1 - 2021 South Central Ag Lab Field Day - Essentials of Irrigation Management
2021 SCAL Field Day - Essentials of Irrigation Management, Steve Melvin, Water and Cropping Systems Extension Educator
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- [00:00:07.910]This is Steve Melvin, Extension Educator
at the University of Nebraska Extension.
- [00:00:11.390]And today we're here at the South Central
Ag Lab talking about some irrigation
- [00:00:15.350]essentials or some fundamentals
related to irrigation.
- [00:00:19.010]One of the old quotes that's been around
for a long time for Vince Lombardi is
- [00:00:22.580]that, gentlemen,
- [00:00:24.140]this is a football and we're able to
basically what he was saying at the first
- [00:00:27.470]day of fall camp was that,
fundamentals was what won games.
- [00:00:31.730]And if you take a look at another,
famous coach, John wooden,
- [00:00:35.450]he even taught his players how
to put their shoes and socks on.
- [00:00:38.450]And so we're not going to
go to that extreme today,
- [00:00:40.670]talking about how to
put irrigation boots on,
- [00:00:43.010]but it's important to keep in
mind that fundamentals first,
- [00:00:45.800]we need to kind of review those and
go back to them to make sure we're not
- [00:00:49.490]forgetting some of those.
- [00:00:50.480]So we can be a champion at
irrigation management as well.
- [00:00:54.650]So what we want to talk about first
is just about why plants need water.
- [00:00:58.310]You know, transportation is
kind of the first one,
- [00:01:00.830]and basically it keeps plants
cool. And of course here today,
- [00:01:03.860]it's really hot and we're
thinking about ways to stay cool.
- [00:01:06.740]And that's the way our crops stay cool.
They, they just like water off. It.
- [00:01:11.240]It's just an evaporative
cooling process. The,
- [00:01:14.270]also then allows the
leaf stemmata to be open.
- [00:01:17.060]So the CO2 can make it into the plant,
- [00:01:18.950]which is an essential
part of the photosynthesis
process keeps the soft Wells,
- [00:01:24.140]a sales Turgeon. In other words, you
can kind of think about it, you know,
- [00:01:27.200]when a plant gets drowsy, it wilts
down and, when it's full of water,
- [00:01:31.170]it's up, right? Like it's supposed to be,
- [00:01:33.110]you think about kind of like the bouncy
house when you first put it together in
- [00:01:35.780]the backyard before you turn the
fan on, it's all drooped down,
- [00:01:39.140]turn the fan on and, and put
air into it and blow it up.
- [00:01:42.440]It gets up to the shape
it's supposed to be.
- [00:01:44.000]That's kind of what water provides
for the, plants, you know,
- [00:01:47.300]flat plants need to be able
to move in the wind. And,
- [00:01:49.640]and so they've gotta be fairly
flexible in order to stay up,
- [00:01:52.990]like they're supposed to, they
use water to keep them pumped up.
- [00:01:57.800]There's a, water, provides
nutrients or moves it from the nutrients,
- [00:02:02.330]of this in the soil,
into the plant. It,
- [00:02:06.740]water transports the nutrients where they
need to be in the plant and then water
- [00:02:10.490]transports the carbohydrates from the
leaves where the photosynthesis is
- [00:02:13.850]primarily taking place into the plant
parts that need it, the roots, the,
- [00:02:18.080]seed or the grain or whatever we're
producing with our, with our crop.
- [00:02:23.060]But also,
- [00:02:24.230]H2O is broken down into its components
and it's used as a crop nutrient
- [00:02:29.180]and too much,
- [00:02:30.560]or not enough either way is damaging to
the overall yield or it suppresses the
- [00:02:34.940]overall yield. So water is, is just an
essential thing that we need to have.
- [00:02:39.470]this chart was done right here at
south central and, and it shows,
- [00:02:43.220]when we don't have any water just
to dry land, we get a lower yield.
- [00:02:46.680]We put on a little bit more,
- [00:02:47.840]a little bit more until we get up
to the amount that's fully watered,
- [00:02:51.050]then we'll have our maximum yield,
- [00:02:53.120]but it also shows what happens
if we put on too much water,
- [00:02:55.880]we can also lose yield when
we, get to the point of,
- [00:02:59.920]of over-watering. So we need to make
sure we're putting on the right amount.
- [00:03:03.490]Fortunately, for, for us with irrigation,
- [00:03:05.830]this is a fairly broad flat
top to our curve. So, you know,
- [00:03:09.520]if we're an inch and a half, or
two above or below the optimum point,
- [00:03:13.450]we're probably still gonna have top yields
just if we're inch and a half or two
- [00:03:17.200]inches above what the
maximum would be.
- [00:03:20.200]we're going to have spent more
money on, on pumping water.
- [00:03:22.780]And we're also going to,
deep percolate that water,
- [00:03:26.320]take it back towards the groundwater,
- [00:03:27.910]which of course it can
take nutrients with it,
- [00:03:29.920]like nitrogen back down
towards the ground water,
- [00:03:32.530]which we don't want in the groundwater
plus that meant we had to spend money on
- [00:03:35.500]nitrogen that we didn't really want to
take a look at wheat and other crop.
- [00:03:40.360]That's about just exactly the same,
- [00:03:42.280]the right amount of water produces a
top yield, but too much, or not enough,
- [00:03:46.150]either side is going to produce less.
- [00:03:49.330]This is a chart that was
put together by FAO,
- [00:03:52.600]kind of a group that does a lot of the,
the, fundamental research work,
- [00:03:56.920]on crops around the world. And
what it is shows is it's a,
- [00:04:00.480]an evapotranspiration
deficit impact on corn yield.
- [00:04:03.580]And they've got these
charts for other crops.
- [00:04:05.590]If you'd like to take a look at those,
but they all come out somewhat similar.
- [00:04:08.980]And the way you read this chart is that
a zero. They're talking about a deficit.
- [00:04:13.240]So this is talking about
crop water use on the top.
- [00:04:16.060]So this would be when the crop had
all of the water that it wanted.
- [00:04:20.110]And over here is on yield.
This would be was zero.
- [00:04:23.440]Then would you'd get the maximum yield
that you could get out of your crop.
- [00:04:26.320]So if we come over here on the
crop water use, it was at 0.5.
- [00:04:30.040]That means the crop had half as much
water as it would like to have used if it
- [00:04:33.700]was fully watered, same way down here.
If we had a 200 bushel grain crop,
- [00:04:38.030]we were at 0.5, we'd be
at 100 bushels. So it's a,
- [00:04:41.320]it's a chart that is kind
of a classic way look at it,
- [00:04:44.260]but it's a little different than
sometimes we think about it.
- [00:04:47.470]So that's why he described
it there a little bit.
- [00:04:49.750]But if you take a look at this, if
we're at 0.2, of a decrease.
- [00:04:53.980]So in other words, that would be
not a very big decrease in water.
- [00:04:57.250]And if we take a look at that, and this
has got the different, vegetative,
- [00:05:00.970]flowering, yield formation
and all of those on here.
- [00:05:05.110]So if we take a look at these lines,
if we're during the vegetative stage,
- [00:05:08.560]when the crop is before tassel time
with corn, we're at about point.
- [00:05:13.570]If we had a 20% decrease, we'd be
at about, 8% loss on yield,
- [00:05:18.250]and that's a fairly long stage.
- [00:05:19.870]And that's from the time the corn comes
up until it gets up to tassel time.
- [00:05:23.710]Versus if we take a look at this
and we come down to the flowering,
- [00:05:26.770]which is a tassel when
we're shedding Paul,
- [00:05:28.600]and it would be about a 30%
yield decrease a penalty for only
- [00:05:33.520]20% loss in water and think about it,
that's the very short time period as well.
- [00:05:37.720]And so, you know, very
little water stress during the,
- [00:05:41.080]the flowering and early Greenfield,
which is what this line combines.
- [00:05:44.740]Those two together, you know, the
20% during that time would be 45%.
- [00:05:49.210]And so that was really the
thing we need to keep in mind,
- [00:05:51.190]a very fundamental principle with
irrigating corn and, and any grain crop.
- [00:05:55.330]As far as that goes, we can stress a
little bit during the vegetative stage,
- [00:05:58.850]not really affect too much, but during
that, flowering and early grain fill,
- [00:06:03.320]we really need to be very,
- [00:06:04.430]very careful and make sure it's fully
watered now for the other side of the
- [00:06:08.960]growth stages, the ripening, when
it's coming down towards the end,
- [00:06:12.680]we can see here that it's very little
penalty for having a stress on the crop,
- [00:06:17.780]during the,
- [00:06:18.400]the light stages when it's just kind
of finishing up a lot of times, I've,
- [00:06:22.070]I've heard farmers say, man, you know,
I feel like it was about 20 bushels,
- [00:06:26.300]less than I thought it should be. If
I, to just put one more irrigation on,
- [00:06:30.080]you know, I got that, wow,
- [00:06:31.430]that's probably not true because
it's really the critical stages that
- [00:06:34.400]pollinating through the early grain fill.
Once you get past the hard dose stage,
- [00:06:39.470]a little drought stress,
isn't going to hurt much.
- [00:06:41.090]Also keep in mind that we can have drier
soils then because the days are shorter
- [00:06:45.950]and cooler and we just don't have the
potential to have stress that we do
- [00:06:49.280]earlier. So really important
chart to keep in mind. Now,
- [00:06:52.790]if we're growing the
verse of this would be,
- [00:06:54.680]if we were growing the
corn for silent, right,
- [00:06:56.800]then we would want to make sure and keep
it well water during that vegetative
- [00:07:00.130]stage. Because if we shorted
a little bit on water here,
- [00:07:03.130]the crop's going to end up
shorter, which of course,
- [00:07:05.200]if we end up later with a wind storm that
caused some green snaps, a good deal,
- [00:07:08.890]but if we're growing for signage,
- [00:07:10.840]then we would want to make
sure and keep it fully watered.
- [00:07:13.010]During the vegetative stage,
alfalfa would be another example.
- [00:07:15.700]The vegetative stage is really
critical, but with our grain crops,
- [00:07:19.600]this flowering and early Greenfield
is the time that's really critical.
- [00:07:23.050]So very important, fundamental
to irrigation management.
- [00:07:26.620]We take a look then at how much water do
different crops use we've got over here
- [00:07:31.030]is yield from zero to 200 bushels.
We've got across here.
- [00:07:35.590]you've apple transpiration. That'd be
the total crop water use from that crop.
- [00:07:39.370]and if we take a look, we see
the top line, it shows up here.
- [00:07:43.600]First is wheat.
- [00:07:44.980]And we know that for those that have
worked with wheat is pretty rare to ever
- [00:07:48.040]get a total zero yield from
drought stress on wheat,
- [00:07:51.310]because it only takes about four inches
of water to get it a planet established,
- [00:07:55.180]growing up, to get it to, head
out and pollinate and produce some grain.
- [00:08:00.310]So where we take a contrast that
with corn, instead of four inches,
- [00:08:03.340]it takes about 10 inches.
It's a much bigger plan.
- [00:08:05.510]It just takes a lot more water to get the
plant grown and established and get it
- [00:08:10.330]to pollinate and, and get
started producing some grain.
- [00:08:14.170]The thing that's different about corn
and why we irrigate it then is because
- [00:08:17.830]look how steep the curve is.
- [00:08:19.720]Or the slope of that line is for every
additional inch of water that we put on
- [00:08:23.740]corn. It yields more than any
other crop. We have, you know,
- [00:08:27.040]grain sorghum sometimes argued in there.
- [00:08:29.080]It doesn't take quite
as much to get started,
- [00:08:31.360]but you see the slope of the
line is a little bit less.
- [00:08:34.120]So at some point we're down in
the dry land areas. you know,
- [00:08:37.750]probably there's some years when
we would have more yield given,
- [00:08:41.260]with a given amount of water
from rain and our grain sorgh
- [00:08:44.440]but on irrigation where we're up
towards the top end of it all the time,
- [00:08:47.920]corn is always going to be more
water efficient than grain sorghum.
- [00:08:51.100]And so that's why we use that soil beans
you see is the bottom line on here at
- [00:08:55.290]some level appears to be the worst crop,
- [00:08:57.120]but you keep in mind is
producing an oil seed.
- [00:08:59.700]Oil takes a lot of energy to produce. So
just the same amount of photosynthesis.
- [00:09:04.050]It doesn't produce as
many bushels of grain,
- [00:09:06.030]but soybeans of course have
a higher value per bushel,
- [00:09:09.120]but it doesn't take as much
water to get started either.
- [00:09:11.370]So kind of keep those
principles in mind,
- [00:09:14.190]on the slopes and why we use
the different crops that we use.
- [00:09:18.570]We take a look at some of the
soil, water basics, again,
- [00:09:20.730]just a couple of principles that
kind of really fundamental stuff,
- [00:09:23.370]precipitation or irrigation applied
to the field, with good drainage,
- [00:09:27.330]which most of our soils in Nebraska
have pretty good drainage.
- [00:09:30.330]we'll do one of three things. They will
evaporate off into the air. Obviously,
- [00:09:34.020]if the soil surface is wet,
it can evaporate pretty easy.
- [00:09:37.410]It'll pond up on a surface and, or run
off. If we've got particularly sloping,
- [00:09:41.520]land water can run off pretty easily.
- [00:09:43.410]And so that's one of
the things it could do,
- [00:09:45.150]or it can infiltrate into the soil
and what do we want to have happen?
- [00:09:48.540]Of course, every bottle
of water we put on,
- [00:09:50.490]we want to have infiltrate into the
soil. Every rain drop that we get,
- [00:09:54.240]we'd like to move into the soil so we
can use that water. You know, what,
- [00:09:58.260]ponds up runs off the field,
- [00:10:00.510]is no longer an opportunity for us to
use for that year's crop production.
- [00:10:04.200]What evaporates off into the air.
Again, if it's when the crop is growing,
- [00:10:08.580]may offset some of the T, but it's still
not as efficient to use as the water.
- [00:10:12.450]So what we really want to
keep in mind as a fundamental,
- [00:10:15.150]we want to do everything we can to move
the water we put on with irrigation or
- [00:10:19.740]rain or snow, as far as
that goes into the soil.
- [00:10:23.460]And so what can we do there? You know,
- [00:10:25.200]probably keeping a residue covered soil
surface is the main thing that we can do
- [00:10:29.310]to keep it in there. no
tail is another way, you know,
- [00:10:32.340]every time we tell it, we kind of
break up some of the pores and,
- [00:10:35.430]and decrease the infiltration rate.
- [00:10:37.240]So we really don't want to have the
water moving into, a tilled soil.
- [00:10:42.060]We'd rather have it into a no-till
soil. In fact, cover crops.
- [00:10:44.910]That's one of the pluses of having
them out there is they increase the
- [00:10:47.850]infiltration rate of the soil. And so
we can increase infiltrate that water,
- [00:10:52.710]more, more quickly and get it into
the soil and, and where we can use it.
- [00:10:57.780]The, water that moves into
the soil after it gets moved in,
- [00:11:01.560]then can be stored in the
soil, move into the crop,
- [00:11:06.000]roots for transpiration needs, or it
can drain below as deep percolation.
- [00:11:11.070]So again, three things that can happen
there. If the soil is already full.
- [00:11:14.640]I mean,
- [00:11:14.880]it implies that if we're going to store
that we've got to have some room to do
- [00:11:18.120]it. That's one reason that late season
irrigation starting about now here,
- [00:11:21.720]the first part of August is really
critical to start using up the stored soil
- [00:11:26.370]water, and,
- [00:11:26.950]and really have a goal of getting
about 60% of the water that stored only
- [00:11:31.020]leaving about 40% of it.
- [00:11:32.450]And the top four feet of the profile
with corn and soybeans or deep rooted
- [00:11:36.960]we want to use up about 60% of that
water and really dry it down on a good,
- [00:11:41.010]heavy soils. Like we've got here.
- [00:11:42.450]Then we could store about
five inches of water.
- [00:11:45.120]The thing though that I've seen
in looking at a lot of,
- [00:11:47.790]irrigation data that I've
gotten, from, from farmers,
- [00:11:50.940]and I've looked at a lot of them through
some of, programs that collect it,
- [00:11:54.370]like the upper big blue
NRD they have,
- [00:11:58.270]showing those log shows that probably
about 50% of the guys leave the
- [00:12:03.070]field at about field capacity when they
are, are done irrigating for the year.
- [00:12:07.240]So thus they can't re store any
of that off season precipitation.
- [00:12:10.840]So keep that in mind. We
want to, we want to keep the,
- [00:12:13.720]the tank down a little ways
because we get that free refill.
- [00:12:17.110]And so we want to not completely
refill it with irrigation,
- [00:12:20.830]the movement into the crops for
transpiration, you know, again,
- [00:12:23.710]that's what we really put
it there for, right? I mean,
- [00:12:25.840]we want our crop to have
plenty of water to do it.
- [00:12:27.790]So this is really the objective of
what we're trying for here with our
- [00:12:31.630]irrigation. And so we need to make
sure we're in good shape there again,
- [00:12:35.230]cover crops.
- [00:12:36.250]One of the claims of that is that it gets
more biological activity in the soil,
- [00:12:40.930]which allows the water to move
within the soil, batter.
- [00:12:44.950]And so we can maybe use a little
bit more of that water up,
- [00:12:48.670]with our crop before we get
into drought stress and,
- [00:12:51.250]and be a little bit more efficient
that way draining below the root zone.
- [00:12:54.760]That's really kind of
Achilles heel if you will,
- [00:12:56.830]of all of irrigation and why we really
need to do a good job of, of,
- [00:13:01.240]monitoring the amount of
soil water that's in there,
- [00:13:03.550]do a good job irrigation
scheduling. You know,
- [00:13:05.740]that water is going down and
below our root zone, you know,
- [00:13:08.710]corn roots we'll get down to about six
feet once the water's deeper than that.
- [00:13:12.070]We have no chance of getting use of
it in that field any longer. I mean,
- [00:13:15.550]it'll head on down eventually
end up in the groundwater,
- [00:13:18.790]depending on how close that is, you know,
- [00:13:20.740]from a few days in a real shallow
to several years in the deep soil.
- [00:13:24.620]So we want to make sure we minimize
this as much as we possibly can.
- [00:13:29.290]And so water monitoring is really
a great way to do that.
- [00:13:32.470]we're not going to get in, don't
have time to get into that today,
- [00:13:34.630]but that's kind of where we're
at, on taking a look at that.
- [00:13:38.560]So if we take a look at the balance
of the soil water and where things are
- [00:13:41.830]coming from with our crop, you know,
we've got our inputs with our rain,
- [00:13:45.340]of course, some off season snow can get
in there, irrigation or crop water uses,
- [00:13:49.840]evaporation of water comes off.
- [00:13:51.520]The soil surface and evaporates
or off of wet leaves.
- [00:13:54.940]The transpiration is the water
that, that, you know,
- [00:13:58.180]comes through the root system
and out through the leaves.
- [00:14:00.670]And that certainly what we is the most
efficient way to water our crop and keep
- [00:14:05.620]it cool. We want to prevent runoff as
much as we possibly can. And again,
- [00:14:10.120]we can focus on that with making sure
we've got good coverage on our soils,
- [00:14:15.310]so we can do that. And then we can,
- [00:14:19.960]use NoTail some of those other
techniques to get big rain events,
- [00:14:23.410]to go into our soils as well. We
also can have this deep percolation.
- [00:14:27.850]We talked about the water moving below
the root zone. We want to minimize that.
- [00:14:31.690]So the best way to do that is to really
monitor the water that's in our S in our
- [00:14:35.980]root zone.
- [00:14:36.970]And a lot of times we see sensors that
are just down maybe 18 or 24 inches,
- [00:14:41.350]but really with our corn,
we really suggest, and, and
soybeans, wheat, alfalfa,
- [00:14:45.580]all of those that we really try to take
a look at the top minimum three feet and
- [00:14:49.720]four feet is even better. And if you're
really in a tight water situation,
- [00:14:52.880]if you monitor your four feet,
try to use that water up again,
- [00:14:55.830]starting here about the first August.
- [00:14:57.170]We really need to start
slowing the irrigations down.
- [00:14:59.750]Those roots are down there. There's
not a lot of ruts down at four feet,
- [00:15:02.930]but it can start extracting some of that
water and get quite a bit of it used
- [00:15:06.890]the top foot. Then where's where
a rain irrigation comes on.
- [00:15:09.470]That's always going to stay pretty wet.
- [00:15:10.850]So we're only looking at the top
foot of soil. We really, you know,
- [00:15:14.270]down here's where we're using it up,
- [00:15:15.680]and we need to figure that out
with some monitoring system.
- [00:15:19.510]So with that in mind, just
a real quick video here today,
- [00:15:22.360]a summary of what we talked about,
and, we've got,
- [00:15:26.650]extension paper, irrigation scheduling
strategies when using soil water data.
- [00:15:30.640]And it's a ISI 30, 36.
That's an excellent,
- [00:15:33.940]addition to what you might
want to take a look at.
- [00:15:36.790]There's also some videos that we've
put together that goes a lot more into
- [00:15:40.750]irrigation scheduling that's at,
- [00:15:43.330]go.unl.edu/irrigation scheduling videos.
- [00:15:47.410]And so take a look at those for a
little bit more information on that.
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