Teaching Organic Farming and Gardening

Soil Biology and Ecology

22 | Unit 2.3
Instructor’s Demonstration 1

4. Have students collect the bags and return
   
   them to a central location.


5. Ask students to observe the soil habitat that
   each bag is in. Suggest they note things like
   
   soil moisture, presence of any soil animals,
   vegetative cover and shading, knowledge of
   prior cultivation, and anything else they think
   may be important in explaining their results.


6. Gently brush soil from discs. Ask students
   to visually estimate percentage of the disc
   remaining.


7. Record results and calculate averages for each
   
   habitat selected. A sample form is provided
   (see appendix 2, Litter Bag Data Sheet) for
   recording data. Appendix 3 provides an
   example of what a filled-out data sheet might
   look like.

PreParatiOn tiMe

1 hour to make 24 bags, 1 hour to bury 24 bags

(allow additional time for gathering materials)

deMOnstratiOn tiMe

1.5 hours

discUssiOn QUestiOns

1. After retrieving the litter bags, ask students
   to offer hypotheses about why the disks
   decompose more rapidly in some habitats
   than others.


2. What environmental factors might have
   influenced the results?


3. What management factors might have
   influenced the results?


4. Can you see any signs of biological activity
   on the disks (e.g., fungal mycelia, soil
   animals, invertebrate feces, comminution)?


5. What do the results suggest about nutrient
   cycling rates in the soils tested?


6. Can these observations for cellulose
   decomposition rates be extrapolated to other
   types of organic matter?


7. What are the limitations of this method?

variatiOns

If possible, pair the litter bag demonstration

with other methods of assessing biological activ-

ity, such as:

•    Carbon dioxide evolution   (see    

Demonstration   2,  Soil    Respiration)

•    Earthworm  density (see    Demonstration   3,  

Earthworm   Populations)

•    Tullgren   funnel  extractions of  

microarthropods (see    Demonstration   4,  Soil    

Arthropods)

•    Microbial  biomass measurements