Weekly Irrigation Newsletter — Irrigation Scheduling Update for Aug. 11, 2025

Steve Melvin Author

08/12/2025 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. 4 of series)

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[00:00:00.000]Hi this is Steve Melvin,
[00:00:07.520]Extension Educator with the
[00:00:09.760]University of Nebraska
[00:00:10.320]Extension with the
[00:00:12.000]next installment of the
[00:00:13.060]irrigation scheduling update
[00:00:14.440]for the week of August 11th.
[00:00:16.060]Just to
[00:00:18.360]review, we're working with a
[00:00:19.980]corn field down in South
[00:00:21.290]Central Ag Lab planted on April
[00:00:23.210]22nd,
[00:00:23.880]117 day hybrid. We're limiting
[00:00:27.050]ourselves to about two inches
[00:00:29.370]per week. 128 inches is the
[00:00:31.260]amount of water from rainfall
[00:00:33.030]was received in a clay center
[00:00:34.690]area on average. The corn is
[00:00:36.590]almost
[00:00:36.960]to the R4 stage so we're going
[00:00:38.590]to leave that there for today
[00:00:40.040]and we're going to use watermark
[00:00:42.080]sensors to collect our data. We're
[00:00:44.600]going to stay with the three
[00:00:45.990]foot root zone. Next week we'll
[00:00:48.720]probably go to four feet but
[00:00:49.800]for now we're going to use
[00:00:50.770]three feet. The crop water
[00:00:53.860]use we're going to estimate it
[00:00:55.610]at 0.22 inches per day or 1.54
[00:00:58.420]inches per week. Again you can
[00:01:00.760]see it drops off pretty
[00:01:02.150]dramatically and I think this
[00:01:03.990]is one mistake as the days get
[00:01:05.920]shorter the
[00:01:06.460]plants get more mature they
[00:01:07.660]just don't use quite as much
[00:01:08.890]water and I think this is
[00:01:10.090]probably one
[00:01:10.600]of the places that that most
[00:01:12.020]guys that do irrigation
[00:01:13.260]scheduling don't take this big
[00:01:15.020]of a drop into account. You can
[00:01:16.910]see it just keeps dropping as
[00:01:18.590]we move on into it and a
[00:01:19.860]lot of people continue to put
[00:01:21.300]on you know thinking they need
[00:01:22.810]two inches per week but
[00:01:23.840]really it really drops off
[00:01:25.300]dramatically towards the end of
[00:01:27.110]the season. Okay we put our
[00:01:30.860]numbers
[00:01:31.260]that we got this morning and
[00:01:33.000]after we took these readings it
[00:01:34.970]started raining again and it
[00:01:36.760]rained
[00:01:37.020]pretty hard clay center this
[00:01:38.510]morning as I was working on
[00:01:39.870]this and you can see that we're
[00:01:41.590]pretty
[00:01:41.720]wet in that top foot. We're up
[00:01:44.580]here we'll put a 5 in and a 31
[00:01:47.830]and we picked the 30 and then
[00:01:51.040]54 so 55 we picked and
[00:01:53.820]so we can take a look again
[00:01:54.770]where we've always talked that
[00:01:55.960]you could make very quick
[00:01:57.210]decisions
[00:01:57.760]with this system and again with
[00:01:59.580]this one above field capacity
[00:02:01.340]you can see that we've got one
[00:02:03.200]at the top foot that's really
[00:02:04.510]wet fortunately we're a little
[00:02:05.940]drier on down below and even at
[00:02:07.440]the fourth foot we're a little
[00:02:08.940]drier yet so this water even
[00:02:10.450]though it's deep percolating
[00:02:11.820]will not
[00:02:12.340]go very far down into the root
[00:02:13.710]zone and so we'll be able to
[00:02:14.950]save all of this rain that we
[00:02:16.260]were able
[00:02:16.920]to get into the soil profile
[00:02:18.660]and we probably could look at
[00:02:20.230]this and say yeah I probably
[00:02:21.840]don't need to
[00:02:23.800]do this for seven days. That's
[00:02:25.180]always a timing frame I want to
[00:02:26.820]take a look at but let's see
[00:02:28.380]what we can
[00:02:28.820]learn from these other two
[00:02:29.960]columns and see if we can make
[00:02:31.190]a little more confident
[00:02:32.500]decision.
[00:02:36.180]Take a look at the chart that
[00:02:37.560]we pulled together you can see
[00:02:39.100]1.74 inches and 0.33 is what we
[00:02:41.620]got
[00:02:41.800]over the weekend and you can
[00:02:43.250]see we put our one and a half
[00:02:44.630]inches on that we were talking
[00:02:46.240]about
[00:02:46.300]last week. This one was
[00:02:48.330]actually earlier on Saturday
[00:02:50.810]before the rain came and so it's
[00:02:53.360]not like we
[00:02:53.780]put water on after it rained
[00:02:55.130]but you can see that we put a
[00:02:56.440]lot of water on this field this
[00:02:59.140]past week
[00:02:59.780]and you can see it really
[00:03:01.180]responded quickly and came up
[00:03:03.010]so not surprising with that
[00:03:04.580]much rain.
[00:03:05.220]So if we take a look at the
[00:03:07.040]next column and extend these
[00:03:09.380]over this is percent of plant
[00:03:11.520]available water it's based off
[00:03:13.350]100 percent as a field capacity
[00:03:15.620]as we go above field capacity
[00:03:17.420]you
[00:03:17.620]can see that we've got the
[00:03:19.180]numbers get higher than 100
[00:03:21.250]percent as we use that water
[00:03:22.910]out it goes down
[00:03:23.760]and like here we've got 77
[00:03:25.240]percent of plant available
[00:03:26.590]water we can't average these
[00:03:28.080]numbers
[00:03:28.560]but we can certainly average
[00:03:30.030]the percents and so we bring
[00:03:31.440]those over add them together
[00:03:33.040]divide by
[00:03:33.600]the three foot root zone we're
[00:03:35.180]using we can see that on
[00:03:36.390]average we're at 110 or 111
[00:03:38.560]percent of
[00:03:39.200]plant available water and since
[00:03:41.180]most of that extra water is in
[00:03:42.650]the top foot we're very
[00:03:44.080]confident that
[00:03:44.880]it will not de-percolate clear
[00:03:46.460]out the bottom of the root zone
[00:03:47.990]where we've got these drier
[00:03:49.520]levels down here so we should
[00:03:51.500]be able to figure on all of it.
[00:03:53.740]We go on to the next column and
[00:03:58.160]take a look at the amount of
[00:03:59.330]water per foot that's in there
[00:04:01.020]we
[00:04:01.180]can see that we've got 0.28
[00:04:03.290]inches above field capacity and
[00:04:05.270]so if we put that number in
[00:04:06.700]times
[00:04:07.100]three we can see that we would
[00:04:08.810]need to use 0.84 inches of the
[00:04:11.080]top three feet to bring that
[00:04:12.780]amount or the amount of water
[00:04:14.730]stored in the soil down to
[00:04:16.420]field capacity so we're in
[00:04:18.240]really good
[00:04:19.100]wet shape in this field right
[00:04:20.780]now and we could probably you
[00:04:22.470]know stop right here you
[00:04:23.720]can see that we have a lot of
[00:04:24.740]water stored in the soil right
[00:04:25.900]now and we could probably take
[00:04:27.590]a look
[00:04:28.020]here again and say yeah we
[00:04:29.070]probably don't need to but let's
[00:04:30.580]irrigate this week but let's go
[00:04:31.640]ahead
[00:04:31.780]and see what else we can figure
[00:04:33.460]out now this week we're going
[00:04:35.360]to go to 50 plant available
[00:04:37.460]water as a
[00:04:38.700]minimum amount of water that we're
[00:04:40.680]going to leave in there and
[00:04:42.090]before we were using 60 because
[00:04:44.700]you
[00:04:44.700]know just in case you do catch
[00:04:46.030]a couple of really hot dry
[00:04:47.210]weeks and the pivot breaks down
[00:04:48.600]and
[00:04:48.660]everything goes wrong we want
[00:04:50.160]to make sure we're in good
[00:04:51.540]shape but now we want to start
[00:04:53.050]focusing on
[00:04:53.700]the amount of water that's on
[00:04:55.450]average in each of the three
[00:04:56.990]feet and so we need to know
[00:04:58.440]this number
[00:04:58.960]here so this is positive this
[00:05:00.770]number being a 1.14 negative
[00:05:02.880]and we're going to subtract so
[00:05:04.670]when we
[00:05:04.920]subtract the negative numbers
[00:05:06.190]like adding we're trying to get
[00:05:07.460]the amount of water between
[00:05:08.590]these
[00:05:08.920]two so 1.42 inches times three
[00:05:12.230]feet gives us 4.26 inches of
[00:05:15.320]water remaining that we
[00:05:17.080]can use before we would
[00:05:18.360]anticipate any yield loss in
[00:05:19.990]this field now if we take a
[00:05:23.680]look at
[00:05:23.680]how many days that would
[00:05:25.120]represent you know 4.26 divided
[00:05:27.630]by the 22 hundredths of an inch
[00:05:29.500]that we
[00:05:29.900]we predicting this next week we
[00:05:31.880]can see that be 19 days but I'm
[00:05:33.980]never going to predict out more
[00:05:36.240]than
[00:05:36.440]a week I want to redo this
[00:05:37.680]calculation at least each week
[00:05:39.290]and sometimes if I'm not
[00:05:40.510]confident I
[00:05:41.240]might even do it in the middle
[00:05:42.360]of the week but we're just
[00:05:43.340]going to say we've got plenty
[00:05:44.560]of water
[00:05:44.800]for seven days and so we're
[00:05:46.090]going to let it go from there
[00:05:47.460]and then we'll next Monday we'll
[00:05:49.120]calculate it again so if we
[00:05:53.660]take a look basically we've got
[00:05:53.660]enough water we're going to let
[00:05:53.660]it go
[00:05:53.660]for seven days we've said and
[00:05:55.180]chances are more than that so
[00:05:56.700]we're not going to put on any
[00:05:58.180]irrigation at all this week
[00:06:00.110]remember from last week I put
[00:06:01.690]on an inch and a half and the
[00:06:03.380]last
[00:06:03.720]half inch of that went on right
[00:06:05.140]before it rained at this point
[00:06:06.550]I wish I hadn't done that but
[00:06:07.900]again
[00:06:08.240]that was my best insight a week
[00:06:10.110]ago on Monday of what we needed
[00:06:11.980]to do last week and so you know
[00:06:13.880]we
[00:06:14.040]want to make sure the corn
[00:06:15.410]stays nice and wet so it gets a
[00:06:16.980]good yield but we don't want to
[00:06:18.800]put on
[00:06:19.060]any more than we absolutely
[00:06:20.560]have to now this has been the
[00:06:22.040]place where we've ended the
[00:06:23.640]the recording each week but for
[00:06:25.320]this next week we're going to
[00:06:26.690]start or starting today we're
[00:06:28.180]going to go and calculate the
[00:06:29.930]amount of water that's left in
[00:06:31.740]the profile and how much water
[00:06:33.680]the corn needs to mature
[00:06:34.930]because we need to start
[00:06:36.080]thinking about slowing down our
[00:06:37.700]irrigation
[00:06:38.400]starting here about the 10th of
[00:06:40.500]August and so if we move on
[00:06:41.760]down typically the the thing
[00:06:43.370]that we've
[00:06:43.920]had to the University of
[00:06:45.110]Nebraska for years and years is
[00:06:46.640]saying that later in the season
[00:06:48.170]we can
[00:06:48.540]use up 40 percent of that plant
[00:06:50.660]available water in four feet so
[00:06:52.560]if we do the same
[00:06:53.620]calculations that we just did
[00:06:55.300]but go to four feet and on down
[00:06:56.900]to 40 percent you can see there's
[00:06:58.710]5.62
[00:06:59.620]inches of water remaining and
[00:07:01.740]we've had a NebGuide out for a
[00:07:03.740]number of years that shows how
[00:07:06.720]to go about this calculation
[00:07:08.210]and so again about the August
[00:07:09.680]10th you can start into this
[00:07:11.460]and you
[00:07:12.340]can use R4 as a as the stage
[00:07:14.250]that we're at today and we
[00:07:15.860]could go to 40 percent of plant
[00:07:18.280]available
[00:07:18.660]water and so if we take a look
[00:07:20.430]at this we can see that it
[00:07:21.950]takes about 34 days
[00:07:23.600]for this variety to mature and
[00:07:25.440]about seven and a half inches
[00:07:27.110]of water to be used so if we
[00:07:28.640]divide
[00:07:29.040]if we add 34 days on to 8-11 we
[00:07:31.690]get about
[00:07:33.210]September 14th as it be about
[00:07:35.580]the approximate
[00:07:36.220]date and again we're just
[00:07:37.270]getting an idea ballpark here
[00:07:38.540]we're going to calculate it
[00:07:39.720]again next week
[00:07:40.600]but we can figure that this
[00:07:42.150]variety that this cornfield
[00:07:43.850]will be matured about the 14th
[00:07:46.230]maybe
[00:07:46.720]just a little longer than that
[00:07:48.900]but again if it's hot it'll
[00:07:50.810]mature quicker if it's cool it
[00:07:52.880]could be
[00:07:53.580]a little longer than that but
[00:07:53.650]again we're just getting an
[00:07:53.710]idea ballpark here we're going
[00:07:53.760]to calculate it again next week
[00:07:53.920]season we're a little bit
[00:07:55.180]behind on our where we're
[00:07:56.080]typically at and this certainly
[00:07:57.840]shows
[00:07:58.360]that maturity so remember we've
[00:08:00.650]had the 5.63 inches and we
[00:08:03.090]subtract off the seven and a
[00:08:04.960]half
[00:08:05.280]inches we can see that we still
[00:08:07.040]need to apply from rain and
[00:08:08.580]irrigation 1.87 inches of water
[00:08:11.160]to this
[00:08:11.560]field so we can see that we're
[00:08:13.230]getting pretty close to having
[00:08:15.150]enough on there but not quite
[00:08:16.880]enough yet but let's keep in
[00:08:19.080]mind that even though most
[00:08:21.000]years we think it doesn't rain
[00:08:23.290]on in August
[00:08:23.560]and September we certainly can
[00:08:25.900]see that on average we get
[00:08:27.790]about seven point seven inches
[00:08:30.160]of rain each
[00:08:30.940]week in August and about point
[00:08:32.840]you know between these two Clay
[00:08:34.810]County is about point six five
[00:08:36.700]during September so if we go
[00:08:38.940]ahead and add those in we can
[00:08:41.010]see that three weeks of August
[00:08:43.070]would be
[00:08:43.360]two point one inches of water
[00:08:45.100]we would receive from rain on
[00:08:46.830]average and again a may or it
[00:08:48.490]may
[00:08:48.800]not the way it's been over the
[00:08:50.780]weekend we certainly got a big
[00:08:53.140]start on things
[00:08:53.540]and then in September that
[00:08:55.300]point six five two weeks of
[00:08:57.060]that so if we add this all
[00:08:58.760]together we
[00:08:59.480]can see that if we got average
[00:09:00.990]rainfall we shouldn't have put
[00:09:02.630]on that inch and a half
[00:09:03.740]last week because it's showing
[00:09:05.490]that we'll have that much left
[00:09:07.060]over in the profile so I think
[00:09:09.200]it certainly shows that maybe
[00:09:10.640]we're done irrigating I'm going
[00:09:12.170]to calculate it each
[00:09:13.220]week because I don't you know
[00:09:15.150]ever want to predict out too
[00:09:17.000]far on these but we'll take
[00:09:18.820]a look at it next week and see
[00:09:20.350]where we're at but for now you
[00:09:21.960]know maybe here the this is
[00:09:23.520]the 11th of August but we may
[00:09:25.060]be done irrigating for the
[00:09:26.320]season but it's always nice to
[00:09:28.300]do the
[00:09:28.740]calculations and know kind of
[00:09:30.530]where we're at and then be able
[00:09:32.310]to to look at it again next
[00:09:33.960]week and see how things are
[00:09:35.580]playing out so for now this is
[00:09:37.180]Steve Melvin Extension educator
[00:09:39.250]with
[00:09:39.480]the University of Nebraska
[00:09:40.980]signing off with this week of
[00:09:42.300]irrigation scheduling update

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Weekly Irrigation Newsletter — Irrigation Scheduling Update for Aug. 11, 2025

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