Pedosphere 24(2): 251–257, 2014 ISSN 1002-0160/CN 32-1315/P c  2014 Soil Science Society of China Published by Elsevier B.V. and Science Press Decomposition of Surface-Applied and Soil-Incorporated Bt Maize Leaf Litter and Cry1Ab Protein During Winter Fallow in South Africa *1 A. KAMOTA 1 , P. MUCHAONYERWA 2,∗2 and P. N. S. MNKENI 3 1 Department of Crop Science, Bindura University of Science Education, Private Bag 1020, Bindura (Zimbabwe) 2 School of Agricultural, Earth and Environmental Sciences, University of KwaZulu-Natal, Private Bag X01, Scottsville 3209 (South Africa) 3 Department of Agronomy, University of Fort Hare, Private Bag X1314, Alice 5700 (South Africa) (Received April 17, 2013; revised January 21, 2014) 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. Key Words: genetic modification, litterbag experiment, maize hybrid, MON810 event, protein degradation Citation: Kamota, A., Muchaonyerwa, P. and Mnkeni, P. N. S. 2014. Decomposition of surface-applied and soil-incorporated Bt maize leaf litter and Cry1Ab protein during winter fallow in South Africa. Pedosphere. 24(2): 251–257. INTRODUCTION The cry1Ab gene in Bt crops may alter compo- sitional quality with possible reduction in litter de- composition and nutrient release. In most agricultural practices in South Africa, maize litter is either left on the surface as mulch in no-till systems or incorporated into the soil to depths from 10 to 20 cm during mold- board plough tillage operations. Leaving maize litter on the surface, including that of Bt maize, is a com- mon practice where conservation agriculture has been adopted. It is estimated that dry matter of 6 and 2.5 t ha −1 is left in the field after harvesting maize grain and plant materials for silage, respectively, and the re- cycling of nutrients in this litter is governed by the rate of its decomposition (Zwahlen et al., 2003). Decomposition of litter is influenced by soil micro- bial composition, activities of enzymes (Flores et al., 2005), soil conditions, particularly moisture, tempera- ture and pH (Donnelly et al., 1990) and lignin and polyphenol contents and C:N ratio of the litter (Palm et al., 1999). There are conflicting reports on the effect of genetic modification on the chemical composition of Bt maize plant materials. Mungai et al. (2005) did not find any consistent differences in the lignin content between Bt maize and non-Bt near isolines. However, Saxena and Stotzky (2001) observed a significantly higher lignin content in the vascular bundle sheath and the surrounding cells of Bt maize as opposed to their corresponding non- Bt near isolines, with the highest lignin content being found in Bt maize cultivars with event Bt11 followed *1 Supported by the National Research Foundation of South Africa (NRF) and the Govan Mbeki Research and Development Center (GMRDC) of the University of Fort Hare (No. GUN62299). *2 Corresponding author. E-mail: muchaonyerwa@ukzn.ac.za.