Soil and Its Origin Most of Earths surface is covered by an unconsolidated layer of regolith (regolit), collective term for sediment, regardless of how it was deposited, as well as layers of pyroclastic materials and residue formed by weathering. Only some of these regolith is soil (toprak), which by definition is made up of weathered rock, air, water and organic matter and supports vegetation. A residual soil (kalnt toprak) is one that develops from weathering of the rock directly beneath it. Transported soil (tanm toprak) soil from elsewhere. Such as flood plain deposits (soils) from rivers or wind-transported deposits (loess ls) Soil profile

Factors in Soil Formation Climate is the most important factor influencing soil type and depth. Intense chemical weathering in the tropics yields deep soils from which most of the soluble minerals have been removed by leaching. In arctic and desert climates, soils tend to be thin, contain significant quantities of soluble minerals and be composed mostly of materials derived by mechanical weathering. Soils in humid regions are generally characterized by downward movement of water through the earth materials. Such soils are called pedalfers for the high content of aluminum and iron oxides they contain. They are marked by effective downward leaching due to high rainfall and to the acids produced by the decay of abundant humus. In dry or arid climates soils called pedocals (pedokal) form. These soils are characterized by little leaching, scant humus, and the upward movement of soil water beneath the land surface. The water is drawn up by subsurface evaporation and capillary action.

In arid climate as water evaporates, calcium carbonate leached from above precipitates in horizon B, where it forms irregular masses of caliche (kali). Laterite (laterit) is a soil formed in the tropics where chemical weathering is intense and leaching of soluble minerals is complete. These soils are red, commonly extend to depths of tens of meters, and are composed largely of aluminum hydroxides, iron oxides and clay minerals; even quartz, a chemically stable mineral, is leached out. 22 Laterit

Pedokal Parent Material Soils that develops on basalts will be rich in iron oxides because basalt contains abundant ferromagnesian silicates, but rocks lacking these minerals will not yield an iron oxide rich soil no matter how thoroughly they are weathered. Activities of Organisms Much of the humus in soils is provided by grasses or leaf litter that microorganisms decompose to obtain food. In doing so, they break down organic compounds within plants and release nutrients back into the soil. In addition, organic acids produced by decaying soil organisms are important in further weathering of parent materials and soil particles. Relief (Rlyef) and Slope (Yama) Relief is the difference in elevation between high and low points in a region. Because climate is such an important factor in soil formation and climate changes with elevation, areas with considerable relief have different soils in mountains and adjacent lowlands.