Cover Crops and Water Use

CropWatch Author

04/30/2025 Added

5 Plays

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Seminar #2 of a four-part series on cover crop production by the University of Nebraska in collaboration with USDA NRCS.

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[00:00:00.000]So thanks again for coming. For those of you who joined us last time, we
[00:00:06.600]were together on the 1st of October for a session about yield impacts that Vesh led.
[00:00:15.960]You're here today for session two, talking about cover crops and water. And we will have another
[00:00:20.640]webinar on the 18th of December. It's a Wednesday at 10 a.m. Central Time. And this webinar is a
[00:00:29.280]part of a collaborative agreement that my research team and I have with NRCS and university to
[00:00:35.220]support conservation delivery. And I want to here just give an opportunity to Carlos and Nathan to
[00:00:42.080]share a few things about our series as we get started. Hey, thanks, Andrea. For those of y'all
[00:00:47.860]that don't know me, my name is Carlos Villarreal. I'm the state soil scientist
[00:00:51.040]here in Lincoln for NRCS and for our NRCS staff. Well, Rob couldn't be here today.
[00:00:58.560]He will be on the next one, but he couldn't be here today, so he just wanted me to emphasize
[00:01:02.160]two points. One, just encouraging you to participate, thanking you for being involved in
[00:01:08.380]this. Like Andrea said, this is made possible through an agreement, and we want you to be
[00:01:15.760]confident that we're using our agreement wisely, and this is one of the extremely valuable,
[00:01:22.240]great things to come out of this agreement. The opportunity to empower our employees with having
[00:01:28.040]conversations with producers and customers about cover crops, to me, that's one of the greatest
[00:01:33.940]investments we can make in ourselves, so I just encourage you to be engaged. The last half of this
[00:01:41.040]webinar is going to be breakout sessions, so please, even if you feel like you're in the wrong
[00:01:46.720]webinar, you're in the wrong place, or don't deal with cover crops, it's still valuable to have you
[00:01:51.380]on and just give your perspective, so encourage you to participate, and also I wanted to thank
[00:01:57.520]our extension educators who are online also. We also want our staff to be familiar with you,
[00:02:05.080]who you are, what your program looks like, and encourage some conversations after the webinar
[00:02:09.940]series, if there's any field days or any ways that we could collaborate, and be more involved
[00:02:17.180]with each other's programs, I think is a really great asset for us to have as we work on that
[00:02:23.200]front line of our customer service, working directly with our customers, and we're going to
[00:02:27.000]directly with private lands and producers, so it's exciting to me to be a part of this,
[00:02:34.900]so thank you all for joining, and I believe Nathan had a couple of things he wanted to add also,
[00:02:38.840]so thanks, y'all. Thanks, Carlos and Andrea. Yeah,
[00:02:43.040]thanks for joining us again for some repeat webinar attendees. I just wanted to let
[00:02:49.640]everybody know within NRCS that the cover crop webinar series back in October is
[00:02:56.480]on the soils, on our SharePoint on soils, and under soils is FY25 cover crop
[00:03:02.680]webinar series, and so you can find the recording, the transcript, and a PDF
[00:03:06.740]version of the PowerPoint from October there, and then within about a week from
[00:03:11.640]now, we'll get the same thing loaded for the webinar today.
[00:03:15.080]Go ahead. Thank you. Great. Thank you, guys.
[00:03:20.020]So what we want to do to start, as we did last time, so when we get into our breakout
[00:03:25.960]rooms, and I'll tell you more about our agenda here in just a minute, but Vesh is going to launch
[00:03:31.420]a poll now, and we just want you to select what part of Nebraska you are primarily focused on
[00:03:39.660]with your work. So this will help us gauge the number of people and the number of breakout rooms
[00:03:43.760]and how we set that up. So, and we can like play this by ear a little bit too, depending on, you
[00:03:50.660]know, if more people come or if we have to combine breakout rooms. So we have, let's see,
[00:03:55.440]right now on the webinar, we've got 29 folks. So we should get
[00:03:58.700]close to that many responses. So we've got 18, 19.
[00:04:07.320]Definitely got some representation from around. So maybe a
[00:04:24.920]few people who have not answered, but Vesh, I think maybe
[00:04:28.840]what we'll do is combine a few rooms. And maybe in Northeast
[00:04:34.880]have maybe two, but we'll, we'll tell you the numbers and how it
[00:04:39.620]works out. So what we'll do when I get to the end of my
[00:04:43.580]presentation is we will open up the breakout rooms, we will
[00:04:47.820]we've got a great slate of extension educators, we're so
[00:04:50.560]glad to have everyone here who will be our main facilitators.
[00:04:54.400]And we'll figure out with the numbers where we land. So Vesh,
[00:05:00.600]I'll let you work on that in the back end as I get presenting. So
[00:05:03.220]probably you could close the poll now. I think there's
[00:05:06.120]probably a few people who did not answer, but I think that is
[00:05:08.300]okay. So I did want to remind you, my colleague Katja Koehler
[00:05:14.620]Cole, if you want to share, I'll share with you who we've got
[00:05:18.620]here, if you want to see where the numbers have shaken
[00:05:21.960]out. So we will let you know where we're at. And I'll let you
[00:05:23.880]know where we want to try to have maybe about five or so
[00:05:26.640]people in all the rooms just to have nice discussion. If you end
[00:05:29.120]up getting a few more folks joining, we'll figure out
[00:05:31.600]from there. So, okay. Yeah, so my colleague Katja Koehler-Cole
[00:05:36.240]last session, she is not able to join us today, just wanted us
[00:05:40.920]to remind the NRCS folks that we have a directory for finding
[00:05:45.600]extension educators, that was a really important point that we
[00:05:49.040]wanted to have with this webinar series to have an opportunity,
[00:05:52.680]you know, even
[00:05:53.360]virtually for educators and for NRCS field staff to get to
[00:05:58.640]know each other. So if you are NRCS field staff, and you're not
[00:06:01.280]sure who some of your water cropping systems or livestock
[00:06:05.240]systems extension educators might be, this is a source for
[00:06:08.040]you to search. And we also have the statewide maps that show
[00:06:12.920]some of the different programs. And again, more contacts that
[00:06:17.120]way. So we hope you can use this opportunity to connect.
[00:06:22.280]Okay, now on to the main event, getting for me to talk about one
[00:06:27.780]of my favorite topics, which is cover crops and water. So I want
[00:06:30.680]to present to you evidence, I want to present to you some
[00:06:32.900]information from Nebraska that can empower you to better answer
[00:06:36.160]questions or just support your producers and folks with NRCS
[00:06:41.300]contracts. So what I want to do first, actually, the teacher in
[00:06:45.560]me wants to make sure we revisit some of the topics that Vesh in
[00:06:50.340]the presentation in October talked about with
[00:06:52.260]respect to what we know about cover crop yield effects. So I'm
[00:06:55.400]just going to spend probably, I don't know, maybe about 10 or so
[00:06:59.260]minutes talking about that, revisiting that, then I will
[00:07:02.220]just give us a refresher water cycle, I want to give us a
[00:07:05.420]healthy dose of evidence that we have from the research about
[00:07:08.220]cover crop water impacts. I'll try to tie that all together.
[00:07:11.360]And then we'll get into our breakout rooms. I hope to do all
[00:07:14.280]that by about 240 or so 140 mountain time and, and then get
[00:07:18.700]you into the breakout rooms that way. So let's, again,
[00:07:22.240]start with what we know, what are some of the processes and
[00:07:25.260]evidence for how cover crops can impact yields? Because of
[00:07:28.180]course, we know that is a major concern, potential barrier is a
[00:07:31.940]cover crop going to negatively impact my cash crop. So,
[00:07:35.880]this is a diagram that best showed in the last presentation
[00:07:39.320]about just some of the processes, what are some of the
[00:07:43.960]pathways that cover crops could be, again, positively or
[00:07:48.000]negatively impacting cash crops, right? So, you know,
[00:07:52.620]improving soil health, suppressing weeds, pest and
[00:07:55.600]disease management, especially that last one, pest and disease
[00:08:00.220]management, there are incidents where cover crops could
[00:08:03.020]increase negative pest pressure, right? We know with
[00:08:07.980]nutrients, they are taking up nutrients, they are using water,
[00:08:11.100]okay? So we know that there could be some, some negative
[00:08:13.640]potential effects. Those are some of the major pathways that
[00:08:16.580]I think about why might a cover crop be impacting cash crops.
[00:08:20.800]Here, we're talking all about
[00:08:22.200]water, but there are other pathways that could be
[00:08:26.260]contributing. And I do think that water is an important
[00:08:29.020]one. And I do think as you'll see in some of the evidence
[00:08:31.200]that in Nebraska, water is really a concern and can lead
[00:08:35.540]to some yield decline. So these are some of the pathways,
[00:08:38.240]but what I want to show you next is evidence from a few
[00:08:41.020]different scales. So we've got some evidence from, from small
[00:08:44.180]scale research, from farmer reported data and from on-farm
[00:08:47.580]research that really point to similar trends, which I'm just
[00:08:50.780]giving you the punchline right now.
[00:08:52.180]And I might start to sound like a broken record, but largely
[00:08:55.020]when we look across in the aggregate, we see that cover
[00:08:58.960]crops can have mostly neutral effects, sometimes a little
[00:09:03.260]positive, sometimes a little negative, but largely neutral
[00:09:06.400]effects on cash crop yield. So the first evidence I'm showing
[00:09:09.660]you is from a paper, actually two of my colleagues who I had
[00:09:13.460]the chance to visit this week, as I've been at the Tri
[00:09:15.320]Societies Conference, Fernando Magas and Guillermo
[00:09:17.780]Marcillo, who were my major advisor and a lab,
[00:09:22.160]mate, colleague of mine, worked on a meta-analysis about corn
[00:09:25.700]yield of cash cover crops before corn.
[00:09:31.160]And so this is something that Vesh showed.
[00:09:34.060]He went into a little bit of detail about it,
[00:09:35.660]and I'm going to try to get through this
[00:09:37.120]without too much emphasis.
[00:09:39.440]But what this kind of experiment or what this kind of paper
[00:09:42.800]does is it synthesizes experiments.
[00:09:44.660]I find these to be really powerful ways
[00:09:48.080]for us to look at effects across a range of studies.
[00:09:50.460]So they looked at--
[00:09:52.140]they looked at all the publications where cover crops
[00:09:55.060]had been grown before corn, and then what were those yield
[00:09:59.760]effects.
[00:10:00.260]So you, in a really systematic way,
[00:10:01.560]organize that information.
[00:10:02.720]And they found that, as you can see here
[00:10:06.100]on the left graph for grasses -- so they sorted the cover crops
[00:10:12.160]by species.
[00:10:13.360]Grasses and this yield effect of a zero
[00:10:16.380]means no difference from a control to no cover crop.
[00:10:20.620]If you're to the right of
[00:10:22.120]this bar, the zero bar, that means the cover crops
[00:10:24.340]were increasing yields.
[00:10:25.340]You can see for corn, if you had a mixture
[00:10:28.380]or if you had a legume that, again,
[00:10:30.280]for all the global studies looking at these effects,
[00:10:33.700]cover crops were increasing yields in mixture
[00:10:37.180]and following mixture and legume cover crops,
[00:10:39.700]but with a neutral effect on grasses.
[00:10:41.740]And that effect did not change, whether that
[00:10:44.260]was a no-till or conventional till system.
[00:10:46.340]That's the graph on the right.
[00:10:48.080]So I think that's really powerful.
[00:10:49.420]It's not just like one year, one study, it's hundreds of studies
[00:10:52.100]compiled in one synthesis to say that corn following a grass
[00:10:57.700]can be neutral, other species can be positive.
[00:11:01.600]So again, in aggregate, a lot of the different scales
[00:11:04.860]of research point to similar trends.
[00:11:06.900]So this is just a snippet from a news report
[00:11:11.700]that was written about long-term, on-farm replicated
[00:11:15.620]trials, like many of you work on with farmers
[00:11:18.740]and with our Extension colleagues, where
[00:11:22.080]corn and soybean were grown for a number of years.
[00:11:27.320]And this is Iowa farms, OK?
[00:11:29.060]And what they found was that just for corn yields,
[00:11:32.480]that in the first two years of the experiments
[00:11:36.360]that farmers did, there were three out of 10 site years,
[00:11:39.400]so basically one place, one year,
[00:11:41.220]where there was a negative effect of the cover crop
[00:11:44.520]on corn, and seven where there was positive or no change.
[00:11:49.220]And then later, the latter year,
[00:11:52.060]there were no yield reductions, some yield improvements,
[00:11:56.460]but mostly neutral.
[00:11:57.520]So that's for corn.
[00:11:58.560]And for soybean, there were yield improvements
[00:12:03.660]even in the beginning and continued,
[00:12:06.120]and then one site year where there was a decline
[00:12:08.980]in the latter year.
[00:12:09.760]So I think that this is a really interesting finding
[00:12:12.420]because, in my opinion, to substantiate
[00:12:14.680]what we just see from small-scale studies,
[00:12:18.020]but that in time, there was less negative
[00:12:22.040]more positive yield effects,
[00:12:23.920]and maybe even more positive here with soybean.
[00:12:26.380]And so what this article talks about, too,
[00:12:28.580]is the importance of management
[00:12:29.700]and that once farmers were able to get through
[00:12:31.940]a learning curve and not have issues with termination,
[00:12:35.080]that they were able to see positive yield effects.
[00:12:37.400]So that's small-scale on-farm research.
[00:12:42.160]And actually, Katja and myself and Laura Thompson
[00:12:46.440]and Jenny Rees from Extension
[00:12:49.080]worked on another synthesis paper
[00:12:52.020]where we just categorized all the experiments
[00:12:54.540]from our on-farm research network
[00:12:56.120]and from the published literature
[00:12:57.800]about cover crops in Nebraska.
[00:13:01.320]So we looked at how much biomass was grown.
[00:13:03.660]We looked at where studies were done.
[00:13:05.400]We looked at yield effects.
[00:13:06.520]And so the graphs that we're showing you on the right
[00:13:08.060]are the yield effects.
[00:13:08.840]And each one of those points are one site experiment year.
[00:13:13.580]And so I like to show graphs like this
[00:13:15.440]because it basically,
[00:13:16.160]rather than just showing you an average,
[00:13:17.580]it shows a distribution
[00:13:18.680]because averages can be deceiving.
[00:13:20.640]We know that...
[00:13:22.000]In agriculture, really,
[00:13:22.860]some of those very good or very bad years
[00:13:25.160]become the most important, right?
[00:13:26.580]So we looked at, again, on-farm research.
[00:13:30.100]So we called those farmer-led
[00:13:31.320]and then researcher-led were the smaller scale studies.
[00:13:34.320]And basically what we found is that
[00:13:36.180]if you took the average of all of these,
[00:13:37.780]even though I'm showing you the distribution,
[00:13:39.240]there were some that were negative.
[00:13:42.400]There were many that were positive.
[00:13:44.000]And the same in the farmer-led studies
[00:13:46.500]that there was actually no significant difference from zero.
[00:13:49.040]So yields with and without cover crops
[00:13:50.680]were basically
[00:13:51.980]statistically the same, right?
[00:13:53.440]So again, similar evidence pointing to the same thing.
[00:13:56.820]I'd like to point out here too,
[00:13:58.120]this panel F in the graph on the left,
[00:14:00.980]just showing that we really have as a research group
[00:14:04.960]and even with the farmers we've worked with
[00:14:06.500]focused on a lot of studies in Eastern Nebraska.
[00:14:09.380]And so work that Vesh and I have been doing
[00:14:11.260]through this agreement,
[00:14:12.000]and we want to continue to share more about that
[00:14:14.400]with all of you,
[00:14:15.240]has tried to expand some of our knowledge
[00:14:18.260]about cover crops into western Nebraska.
[00:14:19.940]So we know how important that is.
[00:14:21.960]And so again, so this is comparing farmer-led
[00:14:24.640]and researcher-led on-farm
[00:14:27.600]and smaller scale experiments.
[00:14:29.860]And then I also wanted to share this with you.
[00:14:32.600]And again, this was in Vesh's slides from October
[00:14:34.980]that from the SARE CTIC farmer survey.
[00:14:39.640]So it's a survey that gets done every year.
[00:14:42.480]Hundreds of farmers fill it out.
[00:14:44.280]They reported the data last year broken out by state.
[00:14:49.360]And so what we see here is that when farmers,
[00:14:51.940]when they report what are your average yields
[00:14:54.020]with cover crops and without cover crops.
[00:14:56.740]So this is for corn.
[00:14:57.820]They show a 14% increase in yields with cover crops.
[00:15:03.180]And across the responses for soybean,
[00:15:07.520]the yields were also reported as higher.
[00:15:10.160]So again, this is not the same kind
[00:15:12.320]of replicated controlled study,
[00:15:14.040]but to me pointing to evidence of how,
[00:15:17.580]once people are confident with management
[00:15:20.620]that they are able to
[00:15:21.920]see a yield improvement.
[00:15:22.980]So I know that this is a slide
[00:15:24.300]that has a lot of words on it,
[00:15:26.700]but I did want to kind of go through,
[00:15:28.840]just real quickly,
[00:15:30.520]we'll put this together
[00:15:31.440]in a summary document for everyone.
[00:15:33.580]This is just all the slides.
[00:15:36.760]Vesh had some really nice slides,
[00:15:38.100]some really detailed information
[00:15:39.480]of experiments that were specific to Nebraska.
[00:15:45.060]So I've got a bullet point
[00:15:46.080]for all of those things that he had,
[00:15:48.120]and I'll just kind of hit the highlights
[00:15:49.700]of them for you here.
[00:15:51.900]So he showed several studies specific to Nebraska,
[00:15:55.020]so not synthesis studies like I've been showing you.
[00:15:57.520]One was a project that a recently finished PhD student
[00:16:01.720]on my team, Tauana Almeida,
[00:16:03.020]did where we looked at corn planted green
[00:16:06.180]with earlier and later termination timings
[00:16:10.840]of cereal rye and hairy vetch at ENREEC,
[00:16:13.520]so east central Nebraska.
[00:16:15.180]And we did find that our late terminated treatments
[00:16:19.060]in cereal rye did decrease,
[00:16:21.880]especially in 2022 when we were drier.
[00:16:24.880]Another study that was done over dry land
[00:16:30.100]and irrigated experiments with earlier
[00:16:32.040]and later planting on average,
[00:16:34.400]when you look across all of those site experiment years,
[00:16:38.060]did not see any differences,
[00:16:39.260]but a few places where there were some corn yield declines,
[00:16:46.000]some corn yield increases too.
[00:16:47.720]So I think you're kind of getting the pattern
[00:16:51.860]here, but some interesting trends,
[00:16:53.920]I think that come out when we look at what's going on
[00:16:56.240]in some of the Nebraska studies.
[00:16:57.780]So a study that was done by a former graduate student,
[00:17:02.300]Trey Stephens looked at planting green with soybean
[00:17:04.980]over two years and found one year of a decline,
[00:17:08.280]one year of increase and the decline associated
[00:17:11.580]with drier conditions.
[00:17:12.700]Another study that Katja and colleagues led
[00:17:15.980]over several years, four years and three sites
[00:17:19.220]with soybean, mostly neutral effects,
[00:17:22.320]one year with lower yield, one year with higher yield, okay?
[00:17:26.500]So corn and soybean, these dry years can have
[00:17:31.800]a potential negative effect.
[00:17:33.320]And then a couple of studies that I will talk more about
[00:17:36.200]when we get into the water section of the presentation
[00:17:38.020]that had to do with wheat.
[00:17:40.160]So hitting corn, soybean, and wheat in all of these studies,
[00:17:44.840]but a paper worked on by Nielsen and colleagues
[00:17:48.340]published in 2016 found, and this was specific to Sydney,
[00:17:52.300]two years of data.
[00:17:53.300]They also had a site in Colorado,
[00:17:54.880]did find that cover crops were reducing crop yields,
[00:17:57.680]both under, this is for wheat,
[00:17:59.740]under irrigated and dry land conditions.
[00:18:01.980]And then Alex Rosa was a former graduate student.
[00:18:06.580]He's now working with Bayer in Gothenburg,
[00:18:09.480]if you've run across Alex.
[00:18:10.680]He's a great contact for many of us.
[00:18:13.160]Two site years in his research at Grant and North Platte
[00:18:16.900]and did see when they had corn before,
[00:18:21.800]after a cover crop, following wheat,
[00:18:23.620]most of those species did have some slight decline
[00:18:26.800]on corn yield except for spring oats.
[00:18:30.080]So I'm going to try to tie that all together.
[00:18:33.140]So again, lots of words.
[00:18:34.240]We'll put this together for you.
[00:18:35.700]What does this all mean when we look at
[00:18:37.560]what's been found in Nebraska
[00:18:38.780]and what has been found on some other synthesis projects?
[00:18:44.040]So these studies, again, across smaller scale,
[00:18:46.580]across on-farm research,
[00:18:49.060]across the farmer survey data,
[00:18:50.520]all generally,
[00:18:51.780]point to neutral effects of cover crops
[00:18:55.140]on cash crops in the aggregate.
[00:18:56.760]Of course, there's some caveats here,
[00:18:58.880]but that is the really general pattern
[00:19:00.620]that we see across a number of different scales.
[00:19:03.220]And then what are some more specifics here?
[00:19:05.980]So one of those slides that I shared,
[00:19:08.040]that meta-analysis found for corn,
[00:19:10.580]legumes and mixtures could lead to higher yields.
[00:19:13.140]And as we see across a number of studies
[00:19:15.700]that the late termination,
[00:19:17.280]especially in drier years,
[00:19:19.120]could lead
[00:19:21.700]to yield declines.
[00:19:22.900]And I would say,
[00:19:23.480]just kind of trying to tie this all together for us,
[00:19:26.560]I think that these same principles
[00:19:28.140]could generally apply for wheat,
[00:19:29.620]but I would say this has been studied
[00:19:31.680]a bit less than for corn.
[00:19:33.300]I would say we have a little bit less information
[00:19:37.200]from research about soybean yields,
[00:19:39.420]but probably lesser effects of soybean.
[00:19:42.060]I think that the competition of the cover crop
[00:19:44.440]is a bit less,
[00:19:47.000]something that soybean,
[00:19:47.680]this is a plant it's able to grow out of
[00:19:49.360]a little bit easier.
[00:19:50.380]But I would say, again,
[00:19:51.680]studied a bit less,
[00:19:52.740]but still I would say neutral
[00:19:53.940]to potentially positive effects.
[00:19:56.240]And this is really our sense
[00:19:59.060]is that once farmers and researchers,
[00:20:01.400]we have to count ourselves as farmers
[00:20:03.340]who can make mistakes
[00:20:04.800]or struggle with the complexities
[00:20:07.140]of cover crop management.
[00:20:08.360]Once the folks get past that learning curve,
[00:20:10.380]typically with termination,
[00:20:12.220]that negative yield effects
[00:20:13.480]are generally pretty limited.
[00:20:14.840]And we'll let you have a little bit
[00:20:16.680]of a discussion about water
[00:20:18.120]and how we can manage for that,
[00:20:21.180]especially,
[00:20:21.520]knowing that drier years
[00:20:22.760]can be a challenge.
[00:20:24.180]So that is what I wanted to share,
[00:20:27.240]just revisiting from last time.
[00:20:28.860]Again, we'll make all of that available
[00:20:30.280]and put together kind of a reference list
[00:20:32.580]of some of these papers
[00:20:33.620]if it is of interest.
[00:20:35.360]I want to next move into the water cycle
[00:20:38.700]because this is generally when people,
[00:20:40.300]how I would answer
[00:20:42.160]when people ask me about
[00:20:43.480]cover crop impacts on water.
[00:20:44.840]I think it's important we think about
[00:20:46.120]the entire water cycle together.
[00:20:48.380]So I want to give you
[00:20:49.540]just a high level look
[00:20:51.180]and reminder, refresh of the water cycle
[00:20:54.580]and all the ways that a cover crop
[00:20:55.940]could be impacting, right?
[00:20:56.880]So essentially,
[00:20:57.920]what is the water cycle, right?
[00:20:59.020]This is the continuous movement
[00:21:00.560]of water molecules
[00:21:01.940]through the earth system.
[00:21:03.880]And so what are some
[00:21:05.960]of the important processes
[00:21:06.940]when we think about ag systems, right?
[00:21:08.960]We might think about precipitation,
[00:21:11.440]how much water is falling
[00:21:12.680]from the atmosphere.
[00:21:14.340]We can think about
[00:21:16.100]what's happening with respect
[00:21:17.920]to water table, groundwater
[00:21:20.840]flow, stream flow,
[00:21:23.020]how we manage
[00:21:24.980]all of those things
[00:21:26.360]when we think about irrigation,
[00:21:27.930]We would think about evapotranspiration. So that's the water that plants use in transpiration and evaporation, the water we lose from the soil surface.
[00:21:37.850]And I like to think a lot about infiltration. That's probably one of my favorite processes. If we had to pick one, maybe that could be your icebreaker question. What's your favorite part of the water cycle?
[00:21:48.350]So infiltration is the water that is moving into the soil rather than over the soil as runoff or soil moisture, what's staying in the soil.
[00:21:59.910]So soil moisture, what's staying in infiltration, what's getting in that active process, surface runoff, what is running off.
[00:22:07.970]So those are some of the obvious elements of the water cycle that are important when we think about agriculture and when we think about cover crops.
[00:22:17.170]So the other way that I like to think about this, too, is if we think about what we're doing in agriculture is really managing a water balance.
[00:22:23.490]So what we're trying to do is maximize how much water is entering our system so that plants have water to be able to grow, to transpire.
[00:22:34.490]And we also want to try to prevent losses from things like evaporation and runoff.
[00:22:40.470]And what I like to think about is the soil surface as this balance is really where the action is happening.
[00:22:47.090]And where all of these processes are really coming to bear.
[00:22:52.070]So this is what we're trying to do.
[00:22:54.590]We are trying to think about the soil profiles, the way I think about it.
[00:22:58.210]It's where the action is happening when it comes to the water cycle.
[00:23:01.030]It's really the central component that regulates the in and out flows of the water cycle.
[00:23:05.910]So I don't probably have to tell you at NRCS the nice diagrams and quantifications that
[00:23:12.870]have tried to be done about how much water can a healthier soil hold.
[00:23:15.990]And we see some.
[00:23:17.010]We have some nice evidence of that, as I'm going to share with you, because research
[00:23:19.430]has been able to quantify this.
[00:23:21.330]But this is really where the action is happening, right?
[00:23:24.490]And I think it's important that we remember that soils are a matrix, not like the matrix,
[00:23:31.890]but they are a, not like the Keanu Reeves matrix, right?
[00:23:35.650]But if we think about soil as a mixture of particles, so different types of soil have
[00:23:41.470]different, and I like to think about this as bricks and the way they kind of lay together,
[00:23:46.930]you know, we want to make sure that our healthy soil has enough air to facilitate movement of
[00:23:51.530]water and gases through it. And in the matrix of the soil, we have organic matter, which is what
[00:23:58.330]remains the decay of plant material. Again, I probably don't need to refresh too many folks
[00:24:04.050]at NRCS about this, but we obviously want to make sure that that orientation of the building blocks
[00:24:10.430]and the mineral components of the soil is such that we can facilitate movement of air. So that
[00:24:16.850]properties like porosity as well as organic matter in the soil, but we're going to think
[00:24:22.550]some about infiltration and soil hydrologic properties here and show you what the research
[00:24:27.870]shows. So that was my quick revisit in a few minutes of the water cycle, a number of ways that
[00:24:35.590]a growing cover crop and a decomposing cover crop could be contributing to all of those
[00:24:42.510]processes. And I want to kind of try to talk you through all of that here. And so,
[00:24:46.770]here's what I'm going to do. So, I've kind of combined in my presentation here
[00:24:51.550]studies that have been done, more synthetic studies, like I've already showed you. So,
[00:24:57.630]studies that have synthesized experiments from around the world. And I also want to talk about
[00:25:01.470]some studies from Iowa and Nebraska. The Iowa one, the reason I get that in is because I did it,
[00:25:05.490]and I get to talk about it. This is one of my favorite research papers that I worked on, but
[00:25:10.450]close enough in the region, I feel. So, I want to talk about some global studies,
[00:25:14.750]and then I also want to talk about, again, some things from our
[00:25:16.690]region. And what these experiments from around the world that synthesize lots of
[00:25:21.250]different experiments, what do they show? They show that cover crops are
[00:25:25.410]consistently increasing infiltration, right? So, I'm going through my water balance components,
[00:25:30.130]that they improve soil hydrology. So, adding some quantification to those numbers at NRCS.
[00:25:35.570]I love those diagrams. I use them a lot about healthy soil and water. Cover crops can reduce
[00:25:42.370]drainage. That has been seen in synthesis of studies, as I'm going to show you in a minute.
[00:25:46.610]The cover crops do reduce evapotranspiration and can increase water storage and overall
[00:25:55.170]water use efficiency. So, those things that I just shared, I'm going to go into a little bit
[00:25:58.450]more detail here because they've been, again, found from these synthesis of studies from all
[00:26:03.570]over. And we've seen some of these things on Nebraska farms, too, that they've increased
[00:26:07.810]infiltration, that they've had limited impact on soil water content, that they can increase
[00:26:13.330]soil water storage in wetter and drier years.
[00:26:16.530]And but they can also, we see the evidence of water use that they have had negative impacts
[00:26:21.810]on crop yields in drier years.
[00:26:24.510]OK, so let me get into it.
[00:26:26.650]So the first study I want to show you, I'm showing you a diagram of this.
[00:26:29.270]I've got the citation here on the bottom was a synthesis of global studies.
[00:26:33.990]They looked at 117 studies that fit their criteria.
[00:26:36.690]So you always like determine what what should an experiment have done for me to be able
[00:26:41.770]to include it in a systematic way in an analysis like this.
[00:26:44.510]And they looked at 117 studies.
[00:26:46.490]That reported soil moisture with and without cover crops.
[00:26:48.910]And they did some calculations from those numbers on things like water use efficiency,
[00:26:53.030]which they calculate by the yield divided by evapotranspiration.
[00:26:57.290]And what they found is evidence of the cover crop using water, that it was reducing
[00:27:04.370]evapotranspiration as well as water in the soil during the fallow period, but that the
[00:27:11.450]cover crops were able to increase water use efficiency overall.
[00:27:15.690]So more.
[00:27:16.450]Yield per unit of evapotranspiration.
[00:27:19.190]So again, I'm starting with this one because I liked how they were creatively able to combine
[00:27:24.670]several components of the water cycle that does help us understand that, you know, the
[00:27:29.810]cover crop is using water, but overall able to contribute to water use efficiency through.
[00:27:34.570]So reducing evapotranspiration, really, they attribute that to the reducing of loss from
[00:27:40.330]the soil surface or reducing evaporation.
[00:27:42.570]So that's good.
[00:27:43.170]That's a way we could eliminate loss as we might expect.
[00:27:46.410]From residue cover, from our cover crops.
[00:27:51.690]So that's a global study.
[00:27:54.150]So here I want to talk about global and also, or global synthesis, I should say.
[00:27:59.090]I want to talk about Nebraska studies and some global studies, global synthesis study
[00:28:06.370]that I've been a part of.
[00:28:07.190]So Fernando Krupek, who was a former graduate student in our department that worked with
[00:28:13.490]me, we had another collaborative agreement.
[00:28:16.370]We presented to NRCS a few times about that, if you've heard us talk about it.
[00:28:20.510]So this was a project that, a collaboration with Nebraska Extension and on-farm research.
[00:28:26.250]So we looked at, in this particular study, four replicated trials on farms that had cover
[00:28:32.570]and no cover over a few years.
[00:28:36.250]So we took these measurements after just a few years that cover crops had been in place.
[00:28:40.150]And what we found was that in three of those four farms, cover crops did increase
[00:28:46.330]infiltration.
[00:28:47.090]And I really like to make this point that that was happening quickly, that we like to
[00:28:52.450]talk a lot about how some soil properties and processes are insensitive to management
[00:28:58.810]and do not change quickly.
[00:28:59.770]But my experience is that infiltration is something that can change very quickly.
[00:29:04.190]OK, so when I say that the bullet point here, this is substantiated by other meta-analyses,
[00:29:08.890]a project that I worked on, and another synthesis study where they looked at impact of cover
[00:29:14.550]crops.
[00:29:16.290]And a number of different soil properties, they found that even within one year, infiltration
[00:29:23.310]was something that cover crops could have a positive impact on.
[00:29:26.370]And that makes a lot of sense when we think about the roots in the soil, the potential
[00:29:30.970]contribution to more labile portions of carbon, infiltration, again, being something sensitive
[00:29:37.710]to management.
[00:29:39.190]So not only have we seen this on Nebraska farms, we also do see this in lots of other
[00:29:45.230]studies as well.
[00:29:46.250]So I did want to mention here, too, when I say results of water storage, infiltration
[00:29:51.070]effects will definitely differ based on our soil texture, right?
[00:29:55.970]So a sandier soil, lower water holding capacity, we might expect more water percolating through
[00:30:03.410]the root zone and the opportunity to refill more quickly as well after the cover crop
[00:30:11.350]has been terminated compared to maybe a coarser or a more finely textured.
[00:30:16.210]So I say this without being, all the things that I'm sharing are not very specific to
[00:30:23.790]soil type, but we know that basic principles of holding capacity, soil texture will come
[00:30:29.890]into play in these effects.
[00:30:30.830]But what was interesting about actually the global synthesis that I worked on, we did
[00:30:35.490]not actually see an effect that was consistent across soil type.
[00:30:40.910]So to me, this is a fairly robust finding in terms of the benefit.
[00:30:46.170]Cover crops with respect to infiltration.
[00:30:47.990]I did want to make mention of a great NRCS article.
[00:30:51.910]I love to share this.
[00:30:53.030]When we think about infiltration, when we think about rainfall variability, one of the
[00:30:57.070]farmers who did see a positive effect of infiltration from the cover crop talked about the flooding
[00:31:04.790]in 2019, which I'm sure is very resonant for many of you.
[00:31:07.410]So this farmer who's in central Nebraska said that in that heavy rain event, that bomb cycle
[00:31:12.770]and that very unusual event that happened in mid-March.
[00:31:16.130]Of 2019, that one of the fields that had a rye cover crop had 70 out of 75 acres underwater
[00:31:23.090]that was underwater for many days when the water finally receded, that the field
[00:31:28.810]was still in good condition.
[00:31:29.830]And you really couldn't have imagined what that would have looked like without the rye
[00:31:33.010]cover crop.
[00:31:33.490]So I do think that there's trade-offs.
[00:31:35.990]Everything in agriculture is a trade-off, right?
[00:31:38.110]When we think about the benefits and rainfall variability and soil conservation, we have
[00:31:46.090]getting past that learning curve and what is the trade-off we have maybe for minor yield
[00:31:52.410]declines in the short term.
[00:31:54.090]So really positive story here that I was glad that NRCS has shared.
[00:31:58.170]Okay, so drainage.
[00:32:02.390]So I didn't explicitly show that in the water cycle, but something of importance when we
[00:32:08.170]think about water moving through the soil profile.
[00:32:10.590]So this was a synthesis of 28 experiments.
[00:32:16.050]They found that compared a bare soil to a cover crop where drainage water was measured,
[00:32:21.710]and they defined that as the water that was unavailable to plant roots and likely to recharge
[00:32:26.890]groundwater.
[00:32:27.330]And they were actually able to calculate an average impact of the cover crop of 27 millimeters
[00:32:34.470]that drainage water was reduced, which is evidence that the cover crop is using water.
[00:32:41.070]So 27 millimeters, just a little over an inch of water, not a huge amount of water use.
[00:32:46.010]Um, they do talk about this as a potential disservice and just thinking about the whole
[00:32:50.050]water balance, but I would say, yes, potential disservice, but also I think it's really neat
[00:32:55.830]that in a synthesis like this, they can actually really calculate some average
[00:33:00.490]number of the water use the difference in water drainage from the cover crop.
[00:33:05.390]So, so again, adding to our balance as we think about what is the overall effect
[00:33:10.790]of the cover crop on the water cycle?
[00:33:15.970]Um, water storage, next component.
[00:33:19.130]So this is some work that I worked on when I was a graduate student at Iowa State University.
[00:33:23.830]And there was a really great long-term USDA site where we were collecting data from that
[00:33:29.950]had had a cover crop in place since about 2002.
[00:33:32.550]And so at the point that we took a look at the soil moisture sensor data from 2008
[00:33:39.490]to 2014, that cover crop had been in place for, you know, six to about 12 years.
[00:33:45.930]So when we looked at soil moisture sensor data, we only looked at two, 30 to 45
[00:33:50.290]centimeters.
[00:33:50.770]So it wasn't very deep, but we did see again, evidence that the cover crop was using water
[00:33:55.790]in the spring.
[00:33:56.390]This was just cereal rye and a corn soybean rotation.
[00:33:59.310]And we did see that, that evidence of water use, but that by the time it was time
[00:34:06.810]to plant corn and soybean, even in wetter and drier years.
[00:34:09.350]So this includes 2012, it includes some, some normal years, really a range of seasons
[00:34:14.710]that there was no cover crop.
[00:34:15.890]There was no difference in planting conditions for, for corn and soybean.
[00:34:21.410]So, that spring rains were able to replenish soil moisture to the same level compared
[00:34:27.330]to bare soil.
[00:34:28.470]And we also did some assessment of the soils at that site.
[00:34:31.970]And we were able to actually see a increase in field capacity.
[00:34:36.750]And when we calculate what that is for plant available water, we saw a significant increase
[00:34:41.610]as well.
[00:34:42.610]So, so that was pretty neat.
[00:34:44.030]And that led me.
[00:34:45.850]And next project in my next role to try to look at have other studies found this have
[00:34:51.290]other studies been able to see cover crops increasing properties of soil hydrology, like
[00:34:58.270]field capacity, porosity.
[00:34:59.570]Those are the two that we looked at in the citation that's here, where we looked at
[00:35:04.090]different continuous living cover practices.
[00:35:06.690]And we did find that those were improving field capacity and porosity in a significant
[00:35:12.650]way.
[00:35:13.230]So we think about soils as a sponge.
[00:35:15.810]Here we have in these projects been able to quantify that that is leading to an improvement,
[00:35:21.710]again, probably contributing to some of those infiltration increases as well.
[00:35:26.310]Okay, so I'm going to just have about two more slides here of evidence, and these are
[00:35:35.070]specific to Nebraska.
[00:35:37.010]So work that was done, Katja Koehler-Kohl and a number of colleagues had some funding from
[00:35:42.910]the Corn and Soybean Board years ago that they were able to do.
[00:35:45.770]They were able to do on multiple sites.
[00:35:48.310]You can see the locations here.
[00:35:50.570]So they had experiments at Brule, Mead, Clay Center, and Concord, so in several regions
[00:35:55.150]of Nebraska, where they looked at a corn-soybean rotation with no cover crop and a mixture
[00:35:59.610]of cover crops.
[00:36:00.410]They monitored soil moisture over several seasons.
[00:36:03.250]As would be expected, there was a range of biomass for their cover crops from zero to
[00:36:10.190]up to about three tons per acre, and that in all of those rotation phases, they were
[00:36:15.750]in years and different locations.
[00:36:17.530]They only found differences in water content between the control and the cover crop in
[00:36:22.830]the top 12 inches of the soil in four of 12 situations, and that those impacts were pretty
[00:36:28.870]minimal, so less than 11 millimeters difference of water in total.
[00:36:33.650]And so I just put in italics here, their final note of their abstract, which was that in
[00:36:41.150]conclusion, the winter cover crops did not have an effect on soil water content that
[00:36:45.130]would impact.
[00:36:45.730]Corn and soybean production is really similar to what we found in my experiment in Iowa.
[00:36:50.090]And I think that's very interesting.
[00:36:51.250]We look at this greater range of geography here in these experiments as well.
[00:36:56.350]And then the last experiments that I want to refer to are specific to western Nebraska
[00:37:03.390]and the potential negatives to be looking out for, right?
[00:37:07.650]So Alex Rosa, whose work, and I've mentioned these two already when I talked about the
[00:37:15.710]where drier years did lead to some negative yield effects.
[00:37:19.770]So Alex's study looked at a couple of locations over a couple of years, Grant and North Platte,
[00:37:26.750]and they had later termination.
[00:37:30.670]This was, again, wheat, cover crop, corn.
[00:37:34.790]They were looking at the corn yield effects, and they did find that later termination
[00:37:38.650]affected corn yields.
[00:37:39.990]And then this study with wheat yields from a few years back now was in Sydney,
[00:37:45.790]and also, as I mentioned before, in Ohio over a couple of years.
[00:37:48.630]They did find a pretty robust trend where the cover crops were reducing wheat yield
[00:37:54.210]by 10%, and that that effect was worse in drier years.
[00:37:58.070]They did also do a lot of nice calculations.
[00:38:01.570]If you're in western Nebraska, and we will share all these things, I encourage you to
[00:38:05.130]look at this, some interesting ways they looked at soil water and water use efficiency.
[00:38:11.670]So they did find that even though the cover crop treatments were using more water,
[00:38:15.950]they were increasing water use efficiency in one of the years of the experiment,
[00:38:20.010]and they had dry land and irrigated conditions.
[00:38:22.170]So of course, I know that those cash crop yield impacts are really important,
[00:38:26.610]but I do think that there's management opportunity to offset some of that.
[00:38:30.490]So let me put this all together for you.
[00:38:34.290]I would say if someone asks you and you're concerned about cover crops water use,
[00:38:41.750]yes, that's a real thing.
[00:38:43.170]It's a plant.
[00:38:44.290]It needs water to grow.
[00:38:46.330]But that cover crops can have an effect on the entire water cycle,
[00:38:49.870]but potential for complicated effects on crop yields.
[00:38:55.970]I would again highlight that there is overall positive effects on water cycle,
[00:39:02.910]improving elements of soil hydrology, including things like infiltration and water storage.
[00:39:08.110]And I would say that in Nebraska, this generally holds true, right?
[00:39:12.250]That there are minimal or limited yield effects.
[00:39:15.630]I've highlighted some of the more negative ones for you there.
[00:39:19.430]But they can contribute to yield effects in drier years.
[00:39:24.830]And those are some of the bigger effects.
[00:39:27.770]And with later termination, right?
[00:39:29.350]So that experiment that I've already mentioned that we did at Mead,
[00:39:31.610]I would have caution recommending planting green for farmers,
[00:39:34.810]even though many of them are trying it.
[00:39:36.390]But especially in drier years, this careful management is key.
[00:39:41.130]So terminating early is important.
[00:39:44.050]I haven't said a lot here yet.
[00:39:45.610]I haven't said a lot about wet springs,
[00:39:46.870]but I think that there could be situations too with rainfall variability
[00:39:49.930]where more water use is a potential positive.
[00:39:52.790]Okay.
[00:39:55.750]Well, that is what I wanted to share for you.
[00:39:59.310]And I appreciate your good attention
[00:40:02.030]and hope I've given you some evidence around cover crops, water use, and more.
[00:40:06.670]So my contact information is here.
[00:40:08.250]Will be on the PowerPoint slides.
[00:40:10.770]And I think now we'll be ready for the breakout rooms.
[00:40:15.590]But point us to them in just a second.
[00:40:18.550]So again, we're going to try to do these by region
[00:40:20.290]based on maybe combining some so that we get several people in the rooms.
[00:40:24.670]And so these are the questions that we want you to look at, right?
[00:40:27.230]So are you working with farmers in your area on cover crops?
[00:40:30.430]What are their goals for cover crops?
[00:40:32.910]Are you hearing stories about cover crops and water use?
[00:40:36.250]And if it's a concern, what are some of the strategies that you might recommend?
[00:40:39.830]So we want you to discuss your ideas.
[00:40:42.630]Since it's about 2.42,
[00:40:45.570]we did schedule, you know, a good 90 minutes for this.
[00:40:48.630]We encourage you to stay and chat as long as you want.
[00:40:51.690]If you want to share as an icebreaker,
[00:40:53.330]your favorite part of the water cycle, encourage you to do that.
[00:40:56.270]Our facilitators are going to help us take some notes
[00:40:59.890]and they want to just help give everybody an opportunity
[00:41:02.490]to share some of their thoughts.
[00:41:04.590]So I think that what we'll do is go ahead and open the rooms now, Vesh.
[00:41:09.470]And we can kind of wait in the main room and see if anybody is,
[00:41:15.550]wanting to come back and visit us and recap a little bit
[00:41:18.450]after maybe 20 or 30 minutes.
[00:41:20.090]But if you also want to just be dismissed from webinar after this,
[00:41:24.490]then you're welcome to do that.
[00:41:25.430]We know at the top of the hour, we'll probably lose some folks anyway.
[00:41:28.230]So Vesh, is there any other instruction you want to give folks
[00:41:31.810]about which rooms?
[00:41:32.830]Go ahead.
[00:41:33.490]So considering the number of participants,
[00:41:39.870]I merged some of the rooms.
[00:41:41.670]I merged northwest, north central,
[00:41:45.530]and southwest into one,
[00:41:46.890]and John will be facilitating that room.
[00:41:49.870]And I merged central and south central,
[00:41:53.050]and Samantha will be facilitating that room.
[00:41:55.290]And considering the number of participants
[00:41:58.330]from eastern part,
[00:41:59.730]so I made two rooms for the eastern part of Nebraska.
[00:42:02.890]So name that starts from A through M
[00:42:07.430]can join room one for northeast, central, and southeast.
[00:42:11.630]And naming that starts from M through G,
[00:42:15.810]may join room two for northeast, central, and southeast.
[00:42:20.110]Okay, so the rooms will be open
[00:42:24.450]and you can jump into the one that fits your region.
[00:42:27.790]And we will hang out.
[00:42:31.990]I will be in the main room
[00:42:33.170]if anybody's not sure where to go.
[00:42:34.590]And then if you wanna just dismiss yourself from main room
[00:42:37.970]after 20, 30 minutes of discussion, that would be fine.
[00:42:41.210]If you wanna come back and join the main room
[00:42:42.990]and share any thoughts, we'll be here.
[00:42:45.490]Thanks, everyone.
[00:42:51.570]Thanks.
[00:42:53.410]Thank you.

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