Soil moisture content
n. The measure of the amount of water per unit of soil.
Soil moisture content can be expressed on either a gravimetric basis or volumetric basis. Gravimetric soil moisture content is the ratio of the mass of water present in a soil sample to the dry mass of the soil sample. Volumetric soil moisture content is the ratio of the volume of water present in a sample to the total volume of the soil sample.
To determine either of these ratios for a particular soil sample, the water mass must be determined by drying the soil to constant mass and measuring the soil sample mass before and after drying. The water mass is the difference between the masses of the wet and oven-dry samples. A soil sample is considered dry if it has been dried to a constant mass in an oven at a temperature of 100° to 110°C (105°C is typical). This temperature range is based on the boiling temperature of water and does not consider the physical and chemical soil characteristics (Black 1965).