以三江平原不同开垦年限水稻田为研究对象，分析了水稻田耕层土壤铁随开垦年限的动态变化情况。结果表明，随开垦年限增加，水稻田耕层土壤全铁呈指数形式递增;游离态铁以波动形式增加，3和11a时为波谷，5和14 a时为波峰;络合态铁开垦前期逐年增加，8 a后增加到1562.41mg/kg，随后逐渐减少;无定形态铁呈指数递减趋势。氧化铁的游离度先升高后降低，开垦8 a时达到最高值0.46;络合度在开垦前8 a逐年上升，5～8a增速降低，8a时达到最高值0.18，之后逐年下降;活化度则呈指数形式下降。土壤淹水状况和耕作管理方式的不同造成水稻田和大豆田氧化铁游离度、络合度和活化度随开垦年限变化趋势的差异。水田开发使湿地表土游离态铁、络合态铁和无定形态铁含量增加，氧化铁游离度升高，水稻田耕层土壤氧化铁络合度和活化度低于天然湿地，高于大豆田。
Temporal changes of the total iron, free iron, chelated iron,amorphous iron,free degree,complex(chelating) degree and activation degree of soil iron oxides in the topsoil of the paddies after reclamation in the Sanjiang Plain were studied.The results showed that total iron in the topsoil of the paddies increased exponentially with time since reclamation. Free iron showed a fluctuating upward trend with the wave troughs appeared in the 3rd year and the 11th year, and the wave peaks in the 5th year and the 14th year. Chelated iron increased during the first eight years after reclamation, reached 1562.41 mg/ kg at the 8th year, and then decreased. Amorphous iron decreased exponentially with time. Free degree of soil iron oxides first increased then decreased, and reached a maximum value of 0.46 at the 8th year.Complex degree increased continuously to a maximum value of 0. 18 during the first 8 years, with a slower increasing rate from the 5th to 8th year;and decreased gradually after the eighth year. Activation degree decreased exponentially with time.Different variation trends of free degree,complex degree and activation degree of soil iron oxides between paddies and soybean fields were caused by water flooding in paddies and differences in farming methods between the two systems. Compared with the natural wetland, rice cultivation increased contents of free iron,chelated iron and amorphous iron as well as free degree of soil iron oxides, but decreased contents of complex degree and activation degree of soil iron oxides. However, complex degree and activation degree of soil iron oxides in paddies were greater than those in soybean cultivation stage.