Submitted to: Soil Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/15/2004
Publication Date: 11/1/2004
Citation: Venteris, E.R., McCarty, G.W., Ritchie, J.C., Gish, T.J. 2004. Soil organic carbon and soil redistribution: Influence of site history and site variables. Soil Science. 169(11):787-795. Interpretive Summary: Soil organic carbon and soil erosion were measured for a long term study site in Beltsville, MD. The goals for the study site are to investigate water and soil quality issues related to agricultural production. A grid of 271 soil cores (30cm depth) was collected as part of the characterization of the site. In addition, historical airphotos and a digital elevation model were compiled. Annual average soil moisture was estimated from cropping response (yield) measurements. The airphoto clearly showed that three quarters of the study site were maintained as swine pasture, and the remaining portion was cropped for forage. A large gradient in soil properties was noted across the boundary between these two land uses. Erosion rates are larger and soil organic carbon amounts lower for the cropped portion of the site. However, causation cannot be confirmed because the crop area occupies a different landscape position than the swine pasture. Soil organic carbon and erosion were not strongly related to terrain parameters (slope, wetness index, etc.) or soil moisture estimated from crop yields. It was found that some wet spots on the field were associated with large soil carbon amounts, and others were not. High carbon was also found in areas that were not predicted to be wet by either terrain or cropping response. The study illustrates the difficulties in interpreting processes for sites with complex interactions between management, topography and soil hydrology. Such complexity may make the mapping of soil properties for areas larger than individual fields challenging.
Technical Abstract: In 1993 a study site was started in Beltsville, MD to investigate the interaction between soils, hydrology, climate and crop management. Soil cores (271) were collected in a 30 meter grid (with 5m nesting) and analyzed as part of the site characterization. Soil organic carbon and 137Cs (for erosion) were measured. Analysis of aerial photography from 1992 and from farm records revealed that part of the site had been maintained as a swine pasture and the other portion as cropping land. Soil properties, particularly erosion and carbon, show large differences in mean values between the two areas, with a sharp gradient near the pasture /crop boundary. The data suggest a management influence, but topographic position is a confounding variable. Soil organic carbon contains strong spatial structure with a regionalized variable of 120m. 137Cs activity lacks spatial structure, suggesting disturbance of the profile by animal activity and past structures such as swine shelters and roads. Neither soil organic carbon nor 137Cs were strongly correlated to terrain parameters or soil moisture predicted from cropping response. In addition, soil organic carbon and 137Cs are not strongly correlated in this landscape (r2~0.2). The study illustrates the importance of gathering past site history when interpreting the landscape distribution of soil properties, especially those strongly influenced by human activity such as SOC and 137Cs. Confounding variables, complex soil hydrology, and incomplete documentation of land use history make definitive interpretations of the processes behind the spatial distribution of these soil properties difficult for the site. Such complexity is significant because it may limit the accuracy of scaling approaches to mapping SOC and soil redistribution.