Iowa Soil Associations

Soil is Iowa’s greatest natural resource. However, there are many diff erent soils in Iowa, Loess with Bedrock Outcrops Loess, Shale, and Glacial Till each possessing a unique set of properties. 8 Downs – Fayette – Nordness Soils 16 Pershing – Gosport – Gara Soils The enclosed map does not attempt to show all of the soils in Iowa. Rather it shows the This region is commonly incorrectly referred to as the “Driftless Area” because it This region consists of gently sloping to strongly sloping soils that formed in geographic areas where major soil groups occur. These soil groups are called soil associa- suggests that this area was never glaciated. However, soil scientists and geologists have loess and strongly sloping to steep soils that formed in shale and glacial till. Pershing, tions, and the map is called a soil association map. A soil association is a group of soils that documented evidence of glacial deposits scattered throughout the area. Scenic land- Gosport, and Gara are the major soil in this region. These soils are gently sloping and mod- are closely associated geographically and occur in a characteristic pattern. More informa- scapes with deep valleys, abundant rock outcrops, high bluff s, caves, crevices, sinkholes erately sloping. They formed in loess under mixed prairie grasses and trees. Gosport soils tion about soil associations is available on the Iowa NRCS web site at and an angular stepped skyline occur in this area. Along many of the steepest slopes, bare formed in residuum from shale under forest vegetation and occupy the steepest parts of www.ia.nrcs.usda.gov/soils.html. More detailed information about soils is available online limestone forms rock outcrops. Often valleys take abrupt, sharp-angled turns indicating the slopes. Gara soils are on strongly sloping to steep convex side slopes. They formed in through the U.S. Web Soil Survey at http://websoilsurvey.nrcs.usda.gov/app/. the local drainage network is controlled by joint patterns in the underlying bedrock. glacial till under mixed prairie grasses and trees. Nearly all this area is in farms, but only about one-half is cropland. Feed grains and forage The steeper areas of this region are used mostly for hay, pasture, and woodland. The gently This brochure is a cooperative eff ort between the Iowa Department of Agriculture and for dairy cattle and other livestock are principal crops. Native vegetation of the upland sloping soils are used for row crops. Land Stewardship, Iowa Department of Transportation, United States Department of soils is hardwood forest. Agriculture’s Natural Resources Conservation Service and Iowa State University Extension. Fun Fact: Fossils dating back 300 million years from extinct marine animals identifi ed Fun Fact: The types of bedrock found in this region have resulted in the formation of as ‘conodonts’ are common in the shales of this region . many sinkholes, springs, and caves. 1 Loess over glacial till – low rainfall Moody - Trent Soils Shallow Loess over Glacial Till Loess Ridges/Glacial Till – SE Iowa These soils formed in a mantle of loess and occur in the far northwest corner of 9 Dinsdale – Klinger Soils 17 Otley – Ladoga Soils the state. This area is considered the driest part of Iowa. Moisture is limited, but is usually present when conditions are suitable for plant growth. The landscape consists of gently The characteristic landscape of this region is wide, gently sloping, convex This region consists of soils developed in loess on broad, convex ridgetops and undulating to steep soils with long smooth slopes and well defi ned drainage ways. The ridgetops and moderately sloping side slopes. The upland soils in this region formed in a upper side slopes. Soils developed in glacial till soils dominate the steeper side slopes. The hills have broad undulating to rolling ridgetops and hilly to steep valley sides. The valleys thin mantle of loess and the underlying glacial till. side slopes are dissected with many drainage ways and small streams. A few large rivers have nearly level and broad valley fl oors. generally are narrow, but the major rivers and other large tributaries have broad fl ood Nearly all of this area is in cropland. Corn and soybeans are the major crops. Many of the plains and terraces. wet soils require artifi cial drainage for timely fi eld operations and good crop growth. Na- Otley and Ladoga formed in loess and contain 35 to 42 percent clay in the subsoil. Gara Nearly all of this area is farmed. Corn and soybeans are the major crops. Feed grains and tive vegetation is mixed tall and short grass prairie. soils formed in glacial till and contain 30 to 35 percent clay in the subsoil. Native vegeta- hay crops are also widely grown. Native vegetation was mixed tall and short grass prairie tion of Otley soil is tall grass prairie. Ladoga and Gara soils developed under mixed prairie Fun Fact: More than 2 billion bushels of corn are produced annually on rich Iowa soils, grasses and deciduous forest. Fun Fact: This area receives the least precipitation at an average of 26 inches. The such as those found in this region. overall State precipitation average is 34 inches. Most of this region in farmed, with about 70 percent in cropland. Common crops are corn and soybeans, with some hay. Swine and cattle operations are common. Loess Ridges and Sideslopes Fun Fact: European settlement occurred in this region as early as the 1830s along the Northwest Iowa Loess 10 Tama – Muscatine - Downs Soils region’s many rivers, which provided a source of fresh water. 2 Galva – Primghar Soils This region consists of nearly level to steep soils that formed in loess. The side Most of the soils of this region formed in loess. Most slopes are nearly level and slopes typically have many drainageways. gently sloping but some slopes bordering major stream valleys are steep. A few large riv- Eolian Sand Tama and Muscatine soils formed under tall prairie grasses, and Downs soils, which typi- 18 Sparta – Chelsea – Dickinson Soils ers have nearly level and broad valley fl oors and stream terraces. cally are located on steeper slopes along the major river systems, formed under a mix Nearly all of this region is cultivated. Corn and soybeans are the principal crops. Native of deciduous trees and tall grass prairie. Nearly all of this region is cultivated. Corn and This region consists of well-drained and excessively-drained soils that formed vegetation varied between tallgrass prairie vegetation on moist soils to short grass vegeta- soybeans are the principal crops. Some of the steeper areas are used for hay and pasture from windblown sandy and loamy parent material. These soils occur on high stream tion on slopes and uplands. Timber made up less than 1 percent of the area. or remain in timber. benches and upland side slopes, mainly along the bluff s and breaks of the major rivers. Fun Fact: Prehistoric fossils found in this area include crocodiles, large turtles, and Fun Fact: The Muscatine Soil is rated as the top crop-producing soil in Iowa. Most of the soils in this area are droughty and are susceptible to wind and water erosion. sharks. Flatter areas are used for cultivated crops but the steeper slopes are used for pasture, woodland, and wildlife habitat. Loess with exposures of Glacial Till Fun Fact: As glaciers melted, strong winds blew the exposed soil and formed sand Tazewell Glacial Till 11 Marshall – Shelby Soils sheets, dunes, and stringers in Iowa. 3 Everly - Wilmonton – Letri Soils This region is characterized by broad, rounded ridgetops and gently sloping to This area has soils formed in a thin mantle of loess or erosional sediments and strongly sloping side slopes with wide river valleys. Most of the soils on the ridgetops and the underlying Tazewell glacial till. The landscape consists of broad, plane and convex upper portions of the slopes in this region formed in deep loess. On the steeper portions Loess –Timbered ridges, long, convex side slopes, and concave drainageways. Slopes are nearly level to of the slopes, glacial till commonly is exposed. Nearly all of this region is cultivated. Corn 19 Fayette Soils moderately sloping. and soybeans are the principal crops. Some of the steeper areas are used for hay and pas- ture. Native vegetation is mixed tall and short grass prairie. This region consists of soils on broad to narrow, convex ridgetops, and long Nearly all of this region is cultivated. Corn and soybeans are the principal crops. Native convex side slopes. Many of these areas occur on the steeper slopes near major streams. vegetation is mixed tall and short grass prairie. Fun Fact: The native prairie vegetation resulted in soils with topsoil as thick as 20 The side slopes are dissected by numerous waterways. The landscape is undulating to very inches. steep. The dominant soil of this area, Fayette, formed in loess under native forest condi- Fun Fact: Unique wetlands called ‘fens’ are common in this region. Fens typically are tions. formed on sidehills from groundwater discharge. Fens in Iowa contain about 200 dif- ferent plant species, of which 20 are rare and endangered. Most of the less sloping areas of this region are farmed but some of the steepest areas Very Deep Loess remain in timber or are used for pasture. 12 Monona – Ida – Napier Soils Fun Fact: The native forest conditions result in an abundance of Morel mushrooms in Loamy Wisconsin Glacial Till This region has nearly level to moderately sloping ridgetops and moderately the Spring. 4 Clarion – Nicollet – Webster Soils sloping to steep side slopes. It is dissected by numerous drainageways in which gullies are common. This area is commonly referred to as the “Des Moines Lobe” of the Wisconsin-age ice sheet that covered the north central United States about 12,000 years ago. Most of this Monona and Ida soils formed in deep loess. Monona soils typically occur on the broader Alluvium area is a nearly level to gently rolling till plain. The city of Des Moines was built on the high ridges and long smooth side slopes. Ida soils typically occur on narrow ridgetops and the 20 Colo – Chequest – Titus Soils moraine at the farthest south extent of this lobe. Natural lakes dot this region and numer- steepest portion of the hill slope. Napier soils formed in local alluvium and occur in most of the narrow drainageways and on footslopes. Nearly all of this region is cultivated. Corn and Alluvial soils occur on fl oodplains along rivers and streams throughout Iowa. In ous bogs, swales and circular depressions indicate sites of previously ponded water. Much the southeastern portion of the state, the poorly drained Colo, Chequest, and Titus soils of the area is tile drained. End moraines have a banded pattern across this area and are soybeans are the principal crops. Some of the steeper areas are used for hay and pasture. Native vegetation is mixed tall and short grass prairie. make up a large portion of fl oodplain soils. Most of these soils are artifi cially drained and in typically described as knob and kettle topography. These soils formed in loamy glacial till, cropland, but some oxbow wetlands remain. Corn and soybeans are the major crops. glacial outwash, and/or local alluvium. Fun Fact: Man-made terraces cross the landscape in this region to protect these soils from gully erosion. Fun Fact: The lowest elevation in Iowa at 480 feet above sea level occurs where the Nearly all this area is cropland. Corn and soybeans are the major crops. Some cropland is Des Moines River joins the Mississippi. used for hay. Native vegetation was mixed tall and short grass prairie. Fun Fact: As the glacial ice stagnated, long ridges called moraines were formed. The Missouri River Bluff s Loess Ridges/Glacial Till Sideslopes Iowa State Capital sits atop the far Southern end of the Wisconsin glacial advance. 13 Ida – Hamburg Soils 21 Grundy – Haig – Arispe – Gara Soils This region consists of a narrow band of soils that formed in thick loess under prairie grasses in the bluff s area east of the Missouri River fl oodplain. It is characterized by This region consists of soils developed in loess on broad, convex ridgetops and Clayey Lake Deposits side slopes and glacial till on strongly sloping to steep side slopes. Grundy, Haig, and 5 Marna – Kossuth – Bode Soils narrow, rounded ridgetops; long, steep to very steep side slopes; and very deep, raw gul- lies. Arispe are the major soils on slopes of less than 9 percent. These soils typically contain 42 These soils formed in silty and clayey glacial lacustrine sediments overlying to 48 percent clay in the subsoil. Many of the side slopes that are steeper than 9 percent calcareous loamy glacial till within the Loamy Wisconsin Till area. They contain more clay These steep and very steep soils formed in deep loess. The Hamburg soils typically occur developed in glacial till. Gara is the major soils on these positions. closest to the fl oodplain and are characterized by the ‘catsteps’ formed by small earth slips and less sand than the typical soils of the Des Moines Lobe. In contrast to the Wisconsin till Nearly all of this area is farmed. Corn and soybeans are the major crops. Native vegetation plain, this area’s relief is low. Knobs of well drained soils are less common and less distinct, on the very steep slopes. Napier soils formed in local alluvium and occur in most of the narrow drainageways and on footslopes. of Grundy, Haig, and Arispe is tall grass prairie. Gara soils formed under a mix of prairie and depressions are few, shallow, and indistinct. grasses and deciduous trees. Some ridgetops and side slopes and small areas along drainageways are cultivated and Nearly all this area is cropland. Corn and soybeans are the major crops. Native vegetation is Fun Fact: Natural geologic erosion in this region has left the oldest landscape surfaces tall grass prairie. used for row crops and pasture. Most of the steeper areas are in permanent pasture or timber. at the highest elevations, while younger surfaces are cut into lower landscape posi- Fun Fact: Nearly all of Iowa’s naturally formed lakes are found in the north central tions. part of the State. Fun Fact: Landscapes similar to the loess bluff s only exist in the corresponding lati- tudes of China along the Yellow River. Loess Ridges/Clay Paleosol Iowan Erosion Surface 22 Seymour – Edina - Clarinda Soils 6 Kenyon – Clyde – Floyd Soils Missouri River Alluvium 14 Albaton – Luton – Onawa Soils This region consists of nearly level to moderately sloping soils formed in loess on This land surface is level to gently rolling with long slopes, low relief and open wide upland divides and upper side slopes, and moderately sloping to steep soils formed views. The soils in this area formed in a mantle of silty or loamy sediments and the underly- This region of the Missouri River fl oodplain is characterized as a nearly level, in glacial till or a paleosol formed in glacial till on side slopes. Seymour, Edina, and Clarinda ing glacial till. Recent alluvium consisting of clay, silt, sand, and gravel fi ll the major river broad, valley fl oor. Although once a braided river system with numerous islands and formed under prairie grasses and are the major soils. Seymour and Edina formed in loess valleys. Drainage is well established, though stream gradients are often low and a few channels, the main channel of the Missouri River was narrowed to about half of its origi- and Clarinda soils formed in a paleosol formed in glacial till. These soils typically contain areas of poor drainage or bog conditions occur. A typical feature of this area is scattered nal width, and most of the islands eliminated. The river carries large loads of sediment. more than 45 percent clay in the subsoil. Gara soils formed in glacial till under mixed prai- large boulders partially buried or lying on the surface. These erratics, composed of rock Tributary streams also carry large loads of sediment because of the erosive nature of the rie grasses and trees, and typically occur on the steepest slopes. adjacent loess mantled hills. types not found in the area are clearly of glacial origin. A few scattered pahas occur in the The majority of the nearly level to moderately sloping soils are farmed. Corn and soybeans southern part of this area. They typically are elongated and are oriented in a distinct north- The soils in this area formed from alluvium deposited by the Missouri River and its tributar- are the major crops. Many of the steeper slopes are in pasture. west-southeast direction. ies, and from soil washed from the adjacent loess covered hills. Fun Fact: This was one of the main coal mining regions in Iowa during the fi rst third of Nearly all of this area is farmed. Corn and soybeans are the major crops. A small portion is Nearly all of this region is dominated by agriculture. Corn and soybeans are the principal the 20th century. wooded, mainly on wet bottom land and on steep slopes bordering stream valleys. Many crops. A few old oxbow river channels still remain as wildlife habitat and recreational areas. of the wet soils require artifi cial drainage for timely fi eld operations and good crop growth. Native vegetation is mixed tall and short grass prairie. Fun Fact: The Lewis and Clark Exploration traveled this region noting the appearance of deer, bear and elk for 37 days in 1804. Fun Fact: Fossils found in this area show that tundra conditions were well established Detailed information about individual soil series can be found at: in Iowa 17,000 years ago. http://ortho.ftw.nrcs.usda.gov/cgi-bin/osd/osdname.cgi Loess Ridges/Glacial Till – SW Iowa Shallow To Bedrock 15 Sharpsburg – Shelby – Adair Soils 7 Rockton Soils Slopes in this region are mostly rolling to hilly but some broad ridge tops are nearly level to undulating. The slopes bordering major stream valleys are steep. A few large This region is located in the northeastern portion of the state. It consists of rivers have nearly level and broad valley fl oors. nearly level to very steep soils underlain by limestone and shale. Limestone is found at a depth of 20 to 40 inches and occur on sides slopes and crests of upland ridges and on Deep loess soils, such as Sharpsburg, make up a good share of the upland hillslopes. stream terraces. Where slopes are steeper and sharper, glacial tills soils such as Shelby and Adair are more prominent. Row crops typically are grown on the nearly level to gently sloping uplands and on the greater part of the stream terraces. The moderately sloping to very steep areas generally Historically, this area was dominated by prairie with the remainder of its landscape cov- are in pasture or woodland. ered by forest, savannas, or shrub lands. Today, this region is dominated by agriculture, with only about 5 percent of land covered by native vegetation. Fun Fact: Dairies are common in northeast Iowa. Iowa ranks 12th in the nation in an- nual milk production. Fun Fact: Thin layers of volcanic ash originating from now extinct volcanoes in Yel- lowstone can be found here sandwiched between layers of glacial till.

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HIGHWAY GUIDE HIGHWAY Glossary of Terms of Glossary

Iowa Soil Regions

Minnesota

Legend South Dakota Soil Regions Lyon 9 Osceola Dickinson 71 Emmet Northwood Mitchell Howard Winnebago Worth Winneshiek Allamakee 1 Loess over glacial till - low rainfall Rock Rapids 26 86 69 218 52 76 Sibley Spirit Lake 9 Cresco Estherville 9 9 2 Northwest Iowa Loess 1 75 4 Decorah Wisconsin Forest City Osage Waukon 3 Kossuth 63 59 18 9 Clay Palo Alto 15 169 Cerro Gordo 7 3 Tazewell Glacial Till 9 218 Sioux OBrien 76 Mason City Chickasaw 51 Emmetsburg Hancock 52 Primghar Garner Floyd 4 Loamy Wisconsin Glacial Till Spencer Algona 18 Orange City Charles City New Hampton 150 18 10 Clayton 65 5 Clayey Lake Deposits 12 17 69 West Union 2 346 18 60 10 14 6 Plymouth 56 Elkader 6 Iowan Erosion Surface Cherokee Pocahontas Fayette 143 15 Wright 3 Buena Vista 10 Humboldt Franklin Butler 188 Bremer 93 35 Cherokee 52 Le Mars Allison 7 Shallow to Bedrock Pocahontas Clarion Hampton 13 8 Dakota City Waverly 12 7 3 140 Storm Lake 8 Loess with Bedrock Outcrops 75 4 7 Webster 5 Black Hawk Buchanan 52 57 150 Sioux City 71 281 187 9 Shallow Loess over Glacial Till 110 Delaware Dubuque Sac 7 Fort Dodge 20 Calhoun Waterloo Woodbury Webster City Independence Ida Sac City Grundy Dubuque 10 Loess Ridges and Sideslopes Rockwell City 20 Hardin Manchester 31 Ida Grove 20 Hamilton 29 Eldora 38 136 196 4 Grundy Center 151 11 Loess with exposures of Glacial Till 175 175 14 61 175 141 21 Jackson Benton Linn Jones 12 Very Deep Loess 62 13 59 52 Monona 96 8 380 39 Carroll 169 17 65 14 4 Boone Marshall Tama Anamosa Crawford 69 Vinton 13 Missouri River Bluffs 175 Greene Maquoketa Onawa Boone Story 64 30 Marshalltown 151 21 Carroll Nevada Toledo Cedar Rapids Denison 67 14 Missouri River Alluvium Jefferson Clinton 136 37 9 144 35 330 146 38 18 141 151 15 Loess Ridges/Glacial Till - SW Iowa 141 Clinton 210 10 13 Audubon 141 1 Cedar 30 30 Shelby 63 Marengo Guthrie Dallas 415 212 Tipton 71 Jasper 16 Loess, Shale, and Glacial Till Harrison 61 Iowa Polk 65 117 Poweshiek Johnson Audubon Newton Scott Guthrie Center 130 12 Harlan 44 80 17 Loess Ridges/Glacial Till - SE Iowa 29 Logan 44 28 Adel Iowa City 191 Des Moines Montezuma 235 85 149 1 18 Eolian Sand 173 Muscatine 280 Davenport 680 63 80 21 19 83 316 80 Cass n 5 22 19 Loess - Timbered Adair Madison Warre 183 28 Pottawattamie 25 Marion 163 Mahaska Keokuk Washington 218 70 Muscatine Atlantic Winterset 92 148 20 Alluvium 6 Indianola 92 92 92 Greenfield Sigourney Council Bluffs Knoxville Oskaloosa Louisa 11 169 Washington 35 17 21 Loess Ridges/Glacial Till Sideslopes 63 Wapello 65 370 16 78 15 5 59 69 149 22 Loess Ridges/Clay Paleosol Nebraska Mills Montgomery Union 137 Adams Clarke Lucas Monroe Wapello Jefferson 78 Glenwood Albia Henry 20 34 23 Water Creston 34 Red Oak 34 Osceola 34 Des Moines 275 Chariton Ottumwa Fairfield 48 Corning 61 21 1 Mount Pleasant 14 Fremont 34 Decatur Davis 16 218 Taylor Ringgold Wayne Appanoose Burlington Page 65 Van Buren 25 Clarinda 148 22 29 Leon Bloomfield 16 Sidney 2 Centerville Illinois 2 Bedford Corydon Keosauqua Lee Mount Ayr 63 2 71 202 Fort Madison 69 5 169 81 61

Miles 27 0 12.5 25 50 75 218

Missouri