No Evidence that Bt Genes and their Products Influence the Susceptibility of Corn Residue to Decomposition

Authors: Lehman, R - Michael; Osborne, Shannon; Rosentrater, Kurt

Submitted to: Agronomy Journal
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/27/2008
Publication Date: 11/7/2008
Citation: Lehman, R.M., Osborne, S.L., Rosentrater, K.A. 2008. No Evidence that Bt Genes and their Products Influence the Susceptibility of Corn Residue to Decomposition. Agronomy Journal. 100:1687-1693.

Interpretive Summary: To determine if the genetics (Bt or non-Bt) of growing or senescing corn plants may influence the decomposition of co-existing corn residue, we evaluated the relative decomposition of residue from two pairs of Bt and non-Bt corn hybrids (different seed manufacturers) buried in the root zone of Bt and non-Bt corn plants. There were 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, including lignin content, were observed among the four hybrids. Mechanical testing of the intact stalk internode sections failed to detect significant differences in flexural strength among the hybrids that could be related to the presence of the Bt genes. However, all residues buried in the root zone of a non-Bt corn hybrid decomposed significantly slower than those buried in the root zone a Bt hybrid after 73 d (p = 0.035), 160 d (p = 0.016) or 384 d (p < 0.001). We conclude that (i) the presence of Bt genes (and ostensibly their products) in chopped residue does not affect its decomposability; and, (ii) Bt products released from growing or senescing Bt corn plants do not adversely affect the decomposition of corn residue in the surrounding soil.

Technical Abstract: Continuing speculation concerning slower residue decomposition for Bt corn (Zea mays L.) hybrids compared to non-Bt corn hybrids has prompted a search for potential explanations. To determine if the genetics (Bt or non-Bt) of growing or senescing corn plants may influence the decomposition of co-existing corn residue, we evaluated the relative decomposition of residue from two pairs of Bt and non-Bt corn hybrids (different seed manufacturers) buried in the root zone of Bt and non-Bt corn plants. Chopped residues were buried in litter bags and residue loss was measured at intervals up to 384 d. There were 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, including lignin content, were observed among the four hybrids. Mechanical testing of the intact stalk internode sections failed to detect significant differences in flexural strength among the hybrids that could be related to the presence of the Bt genes. However, all residues buried in the root zone of a non-Bt corn hybrid decomposed significantly slower than those buried in the root zone a Bt hybrid after 73 d (p = 0.035), 160 d (p = 0.016) or 384 d (p < 0.001). We conclude that (i) the presence of Bt genes (and ostensibly their products) in chopped residue does not affect its decomposability; and, (ii) Bt products released from growing or senescing Bt corn plants do not adversely affect the decomposition of corn residue in the surrounding soil. It appears that even hybrids of the same crop species may differentially influence the decomposition of organic materials in the surrounding soils.