Decomposition of Surface-Applied and Soil-Incorporated Bt Maize Leaf Litter and Cry1Ab Protein During Winter Fallow in South Africa

Abstract

Unintended effects of genetic modification on chemical composition of Bt maize leaf litter may have impacts on its decomposition. In most agricultural systems in South Africa, maize litter is either left on the soil surface or incorporated into the soil during tillage. A litterbag experiment, using leaf litter of three maize hybrids (DKC80-12B, DKC80-10 and DKC6-125), was carried out at the University of Fort Hare Research Farm, South Africa, to determine the effects of genetic modification on decomposition of maize leaf litter when left on the soil surface under field conditions between July and November, the normal fallow period, in 2008. Another litterbag experiment was conducted at the University of Fort Hare Research Farm and Zanyokwe Irrigation Scheme, South Africa, using leaf litter of two maize hybrids genetically modified with the cry1Ab gene (MON810), DKC75-15B and PAN6Q-308B, and their corresponding near isolines, CRN3505 and PAN6Q-121. The degradation of Cry1Ab protein in the litter, both surface-applied and soil-incorporated, was also investigated. Decomposition of Bt maize litter was similar to that of non-Bt maize litter both when applied on the surface and when incorporated into soil. Soil-incorporated litter, as well as its Cry1Ab protein, decomposed faster than that applied on the surface. The leaf litter C:N ratios of PAN6Q-308B and PAN6Q-121 were similar throughout the study, whereas those of DKC75-15B and CRN3505 declined by similar amounts during a 12-week period. These findings suggested that decomposition of leaf litter of Bt maize, with the MON810 event, was not affected by maize genetic modification, and that the Cry1Ab protein broke down together with plant leaf litter during the winter fallow regardless of whether the litter was applied on the soil surface or incorporated into soil.