Interference Between Kentucky Bluegrass (Poa pratensis) and Yellow Nutsedge (Cyperus esculentus) in a Home Lawn Setting
The presence of yellow nutsedge reduces turfgrass uniformity and visual quality in home lawns and playability on golf courses and athletic fields. We found that an actively growing Kentucky bluegrass stand impedes tuber and shoot production of yellow nutsedge from 65 to 99% without using herbicide.
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[00:00:02.250]is part of the agronomy and horticulture seminar series
[00:00:05.830]at the University of Nebraska-Lincoln.
[00:00:07.960]It's pleasure for me to introduce our speaker
[00:00:11.423]I had the privilege of advising Dr. Li on his PhD.
[00:00:15.768]And prior to that,
[00:00:17.280]he got his Master's with Zac Reicher before his departure
[00:00:22.340]in a buffalo grass investigation.
[00:00:24.910]And then prior to that,
[00:00:25.820]he was an undergrad in our program
[00:00:27.420]and is currently serving as a instructor,
[00:00:31.580]working with the outstanding distance-ed's programs.
[00:00:34.280]We're really lucky to have Dr. Li on board
[00:00:36.990]and also I'm proud to have a faculty member,
[00:00:40.270]another faculty in our department,
[00:00:41.980]that I had the privilege of training as a graduate student.
[00:00:47.920]So I'm happy for them and happy for our department
[00:00:52.580]in that regard.
[00:00:54.190]Luqi is a native of China,
[00:00:56.090]has been in the United States
[00:00:57.710]since he started attending here in his undergrad program,
[00:01:00.230]got a degree in Turf and Landscape Management.
[00:01:02.650]And as I already mentioned,
[00:01:03.590]he got his Master
[00:01:05.650]with Dr. Zac Reicher before his departure
[00:01:07.880]and his PhD with me.
[00:01:12.230]Do want to indicate that the work he's presenting here
[00:01:14.910]was a part of his PhD dissertation,
[00:01:17.910]a very interesting ecological study in yellow nutsedge,
[00:01:21.770]a very troublesome weed in lawns
[00:01:24.670]throughout the United States.
[00:01:25.920]And actually except for Antarctica,
[00:01:28.606]yellow nutsedge can be found on every continent
[00:01:32.280]So it's an intriguing, problematic weed.
[00:01:34.340]And with that, I will turn it over to Dr. Luqi Li.
[00:01:39.300]Thank you Roch for the introduction.
[00:01:42.563]So today my topic is
[00:01:44.990]Interference between Kentucky Bluegrass and Yellow Nutsedge
[00:01:48.640]in a Home Lawn Setting.
[00:01:52.260]So as Roch mentioned,
[00:01:53.620]I've been a student here at the UNL.
[00:01:56.150]I'm currently a distance education lecturer.
[00:01:59.300]As a turfgrass scientist,
[00:02:00.920]my research has been focusing on reducing turfgrass reliance
[00:02:05.670]on natural resources
[00:02:07.330]and minimize the environmental impact
[00:02:09.470]of the turfgrass industry.
[00:02:11.260]So in my Master research,
[00:02:12.880]I studied buffalo grass,
[00:02:14.650]which is a low input grass.
[00:02:18.080]So for my PhD,
[00:02:19.420]I studied the management, ecology
[00:02:22.630]and genetic of yellow nutsedge,
[00:02:24.680]which will be today's topic.
[00:02:30.160]So yellow nutsedge is native to North America and Eurasia,
[00:02:34.520]is a grass-like weed with triangular stems,
[00:02:38.470]three rank leaves.
[00:02:40.500]Yellow nutsedge is a C4 perennial weed.
[00:02:44.420]They typically infests crop fields,
[00:02:46.630]turfgrass, and landscapes.
[00:02:48.940]It is known as a wet weed.
[00:02:51.510]We normally see them in area that are poorly drained.
[00:02:56.080]They not only thrive in wet area,
[00:02:57.880]but also tolerates dry soil.
[00:03:00.630]And yellow nutsedge reproduce by seed, tuber,
[00:03:03.860]bulbs and rhizomes.
[00:03:11.210]The tuber is the primary reproduction method
[00:03:14.020]and the way how yellow nutsedge are over winter.
[00:03:17.240]So study have found that under unrestrictive growth,
[00:03:21.250]a single tuber planted in the field
[00:03:23.810]produced approximately 6900 tubers and 1900 plants
[00:03:28.590]within a year
[00:03:29.610]when study was conducted in Minnesota.
[00:03:32.610]And the reason that yellow nutsedge is hard to control
[00:03:35.610]is that these tuber underground,
[00:03:37.520]that the viable tubers may remain dormant in the soil
[00:03:41.700]for multiple years
[00:03:43.020]and may repeatedly sprout.
[00:03:47.700]Yellow nutsedge is also a prolific seed producer.
[00:03:51.490]It can produce
[00:03:52.740]anywhere between 100 to 605 million seeds per hectare.
[00:03:56.940]However, seeds are not believed to play an important role
[00:04:03.020]due to low viability
[00:04:05.550]and also a lack of vigor under field condition.
[00:04:08.420]So that tuber has believed to be the primary mean
[00:04:11.710]of yellow nutsedge reproduction and infestation.
[00:04:17.490]So yellow nutsedge is primarily a weed in crops
[00:04:21.790]that are short growing with low canopy light interception
[00:04:25.610]from sparse canopies,
[00:04:27.150]and these crops are typically frequently irrigated
[00:04:30.430]and which also require high nitrogen fertility.
[00:04:33.380]And so as a turfgrass scientist,
[00:04:35.880]all these features of a yellow nutsedge susceptible crop
[00:04:42.610]And that is because these characters
[00:04:45.880]of yellow nutsedge susceptible crops
[00:04:48.180]coincide with those of a turfgrass system.
[00:04:51.941](mumbles) in the turf grass system,
[00:04:53.460]the mowing, irrigation, fertility,
[00:04:56.430]are our primary cultural practice to sustain turf quality,
[00:05:00.800]so which make turfgrass also susceptible
[00:05:03.980]to invasion of yellow nutsedge.
[00:05:07.400]A study on turfgrass system have found that
[00:05:10.570]increased irrigation has positive effects
[00:05:13.510]on both vegetative and reproductive growth
[00:05:17.090]of yellow nutsedge with increased tuber biomass.
[00:05:20.700]Also that nitrogen promotes vegetative growth
[00:05:24.290]instead of reproductive growth in yellow nutsedge.
[00:05:30.320]So turf is not a yield-driven system,
[00:05:33.150]but the reason that yellow nutsedge is a problem for turf
[00:05:37.600]is that the presence of yellow nutsedge,
[00:05:40.170]they reduce the turf uniformity,
[00:05:42.550]visual quality in lawn,
[00:05:44.230]and also the playability on golf course and athletic field.
[00:05:47.670]This picture showed, like the bottom left one,
[00:05:51.240]that's on the collar of a green.
[00:05:53.580]So between two mowing event,
[00:05:56.050]yellow nutsedge grow faster than surrounding turfgrass,
[00:05:59.700]which produce a undesirable ununiform stand.
[00:06:04.020]And that's also a problem for playability on soccer field,
[00:06:08.430]visual quality on the sidewalk or home lawn.
[00:06:12.150]And that is the reason
[00:06:13.120]why we trying to minimize yellow nutsedge
[00:06:16.750]in the turfgrass system.
[00:06:21.410]So we often heard people saying things like,
[00:06:26.300]when talking about how to manage a healthy turf
[00:06:28.960]and to combat weed problem,
[00:06:30.760]we talk about something like a dense stand of healthy grass
[00:06:34.590]will prevent weed from invading your lawn,
[00:06:37.730]or that your healthy turf is the first line of defense
[00:06:42.640]in controlling weed,
[00:06:44.260]and healthy turf can out-compete weed
[00:06:47.220]and reducing the chance of becoming established.
[00:06:50.350]The general recommendation we often heard
[00:06:53.080]is that the best natural approach to weed control
[00:06:56.280]is maintaining managing a healthy lawn.
[00:06:59.090]Thick, large grass restrict weed growth.
[00:07:02.330]However, this statement often lacks scientific research
[00:07:09.750]to back them up.
[00:07:11.040]We always say this, but this was never quantified.
[00:07:14.990]And in today's talk,
[00:07:16.570]I'll be focusing on how management practice,
[00:07:19.830]especially maintaining a healthy Kentucky bluegrass,
[00:07:23.040]is impact on the invasiveness of yellow nutsedge
[00:07:26.660]to uncover whether these statements are true.
[00:07:32.600]So our objective is to evaluate
[00:07:34.990]the effects of irrigation and fertility on yellow nutsedge
[00:07:38.560]in a established Kentucky bluegrass lawn.
[00:07:42.850]is one of the most commonly used cool season turfgrass.
[00:07:47.130]And in the home lawn setting,
[00:07:50.280]we have a healthy two-year-old Kentucky bluegrass stand.
[00:07:55.660]Our hypothesis is that yellow nutsedge is more competitive
[00:07:59.170]than Kentucky bluegrass in the home lawn setting,
[00:08:02.060]and that is why the yellow nutsedge inversion can occur.
[00:08:07.870]we designed a split-split plot design
[00:08:11.120]with four replications,
[00:08:12.420]they're 0.9 by 0.9 plots.
[00:08:15.340]The treatment was three, at the main plot level,
[00:08:20.440]were three different irrigation.
[00:08:23.170]We either did not apply any water,
[00:08:25.910]or we did a 80% total replacement per week,
[00:08:29.890]based on onsite weather data.
[00:08:32.300]We also have a overwater treatment
[00:08:34.240]because nutsedge is known as a weed thrive in wet area.
[00:08:39.520]So we irrigate 126 liter per plot per week,
[00:08:44.060]regardless of precipitation.
[00:08:46.260]And this number is based on a homeowner survey.
[00:08:50.300]If a homeowner have a,
[00:08:51.213]what we call a set-and-forget irrigation schedule,
[00:08:54.960]they typically put down two inch of water per week,
[00:08:58.840]regardless of precipitation,
[00:09:00.640]and based on the plot area size,
[00:09:02.760]that translate to our number 126 liter.
[00:09:07.470]Three fertility level,
[00:09:09.110]either no additional fertility,
[00:09:10.940]97 or 195 kilograms N per hectare.
[00:09:15.240]There are two plot types.
[00:09:17.905]One we call the polyculture,
[00:09:19.650]is we have yellow nutsedge plants
[00:09:22.260]germinated from a single tuber
[00:09:24.530]that planted within
[00:09:26.490]a two-year-old healthy Kentucky bluegrass stand.
[00:09:29.850]The monocultures are single tuber of yellow nutsedge
[00:09:33.510]germinated in bare soil.
[00:09:36.370]The entire area was mowed at 7.6 centimeter weekly.
[00:09:40.540]This is a standard mowing height
[00:09:42.520]for Kentucky bluegrass home lawn.
[00:09:45.920]So for each of the main and subplot treatment combination,
[00:09:49.690]we had a total of 11 plots,
[00:09:53.390]it's demonstrate on the right,
[00:09:55.890]so there's eight polyculture yellow nutsedge plots.
[00:09:59.490]The reason the plots were repeat eight times
[00:10:02.780]is because to be able to count tubers,
[00:10:05.980]we have to conduct disruptive sampling every month.
[00:10:09.200]So every month we will take out
[00:10:11.820]one of the yellow nutsedge monoculture plot.
[00:10:14.890]So the first year, and four will be removed.
[00:10:17.900]And number five, six, seven, and eight will be removed
[00:10:20.717]for the second growing season.
[00:10:24.460]At the end of the column,
[00:10:25.530]there's two monoculture yellow nutsedge plot.
[00:10:28.400]These were yellow nutsedge germinated in bare soil.
[00:10:32.450]In the end of the first year in September,
[00:10:35.020]we collect the first monoculture plot.
[00:10:37.610]And the second year, we collect samples,
[00:10:40.590]disruptively sample the second plot.
[00:10:43.090]And we have a Kentucky bluegrass check at the end.
[00:10:47.240]So if you have driven past north entrance of east campus,
[00:10:51.610]you'll see our UNL East Campus Turf Research Farm.
[00:10:56.280]And this is a drone image of the research area.
[00:10:59.680]This chessboard-looking area
[00:11:02.220]was where this study was conducted.
[00:11:04.670]The reason it looks this way is for the monoculture,
[00:11:08.030]we first spray glyphosate
[00:11:10.620]to kill all the Kentucky bluegrass.
[00:11:12.420]Then prior to initiation of the study,
[00:11:15.210]we use a sod cutter to completely removed any residual
[00:11:20.250]to be able to enable a bare soil plots
[00:11:23.440]for the monoculture yellow nutsedge.
[00:11:28.020]So yellow nutsedge in area treatment
[00:11:30.680]was germinated from a single tuber
[00:11:33.800]and at the three to five leaf stage,
[00:11:35.960]we transplant them in the field,
[00:11:37.690]either in bare soil or within Kentucky bluegrass.
[00:11:43.010]So this was done by first drilling a hole,
[00:11:45.820]and then we put the plugs at the center of each plot.
[00:11:51.560]And monoculture plot would look like the image on the left
[00:11:55.477]and see that nutsedge has three to five leaf stage
[00:11:58.900]plug into the center of Kentucky bluegrass.
[00:12:04.350]On the right side is monoculture plot,
[00:12:07.302]all the Kentucky bluegrass were removed,
[00:12:09.440]nutsedge were germinated from a single tuber
[00:12:12.570]and in bare soil.
[00:12:15.370]To be able to precisely apply irrigation,
[00:12:18.830]we attach flow meter to the end of the hose.
[00:12:23.090]So for the 80% ET replacement,
[00:12:25.780]those were done at the end of each week
[00:12:28.010]after gathering weather data.
[00:12:30.400]For the overwater,
[00:12:32.730]we want to reduce the risk of surface runoff.
[00:12:37.290]And therefore, we didn't put down the 126 all at once.
[00:12:40.890]Instead, we do that in three event,
[00:12:43.330]Monday, Wednesday and Friday, every week.
[00:12:45.880]That is a similar way
[00:12:47.400]how a homeowner may set up their system.
[00:12:50.700]And like I mentioned, this was regardless of irrigation,
[00:12:55.070]regardless of precipitation,
[00:12:57.220]so there were at times that we put down water
[00:12:59.730]in a pouring down rain.
[00:13:02.560]To evaluate yellow nutsedge shoot production,
[00:13:05.980]every week we use a scissor
[00:13:08.500]to cut off the new shoot growth
[00:13:11.330]above the 7.6 centimeter mowing height.
[00:13:15.220]That way we can estimate a weekly shoot production.
[00:13:19.860]For the monoculture plot,
[00:13:22.187]we will show more image later,
[00:13:24.480]but they grow a lot faster than we anticipated.
[00:13:28.680]And by the third or fourth week,
[00:13:31.750]we can no longer use scissor to cut them,
[00:13:34.410]so we use mower with a catch bag,
[00:13:37.200]we drop the mower on top of the plot,
[00:13:40.290]and then we collect clippings dry and weight them.
[00:13:44.160]so every week after collecting the yellow nutsedge shoots,
[00:13:49.340]we then mowed the entire area
[00:13:51.670]at the 7.6 centimeter mowing height.
[00:13:55.580]This was the disruptive sampling I mentioned earlier.
[00:13:59.280]So during the growing season,
[00:14:00.830]every month we use a 20.3 centimeter soil cup cutter,
[00:14:08.080]soil sampler to extract soil cores.
[00:14:11.160]And these were later washed
[00:14:14.950]and the tubers were identified and hand-separated.
[00:14:20.270]So there's two type of measurements we did in the study.
[00:14:23.960]We name them as outcomes or available resources.
[00:14:29.510]we measured yellow nutsedge shoot and tuber production,
[00:14:32.990]Kentucky bluegrass shoot production,
[00:14:35.400]plant count for poly- and monoculture yellow nutsedge,
[00:14:39.380]leaf chlorophyll content,
[00:14:41.030]carbon dioxide exchange rate.
[00:14:43.230]For available resources,
[00:14:44.900]we measured soil volumetric and gravitational water content,
[00:14:49.530]soil extractable nitrogen,
[00:14:51.880]photosynthetically active radiation measurement,
[00:14:54.560]and also we had data from our onsite weather center
[00:14:59.210]with daily temperature and weekly ET.
[00:15:01.910]So in this seminar,
[00:15:02.960]I'll be focused on presenting result and interactions
[00:15:07.690]that are significant.
[00:15:10.310]For statistical analysis,
[00:15:12.320]the mono- and polyculture shoot and tuber production data
[00:15:16.440]were analyzed separately.
[00:15:18.630]And I will explain why it has to be done this way.
[00:15:21.760]Then weekly yellow nutsedge shoot production of each week
[00:15:25.090]were summed together
[00:15:26.500]as monthly shoot production.
[00:15:29.000]The repeated measure data were analyzed
[00:15:30.800]as a split-split plot
[00:15:32.300]generalized linear mixed model
[00:15:33.930]using PROC GLIMMIX in SAS.
[00:15:36.670]Means separation was performed
[00:15:38.080]using Fisher's Protected LSD at P equal or less than 0.05.
[00:15:45.240]So this image was taken the third week of July,
[00:15:49.070]right before our Turfgrass Field Day.
[00:15:51.580]So at this point,
[00:15:52.740]yellow nutsedge was planted a little over seven weeks.
[00:15:57.150]And this was what looks like in the polyculture plot
[00:16:00.760]versus the monoculture plot.
[00:16:02.730]Look at the yellow nutsedge in polyculture plot,
[00:16:05.540]we probably can see a couple plants there,
[00:16:08.620]whereas on the right side, after seven weeks,
[00:16:12.100]yellow nutsedge germinated from a single tuber
[00:16:15.800]at the center of this 0.9 by 0.9 meter plot
[00:16:19.130]have almost reached the edge of the plot.
[00:16:23.600]And this is the reason
[00:16:24.610]why that data has to be analyzed separately
[00:16:27.890]because on a weekly base,
[00:16:29.800]the shoot production can be 700 folds higher
[00:16:34.740]in the monoculture plot.
[00:16:37.760]So here's a result showing
[00:16:40.420]a month by irrigation interaction.
[00:16:43.850]The y-axis is polyculture
[00:16:46.607]yellow nutsedge monthly shoot production,
[00:16:48.620]yellow nutsedge that grow
[00:16:49.810]within the two-year-old healthy Kentucky bluegrass.
[00:16:54.580]The different shade of blue
[00:16:56.840]representing different irrigation level.
[00:16:59.690]Lighter blue is non-irrigated and ET,
[00:17:02.630]and the dark blue is overwater,
[00:17:05.080]the 126 liter per plot per week,
[00:17:09.060]regardless of precipitation.
[00:17:12.430]As we would expect,
[00:17:13.640]when yellow nutsedge first germinate
[00:17:15.790]and start growing in June,
[00:17:17.280]the monthly shoot production was lowest.
[00:17:20.490]The highest shoot production was observed in August.
[00:17:24.270]And they were observed in the overwater plots.
[00:17:27.980]What we found interesting is that after the first year,
[00:17:31.703]when we come back the second year,
[00:17:34.270]we had yellow nutsedge clippings shoot production
[00:17:38.130]that was lower across the board
[00:17:40.490]compared to the first year,
[00:17:42.260]even though the overwatered August production
[00:17:44.650]were still the highest,
[00:17:46.140]those were lower than we observed in the first year.
[00:17:51.650]And the reason of this is because in the second year,
[00:17:55.310]many yellow nutsedge in the polyculture plot
[00:17:58.247]did not came back.
[00:18:00.130]So there's two way we can deal with this.
[00:18:02.250]We can treat those plots
[00:18:04.740]that we didn't see any yellow nutsedge the second year
[00:18:07.340]as missing data,
[00:18:09.100]or we believe the reason yellow nutsedge did not come back
[00:18:13.670]is because of the interference of Kentucky bluegrass.
[00:18:17.120]We think this is a treatment effect of the plot type
[00:18:20.730]and therefore, data was average across all four reps.
[00:18:25.340]And that is why
[00:18:26.720]the second-year across-board shoot production was lower.
[00:18:32.080]A similar story in the effect of fertility
[00:18:35.620]over a growing season.
[00:18:37.450]In the first year, the highest production was observed
[00:18:41.150]in the fertilized plot and in August.
[00:18:43.777]And again, second year,
[00:18:45.740]because many yellow nutsedge did not come back
[00:18:48.660]across the board, the mean shoot production was lower
[00:18:52.820]compared to 2017.
[00:18:55.290]So next I'm gonna show a series of time lapse photos
[00:18:59.990]about what it look like in the monoculture plot,
[00:19:03.020]how does yellow nutsedge grow?
[00:19:04.480]So this was June 4th, 2017.
[00:19:09.750]By June 23rd,
[00:19:10.670]we can see that yellow nutsedge growing at a very fast pace.
[00:19:15.080]By July 21st,
[00:19:16.803]that was the first series of photo I showed
[00:19:19.690]when we compare poly- versus monoculture.
[00:19:22.493]Yellow nutsedge has almost reached the edge of the plot.
[00:19:26.390]August 18 is where a peak shoot production was observed.
[00:19:33.880]And by September,
[00:19:35.120]with daylight length shorten and temperature drops,
[00:19:38.680]the yellow nutsedge grows slow significantly
[00:19:41.610]after mowing between the two mowing event.
[00:19:44.270]And after the first frost, by the end of September,
[00:19:47.550]yellow nutsedge monoculture nutsedge
[00:19:49.700]die back to the ground.
[00:19:51.650]So we now look at
[00:19:53.040]how irrigation affect the monoculture shoot production.
[00:19:56.550]So now notice on the y-axis,
[00:19:59.500]the unit we use here is grams per square meter.
[00:20:03.190]If you recall the prior slides
[00:20:05.360]when we are looking at the polyculture,
[00:20:07.920]we're using milligrams per square meter.
[00:20:10.870]So compared the two,
[00:20:14.680]there's up to 700 times different on a weekly base.
[00:20:19.470]And as I mentioned earlier,
[00:20:21.510]this is why the data has been analyzed separately.
[00:20:25.310]Similar to what we observed in the polyculture,
[00:20:28.900]in August, we have the highest shoot production,
[00:20:32.260]and they were similar across the ET treatment
[00:20:35.860]or overwater treatment.
[00:20:38.490]Now we look at a three-way interaction,
[00:20:41.130]that's month of the year, by irrigation, by fertility,
[00:20:44.960]different shade of blue
[00:20:46.230]representing different level of irrigation,
[00:20:49.200]different shade of brown
[00:20:50.420]representing different level of fertility.
[00:20:54.030]If we look at 2017,
[00:20:56.480]as we expected,
[00:20:59.676]the more resources we put down,
[00:21:02.140]yellow nutsedge produce more shoot,
[00:21:03.950]compared to the no water, non-irrigated.
[00:21:08.160]What we found interesting
[00:21:09.870]is the data that we collected in 2018.
[00:21:15.090]Now we take a close look.
[00:21:16.350]Again, the y-axis is a monoculture
[00:21:17.967]yellow nutsedge monthly shoot production
[00:21:20.500]in grams per square meter.
[00:21:23.340]And we have a three-way interaction.
[00:21:27.790]We found that the second year,
[00:21:29.330]the yellow nutsedge really came back strong.
[00:21:32.390]Just in the month of June,
[00:21:34.100]the beginning of the second growing season,
[00:21:36.870]they already has a much higher production
[00:21:40.050]than the highest number produced in August of first year.
[00:21:44.160]However, we see that shoot production peaked in June
[00:21:48.050]and they start decline in July, August, September.
[00:21:52.400]So what happened in July?
[00:21:54.010]What causes dramatic decrease
[00:21:55.790]for the subsequential shoot production?
[00:21:58.820]So this is a image on June 8th, 2018.
[00:22:02.430]So in this particular week, between the two mowing event,
[00:22:06.950]after we mow at 7.6 centimeter,
[00:22:09.770]in that single week,
[00:22:11.090]yellow nutsedge grow over 20 centimeter
[00:22:13.880]because the moisture, the precipitation,
[00:22:17.780]and the temperature was optimal
[00:22:20.940]for yellow nutsedge at the time.
[00:22:26.353]we talk about thing called the one-third rule.
[00:22:29.850]The one-third rule suggests that
[00:22:31.670]when mowing your turfgrass,
[00:22:33.270]you should never remove
[00:22:34.630]more than a third of a leaf blade at the time,
[00:22:37.560]because doing so will cause damage to the turf.
[00:22:40.610]It will scalp your turf.
[00:22:42.370]And we observe a similar effect when we mow yellow nutsedge.
[00:22:47.070]So between the two mowing event,
[00:22:49.950]with us mowing at 7.6 centimeter,
[00:22:53.070]we effectively removed
[00:22:55.130]more than 70% of yellow nutsedge leaf blade at once.
[00:22:59.080]So after this mowing,
[00:23:01.060]we see there's a lot of damage
[00:23:03.010]and there's scalping for yellow nutsedge.
[00:23:05.500]Some leaf tissue seems burned.
[00:23:08.770]And after that yellow nutsedge was never,
[00:23:11.910]in monoculture plot,
[00:23:13.020]was never able to produce higher amount of shoot production
[00:23:16.970]on a monthly base or on a weekly base,
[00:23:20.150]which suggests that mowing
[00:23:22.020]can be a powerful cultural practice
[00:23:24.350]in reducing the invasiveness of yellow nutsedge.
[00:23:28.519]So now we take a look of the monoculture yellow nutsedge
[00:23:32.296]versus polyculture yellow nutsedge again.
[00:23:36.506]So here in the photo, this was taken the first year.
[00:23:39.770]This is third week of July.
[00:23:42.060]From the further end to the bottom left,
[00:23:46.270]we have zero or 97, 195 kilograms N per hectare per year.
[00:23:52.070]And this entire block I showed is 80% ET.
[00:23:56.040]We can clearly see how much growth
[00:23:57.990]that we observed in the monoculture plot.
[00:24:00.820]But planted the same day
[00:24:02.900]under the exact same condition,
[00:24:05.930]we can barely see those yellow nutsedge as a polyculture.
[00:24:10.160]With the interference of Kentucky bluegrass,
[00:24:13.310]the yellow nutsedge invasiveness was significantly reduced.
[00:24:18.960]So now we look at the data from above ground.
[00:24:22.590]We know that the most important thing
[00:24:24.330]of controlling yellow nutsedge
[00:24:25.790]is not only the ground cover,
[00:24:28.040]but also look into tuber production.
[00:24:31.490]We want to see how our treatment, how our plot types
[00:24:35.550]affect the formation of tubers underground.
[00:24:40.620]So this is what we did.
[00:24:42.610]So we extract, disruptively sample yellow nutsedge,
[00:24:46.190]and then we wash off all the soil,
[00:24:49.330]and then we can see the tubers here.
[00:24:52.890]We identify them and we separate them by hand and count.
[00:24:56.880]And this is a highly labor-intensive process.
[00:25:02.210]It takes five of us continue to do this
[00:25:06.160]for three to four months,
[00:25:07.870]and first growing season,
[00:25:09.470]and even longer, the second growing season,
[00:25:11.460]to be able to count the tubers.
[00:25:15.180]So here is a comparison of the polyculture sample
[00:25:19.270]and monoculture sample.
[00:25:20.960]So on the left, we have somewhere around 19 tubers.
[00:25:25.720]This was collected by the end of the first growing season
[00:25:28.860]in September of 2017.
[00:25:31.000]Plants germinated from one tuber in the polyculture
[00:25:34.320]form around 19 tubers
[00:25:36.910]whereas in the monoculture plot,
[00:25:39.150]this particular image showing 1500 tubers in this tray.
[00:25:44.270]However, this is not all the tubers
[00:25:46.970]in the 0.9 by 0.9 meter plot.
[00:25:50.010]This is just the one we collected at the center
[00:25:53.160]using a 20.3 centimeter sampler.
[00:25:57.010]So the entire production was much higher
[00:25:59.870]than this image suggests.
[00:26:01.470]But from this two photo,
[00:26:03.370]we can see how much of a difference
[00:26:05.990]with or without interference of Kentucky bluegrass have
[00:26:10.160]on the tuber production capability of yellow nutsedge.
[00:26:16.370]So we're looking at some tuber production number
[00:26:19.900]in the polyculture plot at two growing season.
[00:26:23.600]In June of 2017, as expected, there was no tuber formed
[00:26:28.130]because yellow nutsedge really started their tuber formation
[00:26:31.110]after the longest day of summer.
[00:26:33.460]So in July, we had seven tubers,
[00:26:35.870]and by the end of the first year,
[00:26:38.130]they were across treatment,
[00:26:39.570]we average around 18 tubers.
[00:26:43.680]Those were formed from a single plant.
[00:26:46.380]And so in 2018, the number did not go higher.
[00:26:50.040]And this was,
[00:26:51.170]as the reason I explained earlier,
[00:26:52.820]the second year in many of the plot with Kentucky bluegrass,
[00:26:57.350]yellow nutsedge did not came back.
[00:26:59.450]So we average across the four replications,
[00:27:03.570]the number stays unchanged.
[00:27:05.460]And we think this is a treatment effect
[00:27:08.520]caused by the interference of Kentucky bluegrass.
[00:27:12.240]Now, we look at the irrigation by fertility interaction
[00:27:15.220]and see how this resource input affect the tuber production
[00:27:20.220]in the polyculture plot.
[00:27:24.450]We found that the non-irrigated and no fertility plots
[00:27:30.830]formed less tuber,
[00:27:32.810]and the most tuber in polyculture was formed
[00:27:36.240]in the fertilized
[00:27:38.130]and those that were under ET or overwater treatment.
[00:27:45.480]So how about monoculture tuber production?
[00:27:47.090]What the exact numbers were as the photo I show you earlier?
[00:27:52.020]So to count the entire 0.9 by 0.9 meter,
[00:27:56.140]we did not dug out the entire plot.
[00:27:59.350]What we did is we sample at the center,
[00:28:02.340]then we put down a grade,
[00:28:04.000]and on the radius adjusted base,
[00:28:06.490]we collect multiple samples.
[00:28:08.370]Then we adjusted for the area
[00:28:10.010]to estimate the total production.
[00:28:12.460]In 2017, the tuber production was ranging
[00:28:16.240]between 2900 to 5100 in the first year.
[00:28:25.858]it's an enormous amount of production,
[00:28:27.190]but they were still actually lower
[00:28:29.750]than those reported in the Minnesota study I review earlier.
[00:28:33.820]And that is likely because in that study,
[00:28:36.750]yellow nutsedge was under a unrestrictive growth.
[00:28:40.200]And here nutsedge,
[00:28:41.930]unfortunately, our plot size should have been bigger,
[00:28:45.440]but we reached the edge of the plot
[00:28:47.850]by the end of the first growing season,
[00:28:49.910]that likely reduce the reproductive potential or tuber.
[00:28:55.500]So in 2018, this is the second year,
[00:28:59.540]the end of the growing season,
[00:29:01.350]so germinated from a single tuber,
[00:29:03.920]a yellow nutsedge plant over two years
[00:29:06.360]form an average of 16,000 tubers,
[00:29:12.996]which was a enormous amount,
[00:29:16.280]especially when we compare to the 19 or 22
[00:29:20.380]produced in the polyculture plot,
[00:29:22.510]when Kentucky bluegrass was interferencing.
[00:29:27.370]So that bring us a question.
[00:29:28.690]We see there's 700-fold shoot production difference,
[00:29:33.460]a thousand times more tuber produce in the monoculture
[00:29:38.120]versus the polyculture.
[00:29:40.140]So what is the difference?
[00:29:43.440]So we look into the available resources we measured
[00:29:48.130]and we didn't find a significant amount of difference.
[00:29:52.440]And so then we revisit.
[00:29:55.258]So why yellow nutsedge can invade some crop or turfgrass?
[00:30:00.910]We think one thing we know is that
[00:30:04.030]yellow nutsedge invade crop field
[00:30:06.950]with low canopy light interception.
[00:30:09.470]So then we look into if lights is a driving factor
[00:30:13.460]causing the significant difference
[00:30:16.010]between the poly- and monoculture plots.
[00:30:20.160]So we measured a plant light interception
[00:30:24.298]in Kentucky bluegrass plots.
[00:30:25.990]And these were calculated as total PARin
[00:30:29.890]minus PAR reflected by Kentucky bluegrass
[00:30:34.880]minus reflected by the ground
[00:30:36.940]divided by the total PARin.
[00:30:40.320]And we see there was a significant difference
[00:30:44.010]caused by irrigation.
[00:30:45.450]So in the overwater plots,
[00:30:48.440]the Kentucky bluegrass have a 79% plant light interception,
[00:30:53.950]and anywhere between 62 to 66% light interception
[00:30:59.388]for the 80% ET and the non-irrigated treatment.
[00:31:06.000]So if we look at this image,
[00:31:09.580]when yellow nutsedge was growing or germinating
[00:31:12.710]within a healthy two-year-old Kentucky bluegrass,
[00:31:16.370]based on our data,
[00:31:17.980]we suggest the light interception
[00:31:21.230]was around 62% to 79%.
[00:31:25.800]However, imagine that tuber was germinated in the bare soil,
[00:31:30.970]at the beginning when the tuber start growing,
[00:31:33.440]the plant light interception is effectively zero
[00:31:36.330]because there was no plant,
[00:31:37.630]there was no interference by Kentucky bluegrass.
[00:31:41.100]even though the sparse canopy of yellow nutsedge itself
[00:31:45.690]may have caused some light interception,
[00:31:49.180]but when they were spreading and growing by rhizome,
[00:31:52.620]when a new plant's formed,
[00:31:55.330]the plant light interception was, again, effectively zero.
[00:31:59.040]So we think this is one thing we would speculate,
[00:32:03.150]being the reason
[00:32:04.440]why that there was such a huge production difference
[00:32:08.670]between the polyculture and monoculture.
[00:32:11.270]However, the best way to evaluate,
[00:32:15.700]to proven if our speculation was correct
[00:32:19.390]is either by applying in future studies,
[00:32:23.130]or either apply different level of shade
[00:32:25.660]to simulate the plant light interception
[00:32:28.040]to see if there's a effect
[00:32:29.630]of yellow nutsedge growth and production,
[00:32:32.330]or we can design study
[00:32:34.400]with different mowing height of the turfgrass.
[00:32:37.740]And different mowing height will cause
[00:32:39.540]a different level of plant light interception.
[00:32:42.330]That way we will be able to better answer the question
[00:32:45.790]what is the actual driving factor
[00:32:48.050]cause such a dramatic difference
[00:32:50.600]between the mono- and polyculture.
[00:32:53.760]So to summarize our result,
[00:32:55.720]we found that yellow nutsedge shoot and tuber production
[00:32:58.940]were limited in non-irrigated plots
[00:33:01.370]and non-fertilized plots.
[00:33:03.850]We found that extensive removal
[00:33:05.980]of yellow nutsedge shoot tissue,
[00:33:08.090]such as what we did more than 70% of leaf blade
[00:33:12.060]at once through mowing
[00:33:13.710]could be a cultural method
[00:33:16.020]for reducing yellow nutsedge shoot growth.
[00:33:18.770]And as Roch mentioned earlier,
[00:33:20.130]I done a series of study for my PhD.
[00:33:23.290]In other greenhouse study,
[00:33:25.760]we found that mowing at the 7.6 centimeter weekly
[00:33:29.380]reduced yellow nutsedge rhizome dry mass by 55%
[00:33:33.610]and number of new tuber formed by 63% in greenhouse study
[00:33:38.590]when yellow nutsedge was germinated
[00:33:40.750]from a single tuber in each plot,
[00:33:45.050]so that we confirm that
[00:33:46.700]mowing is a effective cultural practice
[00:33:49.640]to reduce yellow nutsedge growth,
[00:33:51.690]both shoot growth and rhizome and tuber.
[00:33:57.102]We found that importantly that the presence
[00:33:59.330]of actively growing Kentucky bluegrass
[00:34:01.640]impedes tuber and shoot production of yellow nutsedge
[00:34:04.910]anywhere from 65 to 99%.
[00:34:10.120]So with those over 120,000 tubers that we washed, collected,
[00:34:16.680]we are planning to further use them
[00:34:19.837]and to investigate the management effect
[00:34:22.160]on the gene expression of yellow nutsedge.
[00:34:24.190]So this is a ongoing study I'm working on
[00:34:27.890]with Dr. Keenan Amundsen.
[00:34:29.930]So briefly our objectives is to identify treatments
[00:34:34.850]that promote change in gene expression
[00:34:37.370]that are important for yellow nutsedge proliferation,
[00:34:40.500]so that this can help us
[00:34:42.100]to select sustainable management strategy
[00:34:45.550]that mitigate such effect
[00:34:46.980]while impeding yellow nutsedge growth.
[00:34:51.042]For the material and method,
[00:34:52.650]briefly, so we use those tuber we collected
[00:34:55.710]from this field study
[00:34:57.950]and we extract RNAs from these tubers of each treatment,
[00:35:02.050]and then the sample was sequenced
[00:35:04.370]at UNMC Genomic Core Facility.
[00:35:08.430]We conduct pairwise comparison
[00:35:10.660]and a differential gene expression was identified.
[00:35:17.030]In a very preliminary result that we found,
[00:35:20.020]a differential expression of 169 genes identified
[00:35:25.290]when we compare the overwatered and heavily fertilized plot
[00:35:29.730]versus the plot that we did not put down irrigation
[00:35:35.740]So our next step is to further look into this 169 genes
[00:35:41.200]to identify whether they were up- or downregulated
[00:35:44.900]in response to our treatments.
[00:35:47.280]And also we'll conduct a genome annotation
[00:35:50.830]to assign functions to the gene identified
[00:35:53.690]to see maybe there're certain genes
[00:35:55.810]that was about crowding
[00:35:59.100]or there're certain genes maybe about water-use efficiency
[00:36:03.160]or nitrogen uptakes.
[00:36:05.040]So we'll then screening function properties
[00:36:07.630]and this will help us design future study
[00:36:10.340]to better understand the growth
[00:36:13.150]and ecology of yellow nutsedge.
[00:36:17.640]As a conclusion,
[00:36:19.060]we found that in this field study
[00:36:22.470]that deficit-based irrigation should be used
[00:36:26.010]in yellow nutsedge infested turfgrass.
[00:36:29.150]And fertility recommendation
[00:36:31.320]should be based on expectations of turfgrass quality
[00:36:35.460]while avoiding excessive fertilizer applications
[00:36:38.590]in yellow nutsedge invested turfgrass.
[00:36:41.847]And we were able to proven
[00:36:44.260]that old saying of healthy turf is the best way
[00:36:47.230]of combating weed,
[00:36:48.790]we found that a healthy turf grass stand
[00:36:51.580]is a powerful cultural practice
[00:36:54.160]to reduce the invasiveness of yellow nutsedge.
[00:36:56.890]Without any use of herbicide,
[00:36:58.890]by maintaining a healthy turfgrass,
[00:37:01.170]we reduce yellow nutsedge shoot and tuber production
[00:37:04.410]anywhere from 65 to 99%.
[00:37:08.670]So I would like to thank
[00:37:10.140]University of Nebraska-Lincoln the turfgrass program,
[00:37:13.910]Nebraska Turfgrass Association,
[00:37:16.480]also the University of Nebraska Medical Center
[00:37:19.730]Genomic Core Facility
[00:37:21.580]for facilitating with sequencing.
[00:37:24.870]I would like to thank my colleague,
[00:37:26.980]Beth Niebaum, Collin Marshall,
[00:37:29.150]Joe Foral and Jacob Fuehrer.
[00:37:31.380]On the right top photos,
[00:37:35.130]these are my colleagues that helped me
[00:37:37.930]to dig up all those tubers at the first place.
[00:37:41.260]We then germinated them in the greenhouse,
[00:37:43.370]and then we transplant them in the field.
[00:37:46.350]I like to thank Gary Nieuwkoop, Eric Chestnut,
[00:37:49.030]Parker Johnson and Ryan Witkowski.
[00:37:53.070]This four of my colleague and I,
[00:37:54.750]we spent a lot of time washing tubers,
[00:37:57.980]and without their help,
[00:37:59.700]I would never be able to finish the study.
[00:38:03.980]We have months over months of tuber washings every day.
[00:38:08.100]And as I mentioned earlier,
[00:38:10.460]at the end,
[00:38:11.293]we have over 120,000 tubers in bags collected.
[00:38:17.360]And those were all hand-separated by root washing.
[00:38:22.680]I like to thank Matt Sousek and Craig Ferguson
[00:38:26.450]for operating and managing our east campus plot.
[00:38:33.860]And I would like to thank my committee member,
[00:38:36.420]chair Dr. Roch Gaussoin,
[00:38:38.710]Dr. Keenan Amundsen,
[00:38:40.510]Dr. John Lindquist,
[00:38:41.850]Dr. Tim Arkebauer,
[00:38:43.120]and Dr. Dave Wedin.
[00:38:47.040]So I hope I have been able to explain
[00:38:48.910]all the aspect of this study.
[00:38:51.260]And please let me know if you have any questions.
[00:38:56.740]Luqi, this is Roch.
[00:38:57.680]I have one question.
[00:39:01.249]Are the yellow nutsedge tubers edible?
[00:39:04.550]Yeah. So this is a good question.
[00:39:06.260]So the yellow nutsedge tuber is edible.
[00:39:10.440]And I believe in certain Africa country,
[00:39:13.680]it were used as a staple food,
[00:39:16.050]and they can also be used to make tortilla.
[00:39:18.900]So yes, they are edible.
[00:39:20.150]And there's actually a cultivated version of yellow nutsedge
[00:39:24.370]called the tiger nut.
[00:39:26.020]Those were a type of staple food in some Africa country.
[00:39:30.680]Okay. Thank you.
[00:39:31.513]And here's a question from the chat.
[00:39:34.100]Luqi, given the decline of the yellow nutsedge in 2018,
[00:39:37.660]after mowing events in the monoculture plots,
[00:39:40.310]can you completely rule out
[00:39:41.550]that the yellow nutsedge didn't also decline
[00:39:44.160]due to its own aggressive growth and competition
[00:39:46.860]for space to spread in the monoculture plots,
[00:39:51.063]similar to the effect of Kentucky bluegrass interference?
[00:39:56.350]Yeah. Thank you, (indistinct).
[00:39:57.183]Yeah, I think this is a great question.
[00:39:59.757]We won't be able to rule out
[00:40:02.210]this can be a potential effect
[00:40:04.890]caused by the crowding itself.
[00:40:09.700]The reason I speculate those words caused by mowing
[00:40:13.810]is because we see symptoms of scalping
[00:40:16.710]just like when we mow more than a third of leaf blade
[00:40:23.860]So we think, we speculate that can be a reason.
[00:40:27.120]And another reason is that in the other study,
[00:40:31.750]we also find that the mowing
[00:40:33.460]does reduce the invasiveness of yellow nutsedge,
[00:40:35.733]and hence, that is we give the recommendation,
[00:40:39.040]but you are correct,
[00:40:40.980]we cannot decisively conclude
[00:40:43.490]that the subsquential decline
[00:40:50.470]was only caused by the mowing.
[00:40:53.880]Yeah, that was Matt (indistinct) question.
[00:40:55.570]Thank you, Matt.
[00:40:58.954]Keenan has a question.
[00:41:00.030]Do you think your research on competition interference,
[00:41:04.390]can it be applied to other weeds in turf systems
[00:41:07.260]or is it likely unique to yellow nutsedge?
[00:41:09.940]And the second part of the question is,
[00:41:11.700]similarly, is the response unique to Kentucky bluegrass
[00:41:15.300]or can it be extended to other turfgrass species?
[00:41:19.740]Thank you, thank you for the question.
[00:41:21.770]So I think, for the effect of turfgrass on weed,
[00:41:26.790]I think that can be extended to other weed.
[00:41:32.090]So although the recommendation is observational,
[00:41:35.270]but we often see that when you have a healthy lawn,
[00:41:40.710]a healthy lawn that mow at optimal mowing height
[00:41:45.030]can reduce crabgrass
[00:41:47.930]because crabgrass seed does require light to germinate.
[00:41:51.470]So I think for many weed
[00:41:53.480]that require light for their seed to germinate,
[00:41:57.810]the interference of turf
[00:41:59.470]certainly will have a impact on them.
[00:42:02.880]And also it's not only unique to Kentucky bluegrass,
[00:42:06.370]other grass that commonly use for a home lawn,
[00:42:10.770]such as tall fescue,
[00:42:12.650]and also I think buffalo grass,
[00:42:14.880]because of the way they create shade to weed seed
[00:42:19.220]and they interference light,
[00:42:21.270]and they also can compete for resources
[00:42:24.200]available to the weed.
[00:42:25.180]So I think this conclusion can be further expanding
[00:42:29.440]to other turfgrass and to other weed.
[00:42:33.870]Thank you, Luqi.
[00:42:34.703]And then an earlier comment was,
[00:42:37.350]don't discount light quality.
[00:42:40.320]And I think you sort of answered that
[00:42:43.100]with your comment there,
[00:42:44.250]but you didn't say something in the seminar that indicated
[00:42:47.930]that that light quality wasn't as important
[00:42:50.540]as some of these others.
[00:42:51.610]So I think the indication (indistinct),
[00:42:53.790]you need to be careful about making broadbased assumptions
[00:42:56.500]if you don't have all the data.
[00:42:57.740]Yes. That's right. Yes.
[00:43:00.280]We have another question.
[00:43:02.549]Polyculture reduces tuber production significantly,
[00:43:05.740]but even if a single tuber produces
[00:43:08.820]20 tubers in the next generation,
[00:43:11.770]won't that increase yellow nutsedge pressure pretty quickly?
[00:43:15.430]Yep. That is a great question.
[00:43:17.240]So one tuber produce 20 tuber
[00:43:20.790]even in the ones with Kentucky bluegrass interference,
[00:43:23.570]but we also find that in those plot, the second year,
[00:43:27.230]the number did not go higher
[00:43:30.680]because many nutsedge did not came back,
[00:43:33.570]they did not germinate
[00:43:35.200]without the interference of Kentucky bluegrass.
[00:43:37.970]And if we go back to the area,
[00:43:41.280]so after, well, this is purely observational,
[00:43:44.950]but on the third year,
[00:43:46.527]the study was already concluded.
[00:43:48.920]We go back
[00:43:49.970]and we see that in the healthy Kentucky bluegrass turf,
[00:43:52.920]we did not see yellow nutsedge came back
[00:43:55.870]as we would imagine
[00:43:59.480]that the health turf actually had a effect
[00:44:02.530]of reducing the germination of yellow nutsedge.
[00:44:07.512]Did not germinate,
[00:44:08.345]but are those tubers still viable but dormant?
[00:44:12.463]I think unfortunately those tubers is likely still viable
[00:44:18.110]because the tuber produced in the field can stay viable
[00:44:24.350]based on literature for up to 20 years.
[00:44:27.890]So if given the chance with the turf thinning
[00:44:31.940]or a favorable growth condition,
[00:44:33.940]it is possible they can come back.
[00:44:36.570]So to manage yellow nutsedge,
[00:44:38.300]we really need to have a integrated management approach,
[00:44:41.860]and any successful management,
[00:44:43.890]I think, will take multiple years to be effective.
[00:44:48.760]Okay. I see the question By Dr. Lindquist.
[00:44:52.920]Dr. Lindquist ask about assigning gene up- or downregulation
[00:44:58.260]if I can design a experiment
[00:45:00.090]to detect the cause of up- or downregulation,
[00:45:06.363]is it owing to water availability,
[00:45:10.870]light quantity, or light quality?
[00:45:14.160]This is a great question.
[00:45:15.560]I will give it more thought into this,
[00:45:18.460]especially we will first to look if these gene,
[00:45:22.760]we know them, they were differentially identified,
[00:45:25.540]but how relevant they are to the ecology or to the growth
[00:45:30.220]is yet to be seen,
[00:45:31.650]still need to be identified.
[00:45:33.980]Once we have a better idea,
[00:45:36.010]I think it would be great to consider design a study
[00:45:40.550]to better validate the cause of such up-, downregulation.
[00:45:46.343]So Luqi, do you have sufficient...
[00:45:48.083]I mean, I know you have a gazillion tubers,
[00:45:51.110]but you retain enough of those
[00:45:53.060]and know their treatment that were,
[00:45:57.470]that were put on them
[00:45:58.460]that you would have enough seed to confirm
[00:46:02.420]as well as test an additional hypothesis
[00:46:05.490]that Dr. Lindquist suggests?
[00:46:07.613]Yes, we have sufficient amount of tuber left.
[00:46:11.200]But if they're edible,
[00:46:12.040]why don't we just make tortillas and have a big party?
[00:46:15.010]Yeah, those are, yeah.
[00:46:17.020]Right. These weedy type nutsedge tuber are too small.
[00:46:20.390]They're probably not tasty.
[00:46:22.110]We compare them to the cultivated one.
[00:46:24.150]The cultivated one I think is 10 to 20 times larger.
[00:46:28.010]So another question,
[00:46:30.970]and this is Keenan responding to that last question
[00:46:34.120]and the conversation.
[00:46:36.000]You can separate them,
[00:46:37.040]but typically find too many genes in response to management,
[00:46:40.940]so it gets tricky to figure out which are most important
[00:46:44.030]related to treatment.
[00:46:45.280]So thank you Keenan for that response.
[00:46:48.350]I wanna thank everyone for attending
[00:46:49.980]and also thank Luqi for a job well-done
[00:46:53.430]in typical Dr. Li form.
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