Effects of transgenic Btcotton 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 Btcrops release Bttoxins 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 Btcotton with pure crop of peanut to arrive on a valid conclusion. Significantly higher dehydrogenase enzyme activity and KMnO4-N content of soil were observed in Btcotton with cover crop of peanut over pure Btcotton followed by pure peanut at all the crop growth stages. However, higher microbial population was maintained by pure peanut over intercropped Btcotton, but these differences were related to the presence of high amount of KMnO4-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, overBtcotton alone. Btcotton fertilized by combined application of urea and farm yard manure (FYM) maintained higher dehydrogenase enzyme activity, KMnO4-N content of soil and microbial population over urea alone. Significant positive correlations were observed for dry matter accumulation, dehydrogenase enzyme activity, KMnO4-N content, and microbial population of soil of Btcotton, which indicates no harmful effects of Btcotton 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 Bttoxin on microbial activity and thus on enzymatic activities