What is in this article?:
- 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.
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.”