Plants growing on soils with a high content of exchangeable Mn accumulate large amounts of Mn in their tissues and growth is reduced. Liming these soils to pH 5.5 and above decrease the solubility of Mn and uptake of Mn sufficiently to eliminate the toxicity and increase growth. This table shows the effect of soil pH on soluble manganese and soybean yield. Hiwassee loam soil from blue-ridge province. Leaves show marginal chlorosis, curling, and necrotic spots Soybean Leaves are crinkled and cup down.
Youngest leaves show first symptoms.
Leaves die and hang from the stem. Necrotic streaking develops on the main stem. At these low levels of available Ca, the uptake may also be inhibited by Al. A lthough it is often difficult to separate the direct effects of H and Al from those of Ca on plant growth, a number of points can be made about Ca in highly weathered soils. Growth may not be maximum at this Ca saturation because some other factor is limiting yield.