Major Soil Groups of Ecological Factors (complete information)

The interrelations between the basic mineral contents of the parent substrate, biotic reactions, and climate can be seen through an analysis of the development of the great soil groups of the world.

We well give only a simple classification of them. A detailed classification would include many subdivisions and intermediate categories (Lutz and Chandler 1946, Simnoson 1957).

Podzolic soils are formed in humid temperature climate, under forest vegetation. The A₂ horizon is moderately well developed for there is sustained leaching. Soils are more or less acid and only moderately fertile. Podzols develop under coniferous forest and have a more type of humus. Graybrown and brown podzolic soil are found under hardwood forests and have mull humus.

Latosolic soils develop in humid tropical or semitropical forested regions. Humus is quickly oxidized by action of micro organisms and hence does not accumulate. The soil fauna is depauperate. Chemical weathering of the parental materials in intense. Water drainage through the porous soil is rapid, so leaching is extensive. In early stage of its formation, the soil is neutral or slightly alkaline, but as leaching continues, it becomes acidic. The soil has a thin organic layer (A₀ and A_l horizons) on a reddish, leached soil (A₂ horizon) that extends to great depths below the surface.

Chernozemic soil occurs in humid to semiarid temperature climates under grass vegetation. The grasses on dying return considerable organic matter the soil. The A, horizon is consequently dark in colour and of great thickness.

The soil contains more bases and hence is less acid than in the two types above. The B horizon in humid regions is indistinct, but where there is less rainfall, calcium salts may accumulate to form a hard pan. Prairie soils in temperate climates are among the most fertile soils of the world, but fertility decreases in the tropical and desert climates.

Desertic soils are characteristic of acid climates and contain very little organic matter. A profile is poorly developed. The surface soil is brownish gray, and grades quickly into the calcium carbonate horizon which usually forms a hardpan just below the surface. Wind erosion removes the finer particles leaving the coarser materials to form a hard pavement. The soils are but slightly weathered and leached; lacking nitrogen, they are infertile.

Mountains and Mountains Valley soils vary shallow layer or eroding rocks to deep organic soils of valleys and swampy areas.

Tundra soil occurs in cold northern areas where the substratum remains continuously frozen and the vegetation of lichens, mosses, herbs, and shrubs makes a peaty surface layer. The region is poorly drained and characterized by many scattered shallow ponds.

Alluvial soils may be important locally. These soils are mostly without a developed profile and are the result of deposition by streams. They are usually very fertile and support luxuriant vegetation.

Saline soils are found in dry climates where rapid evaporation of water results in surface deposition and accumulation of salts leached from surrounding upland areas.

This classification shows clearly the correlation that exists among soil groups, climates, and vegetation. The compositions and particularly the abundance of animals is also affected. The average biomass of soil animals under different categories of vegetation-soil-climate system is as follow (Ghilarov 1967): Moss tundra: 3 g/m² Coniferous forest: 20 g/m² Broad leaved deciduous forest: 100 g/m² Short grass plains: 25 g/m² Semi-desert; 1 g/m²

Soil Erosion

As rain water drains over the surface of the ground, it picks up and transports particles of soil more or less proportional to the rate of flow. This is a continuous process that has gone on throughout geological time, resulting in base-leveling of mountains, the filling in of valleys, and the formation of river deltas. Normally this is slow process, with changes becoming apparent only in thousand years.

With the ground covered with vegetation, the flow of water is retarded and more of it percolates into the ground or is evaporated. In fertile areas new soil is formed faster than it is eroded or at least there is stabilization.

With removal of the native vegetation and cultivation of the soil in agriculture, surface particles are more easily moved and surface water drainage is more rapid. As a result, topsoil is being lost at an alarming rate.

Much land has been so badly damaged that here is little likelihood that it will ever again be productive crops. Conservation of the fertile top soil is one of the major problems facing modem agriculture. Putting in underground drainage tiles in level farmlands helps to draw rain water into the soil and to decrease surface run off and erosion. Soil conversion procedures should be strictly followed.