An over-riding factor in all of this is that the roots have to reach the manganese to absorb it from the soil. Wet soils, cool weather, soil compaction, root diseases, nitrogen deficiency and herbicide damage can all limit root growth. In this situation, the plant may not be able to absorb enough manganese to fill all of its needs even though there is adequate manganese in the soil. These plants will usually grow out of the deficiency once the weather warms up, and the roots get going again. Foliar applications of manganese are preferred to correct a deficiency, both because it avoids tie up in the soil, and because very small amounts of the nutrient are needed.
Chelated manganese is much easier to use, but much more expensive.
Very low rates of chelated product are not effective. Soil applied manganese is not effective because the mineral gets tied up in unavailable forms. Adding Mn to the soil simply increases the amount of unavailable Mn. There is some suggestion that on some of the acid sandy soils, which have very low manganese content, that adding slag containing Mn can help overcome a Mn deficiency. This makes sense, for that particular situation, but there have been no trials to confirm this.