Soil: Hey, there’s life in my dirt!

 

Timeline:  

40 minutes

Objective:

To gain an understanding that soil is a complex ecosystem containing numerous elements, created over time through the work of soil organisms!  Students will attempt to “make” soil by manipulating the elements in soil (leaf litter, grass clippings, fruit scraps, rocks, twigs, sand etc.), then will investigate well-decomposed leaf mould, worm castings, and garden compost, and finally use these well-decomposed materials to make potting soil.

Materials:

  • sample of great soil
  • elements for building “soil”: Leaf litter, grass clippings, fruit scraps, rocks, twigs, etc
  • for potting soil: worm castings, coco cour, leaf mould, garden compost, sand, perlite
  • potting soil recipe (see below)
  • water
  • containers for each element, and empty containers to make soil in


Vocabulary:

  • soil
  • inorganic vs. organic
  • microbes
  • invertebrates


Background:

Soil is the top layer of the earth’s crust, formed through sedimentation of rock and the cementation of the sediment into distinct layers, called horizons. The introduction of organic materials , air and water  into the very top horizon, and the action of microbes and invertebrates, lead to the creation of topsoil, a fertile growing medium for plants. There are five main components to soil: eroded rock particles (minerals), water, air, organic material, and microbes and invertebrates.
Plant roots and soil organisms actually break down rocks, physically and chemically, releasing nutrients from rocks.  The invertebrates and microbes (fungi, bacteria, algae) in the soil digest organic materials (excreting chemicals we consider plant nutrients), aerate the soil, and distribute nutrients.  There is an entire ecosystem existing just beneath the earth’s surface.   One acre of pasture may contain 2 tons of worms, and another 2 tons of microbes and soil animals!

Procedure:

  • Welcome!  Today we are going to explore the one, most important thing we produce in the garden.  Without this, we would not have the garden as we know it…SOIL!  What is soil?  Is it dirt?  Many of you probably know that soil is a living thing, but what IS it?  What part of it is living?  What is in soil?
  • Prompt: what is a part of this soil?  Present the raw components of soil.  What are these?  Can we make soil with these?  Let’s try!  Have students mix; add water!  Observe.: this does not look like something a plant would want to grow in!  But if you leave this pile of stuff, it WILL become THIS (show worm castings.)  What takes this and makes it into this?  (worms, microbes, soil animals, insects)

  • Look at this chunk of garden soil.  This is a well established piece of the Garden.  Notice the plants and plant roots, the animal burrows.  What do you see in here that we haven’t addressed yet, that makes this soil a great environment for plants to grow in? (the structure)  What kind of structure is best for plants and other soil life?  Here’s a hint: Guess what makes up 50% of soil…pores!  (Air/water spaces)
  • Let’s make soil!  When we start plants indoors, we need to get a nice mix we call potting soil.  At Good Cheer we use a recipe for soil like you would use a recipe for a cake.  Show the potting soil components, then the recipe.  Have students explore the components.  Use the 5 senses (ok, 4, without tasting!) to describe the leaf mould, worm castings, etc.  Now, mix them using the recipe.  Discuss what each component adds (castings/compost/mould=organic matter, perlite/coco cour=porosity, sand=drainage)
  • Conclusion:  When we attempt to make soil on our own, something is missing.  What is the difference between nature’s soil building and our own?  What turns leaves into leaf mould?  And veggies into worm castings?  Microbes and soil animals!  Now who can tell me what the [five] main components of soil are?

Assessment:

  • Name 5 components of soil (inorganic minerals/ground rocks, air, water, organic matter, soil animals/microbes)


Extension Activities:

  1. Soil shakes: Discover the balance of sand, silt and clay in your soil. For each sample of soil, fill a clear container two thirds full of water. Add enough soil until nearly full, cover tightly, and shake. Let kids observe their ‘shakes’ over the next few days as the soil particles settle into layers. The larger particles, like sand, will remain at the bottom while the smaller ones will be closer to the top.

Recipe for Soil:

adapted from Eliot Coleman

2 1/2 parts coconut cour or peat moss

1 1/2 part compost

1/4 part fine perlite

1/4 part corse sand

Resources:

http://landscapeforlife.org/soil/
http://www.extension.umn.edu/distribution/cropsystems/components/7399_02.html

http://edibleschoolyard.org/sites/default/files/Soil%20Block%20Recipe_0.pdf

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