Soil dissolved phosphorus (P) and colloidal P mobilization could be closely related to the degree of phosphorus saturation (DPS). Effects of a wide range of DPS on the distributions of dissolved P and colloidal P in a paddy soil profile were investigated in this study. Dissolved P and colloidal P in water-dispersible soil colloid suspension increased obviously with increasing DPS. The change point of DPS was at 0.12 by using a split-line model. Above the value, dissolved P (3.1 mg P kg-1 ) in soil profile would increase sharply and then transfer downward. Compared with dissolved P, colloidal P was the dominant fraction (78%-91%) of P in soil colloid suspension, and positively related to DPS without a significant change point. The high release of colloids in subsoils with low DPS was attributed to the low ionic strength and high pH value in subsoils. The DPS also had a significant and positive correlation with electrical conductivity (EC), but it showed a negative correlation with pH value. However, the concentration of colloidal P was not greatly correlated to the pH value, EC and optical density of the soil colloid suspension. The results indicated that DPS was an important factor that may affect the accumulation and mobilization of water-extractable colloidal P and dissolved P.
选取浙江省嘉兴市双桥农场的稻田开展田间试验,结合降雨等自然条件研究增施有机肥对稻田田面水中不同粒径磷素的浓度和磷素径流流失量的影响,并利用液态磷核磁共振（31 P NMR）技术对施肥前、后1d田面水中磷素的化学形态进行分析。结果表明,施用有机肥显著提高了稻田田面水中总磷（TP）的浓度,施肥后第1天迅速达到峰值：高（M3）、中（M2）、低（M1）3种施肥量处理的田面水TP浓度（8.37-17.77mg/L）分别是不施肥处理（ck）的18.6,32.8,39.5倍。施肥后前5d田面水TP浓度较高,随着时间的推移,TP、溶解态磷（DP）和胶体态磷（Pcoll）的浓度变化规律相同,都呈现逐渐下降的趋势;3种施肥处理中DP占TP的百分比波动较大（25%-80%）,总体呈现随时间逐渐下降的趋势,但是Pcoll占TP的百分比稳定在9%-22%。31P NMR谱检测结果表明,施肥前、后1d田面水中磷素主要的赋存形态是正磷酸盐（占TP的88%-96%）,磷酸单酯次之（占TP的4%-11%）;在施肥后第1天,正磷酸盐所占比例随着有机肥用量增加而增加,磷酸单酯所占比例随有机肥用量增加而减少;磷酸二酯和聚磷酸盐的含量较少,增施有机肥对两者的影响不大。稻田TP径流流失量随有机肥施用量的增加而增加,最高值（0.983kg/hm2）出现在M3处理下;M1,M2,M3处理下的TP径流流失量存在显著性差异（P〈0.05）,但磷素径流流失率均不超过当季施磷总量的2%。
