The Integrated Biomass Supply Analysis and Logistics (IBSAL) model was used to cal­culate cost and energy inputs for the supply chain of biomass (Sokhansanj et al. 2006) . IBSAL consists of different sub-modules for harvesting, processing, preprocessing (grind­ing), storage, and transportation. Model input data include local weather data, average net yield of biomass, crop harvest progress data (including start and end dates of harvest), dry matter loss with time in storage, moisture content of plant at the time of harvest, operating parameters of equipment, and $/hour cost of machinery. The model is built on the EXTEND™ (Imaginethat, Inc., San Jose, CA) platform (http://www. imaginethatinc. com). Main outputs of the model include delivered cost of biomass ($/t), carbon emission (kg of C per t), and energy consumption (GJ/t). IBSAL also calculates dry matter losses of biomass using limited data available for storing switchgrass bales (Sanderson et al. 1997) and handling hay (Rees 1982) . Details of the model can be found in Sokhansanj et al. )2006, 2008) .

The choice of particular size and operating conditions are based on three objectives: (1) the latest model of equipment that are commercially available for forage harvest; (2) the typical operational performance data that are available given by the American Society of Agricultural Engineering (ASAE, which is now the American Society of Agricultural and Biological Engineering [ASABE]) standard on Agricultural Machinery Management Data, ASAE D497 (ASAE 2004) or from manufacturer’s literature; and (3) limited equip­ment performance data published for switchgrass elsewhere. Hourly costs are calculated using the procedure and data described in Sokhansanj and Turhollow (2002). The rates represent the sum of fixed and variable costs. The hourly rates for the pull-type equipment (e. g., baler) are the sum of the hourly rate for the implement and the power equipment (e. g., tractor).

Collection Cost

Square baling cost is the highest at $23.72/t followed by loafing at $19.21/t (Sokhansanj and Turhollow 2002). The low collection cost using loafer is because of its reduced number of operations and the size of the loaf. The higher cost for dry chopping and piling ($35.17/t) and for ensiling ($35.75/t) is because of the higher cost of the forage chopper. Mowing and raking operations are eliminated in silaging operation but the extra cost of pit and packing the silage offsets the lower cost of harvest. The input data for silaging also includes the cost of silage pit at $4757 per year.

The energy inputs range from 0.319 GJ/dry t for loafing to 0.590 GJ/dry t for the dry chop system. The energy inputs are dependent on the size of power used to operate the equipment. Forage choppers require large amounts of power—more than 200kW. Using 16 GJ/dry t as the energy content of dry switchgrass, the energy input to the system ranges from roughly 2% for loafing to less than 4% for dry chopping. The energy expenditure for silaging is slightly less than for dry chopping. Conrado et al. (2005) analyzed switchgrass collection and handling with various types of equipment and concluded that once optimized for switchgrass loafing can become the most cost-effective option.