Woman: The following presentation is part
of the Agronomy and Horticulture Seminar Series
at the University of Nebraska-Lincoln.
John: Welcome to today's department of agronomy
and horticulture spring seminar series.
Today, I get the pleasure
of welcoming Dr. Alan Franzluebbers.
Alan is a native Nebraskan,
he receiving his bachelor's science
and masters of science at the University of Nebraska-Lincoln
and a PhD from Texas A and M University.
Alan is a research ecologist
with the USDA ARS Plant Sciences Research Unit
out of Raleigh, North Carolina.
And those of you that attended American Society of Agronomy
Crop Science Society Soil science Society
of America annual meetings,
you've probably heard Alan speak before
and that's where I first met Alan
and I've always enjoyed hearing his talks.
Some of his work includes working a lot
with pastures and that's always been my research interest.
And so that has fit well
and I'm happy to happy to hear Alan speak today
but a couple things also about Alan,
he's a Fellow of the Soil and Water Conservation Society
and a Fellow of the American Society of Agronomy
and the Soil Science Society of America.
But now Alan, when you're ready, I'll go ahead
and turn it over to you and you can begin.
Thanks.
-: Thank you, John, for that introduction.
Great to be here with you.
And I was always talking, telling my wife
I'm going to Lincoln today.
So here I am in the cold weather of Lincoln, Nebraska.
I remember it some 30 years ago
I was born in the dust of Nebraska.
I grew up in the Bohemian Alps of...
Close to the Bohemian Alps
of the Northeast part of the state.
And I did do my undergraduate
and a little bit of graduate work in Nebraska.
And I had grandparents that lived near the Bohemian Alps
and actually farmed in there.
They called them that because they, you know,
some rough Hills out there.
And I'm showing you some pictures that I took back
when I was in Nebraska as an undergraduate
and researcher in my master's program
to show you what would kind of inspired me
and dust didn't truly inspire me but it was something
that was quite devastating on my psyche.
And I believe that that helped me to understand a little bit
about nature and what we should be doing
to kind of manage our natural system.
There were a lot of good days in Nebraska
but there were some tough days too.
One of the things that I was charged with
was to work on a project to look at nitrogen management
in various cereal grain systems
and of course that would mean corn, but also sorghum.
And so we took a soil samples for deep nitrate
and that was one of the primary reasons
that we were conducting this research
and we would harvest various plots
either with strips or small plots
and it gave me a really good experience.
And it's interesting because some of my recent research
returns to those same very techniques.
So Dr. Charles Francis was my mentor and Dan Walters
and I really enjoyed the time there
and it's served me well.
So these are some of the publications
that we heard from the research that was done during
when I was employed as a research technologist
at the time with Dr. Mike Johnson
and I worked as a student, a master's student
under Charles Francis.
So Chuck was a great mentor.
He taught me a whole lot.
And I know that those of you that know him
know that he's got a lot of great ideas.
And I learned to, I was really inspired
by many of those great ideas
but also you have to know that people have to do things
and get things done
and he was really able to assemble teams
that that could do that.
There's another person there at the university
that inspired me as well.
Dr. John Duran.
Now, I did not study with him
and did not have a close association
but I understood what his work was about.
I tried to be close to the thought process of him.
And I know he was a big mentor in the world of soil quality
which has transformed into the term soil health nowadays.
And that's led me to explore more during my PhD when I moved
to Texas and went to the Aggies and looking at soil quality.
So we have a long list of soil chemical indicators.
I'm familiar with many of them.
I'm sure many of you are as well
and these all can serve us well.
There are a lot of physical indicators
that we can be concerned with
and these are something that I think
that are important because a lot of them are visual
and so we can kind of see them.
We can see aggregate stability.
We actually can see it rather than just measuring.
And of course, you know water is important
and temperature and porosity.
All of these things are our long list of indicators.
And of course, then the biological indicators
which at the time when John Duran was researching
and I overlapped during my time in Lincoln,
I thought there was of course,
this was a new area and this was something
that we had opportunities to work on.
And so when I moved to Texas I did actually explore
a lot of these things and they gave me a good opportunity
to focus in on some things.
No, I really appreciated the NRCS movement
and for soil health because although it had science
as some background,
it was more of an emotional push.
And I think this was something that is really important
by the leaders in the organization
that if they feel strongly about it,
they can make things happen.
So I'm always encouraged by some aspects of government
and of course, you know,
there's some frustrating parts as well.
But the soil health principles
that they promoted ,I think are really important, you know
of minimizing disturbance,
maximizing soil cover,
maximizing living roots and encouraging biodiversity
whether that's plants or animals.
And of course, we'd like to think
that that occurs in the soil as well.
And I think these principles are really important
and we should really focus on them
because we can actually have agricultural production
with conventional approaches
that don't follow these principles.
But in fact, if we follow these principles,
almost always we can find systems
that can be developed that are equally productive
but much more favorable for the environment
and we really need to focus on the environment
because it's our future.
We can't destroy our environment.
So in soil health science
we want to focus on various functions
and these are some of the functions
that I think are important.
There may be others but these are generally agreed upon.
You know, such as producing plants for food and fiber
and protecting water quality,
storing carbon, cycling nutrients,
creating a reservoir for biodiversity.
All of these are very important.
And you see in this graphic,
I've assembled some of them.
And this is where I'm going to take you down
a little bit of research that I've conducted
of focusing on two aspects,
producing plants and food,
and cycling nutrients.
Because these are two of the very most important
across many agricultural ecosystems.
And I believe that soil test biological activity
is a strong indicator of these two functions of soil
but as well, it's likely,
and we have some evidence
but we don't have all the evidence,
that is related to many of these other functions of soil.
So a simple soil test indicator
could be something that we could use very effectively
to help us manage our land better.
So what is soil-test biological activity?
Well, it is the carbon mineralization that accumulates
during an incubation.
And when I say accumulate,
we have this flush of activity
when we dry a soil and re wet it,
there's a burst of activity of CO2
and then a stabilization of that activity
called basal soil respiration.
When I first started at Texas A and M,
I was told you have to rid yourself
of the flush and focus on basal soil respiration.
That's what we should focus on.
So at the time that was the general thought process
but actually we looked at the flush
of activity because the response that we get
from the first few days relative in this case
of these different depths here,
is relatively the same whether it's at three days,
at 10 days or 24 days.
And so we looked at this more closely
and looked at it to try to use the flush of activity.
CFA could be some indicator that would be relatively simple
or rapid and reliable.
And so the procedure is simply incubating soil
into a canning jar along with, in this case,
the way that I've developed the procedure
is to use an alkali trap.
One could also use an infrared gas analyzer
or a gas chromatograph but we have to detect the CO2
that's evolved from the soil that has reread it.
And that's the key here.
Is simple incubation procedure
that we measure the respiration of soil.
So with that, perhaps, I don't know all
of the reasons why it occurred this way
but there are different methods
that people have chosen to use
for this simple respiration test.
The key though, is that all of these methods
whether it's in my lab
at the Soil Ecology and Management Lab
in NC state University
or the Haney Soil Health Test
or at Solvita-Woods End Lab
or Cornell's Comprehensive Assessment of Soil Health,
all of them use a dried soil that is re wetted.
How you dry it,
what happens to the soil
and how it's manipulated prior to incubation
can have an effect.
So we've looked at some of that.
We have some data on that
and shared that in the public domain.
It does matter but probably it wouldn't matter
if one just settled on the method itself.
So the actual soil mass is important as well.
I believe that we have a lot of variability in soil
and so more soil is better.
Now I've looked at even more soil than what I've shown here
for our 50 grams sub samples that I've used in my research.
That's kind of what we settled on.
We've tried to use more and actually we get some suppression
of the respiration and so we're not detecting as much.
So I think that we're at an optimal level
but there are other research groups
that are trying to use less soil.
I think it's not wise to use less soil,
say less than 10 grams.
It's something that creates perhaps less sensitivity.
How one adds water is also important.
My colleague, Rick Haney developed a procedure
to re wet the soil from capillary action
by using basically small holes in a container
allowing water to wick up
and essentially reach near saturation.
It's not fully saturated but it's near saturation
and this causes problems in certain types of soils.
And the research that I've done shows
that it actually is more of a problem in sandy loam soils,
sandier texture rather than finer textures.
Which was a little bit opposite to my presumption
but it does show that some soils are negatively affected.
So optimizing the water content
with air content is really important.
And then the biggest thing that is really kind
of different is that we now have
in the literature showing methods
that can incubate for one day,
for three days, four days.
Can be of course, longer 10 days, 24 days, 28 days, 60 days.
But the point, if we want to use it as a soil testing tool
we need to use a short period of time.
My research would show that actually three days
is really a good optimum.
It's possible to use one day.
It's just that of course
the narrower timeframe creates more variability.
And then how we detect the CO2 is also important.
Not that I think it really matters too much
because I think all of them are relatively reliable
but there are different ways.
In my lab we use an asset titration
with a sodium hydroxide trap
to capture the CO2 because CO2 is a weak acid
if it's trapped in the sodium hydroxide
and then we back titrate
with acid to a phenolphthalein endpoint.
You can use an infrared gas analyzer
and of course the idea by Solvita
to use a simple gel paddle makes it so that it's a quick
and readily available test that people can use simply
by ordering a kit and you can do it relatively easily.
So that's of course an advantage.
But of course, then you think
about the cost that accumulates over time
and that could be maybe a disadvantage at that point.
So, but for a research situation
we wanna use a good analytical methods.
So, I believe there are some key considerations
when we use the soil-test of biological activity
and that's that we need to first start
with a representative sample from the field of influence.
This is important for any soil analysis
but I think it's worth repeating here.
We want to define the soil depth
because as you see on the graphic here,
that almost always the surface depth
has more biological activity than deeper
in the soil profile.
So we want to make sure that we define
the soil depth well.
In this case, we dry the sample at 55 degrees Celsius
for three days, and that's so that we are normalizing
all soils to optimum condition.
It's possible to perhaps go with an air-dried sample
and I think that would be really interesting and valuable.
It's just that getting a uniform dried sample
takes more time than at a lower temperature.
And so that's an issue.
I believe that it's important to save the soil coarsely
and this is somewhat of an optimization as well
that traditionally soil is sieved to two millimeters
but there's not really good evidence to why that occurs.
I think it's just a historical precedence.
And of course, if we get too course of the soil
then we start getting into variability
and certainly there's variability with 4.75
but of course in sandy soils
it doesn't matter if it's sieved
through two millimeters or 4.75
it's pretty much all the same condition.
And then we re wet to 50% Water-Filled Pore Space
So that half of it is water,
half of it is air of the pore space,
incubate at a constant temperature.
This is really important because some research
would indicate that if we're not defining
the temperature very well we're getting variable results.
And then you have to have some accurate determination
of the CO2 and in this case,
we use alkali trap with titration.
So getting to the what does this represent?
And then in this case,
this was a task that was done in North Georgia
where we had a longterm, no tillage
versus disk tillage system.
This graphic here shows that
there's relatively uniform distribution
with this disk tillage.
Of course, there's a little bit of stratification.
And again, all soils tend to have higher
or higher biological activity,
higher organic matter very near the surface
and declining with depth
but it's much more stratified with no tillage.
And in this case, it shows that a trend between no tillage
and disk tillage that is very similar
to soil organic carbon
or total nitrogen or soil organic matter.
And so something that seems to reflect
the organic distribution.
We've also tested it in grazing systems.
In this case here the soil test biological activity
on the Y-axis compared to years of management
of establishing a Bermuda grass pasture
whether it's hayed, unharvested
or with low or high grazing pressure.
And this Bermuda grass pasture
was following a tilled crop land situation.
So there was a large increase
that occurred with all systems
but there was a greater increase that was occurring
with the recycling of the pasture forage
through the dung and the consumption by the animal
through the dung and re deposition onto the pasture.
So we were improving the soil more
with the grazing than without grazing.
Interestingly, we also looked at some aggregation data
and this was from a study in North Georgia as well.
And we looked at the relationship
between soil tests biological activity
and mean-weight diameter of water stable aggregates
and there was a relatively reasonable relationship.
I think there's more data that could be developed
to show that there's probably some association.
There should not be a strict association
because aggregation is also
a mineralogically determined property
but it is affected by biological activity
and it does show that there is some effect here.
And finally, I wanted to bring your attention
to possibly some work that needs
to be developed even further
but this shows the bacterial diversity in soil
was related to the biological activity.
So diversity and activity could be related
under some situations
but I don't know that it's always going to be related
but in this case my colleague was able to sample soils
from Lake of Prairie
and then from our studies in Georgia
both under grassland systems
and showing that with higher activity
there tended to be greater bacterial diversity.
But there was a point here where there was not
such a strong relationship.
And so if we exclude this point,
this is significant statistically
but if we include this one,
it's really just a marginal relationship there.
So I think there is a possibility
that there can be some association
but I don't know that it's a strict association.
I'd like to take you now to what I believe
are, you know, relatively solid, strict,
repeatable relationships that I've observed over a decade,
more than a decade of research.
So this is between the biological activity
that flush of activity and the basal Soil respiration.
Basal soil respiration being the more linear portion
of the cumulative carbon mineralization curve
and looking at soils from throughout the Eastern US,
we basically see a direct relationship
between basal soill respiration
and soil-test biological activity.
We can go to the tropics and I've had collaborations
with students from from the tropical regions
primarily in Brazil, as well as in Guam
and that's those samples incubated
in the laboratory show a very similar response
if we get this by the flush of activity
compared to the basal respiration,
very similar response.
And we take samples from collaborations from out West,
we also see a strong association
and the point being that really across all three
of these regions there's really very little variation
in the slope that occurs here.
And so really the internally,
the cumulative carbon mineralization curve
can easily be predicted from just the flush of activity.
So that gives us a lot of confidence
because these are very different types of soils.
So I wanted to also bring your attention
to a fact that most everyone asked me,
well, yeah, this could work for certain soil types
but maybe not for all.
And texture is one of the biggest things
that we can see as differences among regions.
So we looked at soils from throughout North Carolina
and Virginia and we have a great diversity
of conditions that we can identify in this region.
And in soils that were relatively sandy
or with less than 20% clay,
we see a strong relationship
between Soil test biological activity
and net nitrogen mineralization.
So this nitrogen mineralization is during 24 days,
we standardize this procedure for nitrogen mineralization
just as much as the standardization
for this whole test biological activity.
And over and over we see kind of similar relationships.
And I'm gonna say that even with medium textured soils
with 20 to 30% clay,
which I suppose would be considered,
you could imagine that silt loans
and perhaps even silty clay loans
in Nebraska might fit this textural class.
And then if we have even soils
with greater than 30% clay,
essentially we're getting about the same relationship.
And if we plot them all together
we do essentially have one relationship
and our square of 87% indicating
that we have a pretty good association
between net nitrogen mineralization
and soil test biological activity.
Which of course then begs the question,
"Well why would you measure nitrogen mineralization
if you can actually get it with a simple test
of soil test biological activity?"
That's the theme that I want to develop further.
So in this case if we know how much biological activity
we have we could actually start predicting.
Well, how much nitrogen mineralization could be there.
So if we have low biological activity,
we have low nitrogen mineralization.
We have high biological activity,
we have high nitrogen mineralization.
And in this case, you know, the simple units
of nitrogen per kilogram soil for 24 days,
the values of 55 and 127 could easily be equated
to relatively closely to pounds of nitrogen per acre
in a given period.
In this case it would be 24 days under ideal conditions
so that means that perhaps you have to take that times three
or four to get into a field condition
because the temperature and moisture
in the field will be suboptimal in most cases
and so it takes a longer period of time
but it shows that actually we could actually
start predicting the nitrogen mineral mineralized from soil.
And this is another dataset from soils that were taken
from throughout the state of North Carolina
under no cover cropping, single species cover cropping
and multi-species cover cropping.
And essentially we get a very similar association
relatively strong relationship of our square of 0.82.
The slope is slightly different
but it's essentially in the same range that was before.
So our next step was to conduct some greenhouse trials
to perhaps convince ourselves,
I did need to convince myself
but of course, to convince our colleagues, right?
I mean, that's always the challenge in science,
is to tell a story that is convincing
and compelling that we can actually use the information.
So we took the soils that we were collecting from the field
dried them, set them to 4.75
and you can see that some of these soils anytime
they have a little bit of clay in them,
they tend to have aggregates.
And those soils that have very little clay in them
their sandier texture, they don't have aggregates.
So they distribute differently
in the size of the aggregates.
But it shows that we have different types of soils.
And basically all we did was re wet the soil,
plant some sorghum sudangrass,
cover them with a shallow layer of sand, wash sand,
so that we'd get no cross-contamination
and let (indistinct) for six weeks.
So this is during the development of them.
We're basically giving them water only
and allowing the soil to (indistinct) grass
it's nitrogen mineralization potential.
So we're gonna then look at harvesting these plants
after six weeks.
And we did not measure anything in the roots
but it just wanted to point out
that the roots explored almost all of the soil
that was in there because it was a relatively
small amount of soil.
It was roughly 150 grams in each of these containers.
And so the plants became nitrogen stressed of course.
You see that the leaves are turning yellow.
That was our goal.
We wanted to stress them.
We wanted the plants to take all of the available nitrogen
and express the nitrogen that was mineralized
into the plant dry matter.
So the plant dry matter was measured
against what we measured in the laboratory
of net nitrogen mineralization.
And you can see that from the coastal plain
we get a pretty good relationship,
very strong association here.
So net nitrogen mineralization,
the mineralization of organic matter
is important for plant dry matter production.
And from the Piedmont we get another relationship.
It's slightly different in this case.
And from the Appalachian region we had soil samples as well.
But we put them all together and essentially, of course we
have some scattered but association would indicate
that 83% of the plant dry matter production
could be predicted by net nitrogen mineralization alone.
Now we did measure residual soil nitrate
and there were some variations
and that's probably why we had some slope
or intercept that was greater than zero.
And so there's some plant production.
Of course the seed has some reserves as well
and so there's a reason for that value greater than zero.
But it shows that the plant dry matter production
was really a function of net nitrogen mineralization.
And we also measured plant nitrogen uptake.
The total nitrogen uptake by the plant.
And then expressed it in association
with soil test biological activity.
It was not quite as strong
but it was a relatively good relationship
of 81% of the plant nitrogen uptake could be expressed
by soil test biological activity.
This gave me confidence that what we were observing
in the laboratory could be expressed
in plants in the greenhouse.
and it also begged the question,
well, why don't we just use organic carbon
to predict nitrogen mineralization?
Because this is a question that I get
on every presentation I have.
And so I thought I might share that information with you.
Nitrogen mineralization is related to total organic carbon.
It's certainly more related
to total soil nitrogen in this case
because we have some variations in our soils
in North Carolina and probably in other States
and regions of the world as well.
But it does show that yes there is an association
between nitrogen mineralization and total organic carbon
but it's not that strong.
There are a lot of variations.
And in this case, of course, I've picked some soils
that I think are important to illustrate.
So these soils were taken
from three different physiographic regions
in North Carolina and there are some reasons why
there were different associations among these regions.
So in the Appalachian region,
we have a really strong relationship
between net nitrogen mineralization
and total organic carbon.
In the Piedmont we have a really strong relationship
and in the coastal plain, we do,
but there are differences among these soils.
In the coastal plain there's a large pool
of resistant soil organic matter
that was submerged and so that old organic matter
that was submerged is not very biologically active.
And so we do measure it as organic carbon
but we don't measure it in an expression
of nitrogen mineralization.
The difference between the Piedmont and the Blue Ridge
or the Appalachian region was because in the Appalachians
we tend to have crop land in Sandy bottom lands
and so they don't have as much clay as in the Piedmont
and so that sandy texture helps to elevate
the nitrogen mineralization per unit of organic Carbon.
But if we were to use these same soils
that I just showed you and plot nitrogen mineralization
against soil-test biological activity,
there was only one association that was needed.
We didn't have to know where the samples came from.
Or physiographic region.
The soil test biological activity was good enough
just by itself to just predict
the net nitrogen mineralization.
And in this case, the R square being 94%
even a stronger association than other datasets.
Well, I'm going to shift to the theme of the rest
of the seminar into how we can actually use this indicator
of soil-test biological activity
as a way of predicting nitrogen availability.
In this case this graphic shows
that a relative yield is a function of available nitrogen.
We know that if we had a soil from the beach
that had no nitrogen in it at all
we would grow no plants.
Or a sand from the kids sand pile.
It has no organic matter.
It would have no growth.
We know this will occur
because plant dry matter production has to have nutrients.
So there's this nonlinear function
that is going to occur
there's going to be a plat owing
of their response with available nitrogen.
But where does the nitrogen come from?
That's our key question.
And that's where we need to focus our attention.
It's gonna come from inorganic nitrogen.
It's right to be able to measure residual soil nitrate.
It's a very good thing to do.
And we can do that in the surface soil
or we can have it residual in the profile.
And of course in Nebraska you would measure residual
in the profile because it's more of
a semi-arid subhumid region.
In North Carolina I've been told
that we don't want to do this
because we don't really carry over any nitrate
in the soil profile.
We have excess precipitation.
I'm not sure that that's always the case
but that's the current strategy.
What we missed in the past though is this organic nitrogen.
If we measure only the total organic nitrogen,
we're always...
I would just say that it's not yet clear.
We're confused because we're not focusing on
that portion, which is biologically active.
So if we had sites with low nitrogen availability
we would likely have high nitrogen fertilizer response.
We would definitely increase profit.
This is the current paradigm.
This is what we definitely should do when we have
low available nitrogen.
The idea is how do we characterize that available nitrogen?
There are sites around the country,
certainly in North Carolina, Virginia,
where I've done some of the research
where we have high nitrogen availability
and we see very low nitrogen fertilizer response.
If we were to reduce the nitrogen input
from fertilizers then we could reduce
our environmental impact.
This would be a very good thing.
Of course, we should try to elevate
the available nitrogen pool into...
If we do it strategically into a more organic form,
then we're sequestering nitrogen,
as well as releasing it simultaneously.
And that will protect us from environmental impact.
Now, that's a simple statement
but it's not quite as simple in reality.
So we do want to increase the organic nitrogen availability
but be able to release it as well.
And that's our real goal.
So the research really focused on surface soil,
inorganic nitrogen
and the biologically active organic nitrogen.
So, if we have this scenario where we have a target
of 200 bushel an acre corn grain yield,
we might have some expectations
on how much nitrogen might be taken out by the corn crop.
Well, we know that sometimes we have actually,
if we do not apply nitrogen fertilizer,
we might have 20% of the relative yield
without any nitrogen.
That means that it's gonna come
from any one of these sources of nitrogen in the soil
and then we supplement with the nitrogen fertilizer.
That means that we should actually
be able to calculate how much nitrogen uptake comes
from this available nitrogen pool.
We might have a soil that has 60% relative yield, okay?
Then that means that we're having a larger nitrogen uptake
and a larger available nitrogen pool.
Something is occurring here.
It could be from residual inorganic nitrogen,
it could be from biological activity.
We have to define that.
And then finally we have some yield response curves
that look more like this.
where we get almost 90% of relative yield
without any fertilizer input.
And only a 10% yield increase
if we we add fertilizer.
This means that we have a large available nitrogen pool
and it could be from inorganic or organic nitrogen sources.
So hacking back to my days in Nebraska
this was one of our goals,
is to find out well, is it coming
from residual soil nitrate?
That was an interesting thing.
Unfortunately I never got to the point of
exploring organic nitrogen.
And fortunately, I've been able to do that
in my research since then.
So if we would focus on a case scenario,
in this case we're applying a 50 pound unit
of nitrogen that yields us 82 bushel an acre more grain.
Well, that yield response,
this 50 pounds and yielding 82 bushel an acre more grain
is equivalent to 92 pounds of grain per pound of nitrogen.
If we just divide these out,
take the 82 times the 56 and then divide that product,
divided by 50, and then we get 92.
So that's a good yield response.
That's something that's obviously 92 pounds
of grain per pound of nitrogen.
You're gonna make money if you apply nitrogen in this case.
But we might also have a case where we apply an increment
of 50 pounds of nitrogen
and only get 27 bushel an acre more grain.
Well, that equals 30 pounds of grain per pound of nitrogen.
I'm highlighting these units of pounds of grain
per pound of nitrogen because these are
the units I'm gonna use further down on in the presentation.
And these are what I believe are important
to understand our yield response intensity
to nitrogen fertilizer.
And then in the case where we have
a 50 pound unit of nitrogen
and then we only get nine bushel an acre more grain,
we're only getting 10 pounds of grain for common nitrogen.
This is getting to the marginal cost
of the yield return from our fertilizer investment.
So the intensity of yield response
at the first dose of nitrogen fertilizer declines
as soil nitrogen availability increases.
This is basically the hypothesis that I'm working with.
So we went to the field and determined yield response
to nitrogen fertilizer at a number of locations.
They were 47 trials in 11 counties over three years
in four different physiographic regions.
So a wide diversity of conditions really.
And so there were some challenges with that
but also some opportunities with that.
And basically what we found was this intensity
of yield response to the initial dose
of fertilizer is the response that I was looking for.
Pounds of grain per pound of nitrogen
and I related that to soil test biological activity
and we saw from field studies of measuring this
with replicated small plot trials
and then taking a simple test prior to the growing season
we can estimate 64% of this yield response
to the initial dose just by soil-test biological activity.
And to illustrate that these conditions here
at the left hand side of the graphic would be
this high yield response condition
whereas those in the middle might be those
that have a more moderate level
of yield response to nitrogen fertilizer.
And certainly those that didn't respond much to,
would follow that scenario
where I explained where we have very little yield response
to nitrogen fertilizer.
So these were really encouraging results
and pretty much astounded me my myself
at the beginning.
Looking at this and trying to kind of average
over a few different levels of the yield response.
These are the nitrogen factors
for economically optimum production.
I'm sure most of you in agronomy
in Nebraska know that the pounds of nitrogen per bushel
of grain is pretty much sat around anywhere
from one to 1.2, something like that.
I'm not sure exactly what you use these days
but the theoretical factor should be closer to 1.4.
But the reality is that there's always some nitrogen
in soil so may be you use 1.0 or 1.2
but this relationship suggested
that actually we could modify the nitrogen factor based
on the soil test biological activity.
We could now start differentiating between a soil
with low biological activity and low nitrogen availability
and one with high biological activity
and high nitrogen availability.
So that range of conditions could be set
but that range of conditions of 0.9 to 1.5
would be an over estimate for a lot of fields,
at least in this study.
And they would be fitting for (indistinct) fields
that were on the low end of the biological activity.
Well, it was encouraging result
but as anybody that knows when a study is conducted
we need to repeat it.
Well, I was definitely willing to repeat it
because I couldn't really believe
for sure that the results were true.
So I definitely needed to repeat it again.
So I went in more sites,
had 111 field trials in 39 counties
during two different years,
had an excellent collaboration
with many different farmers from around the region.
And these people are just, you know
gems as far as research are concerned.
And it was an interesting step for me
because it was exactly what Chuck Francis told me to do
back in 1989 when I was in Nebraska.
To go out to farmers and actually let's do
the research on their fields.
And so I learned a lot from that process.
Well, the results,
I'm just gonna show you the results and not the process.
In this case, we basically got about
the same kind of result.
The same association occurred.
It didn't matter whether we were
on research stations or private farms.
We saw that the nitrogen factor
for economically optimum production,
the factor for fertilization could be reduced
if we had greater biological activity.
This was an important result
because I think this is how we can actually
start modifying our fertilizer inputs
and controlling the loss of nitrogen to the environment.
Well, I wanted to bring you now
to just a review of these corn nitrogen trials.
We separated the data into, in this case here
conventional tillage or no tillage.
We had obviously lot more producers that I'm interested in
of addressing the conservation approach
and so maybe it was a bias on my part
but of course I was interested in
finding information to support this type
of agricultural approach.
But we did have some conventional tillage fields
and so then we looked at the actual soil responses.
Well, biological activity was statistically greater
with no tillage than in conventional tillage.
These are all farmed zero to 10 centimeters.
We did measure at 10 to 20 and 20 to 30 centimeter depth
but essentially in our region
only the zero to 10 centimeters matters
in these yield responses to nitrogen fertilizer.
So these are only of the zero to 10 centimeters.
We also looked at nitrogen mineralization
and statistically greater nitrogen mineralization
with no tillage than conventional tillage.
Corn grain yield was actually statistically
different as well
and this, I don't think this is necessarily
the reality of conservation tillage in our region
but it does show that we have a great opportunity
to elevate a yield to overcome moisture deficits
and to use nitrogen efficiently.
So in the end, the economic return over the STD
which is called, this is short for Standard Recommendation
of 1.2 pounds of nitrogen per bushel of grain.
If we use that standard recommendation,
how do we improve this
with a relationship using soil-test biological activity?
We could actually return $19 and 11 cents.
If we use the biological activity approach compared
to the standard condition.
And that was statistically greater than zero.
But it was not statistically different
than if we just use the conventional tillage
in that, 8.89 is not different than 19.11
but 19.11 is significantly positive.
So these were encouraging results.
These are in results that I share
with farmers in our region.
They're really interested in them.
We also looked at animal manure amendment
whether there was no organic amendment
or with organic amendment
and we had more observations without organic amendment.
Soil-test biological activity was greater
with organic amendment.
This is typically poultry litter.
It is can also be beef pack manure, dairy pack
and nitrogen mineralization also greater than
with no organic amendment.
Corn grain yield in this case was no different
whether it had organic amendment or organic amendment.
And the return over the standard nitrogen recommendation
was greater with organic amendment
than without organic amendment.
And quite significantly in that $36 and 34 cents
could be returned more so
because we were reducing the amount of nitrogen fertilizer
over the standard recommendation using this
whenever there was both no organic amendment
or organic amendment.
Shifting to cover cropping.
We had trials that had no cover crop
a single species cover crop
and a lot of them that were using multi-species cover crop.
And then again, this is the biased approach
that I use to get on farmer's fields that are adopting some
of these practices and understanding what's going on there.
But we of course had some comparisons that we could make.
And here we see that multi-species cover crop leading
to greater surface residue retention
greater soil biological activity
and greater net nitrogen mineralization.
The corn grain yield tended to be greater
with any type of a cover crop than without cover crop.
And the results for the economic return
were significant with the multi-species cover crops.
So this is getting to the point where perhaps
we could be using these multi-species cover crop
to cover the cost of reducing our nitrogen fertilizer
or reducing our nitrogen fertilizer to cover the cost
of the multi-species cover crop.
And this could become a win-win situation
for growers, knowing that they just need that information
to be able to make those adjustments in their practices.
So this system that I'm trying to promote here is
that we need to know something about the soil.
Why do we make nitrogen fertilizer recommendations
if we don't know anything about the soil?
You need to knew more about soil.
This is my simple point that I try to make.
So in this case here we have three different...
Let me just go back.
We have three different costs-to-value thresholds.
We have this low threshold where the fertilizer
would be low price and the grain yield would be a high price
or the grain value would be a high price.
In this case this would be medium
where we have 10 pounds of grains per pound of nitrogen,
intermediate fertilizer costs
and then an intermediate corn grain value.
And then in this case
where the fertilizer cost is very high
and the corn grain price might be quite low.
So we can use these different economic thresholds
and we can start using this
into a soil testing category system
where in under very low soil test biological activity.
We actually see that that's the current recommendation
of one to 1.2 pounds of nitrogen per bushel of grain
is quite adequate.
But if you're a farmer that actually has higher
soil-test biological activity
there may be opportunity for you
to start reducing quite significantly
the amount of nitrogen fertilizer that's applied.
That means that the cycling
of the nitrogen in the soil is going to contribute.
That is not a never-ending process
but that's the reason for saying some periodic testing
and to keep after the conservation approach
to build soil fertility and this could lead to
a more efficient nitrogen fertilizer utilization,
getting more of that nitrogen
into the plant and less of it to the environment.
So the standard approach is to use,
say one pound of nitrogen per bushel of grain
irrespective of what the soil condition is.
But the soil health approach
that I'm trying to explain here would be
that we actually modify the nitrogen factor depending
upon what the soil test biological activity is
which predicts nitrogen mineralization in the soil.
I'm not creating magic here.
I'm just making an association
between soil test biological activity
and nitrogen mineralization in the soil.
So there may be situations where actually we're
under fertilizing with the standard approach.
We should maybe be applying a greater nitrogen
when there's a very low soil-test biological activity
but there are probably conditions where we're over-applying
and that we could be saving fertilizer
and increasing economic return
and decreasing environmental impact
by knowing what the soil-test biological activity is.
If we can measure nitrogen mineralization very effectively
it would be a better tool
but this is a test that is relatively easy to measure
and simple and rapid.
So just to explain, I'm almost done.
I just wanted to explain a little bit
that we've not limited this to corn production,
we have conducted it in wheat
but also I wanted to share a few results in tall fescue.
We stockpile tall fescue in the Southeastern region
where there's an issue with the endophyte
and we can have negative impacts of the tall fescue
on animal gain, on animal performance
because of the fungal endophyte that's in the tall fescue.
And we can avoid this by stockpiling.
So the grass is allowed to grow from about September 1st
until mid December, mid January
and then cattle are grazing this somewhat desiccated forage.
Tall fescue withstands the mild winters
that we have, relatively mild winters
and it actually holds up in nutrient value.
So this is a good strategy
but that stockpiling,
that freezing and thawing that occurs
on the fall stockpile reduces ergot alkaloids concentration
of this, of this fungus.
And so the cattle can consume this forage
without having negative the ergovaline effect.
So this research was conducted over 92 field trials
in three different years.
And I just wanted to give you one snippet of the results.
This is the forage yield response to initial dose
of nitrogen fertilizer,
a similar response where we have pounds of forage
per pound of nitrogen
that I showed you for corn.
And it shows that this value declines
with increasing soil-test biological activity.
In this case, in a non-linear manner.
This follows very closely to what our recommendations are
for fertilization of tall fescue for optimal growth.
In that we are recommending approximately 50 to 60 pounds
of nitrogen per ton of forage for all stock stockpile
across the board.
But unfortunately most of our progressive grazers
in the region are actually having biological activity
that are much greater in this 300 to 400 part
per million range.
And so really our recommendations are not accurate
for a lot of our producers in the region.
It is accurate for those that are the most vulnerable.
Those that respond very much to nitrogen fertilizer.
But it's not accurate for most of the producers
that we have in the region.
We've also looked at this soil test biological activity
geo spatially in pastures across a diversity
of farms in the region.
In three different regions
in the coastal plain, the flat area near the coast,
the Piedmont, the hilly region
and then the Appalachian Blue Ridge region in the mountains.
And what did this research really informed us
was that both organic estimates of soil health
and inorganic estimates,
I think soil test P and K are really still important
but we need to have that combined with organic tests.
So the soil-test biological activity combined
with inorganic tasks are really what we need
for a comprehensive strategy.
And this will tell us a lot more about
this sort of nutrient distribution in perennial pastures.
So to kind of finalize
there are some key soil health indicators.
I'd started the presentation
with a long list of many indicators
under the chemical physical and biological categories.
I believe that there's really only a handful, you know
less than the digits on your hand,
but there are a few key soil health indicators.
Organic matter or as we measured
as carbon or nitrogen is really key.
It's something that we really should be measuring
because it's one of the broadest indicators of soil health.
The routine soil testing for soil chemical fertility
is also still very important.
I think harmonizing that across States would be ideal.
Maybe it has to be separated by regions
because there are some reasons why we have certain extract
and for certain regions
but I think harmonizing would be good
but we should we should not throw out
the routine soil testing but we should modify it.
And of course we should have some indicator
of soil physical condition.
And I think water infiltration would be the best.
It has to be determined in the field
but as a proxy soil aggregation would be a good indicator
I believe and that should be done.
But the biological component
I think there are many opportunities to expand this
in the biological component
but one of the key ones is just
the biological activity itself.
It tells us a lot about the fertility
as well as the physical and biochemical reactions
that are going to occur.
So in the end I would probably recommend four,
but in the very end I think we can actually get rid of
the organic matter and the aggregation
because they are influenced so dramatically
by soil test biological activity.
If we know that indicator right there
we could actually delete the information that we would need
from the aggregation and organic matter
because it becomes a little bit more redundant.
So we might be left with only two sets of analyses.
And the routines all testing is a suite of analysis, right?
We need to know a lot about the different chemicals
and the biological might be also a suite
that we might have to develop further
because I'm not sure there should be a strong association
between activity, biomass and diversity
but they can be linked in some ways.
To summarize, soil health is a vital underpinning
of sustainable agriculture.
I think that we know already.
And then there are various forms
of that sustainability.
Conservation tillage, crop diversity, cover cropping
and organic amendments are key management factors
affecting soil health.
We have available evidence in the literature
to indicate that.
We can see it in the fields.
So it's something that we should be aware of.
Soil-test biological activity.
It's a simple, rapid and robust indicator
of soil nitrogen availability.
What I've shared with you today shows
that it's related to soil nitrogen availability
but I believe that it's much broader than that.
It includes a lot of other things as well.
So it's some indicator that should be of use.
And soil health and nutrient management
are strongly linked through assessment
with soil-test biological activity.
So we can actually start using soil health
as a nutrient management strategy as well.
So to really conclude soil-test biological activity
or as I used to call it,
the flush of CO2,
should be considered a valuable soil testing tool
to indicate potential soil nitrogen mineralization
and the need for supplemental nitrogen fertilizer.
I think we have great opportunity to use this
to more effective use.
Now it just needs more testing
around the country, around the world.
And I believe that we can recognize
that organic fertility is important.
And if we don't have it in our soul fertility
cadre of analysis then we're missing out.
But it also indicates available carbon resources
in soil necessary to promote soil carbon sequestration.
And of course, soil carbon sequestration is a good thing
but we're can only reach a level
that is steady state for a region.
We have to be able to show carbon sequestration,
but always, always when we have soil carbon sequestration.
We're always going to have mineralization.
We're gonna be building and taking down.
It's a continual process.
And we should always keep that in mind that it is dynamic.
But it also indicates potential microbial activity
to transform nutrients, foster soil aggregation
and create a biologically diverse soil habitat.
So it has a lot of value to other soil functions.
I was raised in the Bohemian Alps of Nebraska
and I've shifted to the rolling Hills
of the Appalachian Piedmont
and I just think that the functions
of soil are very similar in the different environments
but we have to be aware, of course,
the environmental constraints
but the processes that occur are very similar.
So I appreciate the opportunity to share
with you today at the University of Nebraska seminar
and I would welcome any questions that you might have.
Thanks so much
Woman: Alan, we have a question from Bijash
and his question is how does your STBA compare
with other respiration tests?
-: Right.
As I tried to explain there are other tests
that are out there,
the Cornell CASH, they actually don't use it anymore.
I believe they now use permanganate oxidizable carbon
instead of respiration but the Woods-Ends Solvita,
they use the CO2 burst.
The Haney Soil Health Test uses a CO2 burst test.
Those use a one day test
and the Cornell used to use a four day test.
They may still use it.
I just saw that they replaced it.
So there are other tests out there.
The issue is that if we use different approaches
we're gonna get different numbers.
It's the same as if we used may lick one
versus may lick three.
Now, that might not be such a big difference
but it's the same concept,
that we have to use standard protocol
otherwise we're gonna get a different number.
So if I get a number of 101
and another test uses a one day test
and I used a three day test,
it's likely that the other test will only get 41.
It's just a simple matter of the calibration
of the tests to get to a common ground.
And that research just needs to be done.
To tell you the truth,
I think that it's important to use a robust method
not something that is gonna be less than robust.
And I just have to be proven wrong
that the other tests are equally as good.
That's all.
John: Alan, you have several other questions.
What are the primary carbon substrates
fueling the flush?
Is it similar across different soils?
-: Ah, the substrates will be of course
from a surface residues and routes.
Those are the primary sources.
Of course, animal manures can be in there.
If that's a system that's well developed.
They're organic sources of carbon and nitrogen
so the organic matter that feeds,
any system that builds organic matter.
And I say builds, we can see activity
from this soil-test biological activity
that is immediately available from the Risal deposition
of growing plants.
So the carbon substrates that are exuded
by living plant roots are easily decomposed
and they can be captured in this test as well.
John: Alan, the next question is,
do you have any producers that are using your approach
for nitrogen application rate?
-: Well, thanks.
The issue is that I'm funded by the USDA.
I'm a research operation.
I don't have a commercial lab.
I won't have a commercial lab.
You know, just to be honest about it,
my colleague Rick Haney and I
were in graduate school together,
he decided to push one day evaluation.
I simply used three days.
All of the data that I have could be transformed
into a one day test.
I believe though the way I would measure the CO2
from the incubation using an alkali trap
with acid titration is not necessarily
the most appropriate for a one day test.
So the test would have...
If one uses a one day test
you have to use an infrared gas analyzer
or gas chromatograph
something that's really much more sensitive.
I believe that the alkali trap is sensitive for three days.
I'm confident of that.
We show that in repeated analysis we can get down
to about four to 8% coefficient of variation.
This is very reasonable for a soil test analysis.
So I'm confident that the alkali trap works.
The problem though is that one has to have
the standardized approach.
I mean if commercial labs want to use one day test only
then we have to use this information.
We have to calibrate it with a one day approach.
Well, the data that I have is only three days.
Now, mathematically, I could actually make a number
that fits one day.
It is possible for me to do that
because all of the data that I collected
has been from three 10 and 24 days.
The fit or the mathematical fit is just extra,
almost always 99% or greater.
So I can easily predict one day so that could be done.
It's gonna require a collaboration.
That's what it's gonna require.
John: Well, Alan you've had several shout outs
for the great presentation
and they've appreciated
the shout out to the Bohemian Alps
but there's one last question here
and it's from Orange River
and she asks how well does the STBA correlate
to measures this soil microbial biomass
say as measured by fumigation or extraction procedures?
-: Okay, yeah that's a good question.
It relates pretty well.
So the soil-test biological activity related
to microbial biomass from fumigation incubation
that's the only technique I've used
in the past.
It's pretty strong.
It depends on the data set
but if I were to plot all of the data that I have,
I would say that the R square is somewhere around 70%.
It's pretty good but, you know
the fumigation step is a unique thing.
It's is significantly different
than just simply drying the soil
and so it does give some variation there.
And as far as fumigation extraction,
I just, you know I have some thoughts
and I'll probably should leave them to myself
but it's the more common approach
for microbial biomass but I'm not sure it's the best.
I'm just saying that I don't think we have great methods
for it but I don't have enough data in my mind
to know what the relationship would be
with CFE, fumigation extraction.
Sorry about that.
John: Well, we're about out of time
but there's one more question
if you guys can hold on
and it's from Tom Hogan Meyer
and he says that one of the big issues
with getting farmers to adopt some of the practices
like cover crops, no till is a yield lag,
a three to five-year lag
between you increased costs and decreased yield or profit.
Do you have suggestions to relieve this?
-: Yeah, that's a good question.
You know, just conceptually having a tilled field
and then switching it to no tillage,
it's kinda like stopping smoking, isn't it?
It's difficult, you have that urge
and not the farmer necessarily
but the soil maybe.
The soil is looking for something
because it's used to being tilled
and I'm not sure that we should put it into those terms
but there are some reasons why.
We're basically starving the soil
when we switched shift to no tillage.
We are putting residues at the surface.
We're not getting the routine mineralization
that's there so it's possible
that there's a greater need for nitrogen.
It depends on the other nutrients,
but it could be for other nutrients as well
but primarily nitrogen.
There could be a greater need for nitrogen early
in that transition period.
And it may be not just the total amount of nitrogen
but the timing of that nitrogen
and the placement of that nitrogen.
Making it very effective for the corn crop.
But the issue is somewhat related
to the corn itself.
It likes to have a good pores for the roots to explore.
The other crops don't seem
to have that dramatic shift.
So soybean, I think, is pretty resilient.
It probably doesn't have such a yield drag
with conversion to no tillage.
I think it does take time.
I think that one of the ways,
the quickest ways to overcome that of course,
is to come out of some situation
that is not a tilled soil,
is maybe there's, there's a forage crop
that could be as a rotational crop.
This is one of the best ways to build up
a little bit of organic matter
and to create a situation of the soil surface
that it's much more receptive
and that yield lag will disappear.
Thanks, for the question though.
John: Alan, we're gonna wrap up.
That's gonna end the seminar today
so thank you again, Alan.
It was a great seminar,
particularly enjoyed it
and making the University of Nebraska proud as well.
So thanks.
-: Thank you all.