SOIL FORMING PROCESS

The soil forming processes include gains and losses of material to the soil profile, movement of matter from one part of the profile to the other and chemical transformation within individual horizons. The major soil processes include weath­ering, translocation, organic changes, gleying, podzolisation and desilication.

TRANSLOCATION This term includes several kinds of movement of material within the soil body, mainly by the agent of water. Leaching is the downward movement of material in solution or colloid suspension. Eluviation is the physical downward washing of clay or other fine particles. Leaching and eluviation may move material right out of the soil system. But commonly the solutes and particles are redeposited at the base of the soil profile, forming an alluvial or enriched ho­rizon.

In calcification, calcium carbonate accumu­lates within soils to form a oncentration. This takes place in arid or semi-arid environments where potential vapotranspiration exceeds pre­cipitation. The movement of soil solution is likely to be upward, drawn by capillary attraction towards the drying surface. The calcification is enhanced in grasslands. Grass uses calcium, drawing it up from the lower layers of soil, and returning it to the soil when it dies. Salinisation or aikalisation is the process by which soils are enriched with salt. In cases where evaporation is very intense, calcium or sodium salts may form a whitish layer on the soil surface, harmful to plant growth. Such accumulation is the result of capillary rise of water from a water table that is saline and close to the surface. Or it is induced by man by irrigation praCtices where evapora­tion is intense and produces salinisation unless counteracted by regular flushing, deep ploughing or chemical treatment.

ORGANIC CHANGES Organic accumulation in the soil profile takes place mainly at the ground surface with the decay of plant material. Its forms are: degradation or the action '.If fungi, algae, small insects and worms, reducing the surface litter to its skeletal material; humification or formation of humus of the dead organic content of the soil, mainly through bacteriological activity; mineralisation or the process of decomposition of humus which releases nitrogen compounds into the soil. All these processes always accompany each other.