Effects of transgenic Bt cotton on soil fertility and biology under field conditions in subtropical inceptisol

Abstract

Although there is large-scale adoption of Bt cotton by the farmers because of immediate financial gain, there is concern that Bt crops release Bt toxins into the soil environment which reduces soil chemical and biological activities. However, the majorities of such studies were mainly performed under pot experiments, relatively little research has examined the direct and indirect effects of associated cover crop of peanut with fertilization by combined application of organic and inorganic sources of nitrogen under field conditions. We compared soil chemical and biological parameters of Bt cotton with pure crop of peanut to arrive on a valid conclusion. Significantly higher dehydrogenase enzyme activity and KMnO(4)-N content of soil were observed in Bt cotton with cover crop of peanut over pure Bt cotton followed by pure peanut at all the crop growth stages. However, higher microbial population was maintained by pure peanut over intercropped Bt cotton, but these differences were related to the presence of high amount of KMnO(4)-N content of soil. By growing cover crop of peanut between Bt cotton rows, bacteria, fungi, and actinomycetes population increased by 60%, 14%, and 10%, respectively, over Bt cotton alone. Bt cotton fertilized by combined application of urea and farm yard manure (FYM) maintained higher dehydrogenase enzyme activity, KMnO(4)-N content of soil and microbial population over urea alone. Significant positive correlations were observed for dry matter accumulation, dehydrogenase enzyme activity, KMnO(4)-N content, and microbial population of soil of Bt cotton, which indicates no harmful effects of Bt cotton on soil biological parameters and associated cover crop. Our results suggest that inclusion of cover crop of peanut and FYM in Bt cotton enhanced soil chemical and biological parameters which can mask any negative effect of the Bt toxin on microbial activity and thus on enzymatic activities.

Effects of long-term cultivation of transgenic Bt rice (Kefeng-6) on soil microbial functioning and C cycling

“…4). Similar results were observed in other short-term studies 21, 30 or long-term studies on Bt maize 36, 56 . The fact that microbial metabolic quotients among Bt rice treatments were close to one another also suggested that soil microbial biomass was not affected by Bt rice Kefeng-6 .…”

“…In addition, soil respiration could be significantly increased 27, 28 or decreased 25 by transgenic Bt maize in different studies. Most of these reported studies were based on short-term field experiments, up to two or three years 13, 29, 30 , enabling us to learn what and how Bt crops affect soil microbial organisms and soil eco-processes. However, short-term cultivation experiments encountered temporal variations in soil environment and crop growth, were not able to reflect the accumulative effects of Bt protein along with the food web in the soil, it is still poorly understood whether long-term cultivation of Bt crops will result in irreversible impacts on soil health.…”

Impact of transgenic cottons expressing cry1Ac on soil biological attributes

“…Soil DHA reflects the total range of oxidative activity of soil microflora and, consequently it may be a good indicator of microbiological activity in the soil (Skujins 1976). Positive correlations between dehydrogenase activity and Bt cotton cultivation are also reported (Singh et al 2013). DHA in soil depends on the content of soluble organic carbon (Zaman et al 2002) and the increased organic matter in the surface soil horizon enhanced the soil enzyme activities.…”

Effects of cultivation of OsrHSA transgenic rice on functional diversity of microbial communities in the soil rhizosphere

“…Numerous studies have been carried out to investigate the effects of transgenic crops on soil microbial communities [1][2][3]. Most results indicate that transgenic Bt crops have not caused significant effects on soil microbes compared to conventional crops [4][5][6][7][8][9][10]. OsrHSA transgenic rice is transformed with the human serum albumin gene that produces a soluble medicinal globular protein [11] that has attracted attention regarding its environmental safety.…”