Evaluating impacts of insecticide seed treatments on the soil microbial community in a grain crop rotation in the Maryland Coastal Plains

Description

This data was collected as part of a larger research study evaluating the potential benefits and non-target impacts of neonicotinoid insecticide seed treatments in a commonly practiced grain crop rotation in the mid-Atlantic United States. We compared three seed treatments (fungicide products only; fungicide products + imidacloprid; and fungicide products + thiamethoxam) to an untreated control in a three-year rotation of full-season soybean, winter wheat, double-cropped soybean, and corn in the Atlantic Coastal Plains of Maryland. Details of the experimental design can be found in a related published study that used the same experimental plots: https://doi.org/10.1111/1365-2664.13595. This data focuses on potential impacts of insecticide seed treatments on soil health. Specifically, we evaluated impacts on overall soil microbial activity measured through basal respiration, on the diversity and structure of the prokaryotic community, and on various soil quality parameters. As part of the larger research project, we determined that insecticide residue levels in the soil were fairly low throughout the crop rotation, but the highest levels were found in the final year, suggesting some accumulation (https://doi.org/10.1111/1365-2664.13595). Based on this, we hypothesized that soil quality parameters, which were measured at the beginning and end of the study, could worsen gradually over time due to the impacts of accumulated pesticides on soil organisms. Our prediction was that soil microbial activity as measured through basal respiration would be altered immediately post-planting, but that the community would recover over the course of each growing season. We anticipated stronger treatment impacts on the diversity and structure of the prokaryotic community in full-season soybean and corn, which were measured shortly after planting, as compared to winter wheat, which was sampled several months later. We also predicted that overall impacts on soil microbial activity and the prokaryotic community could worsen over the course of the study due to pesticide accumulation in the soil. None of the metrics quantified in this study were impacted by neonicotinoid seed treatments, except for an increase in the relative abundance of the bacterial class Verrucomicrobiae in bulk soil in imidacloprid-treated corn. There are several potential explanations for this lack of impacts, such as relatively low insecticide residue levels in the soil, increased health and resilience of soil microbial communities caused by conservation tillage practices, or legacy effects of long-term neonicotinoid usage.

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We used 16S rRNA sequencing to evaluate impacts of insecticide seed treatments on soil quality parameters, soil basal respiration and the soil prokaryotic community in a three-year crop rotation of full-season soybean, winter wheat, double-cropped soybean and corn at two field sites in the Coastal Plains of Maryland. The study included 4 treatments: untreated seeds, fungicides only, fungicides plus one of two widely used neonicotinoids, imidacloprid (Gaucho 600) or thiamethoxam (Cruiser 5FS). At each site, 4 replicate plots of each treatment were arranged in a Latin square. Details of the experimental design can be found in a related published study that used the same experimental plots: https://doi.org/10.1111/1365-2664.13595. Methodological details for each dataset can be found within the metadata tabs of individual files. For the files named using the following format: Soybean/Corn/Wheat_Sequencing Data_Phyloseq_OTU/Taxon/Sample Table.csv. (9 files total), metadata is included separately in the file Sequencing Data_Phyloseq_Metadata.xlsx. Note: For sequencing data, we use the term 'OTU Table' for consistency with the nomenclature used within the Phyloseq Package that was used to process and analyze this data in R. However, these tables consist of Amplicon Sequence Variants (ASVs) and not Operational Taxonomic Units (OTUs).

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