Composting Soils

Description of Activity:

Overview

Students will design experiments and change variables in humus or sediments in soil, and observe the resultant change(s). This activity is designed to begin in the early autumn and may run for 6 months. Obtain a good supply of subsoil (A contractor in your area may have some to donate). Look for any soil that has not been treated before. Commercial mixes and garden soils are not suitable for this activity.

Duration of Activity

• Two days for pre-lab research and observation
• One day to design and begin lab
• Periodicly assign students to turn the soil over at home and note results
• Part of one class period to cultivate crops (optional activity)
• One to two days to present results.

Materials:

• Soil for each student or group of students
• Additional soil minerals in the form of sand, gravel, clay, etc.
• Container for each student or group of students ( ice cream buckets, plastic milk jug, square plastic containers, should be at least 1 gallon size)
• Measuring devices (graduated cylinders, beakers, measuring cups) to measure amount of water given the soils
• Metal forks or other devices for turning the soil
• Soil test kit materials (available from county extension agents, in some cases, or from science supply companies) (optional, depending on your budget and students' projects)
• Composting materials (fruit peels, vegetables, rotten fruit, bread, leaves, grass clippings, etc., DO NOT USE ANY MEAT OR ANIMAL FAT, supplied by students)
• Distilled water for watering compost (prevents addition of salts from treated water)
• pH paper which will cover a 4.5 - 8.5 range
• Experiment Choice equipment
  • Thermometer
  • Fertilizer
  • Inoculates
  • Etc.

Background Information:

Growth has put a tremendous strain on our ability to produce sufficient food for the world's burgeoning population. Composting, traditionally performed routinely by our grandparents and great-grandparents as part of an agricultural life style, has become a seldom-used and seldom-discussed option to improving soils without harming the environment. Yet composting, a low-tech and cheap solution, may be an alternative that family gardeners and agri-businesses alike may find attractive. What IS composting? What effect(s) does it have on soils? How long does it take? Does it make any difference in the types of crops that can be grown? In the amount of yield? Can it be used to change the type and/or quality of soil to one that is better suited to grow food for a hungry family (or a hungry world)?

Composting is the simple addition of organic material to any soil for the purposes of enriching it, by increasing the humus content and thereby providing an environment conducive to earthworms and other beneficial life forms. These organisms aid in breakdown of organic material, and in aeration of soils. Adding compost can enable sandy soils to retain water, and improve the water flow of clayey soils. It also decreases (in the case of sandy soil) or increases (in the case of
clayey soils) the amount of air spaces around roots. It increases the amount of nutrients available to plants (especially nitrates), and increases crop yield. It may be the single greatest soil improver we can use.

Compost can be any organic material, including, but not limited to: coffee grounds, fruit and vegetable wastes, egg shells, grass clippings, leaves, manure, pine needles, and sawdust and wood chips. Meat scraps, bones, eggs, cheese and grease can also be added, but they attract insects and other pests, and so are not recommended for this project. It should also be noted that manure may introduce parasites or insects into the soil unless it has been processed. This can be
accomplished by baking it for several hours at 160o F or the compost pile can generate enough internal heat to do the same job. The carbohydrates and proteins in the organic material provide most of the energy for this. The process has a few necessary components in order to be accomplished successfully: water, oxygen, carbon, nitrogen, and heat. A certain amount of space is necessary also, since the soil and compost should be turned regularly. Most gardeners' compost heaps consist of three piles: one for adding new material to, one for turning compost during decomposition, and one for the completed product. Generally the material to be composted is buried under two to six inches of soil, and enough water added so the soil has a moisture content similar to that of a damp sponge. The correct ratio of carbon to nitrogen is also necessary, which is why the addition of small amounts of nitrogen is sometimes required. This material can be supplied by commercial fertilizers such as ammonium nitrate or calcium nitrate, urea or bone meal. Turning the compost and keeping it loosely packed allows the oxygen to flow through the pile. If conditions are right, the pile should heat up to around 110o F or higher, enough to kill off many parasites and seeds.

Failure to meet any of these criteria results in slowed rate of decay. Insufficient oxygen or too much water may produce a strong odor from anaerobic bacteria. Insufficient nitrogen or too much water will keep a pile from heating up. Insufficient water will prevent or retard composting. An odor of ammonia indicates too much nitrogen has been added, and the need to add more carbon material and turn the pile.

Composting is best accomplished by reducing material to small pieces, but some students might choose to make size a variable for their experiment; if you prefer, do not discuss size as a factor influencing decomposition at this time.

Compost piles need to be turned every so often, so periodically, assign students to do so.

You will need enough soil for each student or group of students to set up their own compost heap. Keep a container of untreated soil, and a container of correctly treated composting soil, as controls for the students' experiments. If you do this, the need for each of them to do so is eliminated.

For larger class sizes

Have students work in groups of two to four. (You may want to assign groups by how close they live to each other so they may make observations of their project together.)

Teaching Strategies:

Prerequisite instruction

1. Students will need information on what composting is. If you have the facilities, ask them to research the topic and write a brief paper about it. Then lead a class discussion about some of the variables that contribute to the success of a decomposition study. Some of these may include, but are not limited to: depth of burial, type or amount of material composted, type or size of sediment in the soil, size of container, amount of water, amount of additives, effect of external heat, color of container, aerobic verses anaerobic decomposition, or chemical or physical changes as the process progresses. You could list possible variables as they are introduced by students in class discussion after their research. Indicate which ones are acceptable (within the parameters of your budget and facilities), and have students decide how they will design their labs (which variable(s) they will test). In this, your job is to provide an overview of what composting is. You should not tell students how it is to be done, nor indicated which of their designs may prove more or less successful. THEY will find that out. Have students supply their own container, and it needs to be at least one gallon in volume. If they use a plastic milk jug, have them cut the top off so they have room to add the soil and compost materials.
2. If you want to provide soil testing materials for such things as pH, nitrate, phosphate, salinity, or humus content, students will need to know how to use the test kits or supplies. pH is relatively easy to measure: just have them take a small amount of soil, and add distilled water to make a slurry. Dip the pH paper in the water from the soil slurry, and compare it to the color chart provided with the paper. If possible, use pH paper in the 4.5 - 8.5 range (often sold as soil testing paper). For other tests, follow the directions supplied with the kit. These kits can be expensive, but you may be able to supply the chemical ingredients at a reduced cost if you chose.
3. Students will need time to learn how to observe carefully and record results so they are intelligible and legible, follow a logical sequence or pattern, and are recorded consistently. The pre-lab activity is designed to help them start learning these skills. They will probably need some help organizing their observations into a useful format for their experiments. If you decide to include soil testing as part of this investigation, you will need to be sure they include soil chemistry data in their observations.

Since students will be monitoring their piles regularly, they will need to have some place to record their observations. To minimize confusion and failure, you might provide students with a folder for each class, in which each team would have a journal (piece of paper) used to record observed changes, dates and amounts of water or other materials added, when the pile is turned, etc. Keeping this in your classroom makes it available when needed, and keeps the record from
getting "lost". Monitoring will probably need to be done at very short intervals for a while, and will depend on the variable each group is testing. Students will make observations at home and then bring their information and record it in the classroom folder.

DEVELOPMENT OF LABORATORY SKILLS:

To successfully complete this experiment, students need to develop skills in close observation and measurement, and careful recording of those observations and measurements. To get started, they should consider the following:

• What can you observe about the control soil?
• What is its color?
• Is it heavy and full of clay, or very sandy, or full of rocks or gravel?
• How moist or dry is it?
• How warm is it?
• How well or loosely packed is it?
• Do you know anything about its chemistry?
• Record at least ten observations about the control soil.
  • Compare your observations with those of others in your class
  • Add to your list anything you think is important, but which you had missed recording in your initial observations.
  • Your teacher may also have some information to add, that is important and has been overlooked by the class.

Using the complete class list, organize your list of observations into a table.

1. Turn your paper so the margin is on the top. On the left side at the top, write the word "DATE". The left column of your table will be used to indicate when you made any observations and/or changes. Observations are to be made at home, and then recorded in the school folder.
2. Next, on the right side at the top, write the word "COMMENTS". The purpose of this column is to record changes you make during the course of your experiment, or in case you see something in your investigation that doesn't "fit" the information categories on the table. These changes need to be recorded in the class folder.
3. In between the DATE and COMMENTS sections, list vertically the observations you made on the control soil, and which you will look for in your own. Try to make the categories such that you can write down in only a very few words what you see. (For example, if "Moisture" is one of your categories, you would want to leave enough space to write the word "damp", "dry", "muddy". etc.)
4. Put your name(s) on the back of the data table and turn it in to your teacher. (If it is not acceptable to your teacher, you may have to redo it.) Every time you make an observation or change to your compost experiment, record the information in the classroom folder as clearly and concisely as you can.

Invitation to Learn:

Review the following wiith students. You may want to provided it in printed format for them to use:

• Can you design an experiment that successfully creates a mini-compost pile in a container?
• Decide what you want your experiment to include as controls, and which variable(s) you want to test.
• Review your planned design with your teacher and have it okayed before proceeding.
• Monitor your results regularly, and compare your results with those of other students and with the control soil.
• Does your experiment indicate that your method works?
• What difference is there in the rate of change in your set-up compared with the experiments of others?
• What are the advantages or disadvantages to your method?
  
• Describe the result of composting techniques on the rate and completeness of decomposition, and changes to your soil, in a written or oral report, complete with a display.
• Prepare a report that indicates the following:
  • Why your technique should be used (or not used) at your home.
  • What changes, if any, would make your effort more successful?
  • In light of your results, how could American consumers change the way they dispose of organic wastes?
  • Is your design practical for home gardeners?
  • Would you recommend your method of composting to farmers in agri-business for use on a larger scale?
  • What impact could composting have on landfills?
  • What impact could composting have on sewage treatment plants?
  • What impact could composting have on world hunger?
  • What impact could composting have on groundwater pollution?

Design an experiment that creates a mini-compost pile in a container.

• Identify the essential components in any pile, and select a variable to test, or to alter from the norm.
• How does your result compare with the control soil?
• Does your experiment indicate that your method works as fast or more slowly than a traditional set-up?
• What are the advantages or disadvantages to your method?

Student Designed Experiment:

1. Formulate a question, or pose a problem.
2. List observations and information relating to the problem.
3. Formulate a hypothesis.
4. Design an experiment
• List controls that will remain the same throughout your experiment.
• List the variables, and indicate the one you will test.
• Perform the experiment, measuring and recording all data accurately.
5. Analyze data and prepare it for presentation.
6. Draw a conclusion, indicating the extent to which your hypothesis was verified.
7. Compare and contrast your results with that of other teams.
8. Report your findings (Your teacher will let you know how s/he wants this to be done).

Summary of Learning:

Assessment

Multiple choice questions:

1. What impact, if any, does compost have on soils?
   1. Compost adds humus to soils.
   2. Composting allows water to accumulate in already saturated soils.
   3. Heat from composting burns the soil.
   4. All of these
   5. None of these
2. The one thing that does not compost well is
   1. Vegetable and fruit scraps
   2. Yard wastes
   3. Sawdust
   4. Plastic
3. Why would you not put meat scraps in your compost pile?
   1. It takes too long to decompose
   2. It make the compost pile too warm
   3. It hold too much water
   4. It will attract animals
4. Why is composting an Earth friendly activity?
   1. It allows bacteria a safe place to grow
   2. It reduces the amount of garbage that goes to landfills
   3. It provides heat
   4. It increases the biodiversity in your community

Answer Key: A, D, D, B

Strategies and tools to share findings:

At the completion of this project, students should prepare a written or oral presentation describing their experiment and its results. This presentation should also include a display of some kind such as: graphing changes in comparison with the control soil; posters showing photographs or drawings of the changes; actual samples of the soil in its "before and after" states; or samples of pre-and post-composted chemical test results. These could promote a lot of discussion in and out of class, especially if displayed in show cases within the school.

Extensions:

You might find a location around your school or home where composting might be undertaken. If your area has a community garden, could you start a heap there? Have students advertise the benefits and ease of composting around your community, especially where yard wastes accumulate. Research the amount of landfill space occupied by yard wastes. Could your community start a resource pile of organic material (especially chipped branches) for use in home-owners' and businesses' yards? Have students find out (might be a useful extra-credit project).

After the composting is finished, you might want to have them plant the same crop (wheat, radish, bean, corn, buckwheat, whatever is easily obtained) in both their treated soil and other soils. Then measure the results in terms of plant growth or seed yield, soil chemistry changes as the plants grow, etc.