If the latter half of the 20th century was about an herbicide revolution in agriculture, the early 21st century will be about nitrogen (N). Public and private researchers are focusing on its role in boosting corn yields above the current average high-yield mark of 164 bu. Seed companies feel they can eventually push this to 300 bu. to meet growing global demand.
“It will be of immense concern to agriculture for at least the next 20 years,” says Tony Vyn, Purdue agronomy professor.
Improving corn’s N use efficiency (NUE) will not only increase yields, but also decrease the amount of runoff. Vyn says there are two avenues to improving NUE: To improve the efficiency of capturing the inherent soil N, and to increase fertilizer N’s efficiency.
Between 1965 and 2010, N use has increased from an average of 75 lbs./acre to 140 lbs./acre, according to the USDA. However, a study by Vyn and colleagues show that current corn hybrids are more efficient in their N use.
Purdue University researchers looked at studies conducted over the past 72 years. They found that 1 lb. N now produces 22% more grain than it did in 1940 (49 lbs. vs. 56 lbs. of grain). Corn’s NUE has improved mainly because corn makes more grain for every pound of N taken up by plants over the growing season, but why that happens is less clear, Vyn says.
About 40% of the plant’s total N is taken up after flowering in modern hybrids, Vyn says. Furthermore, simply looking for hybrids with the darkest green leaves, which suggests healthy N metabolism, may have no bearing on a plant’s final yield or its final NUE.
“So what we’re trying to figure out when and what to measure – and whether you can do this successfully in an automated greenhouse.”
Lloyd Murdock, soil specialist at the University of Kentucky, says research in the state shows similar increased efficiency over the last 10 years. Where it once took 1 lb. N to increase yield 1 bu./acre, it’s now closer to 0.75 lb.
His research on different soils and hybrids over the years found that the plants have become better at N use.
Additionally, “we’ve improved N use with remote sensing,” he says. That and precision application mid-season is how farmers can improve NUE right now.
“Remote sensing can measure the plant health status by looking at crop with two different wavelengths,” he says. “It really pulled us forward as far as N is concerned.”
Although remote sensing has not been widely adopted by American farmers, its use will only advance the industry so far, Murdock says.
”I think the next step is going to have to come from the genetics,” he says.
As universities look for better ways to measure N use, seed companies are beginning a difficult search to find the genetic key to improving the plant’s ability to take up and metabolize N.
At DuPont Pioneer, researchers are studying three areas of potential N improvement:
- Corn roots to improve N uptake from the soil
- N movement through the plant
- N conversion to protein within the plant
“We are looking at multiple potential targets in improving N efficiency,” says Jeff Schussler, a senior research manager at DuPont Pioneer. “The scientific literature would suggest you can improve the efficiencies of those processes. We know we’re not capturing all the N supplied to the corn crop.”
Current research at DuPont Pioneer is still in the discovery phase, and commercialization of a NUE corn seed probably won’t happen until the end of the decade, he says. The company is looking into the corn genome to see if the potential for improved NUE already exists in the plant, as well as researching a transgenic approach and has some “interesting GMO leads” that are currently in field trials.
“We’re convinced there’s potential for improvement in native corn genes. Of the major crops in the world, corn is not that bad,” he says.
Schussler says the drive to increase yields has improved N efficiency, but NUE has not been the focus of research until now.
The direction of genetics research is promising, Vyn says, but he doesn’t think a solution will be soon or simple because looking for a NUE advantage is even more complicated than looking for a yield gain. There are many, many more processes to be tweaked to arrive at these improvements.
He says it’s a question of right product, right rate, right time and right place; along with optimum plant populations, crop rotations and tillage systems.
“There’s a challenge on the breeding side and the production side to ensure sufficient, but not excessive, N is there when the corn plant needs it most,” Vyn says.
Photosynthesis under the microscope
Thepotential to reduce nitrogen and water use is part of a Bill & Melinda Gates Foundation $25 million grant to improve food crops’ photosynthesis. The five-year grant goes to the University of Illinois in Urbana to increase photosynthetic efficiency.