Weekly Irrigation Newsletter — Irrigation Scheduling Update for Aug. 4, 2025

Steve Melvin Author

08/06/2025 Added

7 Plays

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Nebraska Extension Educator Steve Melvin demonstrates how to apply the irrigation scheduling method outlined in "Irrigation Scheduling Strategies When Using Soil Water Data" (Nebraska Extension NebGuide EC3036). (Video No. 3 of series)

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[00:00:00.000]Hi this is Steve Melvin
[00:00:07.490]Extension Educator with the
[00:00:09.720]University of Nebraska
[00:00:10.320]Extension and today
[00:00:12.400]I'm going to give the next
[00:00:13.660]installment of the irrigation
[00:00:15.240]scheduling update for the week
[00:00:16.720]of
[00:00:16.920]August 4th. The field that we're
[00:00:20.290]working with again is down at
[00:00:22.900]the South Central Ag Lab near
[00:00:25.960]Clay Center. It was planted on
[00:00:28.040]April 22nd, 117 day corn. We
[00:00:31.030]have about two inches a week of
[00:00:32.800]water
[00:00:33.180]that we're going to apply. That
[00:00:34.900]Clay Center area gets about 28
[00:00:36.860]inches of rainfall on average.
[00:00:38.680]The
[00:00:38.980]corn is currently somewhere
[00:00:40.620]between that R2 and R3 stage
[00:00:42.430]and we're using watermark
[00:00:43.910]sensors
[00:00:44.500]with urometer data loggers. The
[00:00:47.300]corn is somewhere probably just
[00:00:49.920]a little bit past the blister
[00:00:52.320]stage
[00:00:52.740]but we're still going to stick
[00:00:53.930]with this three foot root zone.
[00:00:55.960]Just to be just a little bit
[00:00:56.990]more conservative and we're
[00:01:01.420]also going to stick with the
[00:01:02.400]two point or
[00:01:03.200]the 0.26 inches of water per
[00:01:05.690]day or the 1.82 inches per week.
[00:01:08.680]Again, just to be a little bit
[00:01:10.240]conservative and make sure we
[00:01:11.750]provide plenty of water for the
[00:01:13.300]corn. The numbers that we have
[00:01:17.500]with
[00:01:18.460]the three foot root zone, two
[00:01:20.640]inches per week of water that
[00:01:22.730]we can apply and the 0.26
[00:01:25.240]inches per
[00:01:25.820]day of water that we're going
[00:01:27.670]to estimate the crop is going
[00:01:29.520]to use. This next week is
[00:01:31.070]supposed
[00:01:31.200]to be kind of average condition
[00:01:32.940]so we were anticipating that
[00:01:34.550]would be fairly similar.
[00:01:35.900]The readings that we got and
[00:01:38.200]taking looks at the watermarks
[00:01:40.790]is 36 for the top foot,
[00:01:43.120]59, 69 and 41 down at the
[00:01:46.350]fourth foot level. So if you
[00:01:48.860]see we come over here and put
[00:01:51.160]them on
[00:01:51.880]the chart we can see that we're
[00:01:53.290]in very good shape. Remember
[00:01:54.770]with these charts,
[00:01:55.820]if you're up in the blue area
[00:01:57.190]that means you're above field
[00:01:58.720]capacity and if you're in this
[00:02:00.650]yellow
[00:02:01.200]zone here you're in the rain
[00:02:02.480]storage zone. In other words,
[00:02:04.040]we don't want to have all of
[00:02:05.360]our
[00:02:05.600]sensors up here so if it does
[00:02:07.020]rain like it did last week we
[00:02:08.530]got some really nice rain down
[00:02:10.160]there
[00:02:10.380]last week and we're able to
[00:02:11.850]store it nicely. And then the
[00:02:13.580]desired range which where a
[00:02:15.180]couple of
[00:02:15.660]them are at. And so that gives
[00:02:17.220]us a pretty good idea. We're
[00:02:18.710]pretty happy with where we're
[00:02:20.220]at this
[00:02:20.620]week and probably just want to
[00:02:22.160]put on enough water to kind of
[00:02:23.770]take care of it for another
[00:02:25.080]week and so
[00:02:25.820]you know if we just went and
[00:02:27.020]put an inch and a half inch
[00:02:28.310]three quarters on we'd be about
[00:02:29.640]in the
[00:02:29.840]same place and we could just
[00:02:31.170]stop at this point. But let's
[00:02:32.690]go ahead and take a look at
[00:02:33.900]these next
[00:02:34.360]two columns of numbers. There's
[00:02:36.130]a lot of more information we
[00:02:37.540]can glean and make decisions
[00:02:39.080]very
[00:02:39.320]quickly with this system. This
[00:02:41.580]is a chart of the data from the
[00:02:45.500]watermark sensors that we have
[00:02:48.360]collected this year. You can
[00:02:50.090]see that early we got some
[00:02:51.520]pretty good rains here in June
[00:02:53.320]and then it didn't rain for a
[00:02:54.390]little bit and the top foot
[00:02:55.820]got pretty dry. But you can see
[00:02:57.430]that the second foot which is
[00:02:58.910]these triangles here was still
[00:03:00.280]in
[00:03:00.360]good shape. The corn was big
[00:03:01.610]enough it was using water from
[00:03:02.860]down there and was in great
[00:03:04.150]shape.
[00:03:04.560]You can see it just kind of
[00:03:05.960]came along. We put some
[00:03:07.370]irrigation water on and and
[00:03:09.400]here a week ago
[00:03:11.160]and it got a pretty good shape.
[00:03:12.690]And then this past week we didn't
[00:03:14.150]end up putting any irrigation
[00:03:15.560]water
[00:03:15.880]on but you can see we got an
[00:03:17.560]inch 55 of rain over a couple
[00:03:19.520]of nights. And one thing when
[00:03:21.120]you're
[00:03:21.320]looking at these you can see
[00:03:22.760]that all four depths of these
[00:03:24.260]sensors got fairly wet all
[00:03:25.820]almost immediately which tells
[00:03:27.230]me there's a little bit of
[00:03:28.220]water slipping down around the
[00:03:29.660]sides of
[00:03:30.140]these sensors and it probably
[00:03:31.790]would be a good idea to go and
[00:03:33.260]pack the soil around them and
[00:03:34.940]and make them just a little bit
[00:03:36.260]tighter. But you can see that
[00:03:37.790]the numbers drop down fairly
[00:03:39.500]quickly
[00:03:39.860]within a day or so and you can
[00:03:41.330]see where pretty much where you're
[00:03:43.190]at. So it's not really anything
[00:03:45.080]other making some noise in the
[00:03:46.370]data that's too big of a
[00:03:47.350]problem. But you can see we're
[00:03:48.700]in really
[00:03:49.260]good shape here yet today. Okay
[00:03:51.080]so let's take a look at this
[00:03:54.370]next column.
[00:03:55.820]As I've said before this is a
[00:03:57.110]percent of plant available
[00:03:58.410]water. So at field capacity it's
[00:04:00.400]100%
[00:04:01.280]of plant available water. We go
[00:04:03.040]above field capacity. This goes
[00:04:04.880]to a more than a hundred
[00:04:06.080]percent. As we start using
[00:04:08.000]water out of it we can see that
[00:04:09.920]it gets drops below a hundred
[00:04:11.820]percent.
[00:04:12.200]And the sensors where we have
[00:04:14.140]them today are 93, 74 percent
[00:04:16.820]and 70 percent. So if we move
[00:04:19.100]these
[00:04:19.340]three over here add them
[00:04:20.810]together we get 237 divided by
[00:04:23.070]the three sensors we're looking
[00:04:24.920]at.
[00:04:25.820]So we've got an average of 79
[00:04:27.690]percent of plant available
[00:04:29.330]water in our root zone. So
[00:04:30.800]again we know
[00:04:31.280]we're in pretty good shape and
[00:04:32.600]and you know if we ended up in
[00:04:33.800]the same place next week this
[00:04:35.660]early
[00:04:35.900]in August that wouldn't be an
[00:04:37.340]all bad thing. And so again we
[00:04:38.900]could just quit right here and
[00:04:40.460]say
[00:04:40.580]we're just going to put an inch
[00:04:41.700]and a half inch and three
[00:04:42.590]quarters on. But let's take a
[00:04:44.120]look at
[00:04:44.360]this third column. It gives us
[00:04:46.250]the ability to know a little
[00:04:47.860]bit more what's going on.
[00:04:49.340]Okay so if we take a look in
[00:04:52.070]here we can know that in order
[00:04:55.320]to bring
[00:04:55.820]this average of 79 percent
[00:04:58.610]plant available water back up
[00:05:00.720]to field capacity we would have
[00:05:02.720]to apply
[00:05:03.260]0.44 inches for each of the
[00:05:05.990]three feet. Because we've got
[00:05:07.750]an average here of 79 or we
[00:05:09.740]just rounded
[00:05:10.220]to 80. So we take 0.44 times
[00:05:12.970]three we can see that we would
[00:05:14.800]have to apply 1.32 inches of
[00:05:17.300]water to
[00:05:17.840]bring it back up to field
[00:05:19.070]capacity. So if we wanted to go
[00:05:20.430]out and start the pivot today
[00:05:21.860]and put an
[00:05:25.820]inch of water back up to field
[00:05:26.830]capacity but it certainly
[00:05:27.670]wouldn't leave much rain
[00:05:28.520]storage zone
[00:05:29.240]either. So probably the main
[00:05:30.920]the at least we want to do is
[00:05:32.240]wait just a little bit of time
[00:05:33.840]to go out
[00:05:34.400]there and apply some water. And
[00:05:35.750]this is a subsurface drip we
[00:05:36.850]put on about a half inch of
[00:05:38.000]water and so
[00:05:39.080]we could easily do that. But
[00:05:40.540]still we're up in this range
[00:05:41.880]storage zone and so you know
[00:05:43.340]there's
[00:05:43.460]no reason to get in a big rush
[00:05:44.840]to go out here right first of
[00:05:46.220]the week and take care of that.
[00:05:47.780]If we take a look at then at
[00:05:50.330]how much water we can use out
[00:05:53.150]of the crop again this early
[00:05:55.820]in the season I kind of like to
[00:05:57.290]keep it at about 60 percent of
[00:05:59.020]plant available water. So if we
[00:06:01.040]look at the 0.44 we can use it
[00:06:02.910]down to this 0.93 probably next
[00:06:04.970]week I'll start going down to
[00:06:06.670]this
[00:06:06.920]50 percent. But right now I'm
[00:06:08.860]going to stay with the 0.93 and
[00:06:11.040]if we subtract two numbers
[00:06:12.590]basically
[00:06:12.980]it's given us how much water is
[00:06:14.520]between these two points we can
[00:06:16.040]see that we've got 0.49 inches
[00:06:18.080]or
[00:06:18.260]almost a half inch of water
[00:06:20.310]that we can use on average out
[00:06:22.630]of these three foot zones in
[00:06:24.980]the
[00:06:25.280]root zone.
[00:06:25.820]So we multiply that times three
[00:06:27.460]we've got about 1.47 inches of
[00:06:30.200]water that we can use before we
[00:06:32.960]would be at the 60 percent of
[00:06:34.550]plant available water.
[00:06:36.000]Certainly an area where we
[00:06:37.620]wouldn't even
[00:06:38.300]be the least bit concerned
[00:06:39.760]about reducing any yields from
[00:06:41.500]being that that much of the
[00:06:43.040]water used up.
[00:06:43.700]Now if we take the 1.47 and
[00:06:48.910]knowing that we're using about
[00:06:50.450]0.26 inches per day on average
[00:06:52.400]there's about enough water left
[00:06:54.570]in there for
[00:06:55.280]5.7 inches per day on average.
[00:06:55.780]There's about enough water left
[00:06:55.780]in there for 5.7 inches per day
[00:06:55.780]on average.
[00:06:55.780]There's about enough water left
[00:06:55.780]in there for 5.7 inches per day
[00:06:55.780]on average.
[00:06:55.780]There's about enough water left
[00:06:55.780]in there for 5.7 inches per day
[00:06:55.780]on average.
[00:06:55.780]There's about enough water left
[00:06:55.780]in there for 5.7 inches per day
[00:06:55.780]on average.
[00:06:55.780]There's about enough water left
[00:06:55.780]in there for 5.7 inches per day
[00:06:55.780]on average.
[00:06:55.780]There's about enough water left
[00:06:55.940]in there for 5.7 inches per day
[00:06:56.140]on average.
[00:06:56.280]There's about enough water left
[00:06:56.450]in there for 5.7 inches per day
[00:06:56.640]on average.
[00:06:56.780]There's about enough water left
[00:06:56.950]in there for 5.7 inches per day
[00:06:57.140]on average.
[00:06:57.280]And so you know we can easily
[00:06:58.720]round that down to five days
[00:07:00.180]and so know that we need to
[00:07:01.630]have our irrigation completed
[00:07:03.080]within five days. So we don't
[00:07:04.550]want to wait too long to get
[00:07:05.800]things started. There really
[00:07:07.340]isn't any rain forecast to
[00:07:08.590]speak of this week. So we know
[00:07:10.300]that we want to get started
[00:07:11.320]pretty quick here.
[00:07:12.580]There's about enough water left
[00:07:12.750]in there for 5.7 inches per day
[00:07:12.940]on average.
[00:07:13.080]There's about enough water left
[00:07:13.240]in there for 5.7 inches per day
[00:07:13.440]on average.
[00:07:13.580]There's about enough water left
[00:07:13.740]in there for 5.7 inches per day
[00:07:13.940]on average.
[00:07:14.080]There's about enough water left
[00:07:14.250]in there for 5.7 inches per day
[00:07:14.440]on average.
[00:07:14.580]So if we take a look at what
[00:07:15.870]data that we've summarized, you
[00:07:17.620]know the amount of water we can
[00:07:19.190]use, the amount that we could
[00:07:20.760]add before we back to field
[00:07:22.200]capacity, the number of days
[00:07:23.710]before we would need to have an
[00:07:25.520]application complete. And
[00:07:27.230]obviously the center pivot if
[00:07:28.500]it takes four days to put the
[00:07:29.630]water on, you know we don't
[00:07:30.780]want to wait too long. We
[00:07:31.880]probably want to get things
[00:07:33.030]going tomorrow. So if we
[00:07:34.500]summarize this stuff together,
[00:07:36.450]I'm going to decide to put
[00:07:37.920]about an inch and a half of
[00:07:39.430]water on this coming week. We
[00:07:41.290]can use just a little bit of
[00:07:42.880]this stored water up.
[00:07:44.540]So if we take a look at what
[00:07:46.770]data that we've summarized, you
[00:07:49.770]know the amount of water we can
[00:07:52.450]use, the number of days before
[00:07:55.230]we would need to have an
[00:07:57.270]application complete. And
[00:07:59.960]obviously the center pivot if
[00:08:02.650]it takes four days to put the
[00:08:05.470]water on, you know we don't
[00:08:07.560]want to wait too long. We
[00:08:09.910]probably want to get things
[00:08:12.380]going tomorrow. So if we
[00:08:14.500]summarize this stuff together,
[00:08:14.500]I'm going to decide to put
[00:08:14.500]about an inch and a half of
[00:08:14.500]water on this coming week. We
[00:08:14.500]probably want to get things
[00:08:14.500]going tomorrow. So if we
[00:08:14.500]summarize this stuff together,
[00:08:14.500]I'm going to decide to put
[00:08:14.500]about an inch and a half of
[00:08:14.500]water on this coming week. We
[00:08:14.500]can use just a little bit of
[00:08:14.500]this stored water up.
[00:08:14.500]So if we summarize this stuff
[00:08:17.040]together, I'm going to decide
[00:08:19.290]to put about an inch and a half
[00:08:21.580]of water on this coming week.
[00:08:24.070]We probably want to get things
[00:08:26.520]going tomorrow. So if we
[00:08:28.580]summarize this stuff together,
[00:08:31.360]I'm going to decide to put
[00:08:33.280]about an inch and a half of
[00:08:35.280]water on this coming week. We
[00:08:38.090]probably want to get things
[00:08:38.430]going tomorrow. So if we
[00:08:38.930]summarize this stuff together,
[00:08:39.380]I'm going to decide to put
[00:08:39.380]about an inch and a half of
[00:08:39.380]water on this coming week. We
[00:08:39.380]probably want to get things
[00:08:39.380]going tomorrow. So if we
[00:08:39.380]summarize this stuff together,
[00:08:39.380]I'm going to say just a little
[00:08:39.380]bit of this stored water up.

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Weekly Irrigation Newsletter — Irrigation Scheduling Update for Aug. 4, 2025

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