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Decomposition Rates & Soil Conservation with Nathan Nielsen

Posted by Blythe Howell | July 16, 2018

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Episode Transcription:

[ Music ]

Drew Lyon: Hello, and 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. We have weekly discussions 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 podcasting app. And leave us a review while you’re there so others can find the show too.

[ Music ]

Drew Lyon: My guest today is Nathan Nielsen. Nathan is a second-year master’s student at WSU in the Department of Crop and Soil Science, working under the WSU Winter Wheat Breeder Doctor Arron Carter. He has a passion for agriculture as he grew up working on Pace-Nielsen Farms, a third-generation family farm, located in Parma, Idaho and graduated with a bachelor’s degree in Agronomy from BYU-Idaho shortly before coming to Pullman to start his graduate studies. His research is focused on developing tools that can aid in predicting decomposition rates of winter wheat straw. Hello Nathan.

Nathan Nielsen: Hi Drew.

Drew Lyon: So, tell us a little bit about these tools and how you’re determining the decomposition rates of winter wheat varieties.

Nathan Nielsen: Great, so, when I say these tools that we’re working on, that really involves two separate parts. We’re working basically two tools. And so, the first one is a genome-wide association study. We’re using the molecular markers that we already know in winter wheat and we’re using those to try to find associations with different characteristics that are also associated with decomposition of winter wheat straw. And so, I’ll explain here in a second a little bit about what those characteristics are. The second part is we’re using what’s called near-infrared spectroscopy to develop a prediction model that will also us to quickly predict how certain varieties will decompose and basically bypassing the current process for doing that, which I’ll explain here for you.

Drew Lyon: Ok.

Nathan Nielsen: So, decomposition it’s a little bit tricky because there’s so much behind it, you know so many different parts playing a role, but what we’re looking at in the lab is we’re, we’ve taken a huge number of varieties, actually 480 different varieties from the Pacific Northwest, and we grew them out over three locations last year, a couple locations the previous year and so we’re combining all of that data. And what we do with those varieties is through just a wet chemistry process and a dry combustion process as well, we’re finding the hemicellulose, cellulose, acid detergent lignin, carbon and nitrogen, because those are all big factors playing into the role of how a certain variety will decompose depending on, you know, different quantities of those. And so, with the near-infrared spectroscopy portion of the project, really what it does is we take a sample of winter wheat, we scan near-infrared light through it and what that does is, it gives us a spectrum and when I say a spectrum, if you’re just looking at a computer monitor after it’s been scanned, it’s setup with our software, then it’s just a squiggly line kind of, it has a lot of peaks and a lot of dips and those all correspond with different organic functional groups and they vary based upon vibrations within the molecular bonds and such. But, we take those spectrum and then we also input all the data that we’ve collected. The actual data from the wet chemistry and those are all connected to the different spectra. You know, so basically, each variety has an actual value that we derived through the wet chemistry process and then it has a spectrum from the near-infrared spectroscopy. And so, what we’re able to do once we’ve done that with all of are varieties and we have a large lump of data, is develop a prediction model so that in the future all we have to do is scan a certain variety through the near-infrared spectroscopy and it will give us a prediction about how much lignin, how much cellulose, how much carbon, is in that variety and basically bypassing the whole chemistry process, which is quite time consuming and expensive. And so that’s the purpose.

Drew Lyon: Ok. And do you correlate these data obtained in the lab with what you see out in the field? Is there a step there where you find out, Ok, lab tells me this should last a long time. Are we seeing that occurring in the field?

Nathan Nielsen: So, for that stage we’re really basing this upon some previous research that was conducted by Tammy Stubbs and some of her associates. She was really the one that kind of got all this started, this whole project that I’m working on. And so, we’re using some data and some results that she has already published where she did some lab incubation studies, actually measuring decomposition for certain varieties. You know, so, doing all the dirty work I guess you’d say as far as actually burying samples, pulling them out, cleaning them off, weighting them, to see how much has actually decomposed to get a rate. And then she associated those with different quantities of lignin, hemicellulose, cellulose, carbon and nitrogen, and so we’re really basing this upon that study that she did with our values.

Drew Lyon: Ok, so you’re building on previous research, developing those tools and the whole wheat breeding game seems to be about being able to choose varieties quickly and these tools will help you focus in on that more quickly than if you had to go out and actually measure things decomposing in the field I suppose.

Nathan Nielsen: Exactly. And we keep in mind that these are predictions coming from the near-infrared, but because we’ve used so many data points that we’re collecting, and this is based upon previous research, there’s been a lot of research in this area, and so it’s something that we are expecting to be able to rely upon in the future.

Drew Lyon: Ok, tell us a little bit about how you see this work affecting farmers in the region?

Nathan Nielsen: Great. So, you know how here in the Eastern half of the state, the precipitation is quite variable really.

Drew Lyon: To say the least.

[ Laughter ]

Nathan Nielsen: And so, here in the higher precipitation zone, such as Pullman, where we’re at, the farmers, you know, that practice some form of tillage, whether it’s conservation tillage or full on plowing or tilling, we’re hoping to be able to facilitate their transition to a no-till system to better conserve soil quality. I mean that, really the big idea behind this entire project, is soil conservation. You know, decreasing erosion by allowing farmers to leave their straw on top of the soil. And so, the picture that we have in our minds as far as how this might all play out effecting the farmers, is we’ll be able to provide them with decomposition rates of each variety that’s available to commercially grow, they’ll be able to select the ones that they want to grow, that, for this I’ll say for this region for high rainfall, we want them to decompose quickly. And the reason behind that is so that farmers will be able to harvest, leave their straw on top of the soil so that it can, you know, keep the soil in content, you know, minimize erosion. And then really from there it would decompose quickly so by the time spring comes around they can just, you know, plant and avoid the difficulties of having tons of straw on top of the soil.

Drew Lyon: Ok.

Nathan Nielsen: And, you know, when you’re looking at the lower rainfall areas, it’s actually kind of just the opposite really. You know, where they’ve got the summer fallow as a big part of their crop rotations, you know, that’s leaving your soils barren, you know, wind erosion is a big issue out there and so if you have varieties that are decomposing slowly we hope that they’d be able to decompose slowly enough to remain on with their, in the soil, on top of the soil and such long enough to prevent or at least minimize erosion. And so that’s what this is all about and.

Drew Lyon: So, trying to measure that and even breed for different characteristics?

Nathan Nielsen: Exactly.

Drew Lyon: Ok. And you’re right, the people here in the high rainfall area would like to see that residue disappear quickly, because they produce a lot of it and they plant right away. And people out West where the yields aren’t quite so high, they don’t want that residue to be durable and hang around. That’s very interesting. And you foresee, say, the wheat variety selection tool, you can go in there and pick varieties that yield the best and have disease resistance to foot rot, or snow mold and this would just be another column of data where you’d rate it on some kind of scale 1 to 10. 1 is being more durable, 10 being less or something like that? People can go in and select varieties based on that characteristic, what’s important to them.

Nathan Nielsen: Exactly.

Drew Lyon: Interesting.

Nathan Nielsen: We’re just hoping to, information we provide to farmers.

Drew Lyon: Once breeders have these tools that you’re working on, what are some of the challenges you foresee in them using these tools?

Nathan Nielsen: Well, the first thing that comes to mind as far as being a challenge with this, you know, we’re assuming that this will all work out, that the genome-wide association study will provide us with molecular markers that will be helpful, and also through the infrared spectroscopy we’ll get rapid estimations. Assuming that all works out the way we hope it will, I think probably one of the biggest challenges is that when those are applied within a breeding program, to make selections for decomposition rates, it’s almost as if breeders in this region, I mean I specifically think of Dr. Carter, because of the winter wheat here, there’s a specific challenge ahead because it’s almost as if he’s going to be breeding against what is already present. And I’ll explain by that, what’s on my mind, is that through previous research, some things I’ve been studying and things that I’ve been seeing with my data already, is that the varieties that are being grown here in Pullman and the higher rainfall region, are naturally adapted to lodging resistance, which also, those same characteristics I mentioned earlier, the lignin, the cellulose, carbon, nitrogen, those all play a role in that. And so, if you’re breeding for slow, excuse me, if you’re breeding for quick decomposition, you’d want those values to be a little bit lower.

Drew Lyon: Right.

Nathan Nielsen: But then, you might have an issue of lodging and so I see that as being a potential challenge. And within breeding, you’re always trying to find a balance. Breeding for the perfect ideal crop is a challenge. And so, finding that balance is going to be one of the biggest.

Drew Lyon: That’s a challenge in many parts of life, including wheat breeding it sounds like. So, where are you at in your research and when do you expect to have some of these tools available?

Nathan Nielsen: So, I’m still, I’m right now working in the lab. I’m finding all those values and by the end of the summer I’m going to be getting all of my near-infrared scans done and so I’m still in the data collection process. But like I said, this model that we’re hoping to put together is building upon previous research by Tammy Stubbs, and also another, another graduate student, Alex Roa, who’s been doing similar research with the decomposition. And so, we’re in that stage right now as far finishing up the data collection, compiling it to make our prediction model. And so, I’m hoping to be all done with my master’s degree next spring.

Drew Lyon: Ok.

Nathan Nielsen: And that’s when I’m hoping also to be publishing this data.

Drew Lyon: Ok. And that’s when maybe the breeders will start to work this into their program a little more, maybe a few years after that, we might see it in some of our brochures that Extension puts out on wheat varieties.

Nathan Nielsen: Right. And in fact, if it all works out the way we’re looking at, if it works out the way it should, then we might actually have some data in next year’s brochures for farmers to see at field days and such.

Drew Lyon: Ok. Excellent. We look forward to seeing that. Thank you very much Nathan.

Nathan Nielsen: No problem. Thanks Drew.

[ Music ]

Drew Lyon: Thanks for joining us and listening to the WSU Wheat Beat Podcast. If you like what you hear, you can subscribe on iTunes or your favorite podcasting app so you never miss an episode. And leave us a review while you’re there. If you have questions for us that you’d like to hear addressed on future episodes, please email me at You can find us online at You can also reach out on Facebook and Twitter @WSUSmallGrains. The WSU Wheat Beat Podcast is a production of CAHNRS communications in the College of Agricultural, Human, and Natural Resource Sciences at Washington State University. I’m Drew Lyon. We’ll see you next week.

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