To date, research on biomass has often been an "either-or" proposition, with the bulk of work to date focused on agronomic production or conversion engineering. However, neither of these two links in the supply chain exists independently, nor will they have any value without a well-designed logistics system to move material from farm to refinery and from refinery to market. While a discussion of logistics warrants its own chapter, we briefly consider the challenges of moving biomass to a refinery, particularly as it relates to the agronomic implications.

The sheer scale of a biomass industry that can provide a significant proportion of US energy supplies will make bioenergy production a prodigious undertaking. Huge quantities of biomass will need to be collected and stored safely to provide a constant feedstock supply to the biorefinery. Biorefineries are expected to store only a 72-hour feedstock supply on site, with the remaining feedstock stored at the edge of field or at satellite storage facilities (Hess et al. 2009; Resop et al. 2011). Offsite storage management will be critical to maintain desirable composition characteristics and to ensure feedstock access under variable weather conditions (Mitchell and Schmer 2012). Ideal storage conditions preserve switchgrass so that it enters and leaves the storage phase in an unaltered state (Hess eta l. 2007). Key factors that minimize DM loss and degradation are low moisture levels prior to storage, protection from moisture during storage, low relative humidity, and low temperatures during storage (Mitchell and Schmer 2012). In Texas, DM losses for switchgrass round bales stored for 6 to 12 months inside had 0 to 2% DM losses, whereas bales stored outside lost 5 to 13% of the original bale weight (Sanderson et al. 1997). Tarped and untarped large rectangular bales had DM losses of 7% and up to 25%, respectively, 6 months after harvest in Nebraska (Mitchell et al. 2010b). Proper storage is critical to limit DM losses and maintain quality, but these costs to the system must be weighed against the added costs of storage, handling and processing required for each system.

It is in this context that we reconsider the harvest frequency and timing issue. There is general agreement in the research literature supporting a single, end-of-season harvest as most advantageous. However, this research typically has been disconnected from the one critical factor, logistics, which might give support to alternative harvest timings. There are cost benefits, particularly for dedicated bioenergy production enterprises, when one increases the productive machine hours of equipment invested in the enterprise (Cundiff 1996). In contrast, the infrastructural demands for a system that must capture a year’s supply of biomass during the "off" season will be further magnified by variable weather and field conditions —especially on marginal sites—which will limit field operations. Viewed in this context, the disadvantages of opening the harvest window (in terms of reduced feedstock quality or greater nutrient inputs) may be more than offset by advantages to the system as a whole. Systems that can reduce costs of collection, transport, processing and storage—by spreading harvests through time—would have a competitive advantage, although such management will likely require incentives to the producer to account for the added production costs. While this treatment is a mere "scratching of the surface" of the issues here, it should be clear to the reader that there are numerous interacting factors to be considered all along a bioenergy supply chain (Fike et al. 2007). The costs and benefits of these different components and practices must not be determined independently but rather in the context of the entire system as bioenergy comes on-line.