Stop Treating Topsoil Like Dirt

By Mary Ellen Connelly
Reprinted with permission.

Topsoil is directly responsible for a beautiful Sioux Falls.  Topsoil is the Minnehaha County’s most important natural resource, as valuable to eastern South Dakota as gold is to the western part of our state.

Topsoil (the top layer of dark-colored soil) has been endowed to the prairie by the decomposition of native plants over thousands of years. In glaciated regions like eastern South Dakota, it took 500 years of native plant growth and decomposition to make one inch of topsoil.

On still-existing beautiful and diverse native prairies, the dark, humus-rich topsoil depths vary – thinner at tops and slopes of hills and deeper in scoops of valleys.  The average topsoil depth in Minnehaha County is 14-16 inches.  (PHOTO of soil profiles from land judging school)

Stripping and stockpiling of topsoil since the approximate decades of the 1960s and 70s have purposely reduced the volumes of topsoil on most Sioux Falls’ real estate developments, even in the most upscale neighborhoods.

Giant loaf-like mounds of it, sometimes behind locked gates, can be observed adjacent to every new development.

(PHOTO of strip-mined pile of topsoil: Contemplate thousands of growing seasons piled up in loaf-like mounds next to every housing development PHOTO:  some piles are under lock and key)

Topsoil has been made thinner as it radiates from the pre 1960s parts of the city.  Older neighborhoods often have many inches of topsoil, two or more feet in some areas.  Newer neighborhoods usually have less than three inches.

On today’s urban sites, topsoil quantity and quality are not prioritized, and subsoil, often highly alkaline, is compacted to a hardness that is near-impenetrable to water and air. On these sites, significant natural precipitation ends up in the guzzling, gaping storm sewers that have no use for it except to send it away, downstream to the Gulf of Mexico.

On cropland, maintaining and improving quantity and quality of topsoil are prioritized in order to achieve best yield and so soil can seize and soak up rainfall and snowmelt like a sponge.

Deep roots act as conduits for water and air infiltration.  So do earthworms.  Some native plants, still found on pastureland and protected native prairies, root to fifteen feet.  On cropland, soybeans might root down four feet; corn, five feet; and alfalfa, twelve feet.

Natural topsoil depths are reservoirs that store natural precipitation.   Deep prairie roots are conduits, like straws, that allow rain and snow melt to percolate down and recharge groundwater and store up in soil reservoirs.