Developing Tropical Maize as a New Biofuel and Forage Crop for Illinois (2013-2015)

Fred E. Below, Principle Investigator, Department of Crop Sciences
Vijay Singh, Dan Shike, Gary Letterly, Laura F. Gentry

Project History

The Dudley Smith Initiative originally funded this study in 2009.  Three field trials were initiated in 2010 and continued in 2011 to investigate using tropical maize hybrids as a bioenergy and forage crop.  Field management practices evaluated included tropical-temperate maize hybrid, N fertilization, plant population, row spacing, effect of shoot bagging, and harvest date.  Treatments were assessed for overall biomass production, grain yield, grain quality, and stalk sugar content.  Field evaluations were made throughout the growing season noting general hybrid vigor and response to treatments.  In 2008, 12 tropical-temperate maize hybrids were tested and in 2009 and 2010 they were further evaluated, crossed to produce new hybrids, and new hybrids were classified as having properties best-suited for either ethanol production, thermal production (or dual purpose use, producing both grain and biomass) or animal forage.  To date, about 60 hybrids have been produced in small quantities, six of which have been selected for bulk production.

Actual ethanol fermentations were conducted under the direction of Dr. Vijay Singh. Bio-butanol was also produced by fermentation of tropical maize juice by the bacterium Clostridium beijernickii NCIMB 8052 with yields exceeding fermentation of glucose and corn stover hydrolysates by 29-35%. (Wang and Blaschek  2011). Predicted ethanol yields per acre were projected based on sugar content, biomass, and extraction efficiencies; data was published in Global Change Biology by White et al. 2012.

Research of tropical maize for thermal energy focused on two co-firing forms, bales and pellets.  Despite densification and related transport advantages of pellets, results suggested that direct firing of bales is the most energy-efficient means of thermal energy production at the local scale.  This study has identified several tropical-temperate maize hybrids as “dual purpose,” meaning that they produce both grain and high biomass.  These hybrids may be especially promising for the thermal model because farmers would produce 75-100 bu/a of grain (depending on hybrid and weather conditions), which they could sell to cover their establishment costs (seed, planting, and maintenance); the remaining biomass can be sold or burned on-farm.  The thermal utility of tropical maize presents opportunities for growers at the local level.  The most likely scenario involves selling bales to facilities heated with a bale-burning furnace; in the course of such an agreement, the grower would probably deliver the bales to the facility and remove the ash produced after the bales have been fired.  We analyzed ash after co-firing and found that it contains reasonably high concentrations of plant nutrients which can be added back to fields to supply a portion of the P, K, and micronutrients that were removed during crop production and harvest.  This would solve the problem of waste disposal by recycling the nutrients in an efficient and environmentally sound manner.

As an animal feed or grazing crop, tropical maize holds strong potential if managed properly.  When ensiled, tropical maize yielded crude protein levels of greater than 8% and total digestible nutrients around 60%, making tropical maize forage quality comparable to corn silage.  In a trial conducted at two locations in 2011 (a hot, dry growing season), we determined that no-till drilled, double-cropped (planted after wheat harvest) tropical maize can produce baled biomass of 5.5 ton/a; for comparison, state hay yields were less than 4 ton/a.  Unlike sweet sorghum, tropical maize does not accumulate dangerously high levels of prussic acid.

This research has supported the work of two graduate students, Wendy White (M.S. earned in 2010) and Mike Vincent (Ph.D. candidate).

Current Project

For each of the three tropical maize utilities – transport fuel, thermal energy, and animal forage – we propose to further address or refine the field management, processing considerations, and conversion to final product.  For instance, field management of tropical maize for transport fuel might differ from management for thermal energy or animal forage due to enhanced efficiency of ethanol production in the presence of greater sugar concentrations.  To manage for greater sugar content, it would be advisable to select hybrids that produce higher sugar concentrations and to harvest the crop earlier, when sugar content is greatest versus later in the season when sugar content has declined (but greater biomass has accumulated).  It may also be advisable to decrease the N fertilizer application rate when managing tropical maize for ethanol production since greater N concentration in the crop may encourage faster and greater vegetative growth at the expense of sugar concentration.  Processing considerations include harvest date, method of harvesting, and storage of materials.  For example, tropical maize grown for thermal energy production would be baled at the height of biomass accumulation, after the crop has dried down to reduce moisture content; prior to baling, however, the crop would be harvested for grain.  In an animal forage system, the biomass might be harvested early, while moisture content is still high, and ensiled to produce high-sugar content silage.  Alternatively, tropical maize might be harvested for bale-feeding later in the season to increase biomass content and lower moisture content for better preservation.  Yet another scenario is to allow cattle to graze it as a standing crop.  Lastly, the conversion to final product step is relatively simple for thermal energy (pending development of a bale furnace) and animal feed utilities, but will require extensive research for ethanol production.  Conversion to ethanol requires further enhancements of the fermentation system and a feasible scale-up protocol.

In addition to addressing management, processing, and conversion issues associated with each tropical maize use, we also wish to investigate three sustainability considerations associated with producing tropical maize – nutrient use efficiency, conservation tillage techniques, and cover crop integration.  Finally, no biofuel crop will be successful without the acceptance of growers, which begins by providing information and exposure to the crop.

The following five interrelated aims will be conducted concurrently to optimize production of transportation fuel, thermal biomass, and animal feed and to identify and mitigate potential barriers to sustainable biofuel and animal feed production.  This approach is designed to expedite near-term commercialization of tropical maize for bioenergy and animal feed production.

Specific Aim 1 – Management, processing, and conversion of tropical maize biomass into liquid transport fuel
Specific Aim 2 – Management, processing, and conversion of tropical maize for thermal energy production
Specific Aim 3 – Management, processing, and conversion of tropical maize biomass as an animal forage source
Specific Aim 4 – Soil Sustainability and Environmental Assessment
Specific Aim 5 – Rural Outreach

Note: Economic analysis of tropical maize is not included in this proposal.  Pending additional support and data collection, we will produce an analysis of profitability of tropical maize production relative to traditional row crops in Illinois.  Information is currently being collected to provide data for such an analysis.

Project Resources