Weekly Irrigation Newsletter — Irrigation Scheduling Update for Sept. 2, 2025

Steve Melvin Author

09/03/2025 Added

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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. 7 of series)

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[00:00:00.000]Hi, this is Steve Melvin,
[00:00:05.030]Extension Educator with the
[00:00:07.990]University of Nebraska
[00:00:10.980]Extension. And today, we've got
[00:00:13.790]the next installation of the
[00:00:15.340]irrigation scheduling update
[00:00:17.210]for the week of September 2nd.
[00:00:19.000]Again, the example is corn
[00:00:21.810]planted on April 22nd, 117-day
[00:00:26.990]hybrid, and we're at about the
[00:00:29.600]half milk line now, so we're
[00:00:32.220]just about done with the
[00:00:34.630]irrigation season.
[00:00:36.540]The rooting depth we're using
[00:00:37.790]is four feet now, and it will
[00:00:38.990]continue that through the
[00:00:40.180]rest of the season.
[00:00:44.440]now at the beginning or at the
[00:00:46.380]full dent stage, so down to 0.18
[00:00:49.470]inches or 0.26 inches per week,
[00:00:52.200]and I think this is a really
[00:00:53.530]significant thing to note. You
[00:00:55.220]know, we were back up here at
[00:00:56.660]silking
[00:00:57.200]time at about 0.3, and so we're
[00:00:59.650]not quite down to half as much
[00:01:01.500]per day, but remember the days
[00:01:03.680]are
[00:01:03.820]shorter, the corn's senescing,
[00:01:05.570]and this is a number that many
[00:01:07.020]people don't keep in mind when
[00:01:08.850]they
[00:01:08.900]irrigate, do irrigation
[00:01:10.820]scheduling late in the season.
[00:01:13.270]Okay, so we went and got the
[00:01:15.280]numbers.
[00:01:15.700]We had a very significant,
[00:01:17.470]about 2.75 inches of rain over
[00:01:20.030]the weekend. So we had
[00:01:21.570]definitely
[00:01:22.500]things got much wetter than
[00:01:24.340]they were the week before. And
[00:01:26.500]we're at 4, 13, 34, and 52 centibars.
[00:01:30.500]We put those over here on the
[00:01:32.120]chart. And again, remember the
[00:01:34.180]blue area is when we're above
[00:01:35.870]field
[00:01:36.340]capacity, so the top couple of
[00:01:38.710]feet are very wet after this
[00:01:40.820]rain. Then the other zones
[00:01:43.020]certainly
[00:01:43.960]have a good amount of water.
[00:01:45.700]And at this point, knowing how
[00:01:47.510]much water we're using, you
[00:01:49.160]know,
[00:01:49.640]if we were just doing a
[00:01:50.620]commercial field and scheduling,
[00:01:52.260]we'd say, yep, we're just not
[00:01:53.670]going
[00:01:54.020]to calculate anything more. We
[00:01:55.640]can see easily from this that
[00:01:57.020]we've got plenty of water for
[00:01:58.390]next week.
[00:01:59.180]But since we're in the middle
[00:02:00.400]of this series and we've taken
[00:02:01.680]a look at the numbers, let's go
[00:02:03.000]ahead
[00:02:03.400]and take a look at the next two
[00:02:04.700]columns and see what we can
[00:02:05.900]learn. And we're getting close
[00:02:07.440]to the
[00:02:07.840]end, so we certainly want to
[00:02:09.280]calculate things on out to the
[00:02:10.780]end of the growing season.
[00:02:12.240]Chart that we've taken a look
[00:02:14.330]at, it's been updated. You can
[00:02:16.760]see this,
[00:02:17.680]most of the rain came on
[00:02:18.950]Saturday and a little bit on
[00:02:20.490]either side, so about two and
[00:02:22.170]three-quarter
[00:02:23.160]inches of rain. You can see we
[00:02:25.000]put on the half inch of rain
[00:02:26.570]earlier last week, which kind
[00:02:28.430]of
[00:02:28.680]stalled out the decline here,
[00:02:30.690]as when you can kind of see in
[00:02:32.450]these others, it really was a
[00:02:34.380]lot of the
[00:02:34.960]water that was used. It ended
[00:02:36.320]up being a very cool week last
[00:02:37.570]week and didn't use a lot of
[00:02:38.720]water.
[00:02:39.260]And then you can see when the
[00:02:40.710]rain came, you know, everything
[00:02:42.530]got much wetter. Even the
[00:02:44.290]fourth foot
[00:02:44.780]got just a little bit wetter.
[00:02:46.360]It hasn't been a lot of water
[00:02:47.770]moved down there yet, but
[00:02:49.240]pretty much got a full profile.
[00:02:52.080]And for this year, we put on 5.4
[00:02:55.620]inches. That 4.4 was for a
[00:02:58.400]chemigation application and
[00:02:59.860]then about 12 and a half inches
[00:03:01.540]from precipitation. So very
[00:03:03.050]good wet
[00:03:03.600]season, particularly late,
[00:03:05.420]early, it was very dry and then
[00:03:07.240]caught a little bit of rain and
[00:03:08.990]then
[00:03:09.300]around tassel time it was
[00:03:10.530]pretty dry and then we've had
[00:03:11.950]pretty good rain since then.
[00:03:13.560]Okay, so let's take a look at
[00:03:15.760]the percent. Remember we can't
[00:03:18.590]average the centibars, they're
[00:03:21.020]not a linear kind of to each
[00:03:22.880]other, but when we get to the
[00:03:24.900]percent we can. And so if we
[00:03:26.920]see we've
[00:03:27.700]got 158, which means that we're
[00:03:30.010]quite a bit above field
[00:03:31.340]capacity. Next foot's at 123,
[00:03:33.710]and then 93
[00:03:34.740]and 80. We put those together,
[00:03:36.980]add them up, divide by four,
[00:03:38.730]and we're at 113 percent of
[00:03:40.840]plant available
[00:03:41.520]water. So yeah, that means we're
[00:03:43.720]above field capacity as of
[00:03:45.350]today when we took the readings.
[00:03:47.580]If we take a look at the amount
[00:03:49.850]of water that we're above field
[00:03:52.610]capacity, 0.28, so we multiply,
[00:03:56.040]We're about 1.12 inches above
[00:03:58.910]field capacity. Now this water
[00:04:01.310]may get used. It isn't the top
[00:04:03.440]part of the profile. This week
[00:04:05.370]is supposed to be fairly cool
[00:04:07.090]as well, and we might only use
[00:04:09.000]about this amount of water, so
[00:04:10.730]we may end up deperculating
[00:04:12.350]some water, but certainly we
[00:04:14.140]can see that we don't want to
[00:04:15.770]be irrigating this week from
[00:04:17.480]this being above field capacity.
[00:04:21.160]We take it how much water is
[00:04:22.920]left. We're at 113% on average.
[00:04:25.750]We can go down to 40%, so 1.35
[00:04:29.080]inches below field capacity. If
[00:04:31.000]we subtract a negative number,
[00:04:32.500]we get a bigger, you know,
[00:04:34.070]these are basically we're
[00:04:35.080]looking at the distance between
[00:04:36.570]these two numbers. So 1.63
[00:04:38.830]inches times 4, so it's about 6.5
[00:04:41.720]inches of water in the profile
[00:04:43.710]that we can use up yet this
[00:04:45.400]season.
[00:04:46.220]If we take a look at the number
[00:04:48.190]of days divided by 18, we can
[00:04:50.490]see it's a big number of days.
[00:04:52.800]Again, I only like to schedule
[00:04:54.560]out about seven days.
[00:04:56.000]And so, but we certainly know
[00:04:57.590]we've got plenty of water in
[00:04:59.060]there, you know, for this next
[00:05:01.000]week.
[00:05:01.320]And we don't need to worry
[00:05:02.090]about irrigation.
[00:05:02.860]And that's what I concluded on
[00:05:05.210]this chart.
[00:05:06.380]You know, if we take a look, we're
[00:05:07.860]at six and a half inches.
[00:05:09.080]Certainly not any irrigation
[00:05:10.850]prescribed for this week.
[00:05:12.600]Well, let's go ahead and
[00:05:13.770]predict on out for the rest of
[00:05:15.120]the season and see if we've got
[00:05:16.530]enough water to finish the
[00:05:17.760]season.
[00:05:18.400]Again, 6.6 and a half inches.
[00:05:22.980]We go to this table we've been
[00:05:24.550]working at.
[00:05:25.400]Half milk line takes about two
[00:05:27.540]and a quarter inches of water
[00:05:29.600]left in about 13 days.
[00:05:31.740]So if we do that, we're about 914.
[00:05:33.680]That's about where we've been
[00:05:35.340]predicting the last couple of
[00:05:37.010]weeks when we'd mature.
[00:05:38.540]If we come down here and
[00:05:40.160]subtract this out, we can see
[00:05:42.310]that we'll have 4.27 inches of
[00:05:45.150]water left over in the profile
[00:05:47.290]that we could have used.
[00:05:49.340]But we're certainly not going
[00:05:51.120]to worry about it at this point.
[00:05:53.180]You know, a good rain is always
[00:05:54.620]appreciated, and we're going to
[00:05:56.190]leave things pretty wet this
[00:05:57.540]year, it's looking like.
[00:05:58.980]So let's go ahead and take a
[00:06:00.860]look.
[00:06:01.500]We're all done with August, so
[00:06:02.600]we don't need to worry about
[00:06:03.560]this one.
[00:06:04.080]In September, 0.65 is about
[00:06:06.640]what we figure per week.
[00:06:08.420]And so if we go ahead and add
[00:06:11.100]that in, we can see the 4.27
[00:06:14.900]plus the two weeks of September
[00:06:18.090]is a 1.3.
[00:06:20.060]So that would be 5.57 inches of
[00:06:22.570]water is what we would predict
[00:06:24.460]to have left.
[00:06:25.520]And that would, if we get
[00:06:26.900]average rainfall, be a little
[00:06:28.620]bit above field capacity.
[00:06:30.300]So we certainly have got plenty
[00:06:31.970]of water to finish the season
[00:06:33.500]out.
[00:06:34.080]And, you know, we really don't
[00:06:35.990]like to leave the field this
[00:06:37.640]wet for obvious reasons.
[00:06:39.380]One is we would just as soon
[00:06:40.950]maybe have tried to pump a
[00:06:42.460]little less water this summer.
[00:06:44.540]But, you know, really looking
[00:06:46.050]back on it, you know, maybe
[00:06:47.380]there was a half inch of water
[00:06:48.710]that we could have saved.
[00:06:50.140]But, you know, you just don't
[00:06:51.700]predict these large rains.
[00:06:53.220]And so, you know, there's a
[00:06:54.530]couple of times that in
[00:06:55.580]retrospect, we probably could
[00:06:57.080]have saved a half inch water a
[00:06:58.400]couple of times and pumped just
[00:06:59.830]a little bit less.
[00:07:00.920]But you just don't know that in
[00:07:02.480]advance.
[00:07:03.320]And so we look at the numbers,
[00:07:05.190]we make our best guess and
[00:07:06.760]prediction of what we want to
[00:07:08.570]do as we move forward and go
[00:07:10.180]from there.
[00:07:11.240]Also, you know, when we leave
[00:07:12.900]the field at field capacity,
[00:07:14.490]you know, if we get some rain
[00:07:16.270]into the fall, which there's
[00:07:17.680]certainly some weather people
[00:07:19.270]are predicting that, you know,
[00:07:20.960]we just soon have a drier field.
[00:07:22.780]So we don't, you know, have a
[00:07:24.320]little better chance of not
[00:07:25.770]being a muddy harvest.
[00:07:27.620]And also, maybe the bigger
[00:07:29.300]thing from an environmental
[00:07:31.060]concern and preserving our nitrate,
[00:07:33.500]we just
[00:07:33.940]soon not have basically every
[00:07:36.490]bit of water that we get from
[00:07:38.970]snow and rain between now
[00:07:41.060]and April is going to depercolate
[00:07:42.740]because we're at field capacity.
[00:07:44.560]So anything we add is going to
[00:07:45.910]depercolate, which is going to
[00:07:47.420]take some nitrates with
[00:07:48.660]it.
[00:07:48.780]So all in all, you know, this
[00:07:50.690]pretty well wraps up the year
[00:07:52.550]and we'll see kind of what's
[00:07:54.480]going on next week yet, but the
[00:07:55.900]corn should be mature in a
[00:07:57.050]couple of weeks. We've got
[00:07:58.360]plenty
[00:07:58.820]of water to finish out the
[00:08:00.290]season. We ended up leaving the
[00:08:02.250]field very wet because of rain,
[00:08:04.140]and
[00:08:04.400]you know, that's the way it
[00:08:05.860]works out. So for now, this is
[00:08:07.580]Steve Melvin, Extension Educator
[00:08:09.480]with the University of Nebraska,
[00:08:10.790]signing off.

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Weekly Irrigation Newsletter — Irrigation Scheduling Update for Sept. 2, 2025

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