Crop Modeling & Cover Cropping on the Palouse with Dr. Erin Brooks

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Episode Transcription:

Drew Lyon: Hello. Welcome to the WSU Wheat Beat podcast. I’m your host, Drew Lyon, and I want to thank you for joining me as we explore the world of small grains production and research at Washington State University. In each episode, I speak with researchers from WSU and the USDA-ARS to provide you with insights into the latest research on wheat and barley production. If you enjoy the WSU Wheat Beat podcast, do us a favor and subscribe on iTunes or your favorite podcast app and leave us a review so others can find the show too.

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Drew Lyon: We regularly have guests from WSU and the USDA-ARS on the show, but today is one of a three episode series I have with colleagues from the University of Idaho for an extended discussion on the role of crop diversity and soil health. My guest today is Dr. Erin Brooks. Erin is a professor at the University of Idaho in the Soil and Water Systems Department. He was trained as an agricultural engineer with a B.S. from Washington State University and M.S. from the University of Minnesota and a Ph.D. from the University of Idaho. He has been at the University of Idaho since 1998. His research generally focuses on adaptive management strategies in agroecosystems, particularly related to water and nutrient availability storage and transport. He often collaborates with WSU and ARS Research scientists in large interdisciplinary research projects, many of which have included extensive field experimentation, complemented with the development and assessment of computer models and decision support tools. Hello, Erin.

Dr. Erin Brooks: Hello, Drew.

Drew Lyon: So we heard from Kendall Kahl in the last podcast that there may be opportunities to start incorporating cover cropping into our wheat based systems, not only in our high precipitation zones, but also a potential replacement of summer fallow. From your perspective, what do you see as the major advantages and disadvantages of incorporating cover or forage cropping into this region?

Dr. Erin Brooks: Well, I think Kendall did a good job of describing the challenges. First of all, in our dryland system, particularly in the low and intermediate pricip. zones, the greatest challenges really involves issues related to timing, storage, and availability of water. Many growers have heard the success stories of some of the pioneers of cover cropping and then regenerative ag movement such as Gabe Brown and he’s come to this region to talk to a lot of growers. However, the Palouse has this really unique climate. We have these winters and dry summers and so we have some unique timing challenges that really limits our ability to directly adopt strategies employed in North Dakota or the Midwest, where we see this happening more often. Specifically, we have questions: how do we get a crop established in the fall in our dry soils, and what are the impacts of a cover crop on our primary cash crop, the winter wheat, especially if we’re looking to replace fallow with these cover crops? Also, if you’re looking to replace an existing crop in a crop rotation like such as you’re trying to take out a spring wheat or spring cereal then there’s also an economic consideration that really you’re not going to get the revenue from that crop. So that’s why many growers are looking at other strategies that attempt to minimize the costs associated with the cover cropping. And this is why considering you could consider this affords crop and then you graze it or you bale it to relieve some economic revenue. So we’re still learning about this potential long term benefits. We think there are many in benefits of soil health, water retention, increased soil carbon, resilience to heat stress, drought, weeds, diseases, and I think that we’re going to see those and more evident with time. But as Kendall suggested and we hear from Dane and Sanford, we’re seeing some initial evidence that some of these changes occur even within a couple of years following the cover crops.

Drew Lyon Okay. So I was in western Nebraska for 22 years as dry land cropping system specialist and one of my goals was to try to minimize or even eliminate summer fallow, and we didn’t quite get there. There are some real challenges, you say, but that’s a summer precip. zone and this is a winter precept zone, which just changes the framework a whole lot.

Dr. Erin Brooks: That’s right.

Drew Lyon: So yeah, it’s trying to deal with those issues. We could, we could grow summer crops, you know, fairly well because we got the rain when the in the heat of the summer and here that those summer crops are pretty, pretty difficult to do right without using the stored water that you want to save for your fall crop. So, can you tell us more about some of the logistical challenges and solutions that your team has been considering and evaluating to minimize the risks of including of cover crop and crop rotations across the place?

Dr. Erin Brooks: Yeah. So there are several management options that we’ve kind of started to look at the girl might consider with cover crops. As I mentioned, the first consideration is whether to treat the cover crop truly is a cover crop or is a forage or a green manure crop. If a grower will be baling or grazing, the crop, which is one of the options, then the grower will want to select a cover crop next that really provides the greatest protein and fiber to feed an animal, as opposed to maybe you thinking of as a cover crop as a primary goal of increase organic matter and maybe feed the soil and the soil microbiology. The second really consideration is really to adopt a policy to crop or a spring crop. So the people have been doing it as a spring cover crop or fall. And really the impact really isn’t in terms of the winter tolerance. And another consideration is really when to terminate the cover crop, which we kind of got into at the modeling quite a bit to make sure really that there’s enough water available for the winter wheat crop, particularly in these drier zones of the Palouse. And really the last one we’ve kind of looked at quite a bit is really whether it’s fertilize the cover crop or not. This adds additional costs but if you’re looking at greater growth, fertilizing the cover crop makes sense. And so we’re trying to use these crop models to really look at these different options and and really investigate the viability and maybe some of the impacts of these decisions.

Drew Lyon: Okay. So tell us more about the crop model use and what sort of confidence you have in the reliability of these models. I think a lot of people out there often view models a bit skeptically, probably, because they don’t really understand what’s behind them. So tell us a little bit more about this.

Dr. Erin Brooks: Yeah, there’s a lot of skepticism and I try to explain to my students that computer models are really the tools to better understand and mimic a natural system. But and they’re good at gaining insight into some of the more complex responses and a cropping system that you can, you know, find out in a field experiment. And we can actually look at how potential changes a management practice might have to system or looking at a change in a weather pattern. And I think it is good to have a healthy amount of skepticism in models as they don’t truly represent the complexity of natural systems. I like the term that you hear oftentimes is that all models are wrong and some models are useful. And I agree that this is probably a good perspective to have. I find a good approach to really understand a system is having a good balance between modeling and field measurements. And this is really the approach we took in this LIT project that we’ve been working on where infants emphasize both field of vision, of field measurement and modeling. So yeah, the model we used is the CROPSYS model and I think you’ve had some other guests on here that maybe talked a little bit about CROPSYS that the USDA-ARS team is even using it and it really was developed here at Washington State University and the Biological Systems Engineering Department, largely by Dr. Claudio Starkel and his programmer, Roger Nelson. So it’s been around for about 40 years and really they’ve used it and it’s pretty effective tool at predicting crop response and water and nitrogen stress from the main crops are grown on the Palouse. And so we in this project, we used a pretty extensive field experiment setup with replicated strip trials and really compare business as usual cropping strategies that we’re currently employing now to these aspirational, you know, they include replacing fallow or a spring cereal crop with a cover crop or forage crop in this rotation. And then documenting that we had the data over a four year period where we measured these measurements in the field and it just so happened that we had, you know, 2021 is a big drought year in 2020 was one of the best years we’ve ever had on the Palouse. And so it’s a good data set to really test the model and really to test the extremes of these cropping systems.

Drew Lyon: Yeah. When I was in western Nebraska, I had a similar– we were looking at dry land corn and I planted it in I think it’s 1999, which was one of the wettest years. And my I was trying to figure out the best population and my highest population wasn’t high enough. We were still going straight up. And then the next year was a drought year. And I didn’t have a low enough population straight down. So I used a model called APSIM that developed in Australia just to put like 50 or 60 years of weather data in there to get okay over a ten year period how might this turn out. So it actually was pretty useful because I think it kind of yes, you will have these extremes and one year one will work. But over the long time, these are the odds of you doing well. And that’s kind of what you’re doing here with this model is running lots of years and taking your data?

Dr. Erin Brooks: That’s exactly right. And that’s why I think that’s why the models are useful. We know that they don’t replicate the real world exactly, but if we wait on field experiments that give us the science to make a management decision, then we’ll never make marriage decisions because every field is unique and every year is somewhat unique. And so we can do the crop modeling, they can extend that out.

Drew Lyon: How well did the model perform for you?

Dr. Erin Brooks: Well, I was actually pretty impressed at how well the model performed. And this was a modeling work that was largely done by my grad student who just defended a few weeks ago a master’s thesis. And we know with models they can be calibrated to fit a single output. And that’s probably one of the reasons I get kind of a bad reputation as you tweak a model and you get this out, this, you know, match it up, maybe crop yield. But then the question becomes whether you tweak the right parameter and are you getting the right answer for the right reasons. And so with that amount of data we had in this project, with all the different strip trials and then the the two years we had at least some of the wet and dry years, we really had a pretty robust assessment, the model, and we found them the good agreement with one of the amount of crop yield, it went pretty well. The biomass, the nites are moved by the biomass and really the change in moisture over the growing season. I’d like to see a little bit better accuracy in getting some of the soil inorganic nitrogen. But overall I was pretty impressed with the model and I pretty good confidence and really the ability to replicate these. What I think are the key issues related to replacing fallow with these cover crops.

Drew Lyon: So what were you able to do with this calibrated model and what did you learn about the challenges and benefits of cover or forage cropping in the Palouse?

Dr. Erin Brooks: Yeah, so we had this idea, okay, that was cover, it was calibrated model works that seems to work over this four year period and this is one a model really becomes useful. You have this calibrated model that we have confidence in. So we started looking at the management scenarios and we decided to do it like let’s feed it weather data from 1980 to 2010. Let’s look over a 30 year period and we’ll just put in these different cropping rotations. And so we looked at replacing file with the cover crop and how it might first reduce the winter wheat yields. That’s a key question. And we focus on the St. John area, that was where our research site was at. And in this area, as you may know, that, you know, we have a growers use a three year rotation where they do two crops and they do some fallow 1 to 3 years. And as you might expect with with replacing fallow, there were certainly dry years where this growing a cover crop instead of keep it in fallow did reduce the winter wheat yield in the subsequent year but according to the model this only happened half the time or even less than half the time. And if you think about this year, the 2022 year of all this rain, this might be a year where growing a cover per crop instead of fallow may really make a lot of sense. So this was encouraging. And the lack of the impact on winter wheat yields is partly due to the fact that summer fall really isn’t a completely efficient approach. As much as we try, we still try, summer fallow can lose a lot of water over the summer itself, just from evaporation and things. So then we use them all to try to explore how a grower might minimize the impact of this wheat crop. So what are the options if if you don’t want to minimize this? And that was really this tool, be this using the termination date so when do you terminate the cover crop? And if you terminated early before the all of the soil moisture is depleted then there probably are less of an impact on the winter wheat and and we found that’s exactly right. When you found that you could avoid that whole winter we hit by moving the cover crop termination date up to 2 to 4 weeks beforehand. In the simulation, we generally terminated the cover crop around July 8th, but we could almost eliminate all the winter wheat reductions by turning it up by June 8th. So now the downside of that would be then if you terminate the cover crop early, then you don’t get quite the biomass production. And so if you’re trying to graze it or bale it, then you’re not getting quite so much the biomass and there’s just less organic matter going back in the soil, but that is certainly an option.

Drew Lyon: Okay, this sounds pretty encouraging, actually, that as much as half the year or more you don’t have a reduction suggest farmers could essentially use termination date as the means of water management to minimize the risk of impacts to their winter wheat we crop.

Dr. Erin Brooks: Yeah, so that’s exactly right. And as you’ve seen around here in the last 5 to 6 years, I know that more and more farmers are putting in soil moisture probes and probes that will essentially sample the entire soil profile. And then that data sent to their phones. And so they could actually watch these the soil moisture depletion during a year and say, hey, this is a dry year, we’re just not getting the moisture. I need to terminate early. Or if they’re doing it like this year in 2022, or you could extend that cover crop into July if there’s there’s plenty of soil moisture and and they’ll have less likely an impact on the the winter wheat coming the next year.

Drew Lyon: And so I would guess that the cover crops can use the shallower water and leave the deeper water for later use by the crop. But how do you get how do you get that surface water replaced so you can get a successful start to your following winter wheat crop?

Dr. Erin Brooks: That’s right. That’s right. And that is the challenge, right. So the Midwest gets those summer rains and they can essentially seed after the combine. And so here in the Palouse, we still need a little bit of moisture so that would be seeding deep to try to get some good growth established and you still need a little bit. So that’s still one of those challenges to get that establishment.

Drew Lyon: So what other management options have you looked at with the model?

Dr. Erin Brooks: Yeah. So in addition to water, we were kind of looking at the implications on fertilizer management. And so depending on where the grower adopts a fall seeded yield to cover crop or a spring cover crop and the type of cover crop mix there, some fertilizer options are a fall seeded cover crop that is resistant to winter kill, maybe more reliant on cereals that could experience nitrogen stress if they’re if they’re not balanced with legumes or fertilizers. So fertilizing the crop in the model when we looked at it, did increase biomass and indicates that growers should potentially consider fertilizing these cover crops if they don’t have high residual nitrogen in their soils. Interestingly, if we bailed the cover crop and it was bailing the cover crop, you have less organic matter go into the soil and we assumed essentially 80% of the cover crop was baled off really only resulted in slight reductions in our long term soil nitrogen fertilizer requirement. So you actually you are getting, and we saw in the model, getting more nitrogen mineralization so more organic sources of nitrogen. So even though baling didn’t seem to indicate an increased need for nitrogen fertilizers.

Drew Lyon: Okay, so if fertilizer prices continue to rise as they have this past year, I would presume that growers could change up the cover crop mix to rely more on legumes and in the long run, these cover crop rotations should decrease the amount of fertilizer that the growers would need to apply to their subsequent winter wheat crop.

Dr. Erin Brooks: That’s right. Overall, we found these these rotations were more water efficient as more of our annual precipitation went towards transpiration or increasing biomass and evaporation. And we found less water leached out the bond the root zone. So this is quite a win-win for both the growers, the soil and the environment.

Drew Lyon: Yeah, I would say, you know, another aspect of cover cropping that’s catching on in the weed science circles is just weed competition. So as our herbicides become less and less effective due to herbicide resistance, people are looking more and more at cover crops as part of that entire package for we control.

Dr. Erin Brooks: Yeah, this is I mean, this is the idea of the project we’re on this Landscapes In Transition and this the idea is our landscape here is going to adapt. We are going to see this, you know, in an increase in herbicide resistant weeds, we see soil pH drop, we have organic matter dropping, and I think the farming systems we’re going to see are going to be changing in the next 10 to 20 years. It’ll be interesting to see what it looks like over time.

Drew Lyon: I think of it’s been a couple of years since I saw these models, but I think the prediction is we’re expected to have warmer, wetter winters and hotter, drier summers, which might push us more towards winter crops like winter pea and the rotation and away from some of our spring crops.

Dr. Erin Brooks: That’s right. And I think in the annual precepts, when we see this year, even Latah county, we have a lot of fields that got planted very late or didn’t get planted at all. And so I think falsely the crops, perennial crops cover crops. I do think things are going to change in up a bit going forward.

Drew Lyon: Well Erin, and this is really interesting work. I like the use of modeling to help us try to make some of these decisions because our climate’s quite variable on top of being challenging compared to much of the country. So I look forward to seeing what you do with this and how you translate to growers in this part of the world.

Dr. Erin Brooks: Yeah, well, thanks for having me on here, Drew.

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Drew Lyon: Thanks for joining us and listening to the WSU Wheat Beat podcast. If you like what you hear don’t forget to subscribe and leave a review on iTunes or your favorite podcast app. If you have questions or topics, you’d like to hear on future episodes please email me at drew.lyon — that’s — ( You can find us online at and on Facebook and Twitter @WSUSmallGrains. The WSU Wheat Beat podcast is a production of CAHNRS Communications and the College of Agricultural, Human and Natural Resource Sciences at Washington State University. I’m Drew Lyon, we’ll see you next time.

The views, thoughts, and opinions expressed by guests of this podcast are their own and does not imply Washington State University’s endorsement.

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