Types of Soil Moisture

Figure 9.8

A block of soil is made up of three components, air, water, soil. The sum of the volume of air and water make up the total pore space in the soil.Volume Metric Soil Water = Vwater/(Vwater+Vair+Vsoil)Porosity=(Vwater+Vair)/(Vwater+Vair+Vsoil)

Soil-Moisture Availability

Figure 9.9

Precipitation Measurement

wind

The eddies created by the rain gauge could deflect rain drop to fall into the rain gauge causing measurement error.

Precipitation Measurement

A shielded rain gauge

Note: Precipitation is highly uneven over space.

Evaporation Measurement

An evaporation pan.

How this measurement compare with the Potential Evapotranspiration, i.e. ET of the surrounding environment without moisture constraint?

Lysimeter and Weather Instruments

Figure 9.7

Death Valley, CALysimeter is able to keep vegetation and soil in a relatively undisturbed condition.