Clean or Dirty?
- Identify characteristics of bad compost
- Describe ways to develop good compost
Not all compost is created equal. The inputs for homemade compost are typically grass clippings, leaves, and food scraps. However, compost at the commercial level is heavily reliant on a dominant input – such as manure, spent mushroom, or food waste – which defines its nutrient profile. For example, compost made with chicken manure is very high in nitrogen whereas mushroom compost is substantially lower. Understanding the nature and origin of compost is imperative to knowing where, when, and how to utilize it.
The quality of the input, not just the type, has a tremendous impact on the final compost quality as well. Consider the diet of the animals that produced the manure. What were they fed? Were chemicals or antibiotics used? Chemicals, pathogens, pesticide residues, and heavy metals can survive the digestive process and find their way into the manure that might have been used in creating the compost you see on the store shelves of your local garden store.
Plus, many commercial composting operations will use straw or hay. How many weed seeds survived the composting process? No one wants to apply a generous amount of compost to their garden only to discover a bunch of volunteers a few weeks later, especially if they’re weeds!
Tools & Materials
- Worm compost
- Mushroom compost
- Manure compost
Introduction (5 minutes)
Begin the lesson with the following pre-assessment question: By a show of hands, how many of you can describe the difference between good and bad compost? Confirm their understanding by asking them to explain. Record the count of Students that answer correctly. Then give the Students an overview of the difference between good and bad compost. Explain the impact that inputs have on the final product.
Activity (20 minutes)
Give each Student 3 cups, each labeled and containing a sample of compost. Ask them to use sight, smell, and touch to evaluate each type of compost. Which one is the lightest and fluffiest? Which one is the most dense? Which compost has the largest particle size? The smallest particle size? Which one has the most pleasant smell? The least pleasant smell?
Discussion (10 minutes)
Can you identify any pesticides, inputs that did not fully decompose, or heavy metals that were present in your samples? How can we manage our composting operation to ensure that we produce good compost? What do we need to avoid?
Assessment (10 minutes)
Use the following question to assess the Students before and after the lesson and tally the responses for a group count:
- By a show of hands, how many of you can describe the difference between good and bad compost?
- Now that you understand the difference between good and bad compost, how many of you think you could assess compost in our system on your own?
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