3 - 2020 South Central Ag Lab Field Day
South Central Ag Lab Field Day
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- [00:00:05.120]Welcome to the skill virtual
field day. I'm Michael Sindelar
- [00:00:07.650]I'm a cropping systems extension
educator, out of Clay Center.
- [00:00:12.320]I'm talking about residue removal today,
- [00:00:14.630]and I'm going to tell and explain what
kind of happens when you do aggressive
- [00:00:19.430]residue removal to some
of, the core,
- [00:00:23.120]physical properties in the field.
So, the experiment,
- [00:00:27.380]I worked out of is here at
the South central ag lab.
- [00:00:29.990]It's a joint project between
the USDA ARS and, Nebraska,
- [00:00:35.090]the university of Nebraska. And,
- [00:00:37.440]a lot of my research was also funded
by the Nebraska corn board. the,
- [00:00:42.140]experiment itself is irrigated.
- [00:00:45.380]and we were trying to use cover crops
to try to remediate some of the negative
- [00:00:49.280]effects that was caused
by a residue removal.
- [00:00:52.580]I'm not going to really talk
about a lot of the methods.
- [00:00:54.440]I'm just going to start diving
into a lot of the research we did.
- [00:00:57.620]So some of the properties we
looked at was soil organic carbon,
- [00:01:01.010]which is another way of
saying soil organic matter.
- [00:01:03.650]And that's the first property
I'm going to talk about.
- [00:01:05.570]So when you look at the slides,
you see this nice big table,
- [00:01:08.540]and as you look through it,
- [00:01:09.710]the thing I really want to point out
on this table is you look at all the
- [00:01:12.350]different depths and you'll start seeing
that there is actually an effect of
- [00:01:15.680]residue removal. Every single
time we removed residue,
- [00:01:18.680]we reduced the amount of organic
carbon when that residue was removed.
- [00:01:23.270]We're moving roughly about 57.6%
of that residue out of the field.
- [00:01:28.010]the first thing I'm going to
point out and in my next slide here,
- [00:01:31.640]when we look at this,
- [00:01:32.330]I'm kind of really focusing on just the
first top two inches of the soil here.
- [00:01:36.320]We can actually see that cover crops
did have an effect when we look when we
- [00:01:39.890]remove residues and we plant cover crop
after we removed that residue, newness,
- [00:01:43.850]that those letters right at
the end, those are the same.
- [00:01:46.460]That means that there's no significant
difference between those values.
- [00:01:49.520]Let's meaning that, when we plant a
cover crop after removing this residue,
- [00:01:53.180]it's, it's having
an effect of either,
- [00:01:55.850]of keeping that carbon at a higher level
than when we look up above where we
- [00:01:59.240]didn't use a cover crop. And we noticed,
you know, that value is a lot lower,
- [00:02:03.080]significantly lower than any of the
other values in the table. And now,
- [00:02:06.500]as we look at the next step on
the next slide, we see that,
- [00:02:12.290]here, once again,
- [00:02:14.240]we still have a cover crop effect down
here in the two to four inch depth.
- [00:02:19.220]and it's, it's a little bit more defined,
- [00:02:21.020]but you see the numbers are a lot closer.
- [00:02:22.580]So we're having a little bit less of
an effect as we move deeper. However,
- [00:02:26.340]all the rest of the effects cover crops
really did not have an effect on soil,
- [00:02:30.020]organic carbon. What had the
effect was removing carbon. So,
- [00:02:35.930]next we're going to move right into
looking at some of the things that affect
- [00:02:39.080]erosion. So the first thing we're going
to look at is a mean weight diameter.
- [00:02:42.980]And this is looking at a water
stable aggregates, the mean weight,
- [00:02:45.740]diameter of water, stable
aggregates, and from here,
- [00:02:49.970]I forgot to convert to
English units. So I'll, I'll,
- [00:02:53.210]I'll do this for you as we talked
to her. So zero to five inches,
- [00:02:55.910]that's our zero to two inches.
- [00:02:58.100]five to 10 is our two to four and
10 to 15 is our four to six inches.
- [00:03:02.740]And when we look at this, our surface,
- [00:03:04.960]we're definitely seeing a significant
difference in our mean weight,
- [00:03:07.690]diameter size.
- [00:03:08.590]So that means that we have larger stable
aggregates when we leave residue in
- [00:03:12.040]place, when we're
aggressively removing it,
- [00:03:14.650]our aggregates are becoming less
stable. And one of the reasons why is,
- [00:03:18.430]if we go back to the previous slides or
you remember those previous slides,
- [00:03:22.600]we're removing that carbon and that
carbon acts as a binding glue to keep the,
- [00:03:27.460]aggregates together without
that they become less stable.
- [00:03:31.780]And we see that results here,
especially in the zero to two,
- [00:03:34.420]and even the two to four inch where
the five to 10 centimeter depth,
- [00:03:37.780]we're seeing a nice, significant
difference in mean white diameter.
- [00:03:41.710]We'll move on onto our next slide.
- [00:03:43.210]Our next thing we looked at
was plant available water.
- [00:03:45.490]What is plant available water?
- [00:03:47.290]That's the difference in the amount of
water that soil is storing between fill
- [00:03:50.420]capacity and permanent wilting point.
- [00:03:52.930]So what I like to think about it is
it's our storage tank for water that our
- [00:03:56.740]plants can easily use and
take out of the field.
- [00:04:00.190]This is really important here in Nebraska,
- [00:04:02.080]because now all parts of the States
get a lot of water and we have to,
- [00:04:06.760]irrigate to make up for water
that we don't get through rain.
- [00:04:09.730]So it's really nice to see, this
property not being affected. However,
- [00:04:14.620]when we look at the slides, unfortunately,
- [00:04:16.900]we're seeing that residue removal is
having an effect on plant available water
- [00:04:21.220]and the zero to two inch depth.
- [00:04:23.350]there is a significant difference
in plant available water.
- [00:04:25.690]And then the two to four,
there's a significant difference.
- [00:04:28.360]So our top four inches of soil,
- [00:04:30.970]the amount of water that's being stored
for plant use is decreasing. Now,
- [00:04:35.110]when we look at four to six inches,
- [00:04:37.420]we're not seeing any
significant difference at
that point. So we'll move on.
- [00:04:42.190]You know, it's important
that we store water.
- [00:04:44.200]Now we're going to look
at water infiltration.
- [00:04:46.840]Why is water infiltration important?
- [00:04:48.610]Because it's important that we can
recharge our water and make sure that what
- [00:04:51.370]we're irrigating and the rain that comes
so you can actually get into the soil
- [00:04:55.660]and it doesn't go off as runoff. So
when we look at the water infiltration,
- [00:04:59.890]we look at, our first few data
points on the slide there really,
- [00:05:04.810]stacked together, really close.
So our, our initial infiltration,
- [00:05:08.530]there's not really an effect,
- [00:05:10.060]but when we start getting
out to our 60 minute point,
- [00:05:12.700]we start seeing a significant difference
in the amount of cumulative to water
- [00:05:16.120]infiltration. And this goes on until the
end. So we're storing a lot more water,
- [00:05:20.290]in longer rain events,
we're in slower rain events.
- [00:05:24.010]when we keep residue in place, however,
- [00:05:25.930]when we remove that residue
aggressively, we are,
- [00:05:30.310]not taking in as much water.
- [00:05:32.230]So now we're not storing as much water
and we're not recharging as much water
- [00:05:36.190]when we remove that residue. Now
we'll advance to our next slide.
- [00:05:40.750]we're kind of done out of
the water area, you know,
- [00:05:44.520]what your aggregate stability that
was our erosion factor. clean,
- [00:05:49.160]available water was our storage tank and
water infiltration was our recharged.
- [00:05:52.330]So we're, we're done looking at
kind of the effects with rain.
- [00:05:55.420]What else is important? Well,
- [00:05:57.290]really important is thinking
about how soil warms and cools.
- [00:05:59.960]So we're going to talk
about a few properties.
- [00:06:01.580]The first one is thermal conductivity,
thermal conductivities, the ability,
- [00:06:05.360]the soil's ability to transfer
heat through the soil profile,
- [00:06:10.310]specific heat capacity is the amount of
energy it takes the soil, the heat up,
- [00:06:14.540]and the energy we're really talking
about is thermal where he energy that's
- [00:06:18.320]coming off the sun or
solar radiation. And then,
- [00:06:21.290]so our last one is thermal
diffusivity, that's our last one.
- [00:06:25.610]And it's actually a ratio of thermal
conductivity over specific heat capacity.
- [00:06:29.870]why are these important? Well, if
your he's not transferring soil,
- [00:06:34.250]very well, it's not going
to heat up the surface.
- [00:06:36.440]It's going to heat up really fast,
- [00:06:37.550]but the deeper depths aren't
going to heat up as nice.
- [00:06:40.460]So you're not going to get that
seeding depth in the rooting zones,
- [00:06:43.190]as warm as you want.
- [00:06:44.120]You're may not have as much
microbial activity as you would.
- [00:06:47.270]Specific heat capacity is important
because as specific heat capacity
- [00:06:51.770]increases, it's going to take a lot
more energy for that soil to either,
- [00:06:55.970]increase or decrease. So that's
also going to have effect on stuff.
- [00:07:00.380]So when we look at the next
slide, we're looking at,
- [00:07:05.570]thermal conductivity
and how we measured it,
- [00:07:07.790]we measured it two
different water capacities.
- [00:07:11.330]We measured it at, feel
capacity. So when the soil saturated,
- [00:07:16.520]and then we measured it
at permit wilting point.
- [00:07:18.300]So we're looking to see
when we remove residue,
- [00:07:21.380]does he and cooled faster or does that
heat transfer differently when it's
- [00:07:26.270]a completely saturate or very close
to being completely saturated,
- [00:07:30.770]versus when it's completely dried
for the first two depths for the,
- [00:07:34.970]or for the zero to two inch depth,
there is a significant difference.
- [00:07:39.920]when you remove residue that heat
doesn't transfer as well through the soil
- [00:07:43.790]profile as when you leave
the residue in place.
- [00:07:46.490]And then for the two to four inch step,
it's very similar at both ones,
- [00:07:50.750]at field capacity and at
permanent Wilton point,
- [00:07:53.330]heat does not transfer as well through
the soil profile that actually we're
- [00:07:57.980]looking at specific heat capacity.
- [00:08:01.030]When you look at the zero to
two inch step, once again,
- [00:08:04.670]we're seeing a significant difference,
at, field capacity, net,
- [00:08:08.900]permanent wilting point on the slides.
- [00:08:10.910]And you noticed really at permanent
wilting point, there's quite, you know,
- [00:08:13.790]that that difference is a lot larger
than, than, at fuel capacity.
- [00:08:18.290]And then when we look at the two to
four inch depth there, once again,
- [00:08:21.800]we have a significant
difference. So it's taking,
- [00:08:24.230]when we leave residue in place, that
soil takes a lot more energy to heat up,
- [00:08:28.130]but here's the other
thing. It takes a lot more,
- [00:08:30.590]it has to lose a lot
more energy to cool down.
- [00:08:33.110]So that could be just as equally important
in the fall and in the winter that it
- [00:08:36.590]takes more energy for that
soil to cool down.
- [00:08:39.530]even though we need more energy for
it to heat up a higher specific heat
- [00:08:43.790]some people think that that can keep
temperatures in the soil more stable.
- [00:08:48.050]when we look next, the next
property we would look at,
- [00:08:51.980]we don't have a slide for this
would be so thermal diffusivity.
- [00:08:56.340]there really wasn't a difference
because while it's soil,
- [00:08:59.100]thermal diffusivity is a ratio again,
- [00:09:00.900]a thermal conductivity over
specific heat capacity.
- [00:09:03.810]And we had changes very similar
changes, between the two.
- [00:09:07.530]So there was no difference, between
treatments for the few [inaudible]. So,
- [00:09:12.570]why did this happen? Well,
- [00:09:14.550]if you come out and you look at the plots
where you look at this picture I have
- [00:09:17.280]on the slide, you can see where
cutting those crown roots. Well,
- [00:09:20.360]like almost only a, this tall, and when
you cut the crown roots down that much,
- [00:09:25.290]there's no, vertical residue
to keep residue in place.
- [00:09:29.160]So even though we're keeping 44% of
the residue in place, wind and other,
- [00:09:34.200]events, move it off, and then,
you know, it also gets broken down.
- [00:09:38.160]The plots are bare and empty by the
time spring comes and it looks like we
- [00:09:41.700]removed a hundred percent
of residue in the spring.
- [00:09:45.270]So the summary of the
impacts from this experiment,
- [00:09:47.700]we do have data that another,
- [00:09:51.390]researcher took from three years and we
can compare it to six years kind of in
- [00:09:55.290]the summary. So the effect
of water infiltration,
- [00:09:58.080]there was non after three years, water
retention at three years, non,
- [00:10:02.670]available, the, the plant
available water, our storage tank.
- [00:10:05.850]There was no effect. However, at,
what aggregate stability,
- [00:10:10.260]in the top inch,
- [00:10:11.130]it was reduced after three years in
Oregon at carbon than the top inch was
- [00:10:15.060]reduced in one year. Now, when
we look at the six year,
- [00:10:18.390]results water infiltration was reduced.
water retention was reduced.
- [00:10:23.760]The plant available water was reduced.
when we look at soil organic matter,
- [00:10:28.740]it was reduced eight inches
down through the soil.
- [00:10:31.700]So our top eight inches
has lost, soil,
- [00:10:34.620]organic carbon or organic matter when
we remove residue very aggressively.
- [00:10:39.690]And then when we look at
water stable aggregates,
- [00:10:41.460]that's been reduced
down to six inches,
- [00:10:43.860]meaning that we're increasing or creating
more potential for soil would be lost
- [00:10:49.050]due to erosion.
- [00:10:51.240]So what can you do after you lose the
soil where you you've degraded her soil?
- [00:10:55.470]Cause you, you know, you started
bailing or you would like to bale,
- [00:10:58.980]you need to use that
residue for something. Well,
- [00:11:01.200]we have some remedial practices
that you can try cover crops,
- [00:11:04.620]as you can see from some of the,
the data show that, you know,
- [00:11:06.870]cover crops did keep that
organic matter in place.
- [00:11:09.630]Another option for our remedial
practices manure. But you know,
- [00:11:14.130]there are a lot of effects of
cover crops in the study.
- [00:11:17.520]especially after three years, when
we look at it, water infiltration,
- [00:11:21.150]water retention, plant available
water, well aggregates of ability.
- [00:11:24.840]None of those in at three years, we're
at six years were affected by,
- [00:11:28.740]cover crops. The only thing that
was affected was organic carbon.
- [00:11:33.870]Why was this well, at this experiment,
- [00:11:37.020]we're trying to mimic a lot
of what producers do,
- [00:11:39.960]out in the fields and trying to
terminate cover crops early enough,
- [00:11:43.740]that it's not a hassle. So we're
only getting maybe at most,
- [00:11:47.250]in a very good year, two inches of growth.
- [00:11:50.370]So what does two inches of growth
actually look like? Or what does that,
- [00:11:54.790]in tonnage? Well, that's
about 0.3, six tons per acre.
- [00:11:58.570]What we're removing for crop residue,
- [00:12:00.430]we're removing about 2.9 tons
per acre of crop residue.
- [00:12:05.470]So think about it.
- [00:12:06.550]We're trying to replace 2.9 tons
of crop residue with 0.3, six,
- [00:12:11.290]tons of cover crop residue.
Those numbers don't add up.
- [00:12:14.500]So that's why we're still losing,
carbon from our system.
- [00:12:18.910]And that's why those physical properties
are degrading. So next, you know,
- [00:12:23.410]when we looked at
Sabrina's talk beforehand,
- [00:12:25.840]they're both residue talks
to different experiments,
- [00:12:28.750]they're at the same location.
- [00:12:30.190]So this gives us a great
opportunity to kind of look at,
- [00:12:33.550]similarities and differences.
So what was similar? Well,
- [00:12:36.610]after six years treatments that
had over 50% of residue removed,
- [00:12:41.590]had a lower amount of organic
matter compared to those
treatments that left that
- [00:12:45.190]organic matter or that residue in
place while aggregate stability.
- [00:12:49.300]It decreased when we removed at least
50% of the residue in both of the studies
- [00:12:54.220]and then plant,
- [00:12:56.080]plant available water also
decreased after residue removal.
- [00:13:00.220]So some of the things that were different,
that would be our thermal properties,
- [00:13:03.250]where my experiment had an
effect on thermal properties.
- [00:13:06.700]and the previous speaker, Dr. Ruis's
experiment did not have an effect on soil,
- [00:13:11.380]thermal properties. So
that just needs our,
- [00:13:13.130]we needed a lot more research
on thermal properties,
- [00:13:15.190]kind of understand what's going on.
And that could be a point of,
- [00:13:18.580]further experimentation.
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