Tag: soil - formation and profile

Leaching is the process by which soluble nutrients are lost from the soil. The A horizon of the soil is the surface layer that consists largely of minerals. The A$ _2$ horizon of this layer shows the maximum leaching. 

Top soil contains detritus micro-organisms  that decompose dead plant and animals and add to the organic content of the soil. The decomposed organic matter is called humus.

• Climate affects soil formation because it determines the amount of water that is available for processes such as the weathering of minerals, the transportation of minerals and the release of elements. Climate also influences the temperature of the soil, which determines the rate of chemical weathering.
• Temperature and rainfall are the two main climatic factors responsible for soil formation. 
• Hence, Climatic factors affect soil profile and bring changes in soil structure.

Humus is dark brown amorphous gummy substance formed by partial decomposition of plant and animal matter. It constitutes the organic component of soil and is rich in lignin and cellulose. Humus is formed from organic remains through the activity of decomposer microorganism. The process of formation of humus from raw organic remains is called humification. Humus is quite resistant to microbial action. It is a reservoir of nutrients and is helpful in the maintenance of soil moisture as well as aeration. It is colloidal in nature. Nutrients are released slowly as the humus is decomposed slowly. Humus is further degraded by some microbes and release of inorganic nutrients occur by the process of mineralization.

All statements are true except the ability of roots to penetrate in sand and hummus are low as compared to clay.

• Soil composition refers to the nutrients and various other substances present in the soil. 
  
• The basic components of soil are minerals, organic matter, water, and air. The typical soil consists of approximately 45% mineral, 5% organic matter, 20-30% water, and 20-30% air.
  
• Hence In addition to the rock particles, the soil contains Minerals, organic matter, air, and water.
• So, the correct answer is 'Minerals, organic matter, air, and water'.

Mineralization is the release of inorganic substances, both non-mineral(e.g., CO2, H2O) and mineral(e.g., Ca2+, Mg2+, K+, NH+4) from organic matter. The process is slow because of trapping of these nutrients in humus and their immobilization in decomposers/detritivores. It prevents their washing out or leaching. Nutrients immobilized in decomposer microbes and detritivores are again exposed to humification and mineralization after the death of these organisms.