Thursday, June 24, 2021  •  Episode 38

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Measuring nitrogen, particularly plant available forms of nitrogen, in the soil in near real-time is a critical missing link furthering nitrogen management in agricultural production systems. Dr. Jonathan Claussen, Associate Professor in the Department of Mechanical Engineering at Iowa State University, joins us for this episode to discuss measuring nitrogen in the soil. His research team has been working in collaboration with a research team at the University of Florida to develop and test soil nitrogen sensors. The sensors they have developed rely on an ion-selective membrane and communicate via telemetry. In this episode, we discuss ion selective membrane technology, the challenges of sensing nitrogen in the soil environment, and what is necessary to translate and commercialize technologies that have been developed for biomedical applications (e.g. ion-selective membranes) for agriculture. This episode concludes the "Nitrogen Management Technologies" series. Next up: Precision Crop Protection.

Opinions expressed on FarmBits are solely those of the guest(s) or host(s) and not the University of Nebraska-Lincoln.

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guest Jonathan Claussen
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Jackson: Welcome to the FarmBits podcast, a product of Nebraska Extension Digital Agriculture, I'm Jackson Stansell.

Sam: And I'm Samantha Teten, and we come to you each week to discuss the trends, the realities, and the value of digital agriculture.

Jackson: Through interviews and panels with experts, producers and innovators from all sectors of digital technology, we hope that you step away from each episode with new practical knowledge of digital agriculture technology.

Jackson: Hello and welcome to the 38th episode of the FarmBits podcast. As you may notice if you're watching the video, or if you're just on audio you may be missing Samantha's voice. For the first time, I'll be hosting a FarmBits episode solo. As you may have heard if you listened to our last episode here on the FarmBits podcast, Samantha has completed her master's degree and has started a position as a developmental agronomist with Golden Harvest. Samantha made a significant impact on many people during her graduate program and she will certainly be missed on our team, and I know that I'm missing co-hosting with her for this episode, and I will in the future for all of our future episodes as well. But, we're very excited to see what she does next and we look forward to having her on the podcast in the future or just hearing more from her and obviously staying connected. So, if you'd like to stay connected with her as well make sure you follow her on Twitter. This episode marks the conclusion of our nitrogen management series and the focus of this episode is measuring nitrogen in the soil. I'm pleased to welcome Dr. Jonathan Claussen as our guest for this episode. Dr. Claussen is an assistant professor in the mechanical engineering department at Iowa State University. His research focuses on nanotechnology and sensor development with a multi-disciplinary focus that includes both biomedical and environmental applications. To date there have been very few if any robust soil nitrogen measurement sensors that have made it to the market and we wanted to get Dr. Claussen's perspective on what makes nitrogen so hard to measure in the soil and his insight from his lab groups innovation and their work on developing a sensor to overcome these challenges. So, without further ado, let's get to it here's my interview with Dr. Jonathan Claussen.

Jon: I did my undergraduate degree at the University of Minnesota in mechanical engineering and then I went on to Purdue university to do my graduate education, and there I was always interested in trying to learn more about nanotechnology and apply that to biological types of sensors. I was really interested in biomedical diagnostics to begin with but then it kind of brought into the environmental sensors and some of the sensors we'll talk about today, but I did my master's in mechanical engineering in engineering at Purdue and then my Ph.D in biological engineering to gain a little more insight into the biological devices and biology in general, and then I went on to do a postdoc at the University of California San Diego in their nanotechnology department and then after that I went ahead and did a postdoc to the us naval research lab in Washington, D.C. on more about nano sensors in biology and then in 2014, I ended up in Iowa State University as an assistant professor.

Jack: Awesome, so I guess you you do a lot of different types of research you mentioned biological and kind of the biomedical side of engineering and you mentioned the environmental side how exactly is that breakdown right now in terms of your recent research since you've become an assistant professor at Iowa State?

Jon: Yeah, I definitely have gotten a lot more into the environmental sensing. I guess it kind of makes sense since Iowa is more of an agricultural based state in terms of its workforce and so forth, but yeah so we do have some biomedical sensors. We're doing some wearable sensing to look at hydration and fatigue levels in sweat but then the majority of that beyond that is kind of environmental sensing. So, we have a USDA NIFA grant to look at a nutrient sensing in or pesticide sensing in the environment and crops and so forth than NIFA grant to look at nutrient ions sensing in soils and also grants we look at salmonella in foodborne pathogens, foodborne pathogens and food products and also looking at cattle disease biomarkers for yoni's disease. So, yeah we've really kind of from farm animals to crops, food safety. It's really evolved a lot around agricultural products sensors.

Jackson: Absolutely yeah, it seems like you're really diving into the food system quite a bit, and I guess I saw an article and Samantha- you know my former co-host as well she saw an article that suggested she'd been working on this you know nutrient sensor for the soil specifically for nitrogen and nitrogen is kind of the focus of the series that we're in now. So, why exactly did you decide that you wanted to begin working on measuring nitrogen, the soil profile and how did that collaboration you know come about that collaborative research venture?

Jon: Yeah absolutely, it was you know it's a huge issue and it's for and Iowa, southern Minnesota and Illinois really are three of the largest nutrient runoff producers if you have from their farms into the Mississippi watershed. So, it's you know we hear about it often in the news, and I have worked on ion-selective sensors before. Some of our wearable sensors are detecting potassium chloride and sodium in sweat, and it seemed to us that you know we could use similar technology to detect nitrite nitrate and ammonium and potentially phosphorus in soils as well, and they worked really well. You know our initial lab results, we're so impressed that because they were working better than some of the commercial sensors that we could buy, and they're holding up longer and a lot of the commercial sensors are geared for working in water and kind of in a steam environment. So, we realized that more engineering had to be done to make them more robust actually work in the soil environment or soil slurries.

Jack: So, was that the really the overarching goal of the project was to specifically develop that sensor and then also offer some kind of robust testing or was it just laboratory testing did you get in the field I guess what was kind of the scope of the project?

Jon: Yeah absolutely, so it's ongoing. We have tested it in the laboratory in various soil slurries that would mimic the you know the water content that you would find in the field and this and we're a little bit delayed because of last year the pandemic. But, this spring as you can imagine. But, this spring we're putting out sciences into two watersheds in Iowa so that would be in water and then also we're going to we have a housing to actually put it in a soil probe and bury it at depth in some farm fields, as well. So, we both want to monitor in kind of a completely aqueous water environment as well as soil and in farm fields.

Jack: And I imagine that's kind of to capture both the the runoff side of nitrogen as well as some of the leaching and nitrogen content for whoever's trying to manage nitrogen on that field is that correct?

Jon: Yep, exactly the leaching and runoff but it also can help the farmer you know how much nitrogen is in that field and now they have more and more equipment where they can deliver that fertilizer throughout the growing season even to corn and soybeans and other crops. So, this could be a way that they could gauge how much is there and you know a third of their costs are roughly the fertilizer inputs, so if they can use less you know fertilizer and maintain their crop yields that's a win-win for the farmer and for the environment.

Jack: So, I guess getting into the sensor a little bit more and specifically measuring nitrogen, these ions that you mentioned earlier what exactly is it that makes nitrogen so hard to measure in general and as you mentioned I guess it's a little bit easier maybe in aqueous solutions and some of the commercial products don't necessarily do all that well, and so what makes it really hard about measuring nitrogen in the soil specifically for these sensors?

Jon: Yeah, exactly so in the soil all that particulate matter can foul or biofoul your sensor and kind of within time prevent those ions from actually reaching your sensor and making a reading. So, that's why in general it's more difficult than in water. The iron selective membranes we work with too do well when they're wet and they stay wet, but if they dry out and re-wet and then dry out that's really that cyclical pattern of wetting it and drying. It can really degrade that sensor quickly and you can kind of almost have to sometimes recalibrate it if it's been dry for too long, so those are some issues that may occur in a soil environment versus you know the water.

Jack: Absolutely so, what exactly does the sensor device look like right now that your team is as engineered and how is it kind of meeting some of those constraints?

Jon: Yep so, the sensors themselves are pretty small you know they're the working part of that sensor is anywhere between three and five millimeters in diameter, and we have it next to a reference electrode that's about the same size. So, we could have you can imagine those little circular patterns on a single test platform device can be made for one could be sensitive ammonium, one could be sensitive to nitrite, one can be sensing nitrite and so forth. And so it is a small package, but what the hardware around it though is what is the bulk of it. So, we need to to interface it with these polymer plastics that we use to package it and make a watertight seal around it so that the electrical connections can be made on the back end and it can stay in the water, soil and not you know and not have that water reach those electrical connections. And then we have to have battery technology and then some sort of telemetry to you know, sometimes we will can transmit that data wirelessly to you know essential server and pick up that data or what have you. So, it works very similarly something like a watermark or maybe a you know some sort of capacitance probe for soil moisture that you would see out there commercially in the field. It looks very much like this capacitor and soil moisture probes.

Jack: Yep, got you, so really a lot of the advances in the technology are centered around kind of this selective membrane that you are putting out there to select for these particular ions, so what exactly makes developing that membrane so challenging and I guess what have been some of the innovative steps that you all have taken to you know make these membranes and truly be able to select for nitrate ammonium nitrate and those sorts of ions?

Jon: Yeah exactly yeah, there's a lot of different issues that go on in making those constituents. You need to have you know it's a hydrophobic membrane that needs to allow the ions to pass through it. So, it's kind of this porous network and then you have ionophores that help shadow those ions across that hydrophobic membrane to the sensor itself too. So that a potential difference can be measured between that sensor and that reference electrode and just the having the right mix of constituents to make sure that it's selective towards that ion of interest and that other ions don't pass through that hydrophobic porous matrix. That's probably the one of the biggest challenges and to you know and if you do that correctly and do that right and prevent particular matter from kind of getting in there too. Sometimes, we have protective coating layers on top of it then the soil can be stable and can really last for you know weeks and up to months at a time. But, if you have your membrane degrading in any way and other ions of interest can get in there or the dirt or other particles get in there the sensor can quickly degrade and foul and not operate properly anymore.

Jack: Sure, and so you say you know weeks to months and so in terms of your your testing, I'm very interested in hearing some of these test results that you've had both in terms of performance of the sensor for getting kind of the concentrations of these different nutrients right there in the soil or even in the you know in an aqueous solution and also how is the robustness of the sensor performed in terms of its longevity there in a soil environment maybe versus a water environment?

Jon: Yep, so we still gotta push further on the soil test, but in the water so far we've gotten it to work up to three months continuously just dipped into the water itself and that's been in the laboratory setting, but we don't see that it should change too much when you'd actually put it in a stream of water. I think that your concern is just with the wetting and drying that may occur in the soil environment. So, we'll have to see how that's the big question once we get to the front. We've tested you know a wide variety of different saturation water saturation levels for soils to try to get a feel for that, but we still you know there's nothing like actually getting into the field and testing them and that would really tell us.

Jack: I think I read in one of the articles that this is kind of a collaborative project with the University of Florida or at least at one point there was some collaboration with the University of Florida is there going to be an opportunity to kind of measure this in a lot of different environments because the soil types are very different you know in a lot of places in Iowa versus what they are in Florida and you know as you go internationally, I mean it's you know it's a totally different ball game as well so.

Jon: Exactly, and Florida is on kind of helping us make the telemetry and the wireless electronics needed to make remote measurements in the soil and yeah and that is part of the grant is to test them in a wide variety of soils right here in the Midwest but also in Florida where you know it's more sandy or more clay concentrations than maybe here. So, that potentially we could get an idea of maybe different membranes have to be constructed for those different soil types, and that might be the next step in the research.

Jack: Sure, that'll be really interesting because just thinking about you know how clay soils you know dry out versus how other you know sandier soils dry out and how big of a change those wet versus dry extremes can have in the soil. I think that'll be a really interesting test to see how much those membranes really fatigue and so in the lab I you know just thinking about kind of the correlation and you talked about some of the commercial sensors out there that this sensor is actually performing better than some of those that are available. How well really has this sensor measured nitrate in these solutions there in the lab?

Jon: Yeah, been really good so you know a lot of these other sensors are liquid junction sensors they have a polymer, so it's a liquid junction sensor, so it has an electrolyte solution so ours is a little bit different. So, we don't have to like regenerate an electrolyte solution like you would with those liquid junction ones that commercial ones are operating on, and you know the solid contact electrodes that we use can be more finicky in that it you know it might not be harder to calibrate them. But, we you know we think we've come up with some methods to overcome those problems but yeah. So, since they're so simplistic and you don't need that regeneration electrolyte that means they can just sit in that solution or in that soil and run continuously for very long periods of time. So, that you know gives us promise or a reason to keep pushing this and keep working on it if we can overcome some of those problems with them they could potentially be really long-lasting ion selective sensors.

Jack: I guess thinking about this practically you know is that calibration issue is that something that you would encounter only during say the manufacturer or the lab side of these sensors, or is that something that you would have to do when you went out to the field to calibrate them you know in some sort of solution and then put them kind of in the ground to continue sensing for the rest of the year?

Jon: Yeah, that's a good question you know we might want to do like a three-point calibration with them and give the person who uses them sample solutions to calibrate them right here right before they use them the first time. If you think about a Ph probe in a chemistry lab, usually some sort of three point calibration with known Ph solutions or solutions with non-Ph, so it may be something like that. It may be you know some sort of mixture that we have to add to the sensors as we you know put them into the ground for the first time to help make that calibration. So, those are things that we'll probably have to work on and figure out.

Jack: Sure yeah, I mean it kind of you know with yield monitors even I think about the fact that we try to get like a two or three-point calibration you know for the yield monitor to make sure that the grain flow is being measured accurately at different speeds in the fields and different amounts of grain. So, it's definitely something that's you know you really can't get around when you have some sort of sensor that's measuring anything in a field or a laboratory. Thinking forward what would be necessary you know we've talked about that you really need to protect this membrane. What do you think is the most efficacious solution that maybe available out there and necessary to kind of push these membrane-based sensors to a commercial level and maybe be a practical solution in the future for farmers?

Jon: There might be some filter technology that might help filter out particular particles for reaching sensitive components within the sensor that needs to be explored as well, but the polymers that we're using and then I think many are using our you know pretty advanced. And I think we're getting to a point where these materials will hold up for weeks and months and the critical months that would be important for in a farm field, so I'm hopeful that you know we could get them to last the entire growing season or the time during the growing season once it's needed. And then perhaps those membrane cartridges can be replaced and electronics in the housing and so forth can be reused of course.

Jack: We were talking about you know basically the sensor would have to cost pennies right to measure every single head of lettuce that's going through kind of a food processing facility. In your experience going from and maybe just in your observations right of the industry going from a biomedical application where you can't afford to have more expensive sensors and getting to a low-cost sensor for agriculture, what are some of the necessary steps that have to happen for a technology in order to kind of bridge that gap because I imagine it's pretty substantial, and I don't know if it's really more technical or more manufacturing or what really has to happen, but I'd be very curious to get your thoughts.

Jon: Yeah, I think both you know in the fabrication standpoint it needs to be something that can be scalable, so you know printing technologies, things that can work in roller manufacturing and that would be the only way that you can really make it that cheaper sensor. So, you know completely automation all the way to fabricating the electrical components of the sensor. You know, down to functionalizing it with the chemicals and biologicals needed to make it selective, to whatever you're trying to detect. So, all that automation and fabrication but then if you know if you look at okay that's how you need to fabricate it hat cost effectively then researchers need to look at well you know since we've been doing it so differently or you know where we could manually pipette things onto to a sensor or maybe we're using silicon chips that are using clean room technology that the same type of technology that goes into computer chip just really wouldn't be cost-effective for these mass-produced sensors. So, is there other fabrication needs that we can do and then you have to then research ways to figure out well how can we still retain a high sensitivity and selectivity for the pathogens or what or other analytes that you're trying to detect by using these other fabrication techniques. So, they kind of go both in hand in order to push for agricultural space, so it's definitely you know we can pull things from biomedical but we have to do more research to figure out how to make it work in the agriculture environment.

Jack: That's super interesting, and I think it's interesting that you brought up automation again because it seems like in most cases right now that automation piece is really what is the next step to a scalable solution. In a lot of ways, I mean if you think about digital lag and trying to implement precision maps, I mean automation is kind of the next step to making sure that more people can do it effectively, and it sounds like even on the fabrication side and scaling biomedical technologies that automation is really kind of the secret sauce there as well. I guess another thing I'm kind of interested in is you know, you're in kind of a  different field right than agriculture but you're still working on a lot of these agricultural problems. Is that something that you aim to continue to do in your lab with this environmental focus and what do you think are the advantages to coming at an agricultural problem from a different discipline?

Jon: Yeah, I think it's really helped me actually, and I do want to keep this kind of multi-disciplinary approach to the lab because a lot of the things that we've developed with the wearable ion selective sensing for example, making it flexible form-fitting to the body, making it robust and last long can be used in those agricultural types of sensors and a lot of times some of the technology, sensor technology has been kind of pushed first in the biomedical space just because the funding is largely there and in your ability to you know the cost basis for this can be much greater because when you're dealing with the human health, human body. You know, products can cost quite a bit and people are okay with that but then agricultural space you know you can imagine you know having a foodborne pathogen to texture sensor, well if you're you know what are you gonna test are you gonna test the rinse water, are you gonna try to test every single head of lettuce that's going through? Well, that sensor has to cost pennies virtually, so you know we've developed and come a long way in the biomedical space, and now I think it's time to hopefully learn how to lower the cost of some of these sensors and bring it into the agricultural space and really push precision agriculture and I think that's kind of in general where the where the field is going.

Jack: That's really cool to hear, and it kind of connects with two other interviews that we've had on the podcast. I think about, we had an interview with with Ryan Raguse from Bushel, and he was talking about how data can be hopefully used to kind of target health solutions right and kind of get people's diets in a way that is pushing for better health. It's literally targeted precision for them and Ranveer Chandra from Microsoft brought that up as well and then I think about Pivot Bio, and he was saying that really he's hoping a lot of these testing procedures that have come out of covid will eventually make their way into kind of the biological space and help us do more rapid testing for different microbes you know in the soil and in other places. So, I think that's a really interesting interface between you know biomedical and the environmental side of sensing, so I guess on that on that front what do you think are some of the other most exciting besides nutrients like some of the exciting potential for biosensors maybe for measuring microbial communities within the soil or something like that?

Jon: Yeah absolutely, that's kind of been a push too you know could we monitor enzymatic activity or you know other parameters in the soil to kind of get the full picture of soil health? You know, we could do moisture temperature Ph levels you know salt different salts concentrations and then maybe an overall microbial health or at least get the picture of that. So, the idea is that you can maximize that soil health so they can maximize crop yields and not kind of have these dead zones in soils where you know things just don't grow anymore because the soil is overworked. ​Yeah, that's definitely something exciting, and I think there's that's exciting.
I think you know there's there's opportunities for carbon sequestration as well, you know could we could we sequester carbon or how much carbon can be squashed through the soils could farmers use that as potential offsets for companies that do emit a lot of emissions. So, you know it's an exciting kind of dynamic things and there's opportunities there for sure .

Jack: Do you think it is possible to actually measure maybe how much carbon is increasing within the soil with a biosensor or some other type of sensor along the lines of the technology that you've already been working with?

Jon: We haven't looked into it yet, but it seems like there may be some promise there to somehow get you know the total you know carbon count so to speak. It would be interesting you know if you know if we could do that, but I think those are things that need to be still further explored.

Jack: So, I guess as we close out this episode, one of the things we always do is we always ask you know what is somebody's final insight or piece of advice and so what I'd like to ask you today is what is some insight that you would like to leave our listeners with regarding like the importance of effective nitrogen management and agriculture and maybe even like working with new sensors and maybe some some piece of advice that you would offer for some of these new technologies that are coming out and becoming available?

Jon: Yeah, I definitely if anyone who's been working in the sensor field who are developing them it's always easy especially with these ions like sensors to get the sensing range and detection you need what's really difficult is selectivity and it seems like all sensitivities are like that. We have a lot of research articles in the literature, and they kind of fall short because they never actually test in the biological medium that they're designed to talk and like do. We test in the laboratory but won't actually be tested in blood or saliva or in case of environmental sensors in soil or water environments. So, really I think selectivity is the challenge and in essence also the the stability and durability because in the biomedical space it was diagnostics this might be one test and you're done. But in the agricultural field you know monitoring for weeks and months at the end is a different ball game. So, new efforts need to be made in terms of longevity for these sensors as well.

Jack: Thank you to Dr. Jonathan Claussen for taking the time to join us today on the FarmBits podcast. In this zoom and work from home world that we live in I appreciate your patience with the audio quality on this particular episode and on other episodes in the past. I hope that you're able to stick with the episode and really listen to Dr. Claussen because he offered many interesting insights during the episode that I think are valuable to anyone who's thinking about nitrogen measurements or monitoring in a soil environment. I thought one of the most interesting aspects of the episode was actually Dr. Claussen's perspective on the crossover between biomedical and environmental sensing you talked about how there's a lot of scalability concerns and also expense concerns that are associated with transferring biomedical technologies to environmental applications such as in agriculture and particularly talking about, for example, you'd really have to make sensors cost pennies to measure every single head of lettuce for some sort of foodborne pathogen in a food processing facility, and so I think his perspective on what it really takes to get those technologies to agriculture was really interesting but also a lot of the crossover and some of the similarities between measuring say potassium or chloride ions that are coming out and sweat and you know on a wearable sensor measuring those. But, also connecting that technology to measuring with ion selectivity in the soil such as, for nitrogen monitoring and measurement, so I think there are a lot of interesting crossovers and this is kind of a theme that's come up in other episodes as well and it's something that we certainly should keep an eye on and maybe delve into a little bit further in future episodes of the FarmBits podcast so if you'd like for us to do that please reach out to us and otherwise we look forward to getting started on our next series in our next episode and we look forward to having you tune in thanks.

Sam: Thank you for taking the time to join us today on the FarmBits podcast, if you enjoyed this episode please subscribe to the podcast on Spotify, Apple Podcast, Youtube or wherever you listen to podcasts to be informed about the latest content each week.

Jack: We welcome your feedback, so if you have comments or questions for us please reach out to us over email, on Twitter or in the review section of your favorite podcast platform our contact information can be found in the show notes.

Sam: We'd like to thank Nebraska extension for their support of this podcast and their commitment to providing high-quality informational material to members of the agricultural community in Nebraska and beyond.

Jack: The opinions expressed by the hosts and guests on this podcast are solely their own and do not reflect reviews of Nebraska extension or the university of Nebraska-Lincoln.

Sam: We look forward to joining us next week on FarmBits. 

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