I am Francisco Arriaga. I'm a state soil scientists with the University of
Wisconsin Extension Service. Today I'm located in Arlington Wisconsin and I
want to talk to you about a soil penetrometer. It is a very useful device for figuring out if
you have any compaction, soil compaction issues in your field. The one you see here in
my left hand is a commercially available unit. You can find them
online and through catalogs, and all of them basically have to have a t-handle,
a shaft, a couple of tips that comes with it, and also a gauge. So I want to go through
some of these parts
briefly to describe to you the penetrometer. So with the penetrometer essentially what
we're trying to do is figure out how much resistance you have as you push the
rod into to the ground. Which kinda relates a little bit to soil compaction and
root growth in soil. Before using this device, one thing I need to point
out is that they come usually with this little collar here to prevent any damage
during transit or storage so make sure that you lower that before you use your
penetrometer. Then the next thing to figure out is, depending on your conditions, there is
actually two different size tips: a half-inch tip and a three quarter inch tip. So the choice
of those tips depends on the type of soil you have. The smaller tip is used
usually on soils that are harder and the bigger tip usually you would use that
on soils that have better structure and are looser, such as the soils here where we are located
in Arlington. You're going to thread that tip at the end of your rod.
so now the penetrometer is ready for use.
Let me talk to you about the gauge, because it's really important to
understand what the gauge is actually telling you. So the gauge actually has a
scale that is measuring PSI (pounds per square inch) and you would see that it
actually has a green area, a yellow area, and then a red area. So, the green area is
usually about 0 to 200 PSI and then from there to 300 starts the yellow area. 300 PSI and
above is usually what is considered rude restrictive
and indicating of some compaction issues, but I want you to take that with a grain of
salt because there's other factors that affect these penetrometer measurements so
if you ever dug hole in dry ground you know that digging a hole in
the dry soil is really really difficult. So, moisture is actually a factor that will
affect how hard or how much you have to push to get this to run in the ground.
Another factor is clay content, and so there's no correction for
soil moisture or clay
content on the gauge but there's things that we can do to kind of account
for that. The one that I usually recommend is actually finding a fence
row in an area near your field, that has similar soil, that you know has received
very very little traffic, that hasn't had any traffic and you can actually test the
penetrometer
look at the gauge, where it lands and you can kind of make a comparison. So
let's go and check out an area where we can check the conditions, loose conditions for
soil and then we can come back to this field and assess it. So now we're near a fence
row where we know there hasn't been a lot of traffic so we can test now the
gauge and see what conditions we find. It's going to get a calibration for our field
(were near our field) and as we push it in and we don't want to look at that scale, we're
paying attention to the outside scale because we're using the bigger tip. As you can
see, very little resistance and that means very good conditions for the soil. So we go a
little bit deeper and you can see it's increasing, we're close to 100 PSI but not not even near.
So as an example, we're gonna test soil compaction in this field that was
harvested for corn silage. Typically, in a corn silage scenario you have a higher risk for
compaction due to all the traffic that occurs during the higher silage
harvest. So you want to go and check your compaction in a
zigzag manner such as soil sampling and you can look at that on the A2100
publication from extension. Another feature of the penetrometer as you can see if you
look at the rod, it actually has these markings in about 3 inch intervals. What that allows you
to do is assess the depth of the thickness of the compacted layer so
later on you can set up your tillage equipment properly.
So, you want to get into your field in any areas that you suspect compaction and start
pushing the penetrometer in. So, as you're pushing the penetrometer into the ground
you want to keep track of that gauge. Recall that we have the larger tip, so
we're looking at the outside scale. You can see it's getting close to two
hundred and really putting a lot of weight on this, so this is actually definitely
where I feel that there's compaction due to the traffic caused during silage
harvest. And as I'm going in, I can tell that that soil is getting looser. So, I go in and the
penetration resistance becomes less so you can actually mark that with your
with your finger. You can see that that denser layer is contained to the
upper foot of the soil.
So, very useful information for setting up your tillage equipment if you want to
take care of this potential issue. For more information, please contact your
local county extension agent or visit our website.