Introduction

• Soil is a three-phase system i.e. it consists of soil solids, soil air and soil water.
• Soil basically contains solid materials or particles and the space between these particles are either filled with water or gas or both.
• And the vacuum or free spaces between these solid particles are called pores. And the water holding capacity of soil mainly depends on its porosity. Porosity is proportion of the soil volume occupied by pore spaces.
• There are mainly two types of pores i.e. micropores or capillary pores (smaller than 0.08 mm) and macropores (larger than 0.08mm).
• In macropores water get drained under gravitational action where as in micropores water is tightly held and cannot be drained out by gravity.
• Soil moisture is usually described in terms of soil moisture content and Soil moisture tension.