SOIL FORMING FACTORS

SOIL FORMING FACTORS
Many types of processes and influences, together known as soil formers, act to develop a soil. Some of these are passive conditions; others are active agents. Many years ago, Russian pedologist Dukuchaiev firmly established five main soil formers: (i) parent material; (H) landform; (Hi) time; (iv) climate; and (v) biological activity. The main ways in which the parent material is liable to have a lasting effect on soils are through texture and fertility. Thus, sandstone grit stones give rise to fr~e-draining coarse-textured soils and shales produce finer soils. Of the relief features, slope and situation determine erosion and depositional factors; topography also affects drainage conditions and controls exposure to the sun. Time is a factor in creating mature soils. Young soils are thin, having evolved, for example, from recently deposited river alluvium of glacial till. How­ever, it is difficult to be precise about the role of time factor in soil formation.

Of the active soil formers, climate is perhaps the most important. (a) Moisture conditions affect the soil; an excess of precipitation over evaporation tends to leach away the soil, while in dry climates when evaporation exceeds precipitation, there is a soil-water deficit, and the soil is dry. (b) Temperature influences chemical activity (which is generally increased by higher temperature and decreased by lower temperature), and the bacterial activity, which is increased by warmer soil temperatures, and consequently, humus is reduced as in the humid tropics. (c) Winds may increase the evaporation from soil surfaces and may remove surface soil in acid regions. Wind-blown dust may accumulate and thus provide the parent material of soil. Both plants and animals, from microscopic bacteria to large mammals including man, influence soil development. Plants. help to che~k erosion and maintain soil fertility.

Influences of animals in the soil is largely mechanical, sometimes also chemical. Earthworms are important agents in humid areas. They rework the soil by burrowing and also change the texture and chemical composition of the soil as it passes through their digestive systems. Ants and termites bring large quantities of soil from lower layers to the surface. Soil characteristics closely determine the type of animals present in the soil. Soils and the ecosystem share a close relationship.