All living organisms have a Carbon to Nitrogen (C:N) ratio for their tissues.  For microorganisms, carbon is the basic building block of life and is a source of energy, but nitrogen is also necessary for such things as proteins, genetic material, and cell structure.

Decomposition of organic materials in your compost pile is greatly increased when you create the proper balance between the carbonaceous materials (called BROWN because they are dry) and the nitrogen-rich materials (called GREEN because they are more fresh and moist). This balance is referred to as the Carbon-Nitrogen ratio, and shown as C:N.

Microorganisms that digest compost need about 30 parts of carbon for every part of nitrogen they consume. That's a balanced diet for them. If there's too much nitrogen, the microorganisms can't use it all and the excess is lost in the form of smelly ammonia gas. Nitrogen loss due to excess nitrogen in the pile (a low C:N ratio) can be over 60%. At a C:N ratio of 30 or 35 to 1, only one half of one percent of the nitrogen will be lost. That's why you don't want too much nitrogen (fresh manure, for example) in your compost: the nitrogen will be lost in the air in the form of ammonia gas, and nitrogen is too valuable for plants to allow it to escape into the atmosphere.

1. A maximum of 35% of the carbon in fresh organic material will be converted into soil humus IF there is sufficient nitrogen present.
2. A minimum of 65% of the carbon in fresh organic material will be given off to the atmosphere as carbon dioxide due to microbial respiration.
3. The humus formed from the decomposition of fresh organic material will contain approximately 50% carbon and 5% nitrogen. In other words, the C:N ratio of the humus is 10:1.
4. Most fresh plant material contains 40% carbon. The C:N ratio varies because of differences in nitrogen content, not carbon content. (Note: Dry materials are generally in the range of 40 to 50 percent carbon, and sloppy, wet materials are generally 10 to 20 percent carbon. Therefore, the most important factor in estimating the carbon-to-nitrogen ratio of plant or food waste is how much water is present).

5.    Generally speaking, you can get C:N ratios of 30:1 to 50:1 by adding two parts of a GREEN material to one part of a BROWN material to your bin. A "part" can be defined as a certain quantity of the material, such as two 5-gallon buckets of GREEN and 1 packed bucket of BROWN.

6.    Play with the chart below. For example, food scraps, grass clippings and leaves come close to an average of 30:1. How? Add-up the Carbon side of the ratio for all three materials, i.e. 15, 17, 60, and divide by the number of materials, i.e. three. 92/3 = about 31:1.

 PROCEDURES:

1. The week before the experiment begins, send “Compost Party” flyer home to families, asking students to bring in food waste (fruit, vegetables and eggshells). Vegetables, especially leafy vegetables, will help provide nitrogen. Fruit provides moisture. No meat, cheese, bread or processed foods are allowed.  For more information click here.

2. The goal is to fill the Jora Composter on one day. Students can help break up green waste and put it in coffee containers. Ideally, put in 1 parts food waste (or 3 part green waste like grass), 1 part manure, and 1 part wood chips. The limiting factor for filling the composter will be how much food waste has been brought in by students. Have them add 1 containers of food waste and then they can add one of manure and one of wood chips.

There are two sides to the, marked Side A and Side B. Hopefully both sides will fill up, but if classes do not have enough material, fill up Side A as much as possible and put the remainder in Side B. This can help students evaluate whether a full composter is more efficient than a partially filled one.

Note: It is best to set the day for filling the Jora early in the week since the compost often reacts quite quickly and reaches its maximum temperature in a few days.

3. After filling the Jora composter, have the students line up and take turns spinning the composter two times each. This mixes the material and aerates it.

4. Take initial temperature readings using the large composting dial probe thermometer. First, take exterior air temperature in the shade. Place the dial probe thermometer in the shade, with the sensor end not touching anything. Next, take the temperature in the composter. Place the probe deep into the center of the mass of material (without touching the back wall of the composter). Students should take the temperature in both Side A and Side B. Have students line up in pairs to observe correct dial probe thermometer placement and practice reading the temperature.

5. Student teams should take daily temperature readings from the exterior air in the shade and from the composter in both Side A and Side B. Each member of the team should observe the thermometer and the team should agree on the temperature before recording it. Students should record observations daily as well. They can record comments on color change, smell (good, bad, earthy, etc.), steam production or other observations. By the end, the compost should look and smell like dirt. Before leaving the composter, students should spin the composter once each.

6. Making compost needs to be monitored to prevent microorganisms from harming people and producing bad smells. Compost needs to exceed 60°C to produce healthy compost. (If after two weeks it has not done so, please contact the compost specialist or MSN.)

7. Temperatures should continue to be taken daily until the temperature in the composter comes back down to a consistent temperature of approximately 20°C for at least 4 days. Students should continue taking the temperature in both Side A and Side B. Once a consistent low temperature is reached, the students can stop daily readings.

8. At the end of 3 months (or before a vacation), take out the pre-compost and put it in the black bins. Cool composters such as worms and pill bugs will continue the decomposition process. The compost will mature in the bins until students use it at the end of the year to put in the garden.

9. Once the experiment has ended, students should graph the temperatures recorded from sides A and B. Days will be on the horizontal “x” axis and temperature will be on the vertical “y” axis. Students should use different colored lines for Side A and Side B data.

10. Students should discuss the results. Did the temperature go over 60°C for 3 days? What day of the experiment was the highest temperature? Review observation comments. What did you notice that went along with the changes in color and temperature?