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United States Department of Agriculture

Agricultural Research Service

Research Overview
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1 - Cover Crops
2 - Conservation Tillage
3 - Organic Potato Production
4 - BioEnergy Research-Oilseeds: Biodiesel
5 - BioEnergy Research-Perennial Biomass Crops: Ethanol
6 - BioEnergy Research-Biochar
BioEnergy Research-Perennial Biomass Crops: Ethanol

Perennial Biomass Crops: Ethanol

Hal Collins,
Rick Boydston
Ashok Alva
S. Fransen

   Another group of bioenegy crop we are studying are residues and perennial warm season grasses like switchgrass. About 90% of the domestic ethanol feedstock supply is derived from corn grain (Zea mays L.). Reasons for having selected corn include: 1) corns’ high starch content which can be rapidly distilled to alcohol, 2) corns’ higher distillation efficiencies are greater than most other feedstocks, 3) most of the ethanol produced is in the mid-West where corn is widely grown, and 4) many refineries are located in the Gulf Coastal States, close to current ethanol distillation centers.

Total dependence of the ethanol market on corn has inherent problems in sustaining feedstock supplies including: 1) as a warm-season crop, corn cannot be grown in all areas, such as those with short growing seasons or low rainfall, 2) corn requires high inputs of fertilizers, herbicides and insecticides to ensure high yields, 3) as an annual crop, corn grown under rain-fed conditions has yield potentials varying significantly from “bin busters to empty bins”, making it risky to grow due to the uncertainty of shifts in rain fall as a result of global climate change, and 4) wind erosion of soils resulting from annual cropping is a major problem in the arid west.
        Switchgrass is adapted to the warmer and irrigated regions of the Pacific Northwest (PNW) and therefore a viable alternative to corn. Switchgrass contrasts to corn in the west by: 1) being a perennial crop, eliminates the need for annual tillage, reducing soil loss from wind erosion, 2) having lower fertilizer requirements, and fewer pest issues decreases fertilizer and pesticide use, 3) ability to produce a harvestable biomass and becoming dormant if irrigation water is restricted compared to corn which would senesce and produce little harvestable yield, and 4) since 2001, switchgrass has proven to be productive and adapted to the lower Columbia Basin region of the PNW in joint ARS/WSU research trials. To be economical for the grower and local ethanol production facilities, a low-cost, high-return sustainable crop is required. Many questions surround the feasibility of switchgrass as an ethanol feedstock in the PNW.

Research yields of switchgrass have ranged from  22 to 30 Mg dry matter per hectare depending upon the cultivar grown. At these sustained yields 7-10,000 hectares would be needed to support a 75 million L per year. When placed in context of the energy return balance of 4.4 and 1.2 (energy output:input ratio) for switchgrass and corn, respectively, corn will be a more expensive feedstock than switchgrass. Comparatively, irrigated corn producers currently grow high yields of grain while our switchgrass research indicates a significant potential for crop improvement and improved ethanol yields.

To produce sustainable feedstocks as alternative energy supplies in the PNW we would likely see a shift from less profitable crops to those that meet feedstock demands while increasing grower returns. 

 

Carbon Sequestration under Irrigated Switchgrass: Perennial herbaceous bioenergy crops have the potential to sequester soil C, supply a portion of U.S. energy needs and reduce atmospheric CO2 enrichment when used as a fuel. Switchgrass production in the warmer irrigated regions of the PNW is a viable bioenergy feedstock producing greater than 12 tons dry matter per acre. Switchgrass production improved soil C reserves; 1.5 tons per acre with an average 15% increase in soil C after three years. This information is useful in the development of secondary markets such as C-credit trading.

Carbon Sequestration and Greenhouse Gas Emissions from the Sustainable Intercropping of Switchgrass and Hybrid Poplar for BioEnergy:  

     This five year research project addresses the “Carbon Sequestration and Sustainable Bioenergy Production” Program Area Priority of the Sustainable Bioenergy Research Program A6121. The overall goal of the project is to quantify biofuel energy biomass production potentials, C sequestration and greenhouse gas emissions within a switchgrass-hybrid poplar intercrop system.

     The objectives are to: 1) Determine the influence of poplar varieties of contrasting leaf area index and canopy architecture on switchgrass biomass production. 2) Determine changes in soil C cycling and C sequestration; 3) Monitor greenhouse gas production and; 4) Produce lifecycle analyses on all aspects of the production chain within an intercropped poplar switchgrass production system.

    The benefits and outcomes include: utilizing local animal waste streams; sustainable reductions in biofuel feedstock production costs; improved environmental quality through increased C-sequestration and reduced greenhouse gas emissions. Our approach of intercropping switchgrass within a perennial non-food crop (poplar) will alleviate “food for fuel” concerns.  Adoption of this intercropping strategy will replace 49 M L of fossil fuels per year and sequester >5,250 Mg C per year in the Pacific Northwest.

 

 

Nutrient Removal by Switchgrass Grown for Bioenergy: Perennial herbaceous bioenergy crops have the potential to improve soil quality, sequester soil C, enhance nutrient cycling improve wildlife habitat, and supply a portion of U.S. energy needs when used as a fuel. Removal of plant biomass removes substantial soil/plant nutrients. Assessments of the export of nutrients off-farm showed removal of 200 lbs N per acre; 40 lbs P per acre; 310 lb K per acre; and 15 lb S per acre. ARS-Prosser data indicate that future bioenergy refineries need to develop technology to recover plant nutrients for return to production fields.

Presentations

2011 Biomass Biofuel Feedstocks
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Last Modified: 4/5/2012
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