County-level Cropland
Carbon Estimates for the Contiguous
Method of Estimation
The United Sates Department of Agriculture (USDA), National Agricultural Statistics Survey (NASS) produces estimates of crop yields per county per year. These yield estimates can be converted to carbon by converting units reported by NASS to one standard unit (kg), converting to dry matter, and multiplying by a carbon content factor of 0.4 (Brady and Weil, 1996). Yield estimates can be divided by the harvest index to estimate total above-ground biomass. Multiplying aboveground biomass with the root:shoot ratio provides an estimate of below-ground biomass. Finally, summing above- and below-ground biomass provides an estimate for total net primary productivity (NPP). This method follows approaches used by Prince et al. (2001), Hicke and Lobell (2004), and Hicke et al. (2004). Factors used in our estimations are provided in Table 1.
Table 1. Factors used to estimate NPP-carbon for
|
Crop |
Reporting
units |
mass per unit (kg) |
Conversion to Dry matter |
Harvest Index |
Root:shoot ratio |
|
corn
grain |
bushel |
25.4 |
0.87 |
0.53 |
0.18 |
|
corn
silage |
ton |
907.2 |
0.26 |
1.00 |
0.18 |
|
soybean |
bushel |
27.2 |
0.92 |
0.42 |
0.15 |
|
oats |
bushel |
14.5 |
0.92 |
0.52 |
0.40 |
|
barley |
bushel |
21.8 |
0.90 |
0.50 |
0.50 |
|
wheat |
bushel |
27.2 |
0.89 |
0.39 |
0.20 |
|
sunflower |
pound |
0.453 |
0.93 |
0.27 |
0.06 |
|
hay |
ton |
907.2 |
0.85 |
1.00 |
0.87 |
|
sorghum
grain |
bushel |
25.4 |
0.87 |
0.44 |
0.08 |
|
sorghum
silage |
ton |
907.2 |
0.26 |
1.00 |
0.18 |
|
cotton |
bale |
217.7 |
0.92 |
0.40 |
0.17 |
|
rice |
hundredweight |
50.8 |
0.91 |
0.40 |
0.46 |
|
peanuts |
lbs |
0.45 |
0.91 |
0.40 |
0.07 |
|
potatoes |
hundredweight |
50.8 |
0.20 |
0.50 |
0.07 |
|
sugarbeets |
ton |
907.2 |
0.15 |
0.40 |
0.43 |
|
sugarcane |
ton |
907.2 |
0.70 |
0.70 |
0.18 |
|
tobacco |
lbs |
0.453 |
0.80 |
0.60 |
0.80 |
|
rye |
bushel |
25.4 |
0.90 |
0.50 |
1.02 |
|
beans |
hundredweight |
50.8 |
0.76 |
0.46 |
0.08 |
Our final results are provided as carbon in net primary
productivity (NPP), aboveground biomass (AgB),
belowground biomass (BgB), harvested and removed biomass (Harvest), and surface
residue remaining following the harvest (Residue). All units are in Mg C yr-1. The following NASS commodity codes are
represented in our analysis: 11199199, 15499199, 11299999, 11399999, 10199999,
15831999, 18999999, 19599999, 11499199, 12121999, 10619999, 15399199, 39199999,
39299999, 13299199, 13199199, 14133699, 14133599, 14133799, 14133199, 14255599,
14244199, 14122299, 14122399, 14111299, 14111399, 14111199, 10499999, 16199999,
30429929. These represents all crops in
Table 1 including subcategories of tobacco and beans.
References
Hicke, J.A. and
D.B. Lobell. 2004. Spatiotemporal patterns of cropland area and net primary
production in the central
Hicke, J.A., D.B. Lobell, and G.P. Asner. 2004. Cropland area and net primary production computer from 30 years of USDA Agricultural Harvest Data. Earth Interactions 8, Paper No. 10.
Prince, S.D., J. Haskett, M. Steininger, H. Strand, and R. Wright. 2001. Ecological Applications 11(4): 1194-1205.
File formats and
Processing
Geographic coordinate system name: GCS_Assumed_Geographic_1
Geographic coordinate units: decimal degrees
Horizontal Datum Name: North American Datum of 1927
Ellipsoid Name: Clarke 1866
Semi-major Axis: 6378206.400000
Denominator of Flattening Ratio: 294.978698
Bounding coordinates
Horizontal
In decimal degrees
West: -178.225250
East: -66.950474
North: 71.383102
South: 18.913826
In projected or local coordinates
Left: -178.225250
Right: -66.950474
Top: 71.383102
Bottom: 18.913826
3. Data location: http://cdiac.ornl.gov/
4. Data set author:
Tristram O. West
Environmental Sciences Division
865-574-7322
westto@ornl.gov