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Manganese and Iron Solubility Changes as a Factor in Tile Drain Clogging: I. Observations During Flooding and Drying¹

ABSTRACT

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 E_h 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 E_h 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.

¹ Contribution from the Imperial Valley Conservation Research Center, USDA, Agr. Res. Ser.

² Soil Scientists, respectively, Imperial Valley Conservation Research Center, Brawley, California and University of California, Riverside.

Received for publication February 2, 1972. Accepted for publication October 12, 1972.