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SOIL & WATER MANAGEMENT & CONSERVATION

Topography Influences Management System Effects on Total Soil Carbon and Nitrogen

^a Department Of Crop and Soil Sciences, Michigan State University, East Lansing, MI 48824
^b W.K. Kellogg Biological Station, Michigan State University, 3700 E. Gull Lake Drive, Hickory Corners, MI 49060

^* Corresponding author (kravche1{at}msu.edu).

Topography is one of the major factors affecting soil 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 Mg C ha^–1 soil (± 2 Mg C ha^–1standard 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 Mg C ha^–1.

Abbreviations: CT, conventional tillage (chisel-plowed) corn–soybean–wheat rotation system with conventional chemical inputs • CT-cover, conventional tillage (chisel-plowed) corn–soybean–wheat rotation with zero chemical inputs and leguminous cover crops • LTER, Long-Term Ecological Research Site • NT, no-till corn-soybean-wheat rotation with conventional chemical inputs