5 - 2020 South Central Ag Lab Field Day
2020 South Central Ag Lab Field Day
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- [00:00:04.310]Hi, my name is Sabrina Ruis
- [00:00:05.900]I'm a research assistant professor at
University of Nebraska Lincoln in the
- [00:00:09.590]department of agronomy and horticulture.
- [00:00:11.150]And I'm going to talk about a study
that has been in place for six years,
- [00:00:15.800]looking at cover crop termination date
on soil properties and crop yields.
- [00:00:21.620]So this topic is,
- [00:00:23.660]an important topic because cover crops
can have variable effects on soils and
- [00:00:28.190]crops, depending on their management.
- [00:00:31.790]So that cover crop
management is going to drive
- [00:00:36.770]the cover crop biomass production.
- [00:00:38.480]So if you have a short window
of growing those cover crops,
- [00:00:42.020]they're not going to
produce a lot of biomass,
- [00:00:43.490]but if we can link them that window,
- [00:00:45.860]then we're going to have
theoretically more biomass.
- [00:00:48.650]So that's part of what we're trying to
do with this study by terminating cover
- [00:00:51.740]crops early or late,
- [00:00:55.580]is trying to get that more biomass and
more impacts positive impacts to the
- [00:01:01.100]So we looked at the impacts of early
and late terminated cover crops in a
- [00:01:06.080]no-till continuous irrigated continuous
corn system here out at South central ag
- [00:01:12.170]And it also has a sister study
that is rain fed near I'm
- [00:01:17.180]actually near Lincoln,
- [00:01:18.590]but I'm going to focus on just
the site here at clay center.
- [00:01:23.180]And so we have a newcomer crop treatment
and early terminate cover crop early
- [00:01:28.010]termination means that we are
terminating it anywhere from about
- [00:01:32.600]two to four weeks before planting corn.
- [00:01:36.770]And then we have a late terminated
cover crop, which is terminated,
- [00:01:40.460]roughly early to mid may kind
of depending on the year.
- [00:01:45.290]So we measured,
- [00:01:48.590]each year we measure cover crop biomass
in the spring at each termination date.
- [00:01:53.030]And we also looked at,
corn yield in the fall.
- [00:01:57.140]And then in terms of soil properties,
- [00:01:59.480]we looked at wet aggregate
stability or water erosion,
- [00:02:02.210]potential particulate organic
matter or label organic matter,
- [00:02:05.960]whichever you want to call
it soil organic matter,
- [00:02:10.160]initial water infiltration,
- [00:02:12.980]compaction and thermal properties.
- [00:02:17.030]So first we're going to talk about
cover crop biomass production.
- [00:02:21.110]And when we terminated the cover
crops early, regardless of the year,
- [00:02:24.950]we had less than one mega
gram per Hector of biomass.
- [00:02:27.890]But when we terminate late, we
can get up to four and a half,
- [00:02:34.520]mega grams per Hector of cover crop
biomass production, which is really great.
- [00:02:38.810]and I'll get to that,
the impacts of that on yield,
- [00:02:43.760]towards the end of this talk.
- [00:02:46.550]So as far as the soils
are concerned, first,
- [00:02:49.850]I want to talk about what's called
particular organic matter or label organic
- [00:02:53.480]matter. Now, when we,
- [00:02:57.200]when we looked at this in year three,
- [00:02:59.530]we saw that the late terminated cover
crop actually increased the particular
- [00:03:03.460]organic matter, which is really good.
- [00:03:06.460]and I'll get into the why and
momentarily. And then again, in year six,
- [00:03:11.470]we also saw that that, same,
- [00:03:16.380]the impact of the late
terminated cover crop,
- [00:03:18.960]increasing particulate organic matter.
- [00:03:21.240]Now particulate organic matter is
really important. You it's,
- [00:03:24.240]a microbial food source. So
anything we can do to,
- [00:03:29.070]boost that will improve
our microbial activity,
- [00:03:32.790]it'll improve the overall
organic matter in the soil.
- [00:03:37.410]And it'll also provide for
better aggregation because as we
- [00:03:42.330]may know, organic matter is,
- [00:03:44.850]and the microbial action on that organic
matter is what glues our soil particles
- [00:03:49.380]and smaller aggregates together. Now,
- [00:03:52.230]when we talk about organic
matter on the next slide,
- [00:03:55.350]and this is our total organic
matter, in year three,
- [00:03:59.010]we saw no effect of cover crop
termination date, but in year six,
- [00:04:04.260]we saw that the late terminated cover
crops increased total organic matter,
- [00:04:09.480]and they increased it by
five, roughly five,
- [00:04:14.220]grass per kilogram.
- [00:04:18.570]Now we're going to talk a little bit about
what aggregates stability and on this
- [00:04:22.530]slide, you can see that I have both
the rain fed and irrigated sites.
- [00:04:25.620]We're going to focus on the
irrigated site and in year three,
- [00:04:30.840]the late terminated
cover crop increased,
- [00:04:33.780]what aggregates stability
or aggregate size.
- [00:04:36.510]And this means that those aggregates
are going to be more stable in water.
- [00:04:39.870]We can have big rain events.
- [00:04:42.100]they're not going to be carried as easily
because they're going to be larger in
- [00:04:44.640]size. And the same story
is true in year six,
- [00:04:49.560]the late terminated cover crops
increased our aggregate size.
- [00:04:52.440]So we're seeing increased organic
matter and increases in aggregate size.
- [00:04:59.010]But what about compaction as our
machinery sizes have increased?
- [00:05:03.960]That is one thing that we
are concerned about.
- [00:05:07.110]but we saw no effect on compaction. We
measured that in two different ways,
- [00:05:11.430]bulk density,
- [00:05:12.930]which is the massive stri soil
over the volume of the soil.
- [00:05:17.670]And then also penetration resistance,
- [00:05:19.710]which is the resistance of the soil to
a probing force that might be a root.
- [00:05:23.760]It might be an earthworm and
neither showed any effect of late
- [00:05:28.470]terminate or cover crop
- [00:05:32.010]now we're going to transition into soil,
hydraulic properties just a little bit,
- [00:05:35.910]and first we want to capture water.
- [00:05:39.870]So we want the water to infiltrate into
the soil and then we want to retain it.
- [00:05:43.530]So we're going to talk about
both pieces, water infiltration.
- [00:05:47.250]We measured that in just the
initial water infiltration.
- [00:05:50.280]So we measured just a much smaller ring.
- [00:05:53.430]If you've had any talks
with Michael Cinderella,
- [00:05:56.040]he might talk about a three test.
we didn't do the three hour test.
- [00:06:00.140]We just did the little short one that
takes no more than 10 minutes. And,
- [00:06:05.030]but we saw no effect of co cover
crop termination date on water
- [00:06:09.590]infiltration. as
far as water retention,
- [00:06:13.490]we have three different parameters
that we look at for water retention.
- [00:06:16.430]One is field capacity and
that is the water content.
- [00:06:20.630]After every, all the gravity
drained water is gone,
- [00:06:25.640]then we have the permanent
wilting point, which is just,
- [00:06:28.750]the water that's held so tightly to
the soil that the plants can't get it.
- [00:06:32.920]It's the point at which the plants will
wilt and there's no rescuing them at
- [00:06:37.090]that point.
- [00:06:38.440]And now the difference between those
two is what is called plant available
- [00:06:41.770]water. And that's the one that we
are generally most concerned about.
- [00:06:47.230]And cause that's kind of
our storage tank for,
- [00:06:51.520]soil water and all three
of those parameters,
- [00:06:55.870]we saw no effective cover
crop termination date,
- [00:06:57.970]which is interesting because we
saw increases in organic matter and
- [00:07:02.560]increases in organic manner
should be track with increases
- [00:07:07.330]in, water content at field
capacity or permit wilting point.
- [00:07:13.810]another topic that is interesting
to discuss with cover crops is the,
- [00:07:19.390]thermal properties or the ability
of the soil to conduct and transfer
- [00:07:24.160]heat and increase in temperature.
So we're going to talk about two,
- [00:07:29.020]thermal properties. The
first is thermal conductivity,
- [00:07:32.740]which is the ability of the soil to
conduct in transfer heat throughout the
- [00:07:37.690]soil profile. The second
is specific heat capacity,
- [00:07:42.400]which is the,
- [00:07:45.430]the amount of energy that it takes
to raise the temperature of the soil.
- [00:07:50.020]And when we look at the effect
of cover crop termination date,
- [00:07:54.670]late terminated cover crops,
- [00:07:56.080]reduced thermal conductivity compared
to no cover crop and early terminated
- [00:07:59.830]cover crop. And that's
probably because of the,
- [00:08:04.150]increase in organic matter.
- [00:08:07.360]soil minerals are going to transfer heat
much more readily than organic matter.
- [00:08:11.620]And that's part of what
we're seeing there,
- [00:08:13.480]but specific key capacity or the
energy that we need to warm up that
- [00:08:18.070]soil didn't change with
cover crop termination date.
- [00:08:23.920]So now I'm going to switch to the topic
that you're probably all wondering
- [00:08:27.820]about, crop yield.
- [00:08:29.860]So I'm going to talk about this in two
stages the first three years in the
- [00:08:33.130]second three years. So in
years, one, two through three,
- [00:08:37.810]we saw that the late terminated
cover crops reduced used
- [00:08:43.030]crop yield in only one year.
- [00:08:46.510]And then in the second set,
- [00:08:48.970]we saw that the late terminated cover
crops also reduced the crop yield
- [00:08:53.740]in one year. So two out of six years,
we saw reductions in crop yield.
- [00:09:00.360]So in summary, after
particular organic matter,
- [00:09:05.010]after three and six years late terminated
Kroeber crops increased organic
- [00:09:09.900]matter was unaffected in year three,
- [00:09:11.790]but late terminate cover crops increased
compared to the early in the no cover
- [00:09:16.950]What I agree is stability or aggregate
sized or water remotion potential late
- [00:09:21.360]terminated cover crop
increased after six years
- [00:09:25.590]and after three years,
- [00:09:27.720]water infiltration and compaction
and plant available water and thermal
- [00:09:31.830]properties were not measured in year
three because they're a little bit slower
- [00:09:34.170]to change with management.
So after six years,
- [00:09:37.950]water infiltration and compaction were
not affected nor West plant available
- [00:09:41.850]water, but late terminated cover
crops, decreased thermal conductivity.
- [00:09:46.440]And again, that goes back to
the organic matter crop yields.
- [00:09:51.390]Again, two out of six years,
- [00:09:53.280]we saw reductions due to the
late terminated cover crops. So
- [00:09:59.610]what does that mean for
you as a farmer? Well,
- [00:10:03.090]if you are looking to see imp,
- [00:10:06.510]improvements in your soil terminated
at cover crops late is the way to go.
- [00:10:11.340]But if you're concerned about yield,
- [00:10:13.860]perhaps realizing that you might
have some reductions and they weren't
- [00:10:18.840]large reductions,
- [00:10:20.940]in two out of six years or
picking something in between,
- [00:10:26.250]like between the early in the late,
- [00:10:29.010]for your termination date might be the
way to go to try and get some of those
- [00:10:33.600]soil health benefits, but
also preserve your crop yield.
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