Soil Organic Carbon under Native and Cropped Land Use
Abstract
Soil samples were collected from soil pits at depths of 0 to 5 and 5 to 10 cm and by genetic soil-horizon thereafter, with data reported to 1 m depth. Weights of soil organic carbon (SOC) by profile layer were calculated using thicknesses, bulk densities, and C analyses data. Recalculation for discrete depth increments from the horizon data was necessary to statistically analyze and report the SOC for depth increments of 0 to 10, 10 to 20, 20 to 30, 30 to 60, and 60 to 100 cm. The Soil Extent Mapping Tool of the NRCS provided a snapshot, by soil survey area, of where and the size of the areas by county of the soil series sampled in this study. Estimated combined acreage of the 21 soil series, for these 30 paired native and cropped sites, was 9 Mha within 18 states. To estimate the equivalent amount of SOC represented required that the data be area-weighted and statistically analyzed. On an area-weighted basis 131,890 and 98,470 kg SOC per ha were found in the top 100 cm of the native and cropped sites, respectively. Comparison of the difference of ‘native minus cropped’ as an estimate of area weighted SOC losses from cropped soils in for the 0-to 100 cm depth was that 43, 58, and 75% of the total was from the 0-to 10, 0-to 20, and 0-to 30 cm depths, respectively. The area-weighted average-decrease of SOC within the 0-to 100 cm depth (native minus cropped) was 3.0 Tg SOC across 9 Mha. If similar differences exist between native vs. cropped land across the entire 137.6 Mha of US cropland, a total SOC loss would be equivalent to 46 Tg SOC, or equivalent to 170 Tg (0.17 Pg) CO2.
- Publication:
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AGU Fall Meeting Abstracts
- Pub Date:
- December 2009
- Bibcode:
- 2009AGUFM.B51C0323F
- Keywords:
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- 0402 BIOGEOSCIENCES / Agricultural systems;
- 0428 BIOGEOSCIENCES / Carbon cycling