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Introduction
Composting occurs when coarse organic materials are broken down into a simpler form by microorganisms. Building a compost pile is a bit like raising livestock. In this case, microorganisms are the livestock, and our goal is to provide them with everything they need for optimum growth. They need proper food (carbon source/organic materials), trace minerals, air, moisture and greens, (green chop, veg clippings, alfalfa etc., as long as it still has some green in it)
Composting is a process in which organic wastes are degraded by microorganisms at elevated temperatures under aerobic conditions. Composting is the aerobic, or oxygen-requiring, decomposition of organic materials by microorganisms under controlled conditions. Maintaining proper oxygen and moisture content and closely monitoring temperature helps achieve maximum degradation efficiency. During composting, the microorganisms consume (O2) while feeding on organic matter. Active composting generates considerable heat, and large quantities of carbon dioxide (CO2) and water vapour are released into the air. The CO2 and water losses can amount to half the weight of the initial materials, thereby reducing the volume and mass of the final product. Typical compost temperatures range from 54° to 65° Celsius. The increased temperatures result from heat produced by microorganisms during the degradation of the organic material in the waste. It produces a byproduct that is stable and in some circumstances results in complete degradation of the contaminant whilst at the same time enough heat is generated to sterilize weed seeds.
Windrow composting is usually considered the most cost-effective composting alternative. The material is layered into long piles, known as windrows. The windrow is thoroughly mixed by turning with a commercially available composting machine. Moisture, pH, temperature, and contaminant concentrations are monitored. At the completion of the composting period the windrows are disassembled and the compost is taken to the final curing area.
Composting waste is much more efficient when the compost windrow is allowed to breathe. Turning the windrow stimulates the microorganisms, which break down coarse organic matter. It is important that the windrow is turned frequently and efficiently. The more the windrow is turned the sooner it matures. Compost can be ready in as little as 6 weeks. You will know when the compost is fully digested when the temperature of the windrow drops. The original materials will no longer be identifiable. The compost will be dark chocolate brown in colour, fluffy and smell sweet and earthy like good quality potting soil. Efficient composting gives you the tools you need to grow more abundant, high quality produce and have a safer healthier environment.
Building Windrows
The first stages of composting are in many ways the most important, and proper windrow construction is the key to getting the process off to a good start. The two aspects of windrow building are: (1) mixing materials, and (2) forming and shaping the windrow. Both are discussed below.
If several different types of waste are going to be composted together they must first be thoroughly blended. Mixing is required to balance the carbon and nitrogen ratio and distribute moisture throughout the pile, and also to ensure an even distribution of large pores so that oxygen can move freely. If grass clippings or other high-nitrogen materials are being composted, this blending process is particularly critical.
Mixing can be accomplished with a front-end loader, although other equipment such as specialized windrow turning machines are commonly used when mixing grass clippings, which tend to mat together.
The size and shape of the windrow are designed to allow oxygen to flow throughout the pile while maintaining temperatures in the proper range. If windrows are too large, oxygen cannot penetrate to the center. If they are too small they will not heat up properly. The optimum size varies both with the type of material and with the time of year and geographical location.
Windrows of autumn leaves should typically be about 2.5 metres tall and 5 metres wide at the base but may be built as high as 3.0 metres in midwinter. A windrow of grass clippings mixed with leaves will need to be considerably smaller, usually about 1.5 metres high and 3.0 metres wide. These sizes are approximate, and may need to be adjusted somewhat.
While constructing the windrows, try to avoid driving on and compacting the yard waste. The sides of the windrow can be as steep as the material will naturally pile up, which typically leads to a windrow about twice as wide as it is high. Windrows can be as long as is convenient for the site, up to several hundred metres in length – if desired.
Rain only penetrates this amount usually |
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Temperature is critical |
Area of maximum heat |
How Does It Work?
During the first stage of composting, the more easily decomposed materials such as sugars and starches are rapidly degraded by cocci bacteria, thermophyllic fungi and actinomycetes, creating high temperatures over 40°C.
In the next stage, population’s shift and actinomycetes rise in numbers breaking down the more resistant materials such as lignin. By this time, there is a suppression of any pathogenic microbes. Aeration, by turning, is important during this period to eliminate anaerobic conditions, which delay completion.
In the final stage during which the ripening of compost occurs, the process is dominated by rod shaped bacterial and gradually leads to the rebuilding of the decomposed organic matter into humus.
Composting changes nitrogen from a mineral (inorganic and water-soluble) form to an organic, insoluble form. This bound or organic nitrogen is then released slowly to plants over a period of time. The result is that all organic nitrogen is recycled into plants and the slow, sustained release of nutrients into soil protects ground water and builds needed organic matter.
Finally, you reach a point when the temperature throughout the mix of compost begins to fall. The moisture is right (using the ball test) and in fact the material has reached that stage when it is no longer easy to distinguish between the manure and the bedding components. At this point, your compost is ready for spreading on the land. Your compost is finished when you no longer recognize what the original materials were. The compost will be sweet smelling like forest soil, fluffy and dark brown.
Moisture and temperature are the factors to keep in mind.
Moisture Moisture is necessary to support the metabolic processes of the microbes. Composting material should be maintained with a range of 40% to 65% moisture. The moisture content will have a direct effect on the amount of turnings that are needed. Experience has shown that the composting process becomes inhibited when the moisture content falls below 40%. Water displaces much of the air in the pore spaces of the composting materials when the moisture content is above 65%. The more moisture the more turnings will be necessary. Moisture content generally decreases as the composting; therefore, you may need to add additional moisture to the compost.
Handy Hint
Take a handful of composting material and squeeze it in your hand. It should form a ball which you can bounce in your hand. If it is too dry, no ball forms. If a ball forms, but it is one that will not break after a few bounces, it is too wet.
Temperature
It is strongly recommend using a thermometer with readings from 0 degrees to 95 degrees C to monitor compost piles or windrows. Take and record measurements daily in the same pre-chosen locations on the windrow. Depending on the length of the windrow up to twenty temperature readings maybe required to obtain a full and comprehensive picture of microbe activity.
When conditions are right, you will notice a steady rise in temperature in a new compost pile as the microbes reproduce and the processes of decay accelerate. If the material is too wet, the temperature may remain quite cool and constant. Such material can be dried by turning as often as every two to three days until the temperature begins moving up.
Handy Hint
Normally it will continue to rise until it reaches 50° to 65° C, at which point it may suddenly stop. Keep on monitoring the temperature. If it stays up, fine. If it drops, turn again.
As long as the temperature stays up in this range, it indicates there is enough oxygen for the microbes.
Condition |
Reasonable Range |
Preferred Range |
Carbon to Nitrogen (C:N) |
20 : 1 > 40 : 1 |
25 : 1 > 30 : 1 |
Moisture content |
40 > 65 % |
50 > 60 % |
| Oxygen Concentrations |
Greater than 5 % |
Much greater than 5 % |
| Particle Size |
5mm > 50mm |
Varies on materials |
| PH |
5.5 > 9.0 |
6.5 > 8.0 |
| Temperature (°C) |
45 > 65 |
55 > 60 |
Particle Size
The rate of aerobic decomposition increases with smaller particle size. Smaller particles, however, may reduce the effectiveness of oxygen movement with the windrow. Optimum composting conditions are usually obtained with particle sizes ranging from 5mm to 50mmaverage diameter.
Time
The length of time required to transform raw materials into compost depends upon the factors listed above. In general, the entire decomposition and stabilization of materials may be accomplished within a few weeks under favorable conditions; but research at tertiary institutions has shown that 10 –14 weeks of active composting for diary cattle waste is more common. Active composting will change depending upon the amount of moisture added to the compost, turning frequency, materials being composted and temperatures reached.
Curing
When windrows no longer reheat after turning, the cure stage begins. The curing stage of compost usually last 3 to 4 weeks. Curing is a very important and often neglected part of the composting process. Curing occurs at mesophilic temperatures. The importance of curing increases if the active composting stage is either shorted or poorly managed. Immature compost can contain high levels of organic acid, a high C:N ratio, and other characteristics which can be damaging to crops and plants.
Monitoring Compost Moisture
Composting precedes best at moisture content of 40-60% by weight. At lower moisture levels, microbial activity is limited. At higher levels, the process is likely to become anaerobic and foul-smelling.
When you are choosing and mixing your compost ingredients, you may wish to measure the moisture content. After the composting is underway, you probably don't need to repeat this measurement because you can observe whether appropriate moisture levels are being maintained.
If your compost starts to smell bad, chances are it's too wet. Excess water fills the pore spaces, impeding diffusion of oxygen through the compost materials and leading to anaerobic conditions. Mixing in additional bulking agent such as dry wood chips, cardboard pieces, or newspaper strips is likely to alleviate the problem. This liquid is often rich in nutrients and can be diluted for use on plants. You may find it useful to record the amount of leachate produced by each system, for comparison with initial moisture content, temperature curves, or other variables.
Once you have calculated the moisture content of your compost mixture, the other important calculation is the carbon-to-nitrogen ratio (C/N). Grass clippings and other green vegetation tend to have a higher proportion of nitrogen (and therefore a lower C/N ratio) than brown vegetation such as dried leaves or wood chips. If your compost mix is too low in nitrogen, it will not heat up. If the nitrogen proportion is too high, the compost may become too hot, killing the compost microorganisms, or it may go anaerobic, resulting in a foul-smelling mess. The usual recommended range for C/N ratios at the start of the composting process is about 30:1, but this ideal may vary depending on the bioavailability of the carbon and nitrogen. As carbon gets converted to CO2 (and assuming minimal nitrogen losses) the C/N ratio decreases during the composting process, with the ratio of finished compost typically close to 10:1.
What Happens During Composting
Composting may begin as soon as the raw materials are mixed together. During the initial stages of the process, the microorganisms rapidly consume oxygen and the easily degradable components of the raw materials. The temperature of the windrow or pile is directly related to the microorganism activity of the windrow and is a good indicator of what is going on inside. The temperature of the composting materials generally follows a pattern of rapid increase to 50°-60°C where it is maintained for several weeks depending on the materials. As active composting slows, temperatures will gradually drop until the compost reaches ambient air temperatures. A curing period usually follows the active composting period. During the curing period, the materials will continue to slowly decompose. Materials continue to break down until the last easily decomposed raw materials are consumed by the remaining microorganisms. At this point, the compost becomes relatively stable and easy to handle.
Compost as a soil amendment vs. fertilizer
Most plant nutrients in compost are in an organic form. Although compost is not high in nitrogen, phosphorous, or potassium, (it contains approximately 2% of each) these nutrients are released slowly over a long period of time. Nutrients become available to plant roots at a slower rate with compost compared to inorganic fertilizers, therefore the nutrients are less likely to leach out of the soil. Only a fraction of the nitrogen, phosphorus, and potassium applied as compost is usable by the crop the first year with more becoming available in the years that follow.
The real benefit of adding compost to the soil lies in its ability to increase soil organic matter levels. Research studies at the Connecticut Agricultural Experiment Station a have shown that a 1 inch thick layer of leaf compost annually applied and incorporated into the soil over a 12 year period increased the organic matter content from 5.9% to 12.6%. The same studies have shown that the water holding capacity of the soil was increased from 1.3 inches to 1.9 inches of water per foot of soil after seven years of compost applications.
| Other benefits of compost include: |
| Improve manure handling |
Possible saleable product |
| Improved land application |
Weed seed destruction |
| Pathogen destruction |
Lower risk of pollution problems |
| Excellent soil conditioner |
Possible revenue form tipping trees |
Windrow Turners are best up to 4 metres in width for proper aerobic composting |
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Note:
The fluffing action from a professional
windrow turner 8
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Troubleshooting
Problem |
Cause |
Solution |
| Anaerobic odor |
Excess moisture |
Turn windrow |
| Windrow too large |
Make windrow smaller |
| Temperature <140EF |
Turn windrow |
| Leaf compaction |
Turn or reduce windrow size Eliminate ponding |
| Surface ponding |
Apply odor masking agent (cures symptom, not problem) |
| Low Windrow Temperature |
Windrow too small
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Combine windrows |
| Insufficient moisture |
Add water while turning windrow |
Poor aeration
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Turn windrow |
| High Windrow Temperature |
Windrow too large |
Reduce windrow size |
Leaf compaction
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Turn windrow |
| Surface Ponding |
Depressions or ruts |
Fill depression and/or re-grade |
Inadequate slope
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Grade site to recommended slope design |
| Vectors (Rats, Mosquitoes) |
Presence of garbage (food, etc.) |
Remove garbage, or use rat bait |
| Presence of stagnant water |
Eliminate ponding |
| Fires/spontaneous combustion |
Excessive temperature |
Make windrow smaller |
| Inadequate moisture |
Add water |
| Stray sparks, cigarettes, etc. |
Keep potential fire sources away from windrows If fire does start, break windrows apart and extinguish completely |
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