External or Environmental Factors
Edaphic or Soil Factors
Plant Biotic Factor
Anthropic or Management
1) Edaphic or Soil factors: Soil can be defined as: Soil is a thin layer of the earth’s crust which serves as a natural medium for the growth of plants. Soils are formed by the disintegrations & decomposition of parent rocks due to weathering and the action of soil organisms & also the interaction of various chemical substances present in the soil. Soil is formed from parent rock by the process of weathering over a long period by the action of rain water, temperature and plant & animal residues.
A vertical cut of 1.5 to 2 m deep soil indicates a layer varying from a few cm to about 30 cm of soil, called surface soil, elbow that a layer of sub soil & at the bottom, the unrecompensed material which is the parent rock.
Role of soil:
1. Soil is the natural media to grow the crop.
2. Soil gives the mechanical support & act as an anchor,
3. Soil supplies the nutrients to the crop plants,
4. Soil conserves the moisture which is supplies to the crop plants
5. Soil is an abode (house) of millions of living organisms which act on plant residues & release food material to plants
6. Soil provides aeration for growth of crop and decomposition of organic matter.
Soil profile: A vertical section of soil in the field extending up to the depth of the parent material shows the presence of more or less distinct horizontal layers such a section is called a profile & individual layers are regarded as horizon.
The depth of soil varies as shallow, medium & deep. The soil which remains where it is formed, known as soil in situ, the soil on the banks of river which is formed from the soil particles washed away by rains from hill slopes & deposited at lower levels is known as alluvial soil which is much deeper & more fertile.
Soil varies in their composition and the arrangement of soil particles depending upon the parent rocks from which they are formed. They also vary in physical properties such as texture & structure. Textural class decided its fitness, fertility & plant growth, infertile soil need to add the org. Matter & fertilizers. Problematic soils need addition of soil amendments (Lime-acid & Gypsum-alkali) and other management practices to correct them. The chemical properties of soil are decided by the parent rocks.
Soil is not an inert mass but an abode of millions of living organisms which act on plant residues & release food material to plants. The decayed OM also loosens the soil to allow circulation & retention of moisture, which are necessary for the life & growth of the plant, soil is not an ordinary mass of dead particles of rock but a medium humming with activity, responsive to the water, plant & management by the farmer.