Changes of iron oxides and phosphorus adsorption-desorption in paddy soils under alternating flooded and dried conditions

The effects of flooding and subsequent air drying of three times in total on the transformation of iron oxides, phosphorus adsorption and desorption in two paddy soils were studied in the laboratory. The results showed that flooding significantly increased the content of amorphous iron oxides and P adsorption capacity accompanying with a sharp decrease of crystalline iron oxides and P desorption in two tested soils. However, this effect could be almost reversed by air drying process. This pattern was observed in three times of continuously alternating flooding and air drying process. The change of amorphous iron oxides should be the most important factor affecting P availability in paddy soil during flooding and drying process as the fact that a very close correlation was found between the content of amorphous iron oxides and P adsorption in the soils.