Soil Organic Matter Accumulation and Oxidation

Hi, my name is Francisco Arriaga, I’m the
soil and water management specialist for UW-Extension and also faculty member in the Department
of Soil Science in the University of Wisconsin–Madison. Today, we are in Arlington, Wisconsin. We
are right next to a long term silt experiment that Dr. Joe Lauer, corn agronomist for UW-Extension,
had been maintaining for the past few decades. What we have here is a system where we have
a conventional tillage system that is chiseled in the fall, followed by … in the spring.
Then we also have a continuous no-till system that has been under no-till for over 25 years.
A third system that we’re going to compare, kind of as an extreme will be the alleyway
which has been roto-tilled 2-5 times during the growing season. Obviously, very little
vegetation growing in the alleyway. So, we have the extreme where we have very little
organic matter residue going into the soil. What I want to talk to you about is actually
organic matter. What are the differences between organic matter and between the systems and
what’s happening? So, typically when we do a tillage operation, we’re incorporating
air and oxygen into the system, which the oxygen tends to be a limiting factor for microbial
activity. Microbes, they actually feed on the organic matter in the soil, so when you
introduce that oxygen, that air, as you do the field abrasion, the microbes start growing
and multiply. They chew on–basically they feed on–that organic matter. That carbon
gets released–carbon dioxide, CO2–into the atmosphere. On the no-till system, we still have what
we call the soil respiration, that process that I just explained, but it happens at a
lower rate relative to a conventional system. Now, in a roto-till system, we have an extreme,
where we’re incorporating a lot of air, in this case many times during the growing
season. We can see that the structure of the soils, which the structure is held by the
organic matter stabilized by the organic matter, is very weak compared to the other systems.
I want to show you a little demo that kind of mimics a little bit of this oxidation that
microbes do, so we can kind of get an idea and see the relative difference in organic
matter in the soils in these three systems. We’ll start by showing you here. First one
to my right, it’s a soil that I took from the conventional tillage system, just from
the surface. In the middle is the roto-soil. On the left is the no-till system. What we
are going to do is add some hydrogen peroxide. This hydrogen peroxide is not the same hydrogen
peroxide that you can get at your local pharmacy, it’s quite a bit higher concentration at
30 percent hydrogen peroxide. We have the same amount of hydrogen peroxide and the same
amount of soil in this cup, so we’re just going to add it in. Basically, what’s going
to happen is that instead of the microbe subsiding the organic matter in the soil, it is actually
the hydrogen peroxide reacting to that organic matter and oxidizing that soil organic matter–that
carbon, organic carbon. This is actually quite a strong reaction. It’s exothermic. You
can see bubbles being created. If I were to touch these cups, you can tell that they’re
getting quite hot, sometimes to the point that you can barely touch it. By looking at
this reaction, how aggressive they proceed, we can kind of gage visually and get a n idea
of the organic matter content on the systems. We can see that the one on the right, the
commissional tillage, started very vigorously and it’s starting to kind of wind down a
little bit. Similarly, we see the same thing with the roto-till soil. Then finally, here
on the left, it is the no-till system and you can see that reaction is still going pretty
strong. You can see that CO2 being released, you can see those bubbles where that CO2 is
being released. So what we can conclude from here is that
under no-till system, we’re going to have a greater amount of carbon accumulation, and
all the benefits realized that having a greater carbon in the soil and soil organic matter,
all the benefits of fertility, chemical properties, and especially physical properties relative
to a conventional tillage system. For more information you can visit my website
or you can contact your local UWEX agent.

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