Submitted to: State University Ag Report
Publication Type: Experiment Station
Publication Acceptance Date: 3/15/2006
Publication Date: 4/1/2006
Citation: Lehman, R.M., Osborne, S.L., Rosentrater, K.A. 2006. Decomposition of stover from Bt corn hybrids after one year using the litter bag technique. 2005 Progress Report #SOIL PR 05-27. Ag. Exp. Stn., Plt.Sci. SDSU. Brookings SD 57007.
Interpretive Summary: Some reports suggest that the genetically-modified Bt corn residue may have higher lignin content and that the residue may be more resistant to decomposition. If true, there are implications for both farming practices, e.g., tillage and planting, as well as global carbon budgets and climate. We compared the C:N ratios and lignin content of three Bt corn hybrids with that of their non-Bt isoline and found no significant differences in these compositional traits among the four varieties. We evaluated the decomposition of Bt corn residue compared to non-Bt corn residue under field conditions using the litter bag approach. At five sampling points spanning one year, no difference in decomposition rates were observed among the four hybrids.
Technical Abstract: Decomposition rates of residue from three genetically-modified corn hybrids expressing one or more Bt endotoxins were compared to that of residue from a near isogenic, unmodified hybrid. The corn hybrids were (i) DKC60-16 (Yieldguard Corn Borer), (ii) DKC60-12 (Yieldguard Corn Rootworm), (iii) DKC60-14 (Yieldguard Plus = stacked), and (iv) DKC60-15 (unmodified base genetics). The decomposition rates of dried, chopped stalks and leaves were evaluated with the litterbag technique using 2-mm mesh poly bags. The litterbags were buried in sandy-clay loam soils into incorporated spring wheat stubble on a research farm located in eastern South Dakota, a subhumid site in the upper Midwest corn belt. The percent of each residue (dry weight basis) decomposed at each of five intervals up to one year was not significantly different among hybrids. No differences were observed among the hybrids with respect to litter C:N ratio and lignin content. In this study, initial litter composition and decomposition rate over one year were invariant of genetic modification. After one year, ca. 20% of the initial dry weight remained for all four hybrids.