Ecologically Boosting Corn Yields

Nebraska researchers studying intensified corn management systems believe it's possible to increase corn production by 50 percent without using any more land, and at the same time improve its environmental impact.
By Susanne Retka Schill | May 09, 2008
A decade ago the world population was burgeoning just as Thomas Malthus, the English demographer and political economist, had predicted 200 years earlier. Although ironically, the widespread famine he also said would be inevitable didn't happen. Indeed, the United States was experiencing such huge surpluses in corn supplies that producers were looking for new markets to remedy low prices. Ken Cassman, director of the Nebraska Center for Energy Sciences at the University of Nebraska-Lincoln, recalls that major corn organizations officially adopted policies to not support research that would further increase corn yields. Other corn producers began to organize efforts to build ethanol plants with the intent of using up some of the local surplus. In spite of those surpluses, and with one eye on Malthus' predictions of the dire consequences of population growth, Cassman and his fellow Nebraska researchers launched long-term studies on the ecological intensification of corn and soybeans, or ways to reach the crops' maximum yield potential. In light of today's high corn prices, the need to produce more corn for both feed and fuel is even more pressing.

If the researchers can learn how to intensify corn production, total production could increase by about 50 percent, without using more land and without factoring in yield gains from the modern genetic manipulation of corn germplasm. The maximum yield potential for corn is the highest yield possible in a given location taking into account solar radiation, temperature, length of the growing season and genetics of the crop itself, says Dan Walters, soil scientist in the Department of Agronomy and Horticulture at the University of Nebraska. "In the Midwest, if there is no limitation in water and nutrients, corn's yield potential is probably about 300 bushels per acre," he says. "If you look at average productivity, we're running about 60 percent of that, and that's with irrigated corn. It's lower with rain-fed corn."

More With Less
"If it was just a question of increasing yields we could do a great job," Cassman says. "And if it was just the job of protecting the environment without worrying about yields that would be really easy: cut back fertilizer and don't use irrigation. But the challenge is how do we massively increase yields on existing land and at the same time protect the environment better than we ever have before. That's what's being asked of corn ethanol systems."

Cassman continues, "What we have is proof of concept." It requires producers to look at the whole system; coordinate every management decision synergistically with every other one; use greater precision in determining nitrogen rates and timing, and irrigation rates and timing; and to pay attention to the optimal planting date and optimal planting population for a given site, and not just for a region. "Putting all that together in one package we've shown you can get a substantial increase in yield and at the same time reduce the amount of fertilization and water that's required," he says.

Nebraska researchers developed a tool, called the Hybrid-Maize Model (www.hybridmaize.unl.edu), that allows producers to simulate the growth of a corn crop, using current and historical weather data. Producers use that information and evaluate changes from different combinations of planting date, hybrid maturity and plant density. "In the first years of our research we tried to plant as early as possible with a target date of April 20 and we could never achieve greater than 260 bushels per acre," Walters recalls. "We knew we should be able to get more." After the Hybrid-Maize model was completed, they altered the planting dates. "We discovered that for Lincoln, Neb.,this heat island of a cityif we planted one month later we could approach yield potential." The climate modeling and corn growth information built into the model matched the growth cycle of the corn plant with typical weather conditions. For two years, they hit 285 bushels per acre and 287 bushels per acre, by only changing the planting date. The third year was extremely hot, and the irrigated test plots reverted to more normal irrigated yields of 230 bushels per acre. Walters says that outside of the city's heat island, the change in the optimal planting date was only one week later than the traditional planting date. "Every single farm is going to be specific based on analysis of the long-term climate data, which determines the optimal planting date and maturity level for the corn hybrid that gives the highest probability of maximum yield potential," he says.

Plant population studies sought to find the optimal population to maximize the amount of leaves in the crop canopy, which harvest energy from the sun, Walters says. They had to be careful, however, that the canopy wasn't so large that the plants had to use more energy to stay alive and thus not as much making grain. Plant populations of 44,000 plants per acre worked best in some years, but when growing conditions weren't favorable yields crashed, he says. The researchers concluded that plant populations of between 34,000 and 37,000 plants per acre were optimal. "We've never put economics to this," Walters adds. "We're looking at physiology." Producers may be skeptical of the risk involved in increasing plant populations and the cost of buying more seed.

Hybrid-Maize modeling is now being used in a series of experiments involving the fine-tuning of water use in irrigated fields. "In typical years, we find it is possible to cut back on water use during the vegetative growth periods," Walters says. "You get more bang for your irrigation dollar during grain fill." The first year of a three-year study has been completed comparing paired fields on eight farms. One field was under pivot irrigation managed normally by the farmer, and the other was managed by the researchers. "We learned you can reduce water use by 25 percent and garner the very same yield, just by using the model to evaluate the impact of water stress on various stages of plant growth," he says. Actually, in six out of the eight farms, the researchers' corn yielded four to six bushels more per acre than the farmer's corn. "We could have failed, but we had the inside track on the odds because we had the analysis of weather data and a crop development model," Walters says.

Work is now underway to analyze optimal nitrogen fertilization by splitting the fertilization applications into four smaller applications through the irrigation system (a process dubbed fertigation among irrigators). "In large fertigation studies we increase nitrogen use efficiency by approximately 10 percent by splitting nitrogen applications versus applying it all pre-plant," Walters says. On rain-fed fields, he adds, it is more economical to do a single split application, putting some of the nitrogen down when planting and side-dressing the remaining nitrogen a month later.

Sequestering Carbon and Nitrogen
In a series of experiments on soil sequestration, the researchers studied what would happen if the corn residue were managed differently in a high-intensity corn system. They choose a corn variety that produced a lot of residue and planted it at populations of about 37,000 plants per acre. Right after harvest, they applied 40 to 50 pounds of nitrogen per acre directly on the stover and plowed it under using a conservation plow. The conservation plow leaves about 30 percent of the residue on the surface. In the studies, they found that a normally managed irrigated corn crop that yielded 230 bushels returned about 4,000 pounds of carbon per acre per year to the soil. The intensively managed plots contributed 6,500 pounds per acre per year. "As we improve the amount of organic matter in the soil we also improve the sequestration of nitrogen and build up the amount of indigenous soil nitrogen," Walters says. "The soil supplies more nitrogen to the crop in the following year and that reduces the amount of fertilizer needed." Over the six years of the study, the soils with intensified, continuous corn have seen about a one-half ton positive gain of sequestered carbon per acre per year, he says. In comparison, the no-till irrigated corn, managed with current recommendations and not pushed to maximize yields, was actually losing carbon at about one-half ton per year. The sequestration study turns current wisdom upside down because it uses some plowing, which many conservationists would like to ban as older methods were the source of much soil erosion.

The researchers also looked at the global warming potential of the systems under study, factoring in fossil fuel consumption, carbon losses and trace gas emissions. The carbon sequestration capability of the intensive continuous corn system had lower net global warming potential. Compared with corn/soybean rotations, the carbon sequestration potential of continuous corn is four times greater, they found.

The UNL work evaluating greenhouse warming potential of intensive corn production is important, says Paul Fixen, research director for the International Plant Nutrition Institute. "There is just a handful of studies in North America," he says. The most important dimension of UNL's work is the concept of refining a production system for local conditions using crop models like Hybrid-Maize, he adds. Fixen says the research that's been demonstrated on a small scale in research plots needs to be scaled up. "We can grow more corn using advanced techniques and we can markedly improve efficiency," he says. "We need to refine these practices." Getting that done will require the ethanol industry to get behind the research. "I've been amazed that the ethanol industry is not more involved in what goes on in the fieldthe production of feedstock supply and the cost of feedstock," he says. While genetic manipulation techniques have helped the seed industry make great advances, at the same time, resources devoted to applied research to improve production practices have been dropping, Fixen says. He would like to see the ethanol industry become more involved, and to put political pressure on the USDA Agricultural Research Service and university agricultural programs to work more on productivity, efficiency and environmental impacts.

Susanne Retka Schill is an Ethanol Producer Magazine staff writer. Reach her at sretkaschill@bbibiofuels.com or (701) 738-4962.