Douglas D. Malo1, Cindy L.
Piearson2, Cheryl L. Reese3
INTRODUCTION
Soils in South
Dakota (SD) may be thick or thin, stony or not stony, saline or non-saline,
sandy, clayey, or have medium texture.
The
unique combinations of soil forming factors in South Dakota give rise to
more than 560 different soils. A soil’s characteristics influence suitability
for various uses. When a state depends heavily upon agriculture for its
livelihood, soil management becomes an especially important matter. Soil
management depends upon a person’s knowledge of the soil's characteristics
and qualities.
South Dakota
is an agricultural state with an area of 77,047 square miles and a population
density of nine persons per square mile. In 1998 cash receipts, excluding
government payments, from farming and ranching totaled more than $3.5 billion
with 45% of the total coming from livestock and livestock product sales
and 55% of the total coming directly from crop sales.
In
1999, SD ranked nationally in agricultural production as follows: 2nd in
flaxseed, grass hay, alfalfa hay, and sunflowers; 3rd in proso
millet; 4th in oats, rye and spring wheat; 5th durum wheat; 7th in all
other hay and in all wheat; 8th in soybeans; 9th in corn and
winter wheat; 12th in grain sorghum; 15th in barley;
19th in potatoes; and 21st in cash receipts from crops. These
crops and their products, along with forage, range and pasture grown in
the state, provide feed for large numbers of livestock. This production
is possible because SD has large areas of productive soils. However,
not all soils are highly productive. The
productivity of a soil is a function of climate, biological organism activity,
parent material, topography and time.
These
five factors interact to produce the soil.
Climate: South
Dakota is located in nearly the center of the North American continent.
Because
of SD’s inland position, the climate varies with extremes of summer heat,
winter cold, and rapid fluctuations of temperature. Annual
precipitation ranges from 26 inches in the southeast to less than 14 inches
in the northwest. Most precipitation is in spring and early summer. Approximately
75% of the total annual precipitation falls when temperatures are ideal
for plant growth. Seasonal snowfall averages about 30 to 50 inches in the
lower elevations of the State to over 100 inches in the Black Hills.
The
average frost penetration depth ranges from 25 inches in southwestern SD
to 50 inches in northeastern SD. Frost
depth depends on amount of residue cover, soil moisture content, soil color,
and, to a large degree, on amount and timing of snowfalls relative to temperature
extremes.
The
prevailing wind during cold seasons is from the northwest, and is from
the southeast during warm seasons. Annual average surface wind velocity
is 10 to 12 miles per hour.
Biological
organisms: Climate
controls the distribution of vegetation.
Together
climate and biological organisms often are called the "active factors"
of soil formation.
The
native vegetation of SD was originally grassland.
Exceptions
include the Black Hills that was forest and the river valleys were trees
occurred. The tall grass prairie
ranged from the eastern SD border to the eastern edge of the James River
Valley. The principal vegetative
were grasses of big bluestem, sand dropseed, and switchgrass and upland
and lowland forbs.
Moving
westward across the James River Valley, medium and short grasses assumed
dominance throughout central SD. Important
species of this area were needle and thread, green needle grass, western wheatgrass,
slender wheatgrass, blue grama, prairie June grass, and buffalo grass.
In
western SD, shorter grasses largely replaced medium grass species, because
of decreased rainfall. Important
grass species in western SD included blue grama, western wheatgrass, needle and thread,
prairie June grass, and little bluestem.
The
flora (plant) and fauna (animal) life that occurs in the soil also affects
soil formation. Decayed plant roots
from previous years growth can provide channels for water and air to move
through the soil profile. Earthworms
also create channels for water and air movement through soil.
Earthworms
literally eat their way through soil and form burrows as they move through
the soil. These burrows also allow
water and air to move through the profile.
Earthworms
also enhance soil fertility and productivity by altering physical and chemical
conditions in soils. For example,
mineral availability to plants is increased when soil is passed through
an earthworm’s digestive tract.
Soil
microorganisms also affect soil structure. Microorganisms
can break down decayed plant material and add organic compounds to the
soil structure. Other microorganisms
can take elemental nitrogen (N) gas from the air and ‘fix’ or change the
N into a form that can be used by plants.
Parent
material: Parent
material is the inorganic material from which the soil was derived. In
eastern SD, the parent material for most soils resulted from glacier activity
that occurred during the Pleistocene Epoch (1.8 million to 11,000 years
ago).The Pleistocene Epoch witnessed
a continued cooling, culminating in a series of ice ages.
Glaciers
entered SD from the northeast or north and flowed south and west. The
western margin of glaciations was the Missouri River. Today, glacial deposits
cover most of SD east of the Missouri River. West of the Missouri River,
the soil parent material is primarily sedimentary rock.
Soil
west of the Missouri River was derived primarily from sedimentary rock.
Eastern SD
contains many productive soils that were derived from glacial deposits. Glacial
deposits are divided physically into main four groups:
1.Till;
2.Outwash;
3.Glacial
lake deposits;
4.Ice
contact stratified drift.
Till: Glacial
till deposits are a mixture of all sized particles, boulders to clay.
Till is thought to have been deposited the flowing ice shield.
Outwash: Glacial
outwash consists mostly of gravel and sand. Outwash
was deposited by glacial melt water as it flowed away from the ice.
Glacial
lake deposits: When
the ice front movement slowed to almost a standstill, there was no ready
escape for water and ponding occurred.
Soil
deposits formed in lake deposits are called lacustrine. The
lacustrine deposits that occurred from these lakes range from sand deposits
near old shorelines to deposits of clay and silt materials from the deeper
more still waters in the center of the lake.
The
deposits in the Red River Valley along the North Dakota and Minnesota state
borders were formed from material settling out of Glacial Lake Agassiz. The
deposits in most of Brown and part of Spink counties in SD were formed
in sediments from Glacial Lake Dakota. These
deposits usually produce soils with high fertility and somewhat poor drainage.
Ice
contact stratified drift: Undifferentiated
sediments deposited by glaciers is called drift.
Ice
contact stratified drift was formed when a glacier was melting. These
deposits occur as knobs or small hills often in rough terrain.
These
deposits are called kames which are short, steep sided hills and eskers
which are serpentine-shaped ridges.
Soils
may form from actions other than glaciers as well. Factors
that can carry and deposit soil from one place to another include the wind,
waterways and gravity. Loess
is a deposit of wind blown silt. Sandy and clay materials may also be carried
and deposited by the wind, Eolian sand and Eolian clay, respectively.
They also are important SD soil parent materials.
Alluvium
is a deposit that occurs when gravel, sand, silt, and/or clay, settle out
of flowing water. Generally, alluvial deposits west of the Missouri River
have a clayey texture while deposits east of the Missouri River are have
a loam texture. Local alluvium is a water-laid deposit along upland swales
and depressions. It is usually finer textured than surrounding soils.
Colluvium
is a deposit of rock fragments and unconsolidated earth materials accumulated
at the base of slopes as a result of gravity and runoff. The deposit is
usually unsorted because gravity can move all sizes. The soils can have
textures ranging from sands to extremely bouldery clay.
A
variety of factors created the landscape that occurs in SD today. Up-lifting
and warping in the west created the Black Eolian
Hills and wind and water erosion
created the badlands and buttes. Glacier
movement formed coteaus (low hills or divides) and plains in the east. The
rocks and soils that make up these regions provide a wealth of resources
upon which life in the state is based.
Topography and Time:
Topography
refers to the lay-of-the-land. The land may be level, undulating, rolling,
hilly, rough broken, or mountainous. It may be smooth with a network of
small streams, or it may be choppy with many closed basins dotting the
landscape.
Topography
determines what drainage a soil will have. Steep slopes have excessively
drained, thin soils; flat or depressed topographic areas usually have poorly
drained, thick soils.The
factor of time (the age of soil stability) can be illustrated by comparing
a soil on a flood plain that receives annual deposits of alluvium with
a soil on a stable upland ridge. The floodplain soil has few developed
horizons, while the soil on the stable upland ridge has a well-developed
soil profile with many horizons.
For additional information on geology in South Dakota, this website may be helpful: http://www.sdgs.usd.edu/geologyofsd/geosd.html
Author Information:
1
Distinguished Professor, South Dakota State University, Brookings, SD
2
6th grade science teacher, Mickelson Middle School, Brookings, SD, South
Dakota State University, Brookings, SD
3
Research Associate, South Dakota State University, Brookings, SD
Funding provided by: North
Central Soybean Board, South Dakota Corn Utilization Council, South Dakota
Soybean Research and Promotion Council, EPA, USDA-IPM, and South Dakota
State University Experiment Station.