|Karlen, Douglas - Doug|
|Moorman, Thomas - Tom|
Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/21/2000
Publication Date: N/A
Citation: Interpretive Summary: To assist Congress in developing and evaluating conservation programs and policies to promote practices that increases soil organic carbon (SOC) levels on private lands in the US, a statistically valid and efficient method is need for monitoring SOC at the field, region, and national scales. The National Resource Inventory (NRI) conducted by the USDA- Natural Resources Conservation Service (NRCS) may provide such monitoring tool, but it has never been evaluated for its potential to monitor SOC levels. The purpose of this research was to evaluate use of the NRI to estimate SOC levels in four different regions of the country. Significant differences in SOC levels under different land-use practices could be detected in each region. The precision with which SOC levels could be estimated ranged from 0.5 to 5.0 Mg ha-1 with greater precision in areas with lower SOC levels. Results indicated that the NRI may be used for evaluating the effects of different land-use practices on SOC levels at a regional scale. Repeated sampling of the same NRI points over time would allow NRCS to estimate the amount of carbon sequestered in or lost from the soil with changes in land-use at a regional scale. The development and adoption of conservation programs in combination with regional and national NRI assessments to evaluate the effectiveness of these programs could help improve the quality and productivity of the nation's soils and help sequester carbon, potentially reducing atmospheric CO2 concentrations.
Technical Abstract: The National Resource Inventory (NRI) may be used to estimate soil organic carbon (SOC) levels at a regional scale if accurate and precise estimates can be made across a wide range of soils, land-uses, and topographic positions. The objectives of this study were: 1) identify important sources of variation in SOC content at a regional scale; and 2) determine the precision with which SOC content can be estimated. Surface soil samples (0 to 10 cm) were collected in four Major Land Resource Areas and analyzed for SOC, sand, silt, and clay content. Land-use, hillslope position, and slope aspect effects on SOC levels were evaluated by analysis of covariance with sand or clay content as a covariate to adjust for textural differences at each sample point. Land-use was a significant source of variation in all four regions. Hillslope position and slope aspect were significant sources of variation in only one of the four regions and there were no significant interactions between land-use and hillslope position or aspect. Standard errors (SE) ranged from 0.5 to 5.0 Mg ha-1 and were lowest in regions where SOC levels were also lowest. Results indicate the NRI can be an effective tool for estimating SOC levels under different land-use and conservation practices on a regional scale.