On the soil:

The Mn present in the soil, at average concentrations between 200 and 3000 ppm, is subject to oxidation and reduction processes depending on the chemical and structural complexity of it.

In general terms, the most favorable conditions for the formation of Mn 2+ occurs under acidic pH conditions and under reducing conditions, this is where the solubility and the potential for root absorption increases. The presence of organic matter for the formation of Mn complexes is also important.

The chelating potential is lower than with other metals such as Cu or Zn. It is worth mentioning that the concentration of Mn2 + is important for the stability of the chelates formed in the soil with Mn.

For a greater solubility of the soil its reducing conditions will favor solubility and so the following should be considered:

• The amount of water: note that the conditions of water saturation (undesirable from the agricultural point of view) are those that achieve the most reduction conditions and therefore, can cause high levels of assimilation of Mn that confers toxicity to the plants.
• The pH: acidic conditions are more favorable; around 6.5.
• Organic matter content: High amounts of organic matter can impair the solubility of Mn by forming stable complexes.
• Microbial activity: as oxidizing agents of Mn.

In the plant:

Note that in terms of interactions with other elements the presence of Mg decreases the absorption of Mn; and that the presence of Mn can decrease the absorption of Fe.

Although it is true that a preference of the citrate anion is not found to form metallic bonds with Mn, its transport to the meristematic tissues is preferential, making young plants normally rich in Mn.