Submitted to: Meeting Abstract
Publication Type: Abstract Only
Publication Acceptance Date: 11/7/2005
Publication Date: 11/7/2005
Citation: Lehman, R.M., Osborne, S.L., Rosentrater, K.A. 2005. Field decomposition of genetically-modified corn residue. ASA-CSSA-SSSA International Annual Meetings in Salt Lake City, Utah, November 6-10, 2005. Interpretive Summary: Genetic modification of crops for a specific purpose, e.g., control of an insect pest, may result in additional, unintended effects to plant structure and function. In the case of corn modified to produce the Bt endotoxin, some data suggests that the genetically-modified (GM) corn residue may have a higher lignin content and some observations indicate 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. On the other hand, published laboratory studies have suggested no difference in decomposition rates of GM corn residue compared to that of non-GM residue. We evaluated the decomposition of GM corn residue compared to non-GM corn residue under field conditions using the litter bag approach. Between November and April, about 70% of the residue was decomposed and there were no significant differences observed between GM corn residue and non-GM corn residue. Subsequent blocks of litter bags will be excavated and analyzed on a monthly basis to calculate decomposition rates. Residue composition including C:N ratios and lignin content will be reported. The measurement of residue decomposition rates in the field will assist in resolving conflicting reports on GM corn residue composition and frame potential implications with respect to carbon budgets and farming practices.
Technical Abstract: The decomposition of residue from three genetically-modified (GM) corn varieties expressing one or more Bt endotoxins was compared to that from a variety with the unmodified base genetics. 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 residue was collected in November, 2004 from experimental plots of each variety cultivated under identical no-till conditions. There was little pressure from corn borers or rootworm reported at this site. The decomposition rates of dried, chopped stalks and leaves were evaluated with the litterbag method using 2-mm mesh poly bags. Nine bags per variety were buried in each of 7 randomly-assigned blocks in a sandy-clay loam soil where spring wheat had been recently harvested and the residue incorporated by chisel plow. The top of the bag was buried 5 cm below the soil surface. The first block was excavated when the ground thawed in the beginning of April. The percent of residue on a dry weight basis (average of 9 replicates with 1 standard deviation in parentheses) decomposed over winter was 30.6 (±4.8) for the base genetics, 31.7 (±2.3) for Yieldguard Corn Borer, 28.4 (±2.9) for Yieldguard Corn Rootworm, and 27.8 (±1.9) for Yieldguard Plus. The initial percent of residue decomposed from the GM varieties was not significantly different than that of the base genetics variety. Subsequent blocks of litter bags will be excavated and analyzed on a monthly basis to calculate decomposition rates. Residue composition including C:N ratios and lignin content will be reported. The measurement of residue decomposition rates in the field will assist in resolving conflicting reports on GM corn residue composition and recalcitrance and frame potential implications with respect to carbon budgets and farming practices.