Question

Soil Components and Properties

Soil is a heterogeneous entity which is described by its physico-chemical properties. Make a list of these physico-chemical properties and describe how each one determines the suitability (or otherwise) of the soil for plant growth.

Answer 1

The presence of different minerals, water, salts and gases determines the physical and chemical properties of the soil. The suitability of these properties in the soil for plant growth are discussed here.

Physical property

• Soil texture: it determines the proportion of salt, clay and sand in the soil. It affects the soil fertility by changing the water retention capacity, increasing permeability and helping in better root penetration.
• Soil structure: It is dependent on soil texture and gives a measure of the amount of soil particles in the area and the spaces between the particles. If the soil has a crumb structure, it becomes porous and permeable but helps in retaining moisture. It also helps in easy transport of nutrients and air in the soil that supports the growth of essential microorganisms.
• Soil temperature: It is an important property of the soil as many nutrients are poorly available if the temperature is low. Apart from this the biological activity of the soil such as fixation and anaerobic respirations are greatly reduced at low temperature.
• Bulk density: It is a measure of the soil health as it reflects the amount of pore spaces in the soil. The value usually ranges between 0.5 to 3 but in most cases it is upto 1.8. Bulk density above 1.8 turns out to be root limiting and needs to improved with addition of crop residues.
• Soil porosity: It increases with increase in the organic content of the soil and decreases with the soil depth. It gives an idea about the space occupied by the air and water in the soil sample. Oxygen is found the pore spaces of the soil which helps in respiration of the plants. The soil must be well aerated for proper plant growth.
• Soil depth: it helps appreciably in root growth to occur and increases the yeild of the crop.

Chemical properties:

The nutrients are supplied to the plants from the organic matters and the minerals.The soil chemistry plays an important role in the concept of plant growth.

• Organic matter of the soil: Most of the organic matters originate from the plant tissues. Carbon, hydrogen, oxygen, nitrogen, sulphur, phosphorus etc. are the primary component of the organic matters which greatly alters the soil fertility. It improves tilth, aeration and buffering capacity of the soil.
• Soil pH: It gives an idea regarding acidity and alkalinity of soil and is determined by the presence of hydrogen and hydroxyl ions in the soil. Acidity increases with the increase in the number of hydrogen ions. It affects the solubility of the minerals, improves the calcium demand of the soil, slows down the decomposition rate of beneficial microorganisms and decreases the N availability of the soil.
• Cation exchange capacity: It gives an idea about the cation exchange and holding ability of the soil. It is related with soil fertility. It increases the soils ability to hold on to essential nutrients beside reducing soil acidification.
• Colloidal properties: The fertility of the soil is greatly related with the colloidal properties, as the soil colloids helps in holding and exchanging cations. Without a good colloidal property of the soil, the vital nutrients will be leached away with percolation.