Ammonium sulfate and urea were added to three soils of widely different composition. After incubation for 28 days at 20°C, from 13 to 89% of the N from ammonium sulfate, and 8 to 71% of the N as urea were not recovered, and at 40°C, 44 to 95% of the N as ammonium sulfate, and 33 to 81% of the N as urea was not recovered as either ammonium‐N or nitrate‐N. Significantly more N was lost from a soil containing 3% calcium carbonate at pH 8.4 as compared to the two other soils containing 25 and 35% calcium carbonate, which have pH's of 7.7 and 7.5, respectively. An incubation temperature of 40°C appeared quite unfavourable for nitrification.