Feel method
- measures soil water depletion

xxx

x

all

NA

High

Requires experience.

Open to misinterpretation.

Operator time

Soil samples
(gravimetric)
- measures water content by mass

xxx

xx

all

NA

High

Time consuming and slow- lots of weighing, waiting and calculating. Highly variable depending on sampling technique, temperature of drying etc.

Operator time - labour cost high; materials cost low

Tensiometers
- measures soil water tension

xxx

xx

Most except clays.

Easy

Requires specialized unit and connections.

Low in season

Indicates when irrigation is needed, not how much. Proper installation is critical for operation. Placement is important to avoid damage from field operations. High maintenance and regular checking of units needed. Soil type dependent ie most suited for sandy soils as tension can be too high in clay soils. In coarse sand, may require a special unit.

$100 + per unit

Usually 2 units are installed at two different depths and the units stay in one site in the field for the season

Electrical resistance blocks
(eg. Water-marks, gypsum blocks etc)
- measures soil water tension

xxx

xx

Most except clays.

Easy.

Requires datalogger and connections.

Buried for crop season but moveable from season to season.

Installation generally easy but depends on soil type. Requires some calibration with soil type. Sensitive to salt levels. Low maintenance. Low impact on field operations with appropriate placement. Not very sensitive at high soil moisture. Lifespan ~3 years +. Readings are affected by soil temperature (1% per degree F).

Meter $300 + and individual units$ 40-50

Similar to tensiometers - often 2 units at different depths

TDR or FDR - Time or Frequency Domain Reflectometry
- measures volumetric soil water

x

depends upon unit used

xxx

All, but clays may pose some prob-lems.

Easy but cost prohibitive.

High. May require installation of an access tube in the soil.

Cost in the past has restricted use to researchers and large scale irrigators
Depending on unit may need calibration
Insertion under dry conditions mat be difficult
FDR - sample volume 10 inches dia. Around probe

Cost has come down in recent years - $600 to 1000+

C-Probe

xx

once probe is installed

xxx

all

Easy.

Requires specialized unit and connections

Can be moved but normally installed in one place for the season.

Installation generally easy but depends on soil type.
Low maintenance.
Gives graphical image of soil profile in near-real time.
Web based access.
Multiple sensor depths.

Sensor cost $1200 with data management extra.

Neutron Probe
- measures moisture content

x

xxx

all

Unit usually too expensive.

High. Requires installation of an access tube in the soil.

Suited to research
Uses a radioactive source of neutrons
Requires calibration

High cost in $1000's.