Course: BFM 101 Biofuels Fundamentals

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Limits of Biomass Supply Continued

Limits of Biomass Supply
Limits of Biomass Supply

Land availability, yield potential, and other important  constraints influence the potential supply of biomass.  Government studies indicate that meeting federal renewable fuel goals would require 1 billion dry tons of biomass annually, including 215 million tons from dedicated perennial energy crops.  Such figures are based on estimates of the amount of available land for specific biomass sources, expected yields across a range of environmental conditions, and assumptions about yield potentials, use of external inputs like nitrogen fertilizers, and efficiencies of management activities (e.g., planting and harvesting).  However, constraints on biomass supply – effects of management activities, producer willingness to grow and harvest biomass, logistics of conversion facility location, and biomass storage losses – may cause a gap between the amount of biomass estimated as potentially available and that which is actually produced.

Several government funded analyses indicate that in terms of suitability of lands for biomass production, sufficient acres exist for biomass production.  However, the actual amount of land that is likely to be used to produce biomass will undoubtedly be somewhat less than these analyses suggest.

Limiting factors

Land availability for the production of biomass is determined by complex decision making about land use (portrayed graphically in figure 4.1). Producers must consider the following factors in decision-making:

1. Geophysical characteristics of a location (e.g., climate, soil type, and slope),

2. Socio-economic factors:

- competing land uses and the perceived financial or other benefits of each use (opportunity cost)
- land owner and land manager experiences and preferences
- policy incentives,
- technology inputs, and whether the farmer has access to appropriate equipment and infrastructure for crop production, harvest, storage, and transportation,
- availability of markets.

Figure 4.1. A number of factors influence land use decision-making, which in turn influences availability of land for production of biomass for bioenergy. (CL Williams, 2011).

Yield Gaps in Bioenergy Crop Production

To meet competing land uses for food, feed, fiber and fuel, many experts assert that crop yields (per acre basis) will need to increase.  Although many experts estimate there is already sufficient supply of biomass from forest, agricultural and waste resources for meeting current and future demands for bioenergy, there is no scientific consensus regarding the simultaneous fulfillment of food and feed needs.  Yield potential of biomass sources is constrained by plant genetics and the environments in which plants grow (specifically solar radiation, temperature and water supply).

The climatic and genetic upper yield boundary of crops (yield potential) far surpasses the average yield (that which farmers actually produce, as an average).  Yield gaps – the difference between average and potential yields – result from environmental stresses (e.g., insufficient water supply) and effects of management (planting dates, tillage methods, pest management, etc.), as depicted in figure 4.2.  Efforts to decrease yield gaps have focused on:

- Decreasing yield gap between average yield and attainable yield through management and technology improvements (e.g., addressing factors that limit yield, such as water and nutrient availability)
- Overcoming the limits of plant traits (using plant breeding or biotechnology) to improve tolerance to environmental stress.

Biotechnology has a significant role in yield improvements of bioenergy crops, including annual and perennial crops and non-forest biomass sources of woody materials such as poplar and aspen trees (discussed further in the fact sheet on biotechnology).

Figure 4.2.  Yield gaps occur between the upper limits of a crop’s potential and that which farmers actually produce.  Crop genetics, environmental conditions, pest pressures and management influence yield gaps.  (CL Williams, after Network for Sustainable Agriculture.)

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

Limits of Biomass Supply Continued