Soil has a storyThe world’s oldest soils are found in Africa and Australia and date back more than 50 million years. These soils are highly weathered and are in regions we now classify as deserts.
By: Kristine Larson, Agweek
The world’s oldest soils are found in Africa and Australia and date back more than 50 million years. These soils are highly weathered and are in regions we now classify as deserts.
According to the University of Minnesota, the Sierra Nevada Mountains and deserts of the Southwest are the oldest soils in the United States at roughly 750,000 years old. All of these soils have managed to stay undisturbed by humans, glaciers, or other catastrophic events. So what exactly is soil? How did it get here?
The process of soil formation is called pedogenesis. Soil is formed under five factors: climate, organisms, relief, parent material and time. Parent material is the building block upon which soil is formed.
This factor determines the minerals and is the basis of soil textures such as sand, silt and clay. Climate is an active factor that is always changing and involves such things as temperatures and precipitation. Organisms include everything from the bacteria, fungi, protozoa and vegetation that can live in a soil. Relief is the topography in which the soil is formed. Time determines the period during which soil is formed, and timezero is the exact moment a soil begins its formation. These five factors create the stable yet continually changing resource we know as soil.
Soil itself is made up of four components: water, oxygen, minerals and organic matter. Sound familiar? This is exactly what comprises our own bodies. If one of these parts is missing, it can no longer function as soil. Parent material gets broken down by weathering caused by climate and by organisms. Pore spaces eventually allow for water and oxygen to move through the profile.
Vegetation provides a shield over the surface of the soil, as well as a food source to the organisms living underneath. Roots can extend feet below the surface, creating more channels as they die off. The biology in the soil helps break down the decaying vegetation, which adds to the organic matter of the soil.
Organic matter holds nutrients that can later be released to the plants as they need them. It also increases water holding capacity, acting as a sponge that can store up to 90 percent of its weight in water for later plant use.
Living plants provide habitat for such organisms as mycorrhizal fungi, which in turn, produce glomalin. Glomalin is nature’s glue. This protein contains 30 to 40 percent carbon and binds to soil particles. Aggregate formation occurs when this binding takes place and helps form the structure of soil while also contributing organic matter.
The process of soil formation takes years. Under perfect conditions, it is estimated that 1 foot of soil forms every 100 years. It takes only seconds to destroy it, leading us back to timezero. According to the 2007 National Resources Inventory, North Dakota alone lost 6.6 tons per acre per year by erosion.
One acre of soil 1 foot deep weighs, on average, 1,699 tons. The 6.6 tons per acre per year don’t sound like a whole lot, but let’s look at that over a 100-year span. At continued trends, we will have lost 660 tons per acre in that time.
Soil is a living system. It is continually changing, and its structure, color and smell tell the story of its aging life. It holds history that has been shared around the world and secrets yet to be discovered.
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Editor’s note: Larson is the watershed coordinator for the Grand Forks County (N.D.) Soil Conservation District.