A Little Bit More
It’s interesting that some of our most important and common animals are rarely seen. Nematodes (NEHM-uh-toads) are believed to be the most numerous, multicellular (many-celled) organisms on earth – they’re that common! There are about 20,000 named species, but there may be as many as 500,000 species in all. Although most nematodes are small, they range from 0.3mm to as large as 8 meters in length! Soil microorganisms, including nematodes, play a crucial role in the decomposition of organic material into humus, and recycling of nutrients and energy. Although many nematodes live in a symbiotic relationship (in which both organisms benefit) with plants and animals, there are some species that are parasitic and therefore considered pests.
Farmers have rotated their crops for years to avoid “soil exhaustion” that they believed was due to a reduction in soil nutrients. But now it is known that crop rotation also prevents nematodes from increasing their populations to levels that adversely affect crops. No question about it, you have nematodes in your garden and in any potted plants in your home – but most will be beneficial and not a problem. Nematodes, are certainly a mixed bag – but then, life’s like that.
Nematodes have been found to be especially resilient too. Nematodes were part of an experiment to have taken place in space on the Columbia shuttle that crashed in February of 2003. A canister of nematodes was found after the crash and the worms inside were still alive and well after their extremely violent reentry – amazing!
Activities
Science – Just Dirt
Objectives: See some of the components of soil
Materials: Soil, microscope or dissecting scope, and toothpicks
This is an exercise that requires more equipment than I like to recommend but if you have a microscope or dissecting scope, I think it’s worth doing. Granted, you can do this with a magnifying glass or eyepiece, but a dissecting or microscope will provide a steadier base to make your observations.
This activity may seem rather “basic” but it really isn’t! Soils and soil components are especially complex and much more involved than you may be aware. However, for this exercise, I think it’s valuable for students to simply look at soil, or “dirt” if you will, if for no other reason than to realize that it is a mixture of materials – it’s not what it may appear to be. Soil is composed of both organic and inorganic material in varying proportions and varies from one part of the country to another, even from one area of your lawn to another in many cases.
Basic Introduction to Soils (younger students?)– If you want just a very basic introduction to soils for your students, bring in some soil from your garden, flowerbed, beneath foundation plantings, or even from your yard. Avoid bringing in any homogenous material (peat moss, pine chips, bark mulch etc) that may be “on top of your soil” and be sure to get the actual dirt that’s there.
Depending on the time of year, allow the soil to warm to room temp and then gently place it under your scope (don’t let it dry out or any organisms living there will die). Using a toothpick, you can very carefully, and gently pick through the soil looking for inorganic material (sand grains, rocks, bits of glass or metal etc) and organic material (bits of leaves, sticks, roots, etc) as well as a possible organism. If students watch carefully for movement, they should be able home in on a worm or insect or something that’s alive. Any organisms can be very carefully moved to where they can be seen better under the scope. Again, don’t let them dry out or they’ll die. Once finished, they can be returned to the original soil container.
More Involved Introduction to Soils (older students?) - For older or more involved students you can obtain soils from several different locations. You be the judge of where the soils come from but variety is the key word here – you don’t want the soil samples to be all the same! Be sure you label each sample so everyone knows which is which. If at all possible, set up the samples beneath multiple scopes so students can go from one sample to another and make notes. It will be interesting for students to go from one sample to another and take notes on what they see. Good observers will see more but all should try to comment on these following points.
Students should be looking for:
- Color differences
- Proportion of organic to inorganic in each sample
- Size of soil components (mostly small material or large?)
- Any organisms or not
If you’d like to take this one step further, you may want to obtain a soils’ map of your area and share this with your class. Soil maps will provide the basic soil types of a given area and it’s always interesting to see what these look like. Students will probably have a notion that dirt is dirt but once they’ve seen a soil map and poked through several samples of soil, they’ll have a better idea of the complexity of soils and maybe even a little more “respect” for dirt.
Take a look at this soils site for the state of Washington. If you click on a county in the map and then click on a soil within that county, you’ll get a rundown of the soil types. I think you’ll quickly realize that soils are quite involved. Have fun!
Key Concepts
Identification, Life Cycles, Populations and Ecosystems
Questions
Do you have a question for a naturalist? Go ahead and ask!
It's easy -- just fill out this form, submit your question and you'll receive an answer shortly.