Peat Soil

any one of a group of soil types formed under conditions of excess moisture from precipitation or from stagnant fresh or slowly running groundwaters that have some mineral content. Peat soils are the upper portion of peat bog deposits, formed below a layer of particular types of vegetation that thrive under conditions of excess moisture. They are distributed primarily in the temperate zone of the northern hemisphere.

The basic processes characteristic of peat soil are the initial stages of peat formation—the accumulation of partially decomposed plant remains. With the accretion of new layers of peat soil, the lower layers become biologically less active; the number of microorganisms in the lower layers decreases sharply, and the soil becomes less fertile as it is transformed into peat-forming soil. The lower boundary of peat soil approximately coincides with the depth to which water in the soil descends in summer (from 30 to 50–60 cm, sometimes deeper).

Peat soils differ from underlying rocks in their higher coefficient of filtration and greater permeability to water. Two types are distinguished: high-moor and low-moor. High-moor peat soils are formed under conditions in which precipitation provides the required moisture. Vegetation characteristic of these soils includes sphagnums, highly compressed pine (more rarely, spruce), ledum, Chamaedaphne, bog bilberry, cloudberry, Oxycoccus, Scheuchzeria, and cotton grass. The soils are highly acidic (pH 2.5–3.6) and have a low ash content (2.4–6.5 percent), a very high moisture capacity (from 700 to 2,000 percent of the dry weight or more), anda bulk density of 0.10–0.15.

Low-moor peat soils are formed in areas fed by abundant underground waters and surface runoff. Eutrophic vegetation flourishes on these soils. Characteristic plants are sedges, hyp-nums and sphagnums, reed grass, shrubs, and trees (spruce, birch, and pine). Low-moor peat soils are weakly acidic or neutral. The ash content is 6–12 percent in normal soils and 30–50 percent in high-ash types. The moisture capacity is 500–700 percent of the dry weight, and the bulk density is 0.15–0.20.