不同脱沼泽阶段土壤中铁锰的比较研究

A COMPARATIVE STUDY ON CHANGES OF IRON AND MANGANESE OF SOIL IN DIFFERENT DESWAMPING STAGES

本文以沼泽土、起源于沼泽土的潜育型水稻土和潴育型水稻土系列为研究对象,研究了土壤脱沼过程中铁锰的变化规律。根据铁锰的剖面分布特征、土体和各粒级硅铁率与钛锰率,以及游离铁和活性铁的变化规律,土壤脱沼过程可分为两个阶段: (1)铁锰强烈淋失阶段。脱沼过程初期,土壤有机质含量甚高,且随着有机质分解加速而破坏性有机物如酸、酚类等物质的含量增加,故土壤还原能力增强,加之随着排水而提高了渗漏性,铁锰便强烈淋失。主要是以较粗粒级中的铁锰,特别是以游离态和活性态淋失为主,然后较细粒级中的铁锰亦发生明显淋失。(2)铁锰再淀积阶段。当土壤有机质下降到一定程度之后,还原能力便减弱,铁锰则氧化淀积。主要是以铁锰新生体等游离态形式向较细粒级再淀积。由于长期渍水,阻碍了铁的老化,因而再淀积的铁活性甚高,其活化度达80%以上。

Changes of iron and manganese of soil in different deswamping stage, including the changes of SiO_2/Fe_2_3 and TiO_2/MnO molecular ratios as well as free and active iron in the soil and different fractious, i.e., <0.002 mm, 0.002—0.005 mm, 0.005—0.01 mm, and 0.01—0.05 mm were studied comparatively. The distribution of iron and manganese in soil profile was also studied. In addition, the reducing capability of soil was also studied through submerged incubation in Laboratory. The two experimental catenas which consisted of swamp soil, gleyed paddy soil and periodically submergic paddy soil were collected from wetiands in Hubei and Jiangsu Provinces respectively. The gleyed paddy soil and, periodically submergic paddy soil were derived from swamp soil. The gleyed paddy soil which was of a higher content of organic matter in gleyed horizon was found in the initial stage of soil deswamping, but the periodically submergic paddy soil with a lower content of organic matter in gleyed horizon was in the late stage of soil deswamping. Except for the <0.002mm fraction, the ratios of SiO_2/Fe_2O_3 and TiO_2/MnO in soil and coarser fractions of gleyed horizon were basically in the sequence in which gleyed paddy soil>periodically submergic paddy soil>swamp soil, but the contents of free and active iron were in the order in which swamp soil and periodically submergic paddy soil>gleyed paddy soil. The distribution of iron and manganese in soil profile showed that iron and manganese of gleyed horizon were leached intensively in the gleyed paddy soil, but they were illuviated significantly in the periodically submergic paddy soil. The data of submerged incubation indicated that the gleyed horizon soil was of a lower Eh value and had a lot of reducing substances in the swamp and gleyed paddy soils, but it had a higher Eh value and a few reducing substances in the periodically submergic paddy soil. The above results suggested that the deswamping process of wetland soils could be divided into two stages: First, the intensive leaching stage' of iron and manganese. In this stage, the content of organic matter gets still higher, the reducing capability becomes stronger, and percolation increases. This results in the leaching of iron and manganese increases, especially the free and active iron in. coarser fractions. Second, the reaccumulative s,age of iron and manganese. When the content of organic matter is very low, the reducing .capability decreases significantly, therefore iron and manganese, especially free iron in finer fractions, are reoxidated and accumulated. Because of waterlogging, aging of iron is blocked, so the activity of iron is over 80 percent.