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Manganese and Iron Solubility Changes as a Factor in Tile Drain Clogging: II. Observations During the Growth of Cotton¹

ABSTRACT

Various levels of oxidation-reduction develop in the soil profile during the irrigation and growing season of the cotton (Gossypium hirsutum L.) crop. Reducing intensity increased with depth during the growing season and reached maximum intensity at the 6.10-m depth. Reducing conditions favorable to increased solubility of Fe and Mn were observed in the surface horizons of the profile during most of the season.

Changes in the solubility of manganese and iron occurred with changes in the oxidation-reduction status in the soil profile. Manganese began to dissolve at 400 mV and became significant at less than 300 mV. Increased concentration of nitrate retarded reduction of oxidized Fe and Mn compounds. The salinity of the soil solution affected the concentration of soluble manganese and iron. The presence of NO₃^- -N in the soil solution in amounts >0.2 ppm retarded the dissolution of Mn compounds.

The solubility of manganese and iron can probably be controlled by controlling or regulating the oxidation-reduction status of the soil profile by reducing the waterlogging period after irrigation to a minimum.

¹ Contribution of the Imperial Valley Conservation Research Center, USDA, Agricultural Research Service.

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

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