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Maintaining soil fertility in biomass for bioenergy production systems John Raison CSIRO Ecosystem Sciences Energy Transformed Flagship IEA Bioenergy, November 2011
Maintaining soil fertility in biomass for
bioenergy production systems
John Raison
CSIRO Ecosystem Sciences
Energy Transformed Flagship
IEA Bioenergy, November 2011
CSIRO.
Outline
•Central role of soils in ecosystem
function
•How biomass production systems can
negatively impact on soil fertility
•The need for active management to
protect soil values, and a few examples
•Conclusions
CSIRO.
Linkages between forest management, soils,
and other forest values
Forest Management Activities
Changed physical, chemical and biological properties of soils
Changed Soil Functional Process
(nutrient and water supply, aeration, root growth, biological activities, carbon cycling and storage)
Ecosystem Functional Responses
(regeneration, species composition and N fixation, habitat and fauna, water quality, productivity, C
storage, wood production)
Socio-Economic Consequences
(e.g. forest industry, biodiversity, recreation, water)
CSIRO.
Management can degrade soil fertility
•Accelerated erosion
•Disturbance/compaction
•Nutrient depletion
•Acidification
•Biological changes
CSIRO.
Bioenergy creates extra challenges
• More frequent harvest
- greater soil disturbance
- increase rate of nutrient removal
• Sometimes more complete (foliage and stems) removal of biomass (C and nutrients). How to judiciously manage fertilizer inputs?
• Sometimes new fast growing species
CSIRO.
Monitoring changes in soil fertility
Broad Soil Indicator Key Functions Field Measure
Physical change root growth bulk density/soil strength
aeration macro-porosity
water movement hydraulic conductivity
Chemical change nutrient supply SOM, N&P availability
acidification pH, base exchange
Erosion risk many disturbed soil,
cover, infiltration
Pollution soil biology, toxicity accumulation of chemicals
CSIRO.
Soil physical disturbance
CSIRO.
Surface (0-10cm) Soil Bulk Density (Mg m-3)
Undisturbed
General Harvest
Snig Tracks
Access road
Landing
0.4 0.6 0.8 1.0 1.2 1.4
E. regnans
CSIRO.
0
2
4
6
8
10
12
14
16
18
Log Landing Primary Snig Heavy
Disturbance
Secondary
Snig
Medium
Disturbance
Tertiary Snig Low
Disturbance
No
Disturbance
Disturbance Level
E.
reg
nan
s s
ap
lin
g d
bh
(cm
)Soil disturbance can lower growth of
the regenerating forest
CSIRO.
Av Rut Depth 85mm Av Rut Depth 102mm Av Rut Depth 156mm
1 Forwarder Pass 4 Forwarder Passes 16 Forwarder Passes
Average Soil Moisture: 38.5% w/w
16.6% Above Lower Plastic Limit
Rutting depthRutting depth
Soil rutting
CSIRO.
Minimizing soil physical damage
•Using harvesting residues to protect the
soil from ‘traffic’
•Ceasing harvest on wet soils
•Machines with low ground pressure
•Harvest when soils frozen
CSIRO.
Soil organic matter is important
Soil
chemical
properties
Soil
physical
properties
Soil
biological
properties
CSIRO.
Soil Organic Carbon Cycle
CSIRO.
Organic C
content = ƒ ) ( Inputs of
organic C
Losses of
organic C ,
Inputs
Losses
Throttles or rate determinants
What determines SOC change?
CSIRO.
Labile soil C controls rates of nutrient
cycling
labile
organic matter
microbes
mineral
nutrients
plant litter
recalcitrant organic matter
plant uptake
charcoal
CSIRO.
Mallee eucalypt production system
CSIRO.
Mallee eucalypts in WA - annual biomass and
nutrient export under 3 - 4 year harvest regimes.
• Biomass 5.9 - 7.5 t/ha
• Nitrogen 46.7 - 50.1 kg/ha
• Phosphorus 3.9 - 4.7 kg/ha
• Calcium 32.2 - 46.6 kg/ha
Amounts exceed those in wheat cropping
CSIRO.
Recovery of nutrients added in
Fertilizer is often very low
•Nitrogen – often < 50%
•Phosphorus - low, but high soil
retention
CSIRO.
Soil acidification after N fertilization
3.6
3.7
3.8
3.9
4.0
4.1
4.2
4.3
4.4
4.5
Soil pH (KCl)
0-10 10-20 20-30 30-40
Depth (cm)
N4P4
N2P2
N0P0
CSIRO.
Acidification increases exchangeable
soil Aluminium
0-10 10-20 20-30 30-40
0
10
20
30
40
50
60N0P0
0-10 10-20 20-30 30-40
0
10
20
30
40
50
60N2P2
0-10 10-20 20-30 30-40
0
10
20
30
40
50
60
Mound
Flat
Trough
N4P4
Depth (cm)
Exchangeable Al.
(m.eq kg-1)
CSIRO.
Depletion of exchangeable soil
Calcium
0-10 10-20 20-30 30-40
0
10
20
30
40
0-10 10-20 20-30 30-40
0
10
20
30
40
0-10 10-20 20-30 30-40
0
10
20
30
40
Mound
Flat
Trough
Depth (cm)
N0P0
Exchangeable Ca. (m.eq kg-1)
N2P2
N4P4
CSIRO.
Cation (Ca, Mg) replacement by ash recycling
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Nutrient Returns
• Ash recycling after combustion
• ‘Natural’ fertilizer treatment
• Ground-based or aerial application
• Cost can be cheaper than landfilling ash
• Precautions - avoid spreading ash from
co-firing
• Ash recycling after combustion
• ‘Natural’ fertilizer treatment
• Ground-based or aerial application
• Cost can be cheaper than landfilling ash
• Precautions - avoid spreading ash from
co-firing
CSIRO.
Soil Protection is critical
•Soil influences most forest values (biological, social, economic). Off-site effects can be significant (eg. on water)
•Difficult to generalize about the risks created by specific management practices
•Need site-level assessments of risks and impacts, and management guidelines. Reflected in manag. plans
CSIRO.
How can we protect soils?
• Undertake ‘local’ assessments of the risks to soil fertility imposed by biomass production systems
• Develop and apply management prescriptions that mitigate risks of erosion and soil compaction
• Retain nutrient-rich biomass, avoid burning of in-field residues
• Lengthen rotations to reduce [nutrient] in harvested biomass
• Incorporate a legume in the production system if possible
• Judicious use of fertilizers, return ash to site
• Drainage and disturbance of peat will lead to massive C losses!
CSIRO.
Adaptive production systems ‘Framework’
(stakeholders set goals, indicators and targets)
Operational guidelines (implementation)
Monitored Outcomes (use of indicators)
Evaluation processes (comparison with goals, targets)
Agreed Responses (adaptation of plans or guidelines)
Reports to stakeholders
Plans
CSIRO.
Tiered Approach to Soil Protection
AIM is to avoid the need for expensive rehabilitation practices.
1.Broadscale auditing for compliance with Codes of Practice (good practice rules/guidelines).
2. Monitoring of soil disturbance classes on selected sites based on risk.
3. R&D on representative important forest types/management systems to calibrate disturbance classes or other simple monitoring methods, and to provide a basis for evaluation of change.
4. Review and improvement ethic.
CSIRO.
Thank you
Energy Transformed Flagship
John Raison
Phone: +61 (0)2 62464053
Email: [email protected]
Web: www.csiro.au/org/EnergyTransformedFlagship
Contact Us
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