Impacts of Seed Size and Rates on Spring Wheat Performance with Dr. Clark Neely

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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.

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My guest today is Dr. Clark Neely. Clark is an extension agronomist and the lead for the WSU Extension Cereal Variety Testing program based in Pullman, Washington with the Crop and Soil Sciences Department. He received degrees from Penn State, University of Idaho, and Texas A&M University.

He worked for six years at Texas A&M University as a statewide small grains and cool season oilseed extension specialist before coming to WSU in 2019. His research program is built around the variety testing program, with previous and current projects looking at the impact that wheat varieties have on soil microbial recruitment in the rhizosphere, wheat varietal impacts on subsequent canola production, and differences in early season emergence and vigor among winter wheat varieties.

Clark also teaches the Advanced Cropping Systems course for the department. Hello, Clark.

Dr. Clark Neely: Hi, Drew.

Drew Lyon: So, I understand you’ve been doing some wheat seeding rate and seed size work. What got you interested in the subject?

Dr. Clark Neely: Right. So, I’ve often heard that seed size is important and there’s a fair amount of evidence in the literature to back that up. And it makes sense that larger seed has more energy reserves [to] be more resilient to adverse conditions. People know we often run into that in the Northwest, whether the soil is too cold, too wet, too dry, any number of pests or diseases that could attack the seedling. But there’s really no–very little research that I could find in the Northwest to see exactly what impact that is having, if any, [as well as] how big of an impact it could have and how often it could have [an impact]. So that was kind of my interest. I am an agronomist, I love talking varieties, but occasionally I like to do other things too. So, I was kind of interested to see what kind of impact that was having.

And then also on the seeding rate size, we know seeding rate can make a difference. But again, there’s very little actual documented trials showing, you know, what is the ideal rate that we should be using. So, I felt like that would be a good thing to document. And actually, both for growers and myself, I want to know if our variety trials are actually being planted at the ideal rate. We think we know, and maybe there’s been stuff done in the past, but I couldn’t find it, so I figured I’d take a look.

Drew Lyon: I know when I give talks about integrated weed management, I often talk about one of the tools you can use is plant larger seed because there is research suggesting it gets up out of the ground quicker, has more energy, and higher seeding rates for greater competition. But a lot of that data comes from the Great Plains where, you know, I did some of it. And so, yeah, it’ll be interesting in quite a different environment here in the Pacific Northwest, whether those same rules hold up. I’ve kind of assumed they do, but I don’t have the data to know that they do. So, yeah, good work.

So, what were the objectives of this research?

Dr. Clark Neely: Okay. Well, basically, just in a nutshell, what I just said was we want to determine whether seed size impacts both early season growth and ultimately grain yield of spring wheat, and then also identify the ideal seeding rate for spring wheat under different precipitation zones because we’re expecting that would change based on your environment. I guess to put things in perspective for listeners, the current rates that we do use in our highest rainfall zone, we plant at 980,000 seeds per acre, which is equivalent to 22 seeds per square foot or, depending on your seed size, on average it’s about 75 pounds per acre. Our intermediate zone, we’re planting at 870,000 seeds per acre currently, which is 20 seeds per square foot or roughly 66 pounds per acre. And then in our lowest rainfall zone, we’re planting at 650,000 seeds per acre, which is equivalent to 15 seeds per acre or roughly 50 pounds per acre.

Drew Lyon: So, tell us a little bit about how the trial treatments were set up and how you executed the trial.

Dr. Clark Neely: Sure. So, this all kind of started like a lot of things that I do–there was some extra room in the variety trial, and I’d already asked companies and breeders if they had any more to submit and they didn’t. And we have a certain number of slots where you have to either round up or round down, so rather than just putting a fill, I thought I would make it useful, and so, we put some treatments in.

So, we embedded the seed size treatments into all of our soft white spring variety trials this past year. The seed sizes that we used–the small seed, well, I’ll take a step back. So, we got one big bag of Ryan and we chose Ryan because that’s our number one soft white spring wheat planted in the state and we sifted that seed. So, it all came from the same source and then we sifted it into small, medium, [and] large. The small seed size was approximately 16,200 seeds per pound. The medium was just over 13,000 seeds per pound, and the large seed size was 9,400 seeds pound. So, there’s a pretty big range there.

On the seeding rate size–seeding rate trial–we only did–these were individual trials. They were not embedded into the variety trials. We did those at four sites, one in each precip zone. So, we had a trial at Horse Heaven, Rearden, St. John, and Farmington. We did two varieties. We had Ryan for soft white spring and then we also chose Hale for our hard red spring. And then at each site we had six seeding rates and those range– they were slightly different–at the low rainfall sites, it ranged from 5 to 30 seeds per square foot [and] at our higher rainfall sites, it ranged from 10 to 35 seeds per square foot. To put that in perspective, if you need that converted, that’s anywhere from 218,000 seeds per acre up to 1.5 million seeds per acre or 17 to 116 pounds per acre on average.

And so, the data we collected, we did go back and we took stand counts and we used an app called Canopeo, where it’s estimating canopy cover. So hopefully [that’ll] answer some of your questions about weed competition there. So, we took that and then in addition to that, we just took our normal measurements that we do for variety testing–so we have yield, test weight, protein, head date, plant height. Yeah.

Drew Lyon: So, what did you find?

Dr. Clark Neely: So, we found that there [were] differences. I was most, I guess, not necessarily surprised that we saw differences; I was more surprised at just how consistent they were. Basically, everything that we measured, I guess I was surprised that we were seeing small but significant differences in like plant height and heading date. We saw consistent differences in yield. I figured we see differences early in the season; I didn’t know if that would translate into yield or not, but it did.

The only things we didn’t see differences in were test weight, protein, and grain moisture at the end, at least for the seed size. There was only one interaction–when I say interaction, that’s just fancy talk for it depended on where you were. For the canopy cover, there were some sites that were significantly different [and] some sites it didn’t make a big difference.

So, in general, I said we saw differences. What were those differences?

So, interestingly we didn’t see really any difference between the medium and the small seed, but where we did see a difference is going from the medium to the large seed. That one was almost always higher.

So, on the yield size that translated into about a 13% bump in yield. We did see increases in stand count and canopy cover, on average. We increased stand by about 17% and canopy cover actually increased roughly 49%. So, pretty substantial differences there. And then on the plant height, we increased plant height by about one inch and shortened our heading date by about a day. So, that was pretty interesting. That was on the seed size.

I should mention, I’ll just briefly mention that the main focus here is the work I did this past year on spring wheat, but we also have done a little bit and are continuing to do work on winter wheat as well. In fact, our first treatments were with LCS Shine, which actually prompted me to continue doing this work with spring wheat, and with the LCS Shine from small to medium seed, which were the only two treatments we had, we saw about a six bushel per acre advantage in our low rainfall sites. I found that really interesting. We’re continuing to do some of that work, too.

So, on the seeding rates side, I was also really pleased with how those results turned out, namely just how consistent we saw results across the rainfall zones. I used a polynomial trend line, which is basically just an arc, and I had really high R-squared value, which is basically telling you how close to the data points were to the trend line. So, there wasn’t a lot of deviation off the trend line, which I thought was really good. Most of the time those R-squared values were over .9, which is really, really good.

As you would expect, location did impact yield, the seeding rate impacted yield, and also there were differences in variety. So, yield potential between the varieties differentiated as well. And we had a pretty good spread in yield potential. I’m hoping to repeat this again to get an even wider spread.

So, our low yielding environment, which was Horse Heaven, actually yielded 28 bushels, which exceeded our average. I would actually like to see some lower yields to get the lower end of the spectrum there. Farmington should have been our highest yielding one, but like I mentioned earlier, that site had to be replanted and our yield potential was way down. So, St. John ended up actually being our highest yielding site and it topped out at about 70 bushels. So, that was kind of the range of yields that we had.

Ryan outyielded Hale in every case. I thought it was interesting, there were some interactions there where Hale–it did respond to the seeding rate, but it was more of a flatter line. It didn’t respond as much as Ryan did to higher seeding rates, I’ll put it that way. And there was in almost all cases, there was a peak at which the yields started to decline if you started to push rates too high.

So, let’s see, what were some of the specifics here? So, what I ended up and did to kind of distill down all the data that I had, I would take the highest yielding point from each variety at each location and then I plotted that on a graph, and I used that as my yield potential for that site because I want to know what seeding rate is going to maximize yield.

So, I took the rate that maximized yield at each location and I plotted that on a graph and got a pretty nice–it wasn’t perfect, but I was actually pretty happy with the relationship that I saw, and it basically was a positive relationship. So, as you went from lower environment yielding potential to higher yielding potential, there was a linear trend that higher rates increased yield potential.

And to put that in perspective, I just kind of took the low and the high end. So, if your yield potential is about 30 bushels per acre, the ideal seeding rate based on our trials was about 20 seeds per square foot. At the higher end with about 70 bushels, actually, the ideal rate was about 30 seeds per square foot.

So, what does that mean for me? It basically was telling me that we could actually be bumping up our seeding rates that we’re currently using. Like I said earlier, [in] our low rainfall [zone], we’re currently using about 15 seeds per square foot, but I think we might benefit from bumping that up. And also, the same is true for the high rainfall [zone]. The only site that looked like we were kind of right on was our like 12- to 16-inch zone. It looked like that 20 seeds per square foot was about the ideal rate that we were seeing.

I did want to mention we’ve also done some work with seeding rates in our irrigated sites–that was actually at the request of our cooperators out there. It was hard to distill that down into any consistent findings. We only have three site years and we did that in 2022 at Moses Lake. We didn’t get any data from Pasco that year, and in 2023 we did it at both Moses Lake and Pasco. In 2022, we actually saw a pretty good response–so higher rates, increased yield. But actually this past year there was not a clear trend. There was a trend from like 10 to 15 seeds per square foot [where] there is a pretty consistent bump across varieties, but then after that, it wasn’t really obvious that you were getting a big bump past that. So, I think we need more data to say with certainty whether we need to change our rates out there or not.

Drew Lyon: Okay. And you said you’re doing this work in some winter wheat as well. Do you think you might see something different in winter wheat? I’m thinking winter wheat tends to tiller more than spring wheat and therefore maybe it has more ability compensate for differences in seeding rates. But I don’t know, I’m just guessing.

Dr. Clark Neely: Yeah, well, I’ve done some work on that as well, and there is an article I wrote up for Wheat Life that came out this past summer. That kind of that looked at data that both I did and then also a lot of that data came from Aaron Esser when he was running the program. He did some work with soft white winter wheat.

Interestingly, I think both Aaron and I, when we started our trials, we were thinking what you were thinking, “maybe we can get away with lower rates because we know winter wheat tillers really well.” His data actually did not show that. It was pretty consistent across two years that higher rates–at least higher rates than what we currently expect–improve yield.

I did not go back and review that data to be able to tell you what that rate was, but it was higher than what we expected. My data, I incorporated some seeding rates into the hard red winter wheat variety trials back in 2021 or 2022–I can’t remember now, I think it’s 2022—[and] we didn’t have quite the same response as Aaron did. I want to say we saw a consistent bump from, I want to say like 500,000 seeds per acre to like 750[,000], we saw a big bump or consistent bump, and then after that it kind of leveled off and we didn’t see much advantage.

Drew Lyon: But at least it sounds like my recommendation from a weed control standpoint to use large seed and plant at higher rates isn’t going to get anybody in trouble and should help with weed control as well. So, that’s good news.

So, what are some of the next steps for this research?

Dr. Clark Neely: Right. So, I do plan to repeat the seed size treatments to get another year, just that more data is always better. So, hopefully that will confirm my findings rather than muddy the waters, but you never know that’s why you repeat things across years. So, [I] plan to repeat that, hopefully get a larger range so hopefully we can get a higher end and a lower end to see if that trend line stays true or if things start to level off on one end or the other.

I’ve mentioned I do have a trial underway with winter wheat where we’re attempting to answer whether growers can adjust seeding rates to compensate for smaller seed size and eliminate the yield gap. So, the data right now the trials are running is basically just telling you, is there a difference. Now I’m kind of moving on to, well, if there is a difference, how can we compensate for that?

So, the trial I have has, I think, three seed size and three seeding rates. I think we also have at least two varieties in there too. So hopefully that will answer whether, you know, okay, you have smaller seed size, which there’s not much you can do about, but maybe if you know you can bump it up by 20% seeds per square foot, you can get the same yield as  larger seed at a lower rate. So, that’s kind of the point of that. And that trial is going in at Douglas, Ritzville, and Creston sites.

I do have–I think I mentioned this already–I do have some LCS Shine seed size treatments in the trials again this year. Previously I did that at our low rainfall sites. This year it’s going to be at our high rainfall sites.

And then I need to do some more stats–so, I have all this data–we started taking stand counts on just a couple of our trials, our variety trials, like the whole trial–not these side trials–to see if seed size, if there’s a trend there, regardless of genetics. I did a little bit of that kind of just a crude look at it last year and the answer was yes, regardless of–obviously genetics plays a huge role, but beyond the genetics, there was still a relationship as larger seed tended to have better stand counts. But what I haven’t done is look at the yield yet. So, I want to look–since we have all that data because we automatically take that on all of our entries for the variety trials. So, I’d like to pair that up and look and see if we can find a relationship.

Drew Lyon: So, interesting work, Clark. I wonder, is there a place growers can go look at or find this data as it’s generated over the next year or two?

Dr. Clark Neely: Right. So, all the variety trial data, as most listeners know, is already on the variety testing website at the Small Grains Extension website. I currently actually do not have a website designated for kind of these side treatment-side trials. I have spoken with our website manager Jenna about creating one, so there will be one made in the future where this will be available whenever they want. Until then, I’ve been trying to push a lot of this data out on my listserv, so most of these findings have been distributed on that. And then like I said, I wrote a Wheat Life article this past summer on some of the seeding rate stuff.

Drew Lyon: Okay, so listeners could go to the variety testing pages on the Small Grains website at some point to see this data or to sign up for the listserv.

Dr. Clark Neely: Yes. And if you want added to that, just email me and say you want on my prelim data listserv and I’ll do that.

Drew Lyon: Okay. And they they’d email you at?

Dr. Clark Neely:

Drew Lyon: All right. Thanks, Clark, this is interesting information to me because it actually has weed science ramifications. So, I’ll be interested in watching what you learn over the next year or two myself.

Dr. Clark Neely: Okay. Thanks, Drew.


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 [X] @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.