There’s a widespread perception that Bt-corn residue resists decomposition, resulting in more surface trash. But a recent series of field experiments found no differences in how rapidly Bt and non-Bt corn residue decayed.

This matters, says Michael Lehman, a microbiologist at the USDA-ARS North Central Agricultural Research Lab in Brookings, SD, because “if more aggressive tillage is needed to manage tougher residue, we will expect a cost in more soil erosion.”

Lehman led three field studies and one greenhouse trial that compared residue decomposition rates for Bt hybrids and their related non-Bt isolines. The trials included genetics from several seed companies. Corn residue was compared from fields with and without corn rootworm and European corn-borer infestations.

The corn residue was chopped and buried, simulating the effects of combining, chopping and fall tillage. “We found no differences in decomposition of corn residue linked to Bt genes,” Lehman says. Nor were there differences in stalk strength related to the presence of Bt genes, he says.

Still, Lehman adds, “I don’t discount farmers’ observations.” It’s likely that the apparent persistence of Bt-corn residue is related to the steady increase in the total amount of residue produced as a result of higher yields and plant populations, he says. Another factor could be the prevalence of hybrids selected for traits that keep stalks standing longer, he adds.