No evidence that Bacillus Thuringiensis genes and their products influence the susceptibility of corn residue to decomposition
The possibility that Bacillus thuringiensis (Bt) corn (Zea mays L.) residues resist decomposition compared to non-Bt residues would present direct (soil carbon turnover times) and indirect (changes in tillage practices) effects on carbon budgets in agricultural systems. We evaluated the relative decomposition of residue from two pairs of Bt and non-Bt corn hybrids from different seed manufacturers buried in the root zone of adjacent Bt and non-Bt corn plots over a period of 384 d. We found no persistent differences in residue decomposition among the different hybrids regardless of the seed manufacturer or the presence of the Bt genes (both cry1Ab and cry3Bb1 genes present in each Bt hybrid) in the residue. No significant differences in residue compositional properties or flexural strength of intact stalk sections were observed among the four hybrids. Both Bt and non-Bt residues buried in the root zone of a Bt corn hybrid decomposed faster than those buried in the root zone of the corresponding, near-isogenic non-Bt hybrid. A subsequent replicated laboratory study showed no difference between the decomposition of cellulose filter paper buried in the root zone of growing and senescing Bt and non-Bt hybrids. We conclude that (i) the presence of Bt genes and their products in chopped residue does not affect its decomposability; (ii) the presence of Bt genes does not affect the mechanical strength of the stalks; and, (iii) Bt products released from growing or senescing Bt corn plants do not adversely affect decomposition activities in the surrounding soil.