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Think of the decomposition column as a miniature compost pile or landfill, or as a blanket of fallen leaves on a forest floor. Through the sides of the bottle you can see different substances decompose and observe how moisture, air, temperature and light affect the process.

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* Three two-liter bottles

* Kitchen scraps (vegetable matter), leaves, newspaper ... you decide!


1. Cut top off bottle No. 1 3/4 to 1-1/4 inches below the shoulder, so that the cylinder has straight sides.

2. Cut top off bottle No. 2 3/4 to 1-1/4 inches above the shoulder. Cut the bottom off 3/4 to 1-1/4 inches below the hip. The resulting cylinder will have two tapered ends.

3. Cut bottom off bottle No. 3 3/4 to 1-1/4 inches above the hip, so the cylinder has a straight end.

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4. Invert C and stack into the base D. Stack B and tape middle seam securely. Poke air holes. Add top A with a piece of tape for a hinge.


What common substance falls from the sky, runs through the soil, collects in puddles and lakes, and then vaporizes back into the atmosphere in a never-ending cycle? Water, of course. The terraqua column - with its three basic components: soil, water, and plants - gives you a model to explore this link between land and water.


* Two 2-liter bottles (one with a base, one without)

* One bottle cap

* Wicking material (fabric interfacing or cotton string)

* Water, soil, and plants


1. Cut the bottle that has no base 2-1/2 to 1-3/4 inches below the shoulder curve, leaving a straight end on cylinder B. Cut off the bottom 2/5 to 4/5 of an inch below the hip curve, leaving a tapered end on cylinder B.

2. Cut top off the second bottle 4/5 of an inch below the shoulder, leaving a straight end on piece C. Punch or drill a hole in cap with an awl or drill. It is important to enlarge the hole to about 2/5 of an inch wide, enough to easily accommodate the wick. Attach cap to A.

3. Invert top A into cylinder B. Tape this joint for stability. Slide A/B unit into C.

4. For the wick, cut a strip of fabric interfacing 2/5 to 4/5 of an inch wide and slightly shorter than the height of the column. Insert a wet wick as shown.

5. When adding soil, make sure the wick runs up into the soil and is not plastered along the sides of the column or protruding above the soil surface. After you fill the column, you may want to tape B and C together.

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