(upbeat music)
-: My name is Katja Koehler-Cole
I'm a research assistant professor
in the department of Agronomy and Horticulture at UNL.
So my talk today is going to be on a project that we had
where we looked at cereal rye and how it influences
soil nutrients and microbial abundance, before soybean.
So this is basically a project on soil health,
and we are focusing on one indicator of soil health
which is the microbial communities
microbial abundance and diversity.
We know that in soybean systems we have some challenges.
We are facing a loss of nutrients especially nitrate,
and the period where we actually lose the most soy nitrate,
in a corn soybean rotation is the period
before planting soybeans
because the soil warms up microbes,
decomposed organic matter
and then there are no plants there
to take up the nitrogen that's released.
So there is potentially quite a bit of nitrogen loss.
We also have a risk of erosion,
water erosion, soil erosion,
and generally soil health issues such as aggregation,
loss of organic matter,
and other things which are a lot of times
due to the fact that there is no crop growing,
between the time of corn harvest and soybean planting.
So we know that cover crops
can help with some of these things.
And today I'm talking mostly about cover crops influence
on soil microbes.
Cover crops are a food source for soil microbes.
When they're growing during the winter
or an early spring,
or really any time of the year their root exudates,
they're simple sugars amino acids
and their preferred food for microbes.
And of course the decomposing cover crop residue,
also provides carbon and nitrogen to microbes.
And that's both above ground and the below ground residue.
Cover crops provide more than just a food source.
They also provide habitat,
roots are actually the preferred habitat for microbes.
Most microbes live in the roots zone
either near or on roots.
And cover crops can also help mitigate
soil surface micro-climates.
For example by lowering the temperature
preventing those temperature extremes
and preventing wind or at slowing evaporation
and things like that.
So I wanna take a few minutes
to just introduce some of those microbes
that we have in the soil.
Of course we all know
that there's numerous little creatures that live there.
So today, I'm mostly focusing on decomposers and predators.
Our largest group of decomposers,
in agricultural fields anyways are bacteria,
they are the most numerous group of decomposers.
And they preferentially decompose simple organic compounds.
So that would be for example things like,
freshly terminated cover crop.
Anything that's easy to break down.
And then we have fungi
they are the other big group of decomposers.
They keep decompose organic compounds
that are harder, tougher.
Things like cornstalks or roots
and they play an important role for other things.
And then we also have a lot of predators
and I put up a picture of the soil food web.
It all starts with plansts
of course the source of organic matter.
Then we have different decomposers
that I just talked about.
And the predators,
some of them are protozoa which feed mostly on bacteria.
We also have nematodes that are predatory.
They feed on fungi and bacteria.
So those predators really keep the populations of Bacteria
and other soil microbes in check.
A little bit more about the fungi.
Why do we really like to see fungi?
They're so important for soil aggregation.
They have a thread like growth it's called hyphae,
and they also release
glue like substance called glomalin
and those two together help bind little soil particles,
and make those nice aggregates.
So fungi improved aggregate size.
They improve aggregate stability.
And that makes soil much more resilient to erosion.
Two large groups of fungi
that we're interested in.
One are the saprophytic fungi,
they are the ones that decompose
things such as cellulose and lignin.
So that's the stuff that's found in corn stover.
And then we have AMF or arbuscular mycorrhizal fungi,
which colonize the roots.
They can increase nutrient uptake
because they can reach on nutrient sources
that are otherwise not accessible to plant roots.
When you have a cover crop growing over the winter,
it can be a host to AMF,
so it can live on the cover crop roots
And then when the cover crop is terminated
your sobering or con plant is planted,
AMF can actually spread from the cover crop roots
to the crop roots colonize the crop roots
and have benefits for crops there as well.
So this project we actually carried this project out
at the soybean management field day sites.
We worked together with Keith gluons
and Justin McMakin steam.
We had several research questions.
Our first research question was can we use cover crops
to reduce soil nitrate, before soybean?
The second question was can rye cover crops,
increase overall microbial abundance?
And then we also wanted to know how different groups
of soil microbes are influenced by a right cover crop.
And in particular,
we wanted to see whether we can increase
the populations of soil fungi.
So again these trials was set up
at a soybean management field day sites.
This year unfortunately due to COVID
we were only able to do it at Arlington and Shelby.
We had a right cover crop and we also had control crops.
It was a replicated randomized design
the rivals planted in mid November
and then terminated at soybean planting in early to mid May.
And then this was done by Keith Clunes
and testing McMahon's teams.
We came in just for the soil testing.
So within a week of soybean planting we took soil tests.
These tests are...
They're only done to a sole depth of four inches.
This is just because
that's where most of the microbial activity is happening
in the soil.
We were testing the solve for NPK.
So major nutrients,
and the other tests we're doing is called PLFA
or forceful lipid fatty acid analysis.
This test to basically,
to indicates what kind of microbial groups are in the soil
by identifying the phospholipid fatty acids
that are in the membranes.
So it doesn't give me the type of species
but certain functional groups for example AMF
and separate phytic fungi and bacteria
we can differentiate those.
We carried out statistical analyzes with Brooklyn mix.
And the differences that I'm talking about
if there were significant differences
they were different at alpha level of 0.05.
So this is what we found.
We had relatively low zero right biomass
at our Arlington site about 1000 pounds
and about 1,300 pallets at the Shelby site.
We analyzed the biomass for carbon and nitrogen
at the Shelby site
it had pretty high amount of nitrogen,
a little bit lower at the Arlington side.
So these cover crops took up between 25 and 40 pounds
of nitrogen per acre.
And they had a carbon to nitrogen ratio of 19 and 14.
So this carbon to nitrogen ratio is important
because that kind of tells us a little bit
about how fast the cover crop may decompose.
Any time the ratio is below 25 to one,
we expect it to decompose pretty quickly.
And with those ratios said we have here
we do think that that cover crop decomposes
within the season for sure.
Relatively fast.
Which also means that it releases its nitrogen
that it took up back to the crop, okay.
Moving into the soil nutrient concentrations
following the cereal rhyme,
we did see differences when it came to soil nitrate,
again, this was a pretty shallow depth
only zero to four inches.
But at that depth we found
that soil rye had significantly lower.
So nitrate levels in May,
at the time when we sampled.
So the blue bars this is my control
where we did not grow a cover crop.
The red bars where we grow a CRO rye cover crop,
As you can see significantly
lower amounts of soil nitrate under the xx rye.
So it takes up some of that nitrate
possibly prevents it from leaching.
In July when we came back in,
there were still some smaller differences
but overall probably some of that nitrogen
from the rye residue had already decomposed
and went back into the soil.
We looked at the other soil nutrients,
but I did not influence phosphorus potassium
or organic carbon.
So absolutely no differences there.
We saw some side effects.
The site at Shelby had more phosphorous
than the site at Arlington,
and decided Shelby also
had less organic carbon than Arlington.
With organic carbon
we kind of expected that zero right cover crop
would not influence that within the short amount of time
that we've grown it.
Does usually you need four or five years or more
to really see differences in the organic carbon.
It's much more determined by soil type really.
So we tested microbial biomass in May as well.
We also did not see any treatment differences
that were due to the cover crop.
And we actually did not see any site differences.
So that was kind of interesting.
So the two bars again, refer to the two sites.
So we have our Arlington and our Shelby sites,
And I just broke it down to give you kind of an overview.
So the blue refers to bacteria.
So they are out of all the groups the most numerous one
in the soil.
Then we have a very, narrow bar there of red
which are the AMF fungi.
So there are a lot less
and to create a separate phytic fungi.XX
So as you can tell fungi only make up
about 10% or even less of the total of microbial biomass.
And then we have a large amount of yellow which is others
which are a lot of other,
soil microbes such as actinomycetes,
Brodo soul and some other nematodes
and things like that are all looped in here.
I did not actually separate them out
because they're usually their numbers are very, very small.
Cell but there's a lot of them, a lot of different groups.
So no treatment differences, at least not in May,
we have not gotten our results back from the summer.
What we found last year, we did the same experiment
we actually did see some increases
in microbial communities following cereal rye.
So I wanted to kind of figure out
why did the rye not have an impact this year?
I looked at my test results again and actually realized
that the microbial biomass at our science
even in the controls was already pretty high
or at least it was average.
So it's probably more difficult to increase it
from populations that are already relatively high.
Another thing that I looked
at as the fungi to pictorial biomass, remember
in agricultural fields
we are really looking to increase the amount
of fungi because they're so important
for our soil aggregation,
also structure and things like that.
And here we actually saw a site difference.
The Arlington side had a higher fungi to bacteria ratio
but again it was not influenced by the rye treatment.
So another thing I think
if we wanted to really influence our
microbial biomass a little bit more
some of the things that we may want to look at...
Oh, I forgot to talk about the organic carbon,
organic carbon in these sites
was also relatively high already.
So again, these sites had relatively good soul health,
probably a reason
why we didn't see more treatment differences.
How can we increase the benefits for soil microbes?
How can we use a cover crop
to really improve microbial abundance and diversity?
We have only focused on Syria, right?
There are plenty of other cover crop species out there.
Mixing cover crops together probably could increase.
Soil microbial diversity.
It could also increase cover crop biomass
at least during certain times of the year.
And generally I think trying to increase cover crop biomass
for example by allowing to grow with the cover crops
for longer period of time would be beneficial
for soil microbial communities as well.
For my take home points,
we do think we could use the right cover crop
to really reduce Soil nitrate levels
which could help reduce soil nitrate contamination
and may reduce leaching.
At least this year we did not see any improvements
in soil microbial abundance.
We have seen it in the past
but this year we did not have very high cover crop biomass.
Increasing cover crop biomass
and probably increasing the amount of plant species,
several growing mainly to create a benefits
for soil microbes.
And this is really the end of my presentation.
I want to thank the participating farmers
Keith and Justin, and their team
George Biliarski who took all of the samples
for this project.
I also wanna thank our sponsors
the Nebraska Soybean Board
who partially funded this project
along with the Nebraska Corn Board.
And with that I take questions.
So the question was
if there is a greater amount of organic matter under soil
with increasing organic matter in the soil.
Are there greater amounts or greater diversity
of bacteria and fungi.
There's are definitely are greater amounts
of them probably also greater diversity.
With my tests I have not seen that
because I generally do not look at different bacteria level.
I look at just the total bacterial biomass.
And as far as this test goes, I looked
at just two groups of fungi, AMF, and separate phytic fungi.
But I do think that from other papers that I read
you can increase the diversity, especially
in the amount for surely, especially that are fungi
with increasing soil organic matter.
So if they are interested in learning
about specific functional groups
of microbes, the PLFA test is a good test for that.
It's a pretty expensive test
and it's also a quite complex test.
It's something they would have to
but they would basically just take the soil sample
and then send it to the lab.
It takes several weeks to return it.
There are some established parameters
because the thing is
this test gives you all these functional groups
but what do the numbers really mean?
So the nice thing about is there are some parameters
some numbers that say
okay, this is a good or desirable level
and this not so much.
So from that point of view you get some information back
from the laboratory that you can actually use
to interpret what your soils look like.
So the question was how important is manure
as a jumpstart to solve health?
Thanks for bringing that question up
because livestock is really or if you can graze then
manure applications are really
a very good way to increase microbial populations.
First of all, there are microbes in the manure themselves
and then just the amount of organic matter
and other nutrients that are relatively easy to access
for the microbes.
That's really, really important.
That's a very good thing to do for soil health.
So the question was, is the optimum cell health
the same for a corn field as for a range land
or another type of cropping system?
Yeah, that's a good question.
I think like Keith said earlier
maybe the standard really was, what was the soil
like before it got turned into something else?
So that's probably a good benchmark to try to maintain
for a cropping system.
Can you maintain that at a similar level?
That may be very hard
but maybe that native part
that it replaced that was the benchmark.
I do think there are exceptions though
to that because some managed soils
have really increased their fertility over what was before
and that's due to probably irrigation, probably manuring
we all can think of some very sandy lands
that probably have been improved by people over time.
So I think some things can be improved on,
whereas others maybe not.