Course: BFM 101 Biofuels Fundamentals

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Limits of Biomass Supply
Use of Invasive Species

Limits of Biomass Supply Continued
Limits of Biomass Supply Continued

Biomass Variability

Suitability of biomass types will vary from place to place (figure 4.3).  Not all biomass types can be grown everywhere, nor can they be grown in the same quantities everywhere.  Suitability to location influences yield.  In places where a crop is well-suited, for example, it is generally expected that yield will be high and in places where it is not suited yield will be low.  In extremely unfavorable conditions, a crop will not grow at all.  Even in locations where plants are well matched to their environment, yields will vary year-to-year as a result of natural fluctuations in precipitation, temperature and cloud cover.

Crop choice is influenced by profitability of a particular crop relative to that of other crops.  Profitability of a particular crop is determined by crop yield and the price the producer can get for the crop minus the costs of crop production (e.g., fertilizer, pesticides, fuel for equipment, seed, etc.) and minus the cost of transporting the harvest to the buyer (figure 4.4).

Figure 4.4.  Profitability of agricultural production is determined by the difference between price for harvested materials minus the costs of production.  For biomass producers hauling materials to conversion facilities is a cost that increases with distance from conversion facility.  (CL Williams, 2011.)

Costs of Transporting Feedstocks

Costs of hauling increases with distance from the buyer of harvested material. Hauling distances may be great enough that costs of hauling materials may be equal to or exceed the price the producer can receive for harvested materials.  Therefore, for biomass producers, there is a maximum distance from a biomass processing facility beyond which it is unprofitable to grow, harvest and transport biomass.  This dynamic is a limiting factor on amount of biomass that will be produced under various economic conditions (e.g., cost of transportation fuel and price for biomass).  That is, producer willingness may reduce the amount of “available biomass” compared to availability of suitable land and estimated yields on those lands.

Impact of Bioenergy Crop Production on Land Productivity

Farmer willingness to market agricultural residues for bioenergy may also be constrained by concerns of agronomic and environmental consequences to the long-term productivity of their lands.  For example, removal of crop residues like corn stover (figure 4.5) have been associated with increased soil erosion, soil compaction (which effects permeability), and loss of soil carbon (which effects soil fertility and thus yields).  Residue removal does not always result in negative impacts on soil or other environmental resources because impacts are highly dependent on geophysical characteristics of specific locations.  However,

robust scientific models (e.g., RUSLE2-Revised Universal Soil Loss Equation, Version 2) are available for estimating likely impacts of residue removal under a variety of location-specific soil and slope conditions.  Management intervention may offset negative impacts of residue removal (e.g., increased nitrogen fertilizer to offset loss of soil organic matter), but such management activities will increase production costs and potentially reduce profitability.

Biomass Storage

Storage of biomass is another potential limiting factor affecting biomass availability. Biomass production is seasonal; as such, biomass must be stored for it to be available on-demand throughout the year.  Storage of biomass materials results in loss of carbon – the essential portion of plant materials for conversion to bioenergy.  Thus, any estimate of the potential volume of biomass available for bioenergy must account for carbon loss during storage

Resources provided by the eXtension Farm Energy Community of Practice at http://www.extension.org/ag+energy

Limits of Biomass Supply
Use of Invasive Species