6- 2021 South Central Ag Lab Field Day - Reducing Nutrient Loss, Increasing Carbon Storage, and Improving Weed Control with Cover Cropping

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10/14/2021 Added

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6- 2021 South Central Ag Lab Field Day - Reducing Nutrient Loss, Increasing Carbon Storage, and Improving Weed Control with Cover Cropping, Katja Koehler-Cole, UNL Research Assistant Professor

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[00:00:08.060]My name is Katja Koehler-Cole.
[00:00:09.650]I'm a research assistant professor with the Department of Agronomy and
[00:00:13.370]Horticulture here at UNL.
[00:00:15.260]And I will be talking today about cover crops and how to reduce nutrient loss,
[00:00:20.480]increase carbon storage and improve weed control with cover crops.
[00:00:24.530]My talk will be followed by talks by my two students,
[00:00:29.360]Christopher Anuo who, who will be covering
[00:00:32.300]the carbon part of this project and Elizabeth Oys
[00:00:35.930]who will be talking about weed management with cover crops.
[00:00:38.240]So please make sure you listen to their talks as well.
[00:00:44.150]So I wanted to start out,
[00:00:46.520]basically just talking about the soil health principles real quick, just
[00:00:50.540]a brief review.
[00:00:53.060]The five soil health principles are to keep soil covered as much as possible,
[00:00:57.770]do not disturb,
[00:00:58.550]so use no till, reduced till management. Have living roots in the ground all year
[00:01:03.470]round, having diverse plants, diverse crops,
[00:01:07.130]because that feeds diverse soil microbial communities,
[00:01:10.520]and integrate livestock if possible.
[00:01:12.290]I really liked this saying here by Sir Albert Howard how mother nature never farms
[00:01:17.150]without animals.
[00:01:18.470]So one reason I like cover crops is because they help us achieve so many
[00:01:23.330]of these soil health principles, by keeping the ground covered.
[00:01:28.400]We're reducing erosion by having these living roots on the ground.
[00:01:32.150]We're improving water infiltration, water holding capacity,
[00:01:35.930]living roots also provide habitat and food source for soil microbes.
[00:01:40.640]We're improving organic matter by adding additional plant residue.
[00:01:46.430]We're improving aggregates stability and we can
[00:01:50.540]increase the retention of nutrients and nutrient cycling,
[00:01:53.330]which is what I'm going to be focusing a little bit today in my talk.
[00:01:59.900]So, back about six years ago,
[00:02:02.630]we started a program in cooperation with the Nebraska soybean board and
[00:02:06.500]Nebraska corn board.
[00:02:08.900]And that was called implementation of cover crops and no-till corn and soybean
[00:02:12.500]systems in Nebraska.
[00:02:14.330]And basically what we did is we went into our corn-soybean
[00:02:18.950]standard two year corn-soybean rotation,
[00:02:22.460]where we have a winter fallow and we replaced the winter fallow by a cover crop.
[00:02:29.510]We carried out this experiment at three different sites.
[00:02:33.290]And at each site we had three cropping sequences.
[00:02:37.250]We had corn with a cover crop followed by soybean. Soybean cover
[00:02:41.900]crop followed by corn. And we also had a continuous corn rotation. This here
[00:02:46.790]as an example from our site at ENREC,
[00:02:51.230]which is near Mead.
[00:02:53.480]All our sites were in no-till and we had the same cover crop in
[00:02:58.370]each plot growing, for four consecutive years. The project is still ongoing,
[00:03:02.950]but here I am presenting the results from 2014 through 2018.
[00:03:08.650]The cover crop species that we planted were cereal rye planted by
[00:03:13.150]itself. A legume cover crop,
[00:03:15.940]which was hairy vetch and winter pea.
[00:03:19.270]We also had two mixes, a four species mix,
[00:03:23.380]which was the cereal rye, the hairy vetch, pea and a brassica.
[00:03:27.790]We also had a second mix,
[00:03:30.430]where we added some additional brassicas and legumes.
[00:03:34.150]And then we compared everything to our control treatment here.
[00:03:38.140]We planted these cover crops at two different times.
[00:03:41.170]One was an early planting where we went in before the main crop was
[00:03:46.030]harvested and basically broadcast the cover crops.
[00:03:49.600]This was done in about mid September,
[00:03:52.330]and we also had a late planting where we drilled the cover crop after corn or
[00:03:56.440]soybean harvest. We used the same seeding rates for both plantings.
[00:04:01.960]A little bit about the management. Cover crops were planted,
[00:04:05.050]the main crops was harvested either before or after cover crop planting.
[00:04:09.790]We allowed the cover crop to over winter.
[00:04:11.920]We killed it in the spring with glyphosate two weeks before we planted the main
[00:04:16.870]crop. I'm gonna step over here a little bit.
[00:04:21.340]Soybean
[00:04:22.870]we plant soybean a little bit later than corn so that cover crops before
[00:04:27.850]soybean were allowed to grow about 10 days to two weeks longer than the cover crops
[00:04:32.830]that were grown before corn.
[00:04:35.920]We know that biomass production is essential for achieving the goals
[00:04:40.780]that we want our cover crops to do so we know that we need at least
[00:04:45.340]1000 better yet 2000 pounds per acre,
[00:04:49.390]to reduce erosion, reduce nitrogen leaching, provide forage or,
[00:04:53.710]or many of the other goals that we have for our cover crops.
[00:04:58.570]And if we want to get into weed control and Elizabeth is going to talk more
[00:05:03.070]about this we probably need even more biomass.
[00:05:08.020]So this picture here shows what a thousand pounds of rye biomass looks like.
[00:05:11.980]It's about six to eight inches of growth.
[00:05:16.540]So which of our planting methods and cover crop species were most productive,
[00:05:20.350]which of them reach that 1000 to 2000 pound threshold?
[00:05:25.270]It kind of depended on the site. In Eastern Nebraska we were
[00:05:28.960]more successful when we planted early.
[00:05:31.000]So when we broadcast pre- harvest of corn or soybean,
[00:05:38.430]that doubled biomass production compared to a late harvesting, however,
[00:05:42.510]at our south central site the delayed planting was more successful.
[00:05:47.370]This site was drier, it was also a warmer site. So the improved seed-
[00:05:51.150]soil contact improved germination and survival of the seeds. At this site,
[00:05:55.410]it was better to drill after harvest. Rye
[00:05:58.730]and in some cases our mixes with rye met that 1000 pound threshold,
[00:06:04.040]whenever planted at the best planting time.
[00:06:07.520]So either early in Eastern Nebraska, or late in south central Nebraska,
[00:06:11.840]Our legumes were not a productive treatment.
[00:06:14.180]Those need to be planted earlier and killed later in the season to
[00:06:18.800]provide sufficient biomass.
[00:06:22.490]One note on our rotations, because as I said earlier,
[00:06:26.840]because we plant soybean later,
[00:06:29.000]we terminated these cover crops in early May.
[00:06:31.910]These cover crops planted before soybean had about twice the biomass as cover
[00:06:36.350]crops planted before corn.
[00:06:40.280]I'm switching over to nutrient retention and cycling with cover crops.
[00:06:44.960]How much nutrients or how much N did our cover crops take up?
[00:06:50.240]Again, I split it up by rotation.
[00:06:52.880]So our cover crops before, planted before corn, planted
[00:06:57.710]after soybean, terminated, before corn, took up
[00:07:02.150]Cereal rye was the most productive cover crops in terms of biomass production,
[00:07:05.300]it took up the most nitrogen. It's a very excellent nitrogen scavenger.
[00:07:09.170]So it took up about 25 pounds of nitrogen per acre here. In the
[00:07:13.940]corn soybean rotation we had a little bit higher nitrogen uptake,
[00:07:18.140]both of the rye and the mixes. Okay.
[00:07:24.520]Because the question now is of course, when does that nitrogen become available?
[00:07:27.700]We hoped that it recycles and serves as a nitrogen source for our
[00:07:32.110]subsequent corn or soybean.
[00:07:36.100]The carbon-to-nitrogen ratio of
[00:07:38.590]plant biomass tells us something about how quickly it decomposes.
[00:07:42.940]We have that magical number of 25 to one,
[00:07:45.970]anything that has a lower carbon to nitrogen ratio than 25 to one
[00:07:50.770]we typically think it decomposes quickly. So it mineralizes nitrogen,
[00:07:56.500]and legumes are a perfect example for low carbon to
[00:08:01.450]nitrogen crops.
[00:08:05.050]Anything with a carbon to nitrogen ratio.
[00:08:07.600]that's greater than 25 to one typically takes a longer time to decompose an
[00:08:12.340]actually immobilizes nitrogen. So here we can think of corn stover,
[00:08:16.840]wheat straw, or also a mature rye cover crop. However,
[00:08:21.460]when we look at the carbon and nitrogen ratios in our own study,
[00:08:26.380]most of the time we are well below that threshold,
[00:08:30.280]even the rye cover crop,
[00:08:32.440]was typically just around 13, 14,
[00:08:36.880]a little bit higher in a corn soybean rotation,
[00:08:39.460]but always below that threshold of 25 to one.
[00:08:43.570]We did not measure when nitrogen becomes available,
[00:08:47.770]but we know from other studies that that had a similar
[00:08:52.330]experimental setup,
[00:08:53.410]we know that rye with a similar carbon to nitrogen ratio released about 40
[00:08:58.320]to 50% of nitrogen by the time corn was at V5.
[00:09:03.720]And that same study vetch released more nitrogen during that time.
[00:09:09.180]In our own experiment we know though that the legumes,
[00:09:13.800]the vetch, took up so little nitrogen, that it was not really,
[00:09:18.450]wasn't really able to provide any nitrogen to the corn.
[00:09:22.500]So based on these numbers,
[00:09:24.420]we don't think that nitrogen immobilization is typically a concern
[00:09:29.490]with the amount of cover crop biomass and the types of cover crops that we're
[00:09:33.420]growing here. However,
[00:09:35.670]it's always a good idea to think a little bit more about your nitrogen
[00:09:38.940]management, maybe adjust it, fertilize preplant for sure.
[00:09:44.160]Maybe use a starter or also do a split application of nitrogen
[00:09:49.020]if you're concerned about mineralization.
[00:09:52.890]I am going to talk a little bit now about the corn yields following our cover crops.
[00:09:57.420]We saw a small decline in corn yields after our rye cover
[00:10:02.220]crop, but not after the other cover crops. So that is,
[00:10:06.630]similar to many other studies here in the Midwest that looked at cereal rye as a
[00:10:10.620]cover crop, that, that corn,
[00:10:13.950]that yield reduction in corn was pretty small, about 4%,
[00:10:18.750]just a few bushels, but there was a small yield lag.
[00:10:24.090]When we looked at soybean, however,
[00:10:25.680]we didn't see an effect of any of the cover crops.
[00:10:30.030]We did see an effect of the planting time on our soybean yields. And I,
[00:10:34.230]I think that was due to the fact that sometimes some of
[00:10:39.120]our early planted cover crops and it was in particular,
[00:10:43.560]the hairy vetch and some of the brassicas that we had in the mixes
[00:10:48.060]survived the actual termination of cover crops. And so they became weedy
[00:10:52.020]and competed with soybean in, in a few years,
[00:10:56.010]we had some issues with that.
[00:10:57.330]So I do think that that's why we saw a small yield decrease,
[00:11:01.920]but overall no effects on soybean yields.
[00:11:06.770]So, in our study, that was done just in corn- soybean rotations.
[00:11:11.390]We, we could tell that rye was
[00:11:14.900]a good cover crop for these systems,
[00:11:17.000]and we were able to achieve some of the goals even with relatively minor biomass
[00:11:21.740]production. Now, if we look at other
[00:11:24.890]crop rotations where we have a longer
[00:11:29.390]vegetation period in the fall, we can really plant a lot more crops.
[00:11:35.060]And some of these other crops,
[00:11:36.620]the picture I have here is from a flowering strip of cover crops that was
[00:11:41.030]planted
[00:11:43.370]to attract pollinators and other beneficial insects. So when we go in,
[00:11:48.050]for example, after wheat or after seed corn, we can plant, we have a lot more,
[00:11:52.580]plant selection, which could improve diversity,
[00:11:57.040]diversity of insect population, probably attract more birds to our farms and
[00:12:01.720]generally make, make better use of resources. So in the future,
[00:12:04.600]that's something that we're interested. So with that
[00:12:08.800]I will end my talk. If you have any questions, please let me know.
[00:12:12.010]My email is up there and I'm going to hand it over now to my,
[00:12:16.810]student Chris Anuo. And
[00:12:19.660]please watch their talk as well on cell carbon and cover crops. Thank you.

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6- 2021 South Central Ag Lab Field Day - Reducing Nutrient Loss, Increasing Carbon Storage, and Improving Weed Control with Cover Cropping

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