Topography Influences Management System Effects on Total Soil Carbon and Nitrogen

Topography is one of the major factors affecting sod C and N contents at the field/landscape level. However, topographical effects are likely to differ in magnitude in different agricultural systems. The objective of this study was to examine the interactions between topography and management systems on Soil C and N. The study was conducted at the Kellogg Biological Station Long-Term Ecological Research (LTER) site in southwest Michigan. The studied treatments were chisel-plow (CT) and no-till (NT) with conventional chemical inputs and a chisel-plow organic management system with winter leguminous cover crops (CT-cover). At the 0- to 5-cm depth in both upperslope and valley positions total C and N contents of NT management were the highest followed by CT-cover and then CT At 0- to 15-, 20- to 30-, and 30- to 40-cm depths, treatment effects varied depending on the landscape position. There were no differences among the treatments in upperslopes, while in the valleys total C and N tended to be the highest in NT and CT-cover followed by CT. The results indicated the importance of accounting for interaction between topography and management practices when assessing C sequestration across landscapes with varying topography. Total C stocks at the 0- to 30-cm depths were around 35,32, and 27 MgC ha(-1) soil (+/- 2 MgC ha(-1) standard error) in CT-cover, NT and CT respectively, across upperslopes and valleys. Overall, CT-cover was found to be as efficient in maintaining C and N content as no-till with conventional chemical inputs. Power analysis for C and N stocks at the 0- to 40-cm depth revealed that because of high variability in total C and N stocks at greater depths, the 10 to 30 samples per treatment available in this study were inadequate to detect differences in C and N stocks if thh differences were < 26 MgC ha(-1).