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LARRY PURCELL University of Arkansas researcher examines a nonnodulating soybean genotype used for research experiments to determine the amount of nitrogen in soybeans that is derived from the soil or from N2 fixation

Mid-South soybean research focusing on high yields, traits, drought avoidance

Crop physiologist Larry Purcell’s research at the University of Arkansas focuses mostly on soybeans.  Means studying “how we can utilize the resources of light, water and nutrients more efficiently through crop management and genetic differences among lines.” Also studying traits, drought-tolerance and irrigation.

Crop physiologist Larry Purcell’s research at the University of Arkansas focuses mostly on soybeans. Lately that means studying “how we can utilize the resources of light, water and nutrients more efficiently through crop management and genetic differences among lines.”

Toward that goal, Purcell and collaborators are working several projects. One concerns maximum yield of soybeans.

“We have on-farm research at Kip Cullers’ operation” in southwest Missouri, he says. Cullers consistently produces huge, award-winning yields.

“We’re measuring crop growth responses under his field conditions, and the response of the crop in terms of seed-growth characteristics and nutrient levels in the plant throughout the season.”

For photos, see here.

Other maximum yield, small plot research is ongoing at the University of Arkansas’ main station in Fayetteville.

“We’re trying to duplicate some of the different treatments Mr. Cullers is using on his farm to see if they pan out for us,” Purcell says. “We’re about 90 miles away from him, so the climate is similar. It’ll be interesting to see if we come up similar responses.

“Along the same lines, we have strip trials on farms at England in central Arkansas and another just south of Helena in extreme eastern Arkansas. We’re trying to implement some of the same maximum yield production practices on large scale fields.”

Just as 2011 was difficult for many producers, it also hasn’t been kind to many researchers’ projects. “This past year was extremely rough,” says Purcell. “I think everyone recognizes that.

“We didn’t get the yield responses at either England or Helena that we had hoped for. However, the yields we got were good. At England, we worked a variety test and the best variety yielded 74 bushels; at Helena, the best yield was 83 bushels per acre.”

While those don’t approach the superb yields Cullers has been producing, “they were still good. We weren’t able to get into the field when we’d have liked; planting was delayed because of the weather.

“Once planted, we had trouble keeping plants out of the water — like everywhere else, we faced a lot of rain. We had a rough time just getting the plants established.”

Regardless, says Purcell, “We’ll be doing the research for at least two more years. A graduate student is working on it. Pioneer is sponsoring the on-farm strip trials at England and Helena, and the Arkansas Soybean Promotion Board is sponsoring the research on Mr. Cullers’ farm and our small plot research efforts.

“I hope, in two years, we’ll speak again and I’ll have a great story to tell.”

Drought tolerance

Purcell is also studying soybean drought tolerance. Sponsored by the United Soybean Board, the project includes researchers in Arkansas, Georgia, North Carolina, Missouri, Nebraska and Minnesota.

“It’s a large, regional project that has been going on for several years,” he says. “The project is led by Tommy Carter with the USDA at Raleigh, N.C.

“We’ve been looking at two main traits. The first involves the differences that we can visually notice in how quickly different soybean genotypes wilt. The second trait involves differences in the sensitivity of nitrogen fixation to drought among soybean genotypes.”

The main focus of the project, says Purcell, “is to get the genetic differences we see — in wild type soybeans and plant introductions and unimproved soybean germplasm — and move those traits into highly adapted, high-yielding varieties. We’ve been able to do that through molecular marker technology, tagging the genes and moving them into more adapted germplasm, and through traditional breeding methods, as well.”

He says “great progress” has been made on both traits. “We have soybean germplasm — related to prolonged nitrogen fixation during drought — that’s been released for breeders to freely use forever. We’ve also had soybean germplasm related to the delayed wilting trait. That’s been in USDA uniform trials, and these lines have outperformed all other germplasm of the same maturity group under drought conditions.”

Under well-watered, high-yielding conditions, “it’s neck-and-neck with other germplasm,” Purcell says. “But when drought has decreased yield to the 30 bushels to 45 bushels per acre range, these genotypes perform very well, having a distinct advantage and providing, usually, a 5 bushel to 9 bushel bump. That’s still very meaningful.”

How might Purcell’s research incorporate the Roundup Ready 1 (RR1) trait that’s becoming available?

“From a breeding perspective, it shouldn’t be a big deal to incorporate the RR1 trait into our germplasm, although this is not something we’ve pursued.

“We’ve taken a bit different approach. That is, we believe the way we can make the biggest impact and get this to the most farmers is by making all this breeding material freely available. That means any public institution or private company can pick it up and make crosses. That’s our philosophy as a group.”

For several years, Purcell has also studied a drought avoidance mechanism. “It incorporates work done by Glenn Bowers, Larry Heatherly, Lanny Ashlock and others on avoiding drought by planting Group 3 and Group 4 soybeans early.

“We’re checking on ratcheting up that practice a bit. We’re looking at planting early-maturing soybeans in the northern portion of the Delta a bit later. Can we still get the same yield bump from drought avoidance or decreased irrigation?”

Purcell and colleagues have looked at “everything from Group 00 to Group 5. “We’ve used narrow-row spacings and increased population densities, while trying to plant north of Interstate Highway 40, where you typically don’t want to plant mid-March, but rather in late April or early May. That’s because the soil temperatures provide a little later planting window.

“The research has shown that when we’re in that planting window with drilled-row spacings and higher plant populations — and I’m not talking about really extreme numbers, maybe 150,000 to 170,000 plants per acre — we have obtained, under irrigated conditions, essentially the same yields from Group 2 soybeans as Group 4s.”

The findings have from been “exciting,” Purcell says. “We’ve shown it again and again, even though it goes against everything that’s been published in the scientific literature. The general idea in agronomic research is that the more light you’re able to capture, the bigger the plant, the larger the crop and the more yield you can expect.

“But we’ve not seen that. Under irrigation, we’ve seen a Group 2 soybean with roughly 95 days from emergence to R-7. And it has almost identical yield to a Group 5 soybean with 120 days from emergence to R-7.”

That provides “a lot of flexibility as far as what the planting and harvest windows can be,” Purcell says. “And we’ve also found that when growing the shorter season varieties it means much less irrigation.”

Apps and nitrogen concentration

Yet another interesting project involves the possibility of eventually developing a smart phone app that provides a reading of “corn leaf nitrogen concentration just by taking a photograph.

“It isn’t available yet, but it’s possible with current technology. You’d run the photo through a software package — maybe also on a smart phone — that would analyze it and then tell you whether your leaf nitrogen is sufficient or deficient.”

The researchers have taken it “a step further and done calibrations looking at color analysis of corn at the six leaf to eight leaf stage. From the photos, the software calculates how much nitrogen is lacking in order to recover 90 percent to 95 percent of yield potential.

“We’d like to extend that technology,” Purcell says. “We’ve looked at using this a bit in wheat, rice and cotton. We’ve looked at the method in these crops — establishing the relationship of the color from the photo to see if it correlates with leaf nitrogen. In every case, it does. But we haven’t done the calibration part like we have in corn.

“In corn, we can actually take a picture of vegetative leaves at V-6 and, from that, tell you how much nitrogen to apply to recover yield potential.”

The technology actually began in turfgrass research. Purcell and Doug Karcher, University of Arkansas turfgrass scientist, have collaborated on this for about four or five years.

“After I saw his work in turfgrass I said, ‘Doug, we should try this in some agronomic crops. Let’s give corn a try.’

“Things really fell into place, and we’re very excited about it. There is actually a patent pending on some of the technology. Perhaps it will be commercialized and be put in farmers’ hands.”

Does the photograph have to be a closeup of a leaf? A wider shot of the field?

“Up until now, most of our work has involved separating the topmost collared leaf from the corn plant,” Purcell says. “Those leaves are put on a pink background — that’s because, on the color spectrum, pink is as far away as you can get from green.

“Then, within each picture, there is a yellow disc and a dark green disc, which serve as color standards. This allows us to use different cameras, or to take the picture in different lighting conditions, under a shade tree or back at the shed under a fluorescent light. Because of the colored discs, we can adjust for those conditions.”

A special camera isn’t needed for the process — just some type of digital camera.

“The things you need for color standards can be picked up at most hardware or paint stores,” Purcell says. “Just tell them which color paint to mix, paint a board, and then you’re ready to go.

“Another possibility we’ve played with is to take the photos from an airplane. At one time, we shot photos from a plane using big plywood boards painted pink with large yellow and green circles to serve as color standards.”

But, he says, “That gets away from the idea that this should be something a farmer can utilize quickly and carry in his truck. If he feels his corn looks a bit yellow or his pre-plant N was lost due to an extended wet period, he can just take out the camera and shoot.

“We want him to be able to answer questions quickly without someone having to fly overhead snapping pictures.”

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