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SOILS ARE COMPLEX MIXTURES of minerals, water, air, organic

matter, and countless organisms—the decaying remains of once-

living things. There are different types of soil, each with its own set

of characteristics. Dig down deep into any

soil, and you’ll see that it is made of layers, or horizons. Put the soil

horizons together, and they form a

soil profile. Like a biography, each

profile tells a story about

the life of that soil.

Young soils left behind by miningFARLEY SERIES This soil series is among the lightest-colored profiles you will see, partly due to its relative youth—a 50-year-old minesoil at Colstrip. It formed on nearly level mine spoils created by surface coal-mining in 1928.

The very thin dark surface horizon shows where 50 generations of plant roots lived, died, and decomposed to form humus, soil organic matter. The clear bands of rust-orange, iron-stained material and the rusty rind around an ac-id-forming feature near the base of this profile are 10,000 times more acidic than the surrounding, lighter-colored materials from mined sandstone and shales. Research at MSU aims to improve reclamation of mine soils.

Soils on fans, terraces and benchesJUDITH SERIES stretching across 3 million acres, this soil supports dryland crops, pasture, and rangeland. Its thick, dark surface layer (known as a ‘mollic’ horizon), produced from decomposed grass roots,

abruptly transitions to a gravelly and lighter-colored subsurface calcium-carbonate-enriched horizon. The surface horizon is derived more from fine-textured, water-deposited sediments and windblown loess than from weathering of underlying gravels.

Soils that tell a story about peopleTIBER is not an official soil series name, but is named for the Tiber Reservoir Archaeological Site near Shelby in northern Montana, a site adjacent to a buffalo jump. Buffalo bones can be observed near the base of this soil profile, buried under a thick layer of material possibly loosened by buffalo hooves.

This sample is a reminder of the power of soil to serve as a time machine, showing bone that is likely associated with early inhab-itants of the area. Radiocarbon analysis dates charcoal in this area as far back as 900 years ago.

Soils that tell a story about soil formationMARTINSDALE SERIES Covering about 2.5 million acres, Martinsdale soils are deep,

well-drained, and suitable for range and cropland. After several thousand years this profile has characteristics typical of a stable soil under semiarid grasslands with about 12 to 14 inches total precipitation yearly. The melting snow and rain has leached nearly all water-soluble salts out of the soil but left the less-soluble calcium carbonate (perhaps 30% by weight) in the white horizons under a foot of dark-colored, organically-enriched horizons (together termed mollic).

Where carbonates are removed, soil materials become more acidic and clays are free to migrate downward. Over time, the clays shrink and swell, forming strong prismatic structures which appear as a vertical feature that extends here to a depth of 12 inches. This horizon with subsurface accumulation of clay is known as an argillic horizon. It feels sticky when wet.

The 3-inch topmost horizon (above the prism) has granular structures held together by gums and resins produced by microbes, that thrive in this rich (6% organic matter) horizon, a kind of fossil record of where many roots have grown and decomposed.

This material is based on work supported by the National

Science Foundation under Grant EPS-1101342. Any opinions, findings and conclusions or

recommendations expressed in this material are those of the author(s) and do not necessarily reflect the views of the National

Science Foundation.

WHAT’S UNDERFOOT IN MONTANA?

A SOIL SERIES is a group of soils with similar soil profiles developed from similar parent materials under comparable climatic and vegetational conditions. Many different soil series occur in Montana. Here are the stories of seven of them.

7 SOILPROFILES

Soils from volcanoes, conifers and glaciersANDIC DYSTROCRYEPT The classic soil from the Hungry Horse part of northwest Montana is distinguished by strong color differences. Its upper volcanic ash layer was deposited by volcanoes upwind (e.g., Mt. St. Helens, 1980 and Mt. Mazama in 5630 BCE) and its lower portion is made of alpine glacial till. Rusty colors near the top are from iron oxides, created as volcanic ash is broken down by strong acids (typical of coniferous vegetation) and moved by cold and wet conditions. Compact glacial till slows chemical weathering, leaving dramatic color and texture difference at about 12 inches.

Prairie soils 12,000 years in the makingPHILLIPS SERIES Comprising 11.5 million acres, the Phillips

series is a widespread soil that likely developed under semiarid shortgrass prairie, since glaciers receded north across the Canada border approximately 12,000 years ago. Its profile shows a dark horizon over a blocky, clay-rich horizon, over lighter, calcium carbonate-rich horizons. Some of the yellower spots at the base contain gypsum.

Shallow soils on river gravelsBEAVERTON SERIES Covering 1 million acres, this soil profile shows a classic sequence of horizons: A dark, organic matter-rich surface horizon over a redder blockier, clay-rich horizon, over a lighter, calcium carbonate-rich horizon. These horizons formed in fine-grained sediments deposited on coarse gravel. The gravel retains little water for plants but provides a strong foundation for roads, buildings, and airports. Soils found near Towne’s Harvest Garden just west of the MSU campus in Bozeman, and the large area near Belgrade where gravel is commercially quarried resemble this profile.

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For more educational resources from the Climate In My Backyard series, visit

http://eu.montana.edu/climb