Tuesday, February 6, 2007

Changes in Total Soil Organic Carbon Caused by Crop Rotation and Bio Cover After Four Years of No Tillage Production.

Jason Wight1, Fred Allen2, Don Tyler1, and Timothy G. Rials3. (1) University of Tennessee, 252 Ellington Plant Science, 2431 Joe Johnson Drive, Knoxville, TN 37996, (2) University of Tennessee, Department of Plant Sciences, 252 Ellington Plant Science, 2431Joe Johnson Drive, Knoxville, TN 37996-4561, (3) University of Tennessee, Tennessee Forestry Products Center, 102 Forest Products, 2512 Jacob Drive, Knoxville, TN 37996

The rate of soil carbon storage no-till farmland is uncertain due to environmental and production factors. The objective of this research is to compare changes in total soil organic carbon (SOC) among different cropping systems in two regions of Tennessee under no-tillage production. The experiment used a split-block treatment design with four replications at each location.  The whole-block treatment was cropping sequences of Roundup Ready® corn (Zea mays), soybeans (Glycine max), and cotton (Gossypium hirsutum) combined with a split-block treatment of bio-covers using winter wheat (Triticum aestivum), hairy vetch (Vicia villosa), poultry litter, and winter weeds. Treatments were applied to fields at the University of Tennessee’s Research and Education Center’s at Milan (RECM) and Spring Hill (MTREC).  Soil samples were taken before treatments began and after two and four years of experimentation. SOC was measured at the surface (0-5 cm) and subsurface (5-15 cm).  Changes in SOC were calculated. Overall, both locations showed small but consistent loss in carbon over all treatments during the first two years, being largest in the surface layer, at the RECM site.  Mean SOC loss at RECM surface was 1.47 Mg ha-1 while that of MTREC was 1.28 Mg ha-1.  The subsurface showed a similar trend, with mean SOC loss at RECM being higher (0.65 Mg ha-1) than at MTREC (0.55 Mg ha-1).  A significant effect (P<0.001) was seen in the surface of the RECM site due to biocover.  Poultry litter (0.9 Mg ha-1) and wheat (1.27 Mg ha-1) resulted in less SOC loss than hairy vetch (1.87 Mg ha-1) and winter weeds (1.88 Mg ha-1). Although non-significant, similar trends were seen in plots under the biocover treatments in the subsurface at both the RECM and MTREC sites. Results will be presented on SOC levels after four years of the cropping systems.