We're going to venture into the world soil fertility, just
a little bit tonight.
The title is Soil Fertility and Health.
But I think under the confines of our time tonight,
we're really only going to get a chance to talk about some
of the more important aspects of soil fertility
as it relates to small grains, both in grain and forage.
So I'd like to start off with a little overview of how
recommendations are developed and tested.
And then, go over what the recommendations
are that Utah State has promulgated
over the years for both irrigated and dry land grain
and forage.
And talk a little bit about rotational adjustments,
particularly following alfalfa, as most of us
are generally following alfalfa with either corn or small grain
rotational crops.
And cover some of the recent work that we've been doing--
Dr. Yost, and Dr. Creech, and others
in combination over the last eight years or so.
So let's delve into how recommendations are developed.
This is what we call a rate response curve.
Typically, what we'll do in relating what the soil test
levels are for various nutrients,
compared to what we might expect to get in terms of response
in yield, this is the kind of thing
that we begin to look at and develop.
And try to interpret, in terms of where
the levels of sufficiency or the critical levels
are in soils, for a given nutrient.
And so what we end up with is as we
get increasing levels of a nutrient in our soil solution,
the response of the crop goes up over time.
Until we get to a threshold or a limit
where we have plenty of soluble and assimilable
nutrient in the system that it supports
maximum or optimal yields.
If you take a look at where universities,
public laboratories, like the US Analytical
Lab and our extension work, we'll
choose recommendation levels that'll
be at the point on these curves where you have nearly
maximum yield without going beyond,
in terms of any economically unjustifiable additional amount
of nutrient.
And we call that the economic optimal levels there.
And we'll choose a critical level based on that.
Commercial laboratories use the same kinds of curves.
The same curves that we use.
It comes from the same research that these have been generated.
But the critical levels from commercial labs
tend to be a little bit further out
on the shoulders of these rate response curves.
And this is a perfectly reasonable business model
to adopt.
If you're a commercial laboratory,
your interest is obtaining and maintaining clientele,
and getting return clientele, and so forth.
Working with your lab to take care of your crop needs.
And so they don't want to be down further on the curve
where you may or may not get the maximum yield and the highest
possible returns.
But it may cost you a little bit more money in terms
of your nutrient inputs.
And that's why a university will be at a lower level.
Now, it would be nice if all of the curves
were as clean and simple as the one you see here.
But what we end up with most of the time,
given a different year that we're
growing the crop and we're testing its performance--
you may have differences in weather.
You may have differences in pest pressures, differences
in soils, and so forth, and conditions.
And so you get a family of curves
like I've depicted here in this particular graph.
Where we see the amount of a nutrient
applied versus the yield.
And it'll be a little bit different from study to study.
And you end up with critical levels, as you see drawn here,
the vertical lines--
critical levels for each one of these curves
that's a little bit different.
And so when you see a recommendation that
comes from a university or a commercial laboratory,
it doesn't matter what, you're going to see a range listed
for the recommendation.
And we'll see that here in a little bit when
we take a look at specific recommendations
from Utah State University.
So you'll get a range of what is the economically optimum
nutrient application depicted.
And the same thing you get with commercial recs,
but they'll be just a little bit higher typically.
In fact, they'll be generally anywhere from maybe
15% to 25% higher because they go out a little bit further
on the shoulders of these rate response curves.
Again, there's nothing right or wrong about that.
But it's a paradigm--
the perspective of where a public laboratory,
like ourselves, being down here at the--
maybe not the maximum, but the reasonable optimum
in terms of economics versus making sure we
don't leave any yield on the table
that a commercial lab might target.
Again, these are stylized curves.
What we really see is data like this.
And I wanted to show this to you because you
can see how messy life science is in many situations.
This is alfalfa yield over here, in terms of the percentage
of total maximum yield.
And the soil test level for phosphorus.
I put this on here.
It's not small grains, but it's illustrative of a point.
You get a lot of point estimates, point values,
when you're out doing these tests of the performance
of the crop versus the level of nutrient in the soil.
And one of the things we have to take into account
is what our starting points are.
We get this mass of data.
And we can draw one of those response curves
in there like we had before.
And we can try to pick off what the critical levels are going
to be down here, in terms of the nutrient content in the soil
solution.
But what we find is as the level of initial nutrient in the soil
solution increases, the likelihood of response
also increases.
As we get lower levels, I'm sorry,
of a nutrient in the solution, the likelihood of response
increases.
So if we take a look at this graph,
and separate it out into different groupings.
Where we started out with a higher level of nutrient
in the soil down to a lower level of nutrient
in the soil, the dotted line, here,
shows you that for a small increment of increase
in the phosphorus applied, the likelihood of a response
is quite high at low soil test levels.
Whereas, if we have a higher residual in the system,
in the soil system, the likelihood of response
is quite a bit less and maybe even negligible in many cases.
And so that's why we're really interested in targeting
these critical levels or threshold
levels of sufficiency.
So we don't encourage the unjustified expense
of that additional bit of nutrient
applied to receive or to obtain a response in the crop.
So with that as background on how these are developed, maybe
you have a little better sense of what
goes into developing a recommendation.
Let's take a look at where we find these.
A lot of times it seems like it's pretty much a black box.
You send in a sample, and you get it analyzed,
and the laboratory comes back with a recommendation.
It would be nice if--
and you can just accept that, and that's fine.
But a lot of people have mentioned
that they would like to be able to go back and take
a look at these recommendations, and get
more familiar with them, and know where to look and find
them.
So that they can compare when they get a laboratory result
from one place or another.
What would the USU recommendation
be, say, if I got my soil test done
at another commercial laboratory?
You can go to this particular fact sheet.
It's called Understanding Your Soil Test Report.
It's in our digital Commons collections on campus.
And you can go to digital Commons USU
and look for a document A25.
Hopefully, you're going to be able to see this.
I'm going to go to that document right now.
Reagan, you can verify whether or not
you're seeing that document on the screen.
Yeah, we are seeing it.
Awesome.
So this is what it looks like.
It's called Understanding Your Soil Test Report.
And we've tried to put the information down as
to where these recommendations come from.
So that it doesn't seem so much like a black box to you.
You go down through here.
And it talks about soil tests, and soil
test reports, and what they look like,
and what's included in them.
And then down in the middle of the report,
you'll see this box that says, click here
for a table of soil test interpretations
and recommendations.
If you click on those, it'll take you to this jump screen,
here, where you can look at the different crops
or other settings for nutrient management.
And you can choose one of these.
Each of these is an active link.
And you can go to the recommendation tables
that we use in the laboratory when
we do a soil test to compare to, in order to generate
a recommendation for you.
So let's go ahead and let's go down here to wheat
to start with.
We'll choose wheat.
And what you'll see is this table, here,
where you have on the left hand side
over here the different soil tests, phosphorus, potassium,
nitrogen, zinc, and so forth.
And then you have--
from all of that research that's been done on rates and response
to levels of nutrient in the soil,
you then see it broken down into various categories
of nutrient content or the soil test
level of that nutrient in your sample.
And so for most of ours, the adequate or normal
is the sufficiency level.
That's where we would think that you have plenty,
as far as the USU recommendation goes.
That additional application of nutrient is not necessary.
It's not economically justifiable.
Below that, however, we get various levels of need.
Everything from very, very low and severe
need to kind of a marginal or nearly adequate condition.
And so you can compare them.
If you get a soil test value let's
say, for phosphorus at eight parts per million,
you know that you're in that low category.
So what does that mean in terms of recommendation?
You slide over to the other side of the table, here.
And your Low B level would say that you
would need, in that case, 40 to 60 pounds of P2O5 per acre
of nutrient, in order to supply adequate amounts
for optimal performance of the crop in that particular soil.
So you can see where you are.
In fact, it's kind of nice to notice
that in all these cases, again, you see
a range in the recommendation.
When you're between such and such levels,
then you apply such and such amounts--
a range of possible amounts.
Well, if you're, in the interest of economics and so forth,
wondering if you can use the upper or the lower
end of that particular recommendation,
you can compare to where you're at in terms of the soil test
level.
If I'm at the low end of low, then
over in the recommendation, I want
to be at the high end of application.
If I'm at the high end of soil test within that category,
then I can probably get away with being
at the lower end of that range in terms of the recommendation
for the nutrient.
So I hope these tables can, maybe, provide a little bit
more context to the nutrient needs
that you see in your soils, when you get your soil test
results back on these.
We'll take a look here at some differences between these
in the different crops.
But if we go back to the crop table,
you can see that we've got several of our grain
crops, our small grains, the barley is in there separately,
as a separate table.
Oats is in there separately as a table-- and wheat.
And then the dryland small grains as a group
are also in there.
Their recommendations are going to be
very different comparatively just because we don't have
the water to support the use of large amounts of nutrient
in the system.
Forage grains will fall into the grass hay category.
And we'll take a look at some nuances
to some of the work that's been recently done on that.
But let me go back now to the PowerPoint.
This is a summary.
We just pulled some of the information
out of those different tables so that you
can see the comparison.
So irrigated wheat, in terms of yield goals and things
like that, you can be upwards of 140 bushels per acre.
And so you could be as high as maybe 170 pounds,
in terms of base and recommendation for the crop.
If you don't have that high of yield goal--
a little bit less, but in between.
If you're yield goal somewhere in between,
then you can adjust by two pounds of nitrogen per bushel
per acre.
And you can see that the barley has a separate table.
And it's a little bit less in terms of overall need.
That's why there's some nuances to each one of these.
Dryland grain, you'll notice, in terms of nitrogen application,
you're only about a third to a half
of the nutrient requirement in those settings,
just because of the differences with respect
to water and water availability in the process.
And then we have some other adjustments
that typically need to be made to our recommendations.
Particularly, if we're in some kind of a rotational situation
where we're following a legume crop like alfalfa.
In the past, we've noted that there's
about 100 units of nitrogen in terms
of credit to a previous alfalfa stand,
for all crops that might be grown in rotation following
that alfalfa.
But let's go to some interesting newer data that's
been generated over the last several years in response
to revisiting these recommendations to make sure
that we're in alignment with these credits
that we've used for so long.
Here, you see a table from some recent work--
Dr. Yost, Dr. Creech, myself, and others
with our students-- in looking at rotational adjustments
to the grain production following alfalfa.
And this is 18 different sites around the state
in 2018 and 19.
And you can see over on the far right hand
side that the requirement for nitrogen, following alfalfa.
And here are the stand ages of the alfalfa that came out
previous to the grain crop.
Only about half of the sites were actually
responsive to added nitrogen.
In fact, if the soil test level for nitrate
was less than 17 parts per million, we got a response.
Where it was not, we generally did not
get any response at all.
And so not only do we have an N credit to the previous alfalfa
crop, but we also need to take a look
at what the actual residual nitrogen is left over
in the system.
And if we are greater than 17 parts per million,
we typically do not need to add additional nitrogen following
alfalfa.
And that's for grain.
In many cases, grain was responsive.
But we need to pay attention to what's actually in the soil.
In terms of--
Dr. Cardon, sorry to interrupt.
We're about out of time.
So you can find an avenue to wrap it up.
This is my last table, here, just
to follow up on the foragers.
Forage is a very different animal
in terms of its response to nitrogen following alfalfa.
In 12 sites, in 18 and 19, only one was responsive.
There was enough nitrogen following
alfalfa to supply maximum forage production on small grains,
regardless of where we found it in the state.
The only responsive site was on a very old, greater than 10
year stand.
And so take home there is apply nitrogen
only if your stand is greater than 10 years old
on forage grains.
And that's consistent with other data.
I want go into the Davis, but it's
consistent with the other data around the country
in various similar tests.
So with that, I'll be done tonight.