FORMATION OF SOIL-PROCESS & FACTOR OF SOIL FORMATION

FORMATION OF SOIL-PROCESS & FACTOR OF SOIL FORMATION

INTRODUCTION
Soil is a mixture of minerals, organic matter, gases, liquids, and organisms that together support life. It is the medium for plant growth and habitat for organisms. A typical soil is about 50% solids (45% mineral and 5% organic matter), and 50% pores of which half is occupied by water and half by gas.

The percent soil water and gas content is considered highly variable, while soil mineral and organic matter is somewhat constant. The pore space allows for the infiltration and movement of air and water, both of which are critical for life existing in soil.

Soil formation is also termed as pedogenesis, which is the combined effect of physical, chemical, biological and anthropogenic processes working on soil parent material. Basically soil formation is the result of weathering of rocks and minerals. Though it is a slow process and needs hundreds of years.

FACTORS OF SOIL FORMATION
five main interacting factors affect the formation of soil are-

1. Parent Material– The parent material is chemically and physically weathered, transported, deposited and precipitated, and then transformed into a soil. It is the mineral materials from which solum develops.
   The typical soil parent mineral materials are Quartz( SiO2), Calcite (CaCO3), Feldspar (KAlSi3O8), Mica {K(Mg,Fe)3AlSi3O10(OH)2}. The types of parent materials and the conditions under which they break down will influence the properties of the soil formed. Parent materials are classified according to how they came to be deposited.

• Residual parent materials– are remained at same place for a longer time and soil formation takes long time from such parent materials e.g. igneous rock, Sedimentary rock and metamorphic rocks.
  
  Read also…TYPE OF ROCKS- DEFINITION, PROPERTIES & EXAMPLES
  
  
• Transported parent material– are those that have been deposited by water, wind, ice or gravity.
• Biological parent material– Decomposed or partially decomposed biological matters.
  
  

2. Relief or Topography– This is characterized by the slope, elevation, and orientation of the terrain. Topography determines the rate of precipitation or runoff and rate of formation or erosion of the surface soil profile. It also affects vegetation.
   
   
3. Climate– It includes precipitation, temperature, humidity and wind in which rainfall and temperature are most important factors. These influence chemical, physical, and biological processes.
   
   Climate is the dominant factor in soil formation, and soils show the distinctive characteristics of the climate zones in which they form, with a feedback to climate through transfer of carbon stocked in soil horizons back to the atmosphere.
   
   Soil properties affected by climatic conditions are pH, base saturation of exchange complex, organic matter content and nature and composition of clay. Temperature affects the rate of weathering and organic decomposition. With a colder and drier climate, these processes can be slow but, with heat and moisture, they are relatively rapid.
   
   Evaporation, transpiration and humidity modify the effect of precipitation by reducing or increasing the quantity of water. In scanty rainfall areas, salts are accumulated on soil surface while, in high rainfall areas, salts are leached out into lower horizons thus soil becomes acidic.
   
   
4. Organisms– Flora (plants, microorganisms, forest and grasses) and fauna (termites, earthworm, and rodents) plays active role in soil formation. Soil animals mix soils as they form burrows and pores, allowing moisture and gases to move. This process is called bioturbation.
   
   In the same way, plant roots penetrate soil horizons and open channels upon decomposition. Micro-organisms, including fungi and bacteria, effect chemical exchanges between roots and soil and act as a reserve of nutrients in a soil biological hotspot called rhizosphere.
   
   Humans impact soil formation by removing vegetation cover with erosion, waterlogging etc. Tillage also mixes the different soil layers, restarting the soil formation process as less weathered material is mixed with the more developed upper layers, resulting increased rate of mineral weathering.
   
   
5. Time- Soil properties may vary depending on how long the soil has been weathered. It is a factor in the interactions of all the above. It has no relevance after the soil reaches its maturity that is why it is a neutral factor.
   
   

SOIL FORMING PROCESS

Basic process– It involves addition of water, organic matter and minerals to soil and vice versa. Thereafter translocation of clay, organic matter and hydrous oxide and then transformation of minerals, organic matter and formation of soil profile takes place.

Fundamental processes

• Humification– It is the process of decomposition of organic matter that leads to formation of humus.
  
  
• Eluviation & Illuviation– Soil constituents are washed out from the upper layers to the lower layers through percolating water (Eluviation) and then deposited in lower layers (Illuviation). “A” horizon is layer of elluviation whereas, B-horizon is illuvation layer.
  
  
• Horizonation– The development of all the horizons as a soil profile is called horizonation.
  
  
• Calcification & Gypsification– Calcification is the deposition of CaCO3 in soil profile.
  
  
• Decalcification– Removal of CaCO3 from soil by leaching is called decalcification.
  
  
• Podzolization– It is just like eluviation in which humus and Fe & Al sesquioxide move out from the upper horizons to lower horizons. As a result whole soil becomes acidic.
  
  
• Laterization– It is the process that removes silica instead of sesquioxides from the upper layer as a result cemented horizon is formed, which when dried become very hard like brick.

Calcification, podzolization and laterization are specific zonal-pedogenic soil forming processes where soil is produced under normal conditions of climate and vegetation.

In the Intrazonal processes, soil profile is more influenced by parent material than climate and vegetation. These are-

• Gleization– This is the development of blue, grey clay in the lower part of soil profile due to poor drainage and water logging. Such soil is called hydromorphic soil.
  
  
• Salination– this is the process of accumulation of soluble salts in soil because of poor drainage, low topography, saline irrigation water in arid & semi-arid regions.
  
  
• Alkalization– It is the accumulation of high exchangeable Na+ ions and pH>8.5. Soil colloids are moved downwards resulting in poor physical condition.
  
  
• Dealkalization– Simply it means removal of Na+ from the soil.
  
  
• Pedoturbation– It is the process of mixing of soils by animal and plants.

Read more..
SOIL STRUCTURE-DEFINITION,TYPES & IMPACT
SOIL PROFILE- DIFFERENT HORIZONS
SOIL TEXTURE- CLASSIFICATION & INFLUENCE
SOIL TYPES IN INDIA: FEATURES
DIFFERENCE BETWEEN MANURE AND FERTILIZERS
CROPPING PATTERN-CROPPING SYSTEM