Compost is used to enrich soil quality by providing organic matter, supplying nutrients and boosting microbial activity (Rodale 1955; Hoitink and Grebus 1994), all of which contribute to disease suppression, leading to healthier plants.
Organic materials such as leaves, grass, manure and kitchen scraps in a compost pile provide rich nutrients for the growth of microbes. Microbes oxidize sugars, cellulose, protein and other sources of available carbon, then use the energy obtained to convert nitrogen in the compost into the structural proteins and enzymes needed for their growth.
A quiet pile of compost is really a mass of microbial growth. As with anything, compost has an optimum period of use where your plants will get the most out of it, this relates to the maturity of the compost. It will reach a hot phase where microbials grow, and mesophilic organisms and pathogens are killed, after this it will begin to cool and the mesophilic organisms will begin to recolonize. A compost is at its matured state when the recolonization is complete. You can monitor the phases by checking the temperatures, however, if they run higher than 180°F (82°C), nutrients will be lost. If a compost pile is overheating it can be cooled by removing some of the material. After the pile has cooled, material can then be added to bring operating temperatures into the correct range (Gotaas 1956).
To make sure that a hot microbial reaction occurs and that no nitrogen is lost to the atmosphere in the form of ammonia, the starting materials in the compost bin should have the proper ratios of carbon and nitrogen. Experiments conducted early in the 20th century showed that most microbes need much more carbon than nitrogen to sustain their lifestyles. About 2/3 of the carbon is burned to supply energy, and 1/3 is used to build amino acids, proteins and other structural materials such as polysaccharides. For every 30 grams of usable carbon fed to the microbes, about 10 grams will become part of their bodies (Gotaas 1956).
Creating your own compost is cost effective and can lead to a healthy, organic garden, as long as you are careful about what you put in it. Do not add meat to an urban compost pile. It will draw pests and possibly release odors. Plastics will be unaffected and should not be added. Colored paper may contain toxic inks. Kitty litter, dog droppings and human waste should not be used because pathogens might not be destroyed if the compost pile does not reach the proper temperatures. Pesticide treated materials should be avoided, especially if you are trying to raise an organic garden. If proper temperatures are reached, diseased plants can be composted. However, some pathogens are easier to destroy with heat than others (Sullivan 2001), so it may be better to leave them out.
The hot composting process can kill most pathogens. In 1992, Avgelis et al. found that cucumber green mottle mosaic tobamovirus was inactivated by thermal composting of infected cucumber residues. The virus was below detection levels after three days of composting. As Fusarium oxysporum is heat resistant, it may be the most difficult pathogenic fungus to destroy by composting. Viruses with high inactivation temperatures, such as tobacco rattle virus, are also resistant to heat (Bollen 1985). Plasmodiophora brassicae that causes brassica club root, and tobacco necrotic virus require three to four days at about 131°F (55°C ) (Lopez and Foster 1985).
Moist compost is important, as it is easier to kill moist seeds with heat. Though some seeds, such as black nightshade, Solanum nigrum, are more resistant than others, all should be killed within three days at 131°F (55°C) (Grundy et al. 1998).
It should be noted that pesticides are not completely removed during the composting process. Organochlorines are especially resistant, and chlordane has shown up in some municipal composts from contaminated soil of termite treatments. Grass clippings are the source of most pesticide contamination in municipal composts. However, most of the time composting will reduce concentrations, and composts may even be helpful in reclaiming contaminated soil (Büyüksönmez et al. 1999; 2000). Herbicides can be a problem, though. Recently, commercial compost produced in Pullman, WA and in Austin, TX was contaminated with picloram, a highly persistent herbicide. Gardeners who used this compost were amazed when their plants were injured.
When making your own compost, proper balance of starting materials and attention to moisture and aeration are all you need as the microorganisms will do all the work for you. Creating your own provides an organic solution to food waste, tree leaves, grass clippings and garden waste and the resulting compost can be added to the soil in your back garden to produce healthier plants.
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