Soil incorporation is probably the simplest method of composting. Food and yard wastes are finely chopped, mixed with soil, and buried 20 cm (8 inches) or deeper in the earth. Depending on soil temperature, bacterial activity, and the carbon content of the wastes, decomposition will take from one month to a year.
One word of caution, however! High-carbon materials (like raw autumn leaves) are not appropriate for this method, because they'll steal their nitrogen from the surrounding soil. Leaves may also acidify the soil or inhibit the growth of plants if they are dug into the ground without first being at least partially composted.
Even high-nitrogen materials should be given ample time to decompose underground before the area is used for planting, because the decomposer organisms will take nitrogen wherever they can find it while they're working. Some people get around the problem of nitrogen loss by adding bloodmeal to the soil before they bury the compost materials.
A posthole digger is a handy tool for soil incorporation, although a spade will do. The idea is to dig a series of holes around the drip line of trees and shrubs, or in a fallow area of the garden (to avoid stealing nitrogen from growing plants), and bury organic wastes there. The compost is made right where it is most needed. You can use what space you have, then start over where the first load has composted. If the holes are dug before the ground freezes, you can continue to dispose of wastes in this way all through the winter.
Trenching involves digging a long pit instead of separate holes, usually between rows in a garden. It is capped with a layer of soil as the wastes are gradually added.
This method is often used by British gardeners in a simple three-year rotation of 1) soil incorporation, 2) crops, and 3) pathways. In the first year a trench is dug, filled with nitrogen-rich wastes, and covered with soil. The row next to it is used to grow crops and a third row is used as a path.
In each successive year, the fertile soil of the previous year's trench is used to grow the crops, and the former path is the composting trench. Thus the garden's soil is continuously renewed. Although this method demands far less space than a conventional composting system, it does require three rows to grow one row of crops. Each garden will suggest its own variations. Trenches can be dug under the pathways in use, one section at a time, as the space is needed. In a garden too small for paths, a two-year rotation of crops and trench is fine.
Mulching copies nature's way of composting on the surface of the soil and gardeners have been doing it for centuries. Woody, "brown" organic materials are spread in a layer on the ground, over a garden, or around shrubs and trees. Because they are not dug into the soil but decompose on the surface, they don't disturb the pH balance of the soil or rob it of nitrogen.
Although it is perhaps the slowest method of composting, mulching offers other benefits. It discourages weeds, protects soil from compacting or eroding, and keeps the roots of plants cool and moist in hot weather, insulated in the winter.