Manganese Sulfate — Frequently Asked Questions

By which leaves are affected. Both produce interveinal chlorosis, but magnesium is mobile within the plant and is withdrawn from old leaves to supply new growth, so its symptoms appear on the oldest leaves first. Manganese is immobile, so deficiency shows on the youngest leaves while older foliage stays green. That distinction determines which correction is needed.

Because manganese availability falls sharply as pH rises above about 6.5. The total manganese in the soil may be perfectly adequate, but at high pH it converts to oxides that plants cannot take up. Over-liming is therefore a common cause of induced manganese deficiency, and correction is usually by foliar application rather than by trying to change soil pH.

It is a cofactor in the oxygen-evolving complex of photosystem II, the site at which plants split water to release oxygen during photosynthesis. A deficient plant cannot photosynthesise efficiently regardless of how much chlorophyll it has, which is why yield effects can be significant even where visible symptoms are mild.

The monohydrate is the most widely traded form and the anhydrous salt is also available. As with all hydrated sulfates, the hydration state determines the manganese content per tonne and should be specified, since dosing and cost comparisons depend on the actual manganese delivered rather than on gross weight.