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Urban compost bins at Sembradores Urbanos
- 1 Intro
- 2 Background
- 3 Natural Soil Formation and Farmer Controls
- 4 Compost Components
- 5 Design
- 6 Build Your Own Tumbling Composter
- 7 Maintenance of Compost
- 8 Contact
- 9 References
Compost can help improve your soil, increase water infiltration, reduce erosion, recycle kitchen and yard waste, and grow healthier plants. In urban environments clean uncontaminated soil is not always available, composting can be used as a way to create soil and has also been found as a way to bioremediate contaminated soils. This composting project is a demonstration by Sembradores Urbanos of creating clean and fertile soil out of food and yard waste. This is one project in a series of urban gardening projects at Sembradores Urbanos.
At the same time that our agricultural soils are being contaminated and built upon with suburban sprawl, we are throwing away precious nutrient resources that could be used to restore contaminated soils. Throwing food in the landfill rather then in the compost wastes precious nutrients that are being depleted from our agricultural soils every time we grow a vegetable or grain and pluck it from the land. Throwing food down the garbage disposal can strain the capacity of sewage treatment systems and result in oxygen depletion in waterways. Throwing it in the landfill means taking up more space, longer break down times, and creates Methane (CH4) a Greenhouse gas 23 x more powerful than carbon dioxide (CO2). Reusing these food and nutrient resources for restoring soil can help close the loop of waste and contamination. Rather then throw away precious nutrient resources Sembradores Urbanos has chosen to compost their food scraps and yard waste for improving their soil .
Natural Soil Formation and Farmer Controls
- In natural systems some of the most important factors in determining soil formation includes rock type, climate and thus vegetation type, and topography.
- For farmers and gardeners some of the most important factors within control include: water levels, aeration, and plant and animal management.
- watering effects: mineral and nutrient availability to plants, rock break down, erosion or stability of soil,
- aeration effects: microbial activity and thus nutrient availability, water permeability, root growth, and erosion or stability of soil.
- plant and animal management effects: the food available for microorganisms and nutrient availability, soil compaction or aeration, 
Humus is the end result of composting. Humus is also the top soil in natural systems and can range from a depth of less then an inch to 20 ft deep. However humus has been largely depleted from practices of ploughing and the 20ft deep soil horizons of humus are no longer common within their natural environments in grasslands. Composting helps restore humus to depleted soils.
For a quick and unsmelly decomposition its important to supply plenty of oxygen and low levels of moisture so that your pile does not turn anaerobic. Basic designs usually include a box made out of pallets or a box with slits for aeration, however this requires a lot of turning and laborious maintenance. The tumbling composter design allows for compost turning without the resistance faced with pitchfork turning and reduces the labor in compost aeration.
Some other important aspects for a functioning compost is the chemical components in what materials you are trying to break down (fruits, leaves, twigs, meats, etc) and the microorganisms that live in the compost.
Tumbling Composter Advantages
- Makes turning and aeration easier
- Speeds up decomposition through increased aeration
Disadvanteages of Tumbler
- Compost is not in contact with the soil, so soil organisms should be introduced by adding a bit of soil to seed the bacteria needed for decomposition.
- Still requires turning for aeration.
Build Your Own Tumbling Composter
- 25 or 50 gallon barrel for container.
- 1- 2 in diameter PVC pipe or metal pipe 10 in longer then the height of the barrel, this will be the axle.
- 4 washers and 4 nuts. These will lock the axle in place with the barrel.
- 1/4 in Wire, for hooks for door hatch.
- Lumber for buck stand.
- 8 Screws for buck stand
Holes for Aeration and Axle:
- Drill holes in center of the top and bottom of your barrel, large enough so that your PVC axle will fit.
- Drill small holes less then 1 inch in the body of the barrel for increased aeration.
- Cut 10in square hole on side of barrel for door for easy loading of compost materials.
- Use scrap wire to make the hinges for the door on this square hole. Use the piece you cut out for the door closure.
- Add a fin to inside of barrel to help mixing while turning barrel. Fin can be made out of galvanized sheet metal bent into an L with one side bolted to inner wall. Curve sheet metal if possible to half moon shape along the inner wall for easier mixing by fins. Make sure the compost is balanced with fins on opposing sides. And make sure the compost barrel still has room to fit the axle through the center.
- Add PVC pipe axle through center, while doing this place the washer on the axle where the axle touches the barrel and a nut after it, then do the same on the opposite side of the barrel. Repeat this for the other end of the barrel so that your washer and nuts lock the axle in place with the barrel. When you turn the axle the entire barrel should move with it.
- The axle should be the part that rests on your stand.
- The stand should have a V wedge that the axle can rest in on both ends of the barrel.
- Use 4 4 by 4 wood pieces to create a balanced stand strong enough to hold the barrel on the axle.
- Cross 2 4 by 4s into a X and cut a square notch out of both pieces so that they fit together like linkon logs and stay ridged when placed together.
- Drill 2 screws at the center of the X.
- Using the same height 4 by 4s and same angle for the cross repeat the 2 previous steps.
- Line the 2 X's across facing each other, but as far apart as the barrel is long. Attach the 2 crosses together using a 2 by 4 wood piece a little longer then the length of the barrel. Screw in the 2 by 4 piece on the bottom edge of the X's right hand side.
- Your now ready to place the barrel and axle length wise across the buck stand.
Maintenance of Compost
- Turn every 7- 14 days for quick decomposition
- Add some soil to the compost to introduce microorganisms if it in a barrel or enclosed from the ground
- If compost is in the sun and dry then add some water until pile is the consistency of a damp sponge
- If too wet try to add more carbon materials: like sawdust or dry leaves.
Fixing Smelly Compost
- Add high carbon containing materials like: dry leaves, sawdust, and woodchips.
- Add two or three handfuls of lime, dolomite or wood ash.
- Turn the compost to increase aeration.
- If the smell persists and you want a quick fix, you can bury your compost in the spot where your garden will be and it will continue to decompose away from the reach of your nose.
- Mollison, Bill. Permaculture a Designers Manual.