Effect of the Conservation Reserve Program (CRP)
on Soil Carbon
By
Jay D. AtwoodSteven R. Potter
Jimmy R. WilliamsM. Lee Norfleet
22 March 2005
Atwood and Norfleet are with USDA, NRCS, Resource Inventory and Assessment Division.Potter and Williams are with The Texas A&M University System, Texas Agricultural Experiment Station, Blackland Research and Extension Center, Temple TX
Presented at the “Third USDA Symposium on Greenhouse Gases and Carbon Sequestration in Agriculture and Forestry”, March 21-24, 2005, in Baltimore, Maryland
* 18,446 total NRI CRP points
Figure 2. Regions defined for analysis of 1997 NRI CRP.(only the 8 – digit Hydrologic Units with analyzed CRP points are shaded)
WestNorthern Great PlainsSouthern Great PlainsUpper MidwestSouth CentralNortheastSoutheast
Figure 3. Domain of the 1997 NRI CRP analysis.
*Acres of practices exceed enrollment since each enrolled acre may have multiple practices.
0102030405060708090
100110120
Northeast NorthernGreat Plains
SouthCentral
Southeast SouthernGreat Plains
UpperMidwest
West NationalTotal
% o
f N
RI
CR
P a
cres
Contracted Practice Acres
Modeled for Crop
Modeled for CRP
Matched Successful Simulations
Figure 4. Acreage of crops modeled.
0
1,000
2,000
3,000
4,000
5,000
6,000
Win
ter W
heat
- Fall
ow
Win
ter W
heat
Spring
Whe
at - F
allow
Soybe
anCor
n
Cropl
and P
astu
re
Alfalfa
Hay
Sorgh
um
Cotto
n
Spring
Whe
at
Barley
Oats
Grass H
ay
Perman
ent P
astu
re
Corn
Silag
e
Potato
Peanu
t
Figure 5. CRP cover by type and region
0
10
20
30
40
50
60
70
80
90
Northeast NorthernGreat Plains
SouthCentral
Southeast SouthernGreat Plains
UpperMidwest
West NationalTotal
Percent of areaIntroduced Grass
Native Grass
Trees (with grass)
Wildlife Habitat
Figure 6. Definition of Model Representative Land Units and Crop and CRP simulations for the 1997 NRI CRP points.
NRI CRP Points
Define Prior Crop simulations,with acreage weights, based on NRI crop history
If not corn, wheat or pasture
If corn, wheat or pasture
Determine acreage shares for corn, pasture, and wheat types
Conduct Crop scenario model simulationsfor 3 tillage types for each crop
Crop type 1
Croptype n
Calculate weighted total/average results for Crop Scenario with acreage weights and shares
Define CRP simulations for 4 cover types withacreage weights based on county level CRP enrollment data, e.g., 75% Introduced Grasses 15% Native Grasses 7% Trees 3% Wildlife habitat
Conduct CRP scenario model simulations for each CRP cover type
Calculate weighted total/average results for CRPScenario using acreage weights and shares
Compare Scenarios
Cluster points by region, state, climate, soil, and type of structural conservation practices
Figure 7. Counts and average acreage representation of model land units and simulations by region.
0
1
2
3
4
5
6
7
8
9
Crop CRP
Upper Midwest
Northern Great Plains
South Central
Southern Great Plains
West
Southeast
Northeast
National
0
200
400
600
800
1000
1200
1400
1600
1800
2000
2200
2400
Count Acres (10s)
Upper Midwest
Northern Great Plains
South Central
Southern Great Plains
West
Southeast
Northeast
National
RepresentativeModelLand Units
Simulations per model land unit
Figure 8. Key analytical assumptions
1. If land had not been enrolled in CRP, the former crop mix would have continued, but tillage,
conservation practice, and nutrient management would have evolved like non-enrolled land.
2. Procedures were applied to set initial soil carbon levels at levels consistent with having a
history of cultivation
3. Simulations made with the EPIC model (version with Century model type carbon accounting)
4. Five sets of simulations, each with different stochastically generated weather, were averaged
5. Continuous mono-cropping except for wheat – fallow rotations.
6. Wind erosion calibrated to 1997 NRI levels via lower limit on soil surface moisture
7. Net field level soil loss estimates with Modified Theoretical Small Watershed (MUST) version
of USLE were on average 50% the magnitude of the NRI USLE soil losses
Figure 9. Overview of soil C and N processes in the EPIC model.
• C and N dynamics interact directly with soil moisture, temperature, erosion, tillage, soil density, leaching, and translocation functions of EPIC;
• Equations describe the role of soil texture in stabilization of soil organic matter;
• C and N compounds are allocated into five compartments in terms of turnover time:
– Metabolic litter, with a time span of months;– Structural litter, with a time span of months to years;– Biomass (active), with a time span of months;– Slow humus, with a time span of 20 to 50 years;– Passive humus, with a time span of 400 to 2000 years;
• C and N can be lost through leaching or in gaseous form to the atmosphere;
• There are four key differences between the equations of EPIC and Century (Izaurralde et al., 2001) :
– EPIC’s leaching equations move organic matter from surface litter to subsurface layers;– Temperature and water controls affecting transformation rates are calculated with equations already
in EPIC;– The surface litter fraction in EPIC has a slow, but not passive compartment; and– Lignin concentration in EPIC is modeled as a sigmoidal function of plant age.
Figure 10. Initialization of Soil Carbon (%) Starting Point
Issue – Many of the pedon samples in the soil survey database appear to be from non-cultivated conditions; soil carbon is high relative to cultivated conditions.
Soils in the soil survey data base were screened for “AP” layer, indicating history of cultivation. Those with an “AP” layer and having less than 10% organic matter (5.7% organic carbon i.e., mineral soils only), were used to fit the following equation:
Y = aX -bX
where Y = soil organic carbon (%)
X = depth (in cm)
The equation was initially fit at the hydrologic group level within each of the 10 USDA Farm Production regions. The regions were subsequently combined into four groups.
The equation was used to set the soil organic carbon by layer in all soils for the study except for the “Organic” and “other” texture groups which were left at soil survey levels.
Figure 11. Hydrologic Group Effect of Formula to Set Initial Soil Carbon (%)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
A B C D National
Layer 1 Survey
Layer 1 Formula
Layer 2 Survey
Layer 2 Formula
A – low runoff potential, high infiltration rateB – moderate infiltrationC – slow infiltrationD – high runoff potential, very slow infiltration rate
Figure 12. Regional Effect of Formula to set Initial Soil Carbon (%)
0.0
0.2
0.4
0.6
0.8
1.0
1.2
1.4
1.6
1.8
2.0
2.2
Northeast NorthernGreatPlains
SouthCentral
South East SouthernGreatPlains
UpperMidwest
West National
Layer 1 Survey
Layer 1 Formula
Layer 2 Survey
Layer 2 Formula
Figure 13. Water Induced Soil Loss Estimation
USLE = C*P*R*K*(LS)where C is the crop management factor (range of 0 to 1)
P is the conservation practice supporting factor (range of 0 to 1)R is the rainfall factorK is the soil erodibility factor(LS) is the factor based on slope length (L) and slope (S)
*EPIC calculates USLE daily, with daily C and R The NRI uses long run average annual C and R, prediction of long term annual average soil erosion
MUST replaces R with R = 2.5*(Q*qp)0.5
where Q is runoff volume in mmis a function of daily rainfall, a retention parameter, and soil water content- retention parameter depends on soil, land use, management, and slope
qp is the peak runoff rate in mm per hour
is a function of infiltration characteristics, rainfall intensity, and watershed area* MUST was theoretically derived from sediment concentration data bases MUST is predicted for every storm event; individual storm events are summed for the year
**Except for a few comparison tables and charts, all results based on MUST.
Figure 14. Crop water erosion rates by region, period, and scenario.
0
1
2
3
4
5
6
7
8
9
Northeast NorthernGreatPlains
SouthCentral
Southeast SouthernGreatPlains
UpperMidwest
West NationalTotal
Crop years 1-10
Crop years 11-20
Crop years 21-30
CRP years 1-10
CRP years 11-20
CRP years 21-30
Figure 15. Crop wind erosion rates by region, period, and scenario.
0
2
4
6
8
10
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14
16
18
Northeast NorthernGreat Plains
SouthCentral
Southeast SouthernGreat Plains
UpperMidwest
West NationalTotal
Crop years 1-10
Crop years 11-20
Crop years 21-30
CRP years 1-10
CRP years 11-20
CRP years 21-30
Figure 16. Regional soil carbon storage benefit due to CRP.
-0.2
-0.1
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0.1
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0.3
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0.8
0.9
Years 1 - 10 Years 11 - 20 Years 21 - 30
ton
s/ac
re/y
ear
Southeast
Northeast
Southern Great Plains
Northern Great Plains
West
South Central
Upper Midwest
National
Figure 17. Year end soil carbon by region for non-forage crops and CRP.
15
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85
90
0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
Years
( ton
s/ac
re)
Upper Midwest-CRPUpper Midwest-cropNortheast-CRPNortheast-cropWest-CRPWest-cropNorthern Great Plains-CRPNorthern Great Plains-cropSoutheast-CRPSoutheast-cropSouth Central-CRPSouth Central-cropSouthern Great Plains-CRPSouthern Great Plains-cropNational - cropNational - CRP
Figure 18. Difference in annual soil C change ((CRPt-CRPt-1)-(cropt-cropt-1))*.
Years
*Only non-forage crops included.
-1.0
-0.5
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
(ton
s/ac
re)
NortheastSoutheastUpper MidwestNorthern Great PlainsSouthern Great PlainsSouth CentralWestNational
Figure 19. CRP affect on soil C storage by region, period, and tillage type(non-forage crops only).
-0.2-0.10.00.10.20.30.40.50.60.7
0.80.91.01.11.21.31.41.51.61.7
Conv. Mulch NoTill Conv. Mulch NoTill Conv. Mulch NoTill
y 1 - 10 y 1 - 10 y 1 - 10 y 11 - 20 y 11 - 20 y 11 - 20 y 20 - 30 y 20 - 30 y 20 - 30
ton
s/a
cre/
yea
r
Northeast
Southeast
South Central
S. Great Plains
Upper Midwest
N. Great Plains
West
National
Figure 20. Percent of area losing and gaining > 5% soil C by region and period.
0
10
20
30
40
50
60
70
80
90
100
Crop Loss>5% Crop Stable Crop Gain >5% CRP Loss >5% CRP stable CRP Gain > 5%
Per
cen
t o
f A
cres
Southeast
Northeast
South Central
Upper Midwest
Southern Great Plains
Northern Great Plains
West
National Total
0
10
20
30
40
50
60
70
80
90
100
Crop Loss>5% Crop Stable Crop Gain >5% CRP Loss >5% CRP stable CRP Gain > 5%
Per
cen
t o
f A
cres
Years 1-10
Years 11-20
Years 21-30
0
10
20
30
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60
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90
100
Crop Loss>5% Crop Stable Crop Gain >5% CRP Loss >5% CRP Stable CRP Gain > 5%
Per
cen
t o
f A
cres
Figure 21. Average (non-acreage weighted) CRP C sequestration rates by soil texture group and period.
-0.3-0.2
-0.1
0.0
0.10.2
0.3
0.4
0.5
0.6
0.7
0.8
0.9
1.0t/y/a
Years 1-10
Years 11-20
Years 21-30
Truncated from 6.5, 5.5, and 1.9
Source Spatial Scope Type tons/acre/year
Gebhart et al. (1994) Great Plains Field studies at 5 sites 0.54
Lal et al. (1999) National Average of published studies 0.22
Paustian et al. (2001) Great Plains - grass cover simulation model 0.30
" Great Plains - tree cover simulation model 1.96" Great Plains - overall simulation model 0.42" Central U.S. Two studies, 19 sites -0.21 to 0.83" Illinois cited study - cropland abandoned to
grass0.45
Eve et al. (2003) U.S. - by 10 USDA Farm Production Regions
Intergovernmental Panel on Climate Change
0.04 to 1.25
Kurcharik (2003) Wisconsin 14 paired crop and CRP sites 0.11Sperow et al. (2003) National Intergovernmental Panel on Climate
Change0.15
Lewandrowski et al. (2004)
National, 13 regions Intergovernmental Panel on Climate Change
0.33 to 0.50
Lewandrowski et al. (2004)
National, 13 regions, subset of cropland converted to forest
Intergovernmental Panel on Climate Change
0.75 to 1.66
This study Regional averages, years 1 to 10 0.33 to 0.89 0.60This study Regional averages, years 11 to 20 -0.02 to 0.43 0.16This study Regional averages, years 21 to 30 -0.20 to 0.14 0.06
Figure 22. Estimated CRP Soil C Benefits
Figure 23. Effect of alternative soil erosion and initial soil C on CRP C sequestration rate estimate, national level.
0.0
0.1
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0.9
1.0
Soil Loss Reduction10.5, Soil Survey C
Soil Loss Reduction10.5, Initialized C
* Soil Loss Reduction7.5, Initialized C
Soil Loss Reduction4.7, Soil Survey C
t/a/y
years 1-10
years 11-20
years 20-30Reported
Alternative: CRP erosion benefit of 10.5 t/a/y Soil survey initial C No smoothing for wheat-fallow
20
30
40
50
60
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90
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130
1 3 5 7 9 11 13 15 17 19 21 23 25 27 29
Figure 24. Effect of alternative soil erosion and initial soil C on selected regional C accumulation (tons/acre).
Upper Midwest alternative CRP and Crop CRP erosion benefit of 10.5 t/a/y Soil survey initial C No smoothing for wheat-fallow
NE alternative CRP and Crop
Upper Midwest report CRP and Crop
NE report CRP and Crop
0.0
0.5
1.0
1.5
2.0
2.5
3.0
3.5
2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30
t/a/
y
Northeast - alternative
Northeast - report
Upper Midwest - alternative
Upper Midwest - report
Figure 25. Effect of erosion and initial C on difference in annual C change ((CRPt-CRPt-1)-(cropt-cropt-1))*.
Alternative: CRP erosion benefit of 10.5 t/a/y Soil survey initial C No smoothing for wheat-fallow