Soil Moisture / Soil Water Relationship

Soil moisture or soil water is the water added to the soil mass during irrigation that gets held in the pores of the sail. Soil provides the necessary medium to the water through which the water gets used by the plants. 

Factors responsible for the growth of crops,

• Rate at which water enters the soil 
• Water retention capacity in the sail
• Available amount of water to plant roots 

Water Holding Capacity of Soil (Porosity):

The main factor which influence irrigation also the water holding capacity of soil mainly depends on its porosity, 

Capillary Pores	Non Capillary Pores
Small size pores	Large size pores
Holds large amount of water against gravity   eg : Clay	Holds less amount of water is there against the gravity eg : Sandy soil
Poor drainage and aeration	Better drainage and aeration

Classification of Soil Water:

• Gravitational Water
• Capillary Water
• Hygroscopic Water

Gravitational Water: Gravitational water is that water which is not held by the soil as this water drains out freely under the action of gravity. When we add a amount of water to a sandy soil at a high discharge, in quick time the pores of the soil becomes completely saturated with water. after sometimes water gets drained off as this water was very loosely held by the sandy soil. This water which gets drained is called as gravitational water. It is not available for the plants for there growth so it is also called as unavailable water.

Capillary Water: Capillary water is that water which is retained in the soil against the gravity. The force which helps to hold this water is surface tension force. Capillary water is the most beneficial for plant growth and it is called called as available water.

Hygroscopic Water: Hygroscopic water is that water which is adsorbed by the particles of dry soil and is held as a very thin film on the surface of soil particle due to adhesion. Hygroscopic water cannot be removed easily from the soil particles as it is held by a soil moisture tension of 32 atm. Hygroscopic water can be removed only at very high temperature. So this water is not available for the growth of plant, hence called as unavailable water.