Building Soils for Better Crops, Third Edition

Making and Using Composts


The reason of our thus treating composts of various soils and substances, is not only to dulcify, sweeten, and free them from the noxious qualities they otherwise retain. . . . [Before composting, they are] apter to ingender vermin, weeds, and fungous . . . than to producewholsome [sic] plants, fruits and roots, fit for the table.


Decomposition of organic materials takes place naturally in forests and fields all around us. Composting is the art and science of combining available organic wastes so that they decompose to form a uniform and stable finished product. Composts are excellent organic amendments for soils. Composting reduces bulk, stabilizes soluble nutrients, and hastens the formation of humus. Most organic materials, such as manures, crop residues, grass clippings, leaves, sawdust, and many kitchen wastes, can be composted.


Some people talk about “low-temperature” composting—including “sheet,” worm (vermicomposting), and small-pile composting—and “high-temperature” composting. We like to use the term “composting” only when talking about the rapid decomposition that takes place at high temperatures.

The microorganisms that do much of the work of rapid composting perform well at elevated temperatures with plenty of oxygen and moisture. These compost adapted organisms cover the entire range of warm, or mesophilic (up to 110°F), and hot, or thermophilic (from 110° up to 130°F and even higher), conditions. Temperatures above 160°F can develop in compost piles, helping kill off weed seeds and disease organisms, but this overheating usually slows down the process, since it may cause extreme drying and triggers a die-off of all but the most heat-resistant organisms. At temperatures below 110°F, the more prolific mesophilic organisms take over and the rate of composting again slows down, especially as it drops toward ambient temperatures, a process known as “curing.” The composting process is slowed by anything that inhibits good aeration or the maintenance of high enough temperatures and sufficient moisture.

Composting farm wastes and organic residues from off the farm has become a widespread practice. Accepting and composting lawn and garden wastes provide some income for farmers near cities and towns. They may charge for accepting the wastes and for selling compost. Some farmers, especially those without animals or perennial forage crops that help increase organic matter, may want to utilize the compost as a source of organic matter for their own soils.

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