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Aerobic Composting
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Aerobic Composting


Why oxygen is important, and tips for keeping it in your pile.

Why oxygen is important, and tips for keeping it in your pile.

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  • 1. Aerobic Composting: Why oxygen is important, and tips for keeping it in your pile Jessica Feeser Rodale Institute ©2013 Rodale Institute
  • 2. What is aerobic compost? Aerobic compost is organic matter that has undergone oxidative decomposition. When produced well, compost is a highly valuable material for farmers and gardeners. ©2013 Rodale Institute
  • 3. Why is compost valuable? Quality compost is an excellent soil amendment. When you apply it to your fields or garden, you are adding: Nutrients – compost has a wide array of valuable plant nutrients. They are stored in such a way that allows a slow release into the soil. Organic Matter – adding organic matter improves soil structure, an important characteristic of healthy soil. Better soil structure means less erosion, better water penetration, and altogether healthier plants. Soil Microorganisms – quality compost is teeming with microorganisms that can provide many services to the soil and the plants living within it. ©2013 Rodale Institute
  • 4. Why is the ecology of the soil important? Having a diverse set of aerobic organisms in your soil is hugely beneficial to the plants that are growing there. The organisms:  cycle nutrients that are already present in the soil’s organic matter and minerals into plant available forms  suppress plant pathogens  build soil structure, allowing for deeper root penetration and improved water absorption  are enlisted by the plant to improve the microclimate in the plant’s rhizosphere (affecting pH, nutrient availability, and the plant’s susceptibility to pathogens) ©2013 Rodale Institute
  • 5. The Soil Food Web ©2013 Rodale Institute
  • 6. Some agricultural practices damage soil biology… Many agricultural practices, including tillage, extended periods of bare soil, and the use of pesticides and fertilizers, damage the communities of organisms living in soil. When looking at soil from conventionally farmed fields under the microscope, it is extremely rare to see any organisms other than bacteria. Organic farms, too, are often lacking in soil microbiology. Even though they don’t use synthetic chemical inputs, many organic farmers still regularly disturb their soil through cultivation and leave soil bare for periods of time. As a result, many farmers are missing out on the benefits that could be gained by having a healthy ecology in their soils. ©2013 Rodale Institute
  • 7. Using compost as an inoculum When soils are lacking in beneficial biology, compost can be used as an inoculum. In cases where there is little organic matter in the soil, compost should be spread, as it contains the organisms themselves and organic matter which will help to sustain those organisms. Alternatively, compost can be extracted into water, and sprayed onto a field or used to water garden beds. This option is more likely to succeed when there is already organic matter in or on the surface of the soil. ©2013 Rodale Institute
  • 8. Not all composts are created equal The role of oxygen in composting: While the microorganisms in your compost pile are decomposing organic matter, they are using up oxygen. If the level of oxygen is used up faster than it is replenished through turning, some changes will start to occur. The aerobic organisms that had been doing most of the decomposing work will die or become dormant, and anaerobic organisms will start to dominate. As the decomposition shifts from being aerobic (in the presence of oxygen) to anaerobic (in the presence of no or very low levels of oxygen), valuable nutrients will be converted into gaseous forms, and will escape from the pile. When a compost pile goes anaerobic: The microorganisms that dominate the pile will no longer be those that are beneficial to the soil and Some of the nutrients will be lost as gasses. ©2013 Rodale Institute
  • 9. Composting according to the NOP ©2013 Rodale Institute
  • 10. Going beyond NOP Tips for maintaining oxygen in your compost pile: 1. Developing your recipe 2. Turning according to temperature 3. Reading the signs: turning when oxygen levels fall ©2013 Rodale Institute
  • 11. 1. Developing your recipe Know your ingredients: While some compost ingredients such as straw, leaf litter, and wood chips will behave in a fairly consistent way, others such as manure and food waste tend to be more variable. It is important to be familiar with your starting materials: how much nitrogen do they contain? How will they affect the moisture of the pile? In this way, you can better understand how to build a pile with the appropriate moisture level and C:N ratio. ©2013 Rodale Institute
  • 12. 1. Developing your recipe Finding the right balance: The key to a good compost recipe is balance. If your goal is to make a compost pile that meets NOP regulations, you need enough nitrogen in the pile to drive the heating of the pile for 15 days. However, too much nitrogen in your compost will cause the oxygen to be used up quickly, and more frequent turning will be required to keep it from going anaerobic. For information on C:N ratios of compost materials, visit: Water is necessary for decomposition to occur. Too much water, however, will make the pile less fluffy, and therefore unable to hold enough oxygen. Again, more frequent turning will be necessary to keep the pile from becoming anaerobic. The ideal moisture for a compost pile is between 40% and 50%. A simple way to gauge this is to dig into the pile at least 18 inches, pull out a handful of compost, and give it a very firm squeeze. If 1-2 drops of water come out, the moisture level is where it should be. ©2013 Rodale Institute
  • 13. 2. Turning according to temperature As decomposition picks up speed, the temperature inside a compost pile starts to climb. High temperatures mean that oxygen is being used quickly, and if turning does happen soon reduced oxygen conditions will set in. Turning before it reaches 160º F (71º C) will help prevent your pile from going anaerobic. ©2013 Rodale Institute
  • 14. 3. Reading the signs of anaerobic conditions in your pile When the level of oxygen in a compost pile starts to drop, certain changes can be observed:  A foul smell, caused by ammonia and other gaseous compounds that are escaping the pile  Flies gather, attracted by the odors  Actinobacteria develops within the pile Actinobacteria thrives in the zone between aerobic and anaerobic environments, and appears in compost as a powdery white layer. While actinobacteria is not in itself bad, its presence lets you know that oxygen levels are dropping in sections of the pile and it’s time to turn. These indicators mean oxygen levels are getting low, and the pile should be turned as soon as possible to maintain aerobic conditions. ©2013 Rodale Institute
  • 15. Acknowledgements This material is based upon work supported by the Natural Resources Conservation Service, U.S. Department of Agriculture, under Grant Agreement 69-2D37-11-499. Any opinions, findings, conclusions or recommendations expressed in this publication are those of the author and do not necessarily reflect the view of the U.S. Department of Agriculture. Special thanks to Mr. Noel Soto, USDA, NRCS, for his continued support of our work. ©2013 Rodale Institute