Abstract: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.