Soil Moisture Measurement

1. Gravimetric water content (w) or Soil water on mass basis:

• It is the mass of water relative to mass of the oven dry soil.
• A sample of moist soil is weighed and then dried in oven at temperature of 105 0C for about 24 hours and finally weighed again.
• The weight loss gives the soil water and has units of Kg of water/Kg of soil or expressed as percentage. It is calculated as:

2. Volumetric water content (θ) or Soil water on volume basis:

• It is the volume of water per unit bulk volume of water and has units m3 of water/m3 of soil or expressed as percentage.
• Volumetric water content is more utilitarian than gravimetric water content because plant uses water from the soil.

3. Soil water depth:

• The volumetric water content (θ) is used in irrigation management to determine how much water to add and how much water has evaporated.
• The θ also represents the depth ratio of soil water i.e. depth of water per unit depth of soil.