Some places have rich, loamy, fertile soil that can grow almost anything; some places have hard, clay-filled dirt that roots have to struggle to break through; some places have barely any dirt and are mostly exposed rock. What drives this difference? Is it possible to look at a place’s geography and predict its soil type?
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Soil type is defined by something scientists call ClORPT (Climate, Organisms, Relief, Parent material, Time).
Climate: More precipitation means more water moving through the soil. Water deposits minerals which make the soil more fertile. Temperature affects how fast that water evaporates which determines how dry the soil will be. Both of these together help make it easier for things to grow in certain areas.
Organisms: Of course, if plants grow, then herbivores will be attracted to the area and carnivores will follow the herbivores. More animals in the area means more organic compounds and, when those animals poop or die, those compounds are then sitting on top of the soil. In addition to water pulling things down further into the soil, animals help these compounds integrate with the soil through movement. Digging, clawing, running, etc all move the soil around which helps all of the stuff at the top get mixed in. Especially smaller animals like worms are a huge factor in soil composition.
Relief: The terrain affects where soil builds up which affects how deep it is and much it can absorb. Soil will naturally be deeper at the bottom of a hill than at the top due to erosion.
Parent material: Soil forms in different ways. Some soil is formed directly from eroded bedrock. Some soil is the result of materials brought into an area by wind, rivers, glaciers, gravity, etc. Where the materials come from determines what the base of the soil is and how it will develop in the future.
Time: Soil forming over bedrock will take longer to form because the bedrock has to erode into soil-sized particles. Soil deposited by wind will already be smaller and so will grow plants faster. Younger soils tend to be more shallow. Depending on the ecosystem, old soil can sometimes be less fertile because all the nutrients have been used by plants and animals and then deposited somewhere else.
All of these things work in tandem to determine what a certain area’s soil will be like.
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