What’s Light Got to Do With It? Exploring the Role of Plant-reflected Light in Crop Yield Loss and Weed Management

ANDREW KNISS, department head and professor of weed science, Department of Plant Sciences, University of Wyoming, Laramie Author

09/23/2022 Added

27 Plays

Description

Early-emerging weeds negatively affect crop yield potential, but the mechanisms by which weeds reduce crop yield are not fully understood. Yield loss is typically attributed to resource depletion by weeds. In this presentation, Kniss will summarize several years of research on shade avoidance responses in sugarbeet and the subsequent impacts on yield.

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[00:00:00.810]The following presentation
[00:00:02.250]is part of the Agronomy and Horticulture Seminar Series
[00:00:05.820]at the University of Nebraska, Lincoln.
[00:00:08.640]Thanks, everyone for being here.
[00:00:09.660]I'd like to welcome Dr. Andrew Kniss.
[00:00:12.720]Dr. Andrew Kniss grew up on a corn,
[00:00:17.280]dry bean, and sugarbeet farm in Bayard, Wyoming,
[00:00:21.000]sorry, Nebraska.
[00:00:21.960]Sorry, I'm getting confused now, Nebraska,
[00:00:25.590]and that is about (indistinct) miles east of Scottsbluff.
[00:00:29.790]It's the closest town to the Chimney Rock
[00:00:36.090]if you're familiar with that going out there.
[00:00:39.810]Andrew went and got his bachelor's degree
[00:00:41.640]from the University of Wyoming
[00:00:42.870]that's why I just got that mixed up.
[00:00:45.390]And then went on to get a master's degree
[00:00:47.760]under Bob Wilson with the University of Nebraska.
[00:00:51.090]So he graduated from here in 2003,
[00:00:54.600]and then went on to get a PhD at the University of Wyoming.
[00:00:57.090]He's currently a professor, weed scientist
[00:00:59.730]and the Department Head
[00:01:02.280]of Plant Science at the University of Wyoming.
[00:01:04.590]And I'll let him take over now.
[00:01:10.530]I'm impressed Nevin got all the years right
[00:01:15.060]'cause Nevin was one of my very first graduate students
[00:01:18.270]and I have no idea what year he graduated.
[00:01:22.050]So kudos on doing your homework, Dr. Lawrence.
[00:01:26.790]So I've also learned while we get slides brought up here.
[00:01:31.860]If there's any younger folk thinking about
[00:01:35.970]trying to get back at their advisors
[00:01:39.060]for all of the misery they put 'em through
[00:01:40.920]during their graduate education,
[00:01:42.300]one of the best ways to do that is become a collaborator
[00:01:45.240]with your advisor after you start in your faculty position.
[00:01:48.300]Because now, Dr. Lawrence comes up
[00:01:50.070]with all these new fangled, crazy experimental designs
[00:01:53.010]that I now have to implement as a collaborator
[00:01:55.920]on some of his projects.
[00:01:58.020]All right, so I am actually really kind of excited
[00:02:01.080]to talk to you today.
[00:02:01.913]So I'm gonna talk about a line of research
[00:02:05.610]that I've been working on for quite a while.
[00:02:09.630]Shortly after Nevin left actually,
[00:02:12.240]is when we kind of started into this.
[00:02:16.320]And it's about light and specifically reflected light.
[00:02:23.130]And so the title of the talk,
[00:02:25.980]what's light got to do with it?
[00:02:28.530]Hopefully I will at least give
[00:02:30.840]some indication of what that is.
[00:02:33.330]So I'm gonna talk specifically about crop weed interactions
[00:02:36.947]'cause I'm a weed scientist by training.
[00:02:40.350]I like to really focus in on kind of how weeds and crops
[00:02:43.740]are doing their thing in the field together,
[00:02:46.800]how they interact.
[00:02:48.240]I do have to give credit to the title though.
[00:02:54.360]Tina helped me out with this,
[00:02:56.400]what's light got to do, got to do with it?
[00:03:00.090]So, I have to give her credit on that.
[00:03:02.490]So, more seriously,
[00:03:05.340]this is a figure that you would see
[00:03:07.680]if you opened almost any weed science textbook, okay?
[00:03:11.940]Where you will have on the y-axis, crop yield,
[00:03:16.290]and on the x-axis, the duration of weed competition.
[00:03:19.860]So how long weeds and crops are actually
[00:03:22.770]in the same field together.
[00:03:24.810]Basically, this is the reason why we control weeds, right?
[00:03:28.680]So the longer the weeds are in that field,
[00:03:32.250]the lower your crop yield is going to be over time.
[00:03:35.130]So, not groundbreaking stuff here at all.
[00:03:37.680]This is just really kind of basics.
[00:03:39.840]So who wants to tell me,
[00:03:42.060]thinking back to your weed science class, why this happens?
[00:03:46.260]Why do we lose yield
[00:03:47.730]as the weed stay in the field longer and longer?
[00:03:51.480]It's not a trick question.
[00:03:55.230]What's that?
[00:03:58.770]There you go, competition.
[00:04:00.510]Nutrients, water, and light, exactly on the slide, see?
[00:04:05.340]It is not a trick question.
[00:04:07.080]This is exactly what happens.
[00:04:10.050]So plants are competing, right?
[00:04:12.660]There's limited resources within any given.
[00:04:14.910]This is basics of crop-weed ecology.
[00:04:19.080]In any given area of land,
[00:04:20.040]there's only so much nitrogen to go around.
[00:04:21.570]There's only so much light to go around.
[00:04:22.950]Light is actually one of the more limiting resources
[00:04:26.460]in crop canopies, right?
[00:04:28.170]Okay, so what we see then is at this point,
[00:04:32.730]at some point you start seeing
[00:04:34.710]the crop yield start decreasing from that horizontal,
[00:04:39.180]because at some point
[00:04:40.560]those weeds have used enough of that light or nitrogen,
[00:04:44.850]or phosphorus, or water,
[00:04:46.410]whatever the most limiting factor is.
[00:04:48.540]At some point, the weeds start using enough of that
[00:04:50.553]that the crop doesn't have enough
[00:04:52.860]to produce its full yield potential, right?
[00:04:58.470]Okay, what if I told you that everything you have been told
[00:05:03.630]up to this point about weed-crop competition was a lie?
[00:05:08.310]It's not, it's mostly true.
[00:05:10.680]But I'm gonna try to spend the next little bit
[00:05:14.520]basically making the case that what I just described,
[00:05:18.540]isn't the whole story.
[00:05:20.130]And not only is it not the whole story, in some cases,
[00:05:24.030]what we just talked about
[00:05:25.410]might not even be a majority of the story,
[00:05:28.620]there might be more important things going on.
[00:05:32.160]And so I want to acknowledge that I'm not the first person
[00:05:35.580]to do this sort of work.
[00:05:37.950]What I'm gonna be talking about mostly today,
[00:05:40.080]is a phenomena called shade avoidance.
[00:05:44.160]It's basically how plants respond
[00:05:46.830]when they sense that there are other plants
[00:05:48.960]in the environment to avoid getting shaded out.
[00:05:52.650]So that body of work actually goes back to,
[00:05:54.900]I think at least the early 1980s.
[00:05:58.470]The first person that I'm aware of that started applying
[00:06:01.830]shade avoidance research to crop-weed interactions,
[00:06:04.620]is actually Dr. Clarence Swanton
[00:06:06.600]from the University of Guelph.
[00:06:09.150]There may have been someone before that
[00:06:10.590]but that's the first that I'm aware of.
[00:06:12.750]And this is the first paper that I read that kind of applied
[00:06:16.980]some of these concepts to crop-weed interactions
[00:06:20.160]written by Dr. Eric Page who I think is now with Ag Canada.
[00:06:26.640]And so they actually were talking about,
[00:06:28.200]does the shade avoidance response
[00:06:29.460]contribute to basically the time
[00:06:31.950]at which weeds are problematic in crop canopies?
[00:06:36.000]And just to give you an example,
[00:06:38.070]a statement directly from that early physiological changes
[00:06:41.580]triggered by leaf reflected light, contribute to the onset
[00:06:45.810]of critical time of weed removal.
[00:06:47.970]So basically that reflected light
[00:06:50.460]is a contributor to when we need to control weeds
[00:06:53.310]before we start seeing that crop yield loss.
[00:06:56.670]So that's kind of what got me interested in this.
[00:06:59.520]And so shade avoidance might be super familiar
[00:07:02.880]to those of you who are very plant physiological minded.
[00:07:06.840]I'm gonna take a step back
[00:07:08.187]and just kinda make sure everybody's on the same page.
[00:07:10.080]I'm gonna explain this in a way
[00:07:12.150]that even the soil scientists among us can understand, okay?
[00:07:15.690]Just kidding, I have nothing against soil scientists.
[00:07:18.420]So reflected light.
[00:07:19.770]Okay, what am I talking when I say reflected light quality?
[00:07:22.140]When we talk about light quality, we're usually talking
[00:07:26.880]about the photosynthetic wavelengths, right?
[00:07:29.310]Red and blue primarily.
[00:07:32.490]And so if you look at what happens when sunlight,
[00:07:35.040]having all the wavelengths of light bounces off a leaf,
[00:07:38.990]what actually bounces off?
[00:07:40.470]Which wavelength is reflected most?
[00:07:43.067]Green. Green, right.
[00:07:44.370]That's why we see it as green.
[00:07:46.170]So this is actually a reflected spectrum
[00:07:49.140]from a sugarbeet plant that we took
[00:07:51.300]and you can see that major peak
[00:07:52.890]right in that green wavelength.
[00:07:55.470]So this is the visible spectrum.
[00:07:57.390]So this is not all of what's going on.
[00:08:00.120]So there's actually also outside the visible spectrum,
[00:08:04.440]other wavelengths that are being reflected,
[00:08:06.570]absorbed, all the same things.
[00:08:08.760]And if you kind of extend that,
[00:08:10.800]what you see is this other peak in the far-red spectrum.
[00:08:16.500]Okay, so remote sensing folks will tell you
[00:08:18.540]that that's where a lot of information exists
[00:08:21.120]on how well watered the crop is, for example.
[00:08:27.450]So plants are actually really good.
[00:08:30.090]They've evolved the ability to basically change their growth
[00:08:34.440]in response to this red to far-red ratio.
[00:08:37.890]So it isn't just the absolute amount of red light,
[00:08:40.860]it's not the absolute amount of far-red light.
[00:08:43.020]It's the ratio of those two.
[00:08:47.460]So, the red to far-red ratio, you might say
[00:08:52.500]that this light drives the phytochrome reactions, see?
[00:08:59.100]Back to Tina Turner.
[00:09:01.530]And those phytochrome reactions are really important
[00:09:04.080]for a lot of things in plants.
[00:09:05.730]So if you talk about trying to get plants to flower,
[00:09:10.140]it's not only day length,
[00:09:11.250]it's also this red to far-red ratio.
[00:09:13.500]Seed germination is controlled by this red to far-red ratio.
[00:09:16.680]There's a lot of things that are controlled within the plant
[00:09:19.680]in this red to far-red ratio
[00:09:21.930]or due to this red to far-red ratio,
[00:09:23.460]including the shade avoidance responses.
[00:09:25.770]And so that's what we're gonna talk about.
[00:09:27.390]So this figure, I blatantly ripped off,
[00:09:31.140]not from Tina Turner, but from Clarence Swanton,
[00:09:34.470]he actually has this photo on, I think, Syngenta website,
[00:09:38.310]basically illustrating what's going on.
[00:09:40.380]So if you think of a corn crop, they've got this top photo
[00:09:45.210]or this top image where you don't have weeds there.
[00:09:49.050]So that reflected light is not going to be enriched
[00:09:52.890]in that far-red spectrum.
[00:09:55.080]But if you have this corn crop growing in a weedy field,
[00:09:58.530]then this reflected light bouncing back up to that corn crop
[00:10:02.670]is going to be enriched in that far-red light.
[00:10:05.820]And so these two plants are going to grow differently.
[00:10:09.270]And the primary things
[00:10:10.860]that we talk about most in shade avoidance,
[00:10:13.740]is that this corn plant tends to devote more resources
[00:10:17.040]to growing tall.
[00:10:18.960]And usually it does that at the expense of the root system.
[00:10:22.860]And that's because if it's growing
[00:10:24.690]in that perceived competitive environment,
[00:10:27.990]that corn plant knows
[00:10:29.700]as much as the corn plant can know anything,
[00:10:32.820]that corn plant knows
[00:10:34.440]that it's going to be limited for light soon
[00:10:36.930]because it's got all these weed neighbors.
[00:10:41.820]So, Clarence and his group actually developed
[00:10:45.840]a method to look at that.
[00:10:47.970]So if you think about these images on the left,
[00:10:51.390]the ones on the right are actually
[00:10:52.530]how they ran some of their studies,
[00:10:54.060]where they have separate pots,
[00:10:55.800]just completely different resource pools.
[00:10:58.110]So there's never any direct shading,
[00:11:00.030]there's never any competition
[00:11:01.500]'cause the root systems are in different pots
[00:11:05.400]and they can actually observe those differences occur
[00:11:08.790]in that system.
[00:11:11.910]So if you look at the list of responses
[00:11:14.160]that have been attributed over the years
[00:11:16.470]in the pretty large body of research on shade avoidance,
[00:11:21.540]there's a whole bunch of things
[00:11:23.010]related to, again, primarily trying to grow tall
[00:11:27.780]at the expense of other things.
[00:11:30.720]And so reduced branching
[00:11:32.460]is one that they've seen in soybeans,
[00:11:34.740]which can be really challenging or yield potential.
[00:11:38.177]If you have fewer branches, you have probably fewer nodes,
[00:11:41.400]fewer flowers, fewer pods.
[00:11:44.910]Same thing in corn, if you basically delay that maturity,
[00:11:48.780]it produces fewer kernels.
[00:11:52.440]I'm mostly interested in some of these that relate to roots,
[00:11:55.920]which I'll talk about in a little bit,
[00:11:58.080]but there's a whole bunch of things.
[00:11:59.790]And depending on the crop plant you're thinking about,
[00:12:03.000]almost all of these relate to at least
[00:12:05.100]some yield component in some crop,
[00:12:08.310]leaves for forage crops, stems for maybe some fiber crops.
[00:12:13.080]You've got the roots for root crops, seeds.
[00:12:17.370]So a lot of these things are yield relevant
[00:12:20.970]when we talk about the effects of shade avoidance.
[00:12:24.720]And so what I'm gonna go through first
[00:12:27.120]is really where we started on this project
[00:12:29.940]primarily looking at sugarbeet
[00:12:31.920]because as far as I could tell,
[00:12:34.620]no one had really looked at shade avoidance
[00:12:37.920]in an agronomic crop
[00:12:38.940]where root is the primary economic product.
[00:12:42.060]And if root to shoot ratio is usually what's being driven
[00:12:45.810]by the shade avoidance responses,
[00:12:47.130]it seems like that's a really important thing
[00:12:48.810]that we should understand better.
[00:12:50.700]So that's the primary thing.
[00:12:52.110]But the other thing that made sugarbeet
[00:12:53.280]kind of an interesting crop
[00:12:54.570]is it's a biennial species that's harvested as an annual.
[00:12:57.120]So there's really nothing in the literature
[00:12:59.820]about shade avoidance responses in biennial species.
[00:13:04.770]It also can't grow tall.
[00:13:06.750]Anybody that has walked through a sugarbeet fields,
[00:13:09.210]know that if knee high, you gotta really tall crop.
[00:13:12.300]So how does a crop that can't grow tall,
[00:13:16.110]respond to these shade avoidance triggers?
[00:13:18.720]Because normally corn, beans, all these other crops
[00:13:21.840]are trying to grow tall, sugarbeets can't do that.
[00:13:24.630]So that's kinda why
[00:13:26.190]we started looking at this in sugarbeet.
[00:13:28.980]And I do want to make sure
[00:13:30.540]that I acknowledge more than just Tina Turner.
[00:13:32.310]I wanna acknowledge all of the graduate students who've done
[00:13:35.160]most of the work
[00:13:36.417]and actually been involved in the project from the get go.
[00:13:39.750]Louise Lorent, Tom Schambow, Albert Adjesiwor,
[00:13:43.410]and my current PhD student, Joe Ballinger,
[00:13:46.620]have all been doing shade avoidance work in sugarbeet
[00:13:50.130]and have been the primary drivers
[00:13:52.770]behind all of the work
[00:13:53.850]that I'm gonna show you getting done today.
[00:13:57.690]Okay, so I'm not gonna spend a lot of time on the methods
[00:14:00.930]other than to say we planted a lot of sugarbeets
[00:14:04.560]in a lot of buckets.
[00:14:06.900]That's pretty much what it boils down to.
[00:14:08.520]Within any given study that I'm gonna show you,
[00:14:12.290]we had at least 15 reps
[00:14:15.060]because one of the primary differences
[00:14:17.400]between sugarbeet and crops
[00:14:19.576]that I think more researchers are more interested in
[00:14:22.290]like corn and soybeans,
[00:14:25.380]sugarbeets have a lot of inherent variability.
[00:14:29.580]Just from plant to plant, there's a lot of variability
[00:14:31.980]so we need to have 15 to 20 individual plants as a replicate
[00:14:36.420]in order to find anything from a statistical standpoint
[00:14:39.060]because there's a lot of plant to plant variability
[00:14:40.980]and how they respond to anything.
[00:14:44.220]And the first bit I'm gonna show you is two treatments,
[00:14:48.660]which is grass versus no grass.
[00:14:51.270]And I'll show you what that means in a minute.
[00:14:52.980]And I'm also gonna show you a little bit of data
[00:14:55.140]comparing sugarbeet, table beet and Swiss chard.
[00:14:57.720]And I'll explain why that's interesting
[00:14:59.370]here in a little bit.
[00:15:00.630]Okay, so the key thing, if you ignore the next,
[00:15:03.180]kind of tune out the next four or five minutes,
[00:15:05.700]just know that all of the treatments that you're seeing
[00:15:08.820]have adequate nutrients and water, no direct shading.
[00:15:12.240]So again, very similar to the way
[00:15:13.650]Swanton set up his studies.
[00:15:15.270]We wanted to make sure that the sugarbeets
[00:15:17.310]and the surrounding grass species
[00:15:20.040]were not competing for the same pools of resources.
[00:15:22.890]So we wanted to limit their interactions
[00:15:25.140]to just that reflected light.
[00:15:27.300]And I guess if you wanna get really technical,
[00:15:28.800]they also might have been responding to like volatile
[00:15:30.810]organic compounds and other things.
[00:15:32.370]But generally speaking,
[00:15:33.750]we're attributing almost all of the things that we've seen
[00:15:35.940]to the reflected light.
[00:15:36.930]So, we started with these 19 liter pales,
[00:15:41.910]which is extremely similar to a five gallon bucket,
[00:15:44.880]if you're interested.
[00:15:47.700]We created cardboard mailing tubes about four inches tall
[00:15:53.670]and then we taped plastic around that.
[00:15:56.520]And then we set that into the bucket.
[00:15:59.250]And so what that allowed us to do then,
[00:16:00.900]is we could plant the sugarbeet into that center ring
[00:16:04.110]once we filled it up
[00:16:05.520]and then it would have the whole bucket to spread its roots.
[00:16:08.940]And then we would plant the grass and the grass treatments
[00:16:12.000]on top of that plastic.
[00:16:13.380]So again, the root treatments
[00:16:15.060]were never actually allowed to interact,
[00:16:17.160]they were not interacting for the same pools of resources.
[00:16:21.060]So we filled all that up with potting media,
[00:16:23.940]soil scientists get really mad when I call it soil,
[00:16:25.890]with potting media, planted sugarbeet in the middle.
[00:16:30.840]In the soil treatments it looked like this
[00:16:33.420]and in the grass treatments it looked like this.
[00:16:37.072]So that's the general setup for all of the research
[00:16:40.740]I'm gonna be presenting related to these sugarbeet studies.
[00:16:45.420]This figure is mostly a plug.
[00:16:47.160]If you have a research project that you want to show
[00:16:50.820]how things work in a really simple diagram,
[00:16:54.330]find yourself a graphic designer who can draw it up for you.
[00:16:57.600]We got so many questions on these methods
[00:17:01.080]every time we went to publication,
[00:17:02.550]every time we presented this work
[00:17:04.140]and I had a friend of mine, who's a graphic designer,
[00:17:06.450]Jessica Perry, draw this.
[00:17:08.940]We never got questions about that again.
[00:17:11.297]It was just so clear and obvious once people can see this.
[00:17:14.310]So hire yourselves a good graphic designer,
[00:17:16.710]pay them what they're worth.
[00:17:19.620]Okay, so one of the most consistent things we saw
[00:17:23.400]across all of the studies.
[00:17:24.750]And so the main one I'm gonna show you
[00:17:27.630]and then I probably won't show you
[00:17:28.530]a similar data on this again,
[00:17:31.080]is that the number of leaves over time in sugarbeet
[00:17:35.700]was dramatically reduced
[00:17:38.010]where it was growing surrounded by grass.
[00:17:42.060]So the grass treatment on average in this particular study
[00:17:46.260]was producing about 12 leaves.
[00:17:48.690]Where the sugarbeet was growing
[00:17:50.220]without that grass surrounding it,
[00:17:52.380]it was producing about 25 leaves by the end.
[00:17:55.140]So a pretty major difference.
[00:17:57.420]And that was by far the most consistent thing.
[00:18:00.570]Year to year
[00:18:01.830]the leaf numbers have been really, really consistent
[00:18:05.520]in terms of differences between the two species.
[00:18:08.400]So in this first set of studies
[00:18:10.170]where we're just looking at season-long competition,
[00:18:13.290]the root weight, which again, for sugarbeet
[00:18:15.510]is the economic product, we observed about a 70% reduction
[00:18:20.130]in root mass just by having that grass growing nearby.
[00:18:25.950]So, a pretty dramatic change in the economic product
[00:18:30.450]again, just due to shade avoidance,
[00:18:32.430]not due to actual resource depletion.
[00:18:35.790]Now, here's where that table beet, sugarbeet,
[00:18:38.760]Swiss chard thing comes in handy.
[00:18:40.350]Anyone know what the species is for sugarbeet?
[00:18:45.180]Beta vulgaris.
[00:18:46.050]What's the species for table beet?
[00:18:48.133](audience speaking indistinctly)
[00:18:49.320]What's the species for Swiss chard?
[00:18:52.320]The miracles of plant breeding,
[00:18:54.330]all three of these are Beta vulgaris.
[00:18:58.710]And so we thought it'd be kind of interesting to see,
[00:19:00.540]okay, we've seen this in sugarbeet,
[00:19:01.950]we know what happens there.
[00:19:03.600]How does table beet, which kind of similar
[00:19:06.390]in form and function respond
[00:19:09.360]and how does that compare to Swiss chard,
[00:19:12.240]which actually has a fibrous root system
[00:19:13.527]and is grown as a leafy vegetable?
[00:19:15.990]And what we saw is basically they all do the same thing.
[00:19:20.940]So this is not something
[00:19:22.320]that we've kind of bred into sugarbeet,
[00:19:24.090]this is something that kind of exists
[00:19:26.550]throughout the species.
[00:19:28.350]So again, this is the sugarbeet data,
[00:19:30.000]looking at the leaf area, leaf biomass, and root biomass.
[00:19:33.480]We saw that the grass treatment reduced all three.
[00:19:36.270]Table beets, almost the exact same trends,
[00:19:39.690]a little bit difference in magnitude here and there,
[00:19:41.880]but huge reductions in all three.
[00:19:44.490]And in the Swiss chard, we're going to assume
[00:19:47.490]the root biomass also, but it turns out washing
[00:19:49.860]a fibrous root system out of that potting media
[00:19:52.440]was a disaster mess and we didn't even try it
[00:19:54.720]after we did the first three or four.
[00:19:57.090]But if you look at the leaf area and leaf biomass,
[00:20:00.000]exact same trends.
[00:20:01.350]And so we probably assumed that the roots probably
[00:20:03.480]did the exact same thing also
[00:20:04.740]but we didn't actually quantify that.
[00:20:08.670]So again, about a 70% reduction in the economic product
[00:20:14.070]in those two species where it's roots.
[00:20:16.950]Again, we know that roots,
[00:20:20.520]plants kind of give up on those roots
[00:20:22.020]to try and grow taller.
[00:20:24.330]Okay, it turns out, though, in sugarbeets,
[00:20:26.160]they don't actually grow taller
[00:20:28.110]because, again, they don't have the ability to grow taller.
[00:20:34.380]One of the things that I learned about myself
[00:20:37.410]during the many years we've been doing this project is,
[00:20:40.320]I don't trust any data that looks kind of exciting
[00:20:44.550]and new and interesting.
[00:20:46.650]So, we did that in the buckets
[00:20:48.210]and I was like, 70% is too big.
[00:20:50.010]There's no way that can be real.
[00:20:51.510]So then we did a greenhouse study
[00:20:52.830]and we saw about 70% reduction.
[00:20:54.390]Well, that can't be real.
[00:20:56.100]So then we did it in the field
[00:20:58.020]using citing and grass as kind of a different method,
[00:21:01.380]seeing almost the exact result.
[00:21:02.670]I'm finally convinced about 10 to 12 years
[00:21:05.490]after kind of doing this line of research,
[00:21:08.160]I'm pretty sure it's real at this point.
[00:21:10.560]I do think what we're seeing is real.
[00:21:13.770]So again, the most consistent thing we saw in sugarbeets
[00:21:17.640]due to shade avoidance mechanism,
[00:21:19.350]is that slowed leaf appearance rate.
[00:21:21.450]So the leaves just appear
[00:21:23.760]at a much lower rate during the growing season.
[00:21:27.690]We assume that that then kind of has
[00:21:30.420]the knock on effect of if you have fewer leaves,
[00:21:32.640]then obviously you're gonna have reduced leaf area.
[00:21:35.370]That's not a one to one relationship, but it seems like
[00:21:38.010]it happened pretty consistently in our studies.
[00:21:40.710]And if you don't have leaves to photosynthesize,
[00:21:43.860]you end up with that reduced root weight.
[00:21:45.750]So we kind of feel like that's probably
[00:21:47.850]the progression that's going on in the plant
[00:21:49.380]although we haven't really,
[00:21:51.900]I guess, identified that for certain.
[00:21:54.720]But those three things,
[00:21:56.310]we are convinced are real effects that happen
[00:21:59.970]pretty consistently
[00:22:01.590]when you have season-long shade avoidance
[00:22:04.140]occurring in sugarbeet.
[00:22:07.050]So obviously the question then
[00:22:08.820]as a weed scientist in particular,
[00:22:11.310]but also the growers that we would present this data to,
[00:22:13.320]is what happens if we control the weeds?
[00:22:16.170]Because growers, it turns out,
[00:22:18.360]are a lot smarter than their weed scientists friends.
[00:22:22.920]They actually go out and kill those weeds
[00:22:24.480]instead of just letting them stay there all year long.
[00:22:29.880]So our question then is,
[00:22:30.960]well, what happens if you control the weeds?
[00:22:32.520]Do we see similar things?
[00:22:34.320]And it turns out weed control in our experimental system
[00:22:37.080]is super easy, we just go pull out the grass ring.
[00:22:41.280]So you take out that side,
[00:22:42.480]you fill it with soil and water,
[00:22:43.680]you've got 100% weed control immediately.
[00:22:46.200]So we can put grass in,
[00:22:48.360]take grass out at any point during the growing season
[00:22:51.810]and we can then just have that present for different times
[00:22:55.230]during that sugarbeet's life.
[00:22:58.050]So we did--
[00:22:58.961](audience speaking indistinctly)
[00:23:06.210]We get that question a lot also and it turns out it depends.
[00:23:11.670]So again, we didn't leave it just white,
[00:23:13.620]we would put soil or potting media in there
[00:23:17.070]so that it was more typical to a soil.
[00:23:20.700]We have actually measured the mulch question.
[00:23:23.580]And mulch responds very similarly to soil
[00:23:27.660]because if you don't have the green, the active chlorophyll,
[00:23:31.290]you don't see that bump in the far-red spectrum.
[00:23:35.820]So we did what most weed scientists will recognize
[00:23:39.450]as a critical period study.
[00:23:42.360]So basically, we have early season removal series
[00:23:47.550]where we have both ends of the spectrum,
[00:23:49.890]where we have a treatment
[00:23:51.120]where we have no weeds season-long
[00:23:53.130]and at the other end we have a treatment that has weeds
[00:23:56.010]throughout the entire crop life cycle.
[00:23:58.470]And then we have,
[00:23:59.520]the green bars represent when weeds are present.
[00:24:03.030]So basically we have then when you control the weeds.
[00:24:06.360]So this one, we control the weeds
[00:24:08.360]at the two true-leaf growth stage.
[00:24:10.980]We control them at 200 growing degree days,
[00:24:13.380]after that, 400 growing degree days after
[00:24:15.540]and then the full season.
[00:24:16.590]So basically when should you control weeds
[00:24:19.050]to avoid these responses?
[00:24:21.270]And then we also have the late season addition series.
[00:24:25.050]So here you assume that you keep it weed-free season-long.
[00:24:28.260]The next treatment you allow the weeds to show up
[00:24:31.140]at 400 growing degree days after planning,
[00:24:33.870]200, 100, two true-leaf stage.
[00:24:38.610]So I'm gonna show you the data
[00:24:40.410]in both of these two series.
[00:24:42.450]So the early season presence,
[00:24:44.280]and then the late season addition.
[00:24:48.810]And this is what that data looks like.
[00:24:51.750]I'll give you two seconds to make sure everybody gets
[00:24:54.900]all the information that you need.
[00:24:56.790]One of the things that you'll see is,
[00:24:58.620]the individual plant differences
[00:25:00.750]that we see from year to year.
[00:25:02.070]And I know like soybean breeders and corn breeders,
[00:25:04.770]their heads are exploding right now
[00:25:06.570]looking at the amount of variability we have plant to plant.
[00:25:10.560]So I'm not expecting you to know what that is.
[00:25:13.400]So I'm gonna walk you through each of the steps.
[00:25:16.830]So I'm gonna start with the late season edition
[00:25:19.320]because this one, frankly,
[00:25:21.000]I think is more in line with what we expected to see.
[00:25:25.140]Okay, so the way you interpret this figure,
[00:25:30.420]on the far left is where we had weeds present
[00:25:34.380]the entire season.
[00:25:36.660]So, basically if you think of the start
[00:25:38.700]of the weedy treatment at planting
[00:25:41.310]and then let to go for the whole season.
[00:25:44.250]And at the other end of that
[00:25:46.350]is the season-long weed-free treatment, okay?
[00:25:50.340]So that's like if you were to start the weeds
[00:25:53.520]on the day after you harvested, okay?
[00:25:56.400]So basically effectively, no weeds.
[00:26:00.390]And that's basically then the trend that we observed
[00:26:03.120]that the longer weeds were in that system,
[00:26:05.940]and I'm saying weeds, but I actually mean the turf ring,
[00:26:09.420]Kentucky bluegrass, for those interested.
[00:26:12.960]The longer that turf was in that system,
[00:26:17.880]the more yield loss we observe.
[00:26:20.910]So our first treatment as I mentioned earlier
[00:26:22.980]was the two true-leaf beets.
[00:26:24.720]That's the earliest timing
[00:26:26.700]at which we basically allowed weeds to start growing.
[00:26:31.800]And if you actually look at that, just as a reference,
[00:26:33.870]'cause two true-leaf sugarbeets is a really common time
[00:26:36.480]for most goers to go out and spray weeds.
[00:26:39.450]And so if we use that kind of a reference,
[00:26:42.900]which doesn't make as much sense in this context,
[00:26:44.550]but will on the next slide,
[00:26:47.310]we observed about a 22% yield reduction if weeds came up
[00:26:51.870]at the two true-leaf stage
[00:26:53.940]and then competed all the way to harvest, okay?
[00:26:59.580]So now let's look at the early season removal timing.
[00:27:03.330]So this one, if you think about the control treatments,
[00:27:05.610]they're flip flopped.
[00:27:07.350]So this now on the left side is the weed-free treatment.
[00:27:11.550]That's where weeds were never present
[00:27:14.730]and at the other side,
[00:27:15.780]you've got the season-long treatment.
[00:27:19.590]And then this, again, is gonna be the two true-leaf weeds.
[00:27:23.880]So basically, if you controlled
[00:27:29.160]two true-leaf beets
[00:27:31.320]or controlled weeds of two true-leaf weeds
[00:27:37.050]up through season-long,
[00:27:39.930]we actually don't see any trend there whatsoever.
[00:27:44.520]So there's no difference between having season-long weeds
[00:27:48.720]and having weeds basically between planting
[00:27:52.050]and the two true-leaf beets.
[00:27:54.150]If you have weeds present for that first two to three weeks
[00:27:58.440]of the sugarbeets life cycle,
[00:28:00.600]you end up with the same yield potential
[00:28:03.450]due to shade avoidance.
[00:28:04.410]Again, not due to overall competition,
[00:28:05.820]but due to shade avoidance
[00:28:06.653]as if you have weeds in there the entire season.
[00:28:11.970]The difference between the weed-free treatment
[00:28:15.450]and the treatment where we remove weeds
[00:28:18.720]at the two true-leaf stage, is a 31% yield reduction.
[00:28:24.360]So we know and have known for a long time
[00:28:27.750]that early season
[00:28:30.120]weed control in sugarbeets is really important
[00:28:31.860]as it is for most crops.
[00:28:34.050]I think we've probably underappreciated
[00:28:37.140]why it's so important
[00:28:40.170]and I think this probably is a major driver.
[00:28:42.570]So if you think of this just kind of on a timeframe,
[00:28:47.280]that time period between sugarbeet emergence
[00:28:50.250]and the two true-leaf stage,
[00:28:51.510]having weeds present for that period,
[00:28:55.230]cause about 30% yield loss.
[00:28:58.290]If weeds come up at the two true-leaf stage
[00:29:01.260]and compete all the way until harvest,
[00:29:03.450]that period of time even though it's much longer
[00:29:05.430]during the crop growth cycle,
[00:29:07.590]that's only worth about 22% in yield potential.
[00:29:11.760]So way more important to keep weeds out of the system
[00:29:16.290]during that early stages of sugarbeet growth.
[00:29:19.290]Again, just due to shade avoidance.
[00:29:22.500]If you actually allow competition,
[00:29:24.300]we've done a little bit work on that front too,
[00:29:27.180]these numbers definitely change
[00:29:29.580]but it never really minimizes
[00:29:31.740]the importance that that shade avoidance is contributing
[00:29:34.080]to that early season part.
[00:29:35.760]Okay, so the nutshell kind of practical implications of this
[00:29:40.890]is what we call starting clean
[00:29:42.750]or planting your crop into a weed-free area
[00:29:45.990]is really important, okay?
[00:29:48.660]So we don't want the sugarbeet emerging into a weedy area
[00:29:53.250]or we're basically setting ourselves up
[00:29:55.290]for a pretty major loss in yield right off the bat.
[00:30:00.120]So how do we control early season weeds in sugarbeet then?
[00:30:03.470]Is the next practical question that we've got.
[00:30:07.440]I'm going to talk a little bit about
[00:30:09.810]a particular weed that is near and dear to my heart
[00:30:12.510]and that's kochia, scientific name Bassia scoparia
[00:30:15.900]for those of you who may be interested,
[00:30:18.240]mostly because it's one of the earliest weeds to come up
[00:30:21.870]in Western Nebraska, Eastern Wyoming, Colorado area.
[00:30:27.480]If you actually look at the optimal
[00:30:29.010]germination temperature in Plata
[00:30:30.480]compared to other weeds that we have in that area,
[00:30:34.230]it has among the lowest thermal requirements
[00:30:36.780]for germination.
[00:30:38.400]I actually have a thermo gradient table in my lab.
[00:30:40.950]We've done studies where we run
[00:30:43.890]basically from zero up to 30 degrees Celsius.
[00:30:47.340]Kochia is the only species I've seen
[00:30:49.950]where you can have ice on part of the filter paper
[00:30:53.520]and a kochia germinating on the other half.
[00:30:56.250]So it won't germinate at zero degree C as far as I can tell,
[00:30:59.970]but really, really close.
[00:31:01.980]So you don't have to accumulate very many heat units
[00:31:04.800]before kochia will germinate.
[00:31:06.630]So it is the early season weed
[00:31:09.120]that I'm gonna talk about most.
[00:31:10.260]So this is what kochia looks like
[00:31:12.060]for those of you who may be unfamiliar
[00:31:14.070]'cause I know it's a lot less common
[00:31:15.510]when you get clear over to this side of the state.
[00:31:20.040]In sugarbeet, kochia is one of the most
[00:31:22.080]economically damaging weeds.
[00:31:24.750]So there's been a lot of data looking at the yield impacts,
[00:31:29.640]about one kochia plant per 10 meters of sugarbeet row,
[00:31:33.990]usually grown in 30-inch rows in the region,
[00:31:36.870]will cause about a 10% yield loss in sugarbeet.
[00:31:39.990]So really a highly competitive weed
[00:31:44.880]probably involved in some way, shape or form
[00:31:46.980]in that shade avoidance response as well.
[00:31:49.980]Okay, so when we talk about starting clean in most crops,
[00:31:53.730]one of the things we're talking about
[00:31:55.530]is pre-emergence herbicides, okay?
[00:31:58.080]So basically burn down if you're in a no-till system,
[00:32:01.080]but also some sort of a herbicide with residual activity
[00:32:06.150]to control those early emerging weeds.
[00:32:09.390]It turns out in sugarbeet, we don't really have that.
[00:32:12.540]We have currently zero effective herbicide options
[00:32:16.440]for kochia control,
[00:32:18.300]especially if we have glyphosate resistant kochia.
[00:32:22.470]Glyphosate is the only post emergence tool that we have
[00:32:25.320]that is effective for controlling weeds in sugarbeet.
[00:32:28.830]So this is actually some study I did
[00:32:31.290]with Nevin's predecessor, Bob Wilson in Scottsbluff
[00:32:35.130]in addition to Phil Stallman at Kansas,
[00:32:38.670]Phil Wester at Colorado, and Mike Nigg in South Dakota
[00:32:43.500]back in 2010, 2011,
[00:32:46.500]where we actually looked at how are we gonna control kochia
[00:32:50.580]without glyphosate?
[00:32:51.810]So this is just as glyphosate resistant kochia
[00:32:54.090]was starting to show up in Western Kansas
[00:32:57.690]and hadn't really spread to most other places yet.
[00:33:00.060]But we wanted to know, "Okay, if we don't have glyphosate,
[00:33:03.810]how are we gonna control it?"
[00:33:04.860]So the way we did this study is we actually chose
[00:33:07.710]what we felt were probably the top three herbicide programs
[00:33:11.010]within each crop where kochia is a problem in the region.
[00:33:15.510]So we have in corn,
[00:33:18.270]we got really good kochia control.
[00:33:19.740]We don't need roundup in corn, right?
[00:33:22.500]In soybean, we got really good kochia control.
[00:33:25.290]We didn't really need glyphosate in soybean.
[00:33:29.190]In fallow, a little bit less.
[00:33:31.320]We had a few stragglers.
[00:33:32.370]But overall, we're still getting
[00:33:34.950]over 95% control in most scenarios.
[00:33:38.220]Wheat, about 90 so a fewer options.
[00:33:41.520]And then we've got sugarbeet,
[00:33:43.200]where a median kochia control in sugarbeet
[00:33:45.810]with our three best options were about 40% kochia control.
[00:33:51.900]So we just don't have,
[00:33:53.940]in fact, this weed, kochia,
[00:33:56.580]is one of the reasons we saw such rapid adoption
[00:34:00.060]of Roundup Ready sugarbeet in the region
[00:34:02.160]is because we didn't really have the ability
[00:34:03.900]to control this weed,
[00:34:05.490]Roundup Ready sugarbeet gave us that tool of glyphosate,
[00:34:08.160]we could control it,
[00:34:09.450]now that we're seeing glyphosate resistance,
[00:34:12.390]we've lost the ability to control that weed again.
[00:34:15.840]Okay, so obviously the answer to this question, then,
[00:34:20.310]is cover crops, right?
[00:34:22.350]We don't have any herbicides,
[00:34:23.640]we've gotta control kochia, cover crops is the solution.
[00:34:29.640]I want to give another shout out,
[00:34:32.250]not to Tina Turner this time,
[00:34:33.510]but to one of my favorite philosophers of all time,
[00:34:37.050]Mr. Homer J. Simpson.
[00:34:39.450]He said this about alcohol,
[00:34:40.830]but I actually like applying it to cover crops.
[00:34:44.557]"The cause of and solution to,
[00:34:47.580]all of agriculture's problems."
[00:34:50.160]And I'll tell you what I mean there in a little bit.
[00:34:53.130]So we know that a good cover crop
[00:34:56.100]can provide good weed suppression if it's managed correctly
[00:35:00.180]for high biomass early enough in the season.
[00:35:03.630]But it turns out if you have a cover crop
[00:35:06.330]that is producing lots of biomass early in the season,
[00:35:10.590]does the sugarbeet know that that's a cover crop or a weed?
[00:35:15.060]No, so it's gonna drive the exact same response.
[00:35:17.370]And in fact, none of the bucket studies I've showed you
[00:35:20.610]had anything to do with weeds, right?
[00:35:22.620]It was basically more similar to a cover crop
[00:35:25.320]than it would be to a weed canopy
[00:35:27.000]because we were using Kentucky bluegrass turf.
[00:35:29.760]So a good solid cover crop
[00:35:31.770]that's gonna provide weed suppression if we plant green,
[00:35:34.530]which is how we are likely to get most
[00:35:36.960]of that early season weed control
[00:35:39.780]is gonna cause that same sort of shade avoidance effect.
[00:35:43.470]Okay, so we can delay the termination or we can apply early,
[00:35:49.200]but the earlier you terminate the cover crop,
[00:35:52.260]the less likely it is you're gonna get
[00:35:53.850]that weed suppressive effect, okay?
[00:35:56.640]And I'll talk about why that is here in a little bit.
[00:36:00.270]One of the questions that I had then is,
[00:36:04.620]what if we break out the old band sprayers
[00:36:06.810]that we used to use in sugarbeet?
[00:36:08.130]So those of you who are unfamiliar with band sprayers,
[00:36:10.560]basically we can apply herbicide in a relatively narrow band
[00:36:14.790]just right around the sugarbeet row, keep it weed-free,
[00:36:18.030]and then we can allow things in between
[00:36:20.490]to grow a little bit more.
[00:36:23.190]So the idea here is can we provide a cover crop-free band
[00:36:28.500]with herbicides that is wide enough
[00:36:31.860]to avoid that negative impact on the crop,
[00:36:34.290]not induce those shade avoidance responses,
[00:36:36.510]but narrow enough that it still might produce
[00:36:38.580]some weed suppression
[00:36:39.720]if we let it grow a little bit further on into the season?
[00:36:43.200]So we did this study at Sheridan.
[00:36:45.090]Again, I'm not gonna spend a lot of time on the methods,
[00:36:47.610]but we basically designed a little
[00:36:51.240]individual row band-sprayer.
[00:36:53.370]So had bicycle,
[00:36:54.930]or actually this one wasn't the bicycle wheels,
[00:36:56.640]they actually had to hand hold it.
[00:36:57.960]And it was kind of a pain, but they did a good job.
[00:36:59.970]And you can see that we basically applied
[00:37:01.860]different size band over that
[00:37:05.250]and sprayed out the winter wheat
[00:37:07.170]and then right over top of the crop row.
[00:37:09.180]And those bands were different sizes
[00:37:10.740]ranging from nine centimeters wide
[00:37:13.200]up to 76 centimeters wide,
[00:37:14.850]which the 76 is just a broadcast application
[00:37:17.190]because sugarbeets are planted in 76 centimeters row,
[00:37:20.880]which is 30-inch rows
[00:37:23.430]for those of you that are not metrically minded.
[00:37:27.570]Okay, so what we measured here is soil moisture
[00:37:30.240]in the sugarbeet row, then stand counts.
[00:37:32.550]We actually measured chlorophyll
[00:37:33.900]because chlorophyll reduction
[00:37:35.850]is actually a really widely agreed upon impact
[00:37:40.800]of shade avoidance responses
[00:37:42.240]as it reduces the chlorophyll concentration in leaves.
[00:37:45.510]So we wanted to see if that had any impact.
[00:37:48.420]Then we did leaf biomass and root biomass.
[00:37:51.900]Okay, I'm not gonna get into a whole lot of details here
[00:37:54.060]other than what I'm gonna show you is we fit a model
[00:37:58.470]that has a right side asymptote to all this data.
[00:38:02.040]And if you look at basically the bandwidth
[00:38:05.700]that gets about 95% of the way up to that asymptote,
[00:38:09.420]we can use that as more or less a bandwidth
[00:38:13.590]where we're minimizing the impact on the crop, okay?
[00:38:16.500]So that's all you need to know for that.
[00:38:18.930]So what did we find?
[00:38:20.100]I'm gonna show you stand loss first.
[00:38:23.490]So again, over on the right side,
[00:38:26.730]that asymptote we can assume is what happens
[00:38:29.640]in the absence of a cover crop.
[00:38:31.200]That's just broadcast applied herbicide
[00:38:33.330]where there's no green
[00:38:34.770]until you get to the next sugarbeet row.
[00:38:37.560]And so as you go further and further left,
[00:38:40.710]if we draw a line
[00:38:42.360]at where that line basically gets to 95% of the asymptote,
[00:38:46.530]that's what I'm gonna call anything to the right of this,
[00:38:49.230]any bandwidth greater than that
[00:38:51.420]is probably gonna have minimal
[00:38:53.370]at least less than 5% impact on the crop.
[00:38:56.970]So this one actually surprised me.
[00:38:59.340]So this is actually sugarbeet stand.
[00:39:02.119]The narrow bands actually reduced sugarbeet stand,
[00:39:10.260]which I did not expect
[00:39:11.340]'cause nothing in the shade avoidance literature
[00:39:14.040]prepared me to think that we would actually reduce
[00:39:17.430]the number of sugarbeets.
[00:39:19.320]So, I still remain a little bit skeptical of that.
[00:39:23.310]The primary explanation that I assumed
[00:39:25.770]probably made the most sense was,
[00:39:27.900]well, the cover crop here is not just shade avoidance.
[00:39:30.960]It's actual competition.
[00:39:32.250]It's probably drying out the soil and we're getting reduced
[00:39:34.800]or stressed emergence, something related to that.
[00:39:38.430]However, that's not well supported by the data.
[00:39:41.250]We actually collected soil moisture.
[00:39:42.990]We collected soil, did volumetric water content.
[00:39:47.250]We didn't really see any trend whatsoever,
[00:39:49.920]even in those narrow rows to reduce the soil moisture.
[00:39:56.160]And we were taking these samples
[00:39:58.260]just before the next irrigation
[00:40:00.180]when the soil was theoretically as dry
[00:40:02.190]as it was going to get before we irrigated again.
[00:40:05.280]And so we did not see that we were having much of an impact
[00:40:08.790]in that top two inches of soil.
[00:40:10.950]So I don't think water is explaining
[00:40:13.110]the standard action that I showed you on the last slide,
[00:40:14.820]but I don't know what is to be honest.
[00:40:16.890]So this is still kind of a mystery to me.
[00:40:20.070]We haven't had an opportunity to repeat this study yet.
[00:40:22.310](audience speaking indistinctly)
[00:40:25.410]We did not look for allelopathic effects.
[00:40:29.910]I am happy to pontificate later
[00:40:31.860]about my opinion of allelopathy,
[00:40:34.740]but yeah, we did not look at that.
[00:40:36.210]It could certainly be playing some role here.
[00:40:40.830]So leaf dry mass per plant
[00:40:43.170]and then I'll show you root dry mass per plant.
[00:40:46.320]Here, again, to get to that right side asymptote,
[00:40:51.330]you needed a bandwidth of about 49 centimeters
[00:40:55.590]in a 76-centimeter row and for root biomass,
[00:41:00.150]so yield in a sugarbeet crop,
[00:41:02.730]you need a cover crop-free band of about 51 centimeters
[00:41:07.140]in order to basically negate the negative impact on the crop
[00:41:13.080]from having that cover crop present.
[00:41:17.580]Chlorophyll, which again,
[00:41:19.950]is one that I'm super interested in,
[00:41:22.410]not entirely relevant to crop yield,
[00:41:26.820]but certainly is an indicator
[00:41:30.300]of the crop responding physiologically
[00:41:32.370]in some way, shape or form.
[00:41:34.530]The ED95 was actually greater than 76,
[00:41:37.020]which doesn't make any sense
[00:41:39.120]but what it is telling us is that really,
[00:41:41.790]there is no bandwidth that you can have a cover crop
[00:41:45.420]where you're not gonna have some impact.
[00:41:47.460]So even as far as up to that 76
[00:41:51.060]or at least past this 43 or whatever it was centimeter,
[00:41:57.180]the sugarbeets can sense
[00:41:58.890]that there's something going on out there.
[00:42:01.140]So in terms of that distance
[00:42:03.450]to where the sugarbeet can tell there's plants growing,
[00:42:08.250]it's probably going pretty darn close
[00:42:10.170]to the next sugarbeet row.
[00:42:13.440]Okay, so the cover crop-free band required
[00:42:18.570]to minimize the effect on sugarbeets.
[00:42:21.450]Again, for stand you can get away
[00:42:22.860]with about a nine-inch band and 30-inch rows,
[00:42:26.490]but for leaf biomass and root biomass,
[00:42:28.290]you need about a 20-inch band and 30-inch rows
[00:42:31.740]in order to make sure you're not negatively impacting
[00:42:35.010]the crop with that cover crop presence.
[00:42:38.250]So getting back to the two questions
[00:42:40.710]that kind of drove this study,
[00:42:43.770]can we provide a cover crop-free band
[00:42:45.930]that is wide enough to avoid negative crop impacts?
[00:42:49.020]Yeah, I'd say if we get into that 20-inch area,
[00:42:52.200]50 centimeters, we're not negatively impacting yield.
[00:42:56.610]And so I would say from an agronomic perspective,
[00:42:58.800]even if we're reducing chlorophyll a little bit,
[00:43:00.240]if we're not reducing yield, fine.
[00:43:03.180]Go ahead and do that.
[00:43:04.740]Is that narrow enough to provide useful weed suppression?
[00:43:10.050]I don't know that I'm buying that.
[00:43:12.660]You can have a hell of a lot of weeds
[00:43:14.520]in a 20-inch band around a crop row.
[00:43:16.950]And so in terms of season-long presence,
[00:43:20.820]I would say this probably isn't a very good solution.
[00:43:23.880]Now, the logical next step of this is what happens
[00:43:26.670]if you terminate it after that two true-leaf stage?
[00:43:30.270]There's still a whole bunch of research
[00:43:32.940]that I think we need to do here to really tease out
[00:43:36.810]how we might be able to implement
[00:43:38.190]something like this in the real world.
[00:43:40.650]But this is I feel like a pretty good starting point
[00:43:43.410]and actually answers one of the questions
[00:43:45.240]that we got a lot early on is,
[00:43:47.220]how close do the weeds need to be to the crop?
[00:43:51.540]This data suggests they can be quite a ways away
[00:43:55.693]if that canopy is thick enough
[00:43:57.240]and still have the shade avoidance effect being induced.
[00:44:01.800]Okay, the last thread that I'm going to talk about,
[00:44:04.620]and I'm gonna try and talk fast
[00:44:05.610]to make sure I get done in time, will a green cover crop
[00:44:09.360]suppress kochia germination?
[00:44:12.330]So seed germination is a whole nother aspect
[00:44:16.770]of not necessarily shade avoidance,
[00:44:19.410]but reflected light quality and transmitted light quality
[00:44:22.950]because in addition to the reflection,
[00:44:25.110]if you look at what happens down at the bottom
[00:44:27.660]of a crop canopy,
[00:44:29.490]all the red light is being absorbed by the plants
[00:44:32.010]because they're using that wave length for photosynthesis.
[00:44:35.700]That far-red light
[00:44:37.110]is being transmitted through to the ground.
[00:44:39.900]And so if you're a seed at the bottom of that canopy,
[00:44:42.900]you are experiencing a far-red enriched environment
[00:44:46.320]or a relatively low red to far-red ratio.
[00:44:50.370]That's one of the reasons
[00:44:52.200]why cover crops work well for weed suppression
[00:44:55.500]because far-red light inhibits seed germination.
[00:44:59.340]And this is true in almost all of our agronomic weeds.
[00:45:02.880]So if you have an environment
[00:45:05.730]that is relatively low red to far-red ratio,
[00:45:09.720]you're gonna have far fewer seedlings
[00:45:12.150]germinating in that environment.
[00:45:16.320]So you can actually induce this in the lab.
[00:45:19.050]This is actually an extremely low tech seed lab
[00:45:23.490]that we've got going on,
[00:45:25.020]where we have two areas right next to each other.
[00:45:29.670]One that we typically use in dark,
[00:45:31.500]but we can also supplement it with red light,
[00:45:33.690]blue light, green light, white light.
[00:45:36.960]And then on the other side,
[00:45:38.250]we can do basically the exact same thing,
[00:45:39.960]but supplementing also with far-red light.
[00:45:43.050]And so this would be an example.
[00:45:44.430]We usually close the curtains
[00:45:45.450]to kind of keep ambient light out,
[00:45:47.160]but over here you'd have a dark scenario
[00:45:49.710]and over here, you've got the, I think this is a red light.
[00:45:53.400]The far-red light doesn't look very red
[00:45:55.290]because again, it's mostly out of the spectrum.
[00:45:57.510]So you get a little bit of bleed
[00:45:58.710]into the red visible spectrum.
[00:46:02.400]And this is what happens if you germinate most seeds
[00:46:06.630]in a setup like that.
[00:46:09.180]So lettuce is kind of our crop species that we use
[00:46:13.860]for kind of our standard control between experiments
[00:46:16.980]because lettuce is just like always responds the same.
[00:46:20.460]Doesn't matter about what's going on,
[00:46:21.930]ambient temperature or anything else.
[00:46:23.760]We know that it will germinate pretty well
[00:46:26.970]in red light or in darkness
[00:46:29.550]and we know that lettuce will not germinate
[00:46:32.820]if there's far-red light present, okay?
[00:46:35.550]And this is actually really true of a lot of species.
[00:46:38.550]So the dark and the red can change depending on the species.
[00:46:42.720]So lamb's quarters, for example, lamb's quarters
[00:46:45.690]will also not germinate very well in the dark.
[00:46:48.990]So it won't germinate well in the dark,
[00:46:50.550]it won't germinate well in far-red light,
[00:46:52.050]it'll germinate really well in red light or white light.
[00:46:56.400]So how does kochia respond?
[00:46:59.610]Well, most species, again, are suppressed by far-red light.
[00:47:05.100]Kochia does not care about your rules.
[00:47:09.720]Kochia will not germinate if you don't have water.
[00:47:15.420]And that's pretty much it.
[00:47:17.370]If you give kochia water,
[00:47:18.870]it doesn't care about the temperature,
[00:47:20.880]it doesn't care about the light environment,
[00:47:23.070]it doesn't care about literally anything else.
[00:47:25.230]If that seed is viable and it imbibes,
[00:47:28.080]it is going to germinate.
[00:47:30.120]And so this is really
[00:47:31.830]kind of disappointing to me as a weed scientist,
[00:47:33.960]thinking, well, we can potentially use cover crops
[00:47:37.110]to suppress some of the germination
[00:47:39.420]because kochia is actually
[00:47:40.440]a really short-lived seed in the seed bank.
[00:47:42.900]Three to four years later,
[00:47:44.310]almost all the kochia seed is dead.
[00:47:46.860]But my guess is from an ecological standpoint,
[00:47:49.110]that's probably why it doesn't give a shit
[00:47:51.360]what the light environment is.
[00:47:52.327]"I'm gonna be dead next year, I'm growing."
[00:47:55.740]And that's probably what's going on here
[00:47:58.050]is it has evolved the ability
[00:47:59.760]to just be totally far-red light insensitive
[00:48:02.520]because this is the one shot it's gonna get
[00:48:05.010]to actually produce seed.
[00:48:07.650]Really disappointing from an agronomic perspective though,
[00:48:10.890]because we're probably not gonna have a whole lot of impact
[00:48:13.500]by trying to suppress germination.
[00:48:14.760]So we actually probably
[00:48:15.593]need to be thinking about the other way,
[00:48:17.130]how do we get more of it to germinate early enough
[00:48:19.250]so we can kill it before we establish the crop
[00:48:21.630]because this method is probably
[00:48:23.640]not going to be super effective.
[00:48:25.140]So I'm gonna skip right over this
[00:48:27.540]because there's a whole bunch of stuff
[00:48:29.460]that we're still trying to look at,
[00:48:30.570]but I do wanna acknowledge all of the other people
[00:48:33.450]who have helped me out on this line of research,
[00:48:36.870]a bunch of graduate students and others,
[00:48:40.200]technicians, cartoon characters and rock singers.
[00:48:45.210]Wanna acknowledge the Department of Plant Sciences,
[00:48:48.300]the Ag Experiment Station, Western Sugar,
[00:48:50.760]who actually funded a lot of the work you just saw.
[00:48:53.820]And the USDA NIFA, which funded
[00:48:56.370]a whole bunch of the rest of the work.
[00:48:58.140]So I do wanna thank everyone for coming
[00:49:02.220]and for being present for the talk.
[00:49:07.500]I'm happy to answer any questions if there's time
[00:49:10.410]and if you are interested.
[00:49:11.910]So thank you very much.
[00:49:13.470]And I also won't be offended
[00:49:14.700]if you all just leave immediately and run away.
[00:49:18.660]I believe they're the same thing.
[00:49:24.000]I think it's just where the terms originated.
[00:49:28.320]Red to far-red has always been used
[00:49:30.270]in the plant ecology literature
[00:49:32.940]and they're pretty narrow in just the wavelengths
[00:49:36.210]that are absorbed by the phytochrome.
[00:49:38.460]So, like red is 680,
[00:49:40.920]not like a range that we would normally think about red
[00:49:43.230]or that a remote sensor might think about red.
[00:49:45.750]Far-red, I think is 740
[00:49:49.050]whereas near infrared is usually explaining
[00:49:52.380]a pretty wide band past that red.
[00:49:55.680]Far-red, you could say the same,
[00:49:58.620]it's a lot of things, but yeah.
[00:50:00.540]It's usually just how it's defined in the origin.
[00:50:05.730]Yes, yes, timing can be important in far-red sensitivity.
[00:50:10.050]And in fact, one of the students,
[00:50:12.060]there's a whole bunch of stuff we've done that was outside
[00:50:15.270]the scope of what I could fit in a 50-minute talk,
[00:50:18.600]Albert Adjesiwor who's now at the University of Idaho,
[00:50:22.680]actually had done some work on the end of day far-red, yeah.
[00:50:26.220]Because in the mornings and evenings,
[00:50:28.350]and actually if you think about even our experimental setup,
[00:50:31.380]in the mornings and evenings,
[00:50:32.640]you tend to have a light environment
[00:50:35.430]that is more enriched in far-red light
[00:50:38.400]partially due to the environment
[00:50:39.690]but also partially if you think about the sun angle.
[00:50:42.750]Even if the grass is not above the sugarbeet,
[00:50:47.640]when the sun is coming in flat,
[00:50:49.890]it's going to be getting more of that far-red
[00:50:52.410]compared to a more upright angle.
[00:50:54.570]So yes, end of day far-red light
[00:50:57.150]is actually one of the things that had been heavily studied
[00:51:00.900]in terms of shade avoidance.
[00:51:03.120]That's one of the things that drives flowering cycles,
[00:51:06.570]is end of day far-red light.
[00:51:08.190]And Albert has actually done some of the work
[00:51:09.900]to see how it compares to that.
[00:51:13.440]Google him and give him a call
[00:51:15.570]if you're interested to discuss that
[00:51:17.280]because he actually has looked at a little bit of that.
[00:51:20.040]But the timing of the far-red light does make a difference.
[00:51:23.610]Talk about the angles.
[00:51:25.500]Yeah, so the question is how does leaf architecture
[00:51:28.560]impact the results generally speaking?
[00:51:32.130]So graph that we use does have a relatively
[00:51:35.040]upright leaf architecture.
[00:51:37.650]But the reason we chose it
[00:51:39.180]isn't necessarily due to the leaf angle,
[00:51:41.730]but just that it creates a mat of a crap ton of green.
[00:51:45.930]That's really what we were shooting for.
[00:51:48.810]So Albert actually also had done some work
[00:51:52.080]on kin recognition, which I'm not gonna get into today,
[00:51:55.290]but basically do all plants show the same response?
[00:52:00.000]And so he used different plant canopies,
[00:52:02.550]some broad leafs, some grasses.
[00:52:04.590]And at least as far as sugarbeet is concerned,
[00:52:07.350]it tends to not matter.
[00:52:08.760]As long as you're reflecting far-red,
[00:52:10.380]it doesn't matter what the species is
[00:52:12.300]that's reflecting it to it, it's responding the same way.
[00:52:16.140]That's not always the case though.
[00:52:17.700]There are some species that will respond differently
[00:52:20.790]depending on if it's a grass versus a broad leaf
[00:52:23.040]or a closely related plant versus a distantly related plant.
[00:52:27.150]So I don't know if those are light quality-driven
[00:52:30.780]or something else going on,
[00:52:32.970]but at least in terms of leaf architecture,
[00:52:35.580]we did not see any impact on how that would affect
[00:52:38.010]the sugarbeet growing.
[00:52:38.970]It kind of responded the same
[00:52:40.230]regardless of what the species growing around it was.
[00:52:43.650]Did we try to simulate the reflectance color without plants?
[00:52:47.340]Yes and no.
[00:52:49.260]So actually that first paper
[00:52:52.680]when Louise and Tom were doing this in the very early days,
[00:52:58.140]we actually weren't using weeds,
[00:52:59.970]we were using different colored plastic mulches.
[00:53:03.810]And we got a lot of different reflectance spectrum
[00:53:06.360]because one of the things
[00:53:07.200]that I have always been skeptical of
[00:53:09.778]it was whether far-red was really required.
[00:53:12.570]'Cause it seems to me that plants are reflecting
[00:53:14.490]a crap ton of green light,
[00:53:16.230]why wouldn't they just respond to green light?
[00:53:18.660]That seems easier to me.
[00:53:20.970]But no, green reflectance,
[00:53:22.830]we had multiple different colors of green,
[00:53:25.140]really didn't see any changes in the plant from those.
[00:53:29.760]So it really is that far-red light.
[00:53:31.440]So we have not been able to find a plastic tarp
[00:53:34.410]that is a very good reflector of that far-red spectrum,
[00:53:38.850]but we have replicated the results
[00:53:40.500]by basically using overhead far-red lambs.
[00:53:43.770]So basically similar to what we did
[00:53:45.360]in the seed germination studies,
[00:53:49.050]some of the end of day stuff
[00:53:51.030]that Albert was doing in the greenhouse was basically
[00:53:53.310]shining that far-red light from the side in the greenhouse
[00:53:56.910]and it would elicit a similar response.
[00:53:59.040]It wasn't quite as dramatic, but basically the same thing.
[00:54:03.810]Yes, are there opportunities
[00:54:05.190]to trick weed seeds into germinating?
[00:54:08.850]Yes, I keep mentioning Albert Adjesiwor.
[00:54:11.340]You're like just totally asking all the questions
[00:54:14.040]that he has already asked or is in the process of asking.
[00:54:16.470]So at Idaho, one of the things he's looking at
[00:54:18.870]is can we use some sort of an implement
[00:54:22.260]that you hook on a tractor?
[00:54:23.700]Or when we had discussed it, like a side roll sprinkler
[00:54:27.090]that basically just shines a bright ass red light
[00:54:29.460]down on the ground to try and stimulate seed germination,
[00:54:34.260]do that or hook it up to a shallow tillage implement
[00:54:38.670]and kind of blow red light trying to get them to germinate.
[00:54:43.890]And it turns out it doesn't require
[00:54:46.200]a very large burst of far-red light
[00:54:48.030]to get some weed seeds to germinate.
[00:54:50.790]And so we actually do feel
[00:54:52.230]like there might be some potential
[00:54:54.690]to use that in a field type setting,
[00:54:57.570]burst red light, get them to grow,
[00:55:00.510]spray them out or till them out,
[00:55:02.190]kind of a stale seed bed approach
[00:55:05.040]that organic weed managers use
[00:55:08.250]but in a way that tries to get more of them to germinate
[00:55:10.590]so you can kill 'em before you establish your crop.
[00:55:12.660]So we have looked a little bit of that.
[00:55:16.080]We think there's promise there,
[00:55:17.250]but we're probably a long ways
[00:55:18.360]from being able to operationalize it.
[00:55:20.910]I guess, to repeat the question for those online,
[00:55:23.580]won't we eventually see resistance
[00:55:25.410]to any kind of light mediated control strategies?
[00:55:28.740]And I guarantee we will.
[00:55:31.410]I think if there's anything we've learned
[00:55:32.760]in weed science over the last 50 years
[00:55:36.150]is that no matter what we do,
[00:55:37.500]if it's effective at controlling weeds,
[00:55:39.660]we will select for the weeds
[00:55:40.890]that it is not effective against.
[00:55:42.240]So, yeah, because there's already preexisting differences
[00:55:45.900]between species and sometimes within species
[00:55:49.140]on how sensitive they are to far-red light,
[00:55:52.530]if we start implementing that for control,
[00:55:54.240]we will see differences.
[00:55:55.290]And in fact, one of the things we know
[00:55:57.360]in common lamb's quarters, for example,
[00:55:59.370]that the far-red dependency decreases over time.
[00:56:04.170]So, a old common lamb's quarter seed that's 20 years old,
[00:56:09.750]is way less sensitive to far-red light
[00:56:12.180]and is more likely to germinate
[00:56:13.620]in the presence of far-red light
[00:56:15.330]compared to a common lamb's quarter seed
[00:56:18.000]that is two years old.
[00:56:19.500]And again, I think probably that evolutionary like,
[00:56:22.200]you're getting to the end of life,
[00:56:23.940]man, this is your last chance.
[00:56:26.670]So, yeah, I think we'll probably
[00:56:28.470]select for different age structures of seed banks
[00:56:31.080]and also we'll probably eventually select for biotypes
[00:56:34.890]that have either more sensitivity or less sensitivity
[00:56:39.780]depending on what we're using for control.
[00:56:42.660]What does cloud cover do to the wavelengths coming in?
[00:56:46.170]I do not know the answer to that one.
[00:56:48.090]Here I thought I was totally prepared
[00:56:49.530]for all the possible questions
[00:56:50.640]as many times as I've presented.
[00:56:51.480]I have no idea, I would not expect cloud cover
[00:56:55.920]to be a major inhibitor of either of those wavelengths,
[00:57:01.410]at least not selectively so but that's pure speculation.
[00:57:05.910]So I'll probably have to do some research on that.
[00:57:08.610]Well, thank you very much.
[00:57:10.567](audience applauding)

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What’s Light Got to Do With It? Exploring the Role of Plant-reflected Light in Crop Yield Loss and Weed Management

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