Wednesday, November 15, 2006

Spatial Distributions of Soil Carbon Pools Affected by Topography and Management Practices.

Xinmei Hao1, Alexandra Kravchenko2, Senthil K. Subramanian1, Alvin Smucker1, and G. P. Robertson3. (1) Michigan State Univ., Crop And Soil Sciences Dept., East Lansing, MI 48824, (2) 376 Plant and Soil Science Bldg, Michigan State Univ, Dept. of Crop & Soil Sciences, Michigan State University, Department of Crop & Soil Sciences, East Lansing, MI 48824-1325, (3) Michigan State University, W.K. Kellogg Biological Station, Hickory Corners, MI 49060

To better describe SOM dynamics, conceptual soil carbon pool models, which distinguish two or more soil C fractions with different decomposition rate in soil organic matter (SOM), have been often employed in SOM models. The objectives of this study were to investigate spatial distributions of soil carbon pools, and their relationships with topography in two management practices: a conventional system with high level of chemical inputs, and an organic system with cover crops and zero chemical inputs. The soil samples were incubated at 25°C and at moisture 65% of soil pore space for about 250 days. The CO2 respiration data were fitted to a double exponential model that separates SOM into active and slow C pools. The resistant pool was obtained by deducting active and slow pools from the total C content. Multiple regressions were conducted to describe relationships between carbon pools with the terrain attributes. The results showed that the sizes of the three C pools were larger in the organic system, relative to the conventional system. In the conventional system, all three pools showed spatial correlation with nugget/sill ratio of 0.5.  In the organic system, the resistant pool showed stronger spatial structure with the nugget/sill ratio close to 0.1 while there was little spatial correlation in the active and slow pools in the system. Multiple regression analysis suggested that active pool was strongly correlated with elevation, with 44 and 38% difference in active pool size explained by elevation in the conventional and organic system, respectively. Topography seemed to have little effect on slow pool in both systems since elevation, slope, plane and profile curvatures all were insignificant in explaining difference of slow pool. In terms of resistant pool, elevation and slope could explain 44 and 32% difference in the conventional and organic systems, respectively.