In what condition do iron and manganese solubility increase in soil?

Iron and manganese solubility in soil is significantly increased under flooded conditions. When soils are flooded, the anaerobic environment reduces the oxidation of iron and manganese oxides, making these nutrients more soluble. This increased solubility is due to the chemical reduction processes that occur in waterlogged conditions, where ferrous iron (Fe²⁺) and manganese (Mn²⁺) ions are formed, allowing for better availability to plants.

In contrast, dry soils tend to have higher oxidation levels, which can lead to precipitation of iron and manganese, decreasing their solubility. Heavily fertilized soils might influence nutrient levels, but they don't have the same immediate effect on the solubility of iron and manganese as flooding does. Similarly, compact soils could restrict aeration and water movement, but they do not inherently alter the chemical dynamics to promote solubility like flooding does. Therefore, the flooding condition is crucial for enhancing the availability of these micronutrients.