Biomass composition in cool-season pastures harvested for energy in southern Iowa
Approximately one hundred fifty thousand hectares of pasture and grassland exist in the four-county area near the Ottumwa Generating Station in Chillicothe, Iowa. Most of this land is dominated by cool-season grass species that are well adapted to the area and are managed with little fertilizer and chemical inputs. If yield and composition of these cool-season species are acceptable, they could be potentially used as the biofuel portion in co-firing with coal. Ten sites in the surrounding area were evaluated. Across these sites, 26 different plant species were identified, with a single site having between 5 and 14 species. Biomass yield was determined at several sampling locations within each site. Biomass yield varied significantly among sites, but there was more variation in yield within sites than among them. Yields at each site ranged from as low as 0.75 mtons/ha to as high as 8.24 mtons/ha. Mean yield across all locations was 4.20 mtons/ha. Fuel characteristics of the cool-season species were evaluated for burning qualities. Concentrations of ash, chlorine, and sulfur are important for determining suitability in a biofuel. Ash content of the sites ranged from 58.5-118.1 g/kg DM. Chlorine content of the sites ranged from 0.8-7.6 g/kg DM and sulfur content ranged from 0.7-3.4 g/kg DM. Near infrared reflectance spectroscopy (NIRS) was evaluated as a means to determine burning quality traits. Acceptable NIRS calibrations were achieved for ash, carbon, and nitrogen, but not for volatile, sulfur, and chlorine. These results indicate that cool-season pastures can produce biomass of sufficient yield and quality to supplement other sources for co-firing with coal to generate electricity.