平原区水田改林地后土壤黏土矿物及氧化铁的变化

近年来水田改为林地在我国南方地区非常普遍,为了解这种转变对土壤矿物(黏土矿物和氧化铁)演变的影响,在浙江省平原地区构建了4个水田改林地系列土壤,采用野外调查和室内分析相结合的方法,研究水田改林地后土壤剖面中氧化铁形态和黏土矿物类型的演变规律。结果表明,改林地后,土壤剖面中全铁含量变化不明显,耕作层和犁底层土壤游离氧化铁有轻微增加趋势。改林地15～20 a后,4个系列土壤耕作层活性铁和活化度降幅分别在18.0%～38.4%和24.7%～48.9%;耕作层土壤铁氧化物的晶胶比增幅在0.73倍～1.62倍;耕作层土壤亚铁含量明显下降,降幅最高达95.8%,变异系数达到143.9%;耕作层络合铁降幅在21.3%～36.2%,并与有机质呈极显著正相关(P<0.01)。改林地后,犁底层土壤中绿泥石相对含量及其与高岭石的比值都呈降低趋势,其他黏土矿物相对含量变化规律不明显,土壤有机质显著下降,土壤明显酸化。土壤铁氧化物形态和数量的变化对土壤结构以及土壤重金属的迁移转化等产生重要影响。

Changes of Soil Clay Minerals and Iron Oxides After Paddy Field Converted into Forest Land in Plain Areas

Paddy field converted into forest land is very common in southern China in recent years. In order to understand the effects of this change on soil minerals (soil clay minerals and iron oxides), A series of paddy and forest soils in Zhejiang Province were selected, and the evolution of the morphology and quantity of iron oxides were studied by using a combination of field investigation and laboratory analysis. The results showed that the morphology and spatial distribution of soil iron oxides changed significantly after land-use change. The content of total iron did not change significantly; free iron in the surface and subsurface soils increased slightly, other layers changed insignificantly; after planting trees for 15 - 20 a, amorphous iron in 4 soil series fell down between 18.0% - 38.4% and 24.7% - 48.9%; the ratio of crystal to colloid of iron oxides in surface soil increased by 0.73 to 1.62 times; soil ferrous iron decreased significantly, which was up to 95.8% at most; complex iron fell down between 21.3% and 36.2%, and significantly correlated with organic matter (P<0.01). The relative content of chlorite and the ratio of chlorite to kaolinite in subsurface soil decreased, while the changes of other clay minerals were unobvious. Soil organic matter decreased significantly, soil was acidified obviously after the conversion, the morphology of soil iron oxides changed obviously. The change of the morphology and quantity of soil iron oxides had important effects on soil structure, the migration and transformation of soil heavy metals.