The mineral and nutrient components of soil are important for the classification of soil types. Iron-rich soils are so named for their high content of iron mineral deposits, and their nutrient composition impacts their ability to be cultivated to support plant life. Understanding the origins and uses of iron-rich soil will help you make decisions about planting and building with or on the ruddy clay-like soil.
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Iron-rich soil is often the result of high levels of iron deposits beneath the top layers of soil. A majority of iron deposits are formed in sedimentary rock beds beneath the Earth's surface, called banded iron formations. Another source of iron-rich soil is magma flow from erupted volcanoes. The liquid magma contains high levels of magnetite phenocrysts that harden over time into magnetite iron. The high iron levels mix with other nutrients and organic materials in the soil to create an iron-rich top soil or clay.
The most distinctive characteristic of an iron-rich soil is a ruddy orange or red color, though not all red soils are rich in iron. When the iron deposits in the soil oxidize, they turn a distinctive rust color that tints the soil red. The texture of iron-rich soils ranges from soft sand to hard, compact clay depending on the ratio of iron deposits to other nutrients, minerals and organic materials in the soil mixture. Because other factors like high levels of sediment or low levels of rainfall can make a soil appear red or orange, soil testing is the only definitive way to determine whether or not red soil is iron-rich.
Iron-rich soils are found all over the world. The Mojave Desert contains high levels of iron deposits that are mined for commercial use. Areas with frequent volcanic eruptions like the Hawaiian islands and Chile also are home to iron-rich soils as the result of hardened iron-depositing magma. Climates that are humid and warm tend to have higher instances of red soil rich in iron. Terra rossa is an Italian term for the orange-red soils found in Mediterranean countries ranging from Italy to Israel. India and Australia also feature a wide variety of types of iron-rich soil, from soft sand to the denser clay soils that are unsuitable for gardening but ideal for ceramics and pottery.
Implications for Planting
Iron is an essential plant nutrient as it serves as one of the main catalysts for a plant's production of chlorophyll, but high levels of iron in soil reduce the levels of other necessary soil elements. When iron levels are too high, organic matter that sustains plant life is reduced and the soils is unsuitable for most crops. Though some plants and trees like the Joshua tree, fruit-bearing trees, huckleberry and black-eyed Susan can withstand high levels of iron, treating iron-rich soil with a fertilizer with high organic content combats the red soil's lack of nutrients. Adding a top layer of more sustaining soil also is an option if you wish to plant in iron-rich soil.