Getting to Know Your
Need a simple way to test your soil
quality? Just dig a hole!
by Mark Liebig, UNL Graduate Research
At a recent scientific meeting on soil
quality, the question was asked, "If a
person was to make one assessment to determine
soil quality, what would it be?"
As expected, this question created a lively
debate among the meeting's participants. Soil
organic matter, salinity, aggregate stability,
infiltration rate, soil respiration, as well as
other soil tests were all offered as being the
assessment needed to determine soil quality.
Unfortunately, but not unexpectedly, the
discussion turned into a bickering session, with
each group defending their assessment as superior
After some time had passed, a well-respected
soil microbiologist, obviously fed-up with the
scientific infighting, stood up and said,
"Just dig a hole." A silence fell over
the room. It was as if a new paradigm in soil
testing was introduced. Somehow 'digging a hole'
seemed to make perfect sense.
Digging a hole has many advantages over
traditional soil quality assessments. In a
nutshell, it's a quick, easy, no-cost test that
does not require specialized equipment. It's a
test that relies on our common sense(s) for
evaluation (i.e., senses of touch, sight, smell,
and taste). Digging a hole is a subjective
activity; the conclusion one person has about a
particular soil property may differ from that of
another person. Nevertheless, it is probably the
most practical test for a quick assessment of
soil condition. Furthermore, because the person
conducting the test is in direct physical contact
with the soil, it is the best way to 'get to
know' the soil.
The first step in digging a hole is to choose
a good shovel. A sharpshooter spade will work
nicely, but any shovel with a sturdy handle will
The next step is to choose an area to
evaluate. 'Problem' areas are often good places
to check. If you're not sure where you want to
dig, let vegetation be your guide. What exists
below ground will affect what grows above ground.
Therefore, inspecting vegetation is a useful
'first step' in determining soil condition.
Noticing variation in crop color, height, and
percent stand can give clues as to what may be
occurring in the soil, whether it be a nutrient
or aeration problem or some other limitation to
Furthermore, weeds, when in clearly defined
areas, are excellent indicators of soil
condition. Calcareous, saline, compacted,
poorly-drained, and nutrient-rich soils are each
characterized by the growth of certain types of
weeds. For instance, bindweed often indicates the
presence of a hardpan, docks usually indicate a
poorly-drained soil, and pigweed typically
indicates high soil fertility.
Once you've chosen an area to evaluate, start
digging. Dig a hole at least four to six inches
past the lowest depth of disturbance by tillage
implements. While you're digging, be sensitive to
how much effort you're putting forth to get the
hole dug. If excavation requires a significant
amount of energy (like standing on the shovel to
get it to go in) you probably have a compaction
Make sure the hole is dug wide enough so that
you can inspect plant roots. Observe their
condition. Are they well branched with lots of
fine root hairs, or are they balled up and
growing sideways at certain depths? A lack of
fine root hairs indicates oxygen deprivation in
the root zone, and sideways root growth is a sure
bet that there is a hardpan.
Having a feel for the amount of earthworm
activity can give you a good idea of the overall
biological health of your soil. Searching for
earthworms can be done as you're removing soil
from the hole. Count the worms as you see them.
If you find ten earthworms in a hole a
foot-square and foot deep, you've got a healthy
soil. If you didn't notice any earthworms while
digging, inspect the wall of the hole for
Once your done looking for earthworms, cut out
a slice of soil from the wall of the hole and lay
it out on the ground. Here's where the fun really
begins! First, look for color changes from the
soil surface downward. If you have a tape measure
with you, measure the topsoil depth. Soil that is
dark brown, very dark gray, or black qualifies as
topsoil in Nebraska. If you happened to leave
your tape measure back in the shop, but know the
distance between the tip of your thumb and pinky
with your hand fully extended, you can estimate
topsoil depth from that.
Next, break off a chunk of soil about the size
of your fist from the top six inches of the hole.
Gently break it apart with your fingers and then
hold it up to your nose. What do you smell? The
smell of soil can range from a strong putrid,
sour, chemical smell, to a strong earthy, sweet,
fresh smell, to no odor at all. It's the earthy,
sweet, fresh smell that we typically associate
with healthy soil.
While you have the soil in your hands, notice
the size and shape of the soil aggregates. Are
the aggregates blocky, granular, or powdery?
Having a range of different types of aggregates
is best, with the majority having a granular
shape and a size of about 1/16th to 1/8th inch in
The next step is to check soil texture. Take
what soil is in your hand and squeeze it. If the
soil does not stay in a ball after squeezing,
then it's sand. If it stays in a ball, try to
make a ribbon with the soil by squeezing it
between you forefinger and thumb. Make as long a
ribbon as you can, and then estimate its length.
If the ribbon is shorter than one inch, it's
probably a silt loam or sandy loam. A silt loam
will feel smooth, while a sandy loam will feel
gritty. If the ribbon is between one and two
inches in length, it's probably a silty clay
loam. If the ribbon is longer than two inches in
length, it's probably a silty clay or clay.
It is important to recognize that digging a
hole is not intended to replace analytical soil
tests; there is no substitute for charting trends
in soil condition in a quantitative manner. What
digging a hole does that analytical soil tests do
not do is that it gives you a quick, down to
earth idea of what the soil condition is like,
without the use of specialized equipment.
Furthermore, you can develop a special
relationship with your soil by digging a hole.
Checking for compaction, observing soil
structure, and looking for earthworms are all
activities that will bring you closer to the
source of much of our food and fiber. By getting
to know your soil in this way, you will almost
certainly increase your respect for it as a
living, dynamic system that is sensitive to
different forms of agricultural management.
For additional information on descriptive
assessments of soil quality, consult The Soul of
Soil: a guide to ecological soil management (3rd
ed.), Grace Gershuny and Joseph Smille, 1995,
agAccess, Davis, CA (Address - agAccess, P.O. Box
2008, Davis, CA 95616; Phone - (916) 756-7177.