26 - 2020 Soybean Management Field Days - Cover Crop Water Use and Planting Considerations in Irrigated Soybeans
Nebraska Soybean Board & Nebraska Extension
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09/25/2020
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Cover Crop Water Use and Planting Considerations in Irrigated Soybeans - Aaron Nygren, Nebraska Extension Educator, Cropping Systems discusses the following: Like any crop, cover crops require management to maximize their benefits.
• When managing cover crops for water use, focus on termination timing depending on the weather conditions at planting; When using cover crops in a center pivot irrigated system, make sure that the center pivot is ready to apply water if needed; and Other than a few specific times, irrigation scheduling for soybeans with cover crops is similar to fields with no cover crops.
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- [00:00:01.061](upbeat music)
- [00:00:07.070]So, this is Aaron Nygren
- [00:00:07.903]with Nebraska Extension and Colfax County.
- [00:00:10.260]So I wanna talk a little bit about water use
- [00:00:12.070]and planting considerations
- [00:00:13.340]in irrigated soybeans when we incorporate cover crops.
- [00:00:17.970]So the big thing with cover crops
- [00:00:19.350]is it's another level of management.
- [00:00:21.190]And I think that's something we really need to keep in mind
- [00:00:23.190]is, we're used to maybe our no-till system,
- [00:00:26.550]but when we lay our cover crops on top,
- [00:00:28.150]that's another management.
- [00:00:29.690]So the management that we really wanna think about
- [00:00:32.520]when it comes to planting time
- [00:00:33.890]is what's happening with the weather?
- [00:00:35.480]Is it a dry spring or a wet spring?
- [00:00:37.410]And how do I manage my cover crop differently
- [00:00:39.390]in those situations?
- [00:00:42.520]The big thing we have to remember with this
- [00:00:44.090]is that cover crops,
- [00:00:45.310]their water use is gonna be a little bit different
- [00:00:47.320]than what we think about.
- [00:00:48.153]If you're just a corn and soybean farmer,
- [00:00:50.050]we think about those using water later in the season.
- [00:00:52.490]Cover crops can be a little bit different.
- [00:00:54.280]So if we look at the crop coefficients here for wheat,
- [00:00:57.870]which is a pretty good approximation of rye.
- [00:01:00.780]If we look at the Kc values,
- [00:01:02.830]that's the crop coefficient.
- [00:01:04.350]So what that is if we were using an ET gauge,
- [00:01:07.420]for instance, if we're at emergence
- [00:01:08.910]and we have the ET gauge dropped an inch that week
- [00:01:11.573]we'd multiplied by 0.1.
- [00:01:13.340]So we'd have 10 hundreds of actual crop water use.
- [00:01:16.200]So right away at visible crown,
- [00:01:17.860]which we would get fairly early in the spring.
- [00:01:19.730]The crop coefficient for wheat is at 0.5.
- [00:01:22.780]So that's using a fair amount of water right away.
- [00:01:25.330]If we get to jointing we're at 1.03.
- [00:01:27.990]So a joining cover crop,
- [00:01:29.410]doesn't look like a lot of biomass out there,
- [00:01:32.470]but it's still going to be using a fair amount of water.
- [00:01:34.940]So that water use, keep that in mind
- [00:01:37.670]depending on what the rainfall is for the year.
- [00:01:40.550]If we contrast that to our soybeans, soybeans,
- [00:01:43.049]if we look at their crop coefficients pretty early on.
- [00:01:46.930]So if we're in may and maybe,
- [00:01:48.712]if it's a little bit later planted even into June
- [00:01:52.140]and we still may be at a fairly low crop coefficient,
- [00:01:54.788]0.1 0.2,
- [00:01:55.910]for first node, even V3 is still only 0.6.
- [00:01:59.650]So that's when we can get that precipitation events
- [00:02:03.070]that are more than what the crop
- [00:02:04.870]is actually using for water.
- [00:02:08.150]So if conditions are dry,
- [00:02:09.910]and you have a cover crop out there,
- [00:02:11.750]we need to be thinking about what do I do
- [00:02:13.650]to minimize that crop water use some years.
- [00:02:16.460]So the one easy solution we have there is termination.
- [00:02:19.720]You may want to move up your termination date.
- [00:02:21.960]Spray that cover crop out
- [00:02:23.440]to help preserve whatever moisture you have.
- [00:02:25.890]This is gonna be especially true here, dry land.
- [00:02:28.730]On the irrigated side, we have the backup plan.
- [00:02:31.870]We can also run the center pivot.
- [00:02:35.190]You may not wanna do that,
- [00:02:36.960]cause that is a cost to that ,but a lot of times,
- [00:02:39.090]a lot of years, if we're dry, anyway,
- [00:02:41.160]there's a benefit to running the center pivot
- [00:02:43.030]to get our herbicides activated
- [00:02:45.820]and especially our prise.
- [00:02:47.250]You know, so we may also just wanna make sure
- [00:02:49.857]we get a good stand,
- [00:02:50.700]even without ,the cover crop out there
- [00:02:52.840]so, that we have the backup plan with irrigation.
- [00:02:55.140]That's the nice thing we have in Nebraska.
- [00:02:57.920]Now, on the other hand, if conditions are wet in the spring,
- [00:03:01.880]the one thing we can really do
- [00:03:03.050]is we can maximize the growth of that cover crop.
- [00:03:05.520]That cover crop is green, it's gonna be using water.
- [00:03:07.820]So take that as, and use that as much as you can.
- [00:03:10.890]So we may look at planting green or terminating
- [00:03:13.690]as close to planting as we can.
- [00:03:15.410]That's going to help use as much water.
- [00:03:17.940]Now, we're, usually getting a challenge with this
- [00:03:20.140]is maybe you get that cover crop a little bit bigger
- [00:03:22.100]than what you're used to,you get worried,
- [00:03:24.240]and then you spray it out.
- [00:03:25.590]And then if we keep catching rain,
- [00:03:27.530]that's when we get into trouble
- [00:03:29.426]because that extra bio-mass keeps the soil wet.
- [00:03:31.520]We have a real hard time planning into that.
- [00:03:33.160]So in those situations, really try to hold off
- [00:03:35.950]as long as you can get that crop
- [00:03:37.270]in the ground before you terminate.
- [00:03:40.720]So, I can mentioned earlier,
- [00:03:42.550]the big thing is just have that management plan in place.
- [00:03:45.250]Don't just go into this, just thinking you're going
- [00:03:47.070]to terminate like normal, really think
- [00:03:48.990]about those different weather conditions
- [00:03:50.440]and how you have to manage your water in your field.
- [00:03:53.980]In either case, if you're going to rely back
- [00:03:56.280]on that center pivot, the number one thing we have to do
- [00:03:58.600]is make sure it's actually ready to apply water.
- [00:04:01.410]Maybe, last fall you had some sprinklers that were broken.
- [00:04:04.320]You had something else, a gearbox break.
- [00:04:06.380]If you don't remember to fix that over the winter.
- [00:04:08.560]And all of a sudden you've got the crop
- [00:04:09.660]in the ground, now you're in trouble.
- [00:04:11.917]So make sure that center pivots ready to roll.
- [00:04:15.560]When we think about the scheduling then the rest
- [00:04:17.470]of the season, there's really not a lot of difference,
- [00:04:21.140]with scheduling with a cover crop versus no cover crop
- [00:04:23.590]in a soybean system,
- [00:04:25.160]there's just a few scenarios
- [00:04:26.630]where we maybe would have to manage it
- [00:04:28.500]a little bit different.
- [00:04:29.940]So the first one is just using irrigation
- [00:04:31.760]to establish the cover crop in the fall.
- [00:04:34.600]Some of you may have the decision already made.
- [00:04:36.460]I'm never gonna do this.
- [00:04:37.480]That's not a time that I'm willing to pump water,
- [00:04:40.170]but if we really wanna make those cover crops work
- [00:04:42.420]in our system, even in an extra inch of water applied
- [00:04:46.030]in the fall may really help that cover crop,
- [00:04:47.660]get off to a good start, get us more biomass
- [00:04:50.220]to help the system out.
- [00:04:52.630]Another time is if we do have some dry conditions just right
- [00:04:55.370]on the top surface,
- [00:04:56.750]if we need to wet that top three
- [00:04:58.190]or four inches of water,
- [00:04:59.390]to get, make sure the soybeans get out of the ground,
- [00:05:01.240]that's going to be helpful.
- [00:05:03.360]And then one that doesn't come up very often
- [00:05:05.070]is a situation that can happen
- [00:05:06.430]when we had the cover crop dried out our top inches of soil.
- [00:05:11.700]We caught a little bit of rain,
- [00:05:13.010]just enough rain to get the soybean crop, to germinate.
- [00:05:16.150]The challenge with that is if we have a dry layer beneath
- [00:05:18.800]that germinating seed, that rod,
- [00:05:21.190]isn't going to get through that dry layer
- [00:05:23.210]that can actually result in the death of that soybean plant.
- [00:05:26.160]So in those situations really need to be checking
- [00:05:28.180]to make sure we have water
- [00:05:29.370]all the way down through the profile
- [00:05:31.310]to avoid that death of that soybean crop.
- [00:05:36.310]So take home points,
- [00:05:37.339]it's important to manage cover crops based
- [00:05:39.800]on the weather conditions, especially at planning time,
- [00:05:42.970]be looking ahead seeing what your cover crop is doing.
- [00:05:46.080]See what the weather's like
- [00:05:48.120]when growing those cover crops,
- [00:05:49.610]make sure to have your center pivot ready
- [00:05:51.660]if you're, that's your form of irrigation,
- [00:05:54.210]as a backup plan.
- [00:05:55.300]If we do get dry that you can make sure crop gets out
- [00:05:57.800]of the ground.
- [00:05:59.240]And then other than a few specific times,
- [00:06:01.570]irrigation scheduling for soybeans with cover crops
- [00:06:03.910]is fairly similar to a field with no cover crops.
- [00:06:06.110]So it doesn't make a big difference in our management.
- [00:06:10.210]The next video,
- [00:06:11.043]we'll focus on the findings of the three years
- [00:06:12.710]of soybean management field day research that we've done
- [00:06:14.700]on this topic.
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