The good news is that, over the last 20 years, average corn yields have increased about 1.5% per year without a significant increase in nitrogen application rates. Even better news is that geneticists and plant breeders are now developing hybrids that will require less nitrogen while maintaining overall yield.

Good news indeed since the price of nitrogen fertilizer, which has continued to rise, is one of the largest farm input costs. It accounts for about one-fifth of a corn grower's operating expenses.

Farmers apply an average 138 lbs. of nitrogen/acre/year, according to Pioneer Hi-Bred, a DuPont company. Over the last three years, farmers have paid an average of $43/acre for nitrogen. Using that figure, a grower could save $8.60/acre if the nitrogen rate could be cut by 20%. Nitrogen rates, of course, vary widely as does the price of nitrogen from year to year.

Corn plants can absorb less than half of the nitrogen fertilizer applied. The rest can enter into waterways or volatilize into the air as a greenhouse gas. This is another reason why growers would welcome nitrogen-use-efficient (NUE) hybrids.

In development

Advances in genomics, map-based cloning and other new technologies are enabling companies such as Pioneer, Monsanto and Syngenta to more quickly identify the numerous genes and genetic pathways responsible for controlling nitrogen use in corn. The sooner these genes can be introduced at the inbred level and then expressed in hybrids, the sooner they will come to market.

NUE hybrids are primarily in the Phase 1, Proof of Concept stage at this time, so they won't likely be on the market for at least 8 to 10 years. But the companies developing these hybrids are intensifying their research.

Last fall, for example, Monsanto announced a collaboration with Israel's Evogene Ltd., in which Monsanto gained exclusive rights to several genes discovered by Evogene that help plants maintain yield with lower applications of nitrogen. These genes complement NUE genes that Monsanto is already testing in its research and development program.

This spring, DuPont and Arcadia Biosciences, Davis, CA, announced a collaboration in which DuPont business Pioneer has exclusive rights to Arcadia's proprietary technology for improving nitrogen use in corn. Pioneer reports that the collaboration complements the progress it has already made in this area.

Marc Albertsen, Pioneer's director of agronomic traits and lead evaluation, is encouraged by the progress of nitrogen use research. Last year, in the company's first set of replicated transgenic yield trials under managed low nitrogen and normal nitrogen conditions, researchers identified multiple transgenes that independently had positive impact on nitrogen use. Several of these transgenes resulted in an 8 to 24% yield improvement over controls under reduced nitrogen conditions, while others resulted in a 7 to 9% yield improvement under normal nitrogen environments.

This year, Pioneer tripled the number of replicated yield trials and plans to expand them again next year. Pioneer will display photos of trial plots at this year's Farm Progress Show, Albertsen says.

Monsanto also has been evaluating corn germplasm for nitrogen use efficiency. Mark Lawson, Monsanto's yield and stress platform lead, says this work has been part of the company's long-term effort to improve base germplasm. “Over the last 20 years, corn yield levels have increased by 1.5% per year under situations where nitrogen application has remained flat. That's a big comment on breeding efforts,” Lawson says.

Monsanto is using genomics and marker-assisted breeding to identify genes and develop hybrids that will maintain yield under reduced nitrogen applications. Someday, growers may be able to reduce nitrogen applications by 20 to 25% while maintaining yield, Lawson says.

Syngenta is pursuing improved nitrogen use through both native trait and genetic modification (GM) platforms, says Wayne Fithian, the company's corn product business lead. “Our native trait effort is focused on identifying favorable alleles of genes that influence nitrogen use efficiency and introducing them into our hybrids,” he explains. “Our GM effort is focused on identifying and introducing genes that improve nitrogen use efficiency. The goal of both efforts is to help farmers produce the same or better yields on less nitrogen.”

Syngenta researchers are using the company's allelic diversity platform to identify candidate genes from a wide diversity of corn parent lines, Fithian says.

Over the years, little has been known about genes that control response to nitrogen. That is because nitrogen use is complex, with numerous genes and pathways involved in virtually every plant function. But advances in genomics are now beginning to pay off because they enable researchers to identify genes involved in nitrogen use, says Fred Below, professor of crop physiology, University of Illinois.

Advances in genomic tools (molecular markers and high throughput screening of genetic traits), along with allelic diversity and gene association panels, present new opportunities for direct testing, identification and rapid integration into commercial germplasm of genes affecting nitrogen use, Fithian says.

“Recent advances in molecular biology are helping us identify nitrogen-related genes from sources other than corn. These genes become candidates for our GM approach,” he adds.

What to do now?

While NUE hybrids won't be ready for the market for years, yields already have increased due to corn breeders' efforts over the last two decades. Growers can manage their fertilizer use by following university guidelines and using tools such as the Corn Nitrogen Rate Calculator (a Corn Belt approach to nitrogen rate guidelines). Visit http://extension.agron.iastate.edu/soilfertility/nrate.aspx.

The calculator enables growers to plug in their fertilizer costs and expected grain prices and whether they plant corn following soybeans or corn following corn, says John Sawyer, extension soil fertility specialist, Iowa State University. They will find that corn following soybeans requires less nitrogen fertilization, one benefit of crop rotation. Growers also can compare up to four corn and fertilizer price scenarios at one time in the calculator. This gives them an opportunity to make informed decisions based on research and expected economic return, Sawyer says.

Fertilizer prices are currently at record levels. Manure can be used effectively in a fertility program, but other than growing more forage legumes and then rotating to corn, there are not a lot of options. “Corn needs nitrogen,” Sawyer says, adding that the issues driving high fertilizer costs (increased global demand, high energy costs and the weak U.S. dollar) are unlikely to go away anytime soon.

Below, from the University of Illinois, adds that if you want to apply nitrogen this fall, wait until temperatures fall below 50°F and use a nitrogen inhibitor. Spring application, with care not to overapply, is preferable. The University of Illinois is currently testing variable-rate application technologies, which also will improve nitrogen use efficiency.