Crop Residues as Biomass Feedstocks: Fact v' Fiction

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Crop Residues as Biomass FeedstocksFact v.
Fiction
Mike Hubbs, Director, Ecological Sciences
Division, Washington, D.C. and Susan Andrews,
Soil Quality Team Leader and Ecologist, East
National Technology Support Center, Greensboro, NC
USDA Natural Resource Conservation Service
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Interest in Fossil Fuel Alternatives is High

• National security
• Environmental concerns
• Need for renewable energy sources

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Obama Administration Emphasis

• Presidential Directive to accelerate biofuel
  investment and production
• Biofuels Interagency Working Group
• Co-Chairs
• Secretary of Agriculture
• Secretary of Energy
• EPA Administrator
• Funds in Recovery Act and farm bill

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FACT OR FICTION Residue harvest will result in

• Improved conversion technology
• Added farmer income
• Inexpensive for energy producer
• Abundant feedstocks

- Nelson, 2003
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FACT Residues perform valuable Ecosystem Services

• Protection from soil erosion
• Increased soil organic matter (SOM) and
  plant-available nutrients
• Increased biological activity
• Better moisture retention (yield effect)

-after Hargrove, 1991
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Presentation Overview

• Review research on soil effects
• Discuss recommendations for removal
• Outline research needs

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Residue Effects Erosion
-after Lindstrom, 1986
This relationship varies with tillage soil
type - Benoit and Lindstrom, 1987
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Residue Effects Erosion
under no-till
under conv. tillage
-after McCool et al., 1995
Residue removal requires conservation tillage!
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Residue Effects SOM Nutrients

• Net losses of nutrients when residue is removed
  Holt, 1979 Lindstrom,
  1986
• SOM increases not found under conventional
  tillage -Clapp et al., 2000
  Reicosky et al, 2002
• Cooler drier climate allowed more C accrual than
  warmer wetter ones Potter et al. 1998
• More root-derived C than shoot-derived C in SOM
  -Gale and
  Cambardella, 2000

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Residue Effects Organisms other Soil Quality
Indicators

• Wildlife food habitat -NRCS, 2004
• Soils organisms
• Reduced earthworms, microbes Karlen et.
  al., 1984
• Effects on soil pathogens vary
• Physical properties
• Increased bulk density
  -Clapp et al., 2000
• Decreased aggregate stability -
  Karlen et al., 1994

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Residue Effects Yield

• Available Water
• Soil Temperature

• Available Water

• Residue increased water conservation
• -Power et al., 1986 Sauer et al,
  1996
• Higher yield in dry years with residue -Linden
  et al., 2000

• Lower soil temperatures decreased germination
• -Swan et al., 1987, Dam et al., 2005
• Issue in poorly drained, fine textured soils
  
• -Benoit Lindstrom, 1987

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Other Effects Economic Trade-offs

• Potential long-term yield loss
• More field passes fuel use
• Opportunity Costs
• C trading
• Conservation Programs
• Other uses

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Removal Recommendations

• Guidelines for residue removal rates
• Additional Conservation Practices
• Alternative Crops
• Periodic monitoring, assessment, and model
  validation

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Removal Guidelines

• Sustainable harvest
• amounts will vary by
• Management practice
• Crop yield
• Climate
• Topography
• Soil type

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Potential Guideline Tools

• Saskatchewan Web Site
• NRCS Practice Standards
• Erosion Models (RUSLE2, WEQ, WEPP)
• Soil Conditioning Index

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Guidelines Web Site Tools
http//www.agr.gov.sk.ca/docs/econ_farm_man/produc
tion/cereals/mgtpractices.asp
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Guidelines USDA-NRCS Residue Tillage
Management Practice Standards

• Vary by tillage
• Use RUSLE SCI
• gt50 cover for soil moisture
• Latest versions
• include multiple criteria
• dependent on stakeholder goals

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Guidelines Soil Conditioning Index (SCI)

• Expresses organic matter trends as a primary
  indicator of soil condition
• Based on three components
• Organic material produced (biomass)
• Field Operations (tillage or operation passes)
• Erosion (from RUSLE2)

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Guidelines Erosion Model Use

• Nelson (2002), Graham et al. (2007)
• Estimated residues available
• Criteria included meeting T 0.5 T
• Used RUSLE WEQ
• Determined availability to be
• 43 M t of stover 8 M t wheat straw (2002)
• Multiple outcomes based on constraints

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Additional Conservation Practices
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Alternative Crops

• Question viability of biofuels
• -Ulgiati, 2001
• Dedicated energy crops more environmentally
  benign -Giampietro et al., 1997
• Use perennials on marginal lands
• 
  Paine et al., 1996

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Periodic monitoring assessment

• Visual monitoring for increased erosion
• SOC checked as part of fertility tests
• Use adaptive management

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Research Needs

• Systems modeling
• Linking C-dynamics and soil erosion
• Adding alternative practices
• Validation!!!
• Monitor long-term removal effects
  Mann et al., 2002
• Continued research on dedicated, perennial
  bioenergy crops

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Research Needs Guidelines for Residue Removal

• What amount can be sustainably harvested?
• Must consider
• tillage practices
• crop
• yield (and other biomass inputs)
• soils
• slopes
• climate

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Research Needs continued

• Guidelines for Residue Removal
• Simple decision aid
• Practical to do
• Educational

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Fact Summary

• Residues are an important part of sustainable
  agroecosystems
• To remove them mitigating conservation practices
  must be used
• Need additional RD to develop specific
  guidelines for feedstock sustainability