Soil Aggregation and Water Infiltration


Hi, I am Francisco Arriaga, I’m a soil and
water management specialist with the UW-Extension and also a faculty member in the Department
of Soil Science at the University of Wisconsin–Madison. Today, we are in beautiful Arlington, Wisconsin
and we have the opportunity to come to the soil pit that has been dug long-term near
a long-term tillage experiment that Dr. Joe Lauer, corn agronomist with the Department
of Agronomy with UW-Extension, has been managing for the last 25-30 years. What we want to show you today is a couple
of demos. First, is an infiltration test, we’re going
to compare a conventional tillage system which consists of a chisel operation done in the
fall, followed by a disking operation in the spring, and then a no-till system. Again, like I mentioned, the systems have
been in place for 25 years. First, we’ll add water to the infiltration
disc. I have about half a gallon, 1500 MLs, of water
and I’m just going to pour it slowly here, carefully trying not to disturb the soil surface
too much. We will track the infiltration as we continue
to talk about this test. We’ll fill it up all the way to the rim. We have a little that we’ll start so we
get an idea of the time. I’ll head over to the other side where we
have the no-till system and do the same amount of water. These rings were actually inserted into the
soil, the same amount, so the amount of ring under the soil surface is actually the same
as the amount of ring above the soil surface. So what we’re trying to determine is differences
in infiltration rates between these two systems long-term tillage management systems. Again, I’ll fill it up to the rim and we’ll
let it infiltrate while we go and show you what’s called a slate test. So, what we have here is aggregates from three
different management systems. Over here, this is some surface aggregates
from the conventional tillage system that we just talked about. In the middle we have the opportunity to take
some aggregates from one of the alleyways, and what that allows us is to show what 2-5
roto-till operations during the growing season will do to your soil structure and your organic
matter. Finally, we have the long-term no-till system,
so we’ll start by inserting the soil into this container
and continue on. You can see how quickly the soil that was
in the roto-till is just disintegrating. It’s not really holding up, so those aggregates
have very, very little integrity–they’re not very stable. This is what the slate test shows you. On the right is a conventional till, so again
we have the no-till system long term, 25 plus, the roto-till alleyway, so 2-5 times roto-till
during the growing system, you can see those aggregates have no stability whatsoever, and
we so on the right the conventional tillage system. So what’s happening with the slate test
is that as we introduce these aggregates into the water, the aggregates are actually dry,
so water gets drawn into the soil. Water in the soil is actually held under a
suction, under a tension, and so this water gets drawn into the aggregate and what’s
happening is that there’s air that gets trapped inside that aggregate and you get
to the point that the pressure is too much and that air needs to come out. At some point it will burst out, and that’s
the action that we’re seeing here, and so it gives us an idea, it’s a great test because
we can do it in the field and demonstrate how stable these aggregates are. And so why are aggregates so important is
because we have spaces between these aggregates in the soil that we call macropore, so these
are large pores. That’s where we get most of our infiltration
and so when we get a rainfall event, that’s what’s going to allow that rainfall to penetrate
into the soil and recharge that soil profile. In Wisconsin, a corn crop, even a soybean
crop, requires about 24 inches of water–of rainfall–to grow. These soils, like I mentioned earlier, they’re
prime soils, plain soil series, they hold about 11 inches of water. So, that means over half of the water that
your crop needs to grow in Wisconsin needs to come from either an irrigation or a rainfall
event that happens during the growing season. So you want to improve that infiltration and
have the best infiltration capacity that you can, to make sure that that water gets into
your soil profile, recharges the soil profile and is available for your crop to use. So we go back, it’s been about three minutes
since we started the infiltration test, close to 4. We can see here on the conventional side,
very little infiltration of this water, still pretty much where we left it at the beginning. And if we go and look back at the no-till,
it has gone down a little bit more, not quite substantially, so one of the issues with this
test is that it takes a long time, but we can see that infiltration happening at a little
bit faster rate. Again, going back to the slate test, it’s
been going on now for a couple of minutes. We can see a tremendous difference. I’ll tap these, and obviously the aggregates
are not immune to breaking down, so if we tap them, we can see that they’ll break
down even in no-till. But you can see that the integrity of the
no-till system, it’s much, much greater. If you have any questions, you can please
contact me through my website, or you can contact your local UWEX agent.

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