Soil in Virginia

healthy farm soil has a high percentage of carbon and a structure that allows for water to flow around roots
Source: Chesapeake Bay Program, Midway Farms in Richmond County, Virginia

Soil develops over time from bedrock and organic material, in a process known as pedogenesis.

Minerals in the geologic material closest to the surface can change as they are exposed to less heat and pressure. Fresh and salt water, ice, carbon from decaying plants and animals, various chemicals from organic material, roots, earthworms, and other living creatures gradually affect the bedrock and transform it over time. Different types of soils evolve under different conditions, and from different source minerals.

Physical disaggregation of molecules and chemical decomposition slowly weather the original minerals into different forms. Bedrock with silica-rich minerals, such as quartz and feldspars, carbonates, and iron oxides can decompose into clays and affect the structure and water-holding capacity of a soil. Soil scientists classify soils by different characteristics, using a taxonomy of terms such as "hapludult" and "podzol" that are comparable to the way botanists classify plants.

A soil scientist at Virginia Tech won the individual competition in an international soil judging contest at the 2022 World Congress of Soil Science. In an interview with the Science Friday host, Clare Tallamy described the difference between soil and dirt:¹

...soil is an in-situ kind of blanket that covers the Earth. It has to be connected to the outer environment and be affected by soil-forming factors like climate, water tables, organisms, all those things that make soil different across the landscape. And then it also has to be in place long enough to experience pedogenic development, or kind of soil development, and so that's not just geologic deposits creating layers. That's actual movement of secondary particles through time, so thinking about clay moving through soil with time, humus moving through soil with time. So it has to have those soil layers not necessarily geologic layers. People can argue that it has to support plant life as well, but...

Dirt could be anything, I feel like. Dirt could be rock. Dirt could be like schmutz on your face after being in the field. It's kind of like soil but not in the context of the environment. So like potting soil isn't soil. Potting soil is just in a vessel, and it's not really connected. So that would be dirt.

marl and oyster beds rich in lime were key to soil fertility projects in the mid-1800's
Source: Northeastern University, Travels into North America (by Peter Kalm, 1770, p.97)

Geotechnical engineers measure the ability of soil to support heavy structures and traffic on roads. Artists creating pottery care about the percentage of clay vs. other impurities in a soil. Farmers care about the ability of soils to grow crops, including the amount of organic material that can provide nutrients and store rainwater:²

In Virginia, the typical organic matter level of ordinary, well-drained soil is from 0.5% to 2.5%. A soil with organic matter greater than 3% would be considered very high for a cultivated field. Due to relatively large amounts of organic materials being commonly added to our gardens, the organic matter in garden soils can be raised into the range of 5% to 10%.

prime farmland in Virginia
Source: Virginia's Land and Energy Navigator (VALEN)

Soil rich in organic material stores rainfall. Since the water table is below the level of plant roots, if there is no rain for 10 days then roots experience drought stress.

A 1% increase in organic matter can store an extra inch of rainwater. Crops on agricultural fields consume a quarter of an inch of water daily during the growing season, so farmers who can increase the organic percentage in their soil can gain extra productivity as plants continue to grow steadily during long gaps between rainstorms.³

Source: Virginia Exension, Common soil types in different regions of Virginia (January 12, 2015)

Links

• Forbes
• Meet The Amazing Fungus That Farms Bacteria (February 27, 2019)
• US Department of Agriculture
• Agricultural Research Service
• About the Universal Soil Loss Equation
• Virginia Cooperative Extension
• 4theSoil
• Common soil types in different regions of Virginia
• Virginia Soil Health Coalition
• Videos and Movies

dirt roads were replaced by paved roads, with impervious asphalt/concrete surfaces that prevented the underlying soil from becoming wet slippery mud
Source: National Archives, Washington-Richmond Road Near Quantico (1919) and Short Turn With Five Loaded Scrapers (1929)

References