K.P. Vogel, M.R. Schmer, R.K. Perrin, L.E. Moser, and R.B. Mitchell
USDA-ARS and the University of Nebraska-Lincoln, Lincoln, NE
|Figure 1. Location of sites growing switchgrass as a bioenergy crop on a commercial scale in the Northern Plains.|
Switchgrass (Panicum virgatum L.) is a warm-season (C4) perennial grass that is native to the tall grass region of the Great Plains and Midwest. Switchgrass is primarily used for summer forage, hay, and conservation plantings and was one of the main species planted in the Conservation Reserve Program (CRP). In 1990, the Department of Energy (DOE) designated switchgrass as a potential biomass energy crop. As a biomass energy crop, switchgrass would be grown on CRP-type land and its biomass or forage would be harvested and baled. The harvested biomass would be trucked to biomass energy conversion plants for processing into ethanol. At the conversion plants, the cellulose and hemi-cellulose that forms the plant cell walls of the biomass would be converted into simple sugars which would then be fermented into alcohol. Improved conversion technology is currently under development. Assuming a conversion rate of 75%, a ton of switchgrass would produce approximately 80 gallons of ethanol.
Economic analysis conducted by DOE and the Economic Research Service, USDA, indicated that the Northern Plains states of North and South Dakota and Nebraska were states in which switchgrass had potential to be an economically viable energy crop. Field scale production information and economic analysis based on field scale results were needed to validate previous small plot research and associated economic analysis. In 2000, the USDA-ARS (Wheat, Sorghum and Forage Unit--Lincoln, Nebraska and the Northern Great Plains Research Laboratory, Mandan, North Dakota) in cooperation with the University of Nebraska-Lincoln, and DOE began growing switchgrass on a commercial scale on 11 fields in Nebraska, South Dakota, and North Dakota (Figure 1). The Central Grassland Research Station, North Dakota State University, Streeter, ND is one of the cooperating locations. All other fields are on privately owned and operated farms. Field sizes range from 7 to 23 acres. The main objectives are (1) to determine economic costs associated with switchgrass biomass production, (2) determine biomass yields of switchgrass at the field scale, (3) determine yield and stand stability over years, and (4) evaluate environmental effects, primarily carbon sequestration, of switchgrass grown as a bioenergy crop. Fields were planted on Nebraska farms in 2000 and on South Dakota and North Dakota farms in 2001. Fields were planted with adapted cultivars identified in previous small plot research. Recommended management practices were based on previous small plot research. The study will be conducted for five years.
The results to date clearly demonstrate the need to obtain good stands and the need to control costs the establishment year by the use of good management. Establishment year costs ranged from $35 to $160 per acre. High establishment costs were due to multiple tillage operations and multiple applications of herbicides. Good stands were obtained on several farms with no-till planting and effective use of herbicides at costs of approximately $45 per acre or less. The data from Streeter and other sites indicates that a frequency grid stand of 40% or greater (equivalent to 1 to 2 plants per square foot) is sufficient to produce switchgrass as a bioenergy crop. Biomass yields have varied widely due to drought conditions in the region.
The 19 acre switchgrass biomass production field on the Central Grassland Research Station was seeded to ‘Sunburst’ switchgrass. The field previously had been seeded to oats which were disked and sprayed with the herbicide Banvel prior to planting. Volunteer oats were the main weed problem the establishment year and were mowed. After the volunteer oats were removed, an adequate stand developed but estimated first year yield was about 0.5 ton per acre. At this yield level, cost of harvest is equivalent to the value of the biomass so the field was not harvested. In 2002, the field was fertilized with 54 lbs N/acre shortly after spring greenup and was harvested after the switchgrass had headed. Harvested biomass yield was 2.2 tons/acre on a dry weight basis. Yields will be harvested on all fields for another three years. The production and economic information from this study will be used in economic analyses to determine the potential profitability of switchgrass grown as a biomass crop in the Northern Plains and to plan research to reduce production costs and increase biomass yields.
Fields on all farms were sampled the first year, either prior to or shortly after planting, for soil property analyses including soil carbon concentration. The fields will be sampled again after the five year trial is completed to determine the amount of carbon sequestered in the soil by switchgrass grown and managed as a biomass energy crop. This information may be useful in establishing potential carbon credits. The soil carbon research is being conducted by Dr. Mark Liebig at the ARS laboratory at Mandan, ND.