BT Cotton, Tillage and Cover Crops Identity: Relative Effects on Above and Below Ground Invertebrate Diversity

BT Cotton, Tillage and Cover Crops Identity: Relative Effects on Above and Below Ground Invertebrate Diversity

Summary

This project, examining effects of Bt cotton on arthropod diversity relative to the effects of tillage and cover crop identity, is now in it’s last year of field work.  To date arthropods have been identified from on-plant samples, soil surface samples and soil samples for one full year of collection.  These samples have all been identified to the level of taxonomic family using a new microscope and taxonomic texts purchased with this SARE grant.  Data analyzed from the first year of collection indicate that none of the management strategies chosen (tillage strategy, cotton or winter crop type) have a significantly stronger effect on arthropod communities.

Objectives/Performance Targets

My research project is examining the above and belowground effects of Bt cotton on non-target organisms relative to the effects of tillage and seasonal crop changes. Belowground diversity measurements are being made on microarthropods, while measurements of above ground diversity focus on non-target arthropod species collected within the cotton field (pollinators, predators, etc.). The inclusion of both above and belowground diversity measurements stems from three sources. First from the recognition of the strong link between above and belowground ecosystem processes (Coleman 2002) second, from the question of whether or not the exclusion of certain target organisms from Bt cotton plots will have an affect on the remaining assemblage of non-target taxa and third, to examine the additive effects of tillage method and cotton type on arthropod diversity. The project is being conducted at Horseshoe Bend Agricultural Research Facility. Horseshoe Bend is a LTREB (Long Term Research in Environmental Biology) site in Athens, GA. Bt cotton is currently being grown at the site under both conventional tillage (CT) and no-till (NT) management regimes. The tillage methods themselves have been practiced at Horseshoe Bend since 1978 (Hendrix et al. 2001). Also employed at the site are winter crops of rye and clover. There are thirty-two subplots within the cotton field (each approximately 14 x 14m.) which host combinations of tillage regiment, winter cover crop, and cotton type (Bt or non-Bt). This offers an extremely useful combination of agricultural settings within which to study the effects, if any, of Bt cotton on above and belowground biodiversity relative to other community-shaping forces within the agroecosystem.

Hypotheses
Arthropod diversity will be higher in non-Bt than in Bt plots
Diversity will be affected to a greater extent by cover crop identity (cotton vs. rye and clover) than by cotton type (Bt vs. non-Bt)
Diversity will be greater in NT plots than in CT plots
Diversity will be affected to a greater extent by tillage practice than by the presence or absence of Bt cotton

Accomplishments/Milestones

To date, all arthropods have been collected for analysis and the project is now in the stage of sample identification and statistical analysis. All arthropod samples from the first sampling year have been identified. This data has also been run through a preliminary statistical analysis using a proc glm procedure in SAS. From analyzing this data it appears that there are no significant impacts of cotton type or cover crop choice on arthropod diversity, abundance, or richness. There does however appear to be a slightly significant difference between arthropod community richness in No-till versus Conventional till treatments. However, this difference appears to be linked to one particular plot rather than all No-till treatments. Samples from the final year of the study have yet to be identified and analyzed.

Impacts and Contributions/Outcomes

A great deal of research has been conducted on genetically modified crops, tillage and crop selection in relation to non-target arthropods. This study is the first attempt to examine the effects of these agricultural practices on arthropod communities in a single system relative to one another. The importance of this may come in the form of prioritization for decision making in sustainable agriculture. With the demand on agricultural production being as high as it is it would benefit us to focus our research efforts where they will have the most power in terms of long term sustainability. Although the data analyzed thus far show no significant effect of any management practice chosen it is important to keep in mind that this is only a portion of the data to be used in the study.

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