Weekly Irrigation Newsletter - Irrigation Scheduling Update for July 21, 2025

Steve Melvin Author

07/22/2025 Added

15 Plays

Description

Nebraska Extension Educator Steve Melvin demonstrates how to apply the irrigation scheduling method outlined in Nebraska Extension NebGuide EC3036, Irrigation Scheduling Strategies When Using Soil Water Data, in a corn field at the South Central Agricultural Lab near Clay Center, Nebraska. This is the first video in a new series on irrigation scheduling featured in the CropWatch Weekly Irrigation Newsletter.

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[00:00:00.000]Hi this is Steve Melvin
[00:00:08.160]Extension Educator with the
[00:00:09.400]University of Nebraska
[00:00:10.010]Extension and today
[00:00:11.580]I would like to tell you about
[00:00:13.190]an irrigation scheduling
[00:00:15.210]procedure that is simple, quick,
[00:00:16.680]and accurate. If you'd like to
[00:00:19.190]read more about in details of
[00:00:21.440]the procedure you can look at
[00:00:23.510]EC
[00:00:23.880]3036 or if you'd prefer to take
[00:00:26.470]a look at a video series on it
[00:00:28.280]you can do that as well.
[00:00:29.520]The references are in this week's
[00:00:31.660]CropWatch irrigation
[00:00:33.030]newsletter. The place we're
[00:00:37.800]going to
[00:00:38.040]take a look today is an example
[00:00:40.200]from a corn field in south-central
[00:00:42.700]Nebraska at the South Central
[00:00:44.760]Ag
[00:00:45.300]Lab near Clay Center. The corn
[00:00:47.790]was planted on April 22nd. It's
[00:00:50.480]117 day corn. The system can
[00:00:53.280]apply about
[00:00:53.900]two inches per week. If you're
[00:00:55.570]not familiar with the Clay
[00:00:56.840]Center area they get about 28
[00:00:58.510]inches of
[00:00:59.040]rainfall per year. The corn is
[00:01:01.270]in the R1 stage and the
[00:01:03.240]equipment we're using is watermark
[00:01:05.100]sensors
[00:01:05.640]connected to Irrometer data loggers.
[00:01:07.880]Okay to start the procedure we
[00:01:11.780]need to go out and get
[00:01:13.320]the numbers and in this
[00:01:14.760]particular situation you can
[00:01:16.650]see where we've got a data logger
[00:01:18.780]right along
[00:01:19.200]the pivot road so we can take a
[00:01:20.680]look at the numbers as we're
[00:01:22.020]driving into the field and
[00:01:23.400]this procedure is intended to
[00:01:25.260]be simple and quick enough that
[00:01:26.970]we can just stop look at the
[00:01:28.550]data
[00:01:28.560]and go in and make our decision
[00:01:30.320]what we want to do. Also many
[00:01:32.070]systems have the ability to
[00:01:34.060]send
[00:01:34.440]you the data to your smartphone
[00:01:36.710]or to put it onto your desktop.
[00:01:39.050]Of course those with the telemetry
[00:01:41.340]cost just a little bit more but
[00:01:43.010]sometimes it's very convenient
[00:01:44.810]to have the data show up.
[00:01:46.140]The system that we're using is
[00:01:49.410]about two inches per week that
[00:01:52.630]can apply so just give
[00:01:53.700]you a perspective that would be
[00:01:55.310]like a 715 gallon a minute
[00:01:57.030]pivot on
[00:01:58.080]230 acres running seven days a
[00:02:00.020]week.
[00:02:00.480]The corn is currently at the R1
[00:02:04.390]stage but we'll use the three
[00:02:07.640]foot soil rooting zone because
[00:02:11.340]of
[00:02:11.700]the fact that I want to be just
[00:02:13.310]a little bit conservative and
[00:02:14.990]also we'll stay with the three
[00:02:16.800]feet.
[00:02:16.980]The water use at this point on
[00:02:20.240]average is about 0.28 inches
[00:02:22.940]per day or 1.96 inches per week.
[00:02:25.960]Sometimes this number can be a
[00:02:27.480]little
[00:02:27.600]bit higher than that or a
[00:02:28.830]little bit lower depending on
[00:02:30.370]the weather and this week is
[00:02:31.920]going
[00:02:32.100]to be at least probably that
[00:02:33.420]high because it's supposed to
[00:02:34.890]be pretty hot and dry. You look
[00:02:37.080]at
[00:02:37.200]this and say from silking till
[00:02:38.940]now it's dropped off just a
[00:02:40.480]little bit and on average that
[00:02:42.220]tends
[00:02:42.600]to be true. Keep in mind that
[00:02:44.520]we've already here on towards
[00:02:46.550]the end of July have lost about
[00:02:48.940]16 17
[00:02:49.860]minutes of daylight and we're
[00:02:51.440]losing about two minutes every
[00:02:53.100]day so the days are getting
[00:02:54.490]shorter
[00:02:55.020]and that's part of the what
[00:02:56.400]goes into how much water the
[00:02:57.850]crop is going to use.
[00:02:59.040]So let's take a look at the
[00:03:01.790]data and put it onto this chart
[00:03:04.490]and this is available if you
[00:03:07.140]would like
[00:03:07.440]to have some of these charts
[00:03:08.800]they're for a given soil type
[00:03:10.050]this one happens to be the soil
[00:03:11.550]type
[00:03:11.760]that's down there a silt loam a
[00:03:13.380]good high water holding
[00:03:14.680]capacity you can see we pulled
[00:03:16.440]our numbers
[00:03:16.860]together the corns at the R1
[00:03:18.430]stage two inches of irrigation
[00:03:20.060]capacity three foot root zone
[00:03:21.720]and the
[00:03:22.560]water use that we talked about
[00:03:24.310]and these are the data that we
[00:03:25.990]got from our watermark sensors
[00:03:28.130]so if
[00:03:28.440]we take and put these over here
[00:03:29.810]we won't use the fourth foot
[00:03:31.060]just yet we'll wait a little
[00:03:32.460]bit later
[00:03:32.820]in the season to use it so we've
[00:03:35.320]got 25 93 we'll use 90 and the
[00:03:38.820]83 we'll use 80 and you can see
[00:03:42.180]that the colors on this relate
[00:03:44.110]to this is field capacity right
[00:03:45.910]here and so anything that's
[00:03:47.570]above
[00:03:47.880]field capacity in other words
[00:03:49.640]the soil is wetter than field
[00:03:51.320]capacity.
[00:03:52.560]We have marked in blue and we've
[00:03:54.380]got an area in here that we'd
[00:03:56.000]like to leave just a little bit
[00:03:57.600]of
[00:03:57.780]room to soak up a rain if we
[00:03:59.070]happen to get one and this time
[00:04:00.700]of year we do frequently get
[00:04:02.240]some rain
[00:04:02.700]and then down here's our
[00:04:03.950]desired water zone this green
[00:04:05.530]area and that's where our other
[00:04:07.260]two sensors
[00:04:07.920]are at and of course if we got
[00:04:09.210]down in this range we'd
[00:04:10.290]certainly want to get the
[00:04:11.490]irrigation keep it
[00:04:12.900]running because we're getting
[00:04:14.450]behind so right now if we take
[00:04:15.780]a look at it just using these
[00:04:17.220]color
[00:04:17.400]bars we can say that well the
[00:04:18.840]top foot's pretty wet that's
[00:04:20.330]great down here is kind of
[00:04:21.630]where we
[00:04:22.260]want to be.
[00:04:22.560]Knowing that we can put on two
[00:04:24.340]inches per week and we're
[00:04:25.900]probably going to use two
[00:04:27.180]inches it's
[00:04:27.720]a really critical time we'd
[00:04:28.980]probably stop right here and
[00:04:30.290]say yep let's just keep the
[00:04:31.560]pivot running
[00:04:32.760]all week but there's a lot more
[00:04:35.040]data that we can gain out of
[00:04:37.000]this by taking a look at the
[00:04:38.960]numbers
[00:04:39.320]in these other two columns this
[00:04:42.190]is a chart of the watermark
[00:04:44.610]readings since they were
[00:04:47.040]installed you
[00:04:48.320]can see a couple of weeks ago
[00:04:49.700]here if the top foot got pretty
[00:04:51.200]dry but the
[00:04:52.560]bottom or the second and third
[00:04:54.310]foot were in good shape and so
[00:04:55.990]the crop wasn't stressed for
[00:04:57.540]water
[00:04:57.760]then we got a little bit of
[00:04:59.230]rain we put on four tenths of
[00:05:00.840]an inch with some nitrogen
[00:05:02.480]application
[00:05:03.120]and so you can see it brought
[00:05:04.660]things back up a little bit and
[00:05:06.410]this past week we put on
[00:05:08.080]about an inch of irrigation
[00:05:09.280]water so you can kind of see
[00:05:10.430]where things are at today we're
[00:05:11.760]the description of what we just
[00:05:13.640]showed a little bit ago and
[00:05:15.260]this is a ongoing series and we'll
[00:05:17.360]be updating this chart each
[00:05:18.690]week and you can kind of see
[00:05:19.940]the decisions that we make and
[00:05:21.520]irrigation
[00:05:22.560]systems that we put on and how
[00:05:24.140]the soil water levels respond
[00:05:25.780]to that
[00:05:26.240]now let's take a look at this
[00:05:28.780]second column of numbers you
[00:05:30.970]can see it's a percent
[00:05:32.640]we look at field capacity you
[00:05:34.410]see it's a hundred percent of
[00:05:36.060]plant available water
[00:05:37.520]is right at field capacity if
[00:05:39.210]we're wetter than that it's
[00:05:40.820]more than a hundred percent
[00:05:42.560]as we use that water out it
[00:05:44.440]goes from a hundred down to 70
[00:05:46.740]down to 50 down to 40 is the
[00:05:48.720]bottom end
[00:05:49.120]of the chart if we take a look
[00:05:50.420]at where our numbers are at we
[00:05:51.780]can see that we're about 105
[00:05:53.600]and so if we put that number
[00:05:55.380]over here and then 62 and 65
[00:05:57.910]and we add those three numbers
[00:06:01.360]together
[00:06:02.080]and to get an average divide by
[00:06:04.010]three we can see that we have a
[00:06:05.630]77 percent of plant available
[00:06:08.000]water
[00:06:08.480]so again that's a pretty useful
[00:06:10.080]number to have and it tells us
[00:06:11.560]that yeah we're in a fine shape
[00:06:13.280]today
[00:06:13.600]but we're using a lot of water
[00:06:14.890]it's really critical so so we're
[00:06:16.370]probably here still going to
[00:06:17.760]stop and say we want to irrigate
[00:06:19.460]but let's take a look at the
[00:06:20.990]information we can glean out of
[00:06:22.640]this
[00:06:22.800]third column that's really
[00:06:24.210]where the the more accurate
[00:06:25.610]comes in and gives us a full
[00:06:27.040]confidence
[00:06:27.600]for making good decisions so if
[00:06:30.240]we take a look at the 77
[00:06:32.540]percent and come over here on
[00:06:34.880]the chart
[00:06:35.600]we can see that on average each
[00:06:37.850]of the three feet of soil and
[00:06:39.780]this is a
[00:06:40.480]number that is inches per foot
[00:06:42.600]of soil so at field capacity
[00:06:44.310]this is a number above or below
[00:06:46.400]field capacity and so as we're
[00:06:48.260]going above field capacity if
[00:06:50.120]we had a 15 reading that would
[00:06:52.140]mean
[00:06:52.320]that foot of soil would have
[00:06:54.280]one half inch of water more in
[00:06:56.330]it than field capacity if we
[00:06:59.360]came
[00:06:59.680]down to 77 that means that that
[00:07:01.980]foot of soil would have one
[00:07:03.630]half inch less water than field
[00:07:05.760]capacity
[00:07:06.320]or in other words we'd have to
[00:07:07.790]add a half inch of irrigation
[00:07:09.290]to bring it back up to field
[00:07:10.800]capacity
[00:07:11.360]so it's a pretty useful number
[00:07:12.670]pretty simple and
[00:07:13.470]straightforward to take a look
[00:07:14.900]at and where we know
[00:07:16.400]we're wanting to think about
[00:07:18.160]not going above field capacity
[00:07:20.050]we want to know how much water
[00:07:21.760]could we apply with irrigation
[00:07:23.810]and rain to stay and still stay
[00:07:25.800]below field capacity so right
[00:07:27.600]now
[00:07:27.840]we're setting at 77 so it'd be
[00:07:31.050]an average of 0.15 or 5 1
[00:07:34.810]inches below so if we take a
[00:07:37.280]look over here
[00:07:38.000]we multiply it by our three
[00:07:39.330]foot root zone we could see
[00:07:40.650]that we're down 1.53 inches or
[00:07:43.760]about
[00:07:43.920]an inch and a half below field
[00:07:45.700]capacity
[00:07:46.400]meaning that we could apply an
[00:07:48.640]inch and a half of water with
[00:07:50.720]irrigation and rainfall and we
[00:07:53.120]would
[00:07:53.280]just be at field capacity so we
[00:07:54.950]know we've got some room to
[00:07:56.420]apply water which is we
[00:07:57.700]certainly
[00:07:58.400]don't want to apply irrigation
[00:07:59.810]water if the soil can't hold it
[00:08:01.180]and even if we had a center
[00:08:02.400]pivot
[00:08:02.640]and we wanted to put an inch on
[00:08:04.220]we would still have about a
[00:08:05.660]half inch of water a room left
[00:08:07.360]to
[00:08:07.520]store a half inch of rain we
[00:08:09.020]look at then how much water is
[00:08:11.800]left in the profile we can do
[00:08:14.560]the same
[00:08:14.960]thing using our 77 it's about a
[00:08:17.160]half inch below so we put that
[00:08:19.120]number over here and if we we
[00:08:21.600]know
[00:08:21.760]we can go down about 50 percent
[00:08:23.960]of plant available water and
[00:08:25.800]not damage the crop from water
[00:08:27.680]stress
[00:08:28.240]so we move that over here and
[00:08:30.190]and when we subtract two
[00:08:31.950]negative numbers we get a
[00:08:33.930]positive in other
[00:08:34.560]words the amount of water that's
[00:08:36.000]left in the soil between these
[00:08:37.340]two and again this is an
[00:08:38.480]average per
[00:08:39.040]foot so we get point six three
[00:08:40.840]inches per foot times our three
[00:08:42.660]foot root zone we can see that
[00:08:44.480]we
[00:08:44.960]use another 1.89 inches of
[00:08:47.590]water before we would expect to
[00:08:50.010]see stress on our crop so that
[00:08:51.930]gives us
[00:08:52.320]a pretty good idea that we're
[00:08:53.810]not you know in bad shape we've
[00:08:55.530]got some room we can put some
[00:08:56.960]water on
[00:08:58.000]and we can wait a day or so if
[00:08:59.440]we want but again it's a really
[00:09:01.100]critical time of year
[00:09:02.400]so if we think about it on the
[00:09:04.010]amount of water we're using
[00:09:05.620]this 0.28 and again this week
[00:09:07.850]may be
[00:09:08.160]a little higher than that but
[00:09:09.710]just to give us a feel we see
[00:09:11.130]that there's enough water in
[00:09:12.720]our
[00:09:12.880]profile for about 6.75 days or
[00:09:15.560]i'd probably round it down to
[00:09:17.510]six days and before we would be
[00:09:19.680]stressing the crop to lower
[00:09:21.160]yields and so we're not in bad
[00:09:22.700]shape but we're really at this
[00:09:24.240]really
[00:09:24.400]critical high period of water
[00:09:26.730]use time and and the crop would
[00:09:29.060]suffer a lot of yield loss
[00:09:30.840]right now
[00:09:31.680]if we ended up stressing it so
[00:09:34.160]if we come over here and wrap
[00:09:36.970]things up here you can see that
[00:09:39.440]the plan for this week we know
[00:09:40.810]we can put on two inches the
[00:09:42.080]crop's going to
[00:09:42.800]use it probably at least two
[00:09:44.180]inches this week maybe it's
[00:09:45.810]going to rain so we might not
[00:09:47.520]have
[00:09:47.680]to put it all on but we know we
[00:09:49.480]could put on one and a half
[00:09:51.110]inches and we know we've still
[00:09:53.280]got six days supply of water
[00:09:55.280]but this time of year with a
[00:09:56.880]high crop water use and the
[00:09:58.720]really
[00:09:59.040]sensitivity of crop to drought
[00:10:01.570]stress my plan this week is to
[00:10:03.050]apply two inches of water from
[00:10:05.120]rain
[00:10:05.680]and irrigation and i hope it
[00:10:06.970]rains this week and we won't
[00:10:08.250]have to pump two inches of
[00:10:09.520]water
[00:10:09.760]but if it doesn't we're going
[00:10:11.060]to plan to put on two inches of
[00:10:12.370]water
[00:10:12.720]so we'll wrap up there for
[00:10:15.030]today you can see this is a
[00:10:16.430]very quick and easy thing to do
[00:10:18.360]you can go out
[00:10:18.880]and make these decisions out in
[00:10:21.220]the field or at your office or
[00:10:23.400]with your cell phone drinking a
[00:10:25.360]cup
[00:10:25.520]of coffee and probably five
[00:10:26.960]minutes or less so it's a very
[00:10:28.500]quick accurate way to make good
[00:10:30.160]decisions
[00:10:31.200]if we've got the watermark data
[00:10:33.050]so that'll wrap it up for today
[00:10:34.870]this has been steve melvin
[00:10:36.610]extension
[00:10:37.120]educator with the university of
[00:10:38.740]nebraska extension we'll see
[00:10:40.240]you next week with the next
[00:10:41.560]update
[00:10:42.720]Subtitles by the Amara.org
[00:10:44.880]community

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Weekly Irrigation Newsletter - Irrigation Scheduling Update for July 21, 2025

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