Effect of natural drainage of soils on the mobility of micro-elements under flooded conditions

The effect of the natural drainage of soils on the dissolution and distribution of Fe, Mn and Cu under laboratory flooding and controlled Eh and pH was investigated using incubated soils samples, collected from the surface horizons of Alfisols and Vertisols. The soils were sampled from sites with both good and imperfect natural drainage conditions. Samples collected from well drained soils contained significantly higher total iron and manganese than those of the imperfectly drained soils. Upon incubation under flooding, decreasing Eh affected significant increases in H2O-soluble Fe only in the samples of well drained soils. Whereas opposite relationships were found for Fe in the samples of the imperfectly drained soils. More H2O-soluble Cu was found at low than at high Eh levels, regardless of the natural drainage of the soils. Water soluble Mn was increased by lowering the Eh in all soils regardless of their natural drainage. Organically bound Fe, Mn and Cu increased with decreasing Eh without being affected by the natural drainage regime of the soils. However, at low Eh levels, higher concentration of organically bound metals were found in samples from well than from imperfectly drained soils. The well drained soils contained less Fe and Cu in residual than in reactive forms, whereas the reactive forms were greater than the residual forms in the imperfectly drained soils. Most of the Mn was found in the reactive forms regardless of the natural drainage.