Decomposition of organic material in the compost pile is dependenton maintaining microbial activity. Any factor which slows orhalts microbial growth will also impede the composting process. Efficient decomposition will occur if the following factors are used to fullest advantage.
AERATION: Oxygen is required for microbes to efficiently decompose the organic wastes. Some decomposition will occur inthe absence of oxygen (anaerobic conditions); however, the processis slow and foul odors may develop. Because of the odor problem, composting without oxygen is not recommended in a residential setting unless the process is conducted in a fully closed system. Turning the pile once or twice a month will provide the necessary oxygen and significantly hasten the composting process. A pilethat is not mixed may take three to four times longer before it can be used. A well mixed compost pile will also reach higher temperatures which will help destroy weed seeds and pathogens.
MOISTURE: Adequate moisture is essential for microbial activity. A dry compost pile will not decompose efficiently. If rainfall is limited, it will be necessary to water the pile periodically to maintain a steady decomposition rate. Enough water should beadded to completely moisten the pile, but over watering should be avoided. Excess water can lead to anaerobic conditions. Waterthe pile so that it is damp, but does not remain soggy. The compost will be within the right moisture range if a few drops ofwater can be squeezed from a handful of material. If no water can be squeezed out, the material is too dry. If water gushes from your hand, it is too wet.
PARTICLE SIZE: The smaller the size of organic wastes, the faster the compost will be ready for use. Smaller particles have much more surface area that can be attacked by microbes. A shreddercan be used before putting material in the pile, and is essentialif brush or sticks are to be composted. A low cost method of reducing the size of fallen tree leaves is to mow the lawn before raking or run the lawn mower over leaf piles after raking. Raked piles should be checked to insure that they do not contain sticks or rocks which could cause injury during operation of the mower. If the mower has an appropriate bag attachment, the shredded leaves can be collected directly. In addition to speeding up the composting process, shredding will initially reduce the volume ofthe compost pile.
FERTILIZER AND LIME: Microbial activity is affected by the carbonto nitrogen ratio of the organic waste. Because microbes requirea certain amount of nitrogen for their own metabolism and growth,a shortage of nitrogen will slow down the composting processconsiderably. Materials high in carbon relative to nitrogen suchas straw or sawdust will decompose very slowly unless nitrogen fertilizer is added. Tree leaves are higher in nitrogen thanstraw or sawdust but decomposition of leaves would still benefitfrom an addition of nitrogen fertilizer or components high innitrogen. Grass clippings are generally high in nitrogen and when mixed properly with leaves will enhance decomposition. Poultry litter, manure or blood meal can be used as organic sources ofnitrogen. Otherwise, a fertilizer with a high nitrogen analysis(10-30%) should be used. Other nutrients such as phosphorus andpotassium are usually present in adequate amounts for decomposition.
During the initial states of decomposition organic acids are produced, decreasing the pH. In the past, small amounts of lime have been suggested for maintaining and enhancing microbial activity at this time. However, high rates of lime will convert ammonium nitrogen to ammonia gas which will lead to the loss of nitrogen from the pile. Research indicated that lime add itions may hasten decomposition; however, the loss of nitrogen from thepile often offsets the benefits of lime. In general, lime is not necessary for degradation of most yard wastes. The pH of finished compost is usually alkaline (pH = 7.1-7.5) without the addition of lime. If large quantities of pine needles, pine bark, orvegetable and fruit wastes are composted, additional lime may benecessary.
Many organic materials are suitable for composting. Yard wastes,such as leaves, grass clippings, straw, and non woody plant trimmings can be composted. Leaves are the dominant organic waste in most backyard compost piles. Grass clippings can be composted; however, with proper lawn management, clippings do not need to beremoved from the lawn. If clippings are used, it is advisable to mix them with other yard wastes, otherwise the grass clippings may compact and restrict airflow. Branches and twigs greater than 1/4inch in diameter should be put through a shredder/chipper. Kitchen wastes such as vegetable scraps, coffee grounds, and eggshells may also be added.
Sawdust may be added in moderate amounts if additional nitrogen isapplied. Approximately 1 lb. of actual nitrogen (6 cups of ammonium nitrate) is required for 100 lbs. of dry sawdust. Wood ashes act as a lime source and if used should only be added insmall amounts (no more than 1 cup per bushel or 10 pounds per tonof compost). Ordinary black and white newspaper can be composted; however, the nitrogen content is low and will consequently slowdown the rate of decomposition. If paper is composted, it should not be more than 10% of the total weight of the material in the compost pile.
Examples of other organic materials that can be used to add nutrients to the pile include: blood meal, bone meal, livestock manure, non-woody clippings, vegetable and flower garden refuse,hay, straw and lake plants. Livestock manure and poultry litterare nitrogen sources for composting. Approximately 100 pounds ofpoultry litter will provide 1.8 pounds of nitrogen.
Some materials may pose a health hazard or create a nuisance andtherefore should not be used to make compost. Adding human or petfeces cannot be recommended because they may transmit diseases. Meat, bones, grease, whole eggs, and dairy products should not beadded because they can attract rodents to the site. Most plant disease organisms and weed seeds are destroyed during the composting process when temperatures in the center of the pilereach 150-160 F.
Although plants that have been treated with herbicides orpesticides should be avoided for composting, small amounts ofherbicide-treated plants (e.g., grass clippings) may be mixed inthe pile as long as one is careful to allow thorough decomposition. Ideally, clippings from lawns recently treated with herbicides should be left on the lawn to decompose.
Use of plastic garbage bags is perhaps the simplest way to make compost. The bags are easy to handle, and require minimal maintenance. To make compost using this method, 30-40 gallon plastic bags should be alternatively filled with plant wastes,fertilizer and lime. About one tablespoon of a garden fertilizer with a high nitrogen content should be used per bag. Lime (onecup per bag) helps counteract the extra acidity caused by anaerobic composting. After filling, add about a quart of water. Close tightly. Set aside for six months to a year. Bags can beset in a basement or heated garage for better decomposition during winter months. Using garbage bags requires no turning or additional water after closing. The main advantage of composting in garbage bags is that it requires little maintenance; however,because oxygen is limited, the process is slow.
The barrel or drum composter generates compost is a relatively short period of time and provides an easy mechanism for turning. This method requires a barrel of at least 55 gallons with a securelid. Be sure that the barrel was not used to store toxic chemicals. Drill 6-9 rows of 1/2 inch holes over the length ofthe barrel to allow for air circulation and drainage of excess moisture. Place the barrel upright on blocks to allow bottom aircirculation. Fill the barrel 3/4 full with organic waste materia land add about 1/4 cup of high (approximately 30%N) nitrogen containing fertilizer. Apply water until compost is moist but notsoggy.
Every few days, turn the drum on its side and roll it around they ard to mix and aerate the compost. The lid can be removed after turning to allow for air penetration. Ideally, the compost should be ready in two to four months. The barrel composter is an excellent choice for the city dweller with a relatively small yard.
For larger quantities of organic waste, bin type structures are the most practical. As an example, a circular bin can be made byusing a length of small spaced woven wire fencing and holding ittogether with chain snaps. The bin should be about three to fivefeet in diameter and at least four feet high. A stake may bedriven in the middle of the bin before adding material to help maintain the shape of the pile and to facilitate adding water. With this design, it is easiest to turn the composting material by simply unsnapping the wire, moving the wire cylinder a few feet,and turning the compost back into it.
A very efficient and durable structure for fast composting is athree-chambered bin. It holds a considerable amount of compost, and allows good air circulation. The three chambered bin works onan assembly line idea, having three batches of compost in varying stages of decomposition. The compost material is started in thefirst bin and allowed to heat up for three to five days. Next, itis turned into the middle bin for another 4-7 days, while a newbatch of material is started in the first bin. Finally, them aterial in the middle bin is turned into the last bin as finishedor nearly finished compost.
To make a three-chambered bin, it is best to use rot resistant wood such as redwood, salt treated wood or wood treated with an environmentally safe preservative or a combination of treated woodand metal posts. Unless the wood is treated or rot resistant, it will decompose within a few years. Each bin should be at least three to five feet in each dimension to contain enough volume to compost properly. Using removable slats in the front offers complete access to the contents for turning.
The compost pile should be located close to where it will be usedand where it will not interfere with activities in the yard oroffend neighbors. From the aesthetic point of view, it is best tocompost in a location screened from view of both your property andneighbor's property. Examples of good locations for the pile include: near the garden or between the garage and house. Do not locate the compost pile near a well or on a slope that drains to surface water such as a stream or a pond. The pile will do best where it is protected from drying winds and in partial sunlight to help heat the pile. The more wind and sun the pile is exposed to,the more water it will need. Locating the pile too close to trees may also create problems as roots may grow into the bottom of the pile and make turning and handling the compost difficult.
Organic wastes, such as leaves, grass, and plant trimmings are put down in a layer eight to ten inches deep. Coarser materials will decompose faster if placed in the bottom layer. This layer should be watered until moist, but not soggy. A nitrogen source shouldbe placed on top of this layer. Use one to two inches of livestock manure, or a nitrogen fertilizer such as ammoniumnitrate or ammonium sulfate at a rate of one third of a cup forevery twenty five square feet of surface area. If these nitrogen sources are not available, one cup of 10-10-10 fertilizer per 25square feet of surface area will also suffice. Do not usefertilizer that contains herbicide or pesticide.
About a one inch layer of soil or completed compost can be appliedon top of the fertilizer layer. One purpose of adding soil is to ensure that the pile is inoculated with decomposing microbes. The use of soil in a compost pile should be considered optional. Inmost cases, organic yards wastes such as grass clippings or leaves contain enough microorganisms on the surface to effect decomposition . Studies have shown that there is no advantage inpurchasing a compost starter or inoculum. One way to insure that activator microbes are present in the new compost is to mix insome old compost as the pile is prepared.
Most compost piles should initially be prepared in layers. This will facilitate decomposition by insuring proper mixing. Eachpile ideally should be about 5 feet high. If only tree leaves areto be composted, layering may not be necessary. Fallen leaves canbe added as they are collected. Leaves should be moistened ifthey are dry and since dead leaves lack adequate nitrogen for rapid decomposition, addition of a high-nitrogen fertilizer (10-30% analysis) should be added to speed up breakdown. Approximately 5 ounces (about 1/2 cup) of 10% nitrogen fertilizer should be added for each 20 gallons of hand compressed leaves.
To prevent odors and hasten decomposition, the pile must be turnedoccasionally. Turning also exposes seeds, insect larvae, and pathogens to lethal temperatures inside the pile. Odors may ariseei ther from the addition of excessive amounts of wet plant materials like fruits or grass clippings, or from overwatering. Aproperly mixed and adequately turned compost heap will not have objectionable odors. An actively decomposing pile will reach temperatures of 130-160 F in the middle.
Reasons for the pile not heating up may be due to: too small apile, not enough nitrogen, lack of oxygen, too much or not enough moisture. The pile should be turned when the temperature in thecenter begins to cool. This will introduce oxygen and undecomposed material into the center and subsequently regenerate heating. The composting process is essentially complete when mixing no longer produces heat in the pile.
Generally, a well managed compost pile with shredded material under warm conditions will be ready in about 2-4 months. A pile left unattended and material not shredded may take over a year to decompose. Piles prepared in the late fall will not be ready for use the following spring. When the compost is finished, the pilew ill be about half its original size and have an earthy smell toit.
Written by: Larry Bass, T.E. Bilderback, North Carolina Cooperative Extension Service
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