A field experiment was conducted on a chernozem soil to estimate fertiliser N efficiency of silage maize (Zea mays L.) by the difference method as influenced by the type of N fertiliser (mineral-MF vs. sewage sludge-SS), and N rate. Eight N treatments were included (0, 60, 120, 180, and 240 kg N/ha prior to maize sowing, 60 kg N/ha at planting in MF; 120, and 240 kg N/ha in SS. The average dry mater (DM) yields were 11.2–14.8 t/ha. Average nitrogen uptakes were 88–185 kg N/ha, when the average N contents in DM were 0.8–1.25%. Nitrogen utilization efficiency (NUE) was a relatively stable value for treatments with MF. The best use of nitrogen from MF was reached by 60 and 120 kg/ha N doses. The average values of recovery efficiency of applied N (RE_N) were calculated as 41–57%. The use of SS increased the yield of silage maize by 19–25% compared to control, above all first and second year after their application. Mineral-fertilizer-N equivalents (MFE) for SS were calculated as 55 and 64%.