Prepare for the long-term cellulosic ethanol market, Taylorville, IL, grower Mel Repscher has been experimenting with tropical maize.

He drilled a tropical maize plot midsummer after wheat at 50,000-60,000 seeds per acre. He cut and crimped the crop using a mower-conditioner, field-dried it for a week, then baled it.

Repscher took about seventeen 1,800-lb bales off 2.5 acres – well below the 12-13 tons per acre the crop can yield under optimal growing conditions, according to University of Illinois (U of I) research. That’s also less than half the per-acre yield of vegetation Repscher’s giant miscanthus plot produced. 

He attributes the yield difference to the maize’s late doublecrop planting and extremely dry weather. The grower plans to plant the crop again next summer, but earlier.

“It’s an experiment,” he concedes. “If tropical maize is going to be a biomass crop of the future, I want to see what it’s like to grow it.” 

As an annual crop, tropical maize permits growers to keep their options open, notes Gary Letterly, U of I Extension energy and environmental stewardship educator. Farmers can grow it as a green energy source or as forage. It produces a lot of biomass with minimal inputs and doesn’t require specialized equipment.  

August Schetterand his dad, Dan, grew a plot of it on their farm near Brighton, IL. They belong to Omni Ventures, Inc., a southwestern Illinois group formed to develop alternative crop markets. The group has been testing giant miscanthus, but is now also considering tropical maize. It’s cheaper and less labor-intensive to plant than giant miscanthus, he says.

The Schetters planted tropical maize as if it were field corn, which is exactly what it looked like early in the season. Then the maize grew taller, had a longer growing season, produced less grain and had higher sugar content in its stalks. The Schetters view tropical maize as a crop that will eventually be grown and baled for power plants to burn.  

The crop can be grazed, too, says graduate student Michael Vincent. “Tropical maize should be managed and grown like a grass crop,” he says. Vincent is evaluating 50 new tropical maize hybrids he developed for biomass yield. The initial hybrids were the product of U of I researcher Fred Below’s work with nitrogen-use efficiency.

Vincent grazed beef cattle on maize at the university’s Dudley Smith Farm near Pana. The crop was drilled at about 100,000 seeds per acre, 60 lbs/acre of nitrogen were applied and conventional corn herbicides were used. The cattle utilized at least 75% of the forage.

“Plant it early in the season to fill in the summer grazing slump or after wheat to use for late-season grazing,” he recommends.

Compared to field corn, tropical maize produces about 33% more biomass per acre. A cross between temperate and tropical inbreds, it has been grown as far north as Michigan and Wisconsin, and to the southern edge of Illinois, notes Vincent. He finds that the crop needs less nitrogen than conventional corn. Some hybrids may also offer drought resistance, resistance to some insects and perform well on marginal soils.

As a cellulosic biofuel crop, however, tropical maize takes precise management. “There’s a narrow peak in its sugar content (three to four weeks). It ferments quickly after harvest and needs to be processed within 24 hours.” 

At this point, tropical maize seed is only available for U of I research programs and nutritional data has yet to be analyzed. But commercial seed may be available within the next few years, Vincent says