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Title: EXAMINING CHANGES IN SOIL ORGANIC CARBON WITH OAT AND RYE COVER CROPS USING TERRAIN COVARIATES

Author
item Kaspar, Thomas
item Parkin, Timothy
item Jaynes, Dan
item Cambardella, Cynthia
item Meek, David
item JUNG, Y - KANGWON NAT'L UNIVERSITY

Submitted to: Soil Science Society of America Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 1/13/2006
Publication Date: 3/29/2006
Citation: Kaspar, T.C., Parkin, T.B., Jaynes, D.B., Cambardella, C.A., Meek, D.W., Jung, Y.S. 2006. Examining changes in soil organic carbon with oat and rye cover crops using terrain covariates. Soil Science Society of America Journal. 70:1168-1177.

Interpretive Summary: Oat and rye cover crops have the potential to increase soil organic matter in corn and soybean rotations in Iowa and reduce emissions of greenhouse gases from agricultural fields. Previous research has shown that cover crops can be established in the upper Midwest by overseeding oat and rye cover crops into soybean in August before leaf drop. Measuring increases in soil carbon caused by cover crops is difficult, however, because of the large variation in soil carbon related to landscape position. This experiment showed that by modeling the variation in soil carbon across the landscape we can remove that variation from the carbon measurements and obtain a more accurate measurement of the change in soil carbon caused by the cover crops. Rye cover crops overseeded into soybean increased soil carbon levels in the year following soybean but this higher soil carbon level was not maintained in the year following corn. Oat and a mixture of oat and rye did not increase soil carbon. Oat and rye cover crops still have the potential to increase soil carbon levels in corn-soybean rotations, but cover crops probably need to be also planted following the corn crop to maintain higher soil carbon levels. This research will benefit scientists because it shows how the background variation in soil carbon across the landscape can be removed to allow more accurate measurement of the change in soil carbon caused by management. The research will also benefit farmers and soil conservationists because it adds to our knowledge of the management and benefits of cover crops.

Technical Abstract: Winter cover crops have the potential to increase soil carbon (C) in the corn (Zea mays L.)-soybean (Glycine max [L.] Merr.) rotation in the upper Midwest. Management effects on soil C, however, are often difficult to measure because of the spatial variation of soil C across the landscape. The objectives of this study were to use terrain covariates to account for part of the spatial variability in soil C and then to determine the effect of oat (Avena sativa L.), rye (Secale cereale L.), and a mixture of oat and rye used as winter cover crops following soybean on soil C levels over three years and both phases of a corn-soybean rotation. Controlled traffic, no-till plots with both phases of a corn-soybean rotation were established in 1996. Oat, rye, and a mixture of oat and rye cover crop treatments were over-seeded into soybean in late August each year. Cover crop treatments were not planted into or after the corn phase of the rotation. Soil C concentration was measured in the late spring of 2000, 2001, and 2002 in a 7.62-m grid pattern. Slope, relative elevation, and wetness index were used as covariates in the analysis of variance to remove some of the variability caused by landscape driven patterns of soil C. Soil C concentrations were higher in 2001 and 2002 than in 2000. The rye cover crop treatment had higher soil C concentrations than the no-cover-crop control following the soybean year of the rotation, which included cover crops, but lower C concentrations than the control following the corn year of the rotation, which did not have cover crops. The oat and oat-rye mixture cover crops treatments did not differ from the control.