In both calcareous and noncalcareous paddy soils, the fate of urea ammonium sulfate and ammonium bicarbonate were investigated in microplot experiments laid out in the rice fields using ¹⁵N tracer technique. The results obtained showed that when the N-fertilizers were surface-broadcasted as basal dressing, the recovery of ammonium bicarbonate was the lowest, while the N-loss was the greatest. The balance sheets of urea-N in the strongly calcareous, slightly acid and strongly acid paddy soils showed that the recoveries in rice plant were 22.3%, 27.5% and 39.8%, the N retained in soils were 30.4%, 18.6% and 16.4%, and the N deficits were 47.3%, 53.9% and 43.8%, respectively. In the two noncalcareous paddy soils, the recovery of ammonium sulfate amounted to 50.1% and 58.7%, but in a calcareous paddy soil, it decreased to 22.5%. Obviously, the nitrogen loss through ammonia volatilization in the calcareous paddy soil may play an important role in addition to denitrification. The deep-dressing of granulated urea and ammonium bicarbonate was the most effective method for the application of N-fertilizers. Besides, experiments also revealed that N-fertilizer top-dressed at the middle stage of rice growth gave a high recovery about 60% by the rice plant. Experiments also showed that the loss of fertilizer nitrogen were not significantly affected either by temporary drainage at the vigorous tillering stage or by the application of nitrification inhibitor (CP).