SOIL TESTING TOOLS

The following are tools that can be used to field test soil compaction and moisture during construction and dig in urban soils.

Soil Augers:

The following are tools that can be used to dig soil samples in urban soil, with notes on my preferences.

There are various augers on the market.  Ben Meadows has the largest assortment of different tool types.  I like the AMS Signature Modle with loarge padded handle, and screw on extensions and digging head.  It breaks down fast when traveling and is adjustable.  Individual parts are also replaceable, so when I bend a head I can replace it.  I use the 3” wide Dutch Auger head for most applications.

However, this is the most expensive option.  Less expensive models are available.  If you are in sandy soils a sand bucket auger is useful but most urban soil will bend this version.  

Full catalog of soil augers from Ben Meadows

My favorite combination

Handle: 
95485 Signature Series Rubber-Coated Cross Handle
Cost $40

Extensions: 
95488 Signature Series Extension, 2'L or 95489 Signature Series Extension, 3'L
Cost $65

Dutch Auger Head: 
95482 Signature Series Dutch Auger, 3"
Cost: $190

Compaction Testers:

These are for measuring soil resistance to penetration.  

Caution: In very dry soils dial will read as overly compacted and in very wet soils will read as under compacted even though these soils may be acceptably compacted.  Soil should be at a moisture level in between field capacity, wet but not saturated; and wilt point (soil is dry to touch).

It is always best to calibrate this tool to a soil of known compaction as determined by an engineer’s densitrometer.  However, for rough estimates, readings are best between 50 and 150 on the dial.  Readings above 200 are over compacted and should not be accepted.  Readings below 50 is not compacted enough and significant settlement will be expected.

Tool can probe to depths of 30 inches and make many soil checks (one per minute).

My preferred product:

agraTronix Soil Compaction Meter or other soil compaction tester (penetrometers) 
Cost: Approximately $200-235.00 plus shipping

Soil Moisture Meters:

Two tools are recommended, one for shallow accurate measurements and one for deep but less accurate measurements.

General Digital Moisture Meter
Very accurate, measures actual percent moisture to 8” deep.  Length of probe is its main limitation.  Tool may be damaged in hard, dry soil.  If you cannot get it into the soil, it is either very compacted or very dry.

Interpreting Readings: below 5% is overly dry, between 5 and 10% additional water may be needed.  10-15% good soil moisture.  15-20% becoming to wet.  20-25% close to field capacity.  Above 25% overly wet.  This device stops reading at 50%.  

Caution:  The point of soil wilt point and field capacity will be different depending on soil type and soil compaction.  Calibrating the readings to other observations in the soil is needed.  Batteries run down fast if left on.  4 AAA Batteries needed.  

My preferred product:

General Digital Moisture Meter
Cost: Approximately $250.00 plus shipping

Portable Soil Moisture Meter AKA Lincoln Soil Moisture Meter

This is a cheaper alternative and is available in a longer probe.  (24 or 36 inch probes)  This allows reading soil at greater depths.  The narrow diameter of the probe is easier to insert in the soil but the tool is relatively fragile compared to the General digital and easily bent.  This tool needs to be calibrated to the soil that you are working in.  There is a setscrew on the back that is easy to calibrate.  Insert the probe into a soil of know moisture.  Obtain this by over watering the soil in a small area the day before and do the calibration after the soil has drained down for 24 hours.  Calibrate the reading to 20-25% and that should be just below field capacity.  Then readings should be similar to the information provided under the General digital meter above.

Caution: Tool is easily bent.  Battery needs to be replaced periodically (1 AA inside meter box).  The dial is very small so readings are not precise.

My preferred product:

Portable Soil Moisture Meter AKA Lincoln Soil Moisture Meter
Cost: Approximately $89.00 plus shipping for the 24” probe; Approximately $105.00 plus shipping for the 36” probe.