County-level Estimates for Carbon Distribution in U.S. Croplands, 1990-2005 - Metadata

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 0.45 (Brady and Weil, 1996). Yield estimates are 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). A mean harvest efficiency of 0.95 was assumed across all crops. Factors used in our estimations are provided in Table 1.

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

• Brady, N.C. and R.R. Weil. 1996. The nature and properties of soils. 11th edition. Prentice-Hall, Inc., Upper Saddle River, New Jersey.
• Hicke, J.A. and D.B. Lobell. 2004. Spatiotemporal patterns of cropland area and net primary production in the central United States estimated from USDA agricultural information. Geophysical Research Letters 31, L20502, doi:10.1029/2004GL020927,2004.
• 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

1. Comma Delimited (CSV)
2. ArcGIS Shapefile (SHP)
   Geographic coordinate system name: GCS_North_American_1983
   Geographic coordinate units: decimal degrees
   Horizontal Datum Name: North American Datum of 1983
   Ellipsoid Name: Geodetic Reference System 80
   Semi-major Axis: 6378137.000000
   Denominator of Flattening Ratio: 298.257222
   Bounding coordinates
   • Horizontal
     • In decimal degrees
         West: -124.732769
         East: -66.969271
         North: 49.371730
         South: 24.956376
     • In projected or local coordinates
         Left: -124.732769
         Right: -66.969271
         Top: 49.371730
         Bottom: 24.956376
3. Data location: http://cdiac.ornl.gov/
4. Data set author:
     Tristram O. West
     Environmental Sciences Division
     Oak Ridge National Laboratory
     P.O. Box 2008
     Oak Ridge, TN 37831-6335
     865-574-7322
     westto@ornl.gov