What can be inferred if significant iron or manganese nodules are present in a soil sample?

The presence of significant iron or manganese nodules in a soil sample indicates that the soil experiences periodic saturation. These nodules typically form in anaerobic conditions, where the soil becomes waterlogged for certain periods, restricting oxygen flow and leading to chemical reactions that precipitate iron and manganese.

When soils are saturated, the limited oxygen also promotes the reduction of iron and manganese oxides, which can then concentrate into these nodules. Thus, their presence reflects a history of fluctuating moisture levels within the soil, suggesting that while the soil may not always be saturated, it does experience periods of saturation that allow for these nodules to develop. This characteristic is essential for understanding soil drainage and hydrology, influencing agricultural practices and land use decisions.