Manganese (Mn)

Manganese is included in the Standard Soil Test. Manganese deficiency is most likely to occur in soybean, peanut, oat, wheat, and cotton grown on soils in Soil Groups 1, 2 and 3 in Area 5 and on some poorly drained soils in Area 4 when the soil pH is high (>6.0 or 6.5, depending on soil type).

Soil factors that contribute to manganese deficiency are:
• waterlogged conditions occurring during a portion of the crop year
• poorly drained soils, natively low in manganese
• when the soil pH is high (>6.0 or 6.5, depending on soil type)

Manganese deficiency can be corrected by either soil or foliar applications of manganese. For soybeans, 15 to 75 pounds manganese sulfate (MnSO4.H2O – 26 to 28% manganese) or its equivalent per acre is recommended for optimum yield when the soil pH is greater than 6.4. However on high pH soils (>7.0), correcting a manganese deficiency by a soil manganese application may not correct the deficiency since most of the applied manganese will most likely be converted to an unavailable form in such soils. For soybean, the best way to correct a manganese deficiency is to apply 1 pound manganese per acre as MnSO4.4H2O as a foliar spray, making two applications during the growing season.

Rotating a crop of soybeans with corn may lower the soil pH sufficiently to prevent a manganese deficiency from occurring in the following soybean crop. Another effective way to correct a marginal manganese deficiency is to row apply a phosphorus-containing fertilizer at planting. If a manganese deficiency is suspected, both plant tissue and soil samples should be collected for analysis to confirm the deficiency.
Manganese toxicity is not likely to occur on most soils except those that are extremely acidic when the soil pH is less than 5.0. In general, those crops sensitive to manganese deficiency are likely to be sensitive to high levels of soil-available manganese. High soil test manganese levels are easily decreased by bringing the soil pH to the level recommended for the crop. Manganese exists in the soil solution as the manganeous (Mn2+) cation. Other valance states may also exist under varying soil physical and chemical conditions.