Grandy, A. Stuart (Michigan State University, W.K. Kellogg Biological Station, 3700 E. Gull Lake Drive, Hickory Corners, MI, 49060; Phone: 269-671-2336; Email: email@example.com)
Is Carbon Sequestration Following No-till Conversion Associated with Changes in Crop Yields and Nitrogen Cycling?
A.S. Grandy *, T.D. Loecke, G.P. Robertson
Soil carbon sequestration and greenhouse gas abatement in agriculture are two of a limited number of rapidly-deployable, high impact CO2 stabilization options now available to policy makers. No-till cropping generally increases soil C stocks but its deployment has been limited by the perception that accelerated rates of N leaching and immobilization may limit N availability and decrease yields. We studied the effects of no-till conversion on C sequestration and annual patterns of nitrous oxide flux, soil moisture, soil physical properties, and crop yields in a corn-soybean-wheat cropping system in southwestern Michigan. Our measurements were initiated six years after no-till conversion in order to target long-term changes in yields and associated environmental processes and continued for six to eight years. No-till increased organic C concentrations from 0.94 to 1.24 kg m-2 (30.0 g C m-2 y-1) but had little effect on total N2O emissions. Although no-till management modified soil inorganic N concentrations during the growing season (e.g. in 1996 average soil NO3-N concentrations were ca. 16 µg g-1soil in conventional till and 13 µg g-1 in no-till ) average yields of all three rotation crops were unaffected by tillage management suggesting that altered N availability did not limit plant productivity. In 2001, 15 years after conversion, no-till increased soil aggregate mean weight diameter from 1.3 to 2.1 mm but did not significantly alter bulk density to 5 cm. Our results suggest that crop yields potentially remain stable long after no-till conversion and that increased C sequestration and aggregation and decreased global warming potential (GWP) are not necessarily accompanied by meaningful declines in N availability.