Index >> Soil, Nature Medium For Plant Growth >> Soil Water

The supply of water to plant roots depends not only on this field capacity of soil but also on water tension or suction tension (pF value) created by the suction of water to the surface of soil particles. The pF a which plants begin to wilt is called the ‘wilting point’.

This wilting point is reversible but later the plant dies at the irreversible stage. Water is bound if pF values are higher than 4.0-4.2 and thus the water available to plants is the field capacity minus this value. Therefore, in clay soil water is unavailable to plants to appreciable extent even though saturated with it. Movement of water by capillarity which is often lower saturated with it. Movement of water by capillarity which is often lower in lay soils and higher in sandy soil influences the availability of water to plants.

The occurrence of water in soil can be three types―gravitational, capillary and hygroscopic. After heavy rain or irrigation. gravitational water is drawn through the soil. Upon drainage of excess water, water is retained at field capacity in soil pores and this water is known as capillary water. Hygroscopic soil water relates to that water absorbed by dry soil from an atmosphere of high relative humidity. Fungi are mostly tolerant to greater water stress than are bacteria. An example of microorganisms less tolerant to water stress is Nitrosomonas, followed by ammonifiers such as Clostridium and Penicillium