Abstract
Haplic and umbric andosols soils were treated in the field with different types of fertilizer and methods of application in an effort to improve field suppression of common scab of potato caused by Streptomyces scabies. Scab severity index of the plot treated with aluminum sulfate was the lowest of all the plots. The exchange acidity y1 in soil was the highest of all plots during the infective stage of common scab of potato. On the other hand, when only ammonium sulfate was fertilized to the rows, and phosphate and potassium were broadcasted to surface soil (fertilization amelioration plot), the ratio of tubers in the serious scab severity class significantly decreased. The electrical conductivity of the soil solution around the potato tuber in the fertilization amelioration plot was lower than that in the plots fertilized with nitrogen, phosphate and potassium to the row during the infective stage of common scab of potato. Aluminum ion activity in the fertilization amelioration plot is higher than in the plots fertilized with nitrogen, phosphate and potassium to the row. Common scab of potato in fields with haplic andosols soil treated with fertilization amelioration was controlled more effectively than in umbric andosols soil. The electrical conductivity of the haplic andosols was lower than that of the umbric andosols, although the concentration of soluble aluminum ions on the haplic andosols was lower than that in the umbric andosols. Common scab of potato may be suppressed by a low concentration of soluble aluminum when electrical conductivity of the soil solution around the potato tubers is low because activities of aluminumions remain high.
