted. This has motivated anticipated maize nitrogen fertilizer application, transferring it from the side-dress system at the stage when plants have 5-6 expanded leaves to when the preceding cover crop is eliminated or to maize sowing. This study was conducted to evaluate the effects of soil tillage system and timing of N fertilizer application on maize grain yield and agronomic efficiency of N applied to a soil with high organic matter content. A three-year field experiment was conducted in Lages, state of Santa Catarina, Brazil, from 1999 onwards. Two soil tillage systems were tested in the main plots: conventional tillage (CT) and no-tillage (NT). Six N management systems were assessed in the split-plots: S1, control (without N application); S2, all N (100 kg ha -1) applied at oat desiccation; S3, all N applied at maize sowing; S4, all N side-dressed when maize had five expanded leaves (V5 growth stage); S5, 1/3 of N rate applied at maize sowing and 2/3 at V5; and S6, 2/3 of nitrogen rate applied at maize sowing and 1/3 at V5. Maize response to the time and form of splitting N was not affected by the soil tillage system. Grain yield ranged from 6.0 to 11.8 t ha -1. The anticipation of N application (S2 and S3) decreased grain yield in two of three years. In the rainiest early spring season (2000/2001) of the experiment, S4 promoted an yield advantage of 2.2 t ha -1 over S2 and S3. Application of total N rate before or at sowing decreased the number of kernels produced per ear in 2000/01 and 2001/02 and the number of ears produced per area in 2001/02, resulting in reduced grain yield. The agronomic efficiency of applied N (kg grain increase/kg of N applied) ranged from 13.9 to 38.8 and was always higher in the S4 than in the S2 and S3 N systems. Short-term N immobilization did not reduce grain yield when no N was applied before or at maize sowing in a soil with high organic matter content, regardless of the soil tillage system.
