Manganese and Iron Solubility Changes as a Factor in Tile Drain Clogging: I. Observations During Flooding and Drying1
- L. B. Grass,
- A. J. MacKenzie,
- B. D. Meek and
- W. F. Spencer2
A field study of waterlogging and subsequent drying of the soil profile has shown that under irrigation culture in Imperial Valley reducing conditions became prevalent. Reducing conditions, as indicated by declining Eh values, became most favorable for dissolution of Mn and Fe near the soil surface. However, the concentrations of Mn2+ and Fe2+ were lowest near the surface, probably because of their leaching from this zone, and the shorter time of contact between soil solution and soil particles. The concentration of Fe2+ and Mn2+ were higher in the deeper horizons of the soil profile.
In the plow layer, the reducing intensity increased, beginning 9 m away from the tile and reaching a maximum 18- to 23-m from the tile drain. The Eh levels in the soil profile declined immediately after irrigation began and rose immediately after irrigation stopped indicating the importance of atmospheric oxygen to the oxidation-reduction status and, therefore, to the solubility of iron and manganese compounds. Soluble organic carbon apparently was not related to the concentration of Mn2+ or Fe2+ in the soil solution even though the decomposition of soil organic matter is important in oxidation-reduction reactions in the soil profile.Please view the pdf by using the Full Text (PDF) link under 'View' to the left.
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