Manganese Toxicity of Potatoes in Relation to Strong Soil Acidity

Abstract

A stem streak necrosis occurs quite commonly in potatoes grown on northern Wisconsin soils more acid than pH 5.0. This necrosis appears as dark brown streaks in the stem with a pale yellow chlorosis in the leaves. As the symptoms progress, the leaves dry and fall of. The affected parts are very brittle and the terminal bud becomes necrotic in severe cases. The plant dies prematurely and tuber yields are seriously reduced. Greenhouse tests with soils showed that fertilizers which lowered the pH of the soil increased the severity of the necrosis, and that it was entirely prevented by the addition of lime. Nutrient solution experiments proved that neither acidity, soluble aluminum, or a deficiency of calcium, magnesium, or iron is the cause of this necrosis, but did show that as little as 2 ppm of soluble manganese in nutrient solutions causes severe necrosis identical to that observed in potatoes in the field, while only trace amounts of manganese were found in the solutions from the same soils after they had been limed in the field. Therefore, it is concluded that an excess of soluble manganese is the soil factor which causes stem streak necrosis in potatoes grown on verymore » acid soils. The application of lime so regulated as to maintain a soil reaction of pH 5.0 to 5.3 is the most practical means of preventing this necrosis.« less