Spatial variability Factors of soil formation (Jenny) Climate Organisms Parent material Topography
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Transcript of Spatial variability Factors of soil formation (Jenny) Climate Organisms Parent material Topography
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Spatial variabilityFactors of soil formation (Jenny)
•Climate•Organisms•Parent material•Topography•Time
We must live with spatial variation – it is unchangeable and irreducible
How can uncertainty of measurements be reduced?
What are the implications for cost-effectiveness?
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Cultivated field in TN
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# samples
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Intial sample
Re-sample
Sampling costs
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Costs and benefits of reducing uncertainty in accounting for soil
carbon credits
R. T. Conant, Colorado State University
S. Mooney, University of Wyoming
K. Gerow, University of Wyoming
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Background: Value of C credits
• Most producers will require economic incentives to change practices
• Money received by producers is a function of price offered for each credit, perceived uncertainty (i.e., discounting) and transaction costs
• Both uncertainty and transaction costs are related to verification and sampling
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1. Increase duration between sampling 2. Aggregate3. Alter risk acceptance 4. Covariance – re-sample same plots5. Use spatial autocorrelation6. Extrapolate using additional information7. Increase # of samples analyzed
What are the costs/benefits associated w/ these?
Methods to reduce sample variability
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1. Increase duration between sampling
Average Cultivated soil C (top 20cm):
14.5 Mg C ha-1
Accumulation rate(top 20cm):
0.27 Mg C ha-1 yr-1
Soil C pool20cm
2 yearschange = 3.7%
25 yearschange = 46.6%
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1. Increase duration between sampling
Two potential outcomes:
• Decreases the number of samples required for a given precision
• Can increase the precision for a given number of samples
Either way, income potential increases
Question:
• Do future earnings justify reduced sampling now?
Cultivated field in TN
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# microplots
Dif
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# samples
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MMT CSub-MLRA high Sub-MLRA low Summed Sub-MLRAs MLRA
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Mooney, S., J. M. Antle, S. M. Capalbo and K. Paustian. 2004. Influence of Project Scale on the Costs of Measuring Soil C Sequestration. Environmental Management 33 (supplement 1): S252 - S263.
2. Aggregation
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3. Alter risk acceptance
• Reduce the standard error
• Results in smaller confidence interval
xx SxSx 96.196.1
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• Reducing the confidence intervals– Higher producer payments– Possible to achieve at low cost
3. Alter risk acceptance
Cultivated field in TN
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1
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0 10 20 30 40 50 60 70 80 90 100
# microplots
Dif
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(tC
/ha)
P=0.05
P=0.20
# samples
What is the balance between risk and sampling costs?
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4. Covariance
Time 1 Time 2Has management led to changes over time?
Diff? = f(2 (t1-t2) = 2t1 + 2
t2 – 2covt1 t2)
Implication: Large covt1 t2 small 2 (t1-t2)
Small 2 (t1-t2) likelihood of difference
covt1 t2 can be maximized by:ensuring uniform treatments, texture, slope, aspect, etc.re-sampling same location
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d (km)
2
)(d
r d (km)
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)(d
r
D*r
D*r
D*r
• Reducing the confidence intervals– Higher producer payments– Possible to achieve at low cost
Mooney, S., K. Gerow, J. Antle, S. Capalbo and K. Paustian. 2005.The Value of Incorporating Spatial Autocorrelation into a Measurement scheme to Implement Contracts for Carbon Credits. Working Paper 2005 – 101. Department of Agricultural and Applied Economics, University of Wyoming
5. Use spatial autocorrelation
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SWF=spring wheat fallow GRA = grass CSW= continuous spring wheatWWF= winter wheat fallow CWW= continuous winter wheat
Payment $10 $30
0.1R 0.15R 0.2R 0.1R 0.15R 0.2R
Crop system change
SWF_GRA 1.93 4.96 6.57 2.69 6.83 8.93
SWF_CSW 4.19 5.44 6.41 4.14 5.22 5.81
SWF_CWW 15.21 20.10 23.30 10.78 13.95 15.62
WWF_GRA 4.89 11.84 15.50 7.93 19.06 24.71
WWF_CSW 12.50 16.86 20.66 8.21 10.72 12.08
WWF_CWW 19.01 24.89 29.15 18.43 23.54 26.27
CSW_GRA 21.62 32.08 38.84 39.59 57.31 66.67
5. Use spatial autocorrelation
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• No studies that directly examine Krieging to date
• Expect that information about spatial autocorrelation will:– Decrease sample size– Decreasing measurement costs
• Krieging with additional information is best method of extrapolation (Doberman et al.)
6. Extrapolation
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• Increase # samples analyzed– Decrease sample error– Increase confidence interval– Increase cost
CreditPrice
Sample Size
e=10%95% Confid.
e=5%95% Confid.
e=10%99% Confid.
10 1,307 5,109 2,239
20 1,242 4,871 2,133
30 1,199 4,711 2,062
40 1,156 4,543 1,984
50 1,152 4,528 1,977
Mooney, S., J. M. Antle, S. M. Capalbo and K. Paustian. 2004. Design and Costs of a Measurement Protocol for Trades in Soil Carbon Credits. Canadian Journal of Agricultural Economics. 52(3):257-287
7. Increase number of samples analyzed
If analytical costs fall dramatically (due to LIBS, NIR, EC, etc.) risk/uncertainty can be reduced and producers will be the beneficiaries.
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Conclusions
• Soil variation is irreducible• There are several things we can do to increase
statistical confidence in our measurements, thus reducing risk/uncertainty and increasing returns to producers
• Improved analytical techniques could be a significant contributor in the future.