Crop Residues and Soil Carbon
Rattan Lal
Carbon Management and Sequestration Center
The Ohio State University
Columbus, OH 43210
Estimates of Crop Residues
Production in the U.S.
Species
1991
2001
- - - - - - 106 Mg - - - - - Cereals
325
367`
Legumes
58
82
Oil Crops
17
20
Sugar Crops
25
14
Tubers
5
5
Total
430
488
(Lal, 2005)
Estimates of Crop Residues
Production in the World
Species
1991
2001
- - - - - - 106 Mg - - - - - Cereals
2563
2802
Legumes
238
305
Oil Crops
162
108
Sugar Crops
340
373
Tubers
145
170
Total
3448
3758
(Lal, 2005)
Crop Residue and
Ecosystem Services
Biofuel
Animal
Feed
Industrial
Raw Material
Soil Quality
Improvement
Traditional
Erosion Control
Modern
Liquid
Biofuels
Nutrient Cycling
Soil Biodiversity
Water Management
Soil Structure & Tilth
Carbon Sequestration
1.
Crop residues have numerous competing uses, such as removal for biofuel production, animal
feed, industrial raw material or returned to soil as an amendment.
2.
Soil application of crop residues as amendment is necessary to enhance/maintain soil quality and
sustain agronomic productivity.
Competing Uses of Crop
Residues
•
•
•
•
Feed
Fuel
Fiber
Construction material
Slope-Soil Loss Relations for
Different Mulch Rates (Lal, 1976)
Mulch
Rate
r
Equation
Average
(Mg/ha)
Relative
Loss
0
0.81
Y = 11.8 S1.13
76.60
851
2
0.35
Y = 0.5 S0.87
2.40
27
4
0.57
Y = 0.07 S1.05
0.37
4
6
0.46
Y = 0.01 S1.0
0.09
1
No-till
0.36
Y = 0.01 S0.5
0.09
1
Energy in Biomass
One Mg of Corn Stover =
• 280 L of Ethanol
• 15 - 18 GJ of Energy
• 16 x 106 BTU
• 2 Barrels of Diesel
• 3 x 106 KCal
(Lal, 2005)
Estimates of Traditional Biofuel Use
in India and Asia in 1995
Country/ Fuel wood
Region
Cattle
Dung
Crop
Residue
Total
Range
Average
- - - - - - - - - - - - - - Tg C yr-1 - - - - - - - - - - - - - - India
109 - 409
35 - 108
20 - 67
164 - 584
374
Asia
800 - 930
130 - 200
430 - 565
1360 - 1675 1018
World
1324 - 1615
150 - 410
442 - 707
1916 - 2732 2324
Biofuel From Industrial CO2
and SOC Sequestration
Bioenergy
Bioreactors
Ethanol
Biodiesel
Biochemicals
Cynobacteria
Cynobacteria
Soil Carbon Sequestration
Residues
NutrientEnriched &
Biochar/
Compost
Application on Ag. Soils
Algae
Algae
Strategic Questions
• Should crop residues be used for carbon
sequestration and soil quality improvement or
producing energy?
• Should the answer to this question be
determined by short-term economics or the
long-term sustainability of natural resources?
• Should the need for fuel override the urgency
to achieve global food security?
Soil Carbon Dynamics
Depletion :
Cinput < Coutput
Sequestration: Cinput > Coutput
Soil C Dynamics
Innovative
Technology II
100
Subsistence
farming, none or
low off-farm input
soil degradation
New
equilibrium
Innovative
Technology I
Adoption of
RMPs
Maximum
Potential
80
Rate
ΔY
60
Attainable
Potential
ΔX
Accelerated erosion
40
20
0
20
40
60
80
Time (Yrs)
100
120
140
160
Recommended Management
Practices and Soil Carbon
Recommended practices
C sequestration potential
(Mg C/ha/yr)
Conservation tillage
0.10-0.40
Winter cover crop
0.05-0.20
Soil fertility management
0.05-0.10
Elimination of summer fallow
0.05-0.20
Forages based rotation
0.05-0.20
Use of improved varieties
0.05-0.10
Organic amendments
0.20-0.30
Water table management/irrigation
0.05-0.10
Lawn & Turf
0.5-1.0
Minesoil reclamation
0.5-1.0
Lal et al., 1998
Terrestrial C Sink Capacity
• Historic Loss from Terrestrial Biosphere = 456
Pg with 4 Pg of C emission = 1 ppm of CO2
• The Potential Sink of Terrestrial Biospheres =
114 ppm
• Assuming that up to 50% can be resequestered
= 45 – 55 ppm
• The Average Sink Capacity = 50 ppm over 50 yr.
Potential of Mitigating Atmospheric
CO2
(Hansen, 2008)
Estimates of Global and Regional
Potential of Soil C Sequestration
Region
1.
2.
3.
4.
5.
6.
7.
World:
USA:
India:
Iceland
Brazil:
W. Europe:
China:
Potential Tg C/yr
600 – 1200
144 – 432
40 – 50
1.2 – 1.6
40 – 60
70 – 190
126 – 364
Crop yield and productivity
effects of SOC pool
Unfertilized
SOC Pool
∆ Yield
Crop Yield
Fertilized
SOC Pool
SOC Pool
Soil Quality
SOC Pool
Soil Quality
SOC Pool
Soil Quality
Economics of Residue Removal for Biofuel
Increase in Food Production in LDCs
by Increasing SOC Pool by 1 Mg C ha-1
yr-1
Crop
Area (Mha)
Cereals
430
Production Increase
(106 Mg yr-1)
21.8 - 36.3
Legumes
68
2.0 - 3.2
Tubers
34
6.6 - 11.3
Total
532
30.4 - 50.8
Food Insecure People
Africa = 200 million
World = 800 million
Areas whe re
current popu lation
exceeds potentia l
agricultural capacity
Food Gap by Region
Region
Sub-Saharan Africa
Latin America
Asia
Food Gap
2000
2010
- - 106Mg yr -1 - 10.7
17.5
0.6
1.0
1.7
3.6
Others
0.2
0.2
Total (67 Countries)
13.2
22.3
(Shapouri, 2005)
Commodification of soil C
How can soil C be made a commodity
that can be traded like any other farm
product?
The value of soil carbon
• Value to farmer: for soil quality
enhancement
• Value to society: for ecosystem services
Societal value of soil carbon
• Reduction in erosion and
sedimentation of water bodies.
• Improvement in water quality.
• Biodegradation of pollutants.
• Mitigation of climate change.
On-farm value of soil carbon
• The quantity of NPK, Zn, Cu etc. and H2O retention in
humus.
• Improvements in soil structure and tilth.
• Decrease in losses due to runoff, leaching and
erosion.
~ $200/ton
Need for determining a just value of
soil carbon
• Under valuing a resource can lead to
its abuse.
• It is important to identify criteria for
determining the societal value of soil
C, and using it for trading purposes.
Trading C Credits
The C market may reach $ trillion by 2020.
We need to make this market accessible
to land managers.
Challenges to Trading Soil Carbon Credits
1.
Aggregating small land holders (1-5 acre farm size) to
make a meaningful transaction of 100,000 t C/yr
2.
Assessing net increase in soil C pool on annual basis
over a country/district level.
3.
Determining the societal value of soil C (~$250/t)
4.
Paying farmers a just/fair value
5.
Minimizing transaction costs
Sustainable Management of
Soils
Use of crop residues as soil amendments is
essential so that:
• soil quality is progressively restored rather than
diminished.
• soil organic carbon pool is enriched rather than
depleted.
• susceptibility to erosion and other degradation
processes is reduced rather than exacerbated. and
• agronomic/biomass productivity per unit input and
time is increased rather than reduced or plateaued.
Ten Options of Sustainable
Management of Soils
1. Retain crop residue as mulch.
2. Adopt no-till farming.
3. Include leguminous cover crops in the
rotation cycle.
4. Maintain a positive nutrient balance
INM (e.g., manure, compost).
5. Use precision farming/site specific
management.
Ten Options (continued)
6. Conserve water through sub/drip
irrigation and water harvesting.
7. Restore marginal/degraded/desertified
soils.
8. Grow improved/GM plants along with
agroforestry measures.
9. Integrate principles of watershed
management.
10. Restore wetlands.
Ultimate Goal of Soil
Management
•
•
•
•
The strategy is to:
Adopting RMPs where extractive farming practices
are widely used.
Enhancing SOC pool through use of residue mulch
and manures where soil has been traditionally
mined for millennia.
Using INM (Manure, biosolids BNF, fertilizers) to
achieve positive nutrient balances, where negative
balances have occurred, and
Making agriculture and soil a solution rather than
cause of the environmental problem.
Sustainability of a Land Use
System
S1 =
CNPP
n
(Σ Ci)
i=1
S1
= Sustainability index of a land use system
CNPP
= C output as net primary productivity
Ci
= C input from all factors of production
A Precious Resource
Irrespective of the climate debate, soil
quality and its organic matter content
must be restored, enhanced and
improved.