27 - 2020 Soybean Management Field Days - SMFD Research on Soil Water Use with Cover Crops in Irrigated Soybeans
SMFD Research on Soil Water Use with Cover Crops in Irrigated Soybeans - Aaron Nygren, Nebraska Extension Educator, Cropping Systems discusses the following: In research conducted in 2018-2019, SMFD plots had significant differences in soil water content between a rye cover crop and no cover crop at planting time. However, after planting, rainfall has exceeded crop water use for a few weeks while the plants were small and refilled the soil profile, resulting in little to no differences in soil water content between a rye cover crop and no cover crop. Most years on irrigated land in the eastern half of Nebraska, the water used by cover crops over the winter and into the spring on irrigated land will not reduce the stored soil water for the soybean crop.
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[00:00:07.830]So this is Aaron Nygren
[00:00:08.663]with Nebraska Extension in Colfax County.
[00:00:11.240]Wanna talk a little bit about the results of our research
[00:00:13.680]at Soybean Management Field days,
[00:00:15.810]on soil water use with cover crops,
[00:00:17.860]in an irrigated soybean situation.
[00:00:21.310]So we have plots that we've established for,
[00:00:23.820]this is the third year.
[00:00:25.180]So the layout with those,
[00:00:27.256]it's been a cover crop versus a no cover crop.
[00:00:29.210]So we planted those in the fall of 2019,
[00:00:31.670]at the four sites across Nebraska this year.
[00:00:34.620]We have four replications of Watermark sensors.
[00:00:37.060]So those were the sensors we chose,
[00:00:39.290]we installed those at a depth of six inches, 18 inches,
[00:00:42.490]and then also 30 inches deep,
[00:00:45.200]to look at what the crop water uses.
[00:00:47.290]So we established those in late April
[00:00:50.310]to early May before planting to try and get a sense of,
[00:00:53.550]what is our soil water like as we head into planting time?
[00:00:58.160]Then they were pulled at planting
[00:00:59.460]to allow for the planting operation to occur,
[00:01:02.140]and then re-installed after planting
[00:01:04.180]in the following days or week, to make sure,
[00:01:06.810]and then we track those the rest of the season,
[00:01:09.140]throughout the growing season.
[00:01:11.870]So this is the results of the last two years,
[00:01:14.470]showing the soil water content at planting time.
[00:01:16.750]I think that's probably the biggest concern we have
[00:01:18.610]with cover crops a lot of times is,
[00:01:20.660]do I have enough water at planting time,
[00:01:23.030]to make sure my crop is gonna get out of the ground?
[00:01:24.940]And also what is the effect of
[00:01:27.500]that soil water use on deep percolation?
[00:01:30.520]That's one of our peak times,
[00:01:31.760]we're starting to get some more rainfall,
[00:01:33.020]so can we reduce deep percolation early in the season?
[00:01:36.630]So these are the seven site years that we had,
[00:01:39.000]we lost one year due to a hailstorm.
[00:01:42.820]So what this graph is showing is,
[00:01:45.440]the soil water content above,
[00:01:47.040]which is with a plus or below
[00:01:48.700]with a minus field capacity in inches.
[00:01:51.730]So field capacity is really the difference of,
[00:01:54.930]how much are we gonna be deep percolating?
[00:01:56.450]For below field capacity it really slows down,
[00:01:58.630]if we're above we're gonna be moving quite a bit of water.
[00:02:01.750]So in this situation we have the no cover plots,
[00:02:04.240]versus the rye plots.
[00:02:06.340]Then at the bottom we also have,
[00:02:07.650]what is the difference in soil water content
[00:02:09.560]of the rye cover crop versus a no cover in inches?
[00:02:13.770]So if we look at one here, for instance, Albion in 2018,
[00:02:18.010]you'll notice that at planting time,
[00:02:19.460]the no cover was plus 1.57 inches above field capacity.
[00:02:24.410]So we had excess water in our soil
[00:02:26.920]at that time at planting time,
[00:02:29.600]compared to the rye with just slightly above field capacity,
[00:02:33.070]almost right at field capacity.
[00:02:35.070]So that notice that it has an A versus a B,
[00:02:37.820]so that one was statistically different.
[00:02:40.610]So not every year we've had those kinds of differences,
[00:02:43.280]there's multiple sites here
[00:02:44.380]where we don't have any statistical difference.
[00:02:47.820]And the big thing to note is that,
[00:02:49.500]of these seven sites, only one of them,
[00:02:51.470]which was Kenesaw in 2018, actually had soil
[00:02:55.230]with the right cover crop that was below field capacity.
[00:02:58.720]So that's where we have to remember our management,
[00:03:01.320]there's years where maybe we need
[00:03:02.540]to determine a little bit earlier
[00:03:04.270]to avoid depleting too much water out of that profile,
[00:03:07.200]so we can make sure we get
[00:03:08.160]our crop out of the ground as well.
[00:03:10.630]So we're gonna continue this again,
[00:03:12.010]we've got this ongoing at four sites,
[00:03:13.930]so we'll include this with our analysis,
[00:03:16.430]but so far the trend has been fairly similar.
[00:03:18.380]That we have seen some drier soils
[00:03:20.220]with the rye at planting time,
[00:03:22.020]but not so much
[00:03:22.853]that it's really hindered our planting ability,
[00:03:25.150]and that's also probably helping us with deep percolation.
[00:03:29.480]So here we have a example graph,
[00:03:31.740]so this is from the Shelby site.
[00:03:33.670]So this is looking at our Watermark sensors,
[00:03:37.060]so the key that I wanna look at is, is field capacity.
[00:03:39.420]Remember if we're above field capacity,
[00:03:41.020]we're likely moving water down to the profile,
[00:03:43.800]if we're below field capacity, we're probably not.
[00:03:47.390]If we look at right at planting time then,
[00:03:49.070]so this is the plots two of the reps of our plots
[00:03:51.870]that had no cover crop.
[00:03:53.600]You'll notice that all of those sensor readings,
[00:03:55.470]right before planTing were above field capacity.
[00:03:57.710]So we had plenty of stored water in that soil,
[00:04:00.410]most likely we were deep percolating through that profile.
[00:04:05.530]In contrast, this is two of our reps
[00:04:08.370]that incorporated a rye cover crop.
[00:04:11.160]So once again, here's field capacity,
[00:04:13.450]you'll notice that both the six inch sensors,
[00:04:16.490]in both of these plots, were below field capacity.
[00:04:18.920]So that means we had a drier layer there,
[00:04:20.570]if we kinda rain, we actually had some storage space,
[00:04:23.930]the 18 inch sensors though,
[00:04:25.930]we're still above a field capacity.
[00:04:29.340]So we hadn't used too much water out of this soil profile,
[00:04:33.150]we had to do a lot of drastic things
[00:04:35.250]to get the crop out of the ground.
[00:04:37.110]Just gave us pra,
[00:04:37.943]a little bit of break from deep percolation,
[00:04:40.250]as much in this field.
[00:04:42.440]Now, if we look going on throughout the season,
[00:04:44.930]this pretty much sums up what we've seen
[00:04:46.810]at most of our sites, basically every site so far,
[00:04:50.270]that we've done this study with, is that after planting time
[00:04:53.570]our rains were greater than what the,
[00:04:56.190]the difference in that stored soil water difference was.
[00:04:59.460]So in this situation, we had three or four events,
[00:05:02.610]where we actually had enough rainfall
[00:05:03.970]to refill the profile well above field capacity.
[00:05:07.290]So in this situation, we, you know,
[00:05:08.940]we wetted them up above ten even, so they were pretty wet.
[00:05:13.340]So that's the difference there is that,
[00:05:15.460]we can use some water with a cover crop,
[00:05:17.480]but we typically get enough rainfall events
[00:05:19.400]in Eastern Nebraska to refill that profile,
[00:05:21.820]which really helps us out.
[00:05:23.550]Doesn't, you know, remember with beans,
[00:05:25.180]the big time when we need water
[00:05:26.520]is much later on in the growing season,
[00:05:28.600]we always talk about August rains a lot of times.
[00:05:30.330]So we can use a little bit early refill that
[00:05:33.560]with these May and June, early June rainfall events,
[00:05:37.910]and it seems like we're not seeing much difference.
[00:05:41.560]So the take home from what we've seen
[00:05:43.280]with water use for our soybean management field day plots,
[00:05:46.180]is that we do have significant differences at planting time,
[00:05:49.250]with a rye versus no cover crop, not so much that
[00:05:52.790]we've had to do
[00:05:53.623]a lot of drastic management options with them.
[00:05:56.570]But then after planting we're getting enough rainfall,
[00:05:59.230]that exceeds the crop water use,
[00:06:01.090]that we're refilling that profile.
[00:06:02.800]So we haven't seen no difference
[00:06:04.160]in soil water content after planting time.
[00:06:08.610]So based on this, our feeling is that most years
[00:06:11.790]for irrigated land in Eastern half of Nebraska,
[00:06:14.570]the water used by that cover crop,
[00:06:17.100]is not gonna reduce the stored soil water
[00:06:18.750]for the soybean crop,
[00:06:19.800]because we're most likely gonna refill it.
[00:06:21.970]So that's a good news for us,
[00:06:23.630]that allows us to use somewhat such sort of soil water
[00:06:25.680]with our cover crop, and doesn't really affect our soybeans.
[00:06:30.840]So the question of grower might often have, you know
[00:06:33.430]and their concern is that,
[00:06:35.030]they're worried about that water use
[00:06:36.750]with that cover crop and affecting their yield.
[00:06:39.950]So the big thing with this is,
[00:06:42.110]you have to remember that everybody's gonna have
[00:06:44.110]a little bit different system of cover crop use.
[00:06:47.200]So in the situations we've been going in,
[00:06:49.560]these have maybe been a little bit later planted cover crop,
[00:06:52.960]and then we actually did terminate at planting time
[00:06:55.700]which has been mid, around the mid May timeframe.
[00:06:58.620]Now somebody else may have a totally different system.
[00:07:00.700]If you have a cover crop
[00:07:02.150]that's established after silage, for instance,
[00:07:04.960]that's early planted
[00:07:05.990]and then you're gonna let it grow and head out,
[00:07:08.490]you may see a different result,
[00:07:09.760]you may have a lot more water use in that situation.
[00:07:13.060]So, you know, our studies have been looking more
[00:07:16.140]at a you know, a typical timeframe
[00:07:17.750]where we're trying to get it in after corn harvest,
[00:07:20.240]we're not really pushing to get it planted very early.
[00:07:23.480]So everybody's gonna have,
[00:07:24.350]maybe have slightly different results.
[00:07:27.200]Everything is, this was in soybeans,
[00:07:29.300]you think corn would be different.
[00:07:30.500]Corn may be different, you know
[00:07:31.810]corn water use ramps up a little bit earlier in the season,
[00:07:35.000]so we may not get as much refill
[00:07:37.530]from those May and June rains
[00:07:39.790]as maybe we did on the soybean system.
[00:07:42.160]So this is been the results for our system.
[00:07:45.640]Like I said you're gonna have to play with it a little bit,
[00:07:47.810]and see, maybe you may have to change that timing
[00:07:50.120]of determination in your true system yourself.
[00:07:54.820]So the one thing that you know, oftentimes,
[00:07:58.010]we have to remember the differences
[00:07:59.560]in our irrigated, versus dry land system.
[00:08:01.780]With dry land, we're gonna probably pull
[00:08:03.520]the determination trigger a lot earlier,
[00:08:05.320]versus an irrigated system.
[00:08:07.380]I know guys don't like to start pivot up early,
[00:08:09.020]but we remember that it is always
[00:08:10.240]a backup case with irrigation.
[00:08:12.590]You know, if we do end up being drier than what we thought,
[00:08:15.690]start the center pivot up,
[00:08:16.800]make sure to get that crop out of the ground.
[00:08:19.110]Realize that's a challenge
[00:08:20.260]because we do have dry land corners, right?
[00:08:22.660]So we may need to think
[00:08:23.800]about managing even dry land corners different
[00:08:25.910]than the irrigated circle,
[00:08:28.040]so that is a challenge with cover crops as well.
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