In the system of NH₄C1-CaCO₃, the pH of solution with aeration was lower than that without aeration, whereas the reverse was found for solution Ca²⁺ concentration. In the system of K₂HPO₄-CaCO₃ no significant differences in P sorption by CaCO₃ were observed between aeration and nonaeration during the entire reaction period of 24 hours. The effect of NH₃ volatilization on P sorption by CaCO₃ gradually diminished during 24 hour reaction time as solution pH increased in the system of DAP-CaCO₃. (diammonium phosphate) In the calcareous soil, very little NH₃ volatilization was found in the treatments of urea+ISSP or urea alone. On the other hand, approximately 56% of DAP-N initially applied was lost as NH₃ from the soil after 6 days. The amount of water soluble P in the soil treated by DAP without aeration was higher than that with aeration, whereas no significant difference was mbserved between treatments of urea+SSP with aeration and without aeration. Furthermore,the amount of water-soluble P in the soil was about the same in the treatments with urea-I-SSP or with SSP alone. All these. observation suggest that NHa volatilization, if it occurs, can enhance P sorption by CaCO₃ in calcareous soils, while the P sorption also enhance the NH₃ volatilization. Thus the NH₃ volatilization and P sorption are promoted and affected by each other.