The type of soil plays a major role in deciding the crop that can grow well on it. It also helps decide about the water needs of the plant – when and how much to irrigate.
The process by which water enters from the surface of soil into the soil is called infiltration. It is all about the penetration into the ground surface. It is also measure of speed with which water enters the soil in case of rain or when it is supplied to the ground through any other means. An instrument called “Infiltrometer” could be used to calculate the rates of water being absorbed per hour.
The soil holds water in the pore space between its particles. These pore spaces get filled with it when it rains or when the land is irrigated (watered). Water tends to move vertically down into the soil. When the rate of downward movement has decreased, the soil is said to have reached its ‘field capacity’. Field capacity is the amount of water retained in the soil after it is allowed to drain for a day or so.
Once the soil reaches its field capacity, the movement continues due to two factors - gravity and capillary action. Capillary action is the tendency of water to rise in narrow spaces against gravity. This capillary action is what helps soil retain it in the soil pores. As the capillary action is stronger than the gravitational pull, some water remains in the soil. It is also because of capillary action that roots absorb water from plants.
The type of soil determines how much water it can hold. Smaller the pore, larger is the retention capacity of the soil. In that way clay is said to exert great capillary action compared to fine sand that exerts least action. The drops moves down through the soil till it reaches the water table or its field capacity.