Hello, my name's Trent Roberts, and I'm an associate professor
and extension soil fertility specialist with the University
of Arkansas System Division of Agriculture.
And today for my corn online corn field day talk, I'm
going to be talking about three scenarios that we've encountered this past season
and specifically how to deal with them.
So the first one has to do with historic flooding
that we've seen in southeast Arkansas this past June.
You know, this is a very atypical situation,
but it does relate back to things that we encounter year after year,
and that's untimely high rainfall amounts that will leave many of our fields
saturated and waterlogged for extended periods of time.
So one of the questions that we've got a lot recently:
"Is there any way that we can predict
or determine the amount of nutrients that we've potentially lost
and then be able to go back and add those nutrients later to ensure
that our yields are not limiting?"
So the first thing that I really want to emphasize to
everyone is don't do anything until the floodwaters have receded
and they are all gone.
Your biggest concern when you have saturated soils
or flooded soils in your cornfields
is actually getting that water removed from the field
and allowing the corn to catch its breath and start new root growth
before we start to concern ourselves with potential nutrient additions
or makeup applications later in the season.
Along those lines,
I'm going to segue into some of the other work that we've done
involving in-season tissue testing
and then some other potash tools that we've talked about in other crops
that were migrating into corn.
So the next thing that I want to discuss is late-season nitrogen applications.
In recent years, we've got a lot more questions
revolving around pre-tassel applications.
And traditionally, we think of those pre-tassel applications
going out as urea via airplane.
But more and more, we're getting producers interested
in the use of Y drops to surface apply UAN 32% as a surrogate
for urea in these late season or pre-tassel/tassel timing of applications.
So one thing is we use UAN a lot in corn production,
but typically we're going to knife that UAN below the soil surface
at the sidedress growth stage somewhere around V6 to V8.
And so by placing that UAN below the soil surface,
we protect it from potential loss mechanisms such as ammonia volatilization.
Now, when we think about using UAN at a pre-tassel application timing.
Those are going to be surface applied.
And so similar to the urea
that we would put out as a pre tassel granular application,
there's a potential that we could get nitrogen loss to ammonia volatilization.
And so part of what we're doing is
we're going to go in and start measuring or quantifying ammonia volatilization
losses of pre-tassel nitrogen not only from granular urea, but also
the surface applied UAN applications using a Y drop type of system.
We've used this quite a bit in rice and wheat in other application timings.
And so our goal here is actually to look at different rates
and sources of urea surface applied at different timings throughout the corn
growing season to determine the loss potential of surface applied urea and urea
ammonium nitrate solutions.
And these chambers are just a semi static ammonia volatilization chamber
that allow us to quantify the nitrogen loss potential
from those surface applied nitrogen sources.
So in the coming years, expect to get information on
the ammonia volatilization loss potential from these different sources
and the potential as to whether or not products
such as NBPT would be useful in mitigating or eliminating that nitrogen loss
potential from ammonia volatilization.
The next thing that I want to talk about is potash applications to corn,
and so similar to the crops such as rice and soybean, you've noticed
that over the past few years, we've been doing a lot more work
on implementing economic potash rate calculators for those other crops.
And what we're hoping to do is develop that and implement it in corn.
And so the idea behind this
is that we would implement things such as soil test K level.
We would implement potash fertilizer prices, expected corn value and use
all of those tools together to give us an economic potash application rate,
and the nice thing about this is it allows us to go out and apply a pre plant
potash fertilizer rate that we know will maximize our economic profitability.
And I think that's very important as we go forward.
The other thing is we're continually looking at our application
rates for phosphorus and potassium to corn,
and we're hoping that we can revise and potentially lower
some of those application rates in the coming years.
The last thing that I want to talk about is some of the work behind me
involving the use of aerial imagery, specifically from drones, to determine
if and when we need additional nitrogen applications late-season
and by late season, I'm referring to V10 and later.
And so what we're going to do is actually walk out in this cornfield
and I'm going to show you a couple of comparisons of plots
where from the visual eye,
we may not see any differences in the greenness of the plants,
but the sensitivity of the drone technology will be using
can actually pick up those color differences
and predict when and where nitrogen applications will be beneficial.
One key component of this particular study
is actually telling us how much nitrogen we need.
So now that we have the leaf
tissue analysis, which is a destructive sampling technique
and we have the drone image analysis, which is a nondestructive
analysis technique, we can predict when and where nitrogen is needed.
The next step is being able to predict how much nitrogen is needed.
And so what we're doing with this particular study
is matching up specific deficiency levels
with different application rates of nitrogen to help determine,
you know, if you're at 2.5% nitrogen, what's the required amount of nitrogen
added to get you back to that 3% ideal target and your maximum yield potential?
So what I'd like to do now is actually take you out
and show you some of the plots and some of the visual differences
that we can and can't see and potentially
what the drone can and can't see when we're taking an aerial view.
So go ahead and follow me into the field here.
So actually, here's a good example of one of our plots
that has received adequate nitrogen throughout the growing season.
And one thing that I want to point out here is that we have good leaf color
from the bottom of the plant all the way up to the top leaves.
So one thing that we really have to remember
is that nitrogen is a mobile nutrient in the plant.
And so what that means is that if it starts to encounter
a deficiency, it's going to take nitrogen out of these lower leaves
and translocate it up to the main growing point
or the leaves that are primarily doing the photosynthesis.
Once we have an ear leaf like we do on this particular plant,
what's going to happen is it's going to put a lot
of the photosynthesis and the metabolism into this particular leaf
because it's what's feeding our ear
that's ultimately going to develop and give us our grain yield.
So once again, nitrogen is mobile in the plant.
And so what it's going to do is pull nitrogen from these lower leaves
to the upper leaves to ensure that these solar panels, right,
where we're making our sugars
are photosynthesizing at their highest capacity.
So one potential problem that that poses for aerial imagery
or that these upper leaves always tend to be the greenest ones on the planet.
And so it's very hard for the naked eye
to identify differences in the greenness of the color as we change
different nitrogen sufficiency or tissue concentration levels.
So what I'd like to do now is actually move down to some of our plots
that have a lower nitrogen application rate,
and we can start to see some of the visual differences
that we can pick up with our naked eye, but are very obvious
to the drones that we take with the aerial imagery.
So what we have here is a side by side comparison of a plot
where we have no nitrogen additions.
So throughout the entire growing season, this plot has actually received
no nitrogen fertilizer additions
next to a plot where we've added roughly
75 to 90 pounds of nitrogen during the growing season.
And so if you look down at the bottom, the first thing you should be able to
notice is the yellowing of these lower leaves,
which is synonymous with nitrogen deficiency symptoms.
And so this is a good example of where
this plant is starting to run out of nitrogen,
and it's basically translocated that nitrogen from the lower leaves
to these upper leaves.
But it's still not enough.
So if you notice, if we compare, you know,
the greenness of this particular leaf to one that has a higher nitrogen rate,
you know, there's a pretty significant difference.
In the greenness of those two leaves,
and it may not be, you know, really easy to pick out
with the naked eye, but these differences in the greenness
are quite easy for our drone imagery to pick up.
And so, you know,
that's part of what we're moving towards is figuring out ways
to increase the sensitivity of our aerial image analysis
so that we can detect these small differences
in nitrogen concentration within the corn leaf tissue
and then be able to predict when and where that nitrogen application is needed.
Like I mentioned before,
the key component of this is OK, we know what the deficiency is now.
How much nitrogen do we need to get back to maximal yield?
As with everything we do,
you know we're going to put economics to it at some point where we determine
with, you know, aerial application or ground application,
you know, when and where those late season applications,
such as a pre-tassel or tassel application,
will be profitable for our Arkansas corn producers.
As always, if you have questions regarding nutrient management
or soil fertility, feel free to reach out to us
and we'll do our best to get you the answers you need. Thanks.