Early results from research by University of Illinois crop scientist Fred Below indicate that tropical maize—the form of corn grown in the tropics—may be an efficient biofuel crop for the US Midwest. Below began investigating maize in search of novel genes for the utilization of nitrogen fertilizer and was hoping to discover information that could be useful to American corn producers.
Maize requires few crop inputs such as nitrogen fertilizer. It also is easier for farmers to integrate into their current operations than some other dedicated energy crops because it can be easily rotated with corn or soybeans, and can be planted, cultivated and harvested with the same equipment that US farmers current utilize. Finally, tropical maize stalks are believed to require less processing than corn grain, corn stover, switchgrass, Miscanthus giganteus and the scores of other plants now being studied for biofuel production.
The long summer days in the Midwest delay flowering of tropical maize, according to Below, which causes the plant to grow very tall—14 or 15 feet tall compared to the 7-1/2 feet height of conventional corn—and produce few or no ears. Without ears, these plants concentrate sugars in their stalks, resulting in 25% or more sugar in the stalks in the forms of sucrose, fructose and glucose than corn.
This differs from conventional corn and other crops being grown for biofuels in that the starch found in corn grain and the cellulose in switchgrass, corn stover and other biofuel crops must be treated with enzymes to convert them into sugars that can be then fermented into alcohols such as ethanol. Storing simple sugars also is more cost-effective for the plant, because it takes a lot of energy to make the complex starches, proteins, and oils present in corn grain. This energy savings per plant could result in more total energy per acre with topical maize, since it produces no grain.
Below said that his early trials also show that tropical maize requires much less nitrogen fertilizer than conventional corn, and that the stalks actually accumulate more sugar when less nitrogen is available. Nitrogen fertilizer is one of major costs of growing corn.
The sugarcane used in Brazil to make ethanol is desirable for the same reason: it produces lots of sugar without a high requirement for nitrogen fertilizer, and this sugar can be fermented to alcohol without the middle steps required by high-starch and cellulosic crops. But sugarcane can’t be grown in the Midwest.
Growing tropical maize doesn’t break the farmers’ rotation. You can grow tropical maize for one year and then go back to conventional corn or soybeans in subsequent years. Miscanthus, on the other hand, is thought to need a three-year growth cycle between initial planting and harvest and then your land is in Miscanthus. To return to planting corn or soybean necessitates removing the Miscanthus rhizomes.—Fred Below
Below is studying topical maize along with doctoral candidate Mike Vincent and postdoctoral research associate Matias Ruffo, and in conjunction with U of I Associate Professor Stephen Moose. This latest discovery of high sugar yields from tropical maize became apparent through cooperative work between Below and Moose to characterize genetic variation in response to nitrogen fertilizers.
Currently supported by the National Science Foundation, these studies are a key element to developing maize hybrids with improved nitrogen use efficiency. Both Below and Moose are members of Illinois Maize Breeding and Genetics Laboratory, which has a long history of conducting research that identifies new uses for the maize crop.
Moose now directs the longest-running plant genetics experiment in the world, in which more than a century of selective breeding has been applied to alter carbon and nitrogen accumulation in the maize plant. Continued collaboration between Below and Moose will investigate whether materials from these long term selection experiments will further enhance sugar yields from tropical maize.
In terms of biofuel production, tropical maize could be considered the Sugarcane of the Midwest. The tropical maize we’re growing here at the University of Illinois is very lush, very tall, and very full of sugar.—Fred Below