• Question: Have you tested out if different organisms affect different types of dirt.

    Asked by Sara to Alex, Ana, Clay, Keegan, Mark on 3 May 2016.
    • Photo: Clay Robinson

      Clay Robinson answered on 3 May 2016:

      First, it is soil, not dirt! Dirt has no ecosystem function or purpose. Dirt is essentially soil that is out of place and not able to do what it should be doing.
      Everything in the ecosystem and biome is interconnected. The soil is the foundation. Microorganisms live in the soil (more in a handful than people on the planet). Plants grow in the soil. Both provide food for larger organisms and animals. Anytime we work to conserve or restore soil, our work has a positive effect on the surrounding environment and its components.
      Soil scientists understand that soil forms from several 5 interacting forces that include Climate, Organisms (plants and animals), Relief (shape of the landscape and position on it), Parent materials (the stuff in which soil forms), and Time (how long the soil has had to form). We call these ClORPT for short.
      And so, yes, they do, I will give a few quick examples.
      Soils that form under grasses are very different than soils that form under trees. Mostly this is due to the difference in the root systems (fibrous grass roots versus the huge taproots and secondary roots on trees), and the fact that tree leaves decompose slowly and remain on the surface when they die, while grass leaves decompose quickly, as do the grass roots which are always growing and dying. Even soils under deciduous trees are often different than under coniferous trees. The pine needles are different in their chemical composition in ways that affect the soil as they decompose.
      Sometimes plants prefer a certain kind of soil. Yucca plants are common in the southwestern USA, and are tolerant of, and maybe even prefer, soils that have carbonates (think chalk), but are not fond of soils with high clay contents.
      There are several kinds of plants that are well-adapted to growing in soils with high concentrations of salt.
      In sediments recently deposited on a stream bank after a flood, subterranean termites and ants were among the first colonizers. As they build their tunnels, they secrete some saliva and other body juices to stabilize the walls. These materials help glue the individual soil particles together and form soil aggregates (clumps of particles, or naturally-occurring clods). Earthworms will do similar things in the soil, mixing the layers as it moves things from the surface to lower layers, then things from lower layers to the surface.
      Bigger organisms such as mice, ground squirrels, and prairie dogs mix soil materials from different layers, too. Soil scientists call the filled in tunnels krotovinas. These burrows are quite obvious when looking at the face of a soil pit (hole about 2 m deep by 1.5 m wide x 3 m long).