Composted material is less bulky than the original material, and easier and more pleasant to handle. During the composting process, carbon dioxide and water are lost to the atmosphere and the size of the pile decreases by 30–60%. In addition, many weed seeds and disease-causing organisms may be killed by the high temperatures in the pile. Unpleasant odors are eliminated. Flies, a common problem around manures and other organic wastes, are much less of a problem with composts. Composting reduces or eliminates the decline in nitrogen availability that commonly occurs when organic materials, such as sawdust or straw, are added directly to soil. Composting is also very useful for recycling kitchen wastes, leftover crop residues, weeds, and manures. Many types of local organic waste, such as apple pumice, lake weeds, leaves, and grass clippings, can be composted.
PROTECTING DRINKING WATER SUPPLIES
Composting of manure is of special interest in watersheds that supply drinking water to cities, such as those that serve New York. The parasites Giardia lamblia (beaver fever) and Cryptosporidium parvum cause illness in humans and are shed through animal manure, especially young stock. These organisms are very resistant in the environment and are not killed by chlorination. Composting of manure, however, is an economical option that kills the pathogen and protects drinking water.
There is evidence that compost application lowers the incidence of plant root and leaf diseases, as mentioned. In addition, the chelates and the direct hormonelike chemicals present in compost stimulate the growth of healthy plants. Then there are the positive effects on soil physical properties that are derived from improving soil organic matter. These are some of the broad benefits to plant growth that are attributed to compost.
If you have a large amount of organic waste but not much land, composting may be very helpful and may create a valuable commercial product that improves farm profitability. Also, since making compost decreases the solubility of nutrients, composting may help lessen pollution in streams, lakes, and groundwater. On many poultry farms and on beef feedlots, where high animal populations on limited land may make manure application a potential environmental problem, composting may be the best method for handling the wastes. Composted material, with about half the bulk and weight of manure, and a higher commercial value, can be economically transported significant distances to locations where nutrients are needed. In addition, the high temperatures and biological activity during the composting process can help to decrease antibiotic levels in manures, which can be taken up by crops growing on manured land. Compost can also be stored easily, so it can be applied when soil and weather conditions are optimal.
The reasons for composting and using composts need to be balanced by good practices such as locating the pile to minimize runoff and possible pollution of surface waters. Compost piles may produce odors when turned, so it’s best to site piles away from where neighbors might get a more powerful whiff than they’d like. Composting in dry regions or under cover may produce composts that contain relatively high levels of salts, and you may need to apply them at lower rates to avoid damaging plants.
Without denying the good reasons to compost, there are frequently very good reasons to just add organic materials directly to the soil, without composting. Compared with fresh residues, composts may not stimulate as much production of the sticky gums that help hold aggregates together. Also, some uncomposted materials have more nutrients readily available to feed plants than do composts. If your soil is very deficient in fertility, plants may need readily available nutrients from residues. Routine use of compost as a nitrogen source may cause high soil phosphorus levels to develop, because of the relatively low N:P ratio. Finally, more labor and energy usually are needed to compost residues than to simply apply the uncomposted residues directly.