Association of manganese effluent with the application of fertilizer and manure on tea field.

Manganese (Mn) concentrations in the tea field effluent were 1.1-3.5 mg/l over a 2 year period from June 1997 to May 1998 (first water year) and June 1998 to May 1999 (second water year). The annual Mn loads were 38,000 g/ha in the first water year and 19,000 g/ha in the second. The highest Mn loads were observed, respectively, in July 1997 (10,000 g/ha) in the first water year and in June 1998 (4100 g/ha) in the second. The water-soluble Mn content of soil of the tea field increased abruptly with decreasing soil pH in the pH region below 4.5. The large Mn load from the tea field during the rainy season is likely due to application of excess fertilizer and manure before the rainy season, which may lead to acidification of the soil.