聚磷酸铵作为一种富含氮、磷元素的新型缓溶性长效氮磷肥，对微量元素具有良好的螯合能力，可有效防止土壤中金属离子被固定，从而被植物更好地利用。采用滴定分析法测定了不同聚合度的水溶性聚磷酸铵（APP）对中量元素镁离子的螯合能力，探索了水溶性聚磷酸铵对镁离子的螯合规律，为聚磷酸铵-中微量元素螯合物的制备奠定基础。实验结果显示，水溶性聚磷酸铵聚合度越高，对镁离子的螯合能力越强，且螯合能力随着pH增大先减小后增大、随着温度升高逐渐降低，在pH=6.0、温度为5 ℃时高聚聚磷酸铵对镁离子的螯合量达到8.2 g（以100 g APP计），在pH=8.0、温度为5 ℃时低聚聚磷酸铵对镁离子的螯合量达到5.6 g（以100 g APP计）。采用傅里叶变换红外光谱分析验证了螯合物的生成。

As a slow release and long acting fertilizer rich in nitrogen and phosphorus，ammonium polyphosphate has a good chelating ability to trace elements，which can effectively prevent metal ions in soil from being fixed，and thus be better used by plants.Titration analysis was used to determine the chelating ability of water soluble ammonium polyphosphate with differ ent degree of polymerization on magnesium ion（Mg2+），and the chelating rule of water soluble ammonium polyphosphate to medium element Mg2+ was studied，which laid a foundation for the preparation of chelate fertilizer.The results showed that the higher the degree of polymerization of water soluble ammonium polyphosphate was，the stronger was the chelating ability to Mg2+.The chelating ability of Mg2+ decreased first and then increased with the increase of pH，and gradually decreased with the increase of temperature.Under the conditions of pH=6.0 and 5 ℃，the chelating amount of ammonium polyphosphate with higher polymerization to Mg2+ reached 8.2 g（per 100 g APP）.Under the conditions of pH=8.0 and 5 ℃，the chelating amount of ammonium polyphosphate with lower polymerization to Mg2+ reached 5.6 g（per 100 g APP）.The chelating reaction was verified by Fourier transform infrared spectrometer（FT-IR）.