Course: BFM 101 Biofuels Fundamentals

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Bioenergy Crop Production: a Crop-by-Crop Analysis
Bioenergy Crop Production: a Crop-by-Crop Analysis
This video provides an introduction to the many considerations involved in choosing a bioenergy crop.
Below you will find a detailed crop-by-crop analysis to further aid in making crop decisions.

"BIOEN2: Crop Production," by AgEnergy, Standard YouTube License

If you cannot see the video above, click here to open it in a new window.

Sugar & Starch Crops

Many of the sugar and starch crops that are candidates to produce biofuels are those currently being grown for sweeteners or for feed and food. Corn grain is currently the primary feedstock being used for ethanol production in the United States, due to the ease of converting corn to ethanol, the abundance of corn already in production and the existing infrastructure to produce, transport, and store corn.

Corn is converted to ethanol through the biochemical process of fermentation, using microorganisms that convert the sugars into alcohol. Most corn grain is converted to ethanol using a dry mill process that produces animal feed – and sometimes CO2 – in addition to ethanol. For non-technical summaries of the process of making ethanol, and issues and opportunities associated with ethanol production, see the Extension publication “Corn for Biofuel Production” (Hay, 2010).

Corn ethanol has created new wealth and opportunity in the rural Midwest. But environmental, economic, and social sustainability concerns have also been raised. There is debate over the impact corn ethanol has had on net energy balance, greenhouse gas emissions, water quality, market volatility, risk for farmers and competition for use of feedstock, as well as on local communities.

Ethanol can also be made from grain sorghum, wheat, sugarcane and sugar beets. In Brazil, sugarcane is used extensively as a bioenergy feedstock. Sugar beets and sweet sorghum can be grown in temperate regions, in the northern U.S. and as far north as Canada.

Fact Sheets:
Corn Grain, Tropical Crops, Tropical Maize

Celluosic Crops

Plants grown for cellulose include herbaceous and woody perennials. Leaves, stems and stalks – the cellulosic parts of plants, can be burned directly to generate electricity, or can be converted to liquid fuels, energy gases and chemicals through a variety of conversion technologies.

Perennial crops grown for bioenergy production offer environmental benefits to soil, water and wildlife resources. One of the main advantages of these crops is that they re-grow from the root system every year, and thus do not need to be replanted annually. Perennial crops maintain cover on the land, provide habitat, and usually require fewer fertilizer and water inputs. These crops can be planted on less productive or marginal agricultural landscapes. Perennial crops under consideration as bioenergy feedstock include switchgrass and other native prairie grasses, Miscanthus spp., reed canary grass and tropical maize. Weed control is essential for stand establishment for switchgrass and other perennial biomass grasses.

At present, the major concern about perennial bioenergy crops is economic: farmers cannot anticipate market demand or estimate the time for a return on their investment, because as yet there is no established market for these crops. However, environmental concerns about these crops have also been raised because of their limited production history in the United States. Sorghum and tropical maize grow very large when planted in the Midwest because Day length does not initiate reproductive growth. Little is known about their input requirements, potential pests, and susceptibility to disease. Some of these species, such as Miscanthus, may cause controversy because they are non-native. Miscanthus is planted using Vegetative propagation with rhizomes and transplanted.

Fact Sheets:
Arundo donax, Prairie Cordgrass, Miscanthus, Sweet Sorghum, Switchgrass, Tropical Maize

Woody Crops

Perennial non-forest woody crops, also called fast growing, short-rotation crops (SRC), provide multiple products and benefits. For example, SRCs such as hybrid poplar and willow yield pulpwood products as well as energy. These crops are typically harvested then chipped on-site. The chips are often combined with some other feedstock during densification (e.g., pelletizing).

Perennial woody crops are usually grown in a monoculture, but can be grown in mixed plantings as well. These short-rotation crops provide long-term yield potential and environmental benefits like wildlife habitat, soil erosion prevention, and water quality improvement. Woody biomass crops are harvested every 3 years. However, keep in mind that monocultures provide fewer wildlife benefits than do polycultures and mixed plantings.

Producing woody biomass crops causes some social and economic concerns, such as competition with traditional forest product industries for land and wood products, and questions about whether the financial returns will be worth the investment.

Fact Sheets:
Poplar, Willow, Woody Biomass

Oilseed Crops

Oilseed crops are grown for their seed, which is harvested and crushed to extract oil. This oil can then be converted into biodiesel through a process called transesterification. There are a number of oilseed crops being evaluated for bioenergy potential. Many of these crops have special adaptations that make them regionally viable based on climatic and soil conditions. Some characteristics include salt tolerance, cold hardiness, drought resistance and low fertility requirements.

Oilseed crops like canola, soybean and sunflower are used to make biodiesel. Oil from the seed is crushed and converted via transesterification. One gallon of canola oil will produce one gallon of biodiesel. Most oilseed crops have growth requirements specific to certain regions of the country. Most U.S. biodiesel is made from Soybeans.

Because a number of oilseed crops, including soybean, canola and sunflower, are grown and used for food-grade vegetable oil, there are concerns that they may be diverted to fuel use at the expense of food production. Indeed, several oilseed importing European countries have determined that oilseed production for export often diverts land from food production. There are now attempts to develop sustainability standards to remedy this situation.   Land use change and competition with food crops will be factors in determining what crops will be eligible for tax credits and incentives for biofuel production in the United States.

Fact Sheets:
Algae, Camelina, Mustard, Soybean, Tropical Crops

Crop residue & Organic Waste

In annual cropping systems, aboveground, non-grain portions of plants—including stalks, leaves, chaff, and husks—are left in the field after harvest. These residues are composed of lignocelluloses and may be used as a bioenergy feedstock, burned for biopower, or converted to a liquid transportation fuel or gas. However, while there is some use of crop residue for heat or biopower through combustion, conversion of crop residue to ethanol is not yet commercially viable. And, as with other biofuel sources, there are both economic and environmental factors to consider.

There are economic concerns about the use of crop residue as a bioenergy feedstock. In the Midwest, corn stover (stalks and leaves) is the leading candidate for production of cellulosic ethanol because it is abundant and relatively inexpensive. Corn stover yields correspond closely to grain yield (nearly 1:1). Corn grain yields a national average of 152 bushels per acre at 56 pounds per bushel will produce 4.2 tons above ground corn stover per acre. However, the farmer incurs a cost in terms of equipment, time, and fuel used to harvest stover. In addition, increased use of some residues for biofuels could reduce their availability for more traditional uses. For example, straw from small-grain crops is typically used as animal bedding, either on-farm or sold as a cash crop. Diverting it to the biofuel market could decrease the supply of animal bedding.

Removal of crop residues for biofuel production also has environmental consequences. When left in the field, these residues reduce erosion and contribute organic matter to the soil. On the other hand, excessive residue cover may interfere with spring planting and hinder soil warming and drying. It will be important to remove residue at sustainable rates, so that it can simultaneously provide an extra income for farmers, improve spring planting, and still prevent erosion and maintain soil organic matter.

Fact Sheets:
Corn Stover/Cobs, Anaerobic Digestion

Other Resources

The Crop Comparison Matrix is a quick reference guide comparing characteristics of various crops. This includes growing requirements, potential yields, crop establishment and cultural practices.

Matrix:
Crop Comparison Matrix

Resources provided by the eXtension Farm Energy Community of Practice at http://www.extension.org/ag+energy

Crop Handling & Logistics