11 - 2020 Soybean Management Field Days -
Chris Proctor, Nebraska Weed Management Extension Educator looks at how to improve the understanding of the effects that soil management practices (conventional tillage, no-till, and no-till + cover crops) have on weed control, residual herbicide fate and crop productivity in a corn-soybean crop rotation.
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[00:00:07.010]Chris Proctor, I'm a weed extension educator,
[00:00:09.950]University of Nebraska, we're talking about a topic,
[00:00:14.470]just looking at the influence of soil practices
[00:00:17.220]on how it controls weeds, kind of the effect of herbicides,
[00:00:21.870]and ultimately crop productivity.
[00:00:26.120]It's really the aim or the goal of the study
[00:00:29.820]I'm gonna highlight was to try to understand
[00:00:33.160]what effect is soil management practices?
[00:00:34.900]How does tillage versus no-till versus use of cover crops,
[00:00:37.840]how does that affect weed control?
[00:00:40.040]What influence might that have on residual herbicides
[00:00:43.270]that are applied in those systems?
[00:00:45.170]And how productive are the crops in those systems?
[00:00:50.280]And so thinking about it, you know, we kind of expected
[00:00:54.980]that there would be a difference between soil management
[00:00:57.430]practices on those different areas of crop production.
[00:01:02.520]So the way this study was set up,
[00:01:03.700]so this was a trial that was actually conducted
[00:01:05.460]up in Wisconsin and we had six different soil management
[00:01:11.930]practices and so that was a combination of tillage,
[00:01:14.830]no-till and cover crops with different cover crop
[00:01:19.090]termination timings, and so we had an early
[00:01:21.240]termination timing that was about May 7th timing
[00:01:27.880]that was right around the time of planting
[00:01:29.920]and so in this instance, this was later in May,
[00:01:33.160]around May 23rd and there's two terminations
[00:01:36.500]at the app plant so there was a forage,
[00:01:38.160]where the forage was harvested and collected,
[00:01:41.130]and then it was also chemically terminated
[00:01:43.290]and then a late termination timing around June six
[00:01:46.080]which was chemically terminated.
[00:01:47.740]And that was also, and then the other part of the study
[00:01:50.480]was a comparison of a pre-merger beside versus
[00:01:53.750]a no pre-merger herbicide to see what effect
[00:01:56.180]that might have.
[00:01:59.170]So looking at how these different components were set up
[00:02:04.290]for the termination and burn down part of the study,
[00:02:08.640]glyphosate was applied, for the pre-merge herbicide
[00:02:12.730]you can see in the table there, we had
[00:02:16.470]different pre-merger herbicides that were applied on
[00:02:18.180]the corn and the soybean, and then there was a post-emerge
[00:02:20.850]herbicide that was applied across the entire study,
[00:02:23.750]so all the treatments received the post emergent herbicide.
[00:02:31.100]Cover crops were planted with cereal rye,
[00:02:33.970]and so we just use one cover crop for this study,
[00:02:35.807]and it was about 60 pounds per acre tillage,
[00:02:40.970]it was kind of a two pass tillage system,
[00:02:42.570]so it was a fall chisel followed by a spring field
[00:02:46.230]cultivator, and then the herbicides were applied
[00:02:49.500]for the burn down at the termination of the cover crop
[00:02:52.600]and the pre-merger beside those were applied
[00:02:54.460]with a research backpack sprayer, but the post-merger
[00:02:57.760]was sprayed over the top of everything with a tractor.
[00:03:01.056]And then we evaluated weed control, so this was right
[00:03:03.640]before the post-merger herbicide was applied,
[00:03:06.430]weed control was evaluated and then yield
[00:03:08.650]was collected at the end.
[00:03:10.970]Another component of the study was to evaluate
[00:03:12.780]herbicide persistence, so how long do those
[00:03:14.540]pre-emerge herbicides remain in the soil?
[00:03:18.090]How long were they there?
[00:03:19.580]How long could we detect their presence?
[00:03:20.980]And what influence did those have?
[00:03:22.210]And so, soil samples were collected about 29 days
[00:03:25.470]after application, and there were applied for the no-till
[00:03:31.430]and that was kind of the control treatment,
[00:03:34.750]and then you had a tillage plus pre-emerge,
[00:03:37.210]no-till plus pre-emerge, and early termination
[00:03:39.580]of the cover crop plus pre -emerge, and then an app plant
[00:03:43.070]termination plus pre-emerge and then late terminatio
[00:03:46.763]So we kinda evaluated kind of the different parts
[00:03:50.280]of the system to see how much of that herbicide
[00:03:53.740]carried over, and then these were analyzed in a laboratory,
[00:03:58.220]they were sent to South Dakota and analyzed there.
[00:04:00.440]And so for corn, while there was a number of herbicides
[00:04:03.690]that applied, the lab was able to detect S-metolachlor
[00:04:09.430]was used and for kind of to evaluate the corn pre-merger
[00:04:13.010]herbicide, and then for soybean, sulfentrazone
[00:04:17.600]was the herbicide that was analyzed.
[00:04:19.610]And so looking at the lab data, really all we saw
[00:04:24.410]was the under tillage, there was higher concentration
[00:04:29.541]of the soybean herbicide Sulfentrazone
[00:04:32.550]compared to no-till and this was pretty similar for corn
[00:04:35.800]but I'm just gonna highlight the soybean data today.
[00:04:39.810]And so some of this is kinda gets into that question
[00:04:43.410]when you start to have residue on the soil,
[00:04:45.150]you have cover crops and residue from the cover crops,
[00:04:48.120]is that begin to tie up some of the herbicide in the soil,
[00:04:51.670]what effect does that have on the persistence
[00:04:54.058]of those herbicides and whether or not
[00:04:57.430]it affects weed control?
[00:04:59.120]And so we did see differences in terms of the amount
[00:05:01.770]that was there, to kind of verify what was being seen,
[00:05:07.210]we use some of those soil samples we need a bioassay,
[00:05:09.800]so we put that soil in pots in a greenhouse,
[00:05:13.671]and then we test it both the use of cucumber
[00:05:19.950]and Palmer amaranth to determine what effect
[00:05:23.940]did the different soil treatments,
[00:05:28.010]soil management treatments have on the persistence
[00:05:30.910]of these herbicides?
[00:05:32.360]And it didn't quite shake out the same as the laboratory
[00:05:35.210]study and so being 29 days out from when we sampled,
[00:05:40.550]I think a lot of the herbicides began to break down
[00:05:43.870]at this point, and so we didn't see as clear
[00:05:47.090]of delineation in terms of no-till having higher injury
[00:05:50.540]on these plants compared to the other treatments.
[00:05:54.030]If you look carefully at some of the polar plants,
[00:05:55.800]you do see a little bit of injury,
[00:05:57.040]but certainly the concentrations weren't high enough
[00:06:00.660]to prevent emergence as we can see emergence all the
[00:06:02.980]way across the board and there weren't strong differences
[00:06:06.880]between the control.
[00:06:09.390]So in this case, kinda given the soils
[00:06:11.930]and the way that the study was conducted,
[00:06:18.020]we didn't see a strong influence of the pre-emerge
[00:06:22.720]herbicide kinda persistent or differences between
[00:06:25.310]the soil treatments in terms of the persistence
[00:06:27.060]of the herbicide.
[00:06:29.110]And so really, I think we might've been too late
[00:06:32.310]when we sampled, I think being a little bit closer
[00:06:34.520]to when those were applied might've given us a little
[00:06:36.090]better picture of what was going on and kinda
[00:06:40.150]looking at that data, I think a combination of lab data
[00:06:42.520]and some of these bioassay screens could give us
[00:06:45.270]a pretty good idea, so this is kind of the first step
[00:06:47.640]at trying to understand what's going on in these situations,
[00:06:52.228]I'll just highlight just a little bit of the field data.
[00:06:55.460]So this is looking at cover crop biomass,
[00:06:57.700]and this is kind of what we would have expected
[00:06:59.780]that the later you terminate, the more biomass
[00:07:01.730]you accumulate, so that kind of followed what was expected.
[00:07:05.030]In terms of weed control, we had one side with pretty low
[00:07:08.080]weed control, the Arlington side on the left,
[00:07:10.180]and so we really didn't see any difference
[00:07:11.660]in percent weed control, compared to the other side
[00:07:15.840]where there was a difference in the using
[00:07:20.870]a pre-merger versus not using a pre-merger beside that side.
[00:07:23.610]So under the tillage condition, including a pre had higher
[00:07:29.060]weed control relative to without the pre-merger herbicide,
[00:07:32.350]but for the other soil treatments
[00:07:33.760]there really wasn't a difference,
[00:07:34.950]which is kind of an interesting outcome.
[00:07:37.870]And then, then looking at yield at the end of the day,
[00:07:42.470]we just didn't see any, yield differences, either the side,
[00:07:45.730]and so, despite I've seen a few differences
[00:07:48.040]in terms of persistence of herbicides
[00:07:51.970]that were detected in the laboratory study,
[00:07:55.303]and some minor differences in weed control early on,
[00:07:58.620]ultimately it didn't translate into any yield differences
[00:08:01.140]in this particular study.
[00:08:02.130]And so, I think kind of the take home is,
[00:08:07.040]we need to pay attention, I think,
[00:08:08.790]to these different systems and how they might affect
[00:08:10.880]our herbicide persistence, because that'll affect
[00:08:15.357]how well we control weeds in these systems,
[00:08:20.900]but ultimately, I think under the soil conditions
[00:08:24.300]tested in the kind of the environmental conditions
[00:08:26.170]that we were looking at, we didn't see strong
[00:08:27.700]differences here, so, that's encouraging in terms of the use
[00:08:31.870]of no-till systems and cover crop systems
[00:08:37.400]'cause of the benefits we can gain there.
[00:08:40.250]So that's what I wanted to highlight related to that study.
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