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CROP RESIDUES

No Differences in Decomposition Rates Observed between Bacillus thuringiensis and Non-Bacillus thuringiensis Corn Residue Incubated in the Field

USDA-ARS-North Central Agricultural Research Lab., 2923 Medary Ave., Brookings, SD 57006

^* Corresponding author (michael.lehman{at}ars.usda.gov).

Recent speculation of slower residue decomposition for Bacillus thuringiensis (Bt) corn (Zea mays L.) hybrids compared with non-Bt corn hybrids has prompted investigative study. We evaluated the residue decomposition rates of Bt and non-Bt corn hybrids over a period of 22 mo under field conditions using the litter bag technique. The four corn hybrids used were (i) DKC60–16 (Bt⁺, Cry1Ab protein active against the leptidopteran European corn borer, event MON810), (ii) DKC60–12 (Bt+, Cry3Bb1 protein active against the coleopteran corn rootworm, event MON863), (iii) DKC60–14 (stacked Bt⁺⁺, Cry1Ab and Cry3Bb1 proteins) and, (iv) DKC60–15 (Bt^–, base genetics). The biochemical and physical properties of the corn residues were determined. No differences in the decomposition rates of the residue from the four corn hybrids were detected. Residue decomposition rate constants were approximately 0.25 d^–1 for all four hybrids with predicted residue half-lives of about 200 d. No differences in compositional properties, including lignin content, were observed among the four hybrids. Physical compression testing of the chopped residue failed to detect significant differences in mechanical strength properties among the hybrids. This is the first report regarding decomposition of Bt corn residue under field conditions following ambiguous reports from laboratory studies on the relative susceptibility of Bt corn residue to decomposition.

Abbreviations: Bt, Bacillus thuringiensis • GM, genetically modified