Making and Using Compost Reviewed by Christopher J. Starbuck Division of Plant Sciences University of Missouri Extension Compost is partially decomposed organic matter. It is dark and easily crumbled and has an earthy aroma. It is created by biological processes in which soil-inhabiting organisms break down plant tissue. When decomposition is complete, compost has turned to a dark-brown powdery material called humus. The processes occurring in a compost pile are similar to those that break down organic matter in soil. However, decomposition occurs much more rapidly in the compost pile because the environment can be made ideal for the microbes to do their work Why make compost? Gardeners often have difficulty disposing of leaves, grass clippings and other garden refuse, particularly in urban areas. Missouri law bans these materials from landfills, so finding environmentally sound ways to dispose of them has become even more important. These byproducts of the garden and landscape can be turned into useful compost with no more effort than it takes to bag and haul them away. Home composters avoid hauling or utility costs associated with centralized composting facilities and end up with a valuable soil conditioner or mulch for the landscape and garden. The value of compost Good compost consists primarily of decomposed or partially decomposed plant and animal residues but may also contain a small amount of soil. Compost improves both the physical condition and the fertility of the soil when added to the landscape or garden. It is especially useful for improving soils low in organic matter. Organic matter in compost improves heavy clay soils by binding soil particles together into “crumbs,” making the soil easier to work. Binding soil particles also helps improve aeration, root penetration and water infiltration and reduces crusting of the soil surface. In sandy soils, additional organic matter also helps with nutrient and water retention. Compost also increases the activity of soil microorganisms that release nutrients and other growth-promoting materials into the soil. Although compost contains nutrients, its greatest benefit is in improving soil characteristics. You should consider compost a valuable soil amendment rather than a fertilizer because additional fertilization may be necessary to obtain acceptable growth and yields. Compost also is a valuable mulching material for garden and landscape plants. It may be used as a top-dressing for lawns and, when it contains a small amount of soil, as part of a growing medium for houseplants or for starting seedlings. How compost forms Composting is a method of speeding natural decomposition under controlled conditions. Raw organic materials are converted to compost by a succession of organisms (Figure 2). During the first stages of composting, bacteria increase rapidly. Later, actinomycetes (filamentous bacteria), fungi and protozoans go to work. After much of the carbon in the compost has been used and the temperature of the pile has fallen, centipedes, millipedes, sowbugs, earthworms and other organisms continue the decomposition. As microorganisms decompose the organic materials, their body heat causes the temperature in the pile to rise dramatically. The center of a properly made heap should reach a temperature of 110 to 140 degrees F in four to five days. At this time, the pile begins “settling,” which is a sign that the pile is working properly. The pH of the pile will be very acidic at first, at a level of 4.0 to 4.5. By the time the process is complete, the pH should rise to about 7.0 to 7.2. The heating in the pile kills some of the weed seeds and disease organisms. However, this happens only in areas where the most intense temperatures develop. In cooler sections toward the outside of the pile, some weed seeds or disease organisms may survive. So, proper turning is important to heat all parts of the pile. The organisms that break down the organic materials require large quantities of nitrogen. So, adding nitrogen fertilizer, or other materials that supply nitrogen, is necessary for rapid and thorough decomposition. During the breakdown period, the nitrogen is incorporated into the bodies of the microbes and is not available for plant use. This nitrogen is released when the decomposition is completed and the compost is returned to the garden. Read on at extension.missouri.edu/publications/DisplayPub.aspx?P=G6956
Posted on: Mon, 29 Dec 2014 23:48:14 +0000
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