Iowa State Soil: Tama Soil Series
Tama soils occur in 28 Iowa counties in eastern Iowa as well southeast Minnesota, southern Wisconsin, northwest Illinois and western Indiana. The soil series was first identified and named in Black Hawk County, Iowa, in 1917. Today, in Iowa, the Tama soil is identified as the soil series on more than 933,000 acres.
Tama soils are formed in wind-blown, dominantly silt-sized particles, known as loess, and are more than 60 inches in depth to an underlying earth material. The topsoil and subsoil have textures of silty clay loam. The soil profile is dominated by silt-sized particles and generally less than 5 percent sand-sized particles. Clay-sized particles range from 27 to 35 percent in the topsoil and subsoil. The soil developed under native prairie vegetation. The deep penetrating fibrous roots of the grasses produced a thick, dark colored topsoil that ranges in thickness of 12 to 14 inches on slopes that experience minimal accelerated erosion. The topsoil layer has a granular structure that provides for water infiltration into the soil. The soil has excellent internal drainage and is termed well-drained meaning that it does not hold excess water for more than 30 consecutive days during the year. The soil occurs on slope gradients ranging from 0 to 18 percent, however, most Tama soils occupy slopes of 2 to 9 percent. In fact, in Iowa, the map unit Tama silty clay loam, 2 to 5 percent slope gradients with a topsoil thickness of more than 7 inches occupies more than 478,000 acres.
The Tama soil has potential to provide 11 to 12 inches of plant available water in the upper 60 inches of the profile. The soil is highly productive. Currently, under high level management estimated corn yield potential ranges from 230 to 240 bushels per acre. On sloping phases of the Tama soil, 2 to 5, 5 to 9, and 9 to 14 percent gradients water erosion is a major concern where row-crop agriculture is practiced. The silt-sized particles are easily eroded by water where not protected by plant residues or sod-based plants. Therefore, Tama soils are both highly productive for plant growth and easily erodible when not protected by conservation practices.
The Tama series is classified in Soil Taxonomy as a fine-silty, mixed, superactive, mesic Typic Argiudolls.
The official soil series description for Tama is located at https://soilseries.sc.egov.usda.gov/OSD_Docs/T/TAMA.html