ACIDITY AND ALUMINUM TOXICITY CAUSED BY IRON OXIDATION AROUND ANODE BARS

Soil acidity and aluminum toxicity are serious environmental problems often found in humid temperate and tropical regions or in areas with a cid rain. Iron oxidation in soils can also cause high concentrations o f H+, which, in turn, causes an increase of Al3+ in the soil solution. To examine this problem, a study was undertaken to discover the cause of crop damage in crops planted over buried anode bars. Anode bars ar e part of an impressed current cathodic protection system for pipeline s near Decatur, Illinois. Soil samples were collected from the problem site and from a non-problem site for comparison. Results showed that Fe oxidation around anode bars at the problem site is stimulated by el ectric current, a situation that results in high concentrations of Hand reduces soil pH to less than 3.0. Under the low pH condition, the content of available Al is very high, and, therefore, the soil solutio n becomes toxic for soybean roots. Exchangeable Al was 360 to 700 ppm in soil immediately adjacent to anode bars but only 3 ppm in the soil midway between anode bars. The damage to the plants, such as reduced v egetative growth and lowered seed yield, developed in a circular patte rn over the anode bars. Factors contributing to the problem were soil Fe content, rectifier voltage, and soil drainage.