N losses were investigated in the field of calcareous paddy soil by ¹⁵N-tracer and micrometeorological mass balance techiques.Results revealed that:1.Total N loss from ammonium bicarbonate and urea broadcast into floodwatcr and incorporated just before transplanting was 72% and 63%,of which 39% and 30% was of ammonia loss which accounted for 54% and 48% of total N loss,respectively.2.The higher N loss from calcareous soil,as compared with acidic one,is primarily due to the higher ammonia loss,because the difference in denitrification loss between the two soils investigated in this series of research was insignif icant.