What’s your favorite soil?

Question: What’s your favorite soil?

Answer: You might just as well ask: Why in the world would someone have a favorite soil?? There are lots of reasons and lots of favorites out there.

dig-it-wall-of-soils

The State Soils of all 50 states will be on display at the Dig It! exhibit in Sacramento, CA, beginning May 1, 2014.

Each state, for example, has a favorite soil that they name their State Soil. You can see them all in one place when the traveling soils exhibit, “Dig It! The Secrets of Soil,” opens again on May 1, 2014 at The California Museum in Sacramento, CA.

Or you can see pictures of their profiles at http://www.nrcs.usda.gov/wps/portal/nrcs/detail/soils/edu/?cid=stelprdb1236841.

There are a variety of reasons why a soil scientist might choose a favorite soil. It may be because it’s the dominant soil in the area, or it may contain evidence of the area’s natural history dating back thousands of years, or it may be an important part of a favorite landscape…..or it just may be a good-lookin’ set of layers, or “horizons.”

Iowa soil scientists, for instance, may favor the Tama series. It’s the Iowa State Soil and represents one of the most productive soils of the state. Or in the arid west of the United States, you can find very dry soils that have an accumulation of clay in the subsoil. The clay in the profile resulted when that soil was under a humid climate, not the desert environment you see today.

favorite-soil-fig-1

Figure 1. The soil profile on the left is a normal Amazonian soil. The soil profile on the right shows how this normal soil was changed to a dark-earth soil by pre-Columbian Indians.

Personally I have two favorite soils. In the Brazilian Amazon, you can find soils called “Terra Preta do Índio” in Portuguese, which translates to “Dark Earth (soil) of the Indians.” These are soils that developed due to the action of pre-Colombian natives. The Indians modified the soil around their villages by incorporating their wastes into them for hundreds of years. Today these soils are high in organic matter and nutrients. The organic matter gives the soil a dark color that can extend down to at least three feet (Figure 1). Terra Preta soil also contains an abundance of broken pottery. It is one of my favorites because of the history it represents and the deep, black color that goes to such a depth.

favorite-soil-fig-2

Figure 2. A Spodosol soil under a pine forest in Florida. Note the organic matter at the surface, followed by a white, leached horizon; a buildup of dark, organic matter near the shovel scoop; and an accumulation of clay at the bottom.

My other favorite soil (Figure 2) is a very sandy soil with organic matter in the surface; a white, leached horizon below it; followed by an accumulation of organic matter; which is often followed by an accumulation of clay. These soils, when they are found in the Southeastern U.S., formed from ocean sediments. Their very sandy nature allowed both clay and organic matter to move down when excess rainfall percolated through the soil profile. We can produce something that looks similar in the laboratory in a short time, but these soils in the landscape took hundreds of thousands of years to form. They are among my favorites because of their unique colors and the arrangement of horizons.

Why not go to the above website and look at the great diversity in soil profiles? Better yet, plan to travel to Sacramento to see them in person. The Dig It! exhibit will be there from May 1, 2014 until March 29, 2015.

–Answered by Nick Comerford, University of Florida

Have a question for Soils Matter? Post it as a comment below, or email us at soils-matter@soils.org

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4 responses to “What’s your favorite soil?

  1. The Dark Mollisols soils, not only in the Midwest, but pockets across the US, anywhere the the grazing was encouraged by burning back the forest.
    Krug et al’s 2003 paper totally supports Mao & Lehmann’s current high Pyro-C SOC numbers found in;
    Abundant and Stable Char Residues in Soils:
    http://pubs.acs.org/doi/abs/10.1021/es301107c
    This important paper, verifying with modern NMR techniques the role of char in total organic content of both Terra Preta soils and US Prairie soils, 40 to 50% of all organic content and capable of accounting for all CEC;

    Abundant and Stable Char Residues in Soils: Implications for Soil Fertility and Carbon Sequestration
    J.-D. Mao, R. L. Johnson, J. Lehmann, D. C. Olk, E. G. Neves, M. L. Thompson and K. Schmidt-Rohr
    Environ. Sci. Technol., Article ASAP
    DOI: 10.1021/es301107c
    Publication Date (Web): August 20, 2012
    Copyright © 2012, American Chemical Society

    Krug’s 2003 Illinois biochar-related paper on BC in soils:
    Identification of Factors that Aid Carbon Sequestration in Illinois Agricultural Systems
    by Edward C. Krug and Steven E. Hollinger (2003)
    http://webh2o.sws.uiuc.edu/pubdoc/CR/ISWSCR2003-02.pdf

    Juicy quotes:
    page 8:
    While humus (especially in organomineral form) helps give soils a black color (Duchaufour, 1978), the literature shows correlation between forest and grassland soil color to BC — the blacker the soil the higher its BC content (Schmidt and Noack, 2000)

    page 10:
    Charcoal has been found to contribute up to 45 percent of SOC in grassland soils (Schmidt et al., 1999) and soil biota mix millimeter-sized BC throughout the soil profile (Carcaillet, 2001). …. By increasing biological productivity BC also may contribute to SOC indirectly. Charcoal has been widely used throughout the world as a soil conditioner to increase crop and tree growth, improve germination, and reduce disease (Tryon, 1948; Goldberg, 1985; Kishimoto and Sugiura, 1985; Schmidt and Noack, 2000). Root growth in charcoal-amended soils is enhanced. Production of various legume crops is increased by 20 to 30 percent (Iswaran et al., 1979; Kishimoto and Sugiura, 1985). Exceptionally heavy nodulation has been reported for soybeans grown in charcoal-enriched soils, along with increased yield and N content of roots and shoots. This has been documented even for charcoal added to organic-rich mineral soils and peats. It has been hypothesized that charcoal sorbs agents toxic to rhizobia and other microorganisms of the rhizosphere, and that this effect is general to legumes (Chakrapani and Tilak, 1974; Rajput et al., 1983). The literature shows that charcoal in soil sorbs heavy metals, organic toxins, stimulates microbial activity, acts as a substrate for enhanced microbial growth, and generally stimulates N fixation, ammonification, and nitrification (Tryon, 1948; Kishimoto and Sugiura, 1985; Pietikainen et al., 2000; Schmidt and Noack, 2000). The literature further shows that prairie burning enhances productivity, root biomass levels, root turnover, and arthropods — the latter being especially active in incorporating surface BC throughout the soil profile (Lussenhop, 1976). Frequent presettlement fires in Illinois created a multi-level, positive-feedback system for sequestering SOC and enhancing soil fertility.

  2. Reblogged this on On the Other Side of the Pond and commented:
    I can’t help but love Virginia’s State soil: Pamunkey soils! It was originally formed along the stream terraces of the James River, where it was first discovered. It’s a pretty good representation of our states history as it was located in Jamestown, which is thought to be the oldest tilled farm in the US. It’s cool to think that the settlers and Native Americans of then fed and sustained themselves using this soil. 🙂

    What’s your favorite soil?

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