Pot trials were conducted to study on availability of several forms of artificial mineral phosphate in light loam and light clay calcareous Chao soils,and mechanisms of effects of NH₄⁺-N,CO(NH₂)₂,and NO₃-N on their availability.The results showed that the order of the five phosphates in availability in light-loam and light-clayed calcareous Chao soils was as follows respectively: DCP> OCP> Al-P> Fe-P> FA and DCP> Al-P> OCP> Fe-P> FA,consistent with those of the corresponding forms of inorganic in soils.Their availability was markedly affected by forms of nitrogen applied.The availability of Al-P and FA coupled with NH₄⁺-N and CO(NH₂)₂ in light-clayed soil was obviously higher than that with NO₃-N,while application of NO₃-N could significantly raised the availability of Fe-P.Their availability varies with nitrogenous form and pH in rhizosphere.