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ABSTRACT
Bt (Bacillus thuringiensis) corn (Zea mays L.) accounted for 74.5% of the corn acreage in eastern Canada in 2009. Reports that Bt corn has greater yield and lignin concentrations than unmodifi ed corn have raised questions about its eff ect on the soil ecosystem. Our objectives were to evaluate the biomass of fi eld-grown Bt and non-Bt corn, the chemical composition of diff erent corn components that remain as residues in the fi eld aft er harvest, and the eff ect of the Bt modifi cation on residue decomposition. Nine Bt corn hybrids and their near isolines were fi eld-grown in 2008 and 2009. Grain and stover yields were measured and leaves, stems, and roots were collected and analyzed for lignin, C, and N concentrations. Stem sections from a Bt/non-Bt corn pair were buried in the fi eld and sampled periodically during 1 yr. No diff erence in yield or lignin concentrations due to the Bt gene was noted; however, N concentration in Bt stems was signifi cantly greater than in non-Bt stems in 1 yr of the 2-yr study. Leaves had less lignin and a lower C/N ratio than stems and roots in both years. In buried fi eld litterbags, the decline in C/N ratio and mass loss suggests that Bt stems were decomposing more rapidly than non-Bt stems. We conclude that the Bt gene does not aff ect the agronomic performance or the chemical composition of corn in fi elds without herbivory, and that Bt corn residue may be more susceptible to decomposition than non-Bt corn residue.
Abbreviations: Bt, Bacillus thuringiensis; ECB, European corn borer; NBt, non-Bacillus thuringiensis.
Genetically modified Bt corn is planted extensively in North America. In 2009, 1.3 million hectares in eastern Canada (Ontario and Quebec) were planted with corn and 74.5% of hybrids were Bt corn (Agriculture and Agri-Food Canada, 2009; Canadian Corn Pest Coalition, 2010). Th e Bt corn hybrids are popular with farmers in this region because the genes from the Bacillus thuringiensis gram-positive bacterium produces crystal-like proteins (Cry proteins) for protection against European corn borer (ECB, Ostrinia nubilalis H.) and corn rootworm (Diabrotica spp.).
Concerns have been raised about other eff ects of Bt corn on the soil ecosystem. Cry proteins can persist in...