Evaluating environmental consequences of producing herbaceous crops for bioenergy

Abstract

The environmental costs and benefits of producing bioenergy crops can be measured both in terms of the relative effects on soil, water, and wildlife habitat quality of replacing alternate cropping systems with the designated bioenergy system, and in terms of the quality and amount of energy that is produced per unit of energy expended. While many forms of herbaceous and woody energy crops will likely contribute to future biofuels systems, The Department of Energy's Biofuels Feedstock Development Program ( B F D P ) , has chosen to focus its primary herbaceous crops research emphasis on a perennial grass species, switchgrass (Panicum virsatum) , as a bioenergy candidate. This choice was based on its high yields, high nutrient use efficiency, and wide geographic distribution, and also on its positive environmental attributes. The latter include its positive effects on soil quality and stability, its cover value for wildlife, and the lower inputs of energy, water, and agrochemicals required per unit of energy produced. A comparison of the energy budgets for corn, which is the primary current source of bioethanol, and switchgrass reveals that the efficiency of energy production for a perennial grass system can exceed that for an energy intensive annual row crop by as much as 15 times. In additions reductions in CO, emissions, tied to the energetic efficiency of producing transportation fuels and replacing non-renewable petrochemical fuels, are very efficient with grasses. Calculated carbon sequestration rates may exceed those of annual crops by as much as [20][21][22][23][24][25][26][27][28][29][30] times, due in part to carbon storage in the soil. These differences have major implications for both the rate and efficiency with which fossil energy sources can be replaced with cleaner burning biofuels. Current research is emphasizing quantification of changes in soil nutrients and soil organic matter to provide understanding of the long term changes in soil quality associated with annual removal of high yields of herbaceous energy crops.

Managing and enhancing switchgrass as a bioenergy feedstock

“…41 In addition to increasing soil carbon (C), growing switchgrass may increase wildlife habitat, increase landscape and biological diversity, increase farm revenues, and return marginal farmland to production. [45][46][47][48] Not harvesting some switchgrass each year would increase the habitat value for grassland bird species that require tall, dense vegetation structure. 47 …”

Effects of nitrogen fertilization on biomass yield and quality in large fields of established switchgrass in southern Iowa, USA

“…Experiments funded principally by the United States Department of Energy over the past two decades have shown that switchgrass is also a model herbaceous species for bioenergy production because of its perenniality, wide geographic distribution, high nutrient use efficiency, relatively low fertilization requirements, high biomass yield potential, and compatibility with conventional farm practices [2,3]. In order for switchgrass to be used to generate electricity by cofiring with coal, a substantial amount of biomass would need to be produced in the area close to the generating plant.…”

“…Previous studies suggest that the annual nitrogen requirement of switchgrass is about half that required for maize (Zea mays L.) production, or between 70 and 100 kg ha À1 [3]. Optimizing the application of nitrogen spatially and temporally is important to reach desirable switchgrass biomass yields without jeopardizing water quality or economic returns in the process [4].…”

Estimation of Rhizome Composition and Overwintering Ability in Perennial Sorghum spp. Using Near-Infrared Spectroscopy (NIRS)

“…Perennial sorghum cropping systems offer agroecological benefits not present in annual row crop production such as increased soil organic carbon, reduced soil erosion, reduced inputs requirements, and higher net energy return [10][11][12][13][14]. Land use change could be minimized in such systems through the utilization of marginal croplands or abandoned grasslands.…”