Healthy soils are the foundation of a healthy agricultural production system. The growing use of transgenic plants within modern agriculture has sparked major debates as to the possible negative affects they could have on the environment. One of the major issues of debate is on what kind of affects these genetically modified plants may have on soil health. One study found that an insecticide compound, produced by a transgenic cotton species, can remain in the soil for as long as 140 days after integration (Palm et al., 1996). The concern is that by accumulating within the soil, these compounds could have a major impact on the soil microbial community.. This is  a debatable issue Dr Tarafdar. , but surely there are ceratain reports of decline  in soil ecology  after few years of Bt cotton cultivation . Infact ,  Bt occurs naturally in soil, growth of transgenic Bt-crop causes a large increase in the amount of Cry endotoxin (approximately 0.25g ha-1 ) in the agricultural systems (Blackwood and Buyer, 2004). Thus transgenic plants have the potential to modify the rhizosphere chemistry, or by altering plant residue quality (Dunsfield and Germida, 2004; Motavalli et al., 2004; O’callaghan et al., 2005). Any change to the quality of rhizosphere exudates can modify the biota composition in soil as well as their activity (Stotzky, 2004; Patra et al., 2006) and may produce changes in microflora and microfauna ..

Another recent study on this subject was performed by Chun et al. in which they tested to see if a transgenic species of rice, which had been modified to be herbicide-resistant, had any impact on the microbial organisms in the soil where it was grown. This study spanned over 2 years in which they grow both the transgenic rice as well as the original rice species from with the transgenic version was derived. Their results, and conclusions, were much the same as those Li et al. found in their study. Chun et al. found that there was no discernable difference in soil microbial composition or diversity between the two soils growing the target species, nor was there a change over time. (Chun et al., 2011).

Effects of Bt transgenic crops on soil ecosystems: a review of a ten-year research in China , Frrontiers of Agriculture in China,June 2009, Volume 3, Issue 2, pp 190–198

Abstract :Bacillus thuringiensis (Bt) transgenic cotton is the unique Bt transgenic crop planted on a large scale in China, and its commercialized varieties and hectareage had increased rapidly in China during the past decade (1997–2006) with broad geographic distribution for the economic, environmental, and health benefits. In 2004, the planting area of Bt transgenic cotton in China ranked first worldwide with up to 370 × 106 hm2. In addition, Bt transgenic rice varieties in field tests have been close to approval for commercialization. However, ecological risks, a complex issue of Bt transgenic crops on soil ecosystem is urgently faced in China due to more than 60 varieties transferred single or bivalent Bt genes grown under diverse geographic regions. Two main pathways, biomass incorporation and root exudates, are involved in the effects of Bt transgenic crops on soil ecosystems. In this paper, the research results in recent years in China involved in the effects of Bt transgenic crops (Bt transgenic cottons and rice) on soil ecosystems were summarized with special attentions paid to the release and persistence of Bt toxins, and the toxicology to microorganisms, as well as the change of soil biochemical properties in soils where Bt transgenic crops were planted or incubated with their biomass. In addition, the complexity and current research defaults of ecological risk evaluation of Bt transgenic crops in China were highlighted.

Healthy soils are the foundation of a healthy agricultural production system. The growing use of transgenic plants within modern agriculture has sparked major debates as to the possible negative affects they could have on the environment. One of the major issues of debate is on what kind of affects these genetically modified plants may have on soil health. One study found that an insecticide compound, produced by a transgenic cotton species, can remain in the soil for as long as 140 days after integration (Palm et al., 1996). The concern is that by accumulating within the soil, these compounds could have a major impact on the soil microbial community.. This is  a debatable issue Dr Tarafdar. , but surely there are ceratain reports of decline  in soil ecology  after few years of Bt cotton cultivation . Infact ,  Bt occurs naturally in soil, growth of transgenic Bt-crop causes a large increase in the amount of Cry endotoxin (approximately 0.25g ha-1 ) in the agricultural systems (Blackwood and Buyer, 2004). Thus transgenic plants have the potential to modify the rhizosphere chemistry, or by altering plant residue quality (Dunsfield and Germida, 2004; Motavalli et al., 2004; O’callaghan et al., 2005). Any change to the quality of rhizosphere exudates can modify the biota composition in soil as well as their activity (Stotzky, 2004; Patra et al., 2006) and may produce changes in microflora and microfauna ..

Another recent study on this subject was performed by Chun et al. in which they tested to see if a transgenic species of rice, which had been modified to be herbicide-resistant, had any impact on the microbial organisms in the soil where it was grown. This study spanned over 2 years in which they grow both the transgenic rice as well as the original rice species from with the transgenic version was derived. Their results, and conclusions, were much the same as those Li et al. found in their study. Chun et al. found that there was no discernable difference in soil microbial composition or diversity between the two soils growing the target species, nor was there a change over time. (Chun et al., 2011).

Effects of Bt transgenic crops on soil ecosystems: a review of a ten-year research in China , Frrontiers of Agriculture in China,June 2009, Volume 3, Issue 2, pp 190–198

Abstract :Bacillus thuringiensis (Bt) transgenic cotton is the unique Bt transgenic crop planted on a large scale in China, and its commercialized varieties and hectareage had increased rapidly in China during the past decade (1997–2006) with broad geographic distribution for the economic, environmental, and health benefits. In 2004, the planting area of Bt transgenic cotton in China ranked first worldwide with up to 370 × 106 hm2. In addition, Bt transgenic rice varieties in field tests have been close to approval for commercialization. However, ecological risks, a complex issue of Bt transgenic crops on soil ecosystem is urgently faced in China due to more than 60 varieties transferred single or bivalent Bt genes grown under diverse geographic regions. Two main pathways, biomass incorporation and root exudates, are involved in the effects of Bt transgenic crops on soil ecosystems. In this paper, the research results in recent years in China involved in the effects of Bt transgenic crops (Bt transgenic cottons and rice) on soil ecosystems were summarized with special attentions paid to the release and persistence of Bt toxins, and the toxicology to microorganisms, as well as the change of soil biochemical properties in soils where Bt transgenic crops were planted or incubated with their biomass. In addition, the complexity and current research defaults of ecological risk evaluation of Bt transgenic crops in China were highlighted.

I think, this is such an issue , we should debate heart out. We lay so little emphasis on the issue of soil health vis-a-vis transgenic crops. Dr Tarafdar must be complimented for bringing  such an issue  on such a platform..

Dr. Srivastava, I personally analyzed a large number of samples in the Vidharbha area of Maharashtra, India, where large scale Bt cotton is growing for last 5-8 years. I find that in most of the field the microbial biomass, beneficial microbial population as well as beneficial soil enzyme activities are declined when compared with adjacent non-Bt cotton growing fields as well as sometimes controlled field. I failed to find all possible reasons for that,  as well as I am eager to know what should be the remedy in future if soil health happens to deteriate after cultivation of long term Bt trangenic crops, which is definitely the prospects for the future.

Well said Dr Tarafdar.I have seen that paper...very thought provoking.. how transgenic plants tea storm rhizosphere biochemistry compared to other field crops

Dr Tarafdar we need to see if there is decline in root biomass with Bt cotton vis-a-vis non Bt-cotton, and whether this is one of the reasons for decline in the microbial biomass and population in Bt cotton fields.

Dr. Korwar, root biomass has been declined between 8-14% under Bt cotton as compared to the non-Bt cotton with the continuous cultivation of 5 years or more. This may be the one of the reason to decline in microbial biomass. But more alarming is the beneficial microbial and enzyme activities is declining gradually with the cultivation of Bt cotton continuously for 5 years or more.

Any possibility of secondary metabolites getting accumulated .

I think the negative effects of Bt cotton on beneficial soil microbes and enzyme activities have to be brought to notice of the strong proponents of transgenics.