Submitted to: Soil/Water Research, Progress Report
Publication Type: Experiment Station
Publication Acceptance Date: 3/16/2007
Publication Date: 4/1/2007
Citation: Lehman, R.M., Osborne, S.L., Rosentrater, K.A. 2007. Studies of Corn Stover Decomposition Using the Litter Bag Technique. 2006 Progress Report #SOIL PR 06-32. Ag. Exp. Stn., Plt. Sci., SDSU. Brookings SD 57007. Available online at http://plantsci.sdstate.edu/soiltest/datafiles/PR%2006-32.pdf.
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, then there are implications for both farming practices, e.g., tillage and planting, as well as global carbon budgets. We evaluated the decomposition of three Bt-containing corn residue compared to non-Bt corn residue (all hybrids from a single seed manufacturer) under field conditions using the litter bag approach. At seven sampling points spanning 22 months, no difference in decomposition rates were observed among the four hybrids. A second study has been initiated to determine if the production of root exudates containing modified Bt endotoxins may influence decomposition rates. Four corn hybrids were used for this study: Bt- and non-Bt-containing near isolines from two different manufacturers. These residues were buried within rows of Bt- and non-Bt- producing corn hybrids in June, 2006. No results are available from this second study. A third study was initiated to determine if insect pressure influences the relative decomposition of Bt- and non-Bt-protected corn. Residue from Bt- and non-Bt-protected hybrids were collected from plots where high insect pressure was recorded and then buried in litter bags in November, 2006. No results are available yet from this third study.
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 (252) 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 seven intervals up to 22 months was not significantly different among hybrids. A second study has been initiated to determine if the production of root exudates containing modified Bt endotoxins may influence decomposition rates. Litter bags containing residue were buried within rows of non-Bt producing corn (Cropland 344) and Bt-producing corn (Cropland 344CRBT). Residue from Bt and non-Bt hybrids were used from two manufacturers: Cropland 344 and 344CRBT; DKC4626 (conventional) and 4625 (stacked Bt). These litterbags (240) were buried June 6, 2006. A third study was initiated to determine if insect pressure influences the relative decomposition of Bt- and non-Bt-protected corn. Above-ground biomass from Cropland 344 and 344CRW was harvested from plots with a strong natural infestation of western corn rootworm. Sixty litterbags with dried residue were buried into incorporated soybean stubble on November 8, 2006.