Crop Water Sensing of the Future

University of Nebraska – Lincoln Author

08/31/2020 Added

47 Plays

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Dr. Kendall DeJonge covers the use of weather data, soil moisture monitoring and canopy cover to evaluate crop water use on corn under different irrigation treatments.
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[00:00:11.120]Hello, my name is Kendall Dion,
[00:00:12.560]I'm an agricultural engineer with the USDA ARS
[00:00:15.390]in Fort Collins, Colorado.
[00:00:17.000]Today we're at the limited irrigation research farm,
[00:00:19.680]right outside of Greeley Colorado,
[00:00:21.640]and today I'm gonna to tell you
[00:00:22.820]about some of the research experiments we're doing
[00:00:25.210]involving scheduling irrigation.
[00:00:26.866]under limited water.
[00:00:28.940]we are using
[00:00:29.773]an onsite weather station and canopy cover imaging
[00:00:34.030]and infrared thermometry
[00:00:35.500]to tell us when the crop needs irrigation.
[00:00:44.750]So, what we're trying to do here is explain the crop
[00:00:47.510]coefficient concept, where we have a reference ET
[00:00:51.540]and a crop coefficient.
[00:00:53.240]So basically, the reference ET
[00:00:55.900]is a function of the environment,
[00:00:57.360]so, as temperature goes up, as relative humidity goes down,
[00:01:01.660]some sunlight goes up, you're going to have more
[00:01:04.970]evapotranspiration, more water use
[00:01:07.290]same if you get more wind,
[00:01:09.440]also we're going to characterize, the crop itself.
[00:01:12.470]So the more canopy we have,
[00:01:13.890]the more evapotranspiration we have.
[00:01:16.020]So basically, this equation separates these two ideas
[00:01:20.630]between the environment and the plant status.
[00:01:23.690]And so you get this day to day variability,
[00:01:26.270]and you multiply that by a crop coefficient,
[00:01:28.110]and that's what you get with overall 18.
[00:01:31.870]Now in Colorado, for example, they have the CoAgMET stations
[00:01:36.200]that can give you an estimate of full
[00:01:37.950]year getting crop ET, which is really nice
[00:01:41.370]and this expanded version of the equation,
[00:01:44.630]we're also taking into account stress by the Ks value,
[00:01:49.240]and so we're trying to characterize basically everything
[00:01:51.940]that's within this equation.
[00:01:53.890]One thing that's nice about CoAgMET,
[00:01:55.527]is that it can give you a full year get crop ET,
[00:01:58.950]but if you have less than that, we need different tools
[00:02:02.523]to help inform that.
[00:02:04.731]Only about full irrigation,
[00:02:06.430]so, we have full irrigation and limited irrigation,
[00:02:09.600]side by side here, in an example,
[00:02:12.830]what we're trying to do is use a weather station
[00:02:15.360]to quantify the ETr which is a reference ET.
[00:02:20.700]The canopy cover identifies what Kcb is,
[00:02:23.870]they're a function of each other,
[00:02:25.360]or we're using canopy temperature
[00:02:27.010]to quantify the Ks, which is a stress factor.
[00:02:30.420]And then this water balance factor,
[00:02:31.890]we can usually make an estimate as typical increase.
[00:02:35.780]And so, just to give an idea of what happens with the crop
[00:02:38.590]between fully in depth study irrigated,
[00:02:41.100]this is a time lapse over 15 minutes.
[00:02:43.590]You can see in the deficit irrigated,
[00:02:45.750]the leaves really shrink up during the day,
[00:02:49.395]and transpire less.
[00:02:51.200]So they have less canopy cover
[00:02:52.970]as we're seeing by the graph going across here.
[00:02:55.450]And, they also, consequently will get warmer
[00:02:59.050]because they're transpiring less.
[00:03:00.400]Now, if we're given the irrigation,
[00:03:01.700]for example, what happens?
[00:03:04.230]This speeds up a little bit, but you see this decrease,
[00:03:07.817]these dips and deficit irrigation canopy cover
[00:03:11.020]become less and less.
[00:03:12.520]So we're trying to understand what time of day is best
[00:03:15.200]to try to quantify this.
[00:03:16.990]Typically we think it's in the morning,
[00:03:18.880]because it's supposed to represent the non-stress crop,
[00:03:21.610]and then we use a canopy temperature
[00:03:24.340]later to quantify that stress.
[00:03:26.840]This is a closer look at a single day,
[00:03:29.650]and you can really see how the deficit irrigated
[00:03:32.890]canopy cover decreases.
[00:03:34.970]So that fully irrigated will represent the Kcb,
[00:03:37.973]of this crop coefficient or full canopy cover.
[00:03:42.290]That top of that line is full canopy cover
[00:03:45.190]for the deficit irrigated crop.
[00:03:46.890]So it's a little bit lower, but what we're really getting
[00:03:49.810]in the middle here, is kind of an integration
[00:03:52.050]of your base of crop coefficient
[00:03:54.250]and your stress coefficient,
[00:03:55.370]which is why we need a separate way to quantify that stress.
[00:03:59.520]And so we use a continuous infrared thermometer (IRT)
[00:04:03.420]and you can see the limited irrigation will get warmer
[00:04:06.050]full irrigations cooler,
[00:04:07.700]and so we're taking measurements of that through the day,
[00:04:10.370]which we'll show you.
[00:04:12.560]And, just to close with the slides, these are some tools
[00:04:16.830]that are becoming more readily available.
[00:04:19.510]There's a lot of thermal imaging solutions
[00:04:22.320]out there that can even be as simple
[00:04:23.700]as connected to your phone.
[00:04:25.350]So we're hoping that at some point,
[00:04:28.110]these will be integrated so that they can help guide
[00:04:31.760]irrigation and management decisions.
[00:04:34.440]We'll take you back to the field.
[00:04:38.150]For one major part of our experiment,
[00:04:40.170]we need to quantify reference ET,
[00:04:43.040]and this is one of the many weather stations
[00:04:44.705]that's available in the State of Colorado
[00:04:46.630]to do exactly that.
[00:04:48.750]As part of the CoAgMET network of stations,
[00:04:51.030]there's over 80 stations throughout the State of Colorado.
[00:04:54.690]Most States have stations very similar to this,
[00:04:58.110]basically it has all the ingredients that you need
[00:04:59.960]to measure reference ET, or more or less how much water
[00:05:03.980]is being used from this graph area.
[00:05:06.690]So you have everything from wind,
[00:05:08.900]incoming solar radiation, temperature, and humidity
[00:05:12.010]and we also have a precipitation gauge
[00:05:14.240]here to measure the precept.
[00:05:16.160]And so these measure's on a continuous basis
[00:05:18.960]and it gives us an idea on what the changes
[00:05:21.219]are in the atmospheric demand and the evaporative demand.
[00:05:26.780]And we use this, as kind of a basis for a reference ET
[00:05:31.120]and later on, multiply that by a crop coefficient,
[00:05:33.656]which is more related to what the crop does itself.
[00:05:40.780]Hi, I'm Katie Aspell ,
[00:05:42.600]I'm gonna be a senior at CSU next year
[00:05:45.710]in Civil Engineering,
[00:05:47.380]and out of the farm, I do a lot
[00:05:49.230]of data collection and processing.
[00:05:51.552]And what I'm gonna show you here,
[00:05:55.220]is how we do our canopy cover data.
[00:05:58.270]And so I have this old light boom
[00:06:00.510]that we've converted into a stand for an iPod
[00:06:04.130]that just will take pictures,
[00:06:05.710]and you simply, hold it over the canopy and take a picture.
[00:06:12.520]I use a remote shutter.
[00:06:14.670]And then, in order to process that color image of the canopy
[00:06:20.680]and figure out canopy cover, I use an app called Canopeo,
[00:06:25.260]which you can use it online,
[00:06:27.870]or I also have it on the iPod here,
[00:06:31.640]and you simply open up the Canopeo app,
[00:06:36.480]and upload the photo that I took there of the canopy cover.
[00:06:45.750]And Canopeo is able,
[00:06:48.018]to convert that into a percent canopy cover.
[00:06:51.070]For example, the picture that I just took
[00:06:53.330]show the canopy of about 73.6%.
[00:06:56.697]And we use that fractional canopy cover
[00:06:59.210]to quantify transpiration and crop stress.
[00:07:04.460]So as Katie showed earlier,
[00:07:05.700]we use the canopy cover to characterize
[00:07:09.420]how much light interception there can be.
[00:07:11.600]So the more canopy you have,
[00:07:13.860]the more of upper transpiration, more transpiration
[00:07:16.230]out of the crop, you will have.
[00:07:18.050]But of course, if you're irrigating things
[00:07:20.410]under limited irrigation, or you're not under
[00:07:22.790]maximum irrigation, sometimes you have water stress.
[00:07:26.120]And what happens in the case of water stress,
[00:07:28.700]you'll have your leaves curl up and they transpire less
[00:07:32.200]and consequently, they get hot.
[00:07:34.260]And so what we do in the field,
[00:07:36.220]is we're measuring the temperature of the crops
[00:07:38.580]using infrared thermometers.
[00:07:41.100]So anytime that crop gets warmer, of course it gets warm
[00:07:45.400]throughout the middle of the day,
[00:07:47.050]but if it gets warmer than our highest irrigated crops,
[00:07:49.880]for example, then we can use that to estimate
[00:07:53.180]what the reduction of transpiration is.
[00:07:55.500]So we're working on new methods
[00:07:56.960]to try to quantify that reduction in transpiration,
[00:08:00.252]which can also help us with irrigation scheduling
[00:08:03.160]because it tells us how much irrigation
[00:08:04.800]we actually need the next time.
[00:08:07.170]We're hoping that this technology,
[00:08:09.490]could be scaled up to, for example,
[00:08:12.520]UAVs or even satellite imagery,
[00:08:14.970]so, at some point
[00:08:16.380]could be able to look at him an entire field
[00:08:18.770]and inform, for example, a variable rate irrigation pivot,
[00:08:22.860]on how much irrigation needs to be applied
[00:08:26.530]at different spaces along that field.
[00:08:30.420]The experiment that we're doing this summer,
[00:08:32.450]is on corn, as you can see,
[00:08:34.820]and we have several different plots
[00:08:37.630]and replications of different levels of irrigation
[00:08:41.440]that we're trying to explore.
[00:08:42.600]So some have small deficit, some have high deficit,
[00:08:46.200]some are using different methods
[00:08:47.860]to determine when and how much you're getting.

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Crop Water Sensing of the Future

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