The formation of soil occurs by the process of weathering and soil development. The weathering is further divided into the physical and chemical types. It is basically a destructive process which changes the rocks into soils. The physical weathering occurs with the help of wind, water and temperature. The chemical weathering occurs with the help of oxidation, reduction, hydration and hydrolysis. On the other hand the soil development is a constructive process that forms a soil profile. In this case a humus layer is formed along with the aggregation of calcium carbonate. These are known as humification and calcification respectively. The silica in the soil is removed and the iron and calcium are left and this process is known as the laterisation.
There are many factors which reduce the fertility of soil. It includes the leaching, overgrazing, silt deposition as the result of flood, wind and water soil erosion, no rain or irrigation, precipitation of minerals due to the fluctuations in the ph, increase in salt content in the upper layer of soil and inability to rotate the crops which may lead to the deficiency of minerals and increase in the soil borne diseases.
