1 - 2021 South Central Ag Lab Field Day - Essentials of Irrigation Management

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10/14/2021 Added

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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
[00:11:35.760]crops.
[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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1 - 2021 South Central Ag Lab Field Day - Essentials of Irrigation Management

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