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									                SOIL BIOLOGY CLASSR OOM ACTIVITIES
       For more soil biology information see The Soil Biology Web Page (from the NRCS Soil Quality Institute) at
                                     http://www.statlab.iastate.edu/survey/SQI/.



                                       Soil Biology Classroom Activity #1
                                        EARTHWORM FARM
DESCRIPTION                                                    increase the amount of water held by soil. They create
                                                               burrows that speed the movement of water into and
Set up an earthworm farm and watch how earthworms
                                                               through the soil and provide nutrient-lined channels for
bury surface residue and mix soil.
                                                               root growth. They create casts that become stable soil
                                                               aggregates.
LESSON
Earthworms are significant for mixing soil, increasing         TIME AND MATERIALS
decomposition of plant material, and improving water
                                                               •   one dozen night crawlers
infiltration and water holding capacity.
                                                               •   one or two dishpans, or deeper containers.
BACKGROUND                                                     •   soil to fill the container(s).
                                                               •   dry plant material
Some earthworms are native to the US, but many species,
including Lumbricus terrestris (the night crawler), were       •   Allow at least one week for surface residue to
introduced from Europe. Most prefer well-aerated, moist            disappear and worm casts to appear. Allow several
soil. Earthworms are uncommon in arid areas, and sandy             weeks or preferably months to observe soil mixing.
soil. Ultraviolet light (sunlight) will kill earthworms.       PROCEDURE: Earthworms bury plant litter
Earthworms ingest soil and organic matter, get their           1 Get a dozen night crawlers. Buy them from a bait
                                                                )
nutrition from the microorganisms living in the organic        shop, or collect them from dark-colored, moist soil.
matter, and then egest “casts” – a mixture of soil and
organic matter. Where earthworms are common, much of           2 Fill one or two dishpans with soil. Use two pans if
                                                                )
the soil has passed through the guts of an earthworm.          you would like to set up an experiment in which one pan
                                                               has earthworms and the other is a control. However, for
The mechanical action of tillage kills some worms, but         demonstration purposes, a single container works fine. Fill
more importantly, tillage removes the surface residue that     the pan(s) with any medium-textured soil. Do not use peat,
earthworms need for food and protection from desiccation       and do not use soil with much sand— it is abrasive to
and predation. Earthworms especially like fungi, which         worms. The soil should be kept moist, but not soggy.
thrive in minimally-tilled soil.                               Moisten the soil slowly, if needed. You may punch a drain
Lumbricus terrestris has many common names including           hole in the pan to insure that no water sits at the bottom.
night crawler, dew worm, and angleworm. They are one of         )       -1
                                                               3 Place 6 2 earthworms on the surface of one pan.
several species (called “anecic”) that form deep, relatively
permanent burrows. In contrast, “endogeic” species             4 Sprinkle plant material on the surface. Use dry
                                                                 )
meander around in the upper soil, filling their channels       leaves, grass clippings, or residue from a farm field. Make a
with casts as they go. Both types are important for mixing     single thin layer leaving some soil visible. If you use two
soil and improving soil structure.                             pans, be sure both have the same type and amount of
                                                               material.
Bacteria and fungi decompose organic matter. Worms
encourage decomposition by shredding plant residue and         5 Make daily observations for at least a week. Look
                                                                )
mixing it with soil, microbes, and water.                      for burrow openings, casts, and the disappearance of plant
                                                               material.
Earthworms change the physical structure of the soil in
ways that improve the rooting environment for plants and
                                                                                                     USDA Natural Resources Conservation Service


Earthworm farm (cont.)


   VARIATION: Earthworms mix soil                                   QUESTIONS FOR DISCUSSION
   1) Acquire a clear container(s). Build one or two plex      i-          h
                                                                    1) Whic leaves will decompose faster—t hose buried
   glass containers 2-3 ft. tall, 1-2 ft. wide, and 2-4 inches      underground by worms, or                 a
                                                                                             those on the surf ce? Why?
   from front-to-back. (As in the first procedure, the second       Buried residue decomposes faster because 1) the worms have shredded
   container is optional, butcan be used as a “control”.) Drill     it into smaller pieces, so bacteria and fungi have more surface area to
   drain holes in the bottom.A fish tank works, but be              work on, and 2) most bacteria need moisture. They cannot live on
                                     l
   careful that waterdoes not colect in the bottom,and              the dry surface residue.
                                            ill
   remember that the amountof soil w be extremely heavy.
           l                            t
   A two iter bottle with the top cu off may wor , but it may
                                                      k                          ms                y
                                                                    2) Earthwor do not live ever where. What happens to
   be more difficult to keep the wor s alive.
                                         m                                             e                ms?
                                                                    surface residue wher there are no wor

   2) Find soil of two different colors. As mentioned               Farmers do part of the work of earthworms by tilling residue into the
   above, avoid sand and pe t. Fill the container(s) with 1”-2”
                              a                                     soil. In some deciduous forests with no earthworms, residue piles up.
   layer of alternating soil colors. A sand or clay layer could
       s                                                            In other places, ants, termites, beetles and other arthropods shred and
   be added to see how wormsespond to bar
                                   r            riers.              bury residue.

   3) Add earthworms and plant material as in steps 3 and                           m               ul?
                                                                    3) Why is earthwor activity helpf
                  e           i
   4 above. Add mor plant materal as it is consumed.                They encourage decomposition, and therefore, the release of nutrients
   4) Observe. If you use two contai ers, the one wihout
                                       n                 t          for use by plants and other soil organisms. They improve the stability,
   earthwor can be used f r comparison as wor s change
            ms                o                     m               porosity and water holding capacity of soil. They improve water
   the other If you use one containertake pictures
            .                          ,                            infiltration by forming deep channels and improving soil aggregation.
   periodically, or mark the location of the original layers.       They may improve root growth.
                                                 i
   You can keep the system going, and watch ncreasing                         ht       ms
                                                                    4) When mig earthwor be undesirable?
                       ing                       s.
   amounts ofsoil mix over months oryear If the worms
   die, remove them if possible and add new ones.                   In some places earthworms remove surface residue too quickly and
                                                                    leave the surface unprotected from rain and wind. Some forest seeds
                                                                    need a thick layer of plant litter to germinate and begin growing.
   HINTS
                l                   too
   Do not overoad the system by using many
                                                                    EARTHWORM INTERNET RESOURCES
            ms,          ch                  ch
   earthwor too mu surface residue, or too mu water.
          e          ing
   You ar not mak a compost pile;you ar imitatinga
                                        e                                     c                                          s:
                                                                    A commer ial site targeted at K-8 students and teacher
   farm field or forest floor.                                                    overy.com (click on Worm World)
                                                                    yucky.kids.disc
   Be sure the worms get plenty ofdarkness every day s they
                                                         o                      u                  a
                                                                    Two sites f ll of earthworm f cts:
            k                          n
   can wor at the surface. If the contai er has clear sides,        res.agr.ca/lond/pmr                 .
                                                                                          c/faq/earthworhtml
   keep it covered most of the time to prevent algae growth.        solum.soils.umn.edu/r                    m.htm
                                                                                            esearch/ars/mn_wor
   The sides can be uncovered briefly each day,or for a             A worm farm variation:
        e
   whol day occas  ionally.                                                                 a        a
                                                                    res2.agr.ca/london/pmrc/f q/worm_f rm.html
              m        e
   A sick wor can inf ct and kill thewholebatch. Avoid this                      -made worm box:
                                                                    A commercially
   by r                  ms
       emoving dead wor quickly (ifpossible), and by                                    science.net/HS- 236.html
                                                                    http://www.everything             1
                    t      m
   starting with heal hy wor s. They should be plump, quick-
           ,
   moving and show no physical damag   e.




           o
   Soil Biol gy C            v
                 lassroom Acti ities Draft 2/01                                                                              Page 2 of 6
                                                                                            USDA Natural Resources Conservation Service



                                       Soil Biology Classroom Activity #2
                                 HOW FAST DOES IT ROT?

DESCRIPTION                                                                   a               er,
                                                                covered by pl nt litter. Howev the plant litter on the soil
                                                                surface will dryout more than if it were buried.
     e                     n
Compar organic matterdecay i different soils.
                                                                Temperature: Bacteria are most active between 70-    100°F.
                                                                Dark, baresoil w will arm morequickly in spring c     ompared
LESSON
                                                                                              o
                                                                to light-colored soil or soil c vered with plant litter.
                           ical ocess performed by living
Decomposition is a biolog pr
                                                                                o
                                                                Food: Most micr bes need org   anic matterfor energy and
                                t
organisms. Soil and climate condiions determine biological
                                                                                                              o        h
                                                                nutrients. Decompositionis faster when the f od is hig in
activity and,therefore, decomposition rates.
                                                                nitrogen. (Generally, young, green plant residue has more
                                                                          o              .)                        o
                                                                N than br wn plant litter Harvesting plants and r ots
BACKGROUND                                                                             g
                                                                from soil means less oranic matterleft to feed microbes.
Nutrients are continuously tr  ansformed and cycl de                                    e                   i
                                                                pH: A pH of6 to 8 is pref rred by most bactera. Many
through the env  ironment.Decomposition by s     oil            fungi prefer a lowerpH.
                                                     a
organisms is a critical part of these cycles. When pl nts and
                        e                        e
animals die, the compl x compounds that mak up living
                                                                    Soil can act as either a sink or a source of
tissue decompose. Decomposition releases carbon dioxide
                                                                    greenhouse gases. An estimated 30 percent of
and nutr                            ients
         ients, and makes the nutr available agin to a
                                                                    the carbon dioxide, 70 percent of the methane,
plants and otherorganisms.
                                                                    and 90 percent of the nitrous oxide released to
Soil org                                           ore
        anisms also decompose would-be pollutants bef               the atmosphere each year pass through the soil.
they r                               .
      each groundwateror surface water
Decomposition is a st   epwise process involving mostsoil
               t
organisms. Arhropods and ear           ms
                                 thwor shred material and
mix it with soil. Then a few fungi with a par  ticular enzyme   MATERIALS AND TIME
                          nd
break a specific compou into simpler parts. Then                •                                i
                                                                      several types of plant materal
different species of fungi or bacteria can attackthe newl  y    •     net bags
created compounds, and so on. Each or      ganism gets          •                        k
                                                                      something to mar the bags’ locations
                      f
energy or nutrients rom the pr   ocess. Usually, but not        •     shovel
       ,
always compounds become simpler after each step. Some
compounds cannot be br                       f
                           oken down any urther. Theymay        •               e           ied
                                                                      Allow sampl s to be bur for up to 2 or 3 weeks.
                                        ex,
combine chemically to become compl hard-to-degrade              PROCEDURE
organic compounds called humic substances. Humic
substances can persist in soil for centuries and are            1.    Collect organic material, such as leaves, grass
important or improving the capacity ofsoil to hold
            f                                                                s,
                                                                      clipping residue from a field, or cotton fabric. Avoid
nutrients and water .                                                                              act
                                                                      kitchen scraps which may attr animals.

Several factors affect the growth of microorganisms and         2. Divide the material into two or more identical
therefore the rate of decomposition in soil.                                          a
                                                                   piles. It is import nt that each pile have the same
                                                                                                                ials
                                                                   kind and size of pieces, because some mater rot
Oxygen: Most microbes require oxygen (aerobic                      faster than others.
                f                          obic
conditions). A ew are active only in anaer conditions.
Tillageaerates the soil and t mporarilyincreases
                             e                                  3. Pack the residue loosely into net bags. The
decomposition rates. Compacti n reduces the air in the
                                 o                                 purpose of the bag is to help you locate the buried
soil and the space for larger organisms to move around.                                              a
                                                                   residue and carry it back to the cl ssroom. Purchase
                                                                                                         s
                                                                   nettingfrom fabric stores or use bag intended f ro
Water: Soil organisms aregenerallymore active in moist                                                      s
                                                                   washingdelicate clothes. Do not use bagof tightly
       y
than dr soil. Soil is protected from drying out if it is           woven fabric. You want small (1mm) arthropods to
                                                                   get at the residue and help shred it.


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Soil Biol gy C            v
              lassroom Acti ities Draft 2/01                                                                       Page 3 of 6
                                                                                                USDA Natural Resources Conservation Service


How fast does it rot? (cont.)

   4. Choose places to compare. Identify several soilsthat      HINTS
      are managed differently. You might compar a    e:
                                                                                      i                    e
                                                                Practice good scientif c method and chang just one
                  ea       r
      wooded ar away f om a path,compacted s under    oil
                                                                variable at a time. For example, if you want to study the
      a path, a farm field, a lawn, a garden, soggy soil, dry
                                                                                  e,                                 cept
                                                                effect of moistur choose soils that are identical ex for
                 c                 -                        l
      soil, dark- olored soil, lightcolored soil, a farm fied
                                                                        s                     t          f
                                                                the moi ture. If you want to sudy the ef ect of the kind of
             w                                  o
      that al ays has bare soil between the cr p plants, and
                                                                material, be sure to burysamples in identical soils that have
                     w
      a field that al ays has plant residue or weeds covering
                                                                similar moisture contents.
                                    c
      the soil surface. Predict whi h places have the most
      biological activity.                                      The optimal le                                 s
                                                                               ngth of time for leaving sample in the soil
                                                                                                                    s
                                                                varies from place to place. The first time you do thi
   5. Bury the bags a few inches down into the soil. Be
                                                                                              hat            our
                                                                activity, allowtime to learn w is best in y situation.
      sure each bag is buried to the same depth.Mark the
      locations.
                                                                QUESTIONS FOR DISCUSSION
   6. Examine the results. After two orthree weeks dig up
      the bags and judge which ones are the most decayed.       1) Where does decomposition of               f
                                                                                               plant residue it in a
      If there is little difference, you may need to e-bury
                                                     r          diagram of the food web/chain?
      them for another2 weeks or longer.
                                                                Only a fraction of plant matter is eaten by above-ground herbivores.
                                                                Most is consumed by the decomposers underground and enters the
   Alternative procedure                                        complex network of organisms called the soil food web. Energy and
                                                                nutrients return to the above-ground food web when plants grow and
   MATERIALS
                                                                animals eat plants and soil organisms.
   •                   ds
        3 X 5 note car or cotton fabric
                                                                                                      ill rease biologic
                                                                2) What characteristics of the soil w inc              al
   •    plastic bags
                                                                                e
                                                                activity and therfore decomposition rates? How do we
   •    trowel for collecting soil                              affect those characteristics in the soil?
   PROCEDURE                                                    (See Background.)
   1.                                       al
        Collect soil samples. Choose sever different soils                    a
                                                                3) What char cteristics oforganic matterdetermine how
                   e          i
        to compar from the lst in #4 above.                     fast it decays?
                      a
        From each pl ce, use a trowel to scrape away any
        surface residue and scoop soil into a labeled plastic   Compared to large pieces, small pieces have more surface area for the
        bag.                                                    bacteria and fungi to attack. Low nitrogen content relative to carbon
                                                                (high C:N ratio) will limit the activity of microbes. Woody materials
   2. Add a note card. In each bag of soil, bury an             contain lignin and other compounds that are difficult to break down.
                                d
      identical piece of note car or cotton fabric.
                                               ou
   3. Make your predictions. Which soil do y think w    ill
                                                                INTERNET RESOURCES
                            al
      have the most biologic activity and will decompose
      the note car or fabric most quickly?
                 d                                              Carbon cycle:
                                                                                      st.org/11226/
                                                                http://library.thinkque
                                                   s
   4. Examine the results. After two orthree week look
      at the note cards or fabric. Which decompos fastest?
                                                ed                           e
                                                                Nitrogen cycl :
                                                                                          aculty/biolog /jason/nitrc.htm
                                                                http://clab.cecil.cc.md.us/f          y
                                                                http://www.bae.ncsu.edu/courses/bae578/nitrog  en.html
                                                                Organic matterand decomposition:
                                                                http://www.montana.edu/wwwpb/ag   /baudr150.html
                                                                             r
                                                                http://www.agic.gov.ab.ca/agdex/500/536-1.html




           o
   Soil Biol gy C            v
                 lassroom Acti ities Draft 2/01                                                                        Page 4 of 6
                                                                                            USDA Natural Resources Conservation Service



                                        Soil Biology Classroom Activity #3
                              WHAT LIVES IN YOUR SOIL?

DESCRIPTION OF ACTIVITY                                          Berlese Funnel
Use two techniques to ex tract large and small arthr pods
                                                   o             MATERIALS AND TIME REQUIRED
                        d
from soil. Students may i entify the organisms, estimate
                                                                 •   Trowel and plastic bags for gathering soil.
       s,           e
number or compar populations in dif     ferent places.
                                                                 •                                                 )
                                                                     Large funnel (2-literbottle, or plastic milk jug
                                                                 •                   e
                                                                     2 mm mesh scr ening
LESSON                                                           •   Jar or cup
A wi e variety of organisms live under our feet and
    d                                                            •   Preservative (ethanol or 50:50 ethanol/water mix)
perform important roles in the environment.                      •                         h             f
                                                                     Incandescent, 60W lig t bulb and ixture
                                                                 •   Dissecting microscope

BACKGROUND                                                       •   Allow one weekafter set up to collect samples.

                              o
“Arthropods” is the name f r a large group of
invertebrates with jointed (arthros) legs (podos). In the        PROCEDURE
soil, they may be mi croscopic or several inches long. They    1. Gather soil samples Arthropods are easiest to ind         f
include insects (springtails, beetles, and ants); crustaceans,              h
                                                                  in soil t at is rarely disturbed by tillage, not compacted
                               s
(sowbugs); arachnids (spider and mites); myr      iapods                  f
                                                                  by traf ic, not treated with pesticides, not per   iodically
                        d
(centipedes and millipe es); and scorpions.                       flooded or dried out, and that has several different
Arthropods are impor    tant because they stimulate microbial                                .
                                                                  kinds of plants growing Push away the sur litterface
activity and enhance decomposition; they help contr    ol pest                                   soil
                                                                  and dig up about 1 liter of from the top f w       e
                                        str
populations; and they improve soil ucture as they                             s
                                                                  centimeter of the soil. (In another     experiment, plant
burrow thr ough the soil or excrete fecal pellets made of                                      e
                                                                  litter can be used in plac of soil in a Be   rlese funnel.)
soil and organic matter Good structure is important for
                         .                                        Refrigerate sample if you will notuse it right away.
improving water intake, drainage, and aeration, thus                                                       f
                                                               2. Set up the Berlese funnel. Cut of the bottom of
                                      e
protecting soil from erosion, and cr ating a good                                                       u
                                                                  the bottle ormilk jugto make a f nnel. Cut and place
               o
environment f r roots.                                            the screen in the bottom ofthe funnel to hold the soil.
A single square yard of soil maycontain 500 to 200,000                        p                  es
                                                                  It may hel to tape the edg of the screen to the
             t
individual arhropods and tens orhundr of different
                                           eds                                        t
                                                                  funnel. Half fill he funnel with soil. Set the funnel
                                        m
species. Most live in the top few centi eters of soil. A          above a jar or cup with a bit of    ethyl alcohol in the
Berlese (pronounced “bur LAY zee”) funnel can be used                                ol
                                                                  bottom. (Glycer can be addedto reduce evaporation.)
to collect micr scopic ar
               o           thropods from soil.A pitf tr
                                                    all ap        Set up a desk lamp orhang a light bulb so the bare 60W
can be used to g  ather larger arthropods.                        bulb is about 4 inches over the soil.
                                                                                                           ht
                                                                 3. Collect the organisms. Leave the lig bulb on f r     o
                                                                    3-7 days to dry out the soil. As the soil dries, organisms
                                                                    will movedeeper into the soil and e                 o
                                                                                                       ventually fall int
                                                                                            bing
                                                                    the alcohol. Avoid distur the setup and knocking
                                                                    soil into the alcohol.
                                                                 4. Examine the sample. Pour the alcohol solution into
                                                                                      amine undera micr
                                                                    a petri dish and ex                   oscope. Put black
                                                                    paper and white paper  behind the sample to highlight
                                                                                               y
                                                                    different organisms. Identif the main g roups of
                                                                    arthropods. An identification key is at
                                                                    www.cals.ncsu.edu/course/ent591k/ident.html




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Soil Biol gy C            v
              lassroom Acti ities Draft 2/01                                                                       Page 5 of 6

								
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